JP5370018B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine, including an air-fuel ratio sensor provided downstream of an exhaust emission control catalyst, and correctly controlling an air-fuel mixture supplied to a combustion chamber in rich control or lean control based on an output value from the air-fuel ratio sensor. <P>SOLUTION: The exhaust emission control catalyst 52 is arranged in an exhaust passage 50, and the air-fuel ratio sensor 54 is arranged in the exhaust passage downstream of the exhaust emission control catalyst. When the rich control over the air-fuel ratio of the air-fuel mixture is started, the amount of fuel supplied to the combustion chamber 25 is increased. Time required for exhaust gas after burning of fuel to reach the air-fuel ratio sensor is called exhaust gas arrival time, and time required for the air-fuel ratio sensor to output an output value corresponding to the air-fuel ratio of the exhaust gas received by the air-fuel ratio sensor is called sensor output time. Control over the air-fuel ratio of the air-fuel mixture based on the output value from the air-fuel ratio sensor in the rich control is started when time with the sensor output time added to the exhaust gas arrival time after the amount of fuel supplied to the combustion chamber is increased is passed or thereafter. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

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

  Patent Document 1 discloses an air-fuel ratio control apparatus for an internal combustion engine. In this air-fuel ratio control device, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled to the target air-fuel ratio based on the output value of the air-fuel ratio sensor disposed in the exhaust passage upstream of the exhaust purification catalyst.

  By the way, in the air-fuel ratio control disclosed in Patent Document 1, it takes a certain time until the exhaust gas reflecting the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber at a specific time reaches the air-fuel ratio sensor. Therefore, the output value of the air-fuel ratio sensor is used for controlling the air-fuel ratio of the air-fuel mixture. That is, the output value of the air-fuel ratio sensor is used for controlling the air-fuel ratio of the air-fuel mixture in consideration of the time until exhaust gas discharged from the combustion chamber reaches the air-fuel ratio sensor.

  Further, in the air-fuel ratio control device disclosed in Patent Document 1, when the air-fuel ratio of the exhaust gas that has arrived at the air-fuel ratio sensor is richer than the stoichiometric air-fuel ratio, the output value corresponding to the air-fuel ratio of the exhaust gas is set to the empty air-fuel ratio control device. When the air-fuel ratio of the exhaust gas arriving at the air-fuel ratio sensor is leaner than the stoichiometric air-fuel ratio, the output value corresponding to the air-fuel ratio of the exhaust gas is empty. The output value of the air-fuel ratio sensor is used for controlling the air-fuel ratio of the air-fuel mixture in consideration of the relatively long time until the output of the fuel-fuel ratio sensor. That is, the output value of the air-fuel ratio sensor is used for controlling the air-fuel ratio of the air-fuel mixture in consideration of the output responsiveness of the air-fuel ratio sensor.

  That is, in the air-fuel ratio control device disclosed in Patent Document 1, when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber at a specific time is to be detected by the air-fuel ratio sensor, the air-fuel mixture supplied to the combustion chamber. If the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio, the time until the exhaust gas discharged from the combustion chamber reaches the air-fuel ratio sensor has elapsed, and the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio When the time until the air-fuel ratio sensor can output the output value corresponding to the air-fuel ratio of the exhaust gas has elapsed, the output value output from the air-fuel ratio sensor becomes the empty air-fuel mixture at the specific time point. Adopted as an output value corresponding to the fuel ratio. On the other hand, if the air-fuel ratio of the air-fuel ratio supplied to the combustion chamber is leaner than the stoichiometric air-fuel ratio when the air-fuel ratio of the air-fuel ratio supplied to the combustion chamber is detected by the air-fuel ratio sensor at a specific time, When the time until the exhaust gas discharged from the combustion chamber reaches the air-fuel ratio sensor has elapsed and the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, the output value corresponding to the air-fuel ratio of the exhaust gas is The output value output from the air-fuel ratio sensor when the time until the air-fuel ratio sensor can output has elapsed is adopted as the output value corresponding to the air-fuel ratio of the air-fuel mixture at the specific time point.

  Thus, when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber at a specific time is detected by the air-fuel ratio sensor, the time until the exhaust gas discharged from the combustion chamber arrives at the air-fuel ratio sensor or the air-fuel ratio It is known that the output value of the air-fuel ratio sensor is corrected in consideration of the output response of the sensor, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled based on the corrected output value.

JP 2007-2111609 A Japanese Patent Laid-Open No. 07-019092

  By the way, an exhaust purification catalyst for purifying a specific component in the exhaust gas is disposed in the exhaust passage and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst to achieve a specific purpose. Rich control is performed to control the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a predetermined air-fuel ratio richer than the stoichiometric air-fuel ratio, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the rich control is When the predetermined air-fuel ratio is controlled based on the output value of the air-fuel ratio sensor, it is preferable that the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the rich control is accurately controlled to the predetermined air-fuel ratio.

  However, as described above, in Patent Document 1, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled to a predetermined air-fuel ratio based on the output value of the air-fuel ratio sensor arranged upstream of the exhaust purification catalyst. Although the technology relating to when the output value output from the air-fuel ratio sensor is used for controlling the air-fuel ratio of the air-fuel mixture is disclosed, the air-fuel ratio sensor disposed downstream of the exhaust purification catalyst When the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled to a predetermined air-fuel ratio based on the output value of the engine, the output value output from the air-fuel ratio sensor at what timing is used to control the air-fuel ratio of the air-fuel mixture The technology regarding what to do is not disclosed. That is, when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled based on the output value of the air-fuel ratio sensor arranged downstream of the exhaust purification catalyst, the exhaust gas arriving at the air-fuel ratio sensor Since the exhaust gas after passing through it is determined at what timing the output value output from the air-fuel ratio sensor is used for controlling the air-fuel ratio of the air-fuel mixture is determined by the air-fuel ratio sensor arranged upstream of the exhaust purification catalyst. When the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled based on the output value, the timing at which the output value output from the air-fuel ratio sensor is used to control the air-fuel ratio of the air-fuel mixture is naturally different. become. Therefore, when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled to a predetermined air-fuel ratio based on the output value of the air-fuel ratio sensor arranged upstream of the exhaust purification catalyst, the timing from the air-fuel ratio sensor Regarding whether to use the output value output for the control of the air-fuel ratio of the air-fuel mixture, a special technique is required when the air-fuel ratio sensor is arranged upstream of the exhaust purification catalyst.

  Of course, this means that an exhaust purification catalyst for purifying a specific component in the exhaust gas is disposed in the exhaust passage, and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst. In order to achieve this, lean control is performed to control the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a predetermined air-fuel ratio leaner than the stoichiometric air-fuel ratio. The same applies when the air-fuel ratio is controlled to the predetermined air-fuel ratio based on the output value of the air-fuel ratio sensor.

  Accordingly, an object of the present invention is to provide an exhaust purification catalyst for purifying a specific component in exhaust gas in the exhaust passage and an air-fuel ratio sensor in the exhaust passage downstream of the exhaust purification catalyst. In order to achieve the above object, rich control is performed to control the air / fuel ratio of the air / fuel mixture to a predetermined air / fuel ratio richer than the stoichiometric air / fuel ratio, or the air / fuel ratio of the air / fuel mixture is theoretically calculated to achieve a specific object. Lean control is performed to control to a predetermined air-fuel ratio leaner than the air-fuel ratio, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in rich control or lean control is controlled based on the output value of the air-fuel ratio sensor In the air-fuel ratio control apparatus for an internal combustion engine, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the rich control or the lean control is accurately controlled to a predetermined air-fuel ratio.

