JP3721897B2 - Three-way catalyst storage oxygen desorption amount calculation apparatus and air-fuel ratio control apparatus for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a three-way catalyst stored oxygen desorption amount calculation device and an air-fuel ratio control device for an internal combustion engine using the three-way catalyst storage oxygen desorption amount calculation device.
[0002]
[Prior art]
The three-way catalyst has a function of oxidizing HC and CO and reducing NOx when the air-fuel ratio is substantially the stoichiometric air-fuel ratio. Therefore, if the air-fuel ratio can be maintained substantially at the stoichiometric air-fuel ratio, HC, CO, and NOx can be simultaneously purified using a three-way catalyst. However, it is difficult to maintain the air / fuel ratio substantially at the stoichiometric air / fuel ratio, and the air / fuel ratio may actually deviate from the stoichiometric air / fuel ratio. However, even if the air-fuel ratio deviates from the stoichiometric air-fuel ratio, HC, CO, and NOx can be purified by the oxygen storage function of the three-way catalyst.
[0003]
That is, the three-way catalyst has a function of taking in and storing excess oxygen in the exhaust when the air-fuel ratio is lower than the stoichiometric air-fuel ratio (hereinafter referred to as “lean”). Can be reduced. On the other hand, when the air-fuel ratio is higher than the stoichiometric air-fuel ratio (hereinafter referred to as “rich”), unburned HC and CO in the exhaust take away oxygen stored in the three-way catalyst, Unburned HC and CO can be oxidized.
[0004]
Therefore, in order to reduce NOx when the air-fuel ratio deviates from the stoichiometric air-fuel ratio, the three-way catalyst needs to be in a state where oxygen can be stored. That is, the oxygen storage amount of the three-way catalyst must be in a state where there is a margin with respect to the maximum oxygen storage amount. Furthermore, in order to oxidize unburned HC and CO, the three-way catalyst needs to be in a state where a certain amount of oxygen is stored. That is, NOx can be reduced when the air-fuel ratio shifts from the stoichiometric air-fuel ratio to the lean side, and unburned HC and CO can be oxidized when the air-fuel ratio shifts to the rich side with respect to the stoichiometric air-fuel ratio. Therefore, it is necessary to keep the storage oxygen amount of the three-way catalyst in a state intermediate between the maximum storage oxygen amount and zero storage oxygen amount.
[0005]
The amount of oxygen adsorbed on the three-way catalyst and the amount of oxygen desorbed from the three-way catalyst can be calculated based on the intake air amount and the deviation amount of the air-fuel ratio with respect to the stoichiometric air-fuel ratio. Therefore, the stored oxygen amount of the three-way catalyst can be calculated from the intake air amount and the deviation amount of the air-fuel ratio.
[0006]
Therefore, the target stored oxygen amount to be stored in the three-way catalyst is determined in advance between the maximum stored oxygen amount and the stored oxygen amount 0, and the calculated stored oxygen amount of the three-way catalyst is the target stored oxygen amount. An air-fuel ratio control apparatus for an internal combustion engine that controls the fuel injection amount has been proposed (Japanese Patent Laid-Open No. 6-249028).
[0007]
In order to control the amount of oxygen to be stored in the three-way catalyst based on the amount of stored oxygen, the amount of oxygen stored in the three-way catalyst must be accurately calculated. However, if the amount of stored oxygen is calculated from the amount of difference between the intake air amount and the air-fuel ratio as described above, there may be a deviation from the actual amount of stored oxygen while the calculation is repeated. Therefore, in order to calculate the stored oxygen amount accurately, it is necessary to correct this deviation amount.
[0008]
In the prior art described above, the guard is applied so that the calculated stored oxygen amount does not become larger than the maximum stored oxygen amount and does not become smaller than the minimum stored oxygen amount (stored oxygen amount = 0). However, such a guard alone does not correct the calculated shift amount of the stored oxygen amount relative to the actual stored oxygen amount. For this reason, the amount of deviation accumulates without being properly corrected, and the calculated stored oxygen amount may deviate significantly from the actual stored oxygen amount. As a result, oxygen is saturated in the three-way catalyst and NOx cannot be reduced, or the amount of stored oxygen becomes 0 and unburned HC and CO cannot be oxidized.
[0009]
In order to solve this problem, in the technique described in JP-A-10-184424, air-fuel ratio sensors are provided upstream and downstream of the three-way catalyst, respectively. Based on the upstream air-fuel ratio, the intake air amount, and the like, the stored oxygen desorption amount, which is a value indicating the amount of oxygen desorbed from the three-way catalyst in the maximum stored oxygen amount state, is calculated. When the calculated stored oxygen desorption amount does not reach the maximum desorption amount, the air-fuel ratio detected by the downstream air-fuel ratio sensor is switched from a state other than rich to rich. The above stored oxygen desorption amount is corrected to the maximum desorption amount. Further, when the air-fuel ratio detected by the downstream air-fuel ratio sensor is switched from a state other than lean to lean even though the calculated stored oxygen desorption amount has not reached 0, the calculated stored oxygen The desorption amount is corrected to zero.
[0010]
In this way, the state of the downstream air-fuel ratio sensor detects the state where the actual stored oxygen desorption amount is the maximum stored oxygen desorption amount and the state where the actual stored oxygen desorption amount is 0. Sometimes the calculated stored oxygen desorption amount is reset to the maximum desorption amount or zero.
[0011]
[Problems to be solved by the invention]
However, in the latter conventional example, the air-fuel ratio sensor on the downstream side of the three-way catalyst is switched from a non-rich state to a rich state in order to determine the appropriate amount of stored oxygen desorption. It is necessary to switch from a state other than the lean state. Thus, in the latter conventional example, a relatively large state change is essential, and the opportunity for correcting the calculated stored oxygen desorption amount is reduced. For this reason, a state where the calculated amount of stored oxygen desorption is inappropriate may continue for a long period of time, during which the emission may be deteriorated.
[0012]
Further, since the correction to the calculated stored oxygen desorption amount is an extreme correction to the maximum stored oxygen desorption amount or the minimum stored oxygen desorption amount, the fluctuation of the stored oxygen desorption amount at the time of correction is severe. For this reason, a state in which the error from the actual stored oxygen desorption amount is large after correction is likely to occur. And since this error affects until later, a state in which the calculated amount of stored oxygen desorption is inadequate continues for a long period of time, and during that time, there is a risk of causing deterioration of emissions.
[0013]
The present invention increases the chances of correcting the calculated stored oxygen desorption amount in the calculation of the stored oxygen desorption amount in the three-way catalyst, and the correction itself suppresses severe fluctuations. The object is to prevent the state where the separation amount is inappropriate from continuing for a long period of time and to contribute to the prevention of emission deterioration.
[0014]
[Means for Solving the Problems]
  In the following, means for achieving the above object and its effects are described.
  The three-way catalyst stored oxygen desorption amount calculating device according to claim 1 is a three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine. Storage oxygen desorption amount integrating means for integrating the storage oxygen desorption amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst, maximum storage oxygen desorption amount and minimum storage oxygen desorption in the three-way catalyst In betweenThe mostA storage oxygen desorption amount existence region that is smaller than the region between the large storage oxygen desorption amount and the minimum storage oxygen desorption amount and is likely to be located in the three-way catalyst.Depending on the operating condition of the internal combustion engineStorage oxygen desorption amount existing region setting means to be set, and storage oxygen desorption amount integrated by the stored oxygen desorption amount integration means is set by the stored oxygen desorption amount existing region setting means The stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means when it is outside the desorption amount existing regionThe value of theTo be close to the storage oxygen desorption amount existing region or within the storage oxygen desorption amount existing region.YouStorage oxygen desorption amount correcting means for correctingWith,The stored oxygen desorption amount existence region setting means determines an air-fuel ratio region by using an air-fuel ratio detected downstream of the three-way catalyst as a state amount representing the operating state of the internal combustion engine, and enters the air-fuel ratio region. Set the corresponding storage oxygen desorption amount existence regionIt is characterized by that.
[0015]
  Here, the storage oxygen desorption amount existence region setting means is between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount.The mostA storage oxygen desorption amount existence region that is smaller than the region between the large storage oxygen desorption amount and the minimum storage oxygen desorption amount and is likely to be located in the three-way catalyst.Depending on the operating condition of the internal combustion engineIt is set. That is, this storage oxygen desorption amount existing region reflects the actual storage oxygen desorption amount by responding to the operating state of the internal combustion engine at that time.
[0016]
  The stored oxygen desorption amount correcting means refers to the stored oxygen desorption amount existing region, and the stored oxygen desorption amount integrated by the stored oxygen desorption amount integrating means is the stored oxygen desorption amount. The stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means when it is outside the storage oxygen desorption amount existing area set by the existing region setting meansThe value of theNear the storage oxygen desorption amount existing region or within the storage oxygen desorption amount existing regionYouIt has been corrected so that.
[0017]
  Thus, as in the prior art, when the stored oxygen desorption amount is out of the storage oxygen desorption amount existing region without requiring a relatively large state change of the air-fuel ratio sensor downstream of the three-way catalyst. Is close to the storage oxygen desorption amount existence region or within the storage oxygen desorption amount existence region.YouStorage oxygen desorption amountThe value of theCan be corrected to a more appropriate state.
[0018]
For this reason, the opportunity to correct the calculated stored oxygen desorption amount increases. In addition, since correction to an extreme value is suppressed, it is difficult to generate a state in which the error from the actual stored oxygen desorption amount is large after correction. Thus, the state where the calculated amount of stored oxygen desorption is inappropriate does not continue for a long time. Therefore, it is possible to correct the calculated stored oxygen desorption amount to an appropriate value before the emission is easily deteriorated, and it is possible to reliably prevent the emission deterioration.
[0022]
  furtherFor example, an air-fuel ratio detected downstream of the three-way catalyst is used as the state quantity representing the operating state of the internal combustion engine. Therefore, for example, if the air-fuel ratio downstream of the three-way catalyst is in a rich state, the storage oxygen desorption amount existence region in this rich state can be set. In the lean state, the stored oxygen desorption in the lean state can be set. A separation amount existence area can be set. In this way, the air-fuel ratio state is independent of the air-fuel ratio change.(Air-fuel ratio region)Therefore, it is possible to set the storage oxygen desorption amount existence region, so that the opportunity for appropriately correcting the calculated stored oxygen desorption amount increases, and the calculated stored oxygen desorption amount is in an inappropriate state. No longer lasting for a long time.
[0023]
  Claim2The three-way catalyst storage oxygen desorption amount calculation device described isA three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine, wherein the three-way catalyst is based on an exhaust state flowing into the three-way catalyst Between the maximum stored oxygen desorption amount and the minimum stored oxygen desorption amount in the three-way catalyst. A storage oxygen desorption amount existence region that is smaller than the region between the desorption amounts and is likely to be located in the three-way catalyst is determined according to the operating state of the internal combustion engine. The stored oxygen desorption amount existing region setting means and the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means are set by the stored oxygen desorption amount existing region setting means. If the amount is out of the region, the storage acid Storage oxygen that is corrected so that the stored oxygen desorption amount accumulated by the desorption amount integrating means approaches the stored oxygen desorption amount existing region or is within the stored oxygen desorption amount existing region A desorption amount correcting means,The stored oxygen desorption amount existence region setting means uses a fuel cut process for stopping the fuel supply to the internal combustion engine during operation of the internal combustion engine as a state quantity representing the operation state of the internal combustion engine, thereby A storage oxygen desorption amount existence region corresponding to the presence or absence of processing is set.
[0024]
As the state quantity representing the operating state of the internal combustion engine, for example, the presence or absence of fuel cut processing is used. Therefore, for example, if the fuel cut process is performed, it is possible to set the storage oxygen desorption amount existence region considering that the supply of the oxygen amount to the three-way catalyst is large. In this way, the storage oxygen desorption amount existence region can be set depending on whether or not the fuel cut process is performed regardless of the change in the air-fuel ratio, so that the opportunity for appropriately correcting the calculated stored oxygen desorption amount is increased. Thus, a state where the calculated amount of stored oxygen desorption is inappropriate does not continue for a long time.
[0025]
  Claim3The three-way catalyst storage oxygen desorption amount calculation device described isA three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine, wherein the three-way catalyst is based on an exhaust state flowing into the three-way catalyst Between the maximum stored oxygen desorption amount and the minimum stored oxygen desorption amount in the three-way catalyst. A storage oxygen desorption amount existence region that is smaller than the region between the desorption amounts and is likely to be located in the three-way catalyst is determined according to the operating state of the internal combustion engine. The stored oxygen desorption amount existing region setting means and the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means are set by the stored oxygen desorption amount existing region setting means. If the amount is out of the region, the storage acid Storage oxygen that is corrected so that the stored oxygen desorption amount accumulated by the desorption amount integrating means approaches the stored oxygen desorption amount existing region or is within the stored oxygen desorption amount existing region A desorption amount correcting means,The stored oxygen desorption amount existence region setting means includes, as state quantities indicating the operation state of the internal combustion engine, presence or absence of a fuel cut process for stopping fuel supply to the internal combustion engine during operation of the internal combustion engine, and downstream of the three-way catalyst. By using the air-fuel ratio detected in step 3, the presence or absence of fuel cut processing and the stored oxygen desorption amount existing region corresponding to the air-fuel ratio detected downstream of the three-way catalyst are set.
[0026]
  As the state quantity representing the operating state of the internal combustion engine, for example, the presence or absence of fuel cut processing for stopping the fuel supply to the internal combustion engine during the operation of the internal combustion engine and the air-fuel ratio detected downstream of the three-way catalyst are used. . Therefore, for example, in the state where the fuel cut process is performed, it is possible to set the storage oxygen desorption amount existence region in consideration of the large amount of oxygen supply to the three-way catalyst. Further, when the fuel cut processing is not performed, the air-fuel ratio detected downstream of the three-way catalyst is used, and the claim1As described above, the storage oxygen desorption amount existence region can be set. In this way, the stored oxygen desorption amount existence region can be set depending on the presence or absence of fuel cut processing and the state of the air-fuel ratio downstream of the three-way catalyst regardless of the change in the air-fuel ratio. Opportunities to appropriately correct the separation amount are increased, and the state where the calculated stored oxygen desorption amount is inappropriate is not continued for a long time.
