JP2008019745A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly learn an air-fuel ratio in all of operational areas of an internal combustion engine, in a control device for an internal combustion engine. <P>SOLUTION: The control device for an internal combustion engine, comprises: an air-fuel ratio sensor measuring an air-fuel ratio of exhaust in an exhaust passage of an internal combustion engine; an air-fuel ratio error learning means learning differences between a target air-fuel ratio and each air-fuel ratios measured by the air-fuel sensor in a plurality of operational areas different in operational status of the internal combustion engine; a fuel adding means adding fuel in an exhaust passage upstream of the air-fuel ratio sensor; a learning prohibiting means prohibiting the learning by the air-fuel ratio error learning means, when the fuel adding means adds the fuel; and an adding frequency changing means changing the frequency of the addition of the fuel by the fuel adding means according to the number of times of execution of the learning by the air-fuel ratio error learning means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine.

  The measurement error of the intake air amount or the error of the fuel injection amount is defined as an air / fuel ratio actually measured by an air / fuel ratio sensor (hereinafter referred to as an actual air / fuel ratio) and a calculated air / fuel ratio (hereinafter calculated air / fuel ratio) at that time. The correction can be made based on the difference between. Then, by storing the difference between the actual air-fuel ratio and the calculated air-fuel ratio, or the correction value of the intake air amount or the fuel injection amount as the learning value, the subsequent air-fuel ratio can be optimized. The storage of the learning value in this way is hereinafter referred to as “air-fuel ratio error learning”.

  By the way, a fuel addition valve and a NOx catalyst are provided in the exhaust passage of the internal combustion engine from the upstream side, and NOx can be purified by adding fuel to the NOx catalyst. However, when an air-fuel ratio sensor is provided downstream of the fuel addition valve, the output value of the air-fuel ratio sensor changes depending on the fuel added from the fuel addition valve. The difference will also change. Therefore, it becomes difficult to learn the air-fuel ratio error.

On the other hand, a technique for prohibiting the learning when fuel is added from the fuel addition valve is known (see, for example, Patent Document 1). That is, since learning is performed only when no fuel is added from the fuel addition valve, the influence of the fuel added from the fuel addition valve can be reduced.
JP 2002-327634 A JP 2003-214245 A

  However, if the air-fuel ratio error learning is prohibited every time the fuel is added, the learning opportunity decreases. Here, since there is an operation region suitable for fuel addition, fuel addition is frequently performed in this operation region. In such a driving region, there are fewer opportunities for learning, which may make learning difficult.

  The present invention has been made in view of the above-described problems, and provides a technique capable of more quickly learning the air-fuel ratio in the entire operation region of the internal combustion engine in the control device for the internal combustion engine. For the purpose.

In order to achieve the above object, a control apparatus for an internal combustion engine according to the present invention provides:
An air-fuel ratio sensor for measuring the air-fuel ratio of the exhaust in the exhaust passage of the internal combustion engine;
Air-fuel ratio error learning means for learning a difference between a target air-fuel ratio and an air-fuel ratio measured by the air-fuel ratio sensor in a plurality of operating regions in which the operating state of the internal combustion engine is different;
Fuel addition means for adding fuel into the exhaust passage upstream of the air-fuel ratio sensor;
Learning prohibiting means for prohibiting learning by the air-fuel ratio error learning means by adding fuel by the fuel adding means;
An addition frequency changing means for changing the frequency of fuel addition by the fuel addition means in accordance with the number of times learning is performed by the air-fuel ratio error learning means in each operation region;
It is characterized by providing.

  Here, based on the difference between the target air-fuel ratio and the air-fuel ratio measured by the air-fuel ratio sensor, the actual air-fuel ratio is adjusted to the target air-fuel ratio by changing the fuel supply amount or intake air amount to the combustion chamber. be able to. If a correction value for the fuel supply amount or the intake air amount is obtained and stored, the correction value can be used next time. If the difference between the target air-fuel ratio and the air-fuel ratio measured by the air-fuel ratio sensor is stored, the correction value for the fuel supply amount or the intake air amount can be quickly obtained based on this difference next time. As described above, the air-fuel ratio error learning means performs learning by storing a value related to the difference between the target air-fuel ratio and the air-fuel ratio measured by the air-fuel ratio sensor. The value stored in this way is hereinafter referred to as “learning value”.