In the first invention, an exhaust purification catalyst for purifying a specific component in the exhaust gas is disposed in the exhaust passage, and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst. In order to achieve this, rich control is executed to control the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a predetermined target rich air-fuel ratio richer than the stoichiometric air-fuel ratio, and the rich control is supplied to the combustion chamber. In the air-fuel ratio control apparatus for an internal combustion engine in which the air-fuel ratio of the air-fuel mixture is controlled to the target rich air-fuel ratio based on the output value of the air-fuel ratio sensor, the air-fuel ratio is supplied to the combustion chamber when the rich control is started The time required for the amount of fuel to increase and the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor is referred to as the exhaust arrival time, and the exhaust gas arrives at the air-fuel ratio sensor. Or Mixing based on the output value of the air-fuel ratio sensor in the rich control when the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the exhaust gas that has arrived is referred to as sensor output time. The control of the air-fuel ratio is started when the amount of fuel supplied to the combustion chamber is increased or when the sensor output time is added to the exhaust arrival time or after that.
Then, before the rich control is executed, a lean that controls the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a predetermined target rich air-fuel ratio that is leaner than the stoichiometric air-fuel ratio in order to achieve a specific purpose. Control is executed, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the lean control is controlled to the target lean air-fuel ratio based on the output value of the air-fuel ratio sensor, and the combustion chamber is started when the lean control is started The time required for the exhaust gas corresponding to the reduced amount of air to reach the air-fuel ratio sensor is referred to as intake air arrival time, and the exhaust gas is supplied to the air-fuel ratio sensor. When the time required for the air-fuel ratio sensor to output an output value corresponding to the air-fuel ratio of the exhaust gas that has arrived after the arrival is referred to as sensor output time, the air-fuel ratio sensor in the lean control The control of the air-fuel ratio of the air-fuel mixture based on the output value is started when the time obtained by adding the sensor output time to the intake air arrival time after the amount of air supplied to the combustion chamber is reduced or after that. The

In the second invention, in the first invention, the exhaust arrival time is calculated based on the amount of air supplied to the combustion chamber and the space volume of the exhaust passage from the combustion chamber to the air-fuel ratio sensor.

In the third aspect of the invention, an exhaust purification catalyst for purifying a specific component in the exhaust gas is disposed in the exhaust passage, and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst. In order to achieve this, rich control is executed to control the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a predetermined target rich air-fuel ratio richer than the stoichiometric air-fuel ratio, and the rich control is supplied to the combustion chamber. In the air-fuel ratio control apparatus for an internal combustion engine in which the air-fuel ratio of the air-fuel mixture is controlled to the target rich air-fuel ratio based on the output value of the air-fuel ratio sensor, the air-fuel ratio is supplied to the combustion chamber when the rich control is started The time required for the amount of fuel to increase and the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor is referred to as the exhaust arrival time, and the exhaust gas arrives at the air-fuel ratio sensor. Or Mixing based on the output value of the air-fuel ratio sensor in the rich control when the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the exhaust gas that has arrived is referred to as sensor output time. The control of the air-fuel ratio is started when the amount of fuel supplied to the combustion chamber is increased or when the sensor output time is added to the exhaust arrival time or after that.
The exhaust arrival time is calculated based on the amount of air supplied to the combustion chamber and the space volume of the exhaust passage from the combustion chamber to the air-fuel ratio sensor.

  In the fourth invention, an exhaust purification catalyst for purifying a specific component in the exhaust gas is disposed in the exhaust passage, and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst. In order to achieve this, lean control is performed to control the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a target lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. In an air-fuel ratio control apparatus for an internal combustion engine in which the air-fuel ratio is controlled to a target lean air-fuel ratio based on the output value of the air-fuel ratio sensor, the amount of air supplied to the combustion chamber is reduced when the lean control is started The time required for the exhaust gas corresponding to the reduced amount of air to reach the air-fuel ratio sensor is referred to as intake air arrival time, and the exhaust gas that has arrived after the exhaust gas arrives at the air-fuel ratio sensor is referred to as the intake air arrival time. When the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the air-fuel ratio is referred to as sensor output time, the air-fuel ratio of the air-fuel ratio based on the output value of the air-fuel ratio sensor in the lean control The control is started when a time obtained by adding the sensor output time to the intake air arrival time after the amount of air supplied to the combustion chamber is reduced or after that.

According to a fifth aspect, in the first, second or fourth aspect, the control amount is given to a component of the internal combustion engine capable of changing the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber, and the lean control As a control amount that can control the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to the target lean air-fuel ratio, a control amount that is the time before the sensor output time is added to the intake air arrival time is learned, The learning of the control amount in the lean control is started when or after the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the lean control is started.

  According to a sixth aspect, in the fifth aspect, the control amount given to the component of the internal combustion engine capable of changing the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is based on the learned control amount. It is determined.

In a seventh aspect, the throttle valve is arranged in the intake passage in the first or second or any one of the fourth to sixth aspects, and the throttle valve is reduced in opening so that it is supplied to the combustion chamber. The amount of air to be reduced is reduced, and the intake arrival time is calculated based on the reduced amount of air and the space volume of the intake passage and the space of the exhaust passage from the throttle valve to the air-fuel ratio sensor Is done.

  In an eighth aspect of the invention, in any one of the first to seventh aspects of the invention, the exhaust gas after combustion of the increased amount of fuel after the amount of fuel supplied to the combustion chamber is increased is the air-fuel ratio. The time required to reach the sensor is referred to as exhaust arrival time, and the air-fuel ratio of the air-fuel mixture when the increased amount of fuel is supplied to the combustion chamber after the amount of fuel supplied to the combustion chamber is increased. When the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the exhaust gas corresponding to the exhaust air-fuel ratio output time is referred to as the exhaust air-fuel ratio output time, the sensor output time from the exhaust air-fuel ratio output time Calculated by subtracting the exhaust arrival time.

According to the first aspect of the invention, rich control is executed to control the air-fuel ratio of the air-fuel mixture to be richer than the stoichiometric air-fuel ratio based on the output value of the air-fuel ratio sensor disposed downstream of the exhaust purification catalyst. In the case where the amount of fuel supplied to the combustion chamber is increased when the rich control is started, whether to start the control of the air-fuel ratio of the mixture based on the output value of the air-fuel ratio sensor in the rich control In the determination, the exhaust arrival time corresponding to the time required for the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor, and the exhaust gas that has arrived after the exhaust gas arrives at the air-fuel ratio sensor. The sensor output time corresponding to the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio is considered separately. Then, before the influence of the increase in the amount of fuel supplied to the combustion chamber reaches the output value of the air-fuel ratio sensor, the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the rich control is started. Is prohibited. For this reason, in the rich control, the air-fuel ratio of the air-fuel mixture is accurately controlled to the target rich air-fuel ratio.
Further, lean control is executed to control the air-fuel ratio of the air-fuel mixture to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio based on the output value of the air-fuel ratio sensor arranged downstream of the exhaust purification catalyst, and the lean control is started. In the case where the amount of air supplied to the combustion chamber is reduced at the time, the air-fuel ratio control value of the air-fuel ratio sensor in the lean control is reduced to determine whether to start control of the air-fuel ratio. An intake air arrival time corresponding to the time required for the exhaust gas corresponding to the amount of air to reach the air-fuel ratio sensor, and an output corresponding to the air-fuel ratio of the exhaust gas that has arrived since the exhaust gas arrived at the air-fuel ratio sensor The sensor output time corresponding to the time required for the air-fuel ratio sensor to output the value is considered separately. Then, before the influence of the decrease in the amount of air supplied to the combustion chamber reaches the output value of the air-fuel ratio sensor, the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the lean control is started. Is prohibited. For this reason, in the lean control, the air-fuel ratio of the air-fuel mixture is accurately controlled to the target lean air-fuel ratio.
According to the second aspect of the invention, the exhaust arrival time corresponding to the time required for the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor when the rich control is started is supplied to the combustion chamber. It is calculated based on the amount of air to be performed and the space volume of the exhaust passage from the combustion chamber to the air-fuel ratio sensor. That is, the exhaust arrival time becomes shorter in inverse proportion to the amount of air supplied to the combustion chamber, and becomes longer in proportion to the space volume of the exhaust passage from the combustion chamber to the air-fuel ratio sensor. According to the present invention, since the exhaust arrival time is calculated by individually considering these factors affecting the exhaust arrival time, the accurate exhaust arrival time is calculated.

