JP2012225308A - Internal combustion engine control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent emission deterioration by reducing a possibility that an oxygen storage amount of a catalyst reaches zero or maximum.SOLUTION: A control apparatus 70 sets a target air-fuel ratio to a rich air-fuel ratio smaller than a theoretical air-fuel ratio when an oxygen storage state of the catalyst 43 is determined to be an excessive oxygen state, and sets the target air-fuel ratio to a lean air-fuel ratio larger than the theoretical air-fuel ratio when the oxygen storage state is determined to lack oxygen. Moreover, the control apparatus does not start executing an evaporation fuel purge until a predetermined time passes after the target air-fuel ratio is changed from/to the rich air-fuel ratio to/from the lean air-fuel ratio, even when an unsatisfied purge execution request condition is changed into a satisfied one.

Description

  The present invention relates to an internal combustion engine comprising a three-way catalyst disposed in an exhaust passage, an evaporated fuel purge means for introducing evaporated fuel generated in a fuel tank into an intake passage, and a fuel injection valve for supplying fuel. The present invention relates to a control device.

  Conventionally, in order to purify exhaust gas discharged from an internal combustion engine, a three-way catalyst is disposed in the exhaust passage of the engine. As is well known, the three-way catalyst has an oxygen storage function. That is, when the gas flowing into the three-way catalyst (catalyst inflow gas) contains excess oxygen, the three-way catalyst stores the oxygen and purifies NOx. When the catalyst inflow gas contains excessive unburned substances, the three-way catalyst releases the stored oxygen and purifies the unburned substances. Hereinafter, the three-way catalyst is also simply referred to as “catalyst”.

  A conventional air-fuel ratio control device (conventional device) includes an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor that are disposed in the exhaust passage of the engine and upstream and downstream of the catalyst, respectively. In the conventional apparatus, the air / fuel ratio (detected upstream air / fuel ratio) represented by the output value of the upstream air / fuel ratio sensor is matched with the target air / fuel ratio (upstream target air / fuel ratio, target air / fuel ratio of catalyst inflow gas). The air-fuel ratio of the air-fuel mixture supplied to the engine (engine air-fuel ratio) is controlled. This control is also referred to as “main feedback control”. Usually, the target air-fuel ratio is set to the stoichiometric air-fuel ratio.

  Further, the conventional apparatus calculates the sub feedback amount so that the output value of the downstream air fuel ratio sensor matches the “target value corresponding to the theoretical air fuel ratio”, and the upstream target air fuel ratio is substantially determined by the sub feedback amount. The air-fuel ratio of the engine is controlled by correcting to (for example, see Patent Document 1). The air-fuel ratio control using the sub feedback amount is also referred to as “sub feedback control”.

JP 2009-162139 A

  By the way, the applicant particularly stated that “when the oxygen storage capacity of the catalyst is low (for example, when the catalyst is deteriorated or when the capacity of the catalyst is small and the maximum oxygen storage amount is small)”. However, an air-fuel ratio control device capable of maintaining good emissions is being studied. For example, one such air-fuel ratio control device under study determines the state of the catalyst (oxygen storage state) without delay based on the output value of the downstream air-fuel ratio sensor, and based on the determination result, the catalyst inflow The air-fuel ratio of the engine is controlled so that the air-fuel ratio of the gas matches an air-fuel ratio other than the stoichiometric air-fuel ratio. Since the air-fuel ratio control device under consideration forms part of the control device of the present invention, it will be hereinafter also referred to as the present invention device.

  More specifically, the catalyst purifies the exhaust gas with high purification efficiency when the oxygen storage amount is between “0” and “maximum oxygen storage amount Cmax”. Therefore, when the present invention apparatus determines that the state of the catalyst has become an oxygen excess state (lean state) based on the output value Voxs of the downstream side air-fuel ratio sensor, the target air-fuel ratio is set to “a target rich value smaller than the stoichiometric air-fuel ratio”. By setting to “air-fuel ratio”, the oxygen storage amount of the catalyst is reduced. Further, when the control device determines that the state of the catalyst has become an oxygen-deficient state (rich state) based on the output value Voxs of the downstream air-fuel ratio sensor, the control device sets the target air-fuel ratio to “a target lean greater than the stoichiometric air-fuel ratio”. By setting to “air-fuel ratio”, the oxygen storage amount of the catalyst is increased.

