JPWO2013084307A1 - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

The present invention includes a catalyst (45) having an active element and a composite oxide supporting the active element in an exhaust passage (40), the catalyst temperature is equal to or higher than a predetermined solid solution temperature, and the internal atmosphere of the catalyst is an oxidizing atmosphere. The exhaust purification of an internal combustion engine in which the active element is dissolved in the composite oxide when the catalyst temperature is equal to or greater than the predetermined deposition temperature and the active element is precipitated from the composite oxide when the internal atmosphere of the catalyst is a reducing atmosphere Relates to the device. In the present invention, when execution of the fuel supply stop control is prohibited when the catalyst temperature is equal to or higher than the execution prohibition temperature, the execution prohibition temperature is lower than the reference temperature while the use degree of the catalyst is equal to or lower than the predetermined degree. When the fuel supply increase control is permitted when the catalyst temperature is equal to or higher than the permitted temperature, the permitted temperature is lower than the reference temperature while the usage level of the catalyst is equal to or lower than the predetermined level. Set to high temperature.

Description

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

  Patent Document 1 discloses a catalyst for purifying components in exhaust gas discharged from a combustion chamber of an internal combustion engine. This catalyst has an active element (that is, an element for activating an oxidation reaction or a reduction reaction of a component in exhaust gas) and a composite oxide composed of a composite oxide supporting this active element. In addition, this catalyst has a property that the active element is dissolved in the composite oxide when the internal atmosphere is an oxidizing atmosphere, and the active element is precipitated from the composite oxide when the internal atmosphere is a reducing atmosphere. doing.

International Publication No. 2008/096575 JP 2006-183624 A JP 2008-12480 A JP 2005-66559 A JP 2008-51063 A

  By the way, the catalyst purifying ability (that is, the ability of the catalyst to purify the components in the exhaust gas) is represented by the catalyst use time (that is, the total time that the catalyst has been used for purifying the components in the exhaust gas). It varies depending on the degree of catalyst use. Therefore, in order for the internal combustion engine to exhibit the desired performance, it is necessary to perform engine control (that is, control related to the internal combustion engine) in consideration of such a change in the catalyst purification capacity, or such a change in the catalyst purification capacity. Therefore, it is necessary to construct a control logic used for engine control. However, it can be said that execution of such engine control and construction of such control logic are complicated.

  Accordingly, an object of the present invention is to make engine control relatively simple, and to make it possible to construct control logic used for engine control relatively easily and to make the catalyst exhibit the desired purification ability. An object of the present invention is to provide an exhaust purification device for an internal combustion engine.

  The invention of the present application for achieving the above object is a catalyst for purifying components in exhaust gas, comprising an active element that activates an oxidation reaction or reduction reaction of a component in exhaust gas and a composite that carries the active element A catalyst having an oxide is provided in the exhaust passage, and the active element is contained in the composite when the temperature of the catalyst is equal to or higher than a predetermined solid solution temperature that is a predetermined temperature and the internal atmosphere of the catalyst is an oxidizing atmosphere. An internal combustion in which the active element is precipitated from the composite oxide when it is dissolved in an oxide and the temperature of the catalyst is equal to or higher than a predetermined deposition temperature, which is a predetermined temperature, and the internal atmosphere of the catalyst is a reducing atmosphere The present invention relates to an exhaust emission control device for an engine.

  In the present invention, when the internal combustion engine can execute the fuel supply stop control for stopping the supply of fuel to the combustion chamber, and the temperature of the catalyst is equal to or higher than the execution prohibition temperature that is a predetermined temperature. When the execution of the fuel supply stop control is prohibited and the execution of the fuel supply stop control is allowed when the temperature of the catalyst is lower than the execution prohibition temperature, the degree of use of the catalyst is determined in advance. The execution prohibition temperature is set to a temperature lower than the reference temperature while the temperature is less than or equal to the degree.

  Alternatively, according to the present invention, the internal combustion engine can execute fuel supply increase control in which the amount of fuel supplied to the combustion chamber is increased from a reference amount, and the execution permission is such that the temperature of the catalyst is a predetermined temperature. Use of the catalyst in a case where execution of the fuel supply increase control is permitted when the temperature is equal to or higher than the temperature and execution of the fuel supply increase control is prohibited when the temperature of the catalyst is lower than the execution permission temperature. While the degree is equal to or lower than a predetermined degree, the execution permission temperature is set to a temperature higher than the reference temperature.

  According to the present invention, the following effects can be obtained. That is, when the fuel supply stop control is executed, the catalyst inflow exhaust air-fuel ratio (that is, the air-fuel ratio of the exhaust gas flowing into the catalyst) becomes an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and as a result, the internal atmosphere of the catalyst Becomes an oxidizing atmosphere. In this case, when the catalyst temperature is relatively high, aggregation of the composite oxide occurs, and as a result, the catalyst purification ability changes. On the other hand, when the fuel supply increase control is executed, the catalyst inflow exhaust air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, and as a result, the internal atmosphere of the catalyst becomes a reducing atmosphere. Here, the catalyst has the property that the active element is precipitated from the composite oxide when the catalyst temperature is equal to or higher than the predetermined deposition temperature, the catalyst temperature is equal to or higher than the predetermined deposition temperature, and the internal atmosphere of the catalyst is a reducing atmosphere. In this case, the active element is precipitated from the composite oxide. Therefore, the amount of the precipitated active element (that is, the active element precipitated from the composite oxide) changes, and as a result, the catalyst purification ability changes.

  On the other hand, in order to make the internal combustion engine exhibit its desired performance, it is used for engine control so that the internal combustion engine can exhibit its expected performance in consideration of changes in the catalyst purification capacity during engine operation. It is necessary to construct a control logic that can be controlled and to perform engine control. However, when the catalyst purification capacity changes due to the execution of the fuel supply stop control or the fuel supply increase control, it is very complicated to construct the control logic or perform the engine control as described above. It can be said. In addition, since the catalyst is not deteriorated while the degree of use of the catalyst is relatively small, the amount of the precipitated active element that determines the catalyst purification ability is set in order to make the catalyst exhibit the desired purification ability. There is no need to increase it. Therefore, it can be said that it is preferable not to change the amount of the precipitated active element as much as possible while the degree of use of the catalyst is relatively small.

  Here, in the present invention, when the fuel supply stop control can be executed, the execution of the fuel supply stop control is prohibited when the catalyst temperature is equal to or higher than the execution prohibition temperature, and the catalyst temperature is lower than the execution prohibition temperature. When the execution of the fuel supply stop control is permitted, the execution prohibition temperature is higher than the reference temperature while the use degree of the catalyst is not more than a predetermined degree (that is, while the use degree of the catalyst is relatively small). Is also set to a lower temperature. According to this, since the opportunity for executing the fuel supply stop control is reduced, there is little opportunity for the aggregation of the composite oxide, and as a result, the change in the catalyst purification capability is small.

  On the other hand, in the present invention, when the fuel supply increase control can be executed, the execution of the fuel supply increase control is permitted when the catalyst temperature is equal to or higher than the execution permission temperature, and the catalyst temperature is lower than the execution permission temperature. When the execution of fuel supply increase control is prohibited, the execution permission temperature is higher than the reference temperature while the catalyst usage is below a predetermined level (that is, while the catalyst usage is relatively small). Set to high temperature. According to this, since the opportunity for executing the fuel supply increase control is reduced, the change in the amount of the precipitated active element is small, and as a result, the change in the catalyst purification capacity is also small.

  As described above, in the present invention, the change in the catalyst purification capacity is small while the degree of use of the catalyst is relatively small. Therefore, it becomes easy to assume the catalyst purification capacity during engine operation. Therefore, according to the present invention, a control logic used for engine control can be constructed relatively easily while the catalyst usage is relatively small, and the engine can be engineered while the catalyst usage is relatively small. Control can be performed relatively easily and the catalyst can exhibit the desired purification ability.

  Further, in another invention of the present application, in the above invention, when the internal combustion engine is capable of executing the fuel supply stop control, when the predetermined degree is referred to as a first degree, the usage degree of the catalyst. The execution prohibition temperature is set to a temperature higher than the reference temperature while the temperature is less than a second degree that is greater than the first degree and greater than the first degree.

  According to the present invention, the following effects can be obtained. In other words, in the present invention, while the degree of use of the catalyst is greater than the first degree and less than or equal to the second degree, the execution prohibition temperature is set to a temperature higher than the reference temperature. According to this, since the opportunity for executing the fuel supply stop control increases, the aggregation of the complex oxide is promoted. For this reason, the effect that the precipitation rate of an active element can be reduced is acquired. In addition, when such an effect is acquired, for example, the active element solid solubility (that is, the ratio of the active element that is dissolved in the composite oxide among the active elements) is set as the target solid solubility (that is, the target active element). In the case of controlling the solid solubility), an effect is obtained that the active element solid solubility can be easily controlled to the target solid solubility.