[0027]
  Claim4The three-way catalyst storage oxygen desorption amount calculation device described isA three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine, wherein the three-way catalyst is based on an exhaust state flowing into the three-way catalyst Between the maximum stored oxygen desorption amount and the minimum stored oxygen desorption amount in the three-way catalyst. A storage oxygen desorption amount existence region that is smaller than the region between the desorption amounts and is likely to be located in the three-way catalyst is determined according to the operating state of the internal combustion engine. The stored oxygen desorption amount existing region setting means and the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means are set by the stored oxygen desorption amount existing region setting means. If the amount is out of the region, the storage acid Storage oxygen that is corrected so that the stored oxygen desorption amount accumulated by the desorption amount integrating means approaches the stored oxygen desorption amount existing region or is within the stored oxygen desorption amount existing region A desorption amount correcting means,The stored oxygen desorption amount existence region setting means is a temperature of the three-way catalyst as a state quantity indicating an operating state of the internal combustion engine.And using, Air fuel detected downstream of the three-way catalystRatioBy usingJudging the air-fuel ratio regionThree-way catalyst temperature andSaidAir-fuel ratioregionThe storage oxygen desorption amount existence region corresponding to is set.
[0028]
  As the state quantity indicating the operating state of the internal combustion engine, for example, the temperature of the three-way catalystAnd using, Air fuel detected downstream of the three-way catalystRatioUseTo determine the air-fuel ratio region. The maximum amount of oxygen stored in the three-way catalyst varies depending on the temperature. For this reason, the air-fuel ratio downstream of the three-way catalystregionEven when the storage oxygen desorption amount existence region is set according to the temperature, it is possible to set an appropriate storage oxygen desorption amount existence region by changing the range of the storage oxygen desorption amount existence region according to the temperature. it can. Therefore, the calculation of the stored oxygen desorption amount can be made more appropriate, and the claim1'sThe effect can be made more remarkable.
[0029]
  Claim5The three-way catalyst storage oxygen desorption amount calculation device described isA three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine, wherein the three-way catalyst is based on an exhaust state flowing into the three-way catalyst Between the maximum stored oxygen desorption amount and the minimum stored oxygen desorption amount in the three-way catalyst. A storage oxygen desorption amount existence region that is smaller than the region between the desorption amounts and is likely to be located in the three-way catalyst is determined according to the operating state of the internal combustion engine. The stored oxygen desorption amount existing region setting means and the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means are set by the stored oxygen desorption amount existing region setting means. If the amount is out of the region, the storage acid Storage oxygen that is corrected so that the stored oxygen desorption amount accumulated by the desorption amount integrating means approaches the stored oxygen desorption amount existing region or is within the stored oxygen desorption amount existing region A desorption amount correcting means,The stored oxygen desorption amount existence region setting means includes a temperature of the three-way catalyst as a state quantity indicating an operation state of the internal combustion engine, and presence / absence of fuel cut processing for stopping fuel supply to the internal combustion engine during operation of the internal combustion engine Are used to set the storage oxygen desorption amount existence region corresponding to the temperature of the three-way catalyst and the presence or absence of the fuel cut processing.
[0030]
  As the state quantity representing the operation state of the internal combustion engine, for example, the temperature of the three-way catalyst and the presence or absence of the fuel cut process are used. Therefore, for example, if a fuel cut process is performed, a storage oxygen desorption amount existence region can be set in consideration of a large amount of oxygen supply to the three-way catalyst. The degree of adsorption of the amount of oxygen to the three-way catalyst accompanying the fuel cut process also changes. For this reason, even when the storage oxygen desorption amount existence region is set according to the execution of the fuel cut process, by changing the range of the storage oxygen desorption amount existence region according to the temperature, an appropriate storage oxygen desorption amount can be obtained. A quantity existing area can be set. Therefore, the calculation of the stored oxygen desorption amount can be corrected more appropriately.Wear.
[0031]
  Claim6The three-way catalyst storage oxygen desorption amount calculation device described isA three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine, wherein the three-way catalyst is based on an exhaust state flowing into the three-way catalyst Between the maximum stored oxygen desorption amount and the minimum stored oxygen desorption amount in the three-way catalyst. A storage oxygen desorption amount existence region that is smaller than the region between the desorption amounts and is likely to be located in the three-way catalyst is determined according to the operating state of the internal combustion engine. The stored oxygen desorption amount existing region setting means and the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means are set by the stored oxygen desorption amount existing region setting means. If the amount is out of the region, the storage acid Storage oxygen that is corrected so that the stored oxygen desorption amount accumulated by the desorption amount integrating means approaches the stored oxygen desorption amount existing region or is within the stored oxygen desorption amount existing region A desorption amount correcting means,The stored oxygen desorption amount existence region setting means includes a temperature of the three-way catalyst as a state quantity indicating an operation state of the internal combustion engine, and presence / absence of fuel cut processing for stopping fuel supply to the internal combustion engine during operation of the internal combustion engine And the air-fuel ratio detected downstream of the three-way catalyst, the temperature of the three-way catalyst, the presence or absence of fuel cut processing, and the presence of stored oxygen desorption corresponding to the air-fuel ratio detected downstream of the three-way catalyst An area is set.
[0032]
Therefore, for example, in the state where the fuel cut process is performed, it is possible to set the storage oxygen desorption amount existence region considering that the supply of the oxygen amount to the three-way catalyst is large. Accordingly, an appropriate storage oxygen desorption amount existence region can be set by changing the range of the storage oxygen desorption amount existence region.
[0033]
  Further, when the fuel cut processing is not performed, the air-fuel ratio detected downstream of the three-way catalyst is used, and the claim1The storage oxygen desorption amount existence region can be set as described in the above, but by changing the range of the storage oxygen desorption amount existence region according to the temperature at this time, an appropriate storage oxygen desorption amount existence region can be set. Can be set.
[0034]
  Thus, an appropriate storage oxygen desorption amount existence region can be set by changing the range of the storage oxygen desorption amount existence region according to the temperature. Therefore, the calculation of the stored oxygen desorption amount can be corrected more appropriately.Wear.
[0035]
  Claim7The three-way catalyst storage oxygen desorption amount calculation device described in claim2,3,5Or6In the configuration described above, the storage oxygen desorption amount existence region setting means is configured to reduce the stoichiometric air-fuel ratio downstream of the three-way catalyst immediately after the end of the fuel cut processing for stopping the fuel supply to the internal combustion engine during operation of the internal combustion engine. However, when the air-fuel ratio with a low fuel concentration continues, a storage oxygen desorption amount existence region corresponding to the presence of fuel cut processing is set.
[0036]
  Immediately after the fuel cut is completed, the increase in the stored oxygen desorption amount may be slower than expected. Therefore, in response to such a case, immediately after the end of the fuel cut process, if an air-fuel ratio with a fuel concentration lower than the stoichiometric air-fuel ratio continues downstream of the three-way catalyst, it corresponds to the presence of the fuel cut process. The storage oxygen desorption amount existence region to be set is set. This makes it possible to more appropriately correct the calculated amount of stored oxygen desorption.2,3,5Or6The effect can be made more prominent.
[0037]
  Claim8The three-way catalyst stored oxygen desorption amount calculation device according to claim 1,7In addition to any one of the configurations described above, a three-way catalyst adsorption capacity estimation means for estimating the oxygen adsorption capacity of the three-way catalyst is provided. The storage oxygen desorption amount existence region in the three-way catalyst is set according to the oxygen adsorption ability of the three-way catalyst estimated by the three-way catalyst adsorption capacity estimating means.
[0038]
  The oxygen adsorption capacity of the three-way catalyst deteriorates with time. For this reason, the oxygen adsorption capacity of the three-way catalyst is estimated by the three-way catalyst adsorption capacity estimation means, and is reflected in the setting of the storage oxygen desorption amount existing region in the three-way catalyst. Thus, an appropriate storage oxygen desorption amount existence region can be set. Therefore, the calculation of the stored oxygen desorption amount can be made more appropriate,7The effect described in any of the above can be made more remarkable.
[0039]
  Claim9The three-way catalyst storage oxygen desorption amount calculation device described in claim8The configuration described above is characterized in that the three-way catalyst adsorption capacity estimating means estimates the oxygen adsorption capacity of the three-way catalyst according to the accumulated usage time of the three-way catalyst.
[0040]
  Since the oxygen adsorption capacity of the three-way catalyst deteriorates with time, the oxygen adsorption capacity of the three-way catalyst can be estimated according to the cumulative usage time of the three-way catalyst. By using the oxygen adsorption capacity of the three-way catalyst estimated in this way, the calculation of the stored oxygen desorption amount can be made more appropriate,7The effect described in any of the above can be made more remarkable.
[0041]
  Claim10The three-way catalyst stored oxygen desorption amount calculation device according to claim 1,7In addition to any one of the configurations described above, a three-way catalyst adsorption capacity detection means for detecting the oxygen adsorption capacity of the three-way catalyst is provided. The storage oxygen desorption amount existence region in the three-way catalyst is set according to the oxygen adsorption ability of the three-way catalyst detected by the three-way catalyst adsorption capacity detecting means.
[0042]
  The oxygen adsorption capacity of the three-way catalyst deteriorates with time. In addition, other factors may affect the degree of this deterioration. For this reason, the oxygen adsorption capacity of the three-way catalyst is detected by the three-way catalyst adsorption capacity detection means and reflected in the setting of the storage oxygen desorption amount existing region in the three-way catalyst. Thus, an appropriate storage oxygen desorption amount existence region can be set. Therefore, the calculation of the stored oxygen desorption amount can be made more appropriate,7The effect described in any of the above can be made more remarkable.
[0043]
  Claim11The three-way catalyst storage oxygen desorption amount calculation device described in claim10In the configuration described above, the three-way catalyst adsorption capacity detecting means is configured such that the air-fuel ratio detected downstream of the three-way catalyst is higher than the stoichiometric air-fuel ratio when oxygen is saturated in the three-way catalyst. The oxygen adsorption capacity of the three-way catalyst is detected in accordance with the integrated value of the excess and deficiency of the fuel concentration calculated based on the exhaust state flowing into the three-way catalyst until the time becomes.
[0044]
When the air-fuel ratio detected downstream of the three-way catalyst becomes a fuel concentration higher than the stoichiometric air-fuel ratio, it is considered that the amount of oxygen stored in the three-way catalyst has become almost zero. Therefore, during the period from when oxygen is saturated in the three-way catalyst to when the air-fuel ratio detected downstream of the three-way catalyst is in a state where the fuel concentration is higher than the stoichiometric air-fuel ratio, the three-way catalyst The integrated value of the excess and deficiency of the fuel concentration calculated based on the exhaust state flowing into the gas indicates the maximum stored oxygen amount of the three-way catalyst. This level of maximum stored oxygen amount represents the degree of oxygen adsorption capacity of the three-way catalyst, that is, the degree of deterioration of the three-way catalyst.
[0045]
  Therefore, an appropriate storage oxygen desorption amount existence region can be set using the oxygen adsorption ability of the three-way catalyst detected in this way. For this reason, the calculation of the stored oxygen desorption amount can be made more appropriate.7The effect described in any of the above can be made more remarkable.
[0046]
  Claim12The three-way catalyst storage oxygen desorption amount calculation device described in claim11In the configuration described above, the three-way catalyst adsorption capacity detecting means is configured such that oxygen is saturated in the three-way catalyst when fuel cut processing for stopping fuel supply to the internal combustion engine continues for a reference time or longer during operation of the internal combustion engine. It is characterized in that integration of the excess / deficiency amount of the fuel concentration calculated based on the exhaust state flowing into the three-way catalyst is started.
[0047]
In this way, when the fuel cut process continues for the reference time or longer, it can be considered that oxygen is saturated in the three-way catalyst. Therefore, accumulation of excess and deficiency of the fuel concentration calculated based on the exhaust state flowing into the three-way catalyst is started, and the air-fuel ratio detected downstream of the three-way catalyst is higher than the stoichiometric air-fuel ratio. The fuel concentration excess / deficiency may be integrated until the state is reached.
[0048]
  Thus, an appropriate storage oxygen desorption amount existence region can be set using the oxygen adsorption capability of the three-way catalyst detected by using the fuel cut process. Therefore, even during operation of the internal combustion engine, the deterioration state of the three-way catalyst can be obtained, and the calculation of the stored oxygen desorption amount can be made more appropriate.7The effect described in any of the above can be made more remarkable.
The three-way catalyst stored oxygen desorption amount calculating device according to claim 13 is the configuration according to any one of claims 1 to 12, wherein the stored oxygen desorption amount integrating means represents an exhaust state flowing into the three-way catalyst. By using the intake air amount to the internal combustion engine and the air-fuel ratio detected upstream of the three-way catalyst as the state quantity, the balance between the oxygen adsorption amount and the separation amount in the three-way catalyst is integrated to obtain a three-way The amount of stored oxygen desorption in the catalyst is obtained.
Here, as a method for obtaining the stored oxygen desorption amount, for example, an intake air amount to the internal combustion engine and an air-fuel ratio detected upstream of the three-way catalyst are state quantities representing an exhaust state flowing into the three-way catalyst. Can be used. From the intake air amount and the air-fuel ratio upstream of the three-way catalyst, the amount of oxygen supplied to the three-way catalyst and the amount of fuel as the reducing agent can be obtained. Therefore, by calculating the balance between the amount of oxygen adsorbed on the three-way catalyst by supplying oxygen and the amount of oxygen released on the three-way catalyst by fuel, the calculated stored oxygen desorption amount can be obtained. The effects described in claims 1 to 12 can be produced.
[0049]
  Claim14An air-fuel ratio control apparatus for an internal combustion engine according to claim 113The three-way catalyst storage oxygen desorption amount calculation device according to any one of the above, and the storage oxygen desorption amount of the three-way catalyst calculated by the three-way catalyst storage oxygen desorption amount calculation device is the target storage oxygen desorption amount The air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is controlled so as to be the amount.
[0050]
  Thus, an air-fuel ratio control apparatus for an internal combustion engine includes:13By using the three-way catalyst stored oxygen desorption amount calculation device described in any one of the above, there is no problem in the difference between the calculated stored oxygen desorption amount and the actual stored oxygen desorption amount. Therefore, oxidation of HC and CO and reduction of NOx are always favorably performed, and the internal combustion engine emission can be maintained well.
[0051]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 1 is a block diagram showing a schematic configuration of a gasoline engine (hereinafter abbreviated as “engine”) 4 to which the above-described invention is applied and an air-fuel ratio control device thereof.
[0052]
A cylinder block 6 of the engine 4 is formed with a first cylinder 8, a second cylinder 10, a third cylinder 12 and a fourth cylinder 14 including a combustion chamber. An intake passage 20 is connected to each cylinder 8 to 14 via an intake manifold 16 and a surge tank 18. An air cleaner 22 is provided upstream of the intake passage 20, and outside air is introduced into the intake passage 20 through the air cleaner 22.