According to the third aspect of the invention, rich control is executed to control the air-fuel ratio of the air-fuel mixture to be richer than the stoichiometric air-fuel ratio based on the output value of the air-fuel ratio sensor disposed downstream of the exhaust purification catalyst. In the case where the amount of fuel supplied to the combustion chamber is increased when the rich control is started, whether to start the control of the air-fuel ratio of the mixture based on the output value of the air-fuel ratio sensor in the rich control In the determination, the exhaust arrival time corresponding to the time required for the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor, and the exhaust gas that has arrived after the exhaust gas arrives at the air-fuel ratio sensor. The sensor output time corresponding to the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio is considered separately. Then, before the influence of the increase in the amount of fuel supplied to the combustion chamber reaches the output value of the air-fuel ratio sensor, the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the rich control is started. Is prohibited. For this reason, in the rich control, the air-fuel ratio of the air-fuel mixture is accurately controlled to the target rich air-fuel ratio.
An exhaust arrival time corresponding to the time required for the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor when the rich control is started, and the amount of air supplied to the combustion chamber And is calculated based on the volume of the exhaust passage from the combustion chamber to the air-fuel ratio sensor. That is, the exhaust arrival time becomes shorter in inverse proportion to the amount of air supplied to the combustion chamber, and becomes longer in proportion to the space volume of the exhaust passage from the combustion chamber to the air-fuel ratio sensor. According to the present invention, since the exhaust arrival time is calculated by individually considering these factors affecting the exhaust arrival time, the accurate exhaust arrival time is calculated.

According to the fourth aspect of the invention, the lean control is executed to control the air-fuel ratio of the air-fuel mixture to an air-fuel ratio leaner than the stoichiometric air-fuel ratio based on the output value of the air-fuel ratio sensor arranged downstream of the exhaust purification catalyst. In the case where the amount of air supplied to the combustion chamber is reduced when the lean control is started, whether or not to start the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the lean control In the determination, the intake air arrival time corresponding to the time required for the exhaust gas corresponding to the reduced amount of air to reach the air-fuel ratio sensor, and the exhaust gas that has arrived after the exhaust gas arrives at the air-fuel ratio sensor. The sensor output time corresponding to the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio is considered separately. Then, before the influence of the decrease in the amount of air supplied to the combustion chamber reaches the output value of the air-fuel ratio sensor, the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the lean control is started. Is prohibited. For this reason, in the lean control, the air-fuel ratio of the air-fuel mixture is accurately controlled to the target lean air-fuel ratio.

  According to the fifth aspect of the invention, the control amount is given to a component of the internal combustion engine related to the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the lean control The amount of air-fuel mixture based on the output value of the air-fuel ratio sensor in lean control is learned by the amount of control preceding the intake air arrival time as the control amount that can be controlled to the target lean air-fuel ratio by adding the sensor output time. It is started when the control of the fuel ratio is started or after that. That is, in the lean control, the air-fuel ratio of the air-fuel ratio is higher when the air-fuel ratio control is started than when the air-fuel ratio control of the air-fuel mixture is not started based on the output value of the air-fuel ratio sensor. The target lean air-fuel ratio is accurately controlled. Therefore, learning of the control amount should be performed when the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor is started. According to the present invention, since the control amount is learned when the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor is started, the air-fuel ratio of the air-fuel mixture is more accurately determined in the lean control. Then, the control amount that can be controlled to the target lean air-fuel ratio is learned. In addition, the exhaust gas corresponding to the air-fuel ratio reflected in the output value of the air-fuel ratio sensor in the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor is the time obtained by adding the sensor output time to the intake air arrival time This corresponds only to the control amount previously given to the components of the internal combustion engine. Here, according to the present invention, since the control amount before the intake air arrival time plus the sensor output time is learned, the air-fuel ratio of the air-fuel mixture is more accurately controlled to the target lean air-fuel ratio in the lean control. A control amount that can be learned is learned.

  According to the sixth aspect of the invention, the control amount given to the component of the internal combustion engine that can change the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the rich control is given to the same component of the internal combustion engine in the lean control. It is determined on the basis of the learned value of the controlled variable. The learning value of the control amount is a control amount that can more accurately control the air-fuel ratio of the air-fuel mixture to the target lean air-fuel ratio in the lean control. That is, the learning value of the control amount reflects a so-called machine difference of the constituent elements of the internal combustion engine that can change the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber. According to the present invention, since the control amount calculated based on the learned value of the control amount is used in the rich control, the function is provided as a component of the internal combustion engine that can change the air-fuel ratio of the air-fuel mixture. Even if there is a difference, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the rich control is more accurately controlled to the target rich air-fuel ratio.

  According to the seventh aspect, the intake air arrival time corresponding to the time required for the exhaust gas corresponding to the reduced amount of air to reach the air-fuel ratio sensor when the lean control is started is reduced. It is calculated based on the amount, and the space volume of the intake passage and the space volume of the exhaust passage from the throttle valve to the air-fuel ratio sensor. That is, the intake air arrival time becomes shorter in inverse proportion to the amount of reduced air, and becomes longer in proportion to the spatial volume of the intake passage and the exhaust passage from the throttle valve to the air-fuel ratio sensor. According to the present invention, since the intake arrival time is calculated by separately considering these factors affecting the intake arrival time, the accurate intake arrival time is calculated.

  According to the eighth aspect, the sensor output time corresponding to the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the exhaust gas after the exhaust gas arrives at the air-fuel ratio sensor is The output value corresponding to the air-fuel ratio of the exhaust gas corresponding to the air-fuel ratio of the air-fuel mixture when the increased amount of fuel is supplied to the combustion chamber after the amount of fuel supplied to the chamber is increased is the air-fuel ratio Subtract the exhaust arrival time corresponding to the time required for the exhaust gas after combustion of the increased amount of fuel to reach the air / fuel ratio sensor from the exhaust air / fuel ratio output time corresponding to the time required for the sensor to output. Is calculated by That is, the sensor output time is calculated based on these exhaust air / fuel ratio output time and exhaust arrival time that can be measured relatively accurately. Therefore, according to the present invention, the sensor output time is accurately calculated.

1 is an overall view of a compression self-ignition internal combustion engine according to an embodiment of the present invention. It is the figure which showed the map utilized in order to determine the target fuel injection quantity in normal control. It is the figure which showed the map utilized in order to determine the target rich air fuel ratio in rich control. FIG. 6 is a diagram showing a map used for determining a target rich in-cylinder intake amount in rich control. It is the figure which showed the map utilized in order to determine a target lean air fuel ratio in lean control. It is the figure which showed the map utilized in order to obtain | require an intake arrival time in lean control. It is the figure which showed the map utilized in order to obtain | require exhaust arrival time in rich control. It is the figure which showed a part of flowchart which performs air-fuel ratio control according to embodiment of this invention. It is the figure which showed a part of flowchart which performs air-fuel ratio control according to embodiment of this invention. It is the figure which showed a part of flowchart which performs air-fuel ratio control according to embodiment of this invention. It is the figure which showed a part of flowchart which performs air-fuel ratio control according to embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 10 denotes a compression self-ignition internal combustion engine (hereinafter simply referred to as “internal combustion engine”). The internal combustion engine 10 supplies air to the cylinder block portion 20 including a cylinder block, a cylinder block lower case, an oil pan, etc., a cylinder head portion 30 fixed on the cylinder block portion 20, and the cylinder block portion 20. And an exhaust passage 50 for releasing the exhaust gas from the cylinder block 20 to the outside.

  The cylinder block unit 20 includes a cylinder head 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 through the connecting rod 23, whereby the crankshaft 24 is rotated. A combustion chamber 25 is formed by the inner wall surface of the cylinder 21, the upper wall surface of the piston 22, and the lower wall surface of the cylinder head portion 30.

  The cylinder head portion 30 includes an intake port 31 that communicates with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake valve drive mechanism 32 a that drives the intake valve 32, and an exhaust that communicates with the combustion chamber 25. A port 33, an exhaust valve 34 for opening and closing the exhaust port 33, an exhaust valve drive mechanism 34a for driving the exhaust valve 34, a fuel injection valve 37 for injecting fuel into the combustion chamber 25, and the fuel injection valve 37 A pressure accumulating chamber 37a for supplying fuel at a high pressure to the pressure accumulating chamber 37a and a fuel pump 37b for pumping the fuel to the pressure accumulating chamber 37a. The intake valve drive mechanism 32a and the exhaust valve drive mechanism 34a are connected to a drive circuit 38.