  The difference between the target air-fuel ratio and the air-fuel ratio measured by the air-fuel ratio sensor is not limited to the value obtained by subtracting the “air-fuel ratio measured by the air-fuel ratio sensor” from the “target air-fuel ratio”. ”And“ the air-fuel ratio measured by the air-fuel ratio sensor ”.

  By the way, when the operating state of the internal combustion engine (for example, engine speed or fuel injection amount) is different, the learning value may also be different. For this reason, the air-fuel ratio error learning means obtains a learning value for each of a plurality of operating regions in which the operating state of the internal combustion engine is different.

  Further, when fuel addition is performed by the fuel addition means, the output of the air-fuel ratio sensor becomes richer, so that it becomes difficult to obtain the learning value. Therefore, the learning prohibiting means prohibits learning when fuel is added. In addition, the case where the fuel is added includes the case where the added fuel is detected by the air-fuel ratio sensor.

  Here, in the operation region where the number of times of fuel addition is large, the number of times the learning of the air-fuel ratio is limited increases, so the number of times of learning the air-fuel ratio decreases. On the other hand, in the operation region where the number of times of fuel addition is small, the learning of the air-fuel ratio can be performed more, so the number of times of learning increases. That is, since the number of times of learning of the air-fuel ratio is related to the frequency of fuel addition, the number of times of learning in the operating region can be controlled by changing the frequency of fuel addition for each operating region.

  In the present invention, the addition frequency changing means can make the fuel addition frequency lower than a reference value in an operation region where the number of learnings by the air-fuel ratio error learning means is less than a predetermined value.

  Lowering the addition frequency means that the number of times of fuel addition is reduced, and that the time from fuel addition to the next fuel addition is made longer. Here, the reference value can be the fuel addition frequency set when learning by the air-fuel ratio error learning means is not performed.

  That is, by lowering the addition frequency, it is possible to lengthen the period during which no fuel is added in the operation region, thereby increasing learning opportunities. Here, the predetermined value may be the number of times required to accurately learn the air-fuel ratio. That is, since the learning opportunity can be increased when the number of learning is less than the predetermined value, the number of learning can be rapidly increased to the predetermined value.

  On the other hand, in the present invention, the addition frequency changing means can make the fuel addition frequency higher than a reference value in an operating region where the number of learnings by the air-fuel ratio error learning means is greater than a predetermined value.

  Increasing the addition frequency means increasing the number of times of fuel addition, and means shortening the time from fuel addition to the next fuel addition.

  That is, when the number of correction learning is greater than a predetermined value, the necessity for learning is low, and there are few problems even if the learning opportunities are reduced by fuel addition. In addition, by performing fuel addition in such a region, the number of times of fuel addition can be reduced in other operation regions where the number of learning is small, so that learning in other operation regions can be promoted. .

  In the present invention, the addition frequency changing means can change the frequency of fuel addition in accordance with the frequency with which the internal combustion engine is operated in each operation region.

  Here, there are many opportunities for learning the air-fuel ratio in the operation region where the internal combustion engine is operated frequently. Therefore, even if the frequency of fuel addition is increased, an opportunity for learning the air-fuel ratio can be obtained. However, when the number of times of learning is small in an operating region where the internal combustion engine is frequently operated, it is considered that the number of times of learning is prohibited due to fuel addition.

  Therefore, in the present invention, the addition frequency changing means may decrease the frequency of fuel addition as the frequency of operation increases in an operation region where the number of learnings by the air-fuel ratio error learning means is less than a predetermined value. it can.

  In other words, the higher the frequency of driving, the more learning opportunities should be due to the greater number of learning opportunities.However, the number of learnings is nevertheless less than a predetermined value. Considered higher. That is, the higher the frequency of operation, the more the opportunities for learning of the air-fuel ratio can be achieved by lowering the addition frequency.