  On the other hand, an evaporated fuel purge means is employed in the engine. The evaporated fuel purge means adsorbs the evaporated fuel generated in the fuel tank to the canister, and introduces the evaporated fuel adsorbed to the canister to the intake passage of the engine when a predetermined purge execution requirement condition is satisfied. As a result, the evaporated fuel is burned in the combustion chamber of the engine and then discharged into the atmosphere. Introducing evaporative fuel into the engine intake passage is called evaporative fuel purge.

  The evaporated fuel purge is one of the factors that change the air-fuel ratio of the engine. The main feedback control described above is also executed during the period in which the evaporated fuel purge is being executed. However, the concentration of the evaporated fuel introduced into the intake passage is not constant over time.

  Therefore, even when the main feedback control is executed, when the evaporated fuel purge is executed (see time t1 and after in FIG. 5), when the evaporated fuel purge is not executed (see FIG. 5). Compared with the time before time t1), the fluctuation range of the air-fuel ratio (upstream air-fuel ratio) flowing into the catalyst becomes larger. In particular, due to the control delay of the main feedback control, the fluctuation of the air-fuel ratio in the period immediately after the evaporative fuel purge is started (time t1 to time t2 in FIG. 5) is the subsequent period (after time t2 in FIG. 5). ) Is larger than the fluctuation of the air-fuel ratio. That is, when the fuel vapor purge is started, the fluctuation range of the upstream air-fuel ratio during a period (time t1 to time t2 in FIG. 5) from when the effect starts to appear in the upstream air-fuel ratio until a predetermined time elapses. Becomes very large.

  Therefore, when the oxygen storage amount of the catalyst is “0” or close to the maximum oxygen storage amount Cmax, if the influence of the evaporated fuel purge appears in the upstream air-fuel ratio, the oxygen storage amount of the catalyst is “0” or the maximum oxygen storage amount. There is a risk that Cmax will be reached and the emission will be worsened.

  Therefore, one of the objects of the present invention is to further reduce the possibility that the oxygen storage amount of the catalyst reaches “0” or the maximum oxygen storage amount Cmax by limiting the timing of starting the evaporated fuel purge. Therefore, an object of the present invention is to provide a control device for an internal combustion engine that can prevent deterioration of emissions.

  An internal combustion engine control apparatus (invention apparatus) according to the present invention includes a catalyst, a downstream air-fuel ratio sensor, catalyst state determination means, target air-fuel ratio setting means, fuel injection valve, fuel injection control means, and evaporation. And a fuel purge means.

The catalyst is disposed in an exhaust passage of the internal combustion engine. The catalyst is a three-way catalyst having an oxygen storage function.
The downstream air-fuel ratio sensor is disposed in the exhaust passage and downstream of the catalyst.

The catalyst state determination means determines whether the oxygen storage state of the catalyst is an oxygen excess state (lean state) or an oxygen shortage state (rich state) based on the output value of the downstream air-fuel ratio sensor. .
The oxygen excess state is a state in which the amount of oxygen stored in the catalyst should be reduced because the amount of oxygen stored in the catalyst is excessive for the catalyst (which tends to be excessive). is there.
The oxygen-deficient state is a state in which the amount of oxygen stored in the catalyst should be increased because the amount of oxygen stored in the catalyst is insufficient (which tends to be insufficient).

  For example, the catalyst state determination means determines that the output value of the downstream air-fuel ratio sensor is greater than the stoichiometric air-fuel ratio from a value (rich corresponding value) corresponding to “a rich air-fuel ratio that is an air-fuel ratio smaller than the stoichiometric air-fuel ratio”. The amount of change in the output value per unit time is a predetermined value (rich determination threshold value) when it is changing toward a value corresponding to the “lean air-fuel ratio that is the air-fuel ratio” (lean-corresponding value). When it becomes larger than that, it is determined that the state of the catalyst has become an oxygen-excess state.