[0053]
The intake manifold 16 is provided with injectors 24, 26, 28, and 30 corresponding to the cylinders 8 to 14, respectively. The injectors 24 to 30 are electromagnetic valves that are driven to open and close by energization control and inject fuel. Fuel in a fuel tank (not shown) is pumped from a fuel pump (not shown). The fuel injected from the injectors 24 to 30 is mixed with the intake air in the intake manifold 16 to become an air-fuel mixture. This air-fuel mixture is introduced into the combustion chamber of each cylinder 8-14 from an intake port (not shown) opened by opening an intake valve (not shown) provided for each cylinder 8-14. . At the time of air-fuel ratio feedback control, the length of the fuel injection time by the injectors 24 to 30 is adjusted based on the air-fuel ratio feedback correction coefficient FAF. Also in the feedback control of the stored oxygen desorption amount of the three-way catalyst described later, the stored oxygen desorption amount is controlled by adjusting the length of the fuel injection time.
[0054]
A throttle valve 32 for adjusting the amount of intake air is provided in the intake passage 20 at a position upstream of the surge tank 18. The throttle valve 32 is driven to open and close by a throttle motor 34 provided in the intake passage 20 so that the opening, that is, the throttle opening TA is adjusted. A throttle opening sensor 36 is provided in the vicinity of the throttle valve 32. The throttle opening sensor 36 detects the throttle opening TA and outputs a signal corresponding to the throttle opening TA.
[0055]
An accelerator pedal 38 is provided in the driver's cab of the automobile, and the amount of depression of the accelerator pedal 38, that is, the accelerator opening ACCP is detected by the accelerator opening sensor 40. An electronic control unit (hereinafter referred to as “ECU”) 50, which will be described later, controls the throttle motor 34 based on the accelerator opening ACCP and the like to adjust the throttle opening TA to an opening corresponding to the operating state. .
[0056]
An exhaust passage 62 is connected to each of the cylinders 8 to 14 via an exhaust manifold 60. The exhaust passage 62 is provided with a catalytic converter 64 and a muffler 66 in which a three-way catalyst 63 is accommodated. Exhaust gas flowing through the exhaust passage 62 passes through the catalytic converter 64 and the muffler 66 and is discharged to the outside. The catalyst temperature sensor 67 detects the temperature of the three-way catalyst 63 inside the catalytic converter 64 and outputs a signal corresponding to the catalyst temperature Tc.
[0057]
The three-way catalyst 63 in Embodiment 1 functions to oxidize HC and CO in the exhaust gas and reduce NOx when the air-fuel ratio of the air-fuel mixture is substantially the stoichiometric air-fuel ratio, that is, simultaneously purify HC, CO and NOx. Has the function of Further, the three-way catalyst 63 of the first embodiment has a function of storing oxygen therein, and even if the air-fuel ratio deviates from the stoichiometric air-fuel ratio by this oxygen storage function, HC, CO and NOx in the exhaust gas are exhausted. Can be purified. This oxygen storage action is performed by, for example, cerium Ce contained in the three-way catalyst 63.
[0058]
An air flow meter 68 is provided between the air cleaner 22 and the throttle valve 32 in the intake passage 20. The air flow meter 68 detects the intake air amount GA introduced into the combustion chambers of the cylinders 8 to 14 and outputs a signal corresponding to the intake air amount GA.
[0059]
The cylinder head 6a of the engine 4 is provided with spark plugs 70, 72, 74, and 76 corresponding to the cylinders 8 to 14, respectively. Each of the spark plugs 70 to 76 is configured as a direct ignition system that does not use a distributor by attaching an ignition coil 70a, 72a, 74a, 76a. Each of the ignition coils 70a to 76a directly applies to the ignition plugs 70 to 76 a high voltage generated based on the interruption of the primary current supplied from the ignition drive circuit in the ECU 50 at the ignition timing.
[0060]
An air-fuel ratio sensor 80 is provided in the exhaust passage 62 upstream of the catalytic converter 64. The air-fuel ratio sensor 80 outputs a signal Vox corresponding to the air-fuel ratio of the air-fuel mixture that appears in the exhaust components. At the time of air-fuel ratio feedback control, the air-fuel ratio is controlled based on this signal Vox, and the air-fuel ratio is adjusted to the stoichiometric air-fuel ratio by the fuel injection amount increasing / decreasing process.
[0061]
An oxygen sensor 82 is provided in the exhaust passage 62 on the downstream side of the catalytic converter 64. The oxygen sensor 82 outputs a signal Vz corresponding to the oxygen concentration in the exhaust gas (corresponding to the air-fuel ratio downstream of the three-way catalyst 63).
[0062]
The rotational speed sensor 90 outputs a pulse signal of a number corresponding to the rotational speed NE of the engine 4 based on the rotation of the crankshaft (not shown) of the engine 4, and the cylinder discrimination sensor 92 discriminates the cylinders 8 to 14. Therefore, a pulse signal serving as a reference signal is output at every predetermined crank angle based on the rotation of the crankshaft. The ECU 50 calculates the rotational speed NE, cylinder discrimination, and crank angle based on the output signals from the rotation speed sensor 90 and the cylinder discrimination sensor 92.
[0063]
The cylinder block 6 is provided with a water temperature sensor 94 for detecting the engine coolant temperature, and outputs a signal corresponding to the coolant temperature THW. A shift position sensor 96 and a vehicle speed sensor 97 are provided in a transmission (not shown), and a signal corresponding to the shift position SHFTP or the vehicle speed Vt is output.
[0064]
Next, the electrical configuration of the control system that performs the function of the air-fuel ratio control apparatus in the first embodiment will be described with reference to the block diagram of FIG.
The ECU 50 includes a central processing unit (CPU) 50a, a read only memory (hereinafter referred to as “ROM”) 50b, a random access memory (hereinafter referred to as “RAM”) 50c, a backup RAM 50d, and the like. And an input circuit 50e, an output circuit 50f, and the like are connected by a bidirectional bus 50g. The ROM 50b stores in advance various control programs such as air-fuel ratio feedback control and stored oxygen desorption amount OSC control, which will be described later, and various data. The RAM 50c temporarily stores calculation results of the CPU 50a in various control processes.
[0065]
The input circuit 50e is configured as an input interface including a buffer, a waveform shaping circuit, an A / D converter, and the like. The throttle opening sensor 36, the accelerator opening sensor 40, the catalyst temperature sensor 67, the air flow meter 68. , An air-fuel ratio sensor 80, an oxygen sensor 82, a rotation speed sensor 90, a cylinder discrimination sensor 92, a water temperature sensor 94, a shift position sensor 96, a vehicle speed sensor 97, lines of ignition confirmation signals IGf of the ignition coils 70a to 76a, etc. are connected. Has been. Output signals from the various sensors 36, 40, 67, 68, 80, 82, 90, 92, 94, 96, 97, etc. are read as digital signals from the input circuit 50e to the CPU 50a via the bidirectional bus 50g.
[0066]
On the other hand, the output circuit 50f has various drive circuits and the like, to which the injectors 24 to 30, the ignition coils 70a to 76a, the throttle motor 34, and the like are connected. The ECU 50 performs arithmetic processing based on the output signals from the various sensors 36, 40, 67, 68, 80, 82, 90, 92, 94, 96, 97, etc., and the injectors 24-30, the ignition coils 70a-76a, the throttle. The motor 34 and the like are controlled.
[0067]
For example, the ECU 50 uses the intake air amount GA detected by the air flow meter 68, the rotational speed NE detected by the rotational speed sensor 90, and the like, the fuel injection amount and fuel injection timing by the injectors 24 to 30, or the ignition coils 70a to 70a. The ignition timing by 76a is controlled. Based on the air-fuel ratio detected by the air-fuel ratio sensor 80, as will be described later, the fuel injection amount is corrected by the injectors 24 to 30 to precisely control the air-fuel ratio of the air-fuel mixture. Further, in order to set the stored oxygen desorption amount OSC in the three-way catalyst 63 in the catalytic converter 64 to the target stored oxygen desorption amount OSCTG, it depends on the detected values of the air-fuel ratio sensor 80 and the oxygen sensor 82 and other engine operating conditions. Thus, correction of the fuel injection amount by the injectors 24 to 30 is executed.
[0068]
Here, the air-fuel ratio sensor 80 on the upstream side of the three-way catalyst 63 generates a current I corresponding to the air-fuel ratio A / F as shown in FIG. This current I is converted into a voltage signal Vox and input to the ECU 50 via an AD converter in the input circuit 50e. Therefore, the air-fuel ratio A / F upstream of the three-way catalyst 63 can be known from the output signal of the air-fuel ratio sensor 80.
[0069]
On the other hand, the oxygen sensor 82 on the downstream side of the catalytic converter 64 generates an output voltage signal Vz that changes suddenly at the stoichiometric air-fuel ratio as shown in FIG. That is, the oxygen sensor 82 generates an output voltage V of about 0.1 V when the air-fuel ratio A / F is lean, and generates an output voltage of about 0.9 V when the air-fuel ratio A / F is rich. Therefore, the state of the air-fuel ratio A / F downstream of the three-way catalyst 63 can be determined based on the level of the output voltage signal Vz. In the first embodiment, when the voltage signal Vz of the oxygen sensor 82 is lower than the voltage determination value VS, it is determined that the air-fuel ratio A / F on the downstream side of the three-way catalyst 63 is lean, and the oxygen sensor 82 When the voltage signal Vz is equal to or higher than the voltage determination value VS, it is determined that the air-fuel ratio downstream of the three-way catalyst 63 is rich.
[0070]
Next, the fuel injection amount control process executed by the ECU 50 in the first embodiment will be described based on the flowchart of FIG. This process is a process periodically executed for each preset crank angle. A step corresponding to each process in the flowchart is represented by “S˜”.
[0071]
When the fuel injection amount control process is started, first, the accelerator opening ACCP obtained from the accelerator opening sensor 40, the engine rotational speed NE obtained from the rotational speed sensor 90, and the air flow meter 68 are obtained. Necessary data such as the intake air amount GA, the coolant temperature THW obtained from the signal of the water temperature sensor 94, and the output voltage value Vox obtained from the air-fuel ratio sensor 80 are read into the work area of the RAM 50c (S110).
[0072]
Next, it is determined whether or not the fuel cut execution flag Fca is set to “OFF” (S120).
Here, the fuel cut processing for setting the fuel cut execution flag Fca is as shown in the flowchart of FIG. 5 and is executed at regular intervals. That is, in the fuel cut process, it is first determined whether or not a fuel cut condition is satisfied (S210). If the fuel cut condition is satisfied (“YES” in S210), “ON” is set to the fuel cut execution flag Fca (S220), and if not satisfied (“NO” in S210), the fuel cut execution flag is set. “OFF” is set in Fca (S230).
[0073]
Here, the fuel cut condition is, for example, a state where the vehicle is in a deceleration state that requires fuel cut based on the accelerator opening ACCP detected from the accelerator opening sensor 40 or the vehicle speed Vt detected from the vehicle speed sensor 97, The engine speed NE detected from the speed sensor 90 is higher than the fuel cut speed, or the vehicle speed Vt is higher than the regulated maximum speed.
[0074]
Returning to the explanation of FIG. 4, when the fuel cut execution flag Fca set in this way is “ON” (“NO” in S120), “0” is set as the fuel injection amount Q ( S130), the fuel injection amount control process is once ended. Therefore, the fuel injection from each injector 24-30 stops. At the same time, high-voltage power supply to the spark plugs 70 to 76 is also stopped in an ignition control process (not shown).
[0075]
On the other hand, if Fca = “OFF” (“YES” in S120), the theoretical sky is calculated from the intake air amount GA and the engine speed NE using the map of FIG. 6 set in the ROM 50b in advance. The basic fuel injection amount QBS is calculated (S140).
[0076]
Next, a high load increase OTP calculation process (S150) is performed. The high load increase OTP calculation process will be described based on the flowchart of FIG. In the high load increase OTP calculation process, it is first determined whether or not the accelerator opening ACCP exceeds the high load increase determination value KOTPAC (S310).
[0077]
If ACCP ≦ KOTPAC (“NO” in S310), “0” is set to the high load increase OTP (S320). That is, the fuel increase correction is not performed. Thus, the high load increase OTP calculation process is temporarily exited.
[0078]
If ACCP> KOTPAC (“YES” in S310), a value M (for example, 1> M> 0) is set to the high load increase OTP (S330). That is, execution of fuel increase correction is set. This increase correction is performed in order to prevent the catalytic converter 64 from overheating during a high load.
[0079]
Returning to FIG. 4, after the high load increase OTP is calculated in step S150, it is next determined whether or not the air-fuel ratio feedback condition is satisfied (S160). For example, “(1) Not at start-up. (2) Activation of the air-fuel ratio sensor 80 has been completed. (3) The value of the high load increase OTP is 0. (4) Other necessary conditions” It is determined whether all are true.
[0080]
If the air-fuel ratio feedback condition is satisfied (“YES” in S160), the air-fuel ratio feedback coefficient FAF and its learning value KG are calculated (S170). The air-fuel ratio feedback coefficient FAF is calculated based on the output of the air-fuel ratio sensor 80. Further, the learning value KG stores a deviation from the center value 1.0 in the average value of the air-fuel ratio feedback coefficient FAF. As the air-fuel ratio feedback control technique using these values, various methods are known as disclosed in JP-A-6-10737.
[0081]
On the other hand, if the air-fuel ratio feedback condition is not satisfied (“NO” in S160), 1.0 is set to the air-fuel ratio feedback coefficient FAF (S180).
Following step S170 or S180, the fuel injection amount Q is obtained as in the following equation 1 (S190).
[0082]
[Expression 1]
Q ← QBS {1 + OTP + (FAF-1.0) + (KG-1.0) + KC} α + β [Formula 1]
Here, α and β are coefficients appropriately set according to the type of engine 4 and the content of control. The stored oxygen desorption amount feedback coefficient KC is a coefficient calculated by a storage oxygen desorption amount feedback coefficient KC calculation process described later.
[0083]
Thus, the fuel injection amount control process is once completed.
Next, the stored oxygen desorption amount calculation process is shown in FIG. This process is repeatedly executed at a preset time period.
[0084]
When the stored oxygen desorption amount calculation process is started, first, the intake air amount GA detected by the air flow meter 68 is read into the work area of the RAM 50c (S400). Next, the upstream air-fuel ratio A / F detected by the air-fuel ratio sensor 80 upstream of the three-way catalyst 63 is read into the work area of the RAM 50c (S410). Next, the downstream air-fuel ratio subA / F detected by the oxygen sensor 82 on the downstream side of the catalytic converter 64 is read into the work area of the RAM 50c (S420). Next, the catalyst temperature Tc detected by the catalyst temperature sensor 67 is read into the work area of the RAM 50c (S430).