  However, in a region where the frequency of driving is low, it is not possible to determine whether the number of times of driving is small and the number of times of learning is small, or because the number of times of addition is large and the number of times of learning is small. Therefore, in the present invention, the addition frequency is lowered in the operation region where the operation frequency is high.

  In this case, the addition frequency changing means can lower the fuel addition frequency as the number of times of learning by the air-fuel ratio error learning means is smaller.

  That is, the smaller the number of learning times, the more learning is required. In addition, it is considered that the less the number of times of learning, the higher the frequency of fuel addition. And, as the number of times of learning is smaller, the frequency of fuel addition can be lowered to increase the opportunities for learning of the air-fuel ratio, so that the number of times of learning can be increased rapidly.

  In the present invention, the addition frequency changing means may increase the frequency of fuel addition as the frequency of operation increases in an operation region where the number of learnings by the air-fuel ratio error learning means is greater than a predetermined value. it can.

  That is, when the driving frequency is high and the number of times of learning is greater than a predetermined value, the necessity for learning becomes lower. Therefore, the frequency of fuel addition can be increased. Also, by increasing the amount of fuel added in such a region, the number of times of fuel addition can be reduced in other operating regions where the number of times of learning is low, so learning of the air-fuel ratio in other operating regions is promoted. Can be made.

  In the present invention, the addition frequency changing means can increase the fuel addition frequency as the number of times of learning by the air-fuel ratio error learning means increases.

That is, the greater the number of times of learning, the lower the need for learning. In addition, it is considered that the frequency of fuel addition becomes lower as the number of times of learning increases. As the number of times of learning increases, the frequency of fuel addition in other operating regions can be reduced by increasing the frequency of fuel addition. Therefore, learning of the air-fuel ratio in other operating regions can be performed. It can be promoted more.

  In the present invention, when the fuel addition frequency is increased, the addition frequency changing means decreases the maximum value of the fuel addition frequency as the ratio of the operation region in which learning is completed with respect to the entire operation region is increased, When learning is completed in the entire operation region, the maximum value of the fuel addition frequency can be made equal to the reference value.

  Here, if the number of times of learning increases in all areas, the frequency of fuel addition need not be increased. Therefore, if the maximum value of the addition frequency is reduced as the ratio of the operation region in which the learning of the air-fuel ratio is completed with respect to the entire operation region is increased, the addition frequency can be suppressed from becoming higher than necessary. In addition, when learning is completed in the entire operation region, it is not necessary to increase the addition frequency, so that it can be set as a reference addition frequency.

  In this invention, the said addition frequency change means can change the addition frequency of one operation area | region according to the value learned in the other operation area | region which adjoins one operation area | region.

  Here, the difference between the learning values is small in the adjacent driving regions. That is, even if the operating state of the internal combustion engine changes slightly, the learning value hardly changes greatly. For this reason, it is considered that the learning value similarly increases in the driving region close to the driving region where the learning value is large. However, if the frequency of fuel addition is high in an operation region close to an operation region where the learning value is large, learning of the air-fuel ratio is limited. Here, since the learning value is large means that the necessity of learning is high, it is desirable to learn the air-fuel ratio at an early stage also in the operation region close to the operation region where the learning value is large. On the other hand, since the learning value is similarly expected to be small in the driving region close to the driving region where the learning value is small, the necessity for learning is reduced.

  That is, if the addition frequency is changed according to the learning value learned in the adjacent driving region, the addition frequency according to the necessity of learning can be set. For example, when the learning value in the adjacent driving region is larger, the learning opportunity can be increased by lowering the frequency of fuel addition.

  The control apparatus for an internal combustion engine according to the present invention can more quickly learn the air-fuel ratio in the entire operation region of the internal combustion engine.

  Hereinafter, specific embodiments of a control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which the control device for an internal combustion engine according to this embodiment is applied and its intake / exhaust system. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  The internal combustion engine 1 is provided with a fuel injection valve 11 that supplies fuel into the cylinder of the internal combustion engine. Further, an exhaust passage 2 leading to the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream.