  The intake passage 40 includes an intake branch pipe 41 connected to the intake port 31, a surge tank 42 connected to the intake branch pipe 41, and an intake duct 43 connected to the surge tank 42. An air filter 44 and a throttle valve 48 are arranged in the intake duct 43 in order from the upstream end. The throttle valve 48 is rotatably attached to the intake duct 43 and is driven by a throttle valve driving actuator 48a. When the opening of the throttle valve 48 (hereinafter referred to as “throttle opening”) is increased, the amount of air taken into the combustion chamber 25 (hereinafter referred to as “in-cylinder intake amount”) is increased, and the throttle opening is reduced. If it is decreased, the intake amount is decreased.

  The exhaust passage 50 includes an exhaust branch pipe 49 connected to the exhaust port 33 and an exhaust pipe 51 connected to the exhaust branch pipe 49. An exhaust purification catalyst 52 that purifies components in the exhaust gas is disposed in the exhaust pipe 51. The exhaust purification catalyst 52 of the present embodiment absorbs nitrogen oxide (hereinafter referred to as “NOx”) in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into it is leaner than the stoichiometric air-fuel ratio. When the air-fuel ratio of the exhaust gas flowing into the exhaust gas is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, the NOx absorbed therein is reduced and purified by unburned fuel in the exhaust gas (hereinafter referred to as “NOx purification capability”) Have). Further, the exhaust purification catalyst 52 occludes oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into it is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into it is greater than the stoichiometric air-fuel ratio. Has a capability of releasing oxygen stored therein when it is rich (hereinafter referred to as “oxygen storage / release capability”).

  An air-fuel ratio sensor 54 that detects the air-fuel ratio of the exhaust gas is disposed in the exhaust pipe 51 downstream of the exhaust purification catalyst 52. In the present embodiment, basically, the in-cylinder intake amount and the fuel injection valve are set so that the air-fuel ratio of the air-fuel mixture (hereinafter also simply referred to as “air-fuel mixture”) formed in the combustion chamber 25 becomes a predetermined air-fuel ratio. The amount of fuel injected from 37 into the combustion chamber 25 (hereinafter referred to as “fuel injection amount”) is controlled based on the output value of the air-fuel ratio sensor 54.

  Further, the internal combustion engine 10 detects an air flow meter 61 that detects the flow rate of air flowing through the intake duct 43, a rotational phase of the crankshaft 24, that is, a crank position sensor 62 that detects a crank angle, and a pressure in the combustion chamber 25. An in-cylinder pressure sensor 63 for detecting, an accelerator opening degree sensor 64 for detecting the depression amount of the accelerator pedal 65, and an electric control unit (ECU) 70 are provided. The crank position sensor 62 outputs a narrow pulse every time the crankshaft 24 rotates 1 °, and outputs a wide pulse every time the crankshaft 24 rotates 360 °. The rotational speed of the internal combustion engine (hereinafter referred to as “engine speed”) can be calculated based on the pulse output from the crank position sensor 62.

  The electric control unit (ECU) 70 is composed of a microcomputer, and a CPU (microprocessor) 71, a ROM (read only memory) 72, a RAM (random access memory) 73, and a backup RAM 74 connected to each other via a bidirectional bus. And an interface 75 including an AD converter. The air-fuel ratio sensor 54, air flow meter 61, crank position sensor 62, in-cylinder pressure sensor 63, and accelerator opening sensor 64 are connected to an interface 75.

  By the way, in this embodiment, when normal operation is performed in the internal combustion engine, that is, when normal control (hereinafter referred to as “normal control”) is performed, the in-cylinder intake air amount and the fuel injection amount are as follows. It is controlled as follows. That is, in this embodiment, the throttle opening is fully opened during normal control. On the other hand, in the present embodiment, a fuel injection amount that can satisfy the demands of the internal combustion engine is obtained in advance by experiments or the like for each operating state of the internal combustion engine (hereinafter referred to as “engine operating state”). For example, as shown in FIG. 2, the ECU 70 stores the target fuel injection amount TQn in the form of a map of a function of the engine operating state N and the engine load L. During normal control, the target fuel injection amount TQn is read from the map of FIG. 2 based on the engine speed N and the engine load L. Then, the operation of the fuel injection valve 37 is controlled so that the fuel injection amount becomes the target fuel injection amount.

  Incidentally, as described above, in the present embodiment, the exhaust purification catalyst 52 absorbs NOx in the exhaust gas and flows into the exhaust gas when the air-fuel ratio of the exhaust gas flowing therein is leaner than the stoichiometric air-fuel ratio. When the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio, it has a NOx purification capacity for reducing and purifying NOx absorbed therein. Therefore, in the present embodiment, as described above, control for controlling the in-cylinder intake amount and the fuel injection amount so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is leaner than the stoichiometric air-fuel ratio, that is, Normal control is performed in the internal combustion engine. According to this, during normal control, NOx in the exhaust gas is absorbed by the exhaust purification catalyst.

  Incidentally, there is a limit to the amount of NOx that can be absorbed by the exhaust purification catalyst 52 (hereinafter referred to as “absorbable NOx amount”). Therefore, when normal control is executed over a relatively long period, the amount of NOx absorbed by the exhaust purification catalyst exceeds the amount of NOx that can be absorbed. In this case, even if the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is leaner than the stoichiometric air-fuel ratio, NOx in the exhaust gas cannot be absorbed, and NOx is downstream of the exhaust purification catalyst. It will leak out. Therefore, in order to avoid NOx flowing out downstream of the exhaust purification catalyst, the amount of exhaust gas flowing into the exhaust purification catalyst before the amount of NOx absorbed by the exhaust purification catalyst exceeds the absorbable NOx amount is reduced. Control for controlling the in-cylinder intake amount and the fuel injection amount so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio (hereinafter referred to as “rich control”) may be executed in the internal combustion engine. However, switching the control of the internal combustion engine directly from normal control to rich control has the following disadvantages.

  That is, as described above, the exhaust purification catalyst 52 has oxygen storage / release capability. Accordingly, when normal control is being performed in the internal combustion engine, the exhaust purification catalyst continues to store oxygen in the exhaust gas. Here, when the control of the internal combustion engine is switched from normal control to rich control, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes richer than the stoichiometric air-fuel ratio, so oxygen stored in the exhaust purification catalyst It is discharged from the exhaust purification catalyst. Therefore, the degree to which the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst is richer than the theoretical air-fuel ratio even though the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is richer than the stoichiometric air-fuel ratio (Hereinafter, the degree of richness than the stoichiometric air-fuel ratio is simply referred to as “rich degree”) is smaller than the richness of the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst, and the exhaust gas flowing into the exhaust purification catalyst Depending on the richness of the air-fuel ratio, the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst becomes leaner than the stoichiometric air-fuel ratio. In this case, the air-fuel ratio of the air-fuel mixture formed in the combustion chamber 25 is controlled to a predetermined rich air-fuel ratio based on the output value of the air-fuel ratio sensor 54 disposed downstream of the exhaust purification catalyst 52. Then, the air-fuel ratio of the air-fuel mixture becomes an air-fuel ratio with a rich degree larger than a predetermined rich degree. Therefore, in the present embodiment, the air-fuel ratio control of the air-fuel mixture is executed in the rich control as follows.