[0085]
Then, the count value TD for obtaining the accumulated usage time of the three-way catalyst 63 is incremented by 1 (S440). Note that the count value TD is maintained by being stored in the backup RAM 50d even when the ECU 50 is powered off.
[0086]
Next, it is determined whether or not a certain time has elapsed after the engine 4 is started (S450). If the predetermined time has not elapsed since the engine 4 was started (“NO” in S450), the calculated stored oxygen desorption amount OSC set in the work area of the RAM 50c is cleared (S460) and temporarily stored. The oxygen desorption amount calculation process is terminated.
[0087]
The above-described processing (S400 to S460) is repeated until a certain time has elapsed after the engine 4 is started.
When a predetermined time has elapsed after the engine 4 is started (“YES” in S450), it is next determined whether or not the catalyst temperature Tc has become higher than the minimum use temperature Tco (for example, 100 ° C.) (S470). If Tc ≦ Tco (“NO” in S470), the three-way catalyst 63 is not yet fully activated, so the stored oxygen desorption amount OSC is cleared (S460), and the stored oxygen desorption amount is once calculated. The process ends.
[0088]
If Tc> Tco is satisfied due to the exhaust of the engine 4 (“YES” in S470), the three-way catalyst 63 is activated, and next, an accumulation process (S500) of the stored oxygen desorption amount OSC is executed.
[0089]
The details of the accumulation process of the stored oxygen desorption amount OSC are shown in the flowchart of FIG. When this process is started, it is first determined whether or not the upstream air-fuel ratio A / F is the stoichiometric air-fuel ratio (S510). If the upstream air-fuel ratio A / F is the stoichiometric air-fuel ratio (“YES” in S510), the integration process is exited as it is.
[0090]
If the upstream air-fuel ratio A / F is not the stoichiometric air-fuel ratio (“NO” in S510), it is next determined whether or not the upstream air-fuel ratio A / F is lean (S520). When the upstream air-fuel ratio A / F is lean (“YES” in S520), the stored oxygen desorption amount OSC is calculated from the following equation 2 (S530).
[0091]
[Expression 2]
OSC ← OSC− {KO2 · GA · (ΔA / F) / (A / F)} · Δt ... [Formula 2]
Here, the OSC on the right side is the stored oxygen desorption amount OSC in the previous control cycle, KO2 is the oxygen concentration in the air, and ΔA / F is the air-fuel ratio deviation (= upstream air-fuel ratio A / F-theoretical air-fuel ratio). , Δt represents the control cycle of the integration process.
[0092]
Within the right side of the above equation 2, the term represented by the following equation 3 represents the oxygen adsorption amount per time Δt.
[0093]
[Equation 3]
{KO2 · GA · (ΔA / F) / (A / F)} · Δt ... [Formula 3]
When the upstream air-fuel ratio A / F is lean, oxygen is adsorbed by the three-way catalyst 63, so that the above equation 3 is used. In this equation, KO2 · GA indicates the amount of oxygen supplied to the engine 4 per unit time, and (ΔA / F) / (A / F) indicates the ratio of excess oxygen when burned. . Therefore, {KO 2 · GA · (ΔA / F) / (A / F)} · Δt represents the amount of excess oxygen per time Δt. Since it is lean here, ΔA / F is positive. If such surplus oxygen exists, it is considered that this surplus oxygen is immediately adsorbed by the three-way catalyst 63. Therefore, the amount of adsorption per time Δt is the same as the amount of surplus oxygen, and the amount of adsorption per time Δt is expressed as in the above equation 3.
[0094]
Thus, when the upstream air-fuel ratio A / F is lean, the surplus oxygen amount of the above equation 3 is stored per time Δt. Therefore, the stored oxygen desorption amount OSC, which is a value indicating the desorption amount of oxygen from the three-way catalyst in the maximum stored oxygen amount state, conversely decreases by the excess oxygen amount of the above equation 3 per time Δt. Become. Therefore, the accumulation of the stored oxygen desorption amount OSC is expressed as shown in Equation 2 above.
[0095]
On the other hand, when it is determined in step S520 that the upstream air-fuel ratio A / F is not lean, that is, rich here (“NO” in S520), the stored oxygen desorption amount OSC is calculated from the following equation 4. (S540).
[0096]
[Expression 4]
OSC
← OSC- {KO2 · GA · k · (ΔA / F) / (A / F)} · Δt ... [Formula 4]
Here, k represents the ratio (desorption rate / adsorption rate) between the desorption rate of oxygen to the three-way catalyst 63 and the adsorption rate. The other symbols are as described in Equation 2 above.
[0097]
Further, in the right side of the above formula 4, the term shown by the following formula 5 represents the amount of oxygen desorption per time Δt.
[0098]
[Equation 5]
{KO2 · GA · k · (ΔA / F) / (A / F)} · Δt ... [Formula 5]
Since the oxygen is desorbed from the three-way catalyst 63 when the upstream air-fuel ratio A / F is rich, the above equation 5 is used. In Equation 5, KO2 · GA indicates the amount of oxygen supplied to the engine 4 per unit time. On the other hand, in this formula 5, (ΔA / F) / (A / F) indicates the ratio of oxygen deficient when burned. For this reason, {KO2 · GA · (ΔA / F) / (A / F)} · Δt represents the deficient oxygen amount per time Δt. Here, ΔA / F is negative.
[0099]
If there is a shortage of oxygen during combustion, unburned HC and CO are generated by the amount of the shortage oxygen, and an amount of oxygen proportional to the amount of unburned HC and CO generated, that is, an amount of oxygen proportional to the amount of shortage Desorbed from the three-way catalyst 63. However, the oxygen desorption rate from the three-way catalyst 63 is slower than the oxygen adsorption rate to the three-way catalyst 63. For this reason, the amount of oxygen desorbed from the three-way catalyst 63 is the amount of oxygen deficient indicated by {KO2 · GA · (ΔA / F) / (A / F)} · Δt, because the desorption rate is slower than the adsorption rate. Less than the amount. Therefore, if the rate ratio between the desorption rate and the adsorption rate is k, the desorption amount per time Δt is an amount obtained by multiplying the deficient oxygen amount by the rate ratio k. Therefore, the amount of desorption per time Δt is expressed as in Equation 5 above.
[0100]
Thus, when the upstream air-fuel ratio A / F is rich, the deficient oxygen amount / speed ratio k per time Δt is desorbed, and the stored oxygen desorption amount OSC is only the deficient oxygen amount / speed ratio k per time Δt. Will increase. Therefore, considering that ΔA / F <0, the stored oxygen desorption amount OSC is expressed by the above equation 4.
[0101]
Thus, after the accumulation of the stored oxygen desorption amount OSC (S530, S540) is executed, the accumulation process is finished.
Returning to FIG. 8, when the stored oxygen desorption amount OSC integration process in step S <b> 500 ends, the stored oxygen desorption amount OSC correction process (S <b> 600) is then performed. The details of the stored oxygen desorption amount OSC correction process are shown in the flowchart of FIG.
[0102]
When the stored oxygen desorption amount OSC correction process is started, it is first determined whether or not the fuel cut execution flag Fca is “ON” for a long time (for example, 3 seconds or more) (S610).
[0103]
The duration time of Fca = “ON” is, for example, time count data measured by a time counter that is counted up when Fca = “ON” and cleared when Fca = “OFF”. In addition to this, when the integrated value of the intake air amount GA is larger than the reference integrated value while Fca = “ON” is continued, the fuel cut execution flag Fca = “ON” is long. It may be determined that it continues.
[0104]
When Fca = “ON” for a long time (“YES” in S610), the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are stored in the ROM 50b. It calculates based on catalyst temperature Tc from the map C shown in FIG. 13 (S630). This map C is an experiment of the region where the stored oxygen desorption amount exists, that is, the region where the stored oxygen desorption amount OSC of the three-way catalyst 63 is likely to be located when the state of Fca = “ON” continues for a long time. This is what we asked for and expressed. The storage oxygen desorption amount existence region upper limit value OSCUL indicates the upper limit position of the storage oxygen desorption amount existence region, and the storage oxygen desorption amount existence region lower limit value OSCDL indicates the lower limit position of the storage oxygen desorption amount existence region.
[0105]
As shown in FIG. 13, the magnitudes of the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are the target storage oxygen desorption amount OSCTG and the stored oxygen desorption amount OSC. (OSCTG−OSC), that is, the difference from the target stored oxygen desorption amount OSCTG. For this reason, in the graph of FIG. 13, the stored oxygen desorption amount existing region upper limit value OSCUL is lower than the stored oxygen desorption amount existing region lower limit value OSCDL. The same applies to maps A and B shown in FIG.
[0106]
In this map C, the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are both positive values, and both tend to increase as the catalyst temperature Tc increases. This is because when the fuel cut state continues for a long time, the three-way catalyst 63 is saturated or close to saturation of the oxygen amount, and the stored oxygen desorption amount OSC is very small.
[0107]
In map C, the storage oxygen desorption amount existence region between the storage oxygen desorption amount existence region upper limit value OSCUL and the storage oxygen desorption amount existence region lower limit value OSCDL is the maximum storage oxygen desorption amount (OSC = OSCmax). ) And the minimum stored oxygen desorption amount (OSC = 0), and is set inside the region. In the map C, the stored oxygen desorption amount existing region lower limit value OSCDL is set to coincide with the position of the minimum stored oxygen desorption amount (OSC = 0). As other positions of the stored oxygen desorption amount existence region lower limit value OSCDL, the position is lower than the position of the minimum stored oxygen desorption amount (OSC = 0), that is, the minimum stored oxygen desorption amount (OSC = 0 in FIG. 13). ) May be set below the position.
[0108]
On the other hand, when Fca is not “ON” for a long time including when Fca = “OFF” (“NO” in S610), it is determined whether the downstream air-fuel ratio subA / F is rich (S620). ). If subA / F = rich (“YES” in S620), the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are stored in the ROM 50b in FIG. It calculates based on the catalyst temperature Tc from the map A shown (S640). This map A experimentally shows the storage oxygen desorption amount existence region in the case where Fca = “OFF” is not long and Fca = “ON” and the downstream of the three-way catalyst 63 is rich. It is what I asked for. In the map A, the storage oxygen desorption amount existence region upper limit value OSCUL is a negative value, and the storage oxygen desorption amount existence region lower limit value OSCDL is a positive value. The higher the catalyst temperature Tc, the smaller the stored oxygen desorption amount existing region upper limit value OSCUL, and the higher the stored oxygen desorption amount existing region lower limit value OSCDL.
[0109]
Further, the storage oxygen desorption amount existence region upper limit value OSCUL is equal to the maximum storage oxygen desorption amount (OSC = OSCmax), but the storage oxygen desorption amount existence region lower limit value OSCDL is close to zero. This is because when the downstream air-fuel ratio subA / F is rich without the fuel cut for a long time, the three-way catalyst 63 is far away from the saturation state of the oxygen amount, and the stored oxygen desorption amount. This is because the OSC is quite large.
[0110]
In map A, the storage oxygen desorption amount existence region between the storage oxygen desorption amount existence region upper limit value OSCUL and the storage oxygen desorption amount existence region lower limit value OSCDL is the maximum storage oxygen desorption amount (OSC = OSCmax). ) And the minimum stored oxygen desorption amount (OSC = 0), and is set inside the region. In the map A, the position of the stored oxygen desorption amount existing region upper limit value OSCUL coincides with the position of the maximum stored oxygen desorption amount (OSC = OSCmax) as described above. Other positions of the stored oxygen desorption amount existence region upper limit value OSCUL are inside the maximum stored oxygen desorption amount (OSC = OSCmax), that is, in FIG. 12, above the maximum stored oxygen desorption amount (OSC = OSCmax). You may arrange in.
[0111]
If subA / F = lean (“NO” in S620), the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are stored in the ROM 50b. 12 is calculated based on the catalyst temperature Tc from the map B shown in FIG. 12 (S650). This map B experimentally shows the region where the stored oxygen desorption amount exists when Fca is not “ON” for a long period of time including when Fca = “OFF” and when the downstream of the three-way catalyst 63 is lean. It is what I asked for. In the map B, the storage oxygen desorption amount existence region upper limit value OSCUL is a negative value, and the storage oxygen desorption amount existence region lower limit value OSCDL is a positive value. Compared with the map A, the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are both set larger. The higher the catalyst temperature Tc, the smaller the stored oxygen desorption amount existing region upper limit value OSCUL, and the higher the stored oxygen desorption amount existing region lower limit value OSCDL.
[0112]
Further, the storage oxygen desorption amount existence region upper limit value OSCUL is close to 0, but the storage oxygen desorption amount existence region lower limit value OSCDL coincides with the minimum storage oxygen desorption amount (OSC = 0). This is because when the downstream air-fuel ratio subA / F is lean in a state where the fuel cut is not performed for a long time, the three-way catalyst 63 is approaching the saturated state of the oxygen amount, and the stored oxygen is desorbed. This is because the amount OSC is considerably small.
[0113]
In the map B, the storage oxygen desorption amount existence region between the storage oxygen desorption amount existence region upper limit value OSCUL and the storage oxygen desorption amount existence region lower limit value OSCDL is the maximum storage oxygen desorption amount (OSC = OSCmax). ) And the minimum stored oxygen desorption amount (OSC = 0), and is set inside the region. In the map B, as described above, the position of the stored oxygen desorption amount existing region lower limit value OSCDL coincides with the position of the minimum stored oxygen desorption amount (OSC = 0). Other positions of the stored oxygen desorption amount existing region lower limit value OSCDL are inside the minimum stored oxygen desorption amount (OSC = 0), and in FIG. 12, than the position of the minimum stored oxygen desorption amount (OSC = 0). It may be arranged on the lower side.
[0114]
After any of the processes in steps S630 to S650, the deterioration coefficient DK is calculated based on the count value TD described above from the map shown in FIG. 15 stored in the ROM 50b (S652). The deterioration coefficient DK is a value that represents the degree of deterioration of the three-way catalyst 63. As can be seen from FIG. 15, the deterioration coefficient DK is a value that gradually decreases from 1.0 to 0 with the passage of time. Note that the map of FIG. 15 is obtained experimentally.
[0115]
Next, the storage oxygen desorption amount existence region upper limit value OSCUL is corrected by the deterioration coefficient DK as shown in the following expression 6 (S654).
[0116]
[Formula 6]
OSCUL ← OSCUL · DK [Formula 6]
Similarly, the storage oxygen desorption amount existence region lower limit OSCDL is corrected by the deterioration coefficient DK as shown in the following expression 7 (S656).
[0117]
[Expression 7]
OSCDL ← OSCDL · DK ... [Formula 7]
Next, the target stored oxygen desorption amount OSCTG is calculated (S660). Details of the target stored oxygen desorption amount OSCTG calculation process are shown in the flowchart of FIG.