An occlusion reduction type NOx catalyst 3 (hereinafter referred to as NOx catalyst 3) is provided in the middle of the exhaust passage 2. The NOx catalyst 3 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present. .

  An air-fuel ratio sensor 4 that outputs a signal corresponding to the air-fuel ratio of the exhaust gas flowing in the exhaust passage 2 is attached to the exhaust passage 2 downstream of the NOx catalyst 3.

  The exhaust passage 2 upstream of the NOx catalyst 3 is provided with a fuel addition valve 5 for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 2. The fuel addition valve 5 is opened by a signal from the ECU 6 described later and injects fuel into the exhaust. The fuel injected from the fuel addition valve 5 into the exhaust passage 2 makes the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 2 rich. At the time of NOx reduction, so-called rich spike control is executed in which the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3 is rich in a spike (short time) in a relatively short cycle. In this embodiment, the fuel addition valve 5 corresponds to the fuel addition means in the present invention.

  Furthermore, an intake passage 7 that leads to the combustion chamber is connected to the internal combustion engine 1. An air flow meter 8 that outputs a signal corresponding to the amount of air flowing through the intake passage 7 is provided in the intake passage 7.

  The internal combustion engine 1 configured as described above is provided with an ECU 6 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 6 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the above sensors, the ECU 6 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 12 by the driver, and an accelerator opening sensor 13 that can detect the engine load, and a crank position that detects the engine speed. Sensors 14 are connected via electrical wiring, and output signals from these various sensors are input to the ECU 6. On the other hand, the fuel injection valve 11 and the fuel addition valve 5 are connected to the ECU 6 via electric wiring, and the ECU 6 controls the opening and closing timing of the fuel injection valve 11 and the fuel addition valve 5.

  By the way, the amount of fuel actually injected from the fuel injection valve 11 (hereinafter referred to as actual fuel amount) becomes the fuel injection amount (hereinafter referred to as command fuel amount) instructed from the ECU 6 to the fuel injection valve 11. However, an error may occur. Further, when the intake air amount detected by the air flow meter 8 (hereinafter referred to as detected air amount) causes an error with respect to the air amount actually sucked into the internal combustion engine 1 (hereinafter referred to as actual air amount). There is. In these cases, the air-fuel ratio of the exhaust gas obtained from the air-fuel ratio sensor 4 (hereinafter referred to as the actual air-fuel ratio) and the air-fuel ratio of the exhaust gas obtained from the detected air amount and the command fuel amount (hereinafter referred to as the calculated air-fuel ratio). ) And make a difference. The ratio between the calculated air-fuel ratio and the actual air-fuel ratio is hereinafter referred to as “air-fuel ratio error”.

  Since this air-fuel ratio error changes according to the engine speed and the fuel injection amount, in this embodiment, the entire operation region is divided into a plurality of regions based on the engine speed and the fuel injection amount. The fuel ratio error is calculated. Then, a correction value based on the air-fuel ratio error is calculated for each operation region. This correction value is a value for correcting the subsequent command fuel amount or detected air amount. Thus, obtaining the correction value of the command fuel amount or the detected air amount based on the air-fuel ratio error and correcting them thereafter is called “learning” or “air-fuel ratio error learning”. An air-fuel ratio error used for such learning is referred to as a “learning value”. In each operation region, the air-fuel ratio control with high accuracy is realized by performing learning a plurality of times. For example, learning is performed a plurality of times, and this average value is finally used as the air-fuel ratio error learning value. Unless otherwise specified, hereinafter, “operation region” refers to each divided operation region.

  Here, FIG. 2 is a flowchart showing a flow for creating an air-fuel ratio error learning map. This routine is repeatedly executed every predetermined time.

  In step S101, it is determined whether a learning execution trigger is ON. The learning execution trigger is turned ON when learning is necessary. For example, it is turned ON every predetermined traveling distance or every predetermined driving time. Furthermore, it may be ON when the driving condition is suitable for learning. For example, it may be ON when the internal combustion engine 1 has been warmed up. If an affirmative determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, this routine is temporarily terminated.