  Further, in still another invention of the present application, in the above invention, when the internal combustion engine can execute the fuel supply stop control, the activity is increased after the use degree of the catalyst is larger than the second degree. The active element solid solubility representing the proportion of the active element dissolved in the composite oxide among the elements flows into the catalyst so that the target solid solubility, which is the target active element solid solubility, is controlled. The air-fuel ratio of the exhaust gas is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, or the air-fuel ratio of the exhaust gas flowing into the catalyst is controlled to be richer than the stoichiometric air-fuel ratio.

  According to the present invention, the following effects can be obtained. During engine operation, the catalyst temperature becomes equal to or higher than a predetermined solid solution temperature or reaches a predetermined precipitation temperature. On the other hand, even if the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio, the catalyst inflow exhaust air-fuel ratio may be temporarily leaner than the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio. There is. Here, if the catalyst inflow exhaust air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio when the catalyst temperature is equal to or higher than the predetermined solid solution temperature, the internal atmosphere of the catalyst becomes an oxidizing atmosphere. When the active element has a property of being dissolved in the composite oxide when the temperature is higher than the solid solution temperature and the internal atmosphere of the catalyst is an oxidizing atmosphere, the active element is dissolved in the composite oxide. On the other hand, if the catalyst inflow exhaust air-fuel ratio becomes richer than the stoichiometric air-fuel ratio when the catalyst temperature is equal to or higher than the predetermined deposition temperature, the internal atmosphere of the catalyst becomes a reducing atmosphere. In the case where the active element has the property of precipitating from the composite oxide when the internal atmosphere of the catalyst is a reducing atmosphere, the active element is precipitated from the composite oxide. In other words, the amount of the precipitated active element changes due to the change in the catalyst temperature and the change in the catalyst inflow exhaust air-fuel ratio during engine operation, and consequently the catalyst purification capacity changes. Also, as the active element usage (ie, the degree to which the active element is used to activate the components in the exhaust gas) increases, the active element may degrade, resulting in the active ability of the active element (ie, The ability of the active element to increase the oxidation reaction activity or the reduction reaction activity of the components in the exhaust gas may decrease. In other words, when the degree of use of the catalyst increases, the catalyst purification capacity may decrease. As described above, the catalyst purification ability also changes due to the change in the active ability of the active element during engine operation.

  Therefore, in order for the internal combustion engine to exhibit the desired performance, it is used for engine control so that the internal combustion engine can exhibit the expected performance in consideration of changes in the catalyst purification capacity during engine operation. It is necessary to construct a control logic that can be controlled and to perform engine control. However, since the change in the catalyst purification capacity during engine operation varies depending on the engine operation mode and the degree of catalyst use, it is very complicated to construct a control logic or perform engine control as described above. It can be said that. On the other hand, the control logic can be constructed relatively easily and engine control can be performed relatively easily if the change in the catalyst purification capacity is assumed regardless of the mode of engine operation and the degree of catalyst use. Can do.

  Here, in the present invention, after the degree of use of the catalyst becomes relatively large (that is, after the degree of use of the catalyst becomes larger than the second degree), the active element solid solubility is controlled to the target solid solubility. As described above, the catalyst inflow exhaust air-fuel ratio is controlled to be an air-fuel ratio leaner than the stoichiometric air-fuel ratio, or the catalyst inflow exhaust air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio. Therefore, when the catalyst inflow exhaust air-fuel ratio is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, if the catalyst temperature is equal to or higher than the predetermined solid solution temperature, the precipitated active element is dissolved in the composite oxide, and as a result The active element solid solubility increases. On the other hand, when the catalyst inflow exhaust air-fuel ratio is controlled to an air-fuel ratio richer than the stoichiometric air-fuel ratio, if the catalyst temperature is equal to or higher than the predetermined deposition temperature, the internal atmosphere of the catalyst becomes a reducing atmosphere, so that the solid solution active element Precipitates from the composite oxide, and as a result, the solid solubility of the active element decreases. That is, the active element solid solubility is controlled to the target solid solubility by appropriately controlling the inflow exhaust air-fuel ratio depending on whether the active element solid solubility is larger or smaller than the target solid solubility. As a result, the amount of the precipitated active element is kept constant, so that the catalyst purification capability during engine operation can be easily assumed. Therefore, according to the present invention, the control logic used for engine control can be constructed relatively easily after the degree of use of the catalyst becomes relatively large, and the degree of use of the catalyst becomes relatively large. Even after this, the engine control can be performed relatively easily and the catalyst can exhibit the desired purification ability.

  In the above invention, the predetermined solid solution temperature and the predetermined precipitation temperature may be equal to or different from each other. In the above invention, the target solid solubility may be constant regardless of the conditions, or may be changed according to the conditions. In the above invention, the active element solid solubility may be the active element solid solubility obtained by any method, for example, the active element solid solubility detected by a sensor that detects the active element solid solubility. The active element solid solubility may be calculated based on various parameters relating to the internal combustion engine.

It is the figure which showed the internal combustion engine provided with the exhaust gas purification device of 1st Embodiment of this invention. (A) It is the figure which showed the output characteristic of the upstream air-fuel-ratio sensor, (B) is the figure which showed the output characteristic of the downstream air-fuel-ratio sensor. It is the figure which showed the map utilized in order to acquire a reference | standard throttle valve opening degree during the engine driving | operation of 1st Embodiment. It is the figure which showed an example of the routine which performs FC control of 1st Embodiment. It is the figure which showed an example of the routine which performs the increase control of 2nd Embodiment. It is the figure which showed an example of the routine which performs FC control of 3rd Embodiment. It is the figure which showed an example of the routine which performs the solid solubility control of 4th Embodiment.

  Hereinafter, embodiments of the present invention will be described. FIG. 1 shows an internal combustion engine equipped with an exhaust emission control device according to a first embodiment of the present invention. The internal combustion engine shown in FIG. 1 is a spark ignition type internal combustion engine (so-called gasoline engine). In FIG. 1, 11 is a fuel injection valve, 12 is a combustion chamber, 13 is a piston, 14 is a connecting rod, 15 is a crankshaft, 16 is a crank position sensor, 17 is a spark plug, 18 is an intake valve, and 20 is a body of an internal combustion engine. , 22 are exhaust valves, 80 is an accelerator pedal, and 81 is an accelerator pedal depression amount sensor. Although only one combustion chamber 12 is shown in FIG. 1, the internal combustion engine 10 has a plurality of combustion chambers (for example, four combustion chambers, six combustion chambers, or eight combustion chambers). )

  In FIG. 1, 30 is an intake passage, 31 is an intake port, 32 is an intake manifold, 33 is a surge tank, 34 is an intake pipe, 35 is a throttle valve, 36 is an actuator for driving the throttle valve 35, 37 is An air flow meter, 38 is an air cleaner, 40 is an exhaust passage, 41 is an exhaust port, 42 is an exhaust manifold, 43 is an exhaust pipe, 44 is a catalytic converter, 46 is an air-fuel ratio sensor, 47 is a temperature sensor, and 48 is an air-fuel ratio sensor. Show. The intake passage 30 includes an intake port 31, an intake manifold 32, a surge tank 33, and an intake pipe 34. On the other hand, the exhaust passage 40 includes an exhaust port 41, an exhaust manifold 42, and an exhaust pipe 43.

  The electronic control unit 90 is composed of a microcomputer. The electronic control unit 90 includes a CPU (microprocessor) 91, a ROM (read only memory) 92, a RAM (random access memory) 93, a backup RAM 94, and an interface 95. The CPU 91, ROM 92, RAM 93, backup RAM 94, and interface 95 are connected to each other by a bidirectional bus.

  Next, each component of the internal combustion engine described above will be described in more detail. In the following description, “target fuel injection timing” means “timing targeted as fuel injection timing from the fuel injection valve”, and “target fuel injection amount” means “amount of fuel injected from the fuel injection valve” As a target amount, “air mixture” means “a gas formed by mixing air and fuel formed in the combustion chamber”, and “target ignition timing” "Target timing as the timing for igniting the fuel" means "engine speed" means "rotational speed of the internal combustion engine", "throttle valve opening" means "throttle valve opening", “Target throttle valve opening” means “target opening as throttle valve opening”, “intake air amount” means “amount of air taken into the combustion chamber”, and “accelerator pedal depression amount” "" It means the amount of depression "in Rupedaru," required engine torque "means the torque" as required as a torque output from the "internal combustion engine.

  The fuel injection valve 11 is attached to the main body 20 of the internal combustion engine so that the fuel injection hole is exposed in the combustion chamber 12. The fuel injection valve 11 is electrically connected to the interface 95 of the electronic control device 90. The electronic control unit 90 supplies the fuel injection valve 11 with a command signal for causing the fuel injection valve 11 to inject the fuel of the target fuel injection amount at the target fuel injection timing. When a command signal is supplied from the electronic control unit 90 to the fuel injection valve 11, the fuel injection valve 11 directly injects fuel into the combustion chamber 12.