  That is, in this embodiment, the air-fuel ratio is rich enough to purify NOx absorbed in the exhaust purification catalyst 52, and is excessive or insufficient to purify NOx absorbed in the exhaust purification catalyst. A rich air / fuel ratio capable of supplying exhaust gas containing a small amount of fuel to the exhaust purification catalyst is obtained in advance by experiments or the like for each engine operating state, and this air / fuel ratio is determined for each engine operating state, for example, in FIG. As shown, the target rich air-fuel ratio TA / Fr is stored in the form of a function map of the engine speed N and the engine load L. Further, in the present embodiment, the in-cylinder intake air amount suitable for achieving the target rich air-fuel ratio is obtained in advance by experiments or the like for each engine operating state, and this in-cylinder intake air amount is determined for each engine operating state, for example, FIG. 4, the target rich in-cylinder intake air amount TGAcr is stored in the form of a function map of the engine speed N and the engine load L. When the rich control is started, the target rich air-fuel ratio TA / Fr and the target rich in-cylinder intake air amount TGacr are calculated from the map of FIG. 3 and the map of FIG. 4 based on the engine speed N and the engine load L, respectively. Is read. Then, the opening degree of the throttle valve 48 is controlled based on the intake air amount detected by the air flow meter 61 so that the in-cylinder intake air amount becomes the target rich in-cylinder intake air amount TGacr, and the air-fuel ratio of the air-fuel mixture becomes the target rich air-fuel ratio. The fuel injection amount is controlled so that the air-fuel ratio TA / Fr is obtained. In this embodiment, at least the time from when the rich control is started until the time when all the oxygen stored in the exhaust purification catalyst is released (hereinafter referred to as “oxygen release time”) elapses. Control of the air-fuel ratio of the air-fuel mixture based on the output value of the fuel ratio sensor 54, that is, control of the fuel injection amount is not executed in this embodiment. According to this, since the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor is not executed at least while oxygen is released from the exhaust purification catalyst, NOx absorbed in the exhaust purification catalyst The exhaust gas containing a larger amount of fuel than the amount that can be purified is suppressed from being supplied to the exhaust purification catalyst.

  Then, after the oxygen release time has elapsed in the rich control, the fuel injection amount is controlled based on the output value of the air-fuel ratio sensor 54 so that the air-fuel ratio of the air-fuel mixture becomes the target rich air-fuel ratio.

  Incidentally, as described above, in the rich control of the present embodiment, based on the intake air amount detected by the air flow meter 61 so that the in-cylinder intake air amount becomes the target rich in-cylinder intake air amount read from the map of FIG. The throttle opening is controlled, and the fuel injection amount is controlled so that the air-fuel ratio of the air-fuel mixture becomes the target rich air-fuel ratio. Here, since the air-fuel ratio control of the air-fuel mixture based on the output value of the air-fuel ratio sensor 54 is not executed until the oxygen release time elapses after the rich control is started in the present embodiment, the air flow of the internal combustion engine When the detection characteristic of the meter 61 is different from the detection characteristic considered to be standard, the in-cylinder intake amount is not accurately controlled to the target rich in-cylinder intake amount, and the operation of the throttle valve 38 of the internal combustion engine is not performed. Even if the characteristics differ from the operating characteristics considered to be standard, the in-cylinder intake air amount is not accurately controlled to the target rich in-cylinder intake amount, and as a result, the air-fuel ratio of the air-fuel mixture becomes the target rich The air-fuel ratio is not controlled. In other words, since there are so-called machine differences for each internal combustion engine, the detection characteristics of the air flow meter and the operating characteristics of the throttle valve when the specific internal combustion engine is used as a standard are set as standard detection characteristics and operating characteristics. When the ECU processes the output value of the air flow meter or controls the control amount applied to the throttle valve, the air-fuel ratio of the air-fuel mixture is not controlled to the target rich air-fuel ratio in each internal combustion engine. Of course, after the oxygen release time has elapsed, the air-fuel ratio of the air-fuel mixture is controlled based on the output value of the air-fuel ratio sensor. As a result, the air-fuel ratio of the air-fuel mixture is controlled to the target rich air-fuel ratio. Will be. However, in this case, an air-fuel mixture having an air-fuel ratio different from the target rich air-fuel ratio will continue to be formed in the combustion chamber 25 until the oxygen release time elapses. Therefore, in this embodiment, when the NOx absorbed in the exhaust purification catalyst 52 should be purified, the air-fuel ratio of the air-fuel mixture is made the stoichiometric air-fuel ratio before the control of the internal combustion engine is switched from the normal control to the rich control. Control (hereinafter referred to as “lean control”) is executed to control the lean air-fuel ratio to an optimum degree that is close to the lean air-fuel ratio and is allowed in the current engine operating state.

  That is, in the present embodiment, the lean air-fuel ratio close to the stoichiometric air-fuel ratio and the optimum degree of lean air-fuel ratio allowed in the current engine operating state is obtained in advance for each engine operating state by experiments or the like. The fuel ratio is stored as the target lean air-fuel ratio TA / Fl in the form of a map of a function of the engine speed N and the engine load L as shown in FIG. When the lean control is started, the target fuel injection amount TQn and the target lean air-fuel ratio TA / Fl are read from the map of FIG. 2 and the map of FIG. 5 based on the engine speed N and the engine load L. The operation of the fuel injection valve 37 is controlled so that the fuel injection amount becomes the target fuel injection amount, and the air-fuel ratio of the air-fuel mixture is set to the target lean when the target fuel injection amount of fuel is injected from the fuel injection valve. The in-cylinder intake amount that can be changed to the air-fuel ratio is set as a target in-cylinder intake amount (hereinafter referred to as “target lean in-cylinder intake amount”), so that the in-cylinder intake amount becomes the target lean in-cylinder intake amount. The throttle opening is controlled based on the output value.

  According to this, the exhaust gas having a lean air-fuel ratio flows into the exhaust purification catalyst 52. In this case, oxygen stored in the exhaust purification catalyst is not released from the exhaust purification catalyst. Therefore, the air-fuel ratio detected by the air-fuel ratio sensor 54 corresponds to the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst, and hence the air-fuel ratio of the air-fuel mixture. Therefore, if the in-cylinder intake air amount is controlled so that the air-fuel ratio of the air-fuel mixture becomes the target lean air-fuel ratio based on the output value of the air-fuel ratio sensor 54, the in-cylinder intake amount is accurately controlled to the target lean in-cylinder intake amount. Is done.

  Incidentally, when the in-cylinder intake amount is controlled to the target lean in-cylinder intake amount, that is, when the air-fuel ratio of the air-fuel mixture is controlled to the target lean air-fuel ratio, the control amount given from the ECU 70 to the throttle valve 48 is This is the control amount necessary to control the cylinder intake air amount to the target lean cylinder intake air amount in the throttle valve of the internal combustion engine. Therefore, in the present embodiment, the control amount given from the ECU 70 to the throttle valve when the in-cylinder intake air amount is controlled to the target lean in-cylinder intake air amount based on the output value of the air-fuel ratio sensor in the lean control is the learning value. Is stored in the ECU 70.

  By the way, the learning value of the control amount described above reflects a so-called machine difference of the internal combustion engine with respect to the standard internal combustion engine. That is, until the oxygen release time elapses in the rich control, the control amount to be given to the throttle valve is calculated based on the learned value of the control amount so that the in-cylinder intake amount becomes the target rich in-cylinder intake amount. If the calculated control amount is given to the throttle valve, the in-cylinder intake amount is accurately controlled to the target rich in-cylinder intake amount. Therefore, in the present embodiment, when the NOx absorbed in the exhaust purification catalyst is to be purified, the lean control described above is executed before the control of the internal combustion engine is switched from the normal control to the rich control. When the in-cylinder intake air amount is controlled to the target lean in-cylinder intake air amount, the control amount given to the throttle valve from the ECU 70 is stored in the ECU 70 as a learning value, and then this control is performed when the rich control is executed. A control amount to be applied to the throttle valve to calculate the in-cylinder intake amount to the target rich in-cylinder intake amount is calculated based on the learning value of the amount, and this calculated control amount is maintained until the oxygen release time elapses. Given to. According to this, even before the oxygen release time elapses in the rich control, the air-fuel ratio of the air-fuel mixture is accurately controlled to the target rich air-fuel ratio.