  In step S102, the actual air amount is read from the output signal of the air flow meter 8.

  In step S103, the command fuel amount is read. A value calculated by the ECU 6 is used as the command fuel amount.

  In step S104, a calculated air-fuel ratio is obtained. A value obtained by dividing the actual air amount by the command fuel amount is taken as the calculated air-fuel ratio.

  In step S105, the actual air-fuel ratio is read from the output signal of the air-fuel ratio sensor 4.

  In step S106, it is determined whether the fuel is being added from the fuel addition valve 5 or within a predetermined period after the fuel addition is completed. That is, it is determined whether or not it is a time when an air-fuel ratio error caused by fuel addition can occur. The predetermined period can be a period of time from when the fuel addition from the fuel addition valve 5 is completed until the air-fuel ratio sensor 4 is no longer affected by the fuel.

  If an affirmative determination is made in step S106, the air-fuel ratio error learning is not performed, so this routine is temporarily terminated. On the other hand, if a negative determination is made, the process proceeds to step S107. In the present embodiment, the ECU 6 that does not perform air-fuel ratio error learning by making an affirmative determination in step 106 corresponds to the learning prohibiting means in the present invention.

  In step S107, an air-fuel ratio error is calculated. A value obtained by dividing the calculated air-fuel ratio by the actual air-fuel ratio is taken as the air-fuel ratio error.

  In step S108, an operation region to be stored in the map is selected based on the engine speed and the fuel injection amount. That is, a map based on the engine speed and the fuel injection amount is created. A map may be created based on the engine speed and the intake air amount (or accelerator opening).

  In step S109, the learning value (air-fuel ratio error) is stored in the selected operation region. Then, learning is performed a plurality of times in each driving region, the learning value for each time is stored, and the number of times of learning is also stored. In this embodiment, the ECU 6 that executes the processing from step S107 to step 109 corresponds to the air-fuel ratio error learning means in the present invention.

  In this way, an air-fuel ratio error is obtained for each operating region of the internal combustion engine 1. In this embodiment, as shown in step S106, air-fuel ratio error learning is performed at a time when there is no possibility that the output value of the air-fuel ratio sensor 4 will change due to the fuel added from the fuel addition valve 5. ing.

  FIG. 3 is a diagram showing an example of the relationship among the engine speed NE, the fuel injection amount Q, and the number of learnings. By dividing the engine speed NE into five and dividing the fuel injection amount Q into five, the entire operation region is divided into 25 operation regions. The numbers shown in each operation region are the number of times learning has been performed in that operation region.

  For example, when learning is required twice or more, the number of learning is insufficient in the driving region where the number of learning is 0 and 1. As one of the causes, it can be considered that fuel is frequently added in these operation regions. That is, since learning is prohibited during the addition of fuel, if the addition of fuel is frequently performed, opportunities for learning are reduced. Thereby, it is thought that the frequency | count of learning decreases.

  Therefore, in the present embodiment, the frequency of fuel addition is reduced in the operation region where the number of learning has not reached the required number (for example, twice). Here, FIG. 4 is a diagram illustrating the relationship between the number of learnings and the addition frequency correction coefficient according to the present embodiment. The addition frequency correction coefficient is a coefficient for changing the addition frequency of the fuel, and is multiplied by the current addition frequency. That is, when the addition frequency correction coefficient is 1, the fuel addition frequency does not change. When the addition frequency correction coefficient is smaller than 1, the fuel addition frequency is low. That is, since the addition interval becomes longer, the number of additions decreases. In this embodiment, the ECU 6 that changes the fuel addition interval based on the addition frequency correction coefficient corresponds to the addition frequency changing means in the present invention.

  As described above, when the frequency of fuel addition decreases, the number of learning increases because the number of learning opportunities increases. That is, in the driving region where the number of learning is small, the number of learning can be quickly increased to the required number. As a result, the air-fuel ratio can be learned more quickly in the entire operation region of the internal combustion engine 1. Further, since learning is not performed when there is a possibility that the air-fuel ratio error is erroneously learned due to fuel addition, a correct learning value can be obtained.