  The spark plug 17 is attached to the main body 20 of the internal combustion engine so that the discharge electrode is exposed in the combustion chamber 12. The spark plug 17 is electrically connected to the interface 95 of the electronic control device 90. The electronic control unit 90 supplies the ignition plug 17 with a command signal for causing the ignition plug 17 to generate a spark at the target ignition timing. When a command signal is supplied from the electronic control unit 90 to the spark plug 17, the spark plug 17 ignites the fuel in the combustion chamber 12. When the fuel in the combustion chamber 12 is ignited by the spark plug 17, the fuel in the combustion chamber 12 is combusted and torque is output to the crankshaft 15 through the piston 13 and the connecting rod 14.

  The crank position sensor 16 is arranged in the vicinity of the output shaft of the internal combustion engine, that is, the crankshaft 15. The crank position sensor 16 is electrically connected to the interface 95 of the electronic control unit 90. The crank position sensor 16 outputs an output value corresponding to the rotational phase of the crankshaft 15. This output value is input to the electronic control unit 90. The electronic control unit 90 calculates the engine speed based on this output value.

  The intake manifold 32 is branched into a plurality of pipes at one end thereof, and these branched pipes are connected to the corresponding intake ports 31. The intake manifold 32 is connected to one end of the surge tank 33 at the other end. The surge tank 33 is connected to one end of the intake pipe 34 at the other end.

  The throttle valve 35 is disposed in the intake pipe 34. An actuator (hereinafter referred to as “throttle valve actuator”) 36 for changing the opening degree is connected to the throttle valve 35. The throttle valve actuator 36 is electrically connected to the interface 95 of the electronic control unit 90. The electronic control unit 90 supplies the throttle valve actuator 36 with a control signal for driving the throttle valve actuator 36 so as to control the throttle valve opening to the target throttle valve opening. When the throttle valve opening is changed, the flow passage area in the intake pipe 34 in the region where the throttle valve 35 is disposed changes. As a result, the amount of air passing through the throttle valve 35 changes, and consequently, the amount of air taken into the combustion chamber changes.

  The air flow meter 37 is disposed in the intake pipe 34 upstream of the throttle valve 35. The air flow meter 37 is electrically connected to the interface 95 of the electronic control unit 90. The air flow meter 37 outputs an output value corresponding to the amount of air passing therethrough. This output value is input to the electronic control unit 90. The electronic control unit 90 calculates the amount of air passing through the air flow meter 37, and thus the intake air amount, based on this output value.

  The air cleaner 38 is disposed in the intake pipe 34 upstream of the air flow meter 37.

  The exhaust manifold 42 is branched into a plurality of pipes at one end thereof, and these branched pipes are connected to the corresponding exhaust ports 41. The exhaust manifold 42 is connected to one end of the exhaust pipe 43 at the other end. The exhaust pipe 43 is open to the outside air at the other end.

  The catalytic converter 44 is disposed in the exhaust passage 40 (more specifically, in the exhaust pipe 43. The catalytic converter 44 houses a catalyst 45 therein. The catalyst 45 has a temperature of A specific component in the exhaust gas flowing into the catalyst when the temperature is equal to or higher than a specific temperature (so-called activation temperature) can be purified at a predetermined purification rate. A composite oxide.

  The composite oxide carries an active element. The composite oxide is retained by absorbing or storing oxygen when the atmosphere around the composite oxide (that is, the internal atmosphere of the catalyst) is an oxidizing atmosphere, and the atmosphere around the composite oxide is reduced. It has an ability to release oxygen retained by the complex oxide when it is in an atmosphere (hereinafter, this ability is referred to as “oxygen retention and release ability”).

  The active element is an element having a property of activating at least one of an oxidation reaction and a reduction reaction of the specific component in the exhaust gas flowing into the catalyst, or both of the oxidation reaction and the reduction reaction. Further, the active element has a catalyst temperature (hereinafter referred to as “catalyst temperature”) that is higher than a certain temperature (hereinafter referred to as “predetermined solid solution temperature”) and the internal atmosphere of the catalyst is oxidized. When the atmosphere is an atmosphere, the composite oxide dissolves in the composite oxide. When the catalyst temperature is equal to or higher than a certain temperature (hereinafter referred to as “catalyst deposition temperature”) and the internal atmosphere of the catalyst is a reducing atmosphere, the composite oxide It has the property to precipitate from. Therefore, the composite oxide dissolves the active element when the catalyst temperature is a predetermined solid solution temperature and the internal atmosphere of the catalyst is an oxidizing atmosphere, and the catalyst temperature is equal to or higher than the catalyst deposition temperature and the internal temperature of the catalyst. It is a complex oxide made of a material having the property of precipitating active elements when the atmosphere is a reducing atmosphere. Therefore, in the catalyst of the first embodiment, when the air-fuel ratio of the exhaust gas flowing into the catalyst when the catalyst temperature is equal to or higher than the predetermined solid solution temperature is an air-fuel ratio leaner than the stoichiometric air-fuel ratio, the catalyst is precipitated from the complex oxide. When the active element is dissolved in the composite oxide and the air-fuel ratio of the exhaust gas flowing into the catalyst is richer than the stoichiometric air-fuel ratio when the catalyst temperature is equal to or higher than the predetermined precipitation temperature, the composite oxidation Active elements that are solid-solved in the material are precipitated from the composite oxide.

  Further, the catalyst 45 has nitrogen oxide (NOx), carbon monoxide (CO), and unburned hydrocarbon (HC) in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst 45 is the stoichiometric air-fuel ratio. Is a so-called three-way catalyst that can simultaneously purify the catalyst at a high purification rate. Note that the air-fuel ratio of the exhaust gas means the ratio of the amount of air taken into the combustion chamber 12 to the amount of fuel supplied to the combustion chamber 12.

The active element may be any element as long as it is an element having a property of being dissolved in the composite oxide as described above and precipitated from the composite oxide as described above, for example, rhodium (Rh). The material constituting the composite oxide may be any material as long as it has the property of dissolving the active element as described above and precipitating the active element as described above, and MgAlO ₄ having a spinel structure. , And a composite oxide such as MAl ₂ O ₃ (where M is a metal) having a perovskite structure.

  An air-fuel ratio sensor (hereinafter also referred to as “upstream air-fuel ratio sensor”) 46 is attached to the exhaust passage 40 upstream of the catalyst 45. The air-fuel ratio sensor 46 is electrically connected to the interface 95 of the electronic control device 90. The air-fuel ratio sensor 46 outputs an output value corresponding to the air-fuel ratio of the exhaust gas arriving there. This output value is input to the electronic control unit 90. The electronic control unit 90 calculates the air-fuel ratio of the exhaust gas that arrives at the air-fuel ratio sensor 46 based on this output value. Therefore, it can be said that the air-fuel ratio sensor 46 is a sensor that detects the air-fuel ratio of the exhaust gas that arrives there. The air-fuel ratio sensor 46 is not limited to a specific sensor as long as it detects the air-fuel ratio of the exhaust gas that arrives there. For example, the air-fuel ratio sensor 46 is shown in FIG. A so-called limiting current type oxygen concentration sensor having output characteristics can be employed. As shown in FIG. 2A, this oxygen concentration sensor outputs a larger current value as an output value as the air-fuel ratio of the exhaust gas arriving there increases.

  An air-fuel ratio sensor (hereinafter also referred to as “downstream air-fuel ratio sensor”) 48 is attached to the exhaust passage 40 downstream of the catalyst 45. The air-fuel ratio sensor 48 is electrically connected to the interface 95 of the electronic control device 90. The air-fuel ratio sensor 48 outputs an output value corresponding to the air-fuel ratio of the exhaust gas that arrives there. This output value is input to the electronic control unit 90. The electronic control unit 90 calculates the air-fuel ratio of the exhaust gas that arrives at the air-fuel ratio sensor 48 based on this output value. Therefore, it can be said that the air-fuel ratio sensor 48 is a sensor that detects the air-fuel ratio of the exhaust gas that arrives there. The air-fuel ratio sensor 48 is not limited to a specific sensor as long as it detects the air-fuel ratio of the exhaust gas that arrives there. For example, the air-fuel ratio sensor 48 is shown in FIG. A so-called electromotive force type oxygen concentration sensor having output characteristics can be employed. As shown in FIG. 2B, this oxygen concentration sensor uses a relatively large constant voltage value as an output value when the air-fuel ratio of the exhaust gas arriving there is richer than the stoichiometric air-fuel ratio. When the air-fuel ratio of the exhaust gas arriving there is leaner than the stoichiometric air-fuel ratio, a relatively small constant voltage value is output as an output value. The oxygen concentration sensor outputs an intermediate voltage value between the relatively large constant voltage value and the relatively small constant voltage value when the air-fuel ratio of the exhaust gas arriving there is the stoichiometric air-fuel ratio. Output as a value. Therefore, when the air-fuel ratio of the exhaust gas arriving there changes from the air-fuel ratio richer than the stoichiometric air-fuel ratio to the air-fuel ratio leaner than the stoichiometric air-fuel ratio, the output value of the oxygen concentration sensor is a relatively large constant value. From the voltage value to the relatively small constant voltage value, the voltage value decreases at a stretch via the intermediate voltage value. On the other hand, the output value of the oxygen concentration sensor is a relatively small constant value when the air-fuel ratio of the exhaust gas arriving there changes from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio. The voltage value increases from the current voltage value to the relatively large constant voltage value via the intermediate voltage value.