[0118]
When the target stored oxygen desorption amount OSCTG calculation process is started, first, the maximum stored oxygen desorption amount OSCmax is calculated as shown in the following equation 8 (S662).
[0119]
[Equation 8]
OSCmax ← G (Tc) · DK [Formula 8]
Here, G (Tc) represents the maximum stored oxygen desorption amount when the three-way catalyst 63 is not used, and is set based on the catalyst temperature Tc by the map of FIG. 14 stored in the ROM 50b. . This map is obtained experimentally, and the maximum stored oxygen desorption amount G (Tc) tends to increase as the catalyst temperature Tc increases.
[0120]
In Equation 8, the current maximum stored oxygen desorption amount OSCmax is obtained by calculating the product of the maximum stored oxygen desorption amount G (Tc) and the deterioration coefficient DK shown in FIG.
[0121]
Then, as shown in the following equation 9, the target stored oxygen desorption amount OSCTG is calculated (S664).
[0122]
[Equation 9]
OSCTG ← OSCmax / 2 [Formula 9]
In this way, by setting the half value of the maximum stored oxygen desorption amount OSCmax as the target stored oxygen desorption amount OSCTG, the upstream air-fuel ratio A / F becomes less than the stoichiometric air-fuel ratio between the lean side and the rich side. Regardless of which one is used, harmful components in the exhaust can be sufficiently purified.
[0123]
Returning to FIG. 10, the stored oxygen desorption amount existence region upper limit value OSCUL, the stored oxygen desorption amount existence region lower limit value OSCDL, and the target stored oxygen desorption amount OSCTG obtained in steps S654, S656, and S660 are used. Then, the stored oxygen desorption amount OSC is corrected.
[0124]
That is, first, it is determined whether or not the relationship shown in the following equation 10 is satisfied (S670).
[0125]
[Expression 10]
OSC ≦ OSCTG−OSCUL [Formula 10]
This relationship represents a state in which the stored oxygen desorption amount OSC calculated in the stored oxygen desorption amount OSC integration process (S500) is within the upper limit position of the stored oxygen desorption amount existence region.
[0126]
If the relationship of Expression 10 is satisfied (“YES” in S670), it is next determined whether or not the relationship shown in the following Expression 11 is satisfied (S680).
[0127]
## EQU11 ##
OSC ≧ OSCTG−OSCDL [Formula 11]
This relationship represents a state in which the stored oxygen desorption amount OSC calculated in the stored oxygen desorption amount OSC integration process (S500) is within the lower limit position of the stored oxygen desorption amount existence region.
[0128]
If the relationship of Equation 11 is satisfied (“YES” in S680), it can be determined that the stored oxygen desorption amount OSC exists within the storage oxygen desorption amount existence region, and thus the stored oxygen desorption amount remains as it is. Exit the OSC correction process.
[0129]
If the relationship of Equation 10 is not satisfied (“NO” in S670), the stored oxygen desorption amount OSC is corrected as shown in the following Equation 12 (S690).
[0130]
[Expression 12]
OSC ← OSCTG-OSCUL ... [Formula 12]
That is, when the stored oxygen desorption amount OSC deviates upward from the stored oxygen desorption amount existing region, the upper limit value of the stored oxygen desorption amount existing region is set as the stored oxygen desorption amount OSC. . Then, the stored oxygen desorption amount OSC correction process is exited.
[0131]
On the other hand, when the relationship of the equation 11 is not satisfied (“NO” in S680), the stored oxygen desorption amount OSC is corrected as shown in the following equation 13 (S700).
[0132]
[Formula 13]
OSC ← OSCTG-OSCDL [Formula 13]
That is, when the stored oxygen desorption amount OSC deviates below the storage oxygen desorption amount existence region, the lower limit value of the storage oxygen desorption amount existence region is set as the storage oxygen desorption amount OSC. . Then, the stored oxygen desorption amount OSC correction process is exited.
[0133]
When the stored oxygen desorption amount OSC correction process ends in this way, the stored oxygen desorption amount calculation process ends once.
The feedback control of the stored oxygen desorption amount OSC performed based on the calculated value of the stored oxygen desorption amount OSC will be described based on the flowchart of FIG. FIG. 16 shows a flowchart of a process for calculating the stored oxygen desorption amount feedback coefficient KC used in Equation 1 for obtaining the fuel injection amount Q. This process is a process periodically executed for each preset crank angle.
[0134]
When the stored oxygen desorption amount feedback coefficient KC calculation process is started, first, the stored oxygen desorption amount OSC obtained by the stored oxygen desorption amount calculation process of FIG. 8 is obtained by the process of FIG. It is determined whether or not the target stored oxygen desorption amount OSCTG is smaller (S810). If OSC ≧ OSCTG (“NO” in S810), it is then determined whether the stored oxygen desorption amount OSC is greater than the target stored oxygen desorption amount OSCTG (S820). If OSC ≦ OSCTG (“NO” in S820), since OSC = OSCTG, 0 is set to the stored oxygen desorption amount feedback coefficient KC (S830), and the process is temporarily terminated.
[0135]
If OSC <OSCTG (“YES” in S810), the stored oxygen desorption amount feedback coefficient KC is set to a constant KR (eg, 1> KR> 0) (S840), and the process is temporarily terminated. Accordingly, in step S190 of FIG. 4, the fuel injection amount Q is increased, the upstream air-fuel ratio A / F is corrected in the direction of decreasing, that is, the rich direction, and the stored oxygen desorption amount OSC of the three-way catalyst 63 is reduced. It is adjusted in the increasing direction.
[0136]
If OSC> OSCTG (“YES” in S820), the stored oxygen desorption amount feedback coefficient KC is set to a constant KL (for example, 0> KL> −1) (S850), and the process is temporarily terminated. Accordingly, in step S190 of FIG. 4, the fuel injection amount Q is reduced, the upstream air-fuel ratio A / F is corrected in the direction of increasing, that is, the lean direction, and the stored oxygen desorption amount OSC of the three-way catalyst 63 is reduced. It is adjusted in the decreasing direction.
[0137]
By repeating such processing and adjusting the upstream air-fuel ratio A / F, feedback control is executed so that the stored oxygen desorption amount OSC becomes the target stored oxygen desorption amount OSCTG.
[0138]
Of the above-described configuration, the stored oxygen desorption amount OSC integration process of FIG. 9 is the process as the stored oxygen desorption amount integration means, and steps S610 to S650, S654, and S656 of FIG. Steps S670 to S700 in FIG. 10 correspond to the processing as the stored oxygen desorption amount correcting means, and steps S440 and S652 in FIG. 10 correspond to the three-way catalyst adsorption capacity estimation means.
[0139]
According to the first embodiment described above, the following effects can be obtained.
(I). In the stored oxygen desorption amount OSC correction process shown in FIG. 10, the operating state of the engine 4 (fuel cut execution is performed between OSC = maximum stored oxygen desorption amount OSCmax and OSC = 0 (minimum stored oxygen desorption amount). The stored oxygen desorption amount existence region is set according to the flag Fca, the downstream air-fuel ratio subA / F, and the catalyst temperature Tc). Thus, the stored oxygen desorption amount existing region set by corresponding to the operating state of the engine 4 reflects the actual stored oxygen desorption amount.
[0140]
  Then, with reference to this storage oxygen desorption amount existence region, the storage oxygen desorption amount OSC is converted into the storage oxygen desorption amount existence region (target storage oxygen desorption amount OSCTG−storage oxygen desorption) by the processing of steps S670 to S700. In the case where it is outside of the separation amount existence region lower limit value OSCDL to the target stored oxygen desorption amount OSCTG−stored oxygen desorption amount existence region upper limit value OSCUL), the stored oxygen desorption amount OSC.The value of theThe stored oxygen desorption amount within the existing region andYouIt has been corrected so that. Actually, the target storage oxygen desorption amount OSCTG−the stored oxygen desorption amount existing region lower limit value OSCDL or the target stored oxygen desorption amount OSCTG−the stored oxygen desorption amount existing region upper limit value OSCUL is corrected.
[0141]
Thus, as in the prior art, the stored oxygen desorption amount OSC deviates from the stored oxygen desorption amount existence region without requiring a relatively large state change in the oxygen sensor 82 on the downstream side of the catalytic converter 64. If so, the stored oxygen desorption amount OSC can be corrected to an appropriate state. For this reason, the opportunity to correct the stored oxygen desorption amount OSC increases, and the state where the stored oxygen desorption amount OSC is inappropriate does not continue for a long time.
[0142]
Next, the effect will be described with a specific example. In the timing chart shown in FIG. 17 (A), the state where the upstream air-fuel ratio A / F is rich for some reason continues, and the actual stored oxygen desorption amount LO indicated by the alternate long and short dash line is the maximum stored oxygen desorption amount. The state changed to OSCmax is shown. In such a state, the voltage signal Vz of the oxygen sensor 82 on the downstream side of the catalytic converter 64 changes as shown in FIG. It is assumed that the actual stored oxygen desorption amount LO starts to decrease from the maximum stored oxygen desorption amount OSCmax state after time t1. At this time, as indicated by the solid line, it is assumed that the stored oxygen desorption amount LS calculated in the first embodiment is deviated from the actual stored oxygen desorption amount LO for some reason.
[0143]
However, the calculated stored oxygen desorption amount LS reaches the lower limit of the stored oxygen desorption amount existence area AR corresponding to the rich state of the voltage signal Vz at time t2 (“NO” in S680), and therefore more than this. The calculated stored oxygen desorption amount LS does not decrease (S700). Therefore, until the voltage signal Vz switches to the lean state and the stored oxygen desorption amount existence region AL is set, the calculated stored oxygen desorption amount LS is corrected so as to approach the actual stored oxygen desorption amount LO. Will be. In this way, the calculated stored oxygen desorption amount LS can be corrected to an appropriate state.
[0144]
On the other hand, in the latter conventional example described above, since the voltage signal Vz does not change so much as 0.7 V or more or 0.2 V or less after the time t1, as shown by the two-dot chain line LB, there is no appropriate change. No corrections will be made.
[0145]
In the timing chart shown in FIG. 18A, the state where the upstream air-fuel ratio A / F is lean for some reason continues, and the actual stored oxygen desorption amount LO indicated by the alternate long and short dash line is the minimum stored oxygen desorption amount. It shows a state changed to (OSC = 0). In such a state, the voltage signal Vz of the oxygen sensor 82 changes as shown in FIG. It is assumed that the actual stored oxygen desorption amount LO starts to increase from the state of the minimum stored oxygen desorption amount after time t11. At this time, as indicated by the solid line, it is assumed that the stored oxygen desorption amount LS calculated in the first embodiment is deviated from the actual stored oxygen desorption amount LO for some reason.
[0146]
However, the calculated stored oxygen desorption amount LS reaches the upper limit of the stored oxygen desorption amount existence region AL corresponding to the lean state of the voltage signal Vz at time t12 (“NO” in S670), and therefore more than this. The calculated stored oxygen desorption amount LS does not increase (S690). Therefore, the calculated stored oxygen desorption amount LS is corrected to approach the actual stored oxygen desorption amount LO until the voltage signal Vz switches to the rich state and the stored oxygen desorption amount existence region AR is set. Will be. In this way, the calculated stored oxygen desorption amount LS can be corrected to an appropriate state.
[0147]
On the other hand, in the latter conventional example described above, since the voltage signal Vz does not change so much as 0.7 V or more or 0.2 V or less after time t11, as shown by the two-dot chain line LB, there is no appropriate change. No corrections will be made.
[0148]
In the timing charts shown in FIGS. 19A and 19B, the state where the upstream air-fuel ratio A / F is rich for some reason continues and the actual stored oxygen desorption amount LO is the maximum stored oxygen desorption amount. It shows a state in which the voltage signal Vz of the oxygen sensor 82 has exceeded 0.7V by changing to OSCmax.
[0149]
In the latter conventional example described above, the voltage signal Vz is 0.7 V even if the stored oxygen desorption amount OSC accurately represents the actual stored oxygen desorption amount until the value of the stored oxygen desorption amount OSCmax reaches the maximum stored oxygen desorption amount OSCmax. As long as this is the case (until time t21), OSC = OSCmax is fixed. For this reason, as shown by a two-dot chain line LB, a large deviation from the actual stored oxygen desorption amount LO occurs.
[0150]
However, in the first embodiment, when the voltage signal Vz is in a rich state as shown in FIG. 19B, the stored oxygen desorption amount existence area AR is set. In the area AR, the stored oxygen desorption amount is calculated as calculated based on the upstream air-fuel ratio. For this reason, when the calculated stored oxygen desorption amount decreases, it changes in substantially the same manner as the actual stored oxygen desorption amount LO.
[0151]
For example, even if a deviation from the actual stored oxygen desorption amount LO occurs as shown by the solid line LS when the calculated stored oxygen desorption amount decreases for some reason in the first embodiment, at time t22. When the voltage signal Vz is switched to the lean state, the stored oxygen desorption amount existence region AL is set. At this time, if the calculated stored oxygen desorption amount LS deviates from the upper limit of the stored oxygen desorption amount existing area AL (“NO” in S670), it is corrected as shown (S690), and the actual stored oxygen desorption amount is determined. It approaches the separation amount LO. In this way, the calculated stored oxygen desorption amount LS can be corrected to an appropriate state.
[0152]
As shown in FIGS. 20A and 20B, the reverse case is the same. In the latter conventional example, the value of the stored oxygen desorption amount OSC is set to the minimum stored oxygen desorption amount (OSC = 0). Even if the actual stored oxygen desorption amount is accurately represented until the time is reached, OSC = 0 is fixed as long as the voltage signal Vz is 0.2 V or less (until time t31). For this reason, as shown by a two-dot chain line LB, a large deviation from the actual stored oxygen desorption amount LO occurs.
[0153]
However, in the first embodiment, when the voltage signal Vz is in the lean state as shown in FIG. 20B, the stored oxygen desorption amount existence region AL is set. The stored oxygen desorption amount is calculated as calculated based on the upstream air-fuel ratio in the region AL. For this reason, even when the calculated stored oxygen desorption amount increases, it changes in substantially the same manner as the actual stored oxygen desorption amount LO.
[0154]
For example, even if a deviation from the actual stored oxygen desorption amount LO occurs as shown by the solid line LS when the stored oxygen desorption amount OSC increases for some reason in the calculation of the first embodiment, at time t32 When the voltage signal Vz is switched to the rich state, the stored oxygen desorption amount existence region AR is set. At this time, if the calculated stored oxygen desorption amount LS deviates from the lower limit of the stored oxygen desorption amount existing area AR (“NO” in S680), it is corrected as shown (S700), and the actual stored oxygen desorption amount is determined. It approaches the separation amount LO. In this way, the calculated stored oxygen desorption amount LS can be corrected to an appropriate state.