  In addition, the addition frequency correction coefficient is set to 1 in the operation region where the number of learning reaches the required number. Thereby, since the frequency of fuel addition becomes a reference value in the operation region where the number of learning is equal to or greater than the required number, the shortage of fuel addition can be suppressed.

  In the first embodiment, the frequency of fuel addition is reduced when the number of learning is less than the required number. However, for example, when learning has just started in the case of a new car or the like, the number of times of learning is less than the required number in any operating region, so the frequency of fuel addition is reduced in all operating regions. Therefore, there is a risk that the exhaust purification rate will decrease due to insufficient fuel addition.

  Therefore, in this embodiment, the frequency of fuel addition is corrected according to the number of times of operation in each operation region (hereinafter referred to as the number of uses). Note that the fuel addition frequency may be corrected according to the operation time in each operation region. Further, the correction of the fuel addition frequency according to the number of times of use can be said to change the frequency of fuel addition according to the frequency at which the internal combustion engine 1 is operated in each operation region.

  Here, FIG. 5 is a diagram illustrating the relationship between the number of learnings and the addition frequency correction coefficient according to the present embodiment.

That is, in the operation region where the number of times of learning is the required number of times, although the number of times of use is relatively large, it is considered that the opportunity for learning is reduced due to the addition of fuel. In such a case, the fuel addition frequency is set lower than the reference value. That is, the addition frequency correction coefficient is made smaller than 1. Thereby, since the opportunity of learning increases, the frequency | count of learning can be increased. In addition, the smaller the number of times of learning, the lower the addition frequency in order to increase learning opportunities. Therefore, the smaller the number of learning times, the smaller the addition frequency correction coefficient.

  Further, the more the number of times of use is, the more the number of times of learning is considered because more fuel has been added, so the frequency of addition is made lower. Therefore, the more frequently used, the smaller the addition frequency correction coefficient.

  If the number of times of use is relatively small, it cannot be determined whether the number of times of learning is small due to the small number of times of use or whether the number of times of learning is small because of the addition of fuel. Therefore, in such a case, the addition frequency is set as a reference value regardless of the number of learnings. That is, the addition frequency correction coefficient is 1.

  Furthermore, when the number of times of use is large and the number of times of learning is sufficient, since sufficient learning has already been performed, the frequency of fuel addition is set higher than the reference value. That is, the addition frequency correction coefficient is made larger than 1. Thereby, since insufficient addition of fuel can be suppressed, the exhaust gas purification rate can be improved. In addition, as the number of times of learning increases, the number of learning opportunities may be smaller, so the frequency of addition can be further reduced. Therefore, the addition frequency correction coefficient is increased as the number of times of learning increases. Furthermore, as the number of times of use increases, more fuel is added, so that the addition frequency can be further reduced, and therefore the addition frequency correction coefficient is made smaller.

  In this manner, fuel addition can be ensured in the entire operation region, and therefore, it is possible to suppress a decrease in the exhaust gas purification rate due to insufficient fuel addition when learning is just started. In this embodiment, the ECU 6 that changes the fuel addition interval based on the addition frequency correction coefficient corresponds to the addition frequency changing means in the present invention.

  In the second embodiment, the fuel addition frequency is changed based on the number of times of learning and the number of times of use. In this case, when learning progresses in the entire operation region, there are more operation regions in which the fuel addition frequency is higher than the reference value. For this reason, fuel is added more than necessary, and fuel consumption may be deteriorated.

  Therefore, in this embodiment, the maximum value of the addition frequency correction coefficient is reduced as learning progresses. Here, FIG. 6 is a diagram showing the relationship between the ratio of the operation region in which learning has been completed in the entire operation region and the addition frequency correction coefficient.

  The driving region in which learning is completed is a driving region in which the number of learning is greater than the required number. The maximum value of the addition frequency correction coefficient is decreased as the ratio of the operation region in which learning is completed increases. Then, when learning is completed in the entire operation region, the maximum value of the addition frequency correction coefficient is set to 1. That is, when learning is completed in the entire operation region, the addition frequency correction coefficient is set to 1, so that the fuel addition frequency returns to the reference state.