  The temperature sensor 47 is attached to the catalytic converter 44. The temperature sensor 47 is electrically connected to the interface 95 of the electronic control device 90. The temperature sensor 47 outputs an output value corresponding to the temperature of the catalyst 45. This output value is input to the electronic control unit 90. The electronic control unit 90 calculates the temperature of the catalyst 45 based on this output value. Therefore, it can be said that the temperature sensor 47 is a sensor that detects the temperature of the catalyst 45.

  The accelerator pedal depression amount sensor 81 is connected to the accelerator pedal 80. The accelerator pedal depression amount sensor 81 is electrically connected to the interface 95 of the electronic control unit 90. The accelerator pedal depression amount sensor 81 outputs an output value corresponding to the depression amount of the accelerator pedal 80. This output value is input to the electronic control unit 90. The electronic control unit 90 calculates the amount of depression of the accelerator pedal 80 and thus the required engine torque based on this output value.

  Next, the air-fuel ratio control of the first embodiment will be described. In the following description, “engine operation state” means “operation state of the internal combustion engine”, “fuel injection amount” means “amount of fuel injected from the fuel injection valve”, and “target air-fuel ratio” Means "target air-fuel ratio as the air-fuel ratio of the air-fuel mixture", "upstream detected air-fuel ratio" means "air-fuel ratio of exhaust gas detected by upstream air-fuel ratio sensor", and "downstream detection “Air-fuel ratio” means “the air-fuel ratio of the exhaust gas detected by the downstream air-fuel ratio sensor”.

  In the first embodiment, the optimum throttle valve opening is obtained in advance by experiments or the like according to the engine operating state. The obtained throttle valve opening is stored in the electronic control unit as a reference throttle valve opening Dthb in the form of a function map of the engine speed NE and the required engine torque TQ as shown in FIG. ing. During engine operation, the reference throttle valve opening degree Dthb corresponding to the engine speed NE and the required engine torque TQ at that time is acquired from the map of FIG. Then, the reference throttle valve opening Dthb acquired in this way is set as the target throttle valve opening.

  Further, in the first embodiment, the reference fuel injection amount Qb is calculated according to the following equation 1, the target fuel injection amount Qt is calculated according to the following equation 2, and the calculated target fuel injection amount becomes the target fuel injection amount. Is set. In the following equation 1, “Ga” is “intake air amount”, “NE” is “engine speed”, “AFt” is “target air-fuel ratio”, and “Qb” in “equation 2” is “expression” 1 is a “reference fuel injection amount” calculated according to “1”, and “Kf” is a “correction coefficient”. In the air-fuel ratio control of the first embodiment, the target air-fuel ratio is set to the stoichiometric air-fuel ratio.

Qb = (Ga / NE) × (1 / AFt) (1)
Qt = Qb × Kf (2)

  Note that the correction coefficient Kf of the above equation 2 is set as follows. That is, while the upstream-side detected air-fuel ratio is larger than the stoichiometric air-fuel ratio (= target air-fuel ratio) (that is, the upstream-side detected air-fuel ratio is leaner than the stoichiometric air-fuel ratio, therefore, the air-fuel mixture While the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the correction coefficient Kf is gradually increased by a relatively small constant value (hereinafter, this value is referred to as a “constant increase value”). According to this, since the target fuel injection amount is gradually increased, the air-fuel ratio of the air-fuel mixture gradually decreases and approaches the stoichiometric air-fuel ratio. On the other hand, while the upstream-side detected air-fuel ratio is smaller than the stoichiometric air-fuel ratio (= target air-fuel ratio) (that is, the upstream-side detected air-fuel ratio is richer than the stoichiometric air-fuel ratio, therefore, the air-fuel mixture While the air-fuel ratio is richer than the stoichiometric air-fuel ratio), the correction coefficient Kf is gradually reduced by a relatively small constant value (hereinafter, this value is referred to as “constant decrease value”). According to this, since the target fuel injection amount is gradually reduced, the air-fuel ratio of the air-fuel mixture gradually increases and approaches the stoichiometric air-fuel ratio.

  Further, when the upstream detected air-fuel ratio changes from an air fuel ratio larger than the stoichiometric air fuel ratio (= target air fuel ratio) to an air fuel ratio smaller than the stoichiometric air fuel ratio (that is, the upstream detected air fuel ratio is leaner than the stoichiometric air fuel ratio). When the air-fuel ratio of the mixture changes from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio). The correction coefficient Kf is decreased by a relatively large value (hereinafter, this value is referred to as “skip reduction value”). According to this, since the target fuel injection amount is reduced at once, the air-fuel ratio of the air-fuel mixture increases at a stretch and approaches the stoichiometric air-fuel ratio (= target air-fuel ratio) at a stretch. On the other hand, when the upstream detected air-fuel ratio changes from an air fuel ratio smaller than the stoichiometric air fuel ratio (= target air fuel ratio) to an air fuel ratio larger than the stoichiometric air fuel ratio (that is, the upstream detected air fuel ratio is richer than the stoichiometric air fuel ratio). When the air-fuel ratio of the mixture changes from an air-fuel ratio richer than the stoichiometric air-fuel ratio to an air-fuel ratio leaner than the stoichiometric air-fuel ratio). The correction coefficient Kf is increased by a relatively large value (hereinafter, this value is referred to as “skip increase value”). According to this, since the target fuel injection amount is increased all at once, the air-fuel ratio of the air-fuel mixture decreases at a stretch and approaches the stoichiometric air-fuel ratio (= target air-fuel ratio) all at once.

  Note that the skip decrease value and the skip increase value used in the air-fuel ratio control of the first embodiment are set as follows. That is, while the downstream side detected air-fuel ratio is larger than the stoichiometric air-fuel ratio (= target air-fuel ratio) (that is, while the downstream-side detected air-fuel ratio is leaner than the stoichiometric air-fuel ratio), skipping is performed. The increase value is increased by a relatively small constant value (hereinafter, this value is referred to as “predetermined correction value”). On the other hand, while the downstream-side detected air-fuel ratio is smaller than the stoichiometric air-fuel ratio (= target air-fuel ratio) (that is, while the downstream-side detected air-fuel ratio is richer than the stoichiometric air-fuel ratio), skipping is performed. The increase value is decreased by the predetermined correction value. Then, the skip decrease value is calculated by subtracting the skip increase value calculated as described above from a predetermined value (hereinafter referred to as “reference value”) of at least zero or more. When the skip increase value calculated as described above is smaller than the reference value, the skip increase value is set to the reference value (that is, the skip increase value is guarded by the reference value).

  In the air-fuel ratio control of the first embodiment, while the upstream-side detected air-fuel ratio is an air-fuel ratio larger than the theoretical air-fuel ratio (= target air-fuel ratio), the correction coefficient is gradually increased by a constant increase value, While the upstream-side detected air-fuel ratio is an air-fuel ratio smaller than the stoichiometric air-fuel ratio, the correction coefficient is gradually decreased by a constant decrease value. However, instead of this, while the upstream detected air-fuel ratio is equal to or higher than the stoichiometric air-fuel ratio (= target air-fuel ratio), the correction coefficient is gradually increased by a constant increase value, and the upstream detected air-fuel ratio is theoretically increased. While the air-fuel ratio is smaller than the air-fuel ratio, the correction coefficient may be gradually decreased by a constant decrease value, or the upstream-side detected air-fuel ratio is larger than the stoichiometric air-fuel ratio (= target air-fuel ratio). For some time, the correction coefficient may be gradually increased by a constant increase value, and the correction coefficient may be gradually decreased by a constant decrease value while the upstream detected air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio.

  In the air-fuel ratio control of the first embodiment, when the upstream-side detected air-fuel ratio changes from an air-fuel ratio larger than the stoichiometric air-fuel ratio (= target air-fuel ratio) to an air-fuel ratio smaller than the stoichiometric air-fuel ratio, the correction coefficient is The correction coefficient is increased by the skip increase value when the upstream-side detected air-fuel ratio changes from an air-fuel ratio smaller than the stoichiometric air-fuel ratio to an air-fuel ratio greater than the stoichiometric air-fuel ratio. However, instead of this, when the detected upstream air-fuel ratio changes from the air-fuel ratio equal to or higher than the stoichiometric air-fuel ratio (= target air-fuel ratio) to an air-fuel ratio smaller than the stoichiometric air-fuel ratio, the correction coefficient is decreased by the skip reduction value. At the same time, when the upstream detected air-fuel ratio changes from an air / fuel ratio smaller than the stoichiometric air / fuel ratio to an air / fuel ratio greater than or equal to the stoichiometric air / fuel ratio, the correction coefficient may be increased by the skip increase value, or the upstream detected air / fuel ratio may be increased. When the air-fuel ratio changes from an air-fuel ratio greater than the stoichiometric air-fuel ratio (= target air-fuel ratio) to an air-fuel ratio that is less than or equal to the stoichiometric air-fuel ratio, the correction coefficient is decreased by the skip reduction value and the upstream-side detected air-fuel ratio becomes the stoichiometric air-fuel ratio. When the air-fuel ratio changes from the following air-fuel ratio to a larger air-fuel ratio than the stoichiometric air-fuel ratio, the correction coefficient may be increased by the skip increase value.