[0155]
The timing chart of FIG. 21 shows a case where a fuel cut has occurred. In the latter conventional example described above, when the fuel is cut (time t41), the calculated stored oxygen desorption amount is immediately set to zero. For this reason, when the fuel cut ends before the actual stored oxygen desorption amount LO does not become zero (time t43), the calculated stored oxygen desorption amount indicated by the two-dot chain line LB is the actual stored oxygen desorption amount LO. Will cause a large deviation.
[0156]
However, in the first embodiment, since the storage oxygen desorption amount existence area AC for fuel cut is set after the fuel cut has elapsed for a long time, the storage oxygen desorption amount existence area AC is stored as calculated in the storage oxygen desorption amount existence area AC. An oxygen desorption amount OSC is calculated. For this reason, it changes in substantially the same manner as the actual stored oxygen desorption amount LO.
[0157]
For example, even if there is a deviation from the actual stored oxygen desorption amount LO as shown by the solid line LS at the start of the fuel cut for some reason in the calculation of the first embodiment, the stored oxygen desorption amount exists at time t42. Area AC is set. As a result, it is determined that it is outside the upper limit (“NO” in S670), corrected as shown (S690), and approaches the actual stored oxygen desorption amount LO. In this way, the calculated stored oxygen desorption amount LS can be corrected to an appropriate state.
[0158]
(B). Furthermore, as shown in FIGS. 12 and 13, the storage oxygen desorption amount existing region is between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount and between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount. It is set as an area smaller than the area between the quantity.
[0159]
For this reason, as shown in FIGS. 17 to 21, the correction of the calculated stored oxygen desorption amount rapidly changes to an extreme value such as the maximum stored oxygen desorption amount or the minimum stored oxygen desorption amount. There is nothing.
[0160]
Since the correction to the extreme value is suppressed in this way, as shown in FIGS. 17 to 21, it becomes difficult to generate a state in which the error from the actual stored oxygen desorption amount is large after the correction, A state in which the calculated amount of stored oxygen desorption is inappropriate does not continue for a long time. Therefore, it is possible to correct the calculated stored oxygen desorption amount to an appropriate value before the emission is easily deteriorated, thereby further ensuring prevention of the emission deterioration.
[0161]
(C). As described above, the storage oxygen desorption amount existing region includes the temperature of the three-way catalyst 63, the presence or absence of fuel cut processing, and the downstream air-fuel ratio subA / F detected by the oxygen sensor 82 downstream of the three-way catalyst 63. Used.
[0162]
In the state where the fuel cut process is performed for a long time (“YES” in S610), the stored oxygen desorption amount existing region is determined from the map C considering that the supply of the oxygen amount to the three-way catalyst 63 is large. Can be set. Furthermore, by changing the range of the stored oxygen desorption amount existing region according to the catalyst temperature Tc at this time, an appropriate stored oxygen desorption amount existing region can be set.
[0163]
In a state where the fuel cut process is not performed for a long time (“NO” in S610), if the downstream air-fuel ratio subA / F is in a rich state, the storage oxygen desorption amount existing region considering the rich state is set. Can be set. Further, when the downstream air-fuel ratio subA / F is in the lean state, it is possible to set the storage oxygen desorption amount existing region in consideration of the lean state. Further, at this time, the range of the stored oxygen desorption amount existing region is changed according to the temperature. Thus, an appropriate storage oxygen desorption amount existence region can be set.
[0164]
Thus, the calculation of the stored oxygen desorption amount OSC can be made more appropriate, and the effects described in the above (a) and (b) can be made more remarkable.
(D). The oxygen adsorption capacity of the three-way catalyst 63 deteriorates with time. For this reason, the degradation coefficient DK is calculated from the map of FIG. 15 using the count value TD counted up in step S440 (S652). Thus, the oxygen adsorption capacity of the three-way catalyst 63 is estimated and reflected in the setting of the storage oxygen desorption amount existing region in the three-way catalyst 63 (S654, S656). Thus, an appropriate storage oxygen desorption amount existence region can be set. Therefore, the calculation of the stored oxygen desorption amount OSC can be made more appropriate, and the effects described in the above (a), (b), and (c) can be made more remarkable.
[0165]
[Embodiment 2]
In the first embodiment, in order to obtain the current maximum stored oxygen desorption amount OSCmax and the stored oxygen desorption amount existence region in consideration of the deterioration of the three-way catalyst 63, the cumulative use time of the three-way catalyst 63 by the count value TD. I was looking for.
[0166]
In the second embodiment, instead of the cumulative usage time of the three-way catalyst 63, the maximum storage oxygen amount is obtained by actual measurement in the deterioration coefficient DK learning process shown in the flowcharts of FIGS. The deterioration coefficient DK is calculated from the amount of oxygen.
[0167]
Therefore, in the second embodiment, the stored oxygen desorption amount calculation process of FIG. 22 is executed instead of the stored oxygen desorption amount calculation process of FIG. 8, and the stored oxygen desorption amount OSC correction process of FIG. 10 is executed. Instead, the stored oxygen desorption amount OSC correction process of FIG. 23 is executed. In the process of FIG. 22, only the process of step S440 in FIG. 8 is not performed, and in the process of FIG. 23, the process of step S652 in FIG. 10 is not performed. Therefore, the processing content of FIG. 22 is as described in the first embodiment except for step S440, and the processing content of FIG. 23 is as described in the first embodiment except for step S652. However, in FIG. 22 and FIG. 23, it shows by the step number which added 1000 to the step number used for the same process in FIG. 8 and FIG.
[0168]
Other configurations of the second embodiment are basically the same as those of the first embodiment unless otherwise described.
Here, the deterioration coefficient DK learning process shown in FIG. 24 will be described. This process is a process repeatedly executed at a period of time Δt. When this process is started, first, the catalyst temperature Tc is read into the work area of the RAM 50c (S1010).
[0169]
Next, the temperature region i is selected according to the catalyst temperature Tc (S1020). Here, it is assumed that the temperature region of the catalyst temperature Tc is divided and set as shown by a broken line in FIG. The temperature region i is selected by calculating to which temperature region the catalyst temperature Tc belongs.
[0170]
Next, it is determined whether or not the temperature region i obtained as described above is the same as the temperature region obtained in the previous control cycle (S1030). If they are not in the same temperature range (“NO” in S1030), then the deterioration coefficient learning execution flag XCATG is set to “OFF” (S1040), and the air-fuel ratio deviation integrated value SUMFC is cleared after fuel cut recovery (S1050). .
[0171]
After step S1050 or when it is determined that the temperature region i is the same as the previous time (“YES” in S1030), it is next determined whether or not the fuel cut execution flag Fca is “ON” for a long time. (S1060). Whether or not it is a long time may be determined, for example, by providing a reference time for determination and determining whether or not Fca = “ON” continues for the reference time or longer.
[0172]
If the fuel cut execution flag Fca is “ON” for a long time (“YES” in S1060), the deterioration coefficient learning execution flag XCATG is set to “ON” (S1070).
[0173]
After step S1070 or when the fuel cut execution flag Fca is “OFF” (“NO” in S1060), it is next determined whether or not the deterioration coefficient learning execution flag XCATG is “ON” (S1080). . If XCATG = “OFF” (“NO” in S1080), the deterioration coefficient DK learning process is temporarily terminated as it is.
[0174]
If XCATG = “ON” (“YES” in S1080), then an integration process (S1090) of the air-fuel ratio deviation integrated value SUMFC after return from fuel cut is executed. FIG. 25 shows the details of the air-fuel ratio deviation integrated value SUMFC integrated processing after the fuel cut is restored.
[0175]
When the air-fuel ratio deviation integrated value SUMFC integration process is started after the fuel cut is restored, it is first determined whether or not the upstream air-fuel ratio A / F is the stoichiometric air-fuel ratio (S1710). If the upstream air-fuel ratio A / F is the stoichiometric air-fuel ratio (“YES” in S1710), the integration process is exited as it is.
[0176]
If the upstream air-fuel ratio A / F is not the stoichiometric air-fuel ratio (“NO” in S1710), it is next determined whether or not the upstream air-fuel ratio A / F is lean (S1720). When the upstream air-fuel ratio A / F is lean (“YES” in S1720), the air-fuel ratio deviation integrated value SUMFC after return from fuel cut is calculated from the following equation 14 (S1730).
[0177]
[Expression 14]
SUMFC
← SUMFC- {KO2 · GA · (ΔA / F) / (A / F)} · Δt ... [Formula 14]
Here, SUMFC on the right side represents an air-fuel ratio deviation integrated value SUMFC after return from fuel cut in the previous control cycle. The meanings of the other symbols and the contents of the equations are as described in Equation 2 above.
[0178]
On the other hand, when it is determined in step S1720 that the upstream air-fuel ratio A / F is not lean, that is, rich (“NO” in S1720), the air-fuel ratio deviation integrated value SUMFC after return from fuel cut is calculated from the following equation 15. Calculated (S1740).
[0179]
[Expression 15]
SUMFC
← SUMFC- {KO2 · GA · k · (ΔA / F) / (A / F)} · Δt ... [Equation 15]
Here, the meanings of the symbols and the contents of the equations are as described in the equations 4 and 14.
[0180]
Thus, after the integration of the air-fuel ratio deviation integrated value SUMFC after fuel cut recovery (S1730, S1740) is executed, the integration process is exited.
Returning to FIG. 24, after step S1090, it is determined whether or not the downstream air-fuel ratio subA / F is rich (S1100). If subA / F is not rich (“NO” in S1100), the deterioration coefficient DK learning process is temporarily terminated as it is.
[0181]
If subA / F = rich (“YES” in S1100), it is considered that the stored oxygen amount of the three-way catalyst 63 is almost 0, that is, the stored oxygen desorption amount OSC is almost the maximum stored oxygen desorption amount OSCmax. For this reason, the post-fuel cut return air-fuel ratio deviation integrated value SUMFC obtained at this time can be regarded as an actually measured value of the maximum stored oxygen desorption amount OSCmax.
[0182]
Therefore, if “YES” is determined in step S1100, then, as shown in the following equation 16, the three-way catalyst shown in FIG. 26 based on the post-fuel cut return air-fuel ratio deviation integrated value SUMFC and the catalyst temperature Tc. A ratio with the maximum stored oxygen desorption amount G (Tc) obtained from the map of the maximum stored oxygen desorption amount 63 when not in use is set as the deterioration coefficient DK (i) of the temperature region i (S1110).
[0183]
[Expression 16]
DK (i) <-SUMFC / G (Tc) ... [Formula 16]
The value of DK (i) is stored in the backup RAM 50d as the deterioration coefficient of the temperature region i.
[0184]
Next, the deterioration coefficient learning execution flag XCATG is set to “OFF” (S1120), and the air-fuel ratio deviation integrated value SUMFC after fuel cut return is cleared (S1130). In this way, the deterioration coefficient DK learning process is once ended.
[0185]
The deterioration coefficient DK (i) for each temperature region i thus obtained is a temperature region corresponding to the catalyst temperature Tc instead of the deterioration factor DK in steps S1654 and S1656 of FIG. 23 and step S662 of FIG. A deterioration coefficient DK (i) of i is used. Note that a value of “1.0” as an initial value is used for the deterioration coefficient DK (i) in the temperature region i where learning of the deterioration coefficient DK is not completed.
[0186]
In the configuration of the second embodiment described above, the stored oxygen desorption amount OSC integration process in FIG. Steps S1670 to S1700 of FIG. 23 are processing as the stored oxygen desorption amount correcting means, and the deterioration coefficient DK learning processing of FIGS. 24 and 25 is the three-way catalyst adsorption capacity detecting means. It corresponds to the process.
[0187]
According to the second embodiment described above, the following effects can be obtained.
(I). The effects (a), (b) and (c) of the first embodiment are produced.
(B). The oxygen adsorption capacity of the three-way catalyst 63 deteriorates with time, or the degree of deterioration varies depending on the temperature range. For this reason, in the second embodiment, the oxygen adsorption capacity of the three-way catalyst 63 is detected by the deterioration coefficient DK learning process of FIGS. 24 and 25 and reflected in the setting of the storage oxygen desorption amount existing region in the three-way catalyst 63. ing.
[0188]
Thus, an appropriate storage oxygen desorption amount existence region can be set. Accordingly, the calculation of the stored oxygen desorption amount OSC can be made more appropriate, and the effect of the first embodiment can be made more remarkable.
[0189]
(C). Further, the detection of the oxygen adsorption capacity of the three-way catalyst 63 starts when oxygen is saturated in the three-way catalyst 63. Then, the process ends when the downstream air-fuel ratio subA / F detected downstream of the three-way catalyst 63 becomes rich. Then, during this period, the three-way catalyst is obtained by calculating the post-fuel cut return air-fuel ratio deviation integrated value SUMFC, which is an integrated value of the excess and deficiency of the fuel concentration calculated based on the exhaust state flowing into the three-way catalyst 63. The oxygen adsorption capacity of 63 is detected.
[0190]
When the downstream air-fuel ratio subA / F becomes rich, it is considered that the amount of oxygen stored in the three-way catalyst 63 has become almost zero. For this reason, the air-fuel ratio deviation integrated value SUMFC after return from fuel cut indicates the maximum stored oxygen amount of the three-way catalyst 63. The level of the maximum stored oxygen amount represents the degree of oxygen adsorption capacity of the three-way catalyst 63 at that time, that is, the degree of deterioration of the three-way catalyst.
[0191]
Therefore, the deterioration coefficient DK is obtained by using the detected air-fuel ratio deviation integrated value SUMFC detected after the fuel cut and the maximum stored oxygen desorption amount G (Tc) when the three-way catalyst 63 is not used. An appropriate storage oxygen desorption amount existence region can be set by the deterioration coefficient DK. For this reason, the calculation of the stored oxygen desorption amount OSC can be made more appropriate.
[0192]
(D). In the second embodiment, when the fuel cut process continues for a reference time or longer, the accumulation of the air-fuel ratio deviation integrated value SUMFC after the fuel cut return is started assuming that the oxygen is saturated in the three-way catalyst 63.
[0193]
When the fuel cut process continues for the reference time or longer in this way, it can be considered that oxygen is saturated in the three-way catalyst 63, and at this timing, the integrated air-fuel ratio deviation integrated value SUMFC after fuel cut recovery is integrated. It becomes possible to start.
[0194]
Thus, an appropriate storage oxygen desorption amount existence region can be set by using the oxygen adsorption ability of the three-way catalyst 63 detected by using the fuel cut. Therefore, even during operation of the engine 4, the deterioration state of the three-way catalyst 63 can be obtained, and the calculated stored oxygen desorption amount OSC can be corrected more appropriately.