  By the way, in the lean control of the present embodiment, control is performed so that the air-fuel ratio of the air-fuel mixture becomes a lean air-fuel ratio close to the stoichiometric air-fuel ratio with the target fuel injection amount determined in the same way as during normal control. Therefore, the throttle opening in the lean control is made smaller than the throttle opening in the normal control. For this reason, the amount of air passing through the throttle valve 48 (hereinafter referred to as “throttle passage air amount”) is reduced, but before the exhaust gas corresponding to the reduced amount of air reaches the air-fuel ratio sensor 54. Takes a certain time (hereinafter referred to as “intake arrival time”). Further, after the exhaust gas corresponding to the reduced amount of air arrives at the air-fuel ratio sensor, the air-fuel ratio sensor outputs an output value corresponding to the air-fuel ratio of the exhaust gas for a certain period of time (hereinafter referred to as the air-fuel ratio sensor). "Sensor output time"). Accordingly, learning of the control amount given to the throttle valve in the lean control is started when a time obtained by adding the sensor output time to the intake air arrival time has elapsed since the lean control was started. Therefore, in this embodiment, learning of the control amount given to the throttle valve is started based on the output value of the air-fuel ratio sensor after the time obtained by adding the sensor output time to the intake air arrival time after the lean control is started. The

  Note that when the in-cylinder intake air amount is controlled to the target lean in-cylinder intake air amount based on the output value of the air-fuel ratio sensor in the lean control, the exhaust gas corresponding to the air-fuel ratio reflected in the output value of the air-fuel ratio sensor is This corresponds to the amount of air passing through the throttle by a time obtained by adding the sensor output time to the intake air arrival time. Therefore, in the present embodiment, when the control amount given to the throttle valve is learned, the control amount given to the throttle valve is learned only by the time obtained by adding the sensor output time to the intake air arrival time.

  In this embodiment, as described above, the fuel injection amount is controlled based on the output value of the air-fuel ratio sensor 54 after the oxygen release time has elapsed in the rich control. Here, when the rich control is started, the fuel injection amount is increased more than the fuel injection amount in the lean control, but before the exhaust gas after combustion of this increased amount of fuel reaches the air-fuel ratio sensor. Takes a certain time (hereinafter referred to as “exhaust arrival time”). Of course, a certain period of time is required until the air-fuel ratio sensor outputs an output value corresponding to the air-fuel ratio of the exhaust gas after the exhaust gas after combustion of the increased amount of fuel arrives at the air-fuel ratio sensor. That is, it takes a sensor output time. Therefore, even if the oxygen release time has elapsed, if the time obtained by adding the sensor output time to the exhaust arrival time has not elapsed, the exhaust gas after combustion of the increased amount of fuel has not reached the air-fuel ratio sensor It will be. In this case, if the fuel injection amount is controlled based on the output value of the air-fuel ratio sensor, the air-fuel ratio of the air-fuel mixture is not controlled to the target rich air-fuel ratio. That is, the control of the fuel injection amount based on the output value of the air-fuel ratio sensor in the rich control should be executed after the exhaust arrival time and the sensor output time have elapsed and the oxygen release time has elapsed since the rich control was started. It is. Therefore, in the rich control of the present embodiment, the fuel injection based on the output value of the air-fuel ratio sensor after the time when the sensor output time is added to the exhaust arrival time after the rich control is started and the oxygen release time has elapsed. Quantity control is started.

  By the way, in this embodiment, the intake arrival time mentioned above is calculated as follows. That is, the intake air arrival time is a volume obtained by adding the space volume of the exhaust passage from the combustion chamber 25 to the air-fuel ratio sensor 54 to the space volume of the intake passage from the throttle valve 48 to the combustion chamber 25 (hereinafter referred to as “intake passage volume”). The amount of air passing through the throttle valve 48 when the lean control is started and the throttle opening is reduced (hereinafter referred to as “the amount of air passing through the throttle valve”) varies. Here, in the internal combustion engine of the present embodiment, since the intake passage volume is constant, the intake arrival time changes according to the throttle valve passage air amount. Therefore, in this embodiment, the intake arrival time corresponding to the throttle valve passage air amount is obtained in advance by experiments or the like, and this intake arrival time Ta is a function of the throttle valve passage air amount Gat as shown in FIG. It is stored in the ECU 70 in the form of a map, and when the lean control is started, the intake air arrival time Ta is obtained from the map of FIG. 6 based on the throttle valve passing air amount Gat. The amount of air passing through the throttle valve can be known from the amount of intake air detected by the air flow meter 61.

  In the present embodiment, the sensor output time described above is calculated as follows. That is, after the lean control is started and the throttle opening is reduced to reduce the in-cylinder intake amount, the output value corresponding to the air-fuel ratio of the exhaust gas corresponding to this reduced amount of air is the air-fuel ratio sensor. The time until output by 54 (hereinafter referred to as “lean air-fuel ratio output time”) includes the intake air arrival time and the sensor output time. Therefore, the sensor output time can be obtained by subtracting the intake air arrival time from the lean air-fuel ratio output time. Here, the intake arrival time is obtained from the map of FIG. Therefore, in this embodiment, the lean air-fuel ratio output time is measured when the lean control is started, and the sensor is obtained by subtracting the intake air arrival time obtained from the map of FIG. 6 from the measured lean air-fuel ratio output time. The output time is calculated. The calculated sensor output time is stored in the ECU 70 every time it is calculated.

  In the present embodiment, the exhaust arrival time described above is calculated as follows. That is, the air that has been sucked into the combustion chamber when the volume of the exhaust passage from the combustion chamber 25 to the air-fuel ratio sensor 54 (hereinafter referred to as “exhaust passage volume”) and rich control is started and the fuel injection amount is increased. And the amount (hereinafter referred to as “in-cylinder intake amount”). Here, in the internal combustion engine of the present embodiment, since the exhaust passage volume is constant, the exhaust arrival time changes according to the in-cylinder intake amount. Therefore, in this embodiment, the exhaust arrival time corresponding to the in-cylinder intake air amount is obtained in advance by experiments or the like, and this exhaust arrival time Te is a function map of the in-cylinder intake air amount Gac as shown in FIG. The exhaust arrival time Te is obtained from the map of FIG. 7 based on the in-cylinder intake air amount Gac when the rich control is started. The in-cylinder intake amount can be known from the intake amount detected by the air flow meter 61 and the space volume of the intake passage from the air flow meter to the combustion chamber, or the space volume of the intake passage from the throttle valve 48 to the combustion chamber. it can.

  In the rich control of the above-described embodiment, the fuel based on the output value of the air-fuel ratio sensor after the time when the sensor output time is added to the exhaust arrival time after the rich control is started and after the oxygen release time has elapsed. The injection amount control is started. However, generally, the time obtained by adding the sensor output time to the exhaust arrival time after the rich control is started is longer than the oxygen release time. Therefore, in the rich control according to the above-described embodiment, the oxygen release time is not taken into consideration, and the time based on the output value of the air-fuel ratio sensor after the time when the sensor output time is added to the exhaust arrival time after the rich control is started is elapsed. Control of the fuel injection amount may be started.

  Since the time from when the air is sucked into the combustion chamber until it is discharged from the combustion chamber (hereinafter referred to as “intake intake / exhaust time”) is extremely short, in the above-described embodiment, the intake intake time is the intake intake time. Does not include discharge time. However, in the above-described embodiment, the intake / exhaust time may be included in the intake arrival time.

  In the embodiment described above, the oxygen release time is set to the time required for all the oxygen stored in the exhaust purification catalyst to be released from the exhaust purification catalyst. However, in the above-described embodiment, the oxygen release time is reduced to an acceptable degree in which the oxygen stored in the exhaust purification catalyst affects the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst. The time required may be set.

  Next, an example of a flowchart for executing the air-fuel ratio control according to the above-described embodiment will be described with reference to FIGS. In the routine of FIGS. 8 to 11, first, at step 100, it is determined whether or not it is required to execute rich control in order to purify NOx absorbed in the exhaust purification catalyst 52. Here, when it is determined that the execution of the rich control is not requested, the routine proceeds to step 110 in FIG. On the other hand, when it is determined that execution of rich control is requested, the routine proceeds to step 101 and subsequent steps.