  In the air-fuel ratio control of the first embodiment, while the downstream-side detected air-fuel ratio is larger than the theoretical air-fuel ratio (= target air-fuel ratio), the skip increase value is increased by a predetermined correction value and the downstream side While the side detected air-fuel ratio is smaller than the stoichiometric air-fuel ratio, the skip increase value is decreased by a predetermined correction value. However, instead of this, while the downstream side detected air-fuel ratio is equal to or higher than the stoichiometric air-fuel ratio (= target air-fuel ratio), the skip increase value is increased by a predetermined correction value and the downstream-side detected air-fuel ratio is increased to the stoichiometric air-fuel ratio. While the air-fuel ratio is smaller than the fuel ratio, the skip increase value may be decreased by a predetermined correction value, or while the downstream-side detected air-fuel ratio is larger than the stoichiometric air-fuel ratio (= target air-fuel ratio). The skip increase value may be increased by a predetermined correction value, and the skip increase value may be decreased by a predetermined correction value while the downstream-side detected air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio.

  Next, the control of the throttle valve of the first embodiment will be described. In the first embodiment, during engine operation, a control signal to be supplied to the throttle valve actuator is calculated in order to open the throttle valve by the target throttle valve opening set as described above. The control signal thus calculated is supplied to the throttle valve actuator. As a result, the throttle valve is opened by the target throttle valve opening.

  Next, control of the fuel injection valve of the first embodiment will be described. In the first embodiment, during engine operation, a command signal to be supplied to the fuel injection valve in order to inject the fuel of the target fuel injection amount set as described above from the fuel injection valve is calculated, and the target fuel is calculated. An injection timing is set (the setting of the target fuel injection timing will be described later). The command signal thus calculated is supplied to the fuel injection valve at the set target fuel injection timing. Thereby, the fuel of the target fuel injection amount is injected from the fuel injection valve at the target fuel injection timing.

  By the way, the internal combustion engine of the first embodiment can execute fuel supply stop control for stopping the supply of fuel to the combustion chamber, that is, so-called fuel cut control for reducing the fuel injection amount from the fuel injection valve to zero. Next, this control will be described. In the following description, “FC control” means “fuel supply stop control”, and “catalyst use degree” means “the catalyst is used to purify components in exhaust gas after a new catalyst is provided in the internal combustion engine. "Degree of used".

  In the first embodiment, when the catalyst temperature is equal to or higher than a predetermined temperature (hereinafter, this temperature is referred to as “execution prohibition temperature”), execution of FC control is prohibited, and when the catalyst temperature is lower than the execution prohibition temperature, Execution of FC control is permitted. The FC control is executed when the catalyst temperature is lower than the execution prohibition temperature, and therefore execution of the FC control is permitted and a specific condition is satisfied.

  Here, in the first embodiment, execution is prohibited while the degree of catalyst use is below a predetermined degree (hereinafter, this degree is referred to as “first degree”) (that is, while the degree of catalyst use is relatively small). The temperature is set to a temperature lower than the reference temperature. Here, the reference temperature is a temperature that is adopted as an execution prohibition temperature after the degree of catalyst use becomes relatively large.

  According to the first embodiment, the following effects can be obtained. That is, when FC control is executed, the catalyst inflow exhaust air-fuel ratio (that is, the air-fuel ratio of the exhaust gas flowing into the catalyst) becomes an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and as a result, the internal atmosphere of the catalyst becomes an oxidizing atmosphere. become. In this case, when the catalyst temperature is relatively high, aggregation of the composite oxide occurs. Therefore, the catalyst purification capacity changes.

  On the other hand, in order to cause the internal combustion engine to exhibit the desired performance, engine control (ie, the internal combustion engine can exhibit the desired performance in consideration of changes in the catalyst purification capacity during engine operation). In addition, it is necessary to construct a control logic used for internal combustion engine control and to perform engine control. However, when the catalyst purification capacity changes due to the execution of the FC control, it can be said that it is very complicated to construct the control logic or to perform the engine control as described above.

  Here, in the first embodiment, the execution prohibition temperature is set to a temperature lower than the reference temperature while the degree of catalyst use is equal to or less than the first degree (that is, while the degree of use of the catalyst is relatively small). According to this, since the FC control execution opportunities are reduced, there is little opportunity for the composite oxides to aggregate, and as a result, the change in the catalyst purification capacity is small.

  As described above, in the first embodiment, while the catalyst use degree is relatively small, the change in the catalyst purification capacity is small, and therefore it becomes easy to assume the catalyst purification capacity during engine operation. Therefore, according to the first embodiment, the control logic used for engine control can be constructed relatively easily while the catalyst usage is relatively small, and the engine is used while the catalyst usage is relatively small. Control can be performed relatively easily and the catalyst can exhibit the desired purification ability.

  Further, according to the first embodiment, the following effects can also be obtained. That is, as described above, in the first embodiment, the change in the catalyst purification capacity is small while the degree of catalyst use is relatively small. In addition, when the composite oxide is aggregated, its oxygen holding / releasing ability decreases. However, in the first embodiment, since there is little opportunity for the composite oxide to aggregate, the decrease in the oxygen holding and releasing ability of the composite oxide is also small. For this reason, since a large control gain can be used as the control gain based on the downstream-side detected air-fuel ratio in the air-fuel ratio control described above, an effect of improving the robustness of the air-fuel ratio control is also obtained.

  In addition, as the catalyst usage degree of the first embodiment, for example, the catalyst usage time (that is, the total time that a new catalyst was used for purifying components in the exhaust gas) or the vehicle travel distance (that is, the internal combustion engine) Is used for driving a vehicle, the total distance traveled by the vehicle after a new catalyst is provided in the internal combustion engine can be employed. In the first embodiment, the specific condition used for determining whether or not to execute FC control is, for example, that the required engine torque is extremely small (particularly, the required engine torque is zero). . Further, in the first embodiment, after the degree of catalyst use becomes greater than the first degree, for example, the execution prohibition temperature is set to the reference temperature.

  Next, an example of a routine for executing the FC control of the first embodiment will be described. An example of this routine is shown in FIG. This routine is a routine that is started every predetermined period.

  When the routine of FIG. 4 is started, first, at step 100, it is determined whether or not the catalyst usage degree Dcat is equal to or less than the first degree Dcatth1 (Dcat ≦ Dcatth1). Here, when it is determined that Dcat ≦ Dcatth1, the routine proceeds to step 101. On the other hand, if it is determined that Dcat ≦ Dcatth1, the routine proceeds to step 105.

  In step 101, a temperature that is lower than the reference temperature Tfcthb of the execution prohibition temperature by a predetermined temperature Kfc1 is set as the execution prohibition temperature Tfcth, and the routine proceeds to step 102. On the other hand, in step 105, the execution prohibition temperature reference temperature Tfcthb is set to the execution prohibition temperature Tfcth, and the routine proceeds to step 102.

  In step 102, it is determined whether or not the catalyst temperature Tcat is equal to or higher than the execution prohibition temperature Tfcth (Tcat ≧ Tfcth). Here, when it is determined that Tcat ≧ Tfcth, the routine ends. On the other hand, when it is determined that Tcat ≧ Tfcth is not satisfied, the routine proceeds to step 103. When the routine proceeds from step 101 to step 102, the execution prohibition temperature Tfcth set in step 101 is used in step 102, and when the routine proceeds from step 105 to step 102, step 102 includes step 105. The execution prohibition temperature Tfcth set in (1) is used.

  In step 103, it is determined whether or not an FC control condition (that is, the specific condition described in the first embodiment) is satisfied. Here, when it is determined that the FC control condition is satisfied, the routine proceeds to step 104 where FC control is executed, and then the routine ends. On the other hand, when it is determined that the FC control condition is not satisfied, the routine ends.

  Next, a second embodiment will be described. The configuration and control of the second embodiment not described below are the same as the configuration and control of the first embodiment, respectively, or in view of the configuration and control of the second embodiment described below. Sometimes the configuration and control are naturally derived from the configuration and control of the first embodiment. In the following description, “reference amount” means “target fuel injection amount calculated according to the above equation 2”.

  The internal combustion engine of the second embodiment is a fuel supply increase control (hereinafter, this control is simply referred to as “increase control”) in which the amount of fuel supplied to the combustion chamber is increased from a reference amount, that is, fuel injection from a fuel injection valve. It is possible to execute control to increase the amount from the reference amount. In the second embodiment, when the catalyst temperature is equal to or higher than a predetermined temperature (hereinafter, this temperature is referred to as “execution permission temperature”), execution of the increase control is permitted, and the catalyst temperature is lower than the execution permission temperature. Sometimes, the execution of the increase control is prohibited. Then, the increase control is executed when the catalyst temperature is equal to or higher than the execution permission temperature, and therefore execution of the increase control is permitted, and when a specific condition is satisfied.