[0195]
[Embodiment 3]
The third embodiment is different from the first embodiment in that the process shown in FIG. 27 is executed instead of steps S610 to S650 in the stored oxygen desorption amount OSC correction process shown in FIG. The processing after step S652 in FIG. 10 is the same. Other configurations are the same as those in the first embodiment unless otherwise specified.
[0196]
The process of FIG. 27 will be described. When the stored oxygen desorption amount OSC correction process is started, it is first determined whether or not the fuel cut execution flag Fca is “ON” for a long time (S2610). This determination process is the same as step S610 in FIG.
[0197]
If Fca = “ON” for a long time (“YES” in S2610), the map C use continuation flag Fcc is set to “ON” (S2612). Next, the storage oxygen desorption amount existence region upper limit value OSCUL and the storage oxygen desorption amount existence region lower limit value OSCDL are determined based on the catalyst temperature Tc from the map C shown in FIG. 13 stored in the ROM 50b. Calculate (S2630).
[0198]
On the other hand, if Fca is not “ON” for a long time including when Fca = “OFF” (“NO” in S2610), it is determined whether the downstream air-fuel ratio subA / F is rich (S2620). ). If subA / F = rich (“YES” in S2620), the map C use continuation flag Fcc is set to “OFF” (S2622). Next, the storage oxygen desorption amount existence region upper limit value OSCUL and the storage oxygen desorption amount existence region lower limit value OSCDL are determined based on the catalyst temperature Tc from the map A shown in FIG. 12 stored in the ROM 50b. Calculate (S2640).
[0199]
If subA / F = lean (“NO” in S2620), it is determined whether the map C use continuation flag Fcc is “OFF” (S2624). If Fcc = “ON” (“NO” in S2624), step S2630 described above is executed, and the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are set. The map C is calculated based on the catalyst temperature Tc.
[0200]
If Fcc = “OFF” (“YES” in S2624), then the stored oxygen desorption amount existence region upper limit value OSCUL and the stored oxygen desorption amount existence region lower limit value OSCDL are stored before being stored in the ROM 50b. Calculation is made based on the catalyst temperature Tc from the map B shown in FIG. 12 (S2650).
[0201]
After any one of steps S2630 to S2650, the process proceeds to step S652 and subsequent steps shown in FIG.
Here, steps S2610 to S2650 in FIG. 27 and steps S654 and S656 in FIG. 10 correspond to the processing as the stored oxygen desorption amount existence region setting means.
[0202]
According to the third embodiment described above, the following effects can be obtained.
(I). The effect of the first embodiment occurs.
(B). Immediately after the fuel cut is completed, the actual increase in the stored oxygen desorption amount may be slower than expected. Accordingly, in response to such a case, it is determined that the map C use continuation flag Fcc is “ON” immediately after the end of the fuel cut processing. As long as Fcc = “ON” and the voltage signal Vz from the oxygen sensor 82 downstream of the three-way catalyst 63 continuously detects the lean state (“NO” in S2620 and “NO” in S2624). The stored oxygen desorption amount existence region is set using the map C (S2630). This makes it possible to more appropriately correct the calculated stored oxygen desorption amount.
[0203]
This effect will be described using a specific example. The timing chart shown in FIG. 28A shows the state of the stored oxygen desorption amount before and after the fuel cut. In such a state, the voltage signal Vz of the oxygen sensor 82 changes as shown in FIG. It is assumed that the fuel cut is completed at time t51. At this time, as shown by the solid line, the value of the stored oxygen desorption amount LS calculated in the third embodiment rises faster, resulting in a deviation from the actual stored oxygen desorption amount LO. To do.
[0204]
As described above, immediately after the fuel cut, as long as the voltage signal Vz of the oxygen sensor 82 continues to be in the lean state, the stored oxygen desorption amount existence region AC for the fuel cut is continuously set. For this reason, the calculated stored oxygen desorption amount LS reaches the upper limit of the storage oxygen desorption amount existence region AC at time t52 (“NO” in S670). The separation amount LS does not increase (S690). Therefore, the calculated stored oxygen desorption amount LS becomes a constant value until the rich stored oxygen desorption amount existence region AR is set after the voltage signal Vz is switched to the rich state.
[0205]
At time t53, when the voltage signal Vz is switched to the rich state and the rich stored oxygen desorption amount existing area AR is set, the calculated stored oxygen desorption amount LS becomes the stored oxygen desorption amount existing area. Step up to the lower limit of AR. The calculated value of the stored oxygen desorption amount LS at times t51 to t53 changes near the upper and lower sides of the actual stored oxygen desorption amount LO, and finally deviates greatly from the actual stored oxygen desorption amount LO. Does not occur. In this way, the calculated stored oxygen desorption amount LS can be corrected to an appropriate state.
[0206]
On the other hand, in the latter conventional example described above, after the voltage signal Vz exceeds 0.2 V, no appropriate correction is performed as shown by the two-dot chain line LB, and the actual stored oxygen desorption amount LO and The deviation is not corrected sufficiently.
[0207]
[Other embodiments]
In each of the above embodiments, the feedback control in which the stored oxygen desorption amount OSC of the three-way catalyst is the target stored oxygen desorption amount OSCTG is performed by correcting the fuel injection amount calculated by the air-fuel ratio feedback control. It was. In addition to this, feedback control of the stored oxygen desorption amount may be executed by correcting the target air-fuel ratio itself in the air-fuel ratio feedback control.
[0208]
In each of the above embodiments, the temperature of the three-way catalyst 63 is detected by the catalyst temperature sensor 67, but without using the catalyst temperature sensor 67, it depends on the engine load such as the intake air amount obtained from the air flow meter 68. The temperature of the three-way catalyst 63 may be estimated.
[0209]
In each of the above embodiments, the correction of the stored oxygen desorption amount OSC when the storage oxygen desorption amount existing region is out of the range is corrected to the upper and lower limit positions of the stored oxygen desorption amount existing region. In addition to this, the stored oxygen desorption amount existing region may be corrected further than the upper and lower limit positions. Further, outside the storage oxygen desorption amount existence region, it may be brought close to the storage oxygen desorption amount existence region.
[0210]
In each of the above embodiments, when the voltage signal Vz of the oxygen sensor 82 is lower than the voltage determination value VS, it is determined that the air-fuel ratio A / F on the downstream side of the three-way catalyst 63 is lean, and the oxygen sensor 82 When the voltage signal Vz is equal to or higher than the voltage determination value VS, it is determined that the air-fuel ratio on the downstream side of the three-way catalyst 63 is rich, and the stored oxygen desorption amount existence region is set correspondingly. In addition to this, by providing a plurality of voltage determination values for the voltage signal Vz of the oxygen sensor 82, determining three or more air-fuel ratio regions, and providing a stored oxygen desorption amount existing region corresponding to each air-fuel ratio region, Further, the stored oxygen desorption amount OSC may be corrected more precisely.
[0211]
The configuration of FIG. 27 of the third embodiment can be applied to the second embodiment by using instead of steps S1610 to S1650 of FIG. 23 of the second embodiment. The effect (b) described in (2) can be produced.
[0212]
Although the embodiments of the present invention have been described above, it should be noted that the embodiments of the present invention include the following forms (1) to (15). That is, the stored oxygen desorption amount is a value indicating the desorption amount of oxygen from the three-way catalyst in the maximum stored oxygen amount state, and is equivalent to “maximum stored oxygen amount−stored oxygen amount”. Even if the stored oxygen amount is used instead of the oxygen desorption amount, the same control is possible. From this, each embodiment mentioned above contains the following forms (1)-(15).
[0213]
(1). A three-way catalyst stored oxygen amount calculating device for calculating a stored oxygen amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine,
A stored oxygen amount integrating means for integrating the stored oxygen amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst;
Between the maximum stored oxygen amount and the minimum stored oxygen amount in the three-way catalyst, the region is smaller than the region between the maximum stored oxygen amount and the minimum stored oxygen amount, depending on the operating state of the internal combustion engine. A storage oxygen amount existence region setting means for setting a storage oxygen amount existence region where the storage oxygen amount of the original catalyst is likely to be located;
When the stored oxygen amount integrated by the stored oxygen amount integrating unit is out of the stored oxygen amount existing region set by the stored oxygen amount existing region setting unit, the stored oxygen amount integrating unit A stored oxygen amount correcting means for correcting the accumulated stored oxygen amount so as to be close to the stored oxygen amount existing region or within the stored oxygen amount existing region;
A three-way catalyst stored oxygen amount calculating device.
[0214]
(2). The stored oxygen amount integrating means uses a three-way catalyst by using an intake air amount to the internal combustion engine and an air-fuel ratio detected upstream of the three-way catalyst as a state quantity representing an exhaust state flowing into the three-way catalyst. The three-way catalyst stored oxygen amount calculating device according to (1), wherein the amount of oxygen stored in the three-way catalyst is obtained by integrating the balance between the amount of oxygen adsorbed and the amount of desorption in the catalyst.
[0215]
(3). The stored oxygen amount existence region setting means sets the stored oxygen amount existence region corresponding to the air-fuel ratio by using the air-fuel ratio detected downstream of the three-way catalyst as the state amount representing the operating state of the internal combustion engine. The three-way catalyst stored oxygen amount calculation device according to (1) or (2), wherein:
[0216]
(4). The stored oxygen amount existence region setting means uses the presence or absence of a fuel cut process to stop the fuel supply to the internal combustion engine during operation of the internal combustion engine as a state quantity representing the operation state of the internal combustion engine. The three-way catalyst stored oxygen amount calculation device according to (1) or (2), wherein a storage oxygen amount existence region corresponding to is set.
[0217]
(5). The storage oxygen amount existence region setting means detects whether or not there is a fuel cut process for stopping the fuel supply to the internal combustion engine during the operation of the internal combustion engine and a downstream of the three-way catalyst as a state quantity representing the operation state of the internal combustion engine. (1) or (2), wherein the storage oxygen amount existence region corresponding to the presence or absence of fuel cut processing and the air-fuel ratio detected downstream of the three-way catalyst is set by using Three-way catalyst storage oxygen amount calculation device.
[0218]
(6). The stored oxygen amount existence region setting means uses the temperature of the three-way catalyst and the air-fuel ratio detected downstream of the three-way catalyst as the state quantity representing the operating state of the internal combustion engine, thereby And a storage oxygen amount existence region corresponding to an air-fuel ratio detected downstream of the three-way catalyst, wherein the three-way catalyst storage oxygen amount calculation device according to (1) or (2) is set.
[0219]
(7). The stored oxygen amount existence region setting means, as a state quantity indicating the operating state of the internal combustion engine, the temperature of the three-way catalyst and the presence or absence of a fuel cut process for stopping the fuel supply to the internal combustion engine during the operation of the internal combustion engine. The three-way catalyst stored oxygen amount calculation device according to (1) or (2), wherein the storage oxygen amount existence region corresponding to the temperature of the three-way catalyst and the presence or absence of the fuel cut processing is set.
[0220]
(8). The stored oxygen amount existence region setting means, as a state quantity representing the operating state of the internal combustion engine, the temperature of the three-way catalyst, the presence or absence of fuel cut processing to stop the fuel supply to the internal combustion engine during the operation of the internal combustion engine, By using the air-fuel ratio detected downstream of the three-way catalyst, the temperature of the three-way catalyst, the presence or absence of fuel cut processing, and the storage oxygen amount existence region corresponding to the air-fuel ratio detected downstream of the three-way catalyst are set. The three-way catalyst stored oxygen amount calculating device according to (1) or (2), wherein:
[0221]
(9). The storage oxygen amount existence region setting means is an air-fuel ratio in which the fuel concentration is lower than the stoichiometric air-fuel ratio downstream of the three-way catalyst immediately after the end of the fuel cut processing for stopping the fuel supply to the internal combustion engine during operation of the internal combustion engine. Is continued, the storage oxygen amount existence region corresponding to the presence of fuel cut processing is set, and the three-way catalyst storage oxygen described in (4), (5), (7) or (8) Quantity calculation device.
[0222]
(10). In addition to the configuration according to any one of (1) to (9),
A three-way catalyst adsorption capacity estimation means for estimating the oxygen adsorption capacity of the three-way catalyst is provided.
The storage oxygen amount existence region setting means sets the storage oxygen amount existence region in the three-way catalyst according to the operating state of the internal combustion engine and the oxygen adsorption ability of the three-way catalyst estimated by the three-way catalyst adsorption ability estimation means. A three-way catalyst stored oxygen amount calculating device characterized by setting.
[0223]
(11). The three-way catalyst stored oxygen amount calculating device according to (10), wherein the three-way catalyst adsorption capacity estimating means estimates the oxygen adsorption capacity of the three-way catalyst according to the accumulated usage time of the three-way catalyst.
[0224]
(12). In addition to the configuration according to any one of (1) to (9),
Equipped with a three-way catalyst adsorption capacity detection means for detecting the oxygen adsorption capacity of the three-way catalyst,
The storage oxygen amount existence region setting means sets the storage oxygen amount existence region in the three-way catalyst according to the operating state of the internal combustion engine and the oxygen adsorption ability of the three-way catalyst detected by the three-way catalyst adsorption ability detection means. A three-way catalyst stored oxygen amount calculating device characterized by setting.
[0225]
(13). The three-way catalyst adsorption capacity detecting means is used from when oxygen is saturated in the three-way catalyst until when the air-fuel ratio detected downstream of the three-way catalyst is in a state where the fuel concentration is higher than the stoichiometric air-fuel ratio. The oxygen adsorption capacity of the three-way catalyst is detected according to the integrated value of the excess and deficiency of the fuel concentration calculated based on the exhaust state flowing into the three-way catalyst in (3). Catalyst storage oxygen amount calculation device.
[0226]
(14). The three-way catalyst adsorption capacity detecting means determines that the oxygen is saturated in the three-way catalyst when the fuel cut processing for stopping the fuel supply to the internal combustion engine during the operation of the internal combustion engine continues for a reference time or longer. 3. The three-way catalyst stored oxygen amount calculating device according to (13), wherein integration of excess / deficient amount of fuel concentration calculated based on an exhaust state flowing into the catalyst is started.
[0227]
(15). The three-way catalyst stored oxygen amount calculating device according to any one of (1) to (14), wherein the three-way catalyst stored oxygen amount calculated by the three-way catalyst stored oxygen amount calculating device is a target stored oxygen amount. An air-fuel ratio control apparatus for an internal combustion engine that controls an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of the internal combustion engine so that
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a gasoline engine and an air-fuel ratio control apparatus as a first embodiment.
FIG. 2 is a block diagram of a control system in the first embodiment.