  When the routine proceeds to step 110, execution of rich control is not requested. Therefore, normal control is executed by steps after step 110. That is, at step 110, the target fuel injection amount TQn is read from the map of FIG. 2 based on the engine speed and the engine load. Next, in step 111, the operation of the fuel injection valve 37 is controlled so that the fuel injection amount becomes the target fuel injection amount read in step 110. Next, at step 112, the operation of the throttle valve 48 is controlled so that the throttle opening is fully opened, and the routine is terminated.

  On the other hand, when the routine proceeds to step 101, execution of rich control is requested. Therefore, the lean control and the rich control are executed by the steps after step 101. That is, at step 101, the target fuel injection amount TQn is read from the map of FIG. 2 based on the engine speed and the engine load. Next, at step 102, the target lean air-fuel ratio TA / Fl is read from the map of FIG. 5 based on the engine speed and the engine load. Next, in step 103, when the fuel of the target fuel injection amount read in step 101 is injected from the fuel injection valve 37, the air-fuel ratio of the air-fuel mixture can be made the target lean air-fuel ratio read in step 102. The in-cylinder intake air amount is calculated as the target in-cylinder intake air amount. Next, at step 104, the throttle opening is reduced to an opening at which the in-cylinder intake amount can be made equal to the target in-cylinder intake amount calculated at step 103. Next, at step 105, the amount of air passing through the throttle valve 48 (throttle valve passing air amount) Gat when the throttle opening is decreased at step 104 is calculated from the output value of the air flow meter 61. Next, at step 106, the intake arrival time Ta is obtained from the map of FIG. 6 based on the throttle valve passing air amount calculated at step 105. Next, at step 107, the sensor output time Ts is read from the ECU 70.

  Next, at step 108, a counter C1 representing the time elapsed after the throttle opening is reduced at step 104 is incremented. Next, at step 109, whether the counter C1 incremented at step 108 exceeds the intake air arrival time Ta calculated at step 106 plus the sensor output time Ts read at step 107 (C1 ≧ Ta + Ts). It is determined whether or not. Here, when it is determined that C1 <Ta + Ts, the output value corresponding to the air-fuel ratio of the exhaust gas corresponding to the amount of air reduced by reducing the throttle opening in step 104 is the air-fuel ratio sensor. Since it is not output from 54, the routine returns to step 108, and the counter C1 is incremented again. That is, step 108 is repeated until it is determined in step 109 that C1 ≧ Ta + Ts. On the other hand, when it is determined in step 109 that C1 ≧ Ta + Ts, the routine proceeds to step 113 in FIG.

  When the routine proceeds to step 113, the air-fuel ratio sensor 54 outputs an output value corresponding to the air-fuel ratio of the exhaust gas corresponding to the amount of air reduced by reducing the throttle opening in step 104. Will be. Therefore, in step 113, the control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the lean control (lean control by the air-fuel ratio sensor output value) is executed. Next, at step 114, the control amount given to the throttle valve 48 just before the time when the sensor output time is added to the intake air arrival time is stored in the ECU 70 as a learning value (learning of the control amount). Next, in step 115, it is determined whether or not learning of the control amount in step 114 has been completed. Here, when it is determined that the learning of the control amount has not been completed, the routine returns to step 114, the lean control by the air-fuel ratio sensor output value is continued, and then, in step 114, given to the throttle valve. Control amount learning is executed. That is, step 113 and step 114 are repeated until it is determined in step 115 that the learning of the control amount in step 114 is completed. On the other hand, when it is determined in step 115 that the control amount learning in step 114 has been completed, the routine proceeds to step 116.

  When the routine proceeds to step 116, learning of the control amount at step 114 is completed. Therefore, rich control is executed in steps subsequent to step 116. That is, at step 116, the target rich air-fuel ratio TA / Fr is read from the map of FIG. 3 based on the engine speed and the engine load. Next, at step 117, the target rich in-cylinder intake air amount TGAcr is read from the map of FIG. 4 based on the engine speed and the engine load. Next, at step 118, when the air of the target rich in-cylinder intake amount read at step 117 is drawn into the combustion chamber 25, the air-fuel ratio of the air-fuel mixture is made the target rich air-fuel ratio read at step 116. The possible fuel injection amount is calculated as the target fuel injection amount. Next, at step 119, the throttle opening is controlled so that the in-cylinder intake air amount becomes the target rich in-cylinder intake air amount read at step 117. Next, at step 120, the fuel injection amount is increased so that the fuel injection amount becomes the target fuel injection amount calculated at step 120. Next, at step 121, the exhaust arrival time Te is obtained from the map of FIG. 7 based on the in-cylinder intake amount. Next, at step 122, a counter C2 representing the time elapsed since the fuel injection amount was increased at step 120 is incremented. Next, in step 123, is the counter C2 incremented in step 122 exceeded the time obtained by adding the sensor output time Ts read in step 107 to the exhaust arrival time Te calculated in step 121 (C2 ≧ Te + Ts)? It is determined whether or not. Here, when it is determined that C2 <Te + Ts, the output value corresponding to the air-fuel ratio of the exhaust gas after combustion of the amount of fuel increased in step 120 is not output by the air-fuel ratio sensor 54. Thus, the routine returns to step 122 and the counter C2 is incremented again. That is, step 122 is repeated until it is determined in step 123 that C2 ≧ Te + Ts. On the other hand, when it is determined in step 123 that C2 ≧ Te + Ts, the routine proceeds to step 124 in FIG.

  When the routine proceeds to step 124, the output value corresponding to the air-fuel ratio of the exhaust gas after combustion of the amount of fuel increased in step 120 is output from the air-fuel ratio sensor 54. Therefore, in step 124, control of the air-fuel ratio of the air-fuel mixture based on the output value of the air-fuel ratio sensor in rich control (rich control based on the air-fuel ratio sensor output value) is executed. Next, in step 125, the counter C2 is incremented in the same manner as in step 122. Next, at step 126, it is determined whether the time Tr sufficient for the counter C2 to purify NOx absorbed by the exhaust purification catalyst 52 has been exceeded (C2 ≧ Tr). Here, when it is determined that C2 <Tr, the NOx absorbed in the exhaust purification catalyst is not sufficiently purified, so the routine returns to step 125, where the rich by the air-fuel ratio sensor output value is obtained. Control continues and then in step 125 the counter C2 is incremented again. That is, step 124 and step 125 are repeated until it is determined in step 126 that C2 ≧ Tr. On the other hand, when it is determined in step 126 that C2 ≧ Tr, the NOx absorbed in the exhaust purification catalyst has been sufficiently purified, so the routine proceeds to step 127, where the counter C1 and the counter C2 are processed. Is reset and the routine ends.

  In the lean control of the above-described embodiment, learning of the control amount given to the throttle valve is started when a time obtained by adding the sensor output time to the intake air arrival time after the lean control is started. However, in the lean control of the above-described embodiment, learning of the control amount given to the throttle valve is started after a time obtained by adding the sensor output time to the intake air arrival time after the lean control is started. May be.

  Further, in the rich control of the above-described embodiment, the air-fuel ratio control of the air-fuel mixture based on the output value of the air-fuel ratio sensor when a time obtained by adding the sensor output time to the exhaust arrival time has elapsed since the rich control was started. Is started. However, in the rich control of the above-described embodiment, the air-fuel ratio of the air-fuel ratio based on the output value of the air-fuel ratio sensor after the time when the sensor output time is added to the exhaust arrival time after the rich control is started elapses. Control may be started.

  Further, the above-described embodiment is an internal combustion engine having an exhaust purification catalyst having NOx purification capability and oxygen storage / release capability, and rich control is executed to purify NOx absorbed in the exhaust purification catalyst. The air-fuel ratio control apparatus of the present invention is applied to a required internal combustion engine. However, the air-fuel ratio control apparatus of the present invention is an internal combustion engine having an exhaust purification catalyst having a purification ability for purifying a specific component in exhaust gas and having an oxygen storage / release capability, and has a specific object related to the exhaust purification catalyst. The present invention is also applicable to an internal combustion engine that requires execution of rich control to achieve the above.