  Here, in the second embodiment, the execution permission is given while the catalyst usage level is equal to or lower than a predetermined level (hereinafter, this level is referred to as “first level”) (that is, while the catalyst usage level is relatively small). The temperature is set to a temperature higher than the reference temperature. Here, the reference temperature is a temperature that is adopted as an execution permission temperature after the degree of catalyst use becomes relatively large. Further, the first degree here may be the same degree as or different from the first degree of the first embodiment.

  According to the second embodiment, the following effects can be obtained. That is, when the increase control is executed, the catalyst inflow exhaust air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, and as a result, the internal atmosphere of the catalyst becomes a reducing atmosphere. Here, when the catalyst temperature is equal to or higher than the predetermined deposition temperature, the active element is precipitated from the composite oxide. That is, the amount of the deposited active element (that is, the active element deposited from the composite oxide) changes, and as a result, the catalyst purification ability changes.

  On the other hand, in order for the internal combustion engine to exhibit the desired performance, as described above, the internal combustion engine can exhibit the expected performance in consideration of changes in the catalyst purification capability during engine operation. It is necessary to construct a control logic used for engine control and to perform engine control. However, when the catalyst purification capacity changes due to the execution of the increase control, it can be said that it is very complicated to construct the control logic or perform the engine control as described above. In addition, since the catalyst is not deteriorated while the degree of use of the catalyst is relatively small, the amount of the precipitated active element that determines the catalyst purification ability is used in order for the catalyst to exhibit the desired purification ability. There is also no need to increase. In other words, it can be said that it is preferable not to change the amount of the precipitated active element as much as possible while the degree of use of the catalyst is relatively small.

  Here, in the second embodiment, while the catalyst use degree is equal to or less than the first degree (that is, while the catalyst use degree is relatively small), the execution permission temperature is set to a temperature higher than the reference temperature. According to this, since the execution opportunity of the increase control is reduced, the change in the amount of the precipitated active element is small, and as a result, the change in the catalyst purification capacity is also small.

  As described above, in the second embodiment, the change in the catalyst purification capacity is small while the degree of use of the catalyst is relatively small. Therefore, it becomes easy to assume the catalyst purification capacity during engine operation. Therefore, according to the second embodiment, a control logic used for engine control can be constructed relatively easily while the catalyst usage is relatively small, and the engine can be used while the catalyst usage is relatively small. Control can be performed relatively easily and the catalyst can exhibit the desired purification ability.

  In addition, as a catalyst use degree of 2nd Embodiment, a catalyst use time or a vehicle travel distance can be employ | adopted, for example. In the second embodiment, the specific condition used for determining whether or not to perform the increase control is, for example, that the engine speed is very high and the engine required torque is very large. Further, in the second embodiment, after the catalyst use degree becomes larger than the first degree, for example, the execution permission temperature is set to the reference temperature.

  In the second embodiment, the FC control of the first embodiment may be employed. In this case, while the catalyst use degree is equal to or lower than the first degree mentioned in the first embodiment, the execution prohibition temperature is set to a temperature lower than the reference temperature. Note that the first degree used for FC control at this time may be the same as or different from the first degree used for the increase control in the second embodiment.

  Next, an example of a routine for executing the increase control of the second embodiment will be described. An example of this routine is shown in FIG. This routine is a routine that is started every predetermined period.

  When the routine of FIG. 5 is started, first, at step 200, it is determined whether or not the catalyst usage degree Dcat is equal to or less than the first degree Dcatth1 (Dcat ≦ Dcatth1). Here, when it is determined that Dcat ≦ Dcatth1, the routine proceeds to step 201. On the other hand, when it is determined that Dcat ≦ Dcatth1, the routine proceeds to step 205.

  In step 201, a temperature that is higher than the reference temperature Tfitb of the execution permission temperature by a predetermined temperature Kfi is set as the execution permission temperature Tfit, and the routine proceeds to step 202. On the other hand, in step 205, the reference temperature Tfitb of the execution permission temperature is set to the execution permission temperature Tfit, and the routine proceeds to step 202.

  In step 202, it is determined whether or not the catalyst temperature Tcat is equal to or higher than the execution permission temperature Tfit (Tcat ≧ Tfit). Here, if it is determined that Tcat ≧ Tfit, the routine proceeds to step 203. On the other hand, when it is determined that Tcat ≧ Tfit is not satisfied, the routine ends. When the routine proceeds from step 201 to step 202, the execution permission temperature Tfith set in step 201 is used in step 202, and when the routine proceeds from step 205 to step 202, step 202 includes step 205. The execution permission temperature Tfith set in is used.

  In step 203, it is determined whether or not an increase control condition (that is, the specific condition described in the second embodiment) is satisfied. If it is determined that the increase control condition is satisfied, the routine proceeds to step 204 where the increase control is executed, and then the routine ends. On the other hand, when it is determined that the increase control condition is not satisfied, the routine ends.

  Next, a third embodiment will be described. The configuration and control of the third embodiment not described below are the same as the configuration and control of the above-described embodiment, respectively, or in view of the configuration and control of the third embodiment described below. This is a configuration and control that is naturally derived from the configuration and control of the above-described embodiment. In the following description, “execution prohibition temperature” is “execution prohibition temperature described in relation to the first embodiment”.

  In the third embodiment, the execution prohibition temperature is set to a temperature lower than the reference temperature while the catalyst use degree is equal to or less than a predetermined degree (hereinafter, this degree is referred to as “first degree”). While the degree of catalyst use is less than or equal to another predetermined degree (hereinafter referred to as “second degree”) that is greater than the first degree and greater than the first degree, A temperature higher than the reference temperature is set.

  According to the third embodiment, the following effects can be obtained. That is, in the third embodiment, while the degree of catalyst use is greater than the first degree and less than or equal to the second degree, the execution prohibition temperature is set to a temperature higher than the reference temperature. According to this, since the opportunity for executing the fuel supply stop control increases, the aggregation of the complex oxide is promoted. For this reason, the effect that the precipitation rate of an active element can be reduced is acquired. In addition, when such an effect is acquired, for example, the active element solid solubility (that is, the ratio of the active element that is dissolved in the composite oxide among the active elements) is set as the target solid solubility (that is, the target active element). In the case of controlling the solid solubility), an effect is obtained that the active element solid solubility can be easily controlled to the target solid solubility. Further, since the aggregation of the composite oxide is promoted, the oxygen holding and releasing ability of the composite oxide becomes small. That is, the composite oxide is stabilized to a small extent that the oxygen holding / releasing ability is small. For this reason, when the above-described air-fuel ratio control is performed, a large control gain can be used as the control gain based on the downstream-side detected air-fuel ratio, so that the effect of improving the robustness of the air-fuel ratio control is also obtained. .

  The first degree in the third embodiment may be the same as or different from the first degree in the first embodiment. Further, in the third embodiment, after the degree of catalyst use becomes greater than the second degree, for example, the execution prohibition temperature is set to the reference temperature.

  In the third embodiment, the increase control of the second embodiment may be employed. In this case, while the catalyst use degree is equal to or lower than the first degree mentioned in the second embodiment, the execution permission temperature is set to a temperature higher than the reference temperature. Note that the first degree used for the increase control at this time may be the same as or different from the first degree used for the FC control of the third embodiment.

  Next, an example of a routine for executing the FC control of the third embodiment will be described. An example of this routine is shown in FIG. This routine is a routine that is started every predetermined period.

  When the routine of FIG. 6 is started, first, at step 300, it is determined whether or not the catalyst usage degree Dcat is equal to or less than the first degree Dcatth1 (Dcat ≦ Dcatth1). Here, when it is determined that Dcat ≦ Dcatth1, the routine proceeds to step 301. On the other hand, if it is determined that Dcat ≦ Dcatth1, the routine proceeds to step 305.

  In step 305, it is determined whether or not the catalyst usage degree Dcat is equal to or less than the second degree Dcatth2 (Dcat ≦ Dcatth2). If it is determined that Dcat ≦ Dcatth2, the routine proceeds to step 306. On the other hand, if it is determined that Dcat ≦ Dcatth2, the routine proceeds to step 307.

  In step 301, a temperature that is lower than the reference temperature Tfcthb of the execution prohibition temperature by a predetermined temperature Kfc1 is set as the execution prohibition temperature Tfcth, and the routine proceeds to step 302. In step 306, a temperature that is higher by a predetermined temperature Kfc2 than the reference temperature Tfcthb of the execution prohibition temperature is set as the execution prohibition temperature Tfcth, and the routine proceeds to step 302. In step 307, the execution prohibition temperature reference temperature Tfcthb is set to the execution prohibition temperature Tfcth, and the routine proceeds to step 302. The predetermined temperature Kfc2 may be the same value as the predetermined temperature Kfc1 or a different value.