3 is an output explanatory diagram of an air-fuel ratio sensor and an oxygen sensor according to Embodiment 1. FIG.
FIG. 4 is a flowchart of a fuel injection amount control process in the first embodiment.
FIG. 5 is a flowchart of fuel cut processing in the first embodiment.
FIG. 6 is a configuration explanatory diagram of a map for calculating a stoichiometric air-fuel ratio basic fuel injection amount QBS in the first embodiment.
FIG. 7 is a flowchart of a high load increase calculation process in the first embodiment.
FIG. 8 is a flowchart of stored oxygen desorption amount calculation processing in the first embodiment.
FIG. 9 is a flowchart of stored oxygen desorption amount integration processing in the first embodiment.
FIG. 10 is a flowchart of stored oxygen desorption amount correction processing in the first embodiment.
FIG. 11 is a flowchart of a target stored oxygen desorption amount calculation process in the first embodiment.
FIG. 12 is a configuration explanatory diagram of a map A and a map B for setting a storage oxygen desorption amount existence region in the first embodiment.
FIG. 13 is a configuration explanatory diagram of a map C for setting a storage oxygen desorption amount existence region in the first embodiment.
FIG. 14 is a configuration explanatory diagram of a map for obtaining the maximum stored oxygen desorption amount G (Tc) based on the catalyst temperature Tc when the three-way catalyst is not used in the first embodiment.
FIG. 15 is an explanatory diagram of a map configuration for obtaining a deterioration coefficient DK based on a count value TD in the first embodiment.
FIG. 16 is a flowchart of stored oxygen desorption amount feedback coefficient KC calculation processing according to the first embodiment;
FIG. 17 is a timing chart for explaining the effect of the first embodiment;
FIG. 18 is a timing chart for explaining the effect of the first embodiment;
FIG. 19 is a timing chart for explaining the effect of the first embodiment;
FIG. 20 is a timing chart for explaining the effect of the first embodiment;
FIG. 21 is a timing chart for explaining the effect of the first embodiment;
FIG. 22 is a flowchart of stored oxygen desorption amount calculation processing according to the second embodiment.
FIG. 23 is a flowchart of stored oxygen desorption amount correction processing in the second embodiment.
FIG. 24 is a flowchart of a degradation coefficient learning process in the second embodiment.
FIG. 25 is a flowchart of an air-fuel ratio deviation integrated value integration process after return from fuel cut according to the second embodiment.
FIG. 26 is an explanatory diagram of a temperature region of the catalyst temperature Tc in the second embodiment.
27 is a flowchart of stored oxygen desorption amount correction processing in Embodiment 3. FIG.
FIG. 28 is a timing chart for explaining an effect of the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 4 ... Engine, 6 ... Cylinder block, 6a ... Cylinder head, 8-14 ... Cylinder, 16 ... Intake manifold, 18 ... Surge tank, 20 ... Intake passage, 22 ... Air cleaner, 24-30 ... Injector, 32 ... Throttle valve, 34 ... throttle motor, 36 ... throttle opening sensor, 38 ... accelerator pedal, 40 ... accelerator opening sensor, 50 ... ECU, 50a ... CPU, 50b ... ROM, 50c ... RAM, 50d ... backup RAM, 50e ... input circuit, 50f ... Output circuit, 50g ... Bidirectional bus, 60 ... Exhaust manifold, 62 ... Exhaust passage, 63 ... Three-way catalyst, 64 ... Catalytic converter, 66 ... Muffler, 67 ... Catalyst temperature sensor, 68 ... Air flow meter, 70-76 ... Ignition plug, 70a to 76a ... Ignition coil, 8 DESCRIPTION OF SYMBOLS 0 ... Air-fuel ratio sensor, 82 ... Oxygen sensor, 90 ... Revolution sensor, 92 ... Cylinder discrimination | determination sensor, 94 ... Water temperature sensor, 96 ... Shift position sensor, 97 ... Vehicle speed sensor

Claims (14)

A three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine,
Stored oxygen desorption amount integrating means for integrating the stored oxygen desorption amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst;
In between the maximum oxygen stored desorption amount and minimum storage oxygen desorption amount in the three-way catalyst, and (iii) A region smaller than the region between the maximum oxygen stored desorption amount and the minimum oxygen stored desorption amount A storage oxygen desorption amount existence region setting means for setting a storage oxygen desorption amount existence region where the storage oxygen desorption amount of the original catalyst is highly likely to be located according to the operating state of the internal combustion engine ;
When the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means is out of the stored oxygen desorption amount existing area set by the stored oxygen desorption amount existing area setting means, the value of the integrated shelf oxygen desorption amount in the storage of oxygen desorption amount integrating means, as close to the storage of oxygen desorption amount present area, or so that you and within said reservoir oxygen desorption amount existing region and a reservoir of oxygen desorption amount correction means for correcting,
The stored oxygen desorption amount existence region setting means determines an air-fuel ratio region by using an air-fuel ratio detected downstream of the three-way catalyst as a state amount representing the operating state of the internal combustion engine, and enters the air-fuel ratio region. A three-way catalyst stored oxygen desorption amount calculating apparatus, wherein a corresponding storage oxygen desorption amount existence region is set . A three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine,
Stored oxygen desorption amount integrating means for integrating the stored oxygen desorption amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst;
A region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount in the three-way catalyst that is smaller than the region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount and is ternary A storage oxygen desorption amount existence region setting means for setting a storage oxygen desorption amount existence region where the storage oxygen desorption amount of the catalyst is highly likely to be located according to the operating state of the internal combustion engine;
When the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means is out of the stored oxygen desorption amount existing area set by the stored oxygen desorption amount existing area setting means, The stored oxygen desorption amount integrated by the stored oxygen desorption amount integrating means is corrected so as to be close to the stored oxygen desorption amount existing region or within the stored oxygen desorption amount existing region. A stored oxygen desorption amount correcting means,
The stored oxygen desorption amount existence region setting means uses a fuel cut process for stopping the fuel supply to the internal combustion engine during operation of the internal combustion engine as a state quantity indicating the operation state of the internal combustion engine, thereby A three-way catalyst stored oxygen desorption amount calculation device, wherein a storage oxygen desorption amount existence region corresponding to the presence or absence of processing is set . A three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine,
Stored oxygen desorption amount integrating means for integrating the stored oxygen desorption amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst;
A region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount in the three-way catalyst that is smaller than the region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount and is ternary A storage oxygen desorption amount existence region setting means for setting a storage oxygen desorption amount existence region where the storage oxygen desorption amount of the catalyst is highly likely to be located according to the operating state of the internal combustion engine;
When the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means is out of the stored oxygen desorption amount existing area set by the stored oxygen desorption amount existing area setting means, The stored oxygen desorption amount integrated by the stored oxygen desorption amount integrating means is corrected so as to be close to the stored oxygen desorption amount existing region or within the stored oxygen desorption amount existing region. A stored oxygen desorption amount correcting means,
The stored oxygen desorption amount existence region setting means includes, as state quantities representing the operation state of the internal combustion engine, presence or absence of a fuel cut process for stopping fuel supply to the internal combustion engine during operation of the internal combustion engine, and downstream of the three-way catalyst. The three-way catalyst storage is characterized in that, by using the air-fuel ratio detected in step 3, the storage oxygen desorption amount existence region corresponding to the presence or absence of fuel cut processing and the air-fuel ratio detected downstream of the three-way catalyst is set. Oxygen desorption amount calculation device. A three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine,
Stored oxygen desorption amount integrating means for integrating the stored oxygen desorption amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst;
A region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount in the three-way catalyst that is smaller than the region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount and is ternary A storage oxygen desorption amount existence region setting means for setting a storage oxygen desorption amount existence region where the storage oxygen desorption amount of the catalyst is highly likely to be located according to the operating state of the internal combustion engine;
When the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means is out of the stored oxygen desorption amount existing area set by the stored oxygen desorption amount existing area setting means, The stored oxygen desorption amount integrated by the stored oxygen desorption amount integrating means is corrected so as to be close to the stored oxygen desorption amount existing region or within the stored oxygen desorption amount existing region. A stored oxygen desorption amount correcting means,
The stored oxygen desorption amount existence region setting means uses the temperature of the three-way catalyst as the state amount representing the operating state of the internal combustion engine, and uses the air-fuel ratio detected downstream of the three-way catalyst, thereby The three-way catalyst stored oxygen desorption amount calculating device is characterized in that the temperature of the three-way catalyst and the stored oxygen desorption amount existing region corresponding to the air-fuel ratio region are set . A three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine,
Stored oxygen desorption amount integrating means for integrating the stored oxygen desorption amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst;
A region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount in the three-way catalyst that is smaller than the region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount and is ternary A storage oxygen desorption amount existence region setting means for setting a storage oxygen desorption amount existence region where the storage oxygen desorption amount of the catalyst is highly likely to be located according to the operating state of the internal combustion engine;
When the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means is out of the stored oxygen desorption amount existing area set by the stored oxygen desorption amount existing area setting means, The stored oxygen desorption amount integrated by the stored oxygen desorption amount integrating means is corrected so as to be close to the stored oxygen desorption amount existing region or within the stored oxygen desorption amount existing region. A stored oxygen desorption amount correcting means,
The stored oxygen desorption amount existence region setting means includes a temperature of the three-way catalyst as a state quantity indicating an operation state of the internal combustion engine, and presence / absence of fuel cut processing for stopping fuel supply to the internal combustion engine during operation of the internal combustion engine Is used to set the storage oxygen desorption amount existence region corresponding to the temperature of the three-way catalyst and the presence or absence of fuel cut processing . A three-way catalyst stored oxygen desorption amount calculating device for calculating a stored oxygen desorption amount in a three-way catalyst disposed in an exhaust passage of an internal combustion engine,
Stored oxygen desorption amount integrating means for integrating the stored oxygen desorption amount in the three-way catalyst based on the exhaust state flowing into the three-way catalyst;
A region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount in the three-way catalyst that is smaller than the region between the maximum storage oxygen desorption amount and the minimum storage oxygen desorption amount and is ternary A storage oxygen desorption amount existence region setting means for setting a storage oxygen desorption amount existence region where the storage oxygen desorption amount of the catalyst is highly likely to be located according to the operating state of the internal combustion engine;
When the stored oxygen desorption amount accumulated by the stored oxygen desorption amount integrating means is out of the stored oxygen desorption amount existing area set by the stored oxygen desorption amount existing area setting means, The stored oxygen desorption amount integrated by the stored oxygen desorption amount integrating means is corrected so as to be close to the stored oxygen desorption amount existing region or within the stored oxygen desorption amount existing region. A stored oxygen desorption amount correcting means,
The stored oxygen desorption amount existence region setting means includes a temperature of the three-way catalyst as a state quantity indicating an operation state of the internal combustion engine, and presence / absence of fuel cut processing for stopping fuel supply to the internal combustion engine during operation of the internal combustion engine And the air-fuel ratio detected downstream of the three-way catalyst, the temperature of the three-way catalyst, the presence or absence of fuel cut processing, and the presence of stored oxygen desorption amount corresponding to the air-fuel ratio detected downstream of the three-way catalyst A three-way catalyst storage oxygen desorption amount calculation device characterized by setting a region . The stored oxygen desorption amount existence region setting means has a fuel concentration lower than the stoichiometric air-fuel ratio downstream of the three-way catalyst immediately after the end of the fuel cut processing for stopping the fuel supply to the internal combustion engine during operation of the internal combustion engine. The three-way catalyst storage oxygen desorption according to claim 2, 3, 5, or 6, wherein when the air-fuel ratio continues, a storage oxygen desorption amount existence region corresponding to the presence of fuel cut processing is set. Quantity calculation device. In addition to the structure according to any one of claims 1 to 7,
A three-way catalyst adsorption capacity estimating means for estimating the oxygen adsorption capacity of the three-way catalyst is provided.
The storage oxygen desorption amount existence region setting means is configured to store the stored oxygen desorption in the three-way catalyst according to the operating state of the internal combustion engine and the oxygen adsorption capacity of the three-way catalyst estimated by the three-way catalyst adsorption capacity estimation means. A three-way catalyst storage oxygen desorption amount calculation device , characterized in that a quantity existence region is set . 9. The three-way catalyst storage oxygen desorption amount calculation according to claim 8, wherein the three-way catalyst adsorption capacity estimation means estimates the oxygen adsorption capacity of the three-way catalyst according to the accumulated usage time of the three-way catalyst. apparatus. In addition to the structure according to any one of claims 1 to 7,
Equipped with a three-way catalyst adsorption capacity detection means for detecting the oxygen adsorption capacity of the three-way catalyst,
The storage oxygen desorption amount existence region setting means is configured to store the stored oxygen desorption in the three-way catalyst according to the operating state of the internal combustion engine and the oxygen adsorption capacity of the three-way catalyst detected by the three-way catalyst adsorption capacity detection means. A three-way catalyst storage oxygen desorption amount calculation device , characterized in that a quantity existence region is set . The three-way catalyst adsorption capacity detecting means is used from when oxygen is saturated in the three-way catalyst until when the fuel concentration of the air-fuel ratio detected downstream of the three-way catalyst is higher than the stoichiometric air-fuel ratio. 11. The three-way catalyst according to claim 10, wherein the oxygen adsorption capacity of the three-way catalyst is detected according to an integrated value of an excess / deficiency amount of the fuel concentration calculated based on an exhaust state flowing into the three-way catalyst. Catalyst storage oxygen desorption amount calculation device. The three-way catalyst adsorption capacity detecting means determines that the oxygen is saturated in the three-way catalyst when the fuel cut processing for stopping the fuel supply to the internal combustion engine during the operation of the internal combustion engine continues for a reference time or longer. 12. The three-way catalyst storage oxygen desorption amount calculation device according to claim 11, wherein integration of fuel concentration excess / deficiency calculated based on an exhaust state flowing into the catalyst is started . The stored oxygen desorption amount integrating means uses a quantity of intake air to the internal combustion engine and an air-fuel ratio detected upstream of the three-way catalyst as a state quantity that represents the exhaust state flowing into the three-way catalyst. The three-way catalyst storage oxygen desorption according to any one of claims 1 to 12, wherein a storage oxygen desorption amount in the three-way catalyst is obtained by integrating a balance between an oxygen adsorption amount and a desorption amount in the two-way catalyst. Separation amount calculation device. The three-way catalyst stored oxygen desorption amount calculation device according to any one of claims 1 to 13, wherein the three-way catalyst storage oxygen desorption amount calculation device calculated by the three-way catalyst storage oxygen desorption amount calculation device, An air-fuel ratio control apparatus for an internal combustion engine, wherein the air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of the internal combustion engine is controlled so as to achieve a target stored oxygen desorption amount.

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