  In the above-described embodiment, the air-fuel ratio of the air-fuel mixture is less than the stoichiometric air-fuel ratio based on the output value of the air-fuel ratio sensor arranged downstream of the exhaust purification catalyst in order to purify NOx absorbed in the exhaust purification catalyst. The air-fuel ratio control apparatus of the present invention is applied to an internal combustion engine controlled to a rich air-fuel ratio. However, the air-fuel ratio control apparatus of the present invention is simply richer than the stoichiometric air-fuel ratio based on the output value of the air-fuel ratio sensor disposed downstream of the exhaust purification catalyst in order to achieve a specific purpose. The present invention can also be applied to an internal combustion engine that is controlled to have an air-fuel ratio.

  In the above-described embodiment, the air-fuel ratio of the air-fuel mixture is exhausted before the air-fuel ratio of the air-fuel mixture is controlled to be richer than the stoichiometric air-fuel ratio in order to purify NOx absorbed in the exhaust purification catalyst. The air-fuel ratio control apparatus of the present invention is applied to an internal combustion engine that is controlled to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio based on the output value of an air-fuel ratio sensor arranged downstream of the catalyst. However, the air-fuel ratio control apparatus of the present invention is merely a method in which the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio based on the output value of the air-fuel ratio sensor disposed downstream of the exhaust purification catalyst in order to achieve a specific purpose. The present invention can also be applied to an internal combustion engine that is controlled to have an air-fuel ratio.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 37 ... Fuel injection valve, 48 ... Throttle valve, 52 ... Exhaust gas purification catalyst, 54 ... Air-fuel ratio sensor

Claims (8)

An exhaust purification catalyst for purifying specific components in the exhaust gas is disposed in the exhaust passage, and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst, and combustion is achieved to achieve a specific purpose. Rich control for controlling the air-fuel ratio of the air-fuel mixture supplied to the chamber to a predetermined target rich air-fuel ratio richer than the stoichiometric air-fuel ratio is executed, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the rich control there a air-fuel ratio control apparatus for an internal combustion engine is controlled to the target rich air-fuel ratio based on the output value of the air-fuel ratio sensor, the amount of fuel supplied to the combustion chamber when the rich control is started The time required for the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor is referred to as exhaust arrival time, and the time after the exhaust gas arrived at the air-fuel ratio sensor Exhaust gas When the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the air-fuel ratio is referred to as sensor output time, the air-fuel ratio of the air-fuel ratio based on the output value of the air-fuel ratio sensor in the rich control in air-fuel ratio control system of combustion engine control Ru is started or later when the time obtained by adding the sensor output time has elapsed in the exhaust arrival time since the increased amount of fuel supplied to the combustion chamber,
Lean control for controlling the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a predetermined target rich air-fuel ratio leaner than the stoichiometric air-fuel ratio in order to achieve a specific purpose before the rich control is executed. The air-fuel ratio of the air-fuel mixture that is executed and is supplied to the combustion chamber in the lean control is controlled to the target lean air-fuel ratio based on the output value of the air-fuel ratio sensor, and is supplied to the combustion chamber when the lean control is started The time required for the amount of air to be reduced and the exhaust gas corresponding to the reduced amount of air to reach the air-fuel ratio sensor is referred to as intake air arrival time, and the exhaust gas arrives at the air-fuel ratio sensor. When the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the exhaust gas that has arrived after is called the sensor output time, the output value of the air-fuel ratio sensor in the lean control The control of the air-fuel ratio of the air-fuel mixture is started when the amount of air supplied to the combustion chamber is reduced or when the sensor output time is added to the intake air arrival time or after that. An air-fuel ratio control apparatus for an internal combustion engine characterized by the above . 2. The internal combustion engine according to claim 1, wherein the exhaust arrival time is calculated based on an amount of air supplied to the combustion chamber and a space volume of an exhaust passage from the combustion chamber to the air-fuel ratio sensor. Air-fuel ratio control device. An exhaust purification catalyst for purifying specific components in the exhaust gas is disposed in the exhaust passage, and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst, and combustion is achieved to achieve a specific purpose. Rich control for controlling the air-fuel ratio of the air-fuel mixture supplied to the chamber to a predetermined target rich air-fuel ratio richer than the stoichiometric air-fuel ratio is executed, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the rich control Is an air-fuel ratio control apparatus for an internal combustion engine that is controlled to the target rich air-fuel ratio based on the output value of the air-fuel ratio sensor, and the amount of fuel supplied to the combustion chamber when the rich control is started is The time required for the exhaust gas after combustion of the increased amount of fuel to reach the air-fuel ratio sensor is referred to as exhaust arrival time, and the time after the exhaust gas arrived at the air-fuel ratio sensor Exhaust gas When the time required for the air-fuel ratio sensor to output the output value corresponding to the air-fuel ratio of the air-fuel ratio is referred to as sensor output time, the air-fuel ratio of the air-fuel ratio based on the output value of the air-fuel ratio sensor in the rich control In an air-fuel ratio control apparatus for an internal combustion engine that is started when a time obtained by adding the sensor output time to the exhaust arrival time has elapsed after the amount of fuel supplied to the combustion chamber is increased or after that,
Air-fuel ratio control apparatus for an internal combustion engine the exhaust arrival time you characterized in that it is calculated on the basis of the space volume of the exhaust passage from the combustion chamber to the amount of air supplied to the combustion chamber to the air-fuel ratio sensor .   An exhaust purification catalyst for purifying specific components in the exhaust gas is disposed in the exhaust passage, and an air-fuel ratio sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst, and combustion is achieved to achieve a specific purpose. Lean control is performed to control the air-fuel ratio of the air-fuel mixture supplied to the chamber to a target lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the lean control is In an air-fuel ratio control apparatus for an internal combustion engine that is controlled to a target lean air-fuel ratio based on an output value of a sensor, the amount of air supplied to the combustion chamber when the lean control is started is reduced and the reduced The time required for the exhaust gas corresponding to the amount of air to reach the air-fuel ratio sensor is referred to as the intake air arrival time, and corresponds to the air-fuel ratio of the exhaust gas that has arrived after the exhaust gas arrives at the air-fuel ratio sensor. When the time required for the air-fuel ratio sensor to output the output value is referred to as sensor output time, the air-fuel ratio control of the air-fuel mixture based on the output value of the air-fuel ratio sensor in the lean control is supplied to the combustion chamber. An air-fuel ratio control apparatus for an internal combustion engine, which is started when a time obtained by adding the sensor output time to the intake air arrival time after the amount of air to be reduced has elapsed or thereafter. A control amount given to a component of the internal combustion engine capable of changing the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber, wherein the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber in the lean control is set to the target lean As a control amount that can be controlled to an air-fuel ratio, a control amount that is the amount preceding the intake air arrival time plus the sensor output time is learned, and learning of the control amount in the lean control is the air-fuel ratio sensor in the lean control. air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2 or 4, characterized in that it is initiated or subsequently when the control of the air-fuel ratio of the mixture based on the output value is the beginning of.   The control amount given to the component of the internal combustion engine capable of changing the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is determined based on the learned control amount. An air-fuel ratio control apparatus for an internal combustion engine as described. A throttle valve is disposed in the intake passage, and the amount of air supplied to the combustion chamber is reduced by reducing the opening of the throttle valve, and the intake air arrival time is reduced to the reduced amount of air. any one of claims 1 or 2 or claims 4 to 6, characterized in that it is calculated on the basis of the space volume of the space volume and the exhaust passage of the intake passage from the throttle valve to the air-fuel ratio sensor An air-fuel ratio control device for an internal combustion engine according to claim 1. The time required from when the amount of fuel supplied to the combustion chamber increases until the exhaust gas after combustion of the increased amount of fuel reaches the air-fuel ratio sensor is referred to as exhaust arrival time, and is supplied to the combustion chamber. The air-fuel ratio sensor outputs an output value corresponding to the air-fuel ratio of the exhaust gas corresponding to the air-fuel ratio of the air-fuel mixture when the increased amount of fuel is supplied to the combustion chamber after the amount of fuel to be increased is increased. 2. The sensor output time is calculated by subtracting the exhaust arrival time from the exhaust air / fuel ratio output time when a time required for output is referred to as an exhaust air / fuel ratio output time . The air-fuel ratio control apparatus for an internal combustion engine according to any one of 7 .

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