  In step 302, it is determined whether or not the catalyst temperature Tcat is equal to or higher than the execution prohibition temperature Tfcth (Tcat ≧ Tfcth). Here, when it is determined that Tcat ≧ Tfcth, the routine ends. On the other hand, when it is determined that Tcat ≧ Tfcth is not satisfied, the routine proceeds to step 303. When the routine proceeds from step 301 to step 302, at step 302, the execution prohibition temperature Tfcth set at step 301 is used. When the routine proceeds from step 306 to step 302, at step 302, step 306 is performed. When the execution prohibition temperature Tfcth set in step 307 is used and the routine proceeds from step 307 to step 302, the execution prohibition temperature Tfcth set in step 307 is used in step 302.

  In step 303, it is determined whether or not an FC control condition (that is, the specific condition described in the first embodiment) is satisfied. Here, when it is determined that the FC control condition is satisfied, the routine proceeds to step 304, where FC control is executed, and then the routine ends. On the other hand, when it is determined that the FC control condition is not satisfied, the routine ends.

  Next, a fourth embodiment will be described. The configuration and control of the fourth embodiment not described below are the same as the configuration and control of the above-described embodiment, respectively, or in view of the configuration and control of the fourth embodiment described below. This is a configuration and control that is naturally derived from the configuration and control of the above-described embodiment. Further, in the following description, “active element solid solubility” means “a proportion of active elements that are dissolved in a composite oxide among active elements”.

  In the fourth embodiment, the execution prohibition temperature is set to a temperature lower than the reference temperature while the catalyst use degree is equal to or less than a predetermined degree (hereinafter, this degree is referred to as “first degree”). While the catalyst use degree is less than or equal to another predetermined degree (hereinafter referred to as “the third degree”) that is greater than the first degree and greater than the first degree, A temperature higher than the reference temperature is set. Then, after the degree of catalyst use becomes greater than the second degree, the catalyst inflow exhaust air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio so that the active element solid solubility is controlled to the target solid solubility. Alternatively, control for controlling the catalyst inflow exhaust air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio (hereinafter, this air-fuel ratio control is referred to as “solid solubility control”) is executed.

  According to the fourth embodiment, the following effects can be obtained. That is, during engine operation, the catalyst temperature becomes equal to or higher than a predetermined solid solution temperature or reaches a predetermined precipitation temperature. On the other hand, even if the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio, the catalyst inflow exhaust air-fuel ratio may be temporarily leaner than the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio. There is. Here, if the catalyst inflow exhaust air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio when the catalyst temperature is equal to or higher than the predetermined solid solution temperature, the internal atmosphere of the catalyst becomes an oxidizing atmosphere. When the active element has a property of being dissolved in the composite oxide when the temperature is higher than the solid solution temperature and the internal atmosphere of the catalyst is an oxidizing atmosphere, the active element is dissolved in the composite oxide. On the other hand, if the catalyst inflow exhaust air-fuel ratio becomes richer than the stoichiometric air-fuel ratio when the catalyst temperature is equal to or higher than the predetermined deposition temperature, the internal atmosphere of the catalyst becomes a reducing atmosphere. In the case where the active element has the property of precipitating from the composite oxide when the internal atmosphere of the catalyst is a reducing atmosphere, the active element is precipitated from the composite oxide. In other words, the amount of the precipitated active element changes due to the change in the catalyst temperature and the change in the catalyst inflow exhaust air-fuel ratio during engine operation, and consequently the catalyst purification capacity changes. Also, as the active element usage (ie, the degree to which the active element is used to activate the components in the exhaust gas) increases, the active element may degrade, resulting in the active ability of the active element (ie, The ability of the active element to increase the oxidation reaction activity or the reduction reaction activity of the components in the exhaust gas may decrease. In other words, as the degree of catalyst use increases, the catalyst purification capacity may decrease. As described above, the catalyst purification ability also changes due to the change in the active ability of the active element during engine operation.

  Therefore, in order for the internal combustion engine to exhibit the desired performance, it is used for engine control so that the internal combustion engine can exhibit the expected performance in consideration of changes in the catalyst purification capacity during engine operation. It is necessary to construct a control logic that can be controlled and to perform engine control. However, since the change in the catalyst purification capacity during engine operation varies depending on the engine operation mode and the degree of catalyst use, it is very complicated to construct a control logic or perform engine control as described above. It can be said that. On the other hand, the control logic can be constructed relatively easily and engine control can be performed relatively easily if the change in the catalyst purification capacity is assumed regardless of the mode of engine operation and the degree of catalyst use. Can do.

  Here, in the fourth embodiment, after the degree of catalyst use becomes relatively large (that is, after the degree of catalyst use becomes larger than the second degree), the active element solid solubility is controlled to the target solid solubility. As described above, the catalyst inflow exhaust air-fuel ratio is controlled to be an air-fuel ratio leaner than the stoichiometric air-fuel ratio, or the catalyst inflow exhaust air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio. Therefore, when the catalyst inflow exhaust air-fuel ratio is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, if the catalyst temperature is equal to or higher than the predetermined solid solution temperature, the precipitated active element is dissolved in the composite oxide, and as a result The active element solid solubility increases. On the other hand, when the catalyst inflow exhaust air-fuel ratio is controlled to an air-fuel ratio richer than the stoichiometric air-fuel ratio, if the catalyst temperature is equal to or higher than the predetermined deposition temperature, the internal atmosphere of the catalyst becomes a reducing atmosphere, so that the solid solution active element Precipitates from the composite oxide, and as a result, the solid solubility of the active element decreases. That is, the active element solid solubility is controlled to the target solid solubility by appropriately controlling the inflow exhaust air-fuel ratio depending on whether the active element solid solubility is larger or smaller than the target solid solubility. As a result, the amount of the precipitated active element is kept constant, so that the catalyst purification capability during engine operation can be easily assumed. For this reason, according to the fourth embodiment, the control logic used for engine control can be constructed relatively easily after the degree of catalyst use becomes relatively large, and the degree of catalyst use becomes relatively large. Even after this, the engine control can be performed relatively easily and the catalyst can exhibit the desired purification ability.

  The first degree in the fourth embodiment may be the same degree as or different from the first degree in the first embodiment, and may be the same degree as the first degree in the second embodiment. May be of different degrees. Further, the second degree in the fourth embodiment may be the same degree as the second degree in the second embodiment or a different degree. Further, in the fourth embodiment, after the degree of use of the catalyst becomes larger than the second degree, for example, the execution prohibition temperature is set to the reference temperature.

  In the fourth embodiment, the increase control of the second embodiment may be employed. In this case, while the catalyst use degree is equal to or lower than the first degree mentioned in the second embodiment, the execution permission temperature is set to a temperature higher than the reference temperature. Note that the first degree used for the increase control at this time may be the same as or different from the first degree used for the FC control of the fourth embodiment.

  In addition, in the solid solubility control of the fourth embodiment, in order to control the catalyst inflow exhaust air-fuel ratio to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, for example, the fuel injection amount is made smaller than the target fuel injection amount. In order to control the catalyst inflow exhaust air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio, for example, the fuel injection amount may be made larger than the target fuel injection amount. Alternatively, in the solid solubility control of the fourth embodiment, in order to control the catalyst inflow exhaust air-fuel ratio to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, for example, the throttle valve opening is set larger than the target throttle valve opening. In order to control the catalyst inflow exhaust air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio, for example, the throttle valve opening is set to the target throttle valve opening. (That is, the amount of intake air may be reduced).

  In the solid solubility control of the fourth embodiment, more specifically, when the active element solid solubility is smaller than the target solid solubility, the catalyst inflow exhaust air-fuel ratio is made leaner than the stoichiometric air-fuel ratio. When the active element solid solubility is greater than the target solid solubility, the catalyst inflow exhaust air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, and the active element solid solubility matches the target solid solubility. In this case, the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

  In addition, when the active element solid solubility is smaller than the target solid solubility, the condition that the catalyst inflow exhaust air / fuel ratio is controlled to an air / fuel ratio leaner than the stoichiometric air / fuel ratio is that the catalyst temperature is equal to or higher than the predetermined solid solution temperature. It is preferable to add. That is, in this case, when the active element solid solubility is smaller than the target solid solubility and the catalyst temperature is equal to or higher than the predetermined solid solution temperature, the catalyst inflow exhaust air-fuel ratio is controlled to a lean air-fuel ratio than the stoichiometric air-fuel ratio. When the active element solid solubility is smaller than the target solid solubility but the catalyst temperature is lower than the predetermined solid solution temperature, the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio. In addition, as a condition for controlling the catalyst inflow exhaust air / fuel ratio to be richer than the stoichiometric air / fuel ratio when the active element solid solubility is larger than the target solid solubility, it is added that the catalyst temperature is equal to or higher than the predetermined precipitation temperature. It is preferable. That is, in this case, when the active element solid solubility is larger than the target solid solubility and the catalyst temperature is equal to or higher than the predetermined precipitation temperature, the catalyst inflow exhaust air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, When the active element solid solubility is larger than the target solid solubility but the catalyst temperature is lower than the predetermined deposition temperature, the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