  The lower the ratio of the operation region in which learning is completed, the higher the fuel addition frequency is. Therefore, the maximum value of the addition frequency correction coefficient in the operation region in which learning has been completed is increased. be able to. In other words, the lower the ratio of the operation region where learning is completed, the lower the fuel addition frequency in the more operation region than the reference value, but the higher the fuel addition frequency in the operation region where learning is completed, Insufficient fuel addition can be suppressed.

On the other hand, as the ratio of the operation region in which learning is completed increases, the maximum value of the addition frequency correction coefficient is reduced to 1 so that the fuel addition frequency in the operation region in which learning has been completed approaches the reference value. . Thereby, it can suppress that the fuel more than necessary is added. In other words, the higher the percentage of the operation region in which learning is completed, the more the operation region in which the fuel addition frequency is lower than the reference value is decreased. The need for higher is lower. And it can suppress adding more fuel than necessary by making the addition frequency of fuel low in the driving | running | working area | region where learning was completed.

  Here, in order to reduce the minimum value of the addition frequency correction coefficient, the increase amount of the addition frequency correction coefficient with respect to the increase amount of the number of learnings in FIG. 5 may be reduced. That is, the slope of the line shown in FIG. In FIG. 5, the addition frequency correction coefficient may be set to a constant value larger than 1 when the number of learning becomes a predetermined value or more without changing the increase amount of the addition frequency correction coefficient with respect to the increase in the learning frequency. .

  In this embodiment, the ECU 6 that changes the fuel addition interval based on the addition frequency correction coefficient corresponds to the addition frequency changing means in the present invention.

  In the first to third embodiments, the frequency of fuel addition in the target operation region is changed based on the number of times of learning or use of the target operation region.

  Here, the learning values are close to each other in adjacent operation regions. That is, the engine speed and the fuel injection amount are close to each other in the adjacent operation region, and the actual air-fuel ratio hardly changes greatly only by shifting the operation region to the next. Therefore, the learning value does not change greatly, and the learning value becomes a close value.

  Therefore, the learning value is expected to increase in the driving region adjacent to the driving region where the learning value is large. In such an operation region, even if fuel is added, the air-fuel ratio in the NOx catalyst 3 cannot be set to an appropriate value. Therefore, the necessity of learning is higher in the driving region where the learning value is expected to increase and learning is not completed.

  Therefore, in this embodiment, the frequency of fuel addition is reduced so that learning can be performed preferentially in an operation region where the necessity of learning is higher. Note that the adjacent operation areas refer to, for example, eight operation areas that surround one operation area in FIG. Hereinafter, the operation region adjacent to the target operation region is referred to as a proximity region.

  FIG. 7 is a diagram showing the relationship between the maximum learning value in the proximity region and the addition frequency correction coefficient. The addition frequency correction coefficient is reduced as the learning value increases in the adjacent region.

  In other words, the maximum value of the air-fuel ratio error in the proximity region is obtained, and the larger the maximum value, the lower the fuel addition frequency. That is, as the maximum value of the air-fuel ratio error in the proximity region is larger, it is desirable to perform the air-fuel ratio error learning more quickly in the target operation region. There are many.

  In addition, when the maximum value of the air-fuel ratio error in the proximity region becomes higher than the threshold value, fuel addition in the target operation region is prohibited. That is, when the air-fuel ratio error exceeds the allowable range, the fuel addition is prohibited, so that learning can be quickly performed when the vehicle is operated in the target operation region.

  Further, when the maximum value of the air-fuel ratio error in the proximity region is 0, it is considered that there is almost no air-fuel ratio error in the target operation region, so the fuel addition frequency is used as the reference value. Thereby, it is possible to suppress the occurrence of insufficient fuel addition.

  In this way, air-fuel ratio error learning can be performed preferentially in an operating region where the air-fuel ratio error is large. In this embodiment, the ECU 6 that changes the fuel addition interval based on the addition frequency correction coefficient corresponds to the addition frequency changing means in the present invention.