  In the fourth embodiment, when the method of reducing the fuel injection amount to be smaller than the target fuel injection amount in order to control the catalyst inflow exhaust air / fuel ratio to an air / fuel ratio leaner than the stoichiometric air / fuel ratio, the fuel injection amount becomes the target When the fuel injection amount is significantly reduced, the air-fuel ratio of the air-fuel mixture (that is, the air-fuel ratio of the air-fuel mixture formed in the combustion chamber) becomes an air-fuel ratio that is significantly leaner than the stoichiometric air-fuel ratio. Gas emission performance may be reduced. Therefore, from the viewpoint of suppressing a reduction in the emission performance related to the exhaust gas, the fuel injection amount is controlled from the target fuel injection amount in order to control the catalyst inflow exhaust air / fuel ratio to an air / fuel ratio leaner than the stoichiometric air / fuel ratio in the fourth embodiment. In the case of adopting a method of reducing the amount of fuel, the fuel injection amount is preferably close to the target fuel injection amount. Further, in the fourth embodiment, when the method of increasing the fuel injection amount beyond the target fuel injection amount in order to control the catalyst inflow exhaust air / fuel ratio to an air / fuel ratio richer than the stoichiometric air / fuel ratio, the fuel injection amount is set to the target fuel injection amount. If the fuel injection amount is significantly increased, the air-fuel ratio of the air-fuel mixture becomes a richer air-fuel ratio than the stoichiometric air-fuel ratio. descend. Therefore, from the viewpoint of suppressing a decrease in emission performance and a decrease in fuel consumption related to exhaust gas, the target fuel injection amount is set to control the catalyst inflow exhaust air / fuel ratio to an air / fuel ratio richer than the stoichiometric air / fuel ratio in the fourth embodiment. When the method of increasing the fuel injection amount is employed, the fuel injection amount is preferably close to the target fuel injection amount.

  In the fourth embodiment, when the active element solid solubility is smaller than the target solid solubility, the catalyst inflow exhaust air-fuel ratio is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. However, instead of this, the target active element solid solubility range as the active element solid solubility is set as the target solid solubility range, and the active element solid solubility is lower than the lower limit of the target solid solubility range. May be controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. In this case, when the active element solid solubility is within the target solid solubility range, the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio. In the fourth embodiment, when the active element solid solubility is larger than the target solid solubility, the catalyst inflow exhaust air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio. However, instead of this, the target active element solid solubility range as the active element solid solubility is set as the target solid solubility range, and the active element solid solubility is higher than the upper limit of the target solid solubility range. May be controlled to a richer air-fuel ratio than the stoichiometric air-fuel ratio. In this case, when the active element solid solubility is within the target solid solubility range, the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

  Next, an example of a routine for executing the solid solubility control of the fourth embodiment will be described. An example of this routine is shown in FIG. This routine is a routine that is started every predetermined period. Moreover, as a routine for executing the FC control of the fourth embodiment, the routine shown in FIG. 6 can be adopted.

  When the routine of FIG. 7 is started, first, at step 400, it is determined whether or not the catalyst usage degree Dcat is larger than the second degree Dcatth2 (Dcat> Dcatth2). Here, when it is determined that Dcat> Dcatth2, the routine proceeds to step 401. On the other hand, when it is determined that Dcat> Dcatth2 is not satisfied, the routine proceeds to step 405.

  In step 401, it is determined whether or not the active element solid solubility Ds is smaller than the target solid solubility Dst (Ds <Dst). If it is determined that Ds <Dst, the routine proceeds to step 402. On the other hand, when it is determined that Ds <Dst is not satisfied, the routine proceeds to step 403.

  In step 403, it is determined whether or not the active element solid solubility Ds is larger than the target solid solubility Dst (Ds> Dst). If it is determined that Ds> Dst, the routine proceeds to step 404. On the other hand, when it is determined that Ds> Dst is not satisfied, the routine proceeds to step 405.

  In step 402, the catalyst inflow exhaust air-fuel ratio is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and then the routine ends. In step 404, the catalyst inflow exhaust air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, and then the routine ends. In step 405, the catalyst inflow exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio, and then the routine ends.

  In addition, although embodiment mentioned above is embodiment at the time of applying this invention to a spark ignition type internal combustion engine (so-called gasoline engine), this invention is internal combustion engines other than a spark ignition type internal combustion engine, for example, The present invention is also applicable to a compression self-ignition internal combustion engine (so-called diesel engine). Further, the above-described embodiment is an embodiment in which the present invention is applied to a three-way catalyst, but the present invention is when the air-fuel ratio of the exhaust gas flowing in is leaner than the stoichiometric air-fuel ratio. The present invention can also be applied to a so-called NOx catalyst that can purify nitrogen oxide (NOx) in exhaust gas at a high purification rate.

The active element is an element having a property of activating at least one of an oxidation reaction and a reduction reaction of the specific component in the exhaust gas flowing into the catalyst, or both of the oxidation reaction and the reduction reaction. Further, the active element has a catalyst temperature (hereinafter referred to as “catalyst temperature”) that is higher than a certain temperature (hereinafter referred to as “predetermined solid solution temperature”) and the internal atmosphere of the catalyst is oxidized. When the atmosphere is an atmosphere, the composite oxide dissolves in the composite oxide. When the catalyst temperature is equal to or higher than a certain temperature (hereinafter, this temperature is referred to as “ predetermined deposition temperature”) and the internal atmosphere of the catalyst is a reducing atmosphere, the composite oxide It has the property to precipitate from. Therefore, the composite oxide dissolves the active element when the catalyst temperature is the predetermined solid solution temperature and the internal atmosphere of the catalyst is the oxidizing atmosphere, and the catalyst temperature is equal to or higher than the predetermined precipitation temperature and the internal temperature of the catalyst. It is a complex oxide made of a material having the property of precipitating active elements when the atmosphere is a reducing atmosphere. Therefore, in the catalyst of the first embodiment, when the air-fuel ratio of the exhaust gas flowing into the catalyst when the catalyst temperature is equal to or higher than the predetermined solid solution temperature is an air-fuel ratio leaner than the stoichiometric air-fuel ratio, the catalyst is precipitated from the complex oxide. When the active element is dissolved in the composite oxide and the air-fuel ratio of the exhaust gas flowing into the catalyst is richer than the stoichiometric air-fuel ratio when the catalyst temperature is equal to or higher than the predetermined precipitation temperature, the composite oxidation Active elements that are solid-solved in the material are precipitated from the composite oxide.

Claims (3)

A catalyst for purifying a component in exhaust gas, the catalyst having an active element that activates an oxidation reaction or a reduction reaction of a component in exhaust gas and a composite oxide supporting the active element in an exhaust passage, When the temperature of the catalyst is equal to or higher than a predetermined solid solution temperature which is a predetermined temperature and the internal atmosphere of the catalyst is an oxidizing atmosphere, the active element is dissolved in the composite oxide, and the temperature of the catalyst is In an exhaust gas purification apparatus for an internal combustion engine in which the active element is deposited from the complex oxide when the temperature is equal to or higher than a predetermined deposition temperature, which is a predetermined temperature, and the internal atmosphere of the catalyst is a reducing atmosphere,
The fuel supply stop control when the internal combustion engine can execute a fuel supply stop control for stopping the supply of fuel to the combustion chamber, and the temperature of the catalyst is equal to or higher than an execution prohibition temperature that is a predetermined temperature. And when the fuel supply stop control is allowed to be executed when the temperature of the catalyst is lower than the prohibition temperature, the use degree of the catalyst is not more than a predetermined degree. Is set to a temperature at which the prohibition temperature is lower than its reference temperature,
When the internal combustion engine can execute fuel supply increase control for increasing the amount of fuel supplied to the combustion chamber from a reference amount, and the temperature of the catalyst is equal to or higher than an execution permission temperature that is a predetermined temperature. When the execution of the fuel supply increase control is permitted and the execution of the fuel supply increase control is prohibited when the temperature of the catalyst is lower than the execution permission temperature, the degree of use of the catalyst is predetermined. An exhaust purification device for an internal combustion engine in which the execution permission temperature is set to a temperature higher than the reference temperature while the temperature is below the degree. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
In the case where the internal combustion engine is capable of executing the fuel supply stop control, when the predetermined degree is referred to as a first degree, the usage degree of the catalyst is greater than the first degree and the first degree. An exhaust emission control device for an internal combustion engine, wherein the execution prohibition temperature is set to a temperature higher than a reference temperature while the second execution degree is equal to or less than a second degree that is a predetermined degree greater than the reference temperature. The exhaust gas purification apparatus for an internal combustion engine according to claim 2,
In the case where the internal combustion engine can execute the fuel supply stop control, the activity of the active element dissolved in the composite oxide after the use degree of the catalyst becomes larger than the second degree. The air-fuel ratio of the exhaust gas flowing into the catalyst is leaner than the stoichiometric air-fuel ratio so that the active element solid solubility representing the element ratio is controlled to the target solid solubility that is the target active element solid solubility. An exhaust emission control device for an internal combustion engine, which controls the air-fuel ratio to an air-fuel ratio which is controlled to a fuel ratio or richer than a stoichiometric air-fuel ratio.

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