It is a figure which shows schematic structure of the internal combustion engine which applies the control apparatus of the internal combustion engine which concerns on an Example, and its intake / exhaust system. 5 is a flowchart showing a flow for creating an air-fuel ratio error learning map. It is the figure which showed an example of the relationship between the engine speed NE, the fuel injection quantity Q, and the learning frequency. It is the figure which showed the relationship between the frequency | count of learning which concerns on Example 1, and an addition frequency correction coefficient. It is the figure which showed the relationship between the frequency | count of learning which concerns on Example 2, and an addition frequency correction coefficient. It is the figure which showed the relationship between the ratio of the driving | operation area | region which completed the learning which occupies for all the driving | running areas, and an addition frequency correction coefficient. It is the figure which showed the relationship between the maximum value of the learning value in an adjacent area | region, and an addition frequency correction coefficient.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 NOx catalyst 4 Air-fuel ratio sensor 5 Fuel addition valve 6 ECU
7 Intake passage 8 Air flow meter 11 Fuel injection valve 12 Accelerator pedal 13 Accelerator opening sensor 14 Crank position sensor

Claims (10)

An air-fuel ratio sensor for measuring the air-fuel ratio of the exhaust in the exhaust passage of the internal combustion engine;
An air-fuel ratio error learning means for learning a difference between a target air-fuel ratio and an air-fuel ratio measured by the air-fuel ratio sensor in a plurality of operating regions in which the operating state of the internal combustion engine is different;
Fuel addition means for adding fuel into the exhaust passage upstream of the air-fuel ratio sensor;
Learning prohibiting means for prohibiting learning by the air-fuel ratio error learning means by adding fuel by the fuel adding means;
An addition frequency changing means for changing the frequency of fuel addition by the fuel addition means in accordance with the number of times learning is performed by the air-fuel ratio error learning means in each operation region;
A control device for an internal combustion engine, comprising:   2. The internal combustion engine according to claim 1, wherein the addition frequency changing unit makes the fuel addition frequency lower than a reference value in an operation region in which the number of learnings by the air-fuel ratio error learning unit is less than a predetermined value. Engine control device.   2. The internal combustion engine according to claim 1, wherein the addition frequency changing unit makes the fuel addition frequency higher than a reference value in an operation region in which the number of times of learning by the air-fuel ratio error learning unit is greater than a predetermined value. Engine control device.   2. The control device for an internal combustion engine according to claim 1, wherein the addition frequency changing unit changes the frequency of fuel addition in accordance with a frequency at which the internal combustion engine is operated in each operation region.   5. The fuel addition frequency changing means according to claim 4, wherein in the operation region where the number of times of learning by the air-fuel ratio error learning means is less than a predetermined value, the frequency of fuel addition decreases as the operation frequency increases. The internal combustion engine control device described.   The control apparatus for an internal combustion engine according to claim 2 or 5, wherein the addition frequency changing means lowers the fuel addition frequency as the number of times of learning by the air-fuel ratio error learning means decreases.   5. The fuel addition frequency according to claim 4, wherein the addition frequency changing means increases the fuel addition frequency as the operation frequency is higher in an operation region where the number of times of learning by the air-fuel ratio error learning means is greater than a predetermined value. The internal combustion engine control device described.   The control apparatus for an internal combustion engine according to claim 3 or 7, wherein the addition frequency changing means increases the fuel addition frequency as the number of times of learning by the air-fuel ratio error learning means increases.   When the fuel addition frequency is increased, the addition frequency changing means decreases the maximum value of the fuel addition frequency as the ratio of the operation region in which learning has been completed with respect to the entire operation region is increased. 9. The control device for an internal combustion engine according to claim 3, wherein the maximum value of the fuel addition frequency is made equal to a reference value when learning is completed.   The said addition frequency change means changes the addition frequency of one operation area | region according to the value learned in the other operation area | region which adjoins one operation area | region, The any one of Claim 1 to 9 characterized by the above-mentioned. The control apparatus of the internal combustion engine described in 1.

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