  On the other hand, the catalyst state determination means is a case where the output value of the downstream air-fuel ratio sensor changes from the lean corresponding value to the rich corresponding value, and the amount of change in the output value per unit time is large. When is larger than a predetermined value (rich determination threshold value), it is determined that the state of the catalyst has become an oxygen-deficient state.

  Alternatively, the catalyst state determination unit compares the output value of the downstream air-fuel ratio sensor with the oxygen excess state determination threshold value in a state where the catalyst state is determined to be an oxygen deficient state, and based on the comparison, It may be determined that this state has become an oxygen-excess state. Further, the catalyst state determination means compares the output value of the downstream air-fuel ratio sensor with the oxygen deficiency state determination threshold value in a state where the catalyst state is determined to be an oxygen excess state, and based on the comparison, It may be determined that this state has become an oxygen-deficient state.

  When the oxygen storage state is determined to be the oxygen excess state, the target air-fuel ratio setting means sets the “target air-fuel ratio that is the target value of the air-fuel ratio of the gas flowing into the catalyst” as “the stoichiometric air-fuel ratio”. Smaller than the target rich air-fuel ratio. Further, the target air-fuel ratio setting means sets the target air-fuel ratio to “a target lean air-fuel ratio larger than the theoretical air-fuel ratio” when it is determined that the oxygen storage state is the oxygen-deficient state.

The fuel injection valve injects fuel to the engine.
The fuel injection control means determines a fuel injection amount which is “amount of fuel injected from the fuel injection valve” according to “the set target air-fuel ratio”. Further, the fuel injection control means injects fuel of the determined fuel injection amount from the fuel injection valve.
The evaporative fuel purge means performs an evaporative fuel purge that introduces the evaporative fuel generated in the “fuel tank that stores fuel supplied to the fuel injection valve” into the intake passage of the engine as a “predetermined purge execution requirement condition”. Executes when is true.

Further, the evaporated fuel purge means includes:
The target air-fuel ratio is changed from the target rich air-fuel ratio to the target lean air-fuel ratio, and the target air-fuel ratio is changed from the target lean air-fuel ratio to the target rich air-fuel ratio. The evaporative fuel purge is executed even when the purge execution request condition is satisfied during a period until a predetermined time elapses from at least one of the target air-fuel ratio lean-rich change time, which is the time when the target is changed to Configured to not start.

  The target air-fuel ratio rich-lean change time is a time when the oxygen storage amount of the catalyst approaches “0”. Accordingly, the oxygen storage amount of the catalyst is close to “0” in a period from when the target air-fuel ratio rich lean is changed until a predetermined time elapses. Therefore, if a change in the air-fuel ratio due to the start of the evaporated fuel purge appears in the upstream air-fuel ratio in the period from the time when the target air-fuel ratio rich lean is changed until the predetermined time elapses, the oxygen storage amount of the catalyst becomes “ The possibility of reaching “0” increases.

  On the other hand, according to the above configuration, it is possible to prevent the execution of the evaporated fuel purge from being started for a period from when the target air-fuel ratio rich lean is changed until a predetermined time elapses. In other words, after the time when the predetermined time has elapsed since the target air-fuel ratio rich-lean change time, that is, after the time when the oxygen storage amount of the catalyst has increased to some extent, the air-fuel ratio due to the start of the evaporated fuel purge. The fluctuation can appear in the upstream air-fuel ratio. Therefore, since the possibility that the oxygen storage amount of the catalyst reaches “0” can be reduced, the possibility that the emission deteriorates can be reduced.

  Similarly, the target air-fuel ratio lean rich change time is a time when the oxygen storage amount of the catalyst approaches the maximum oxygen storage amount Cmax. Therefore, the oxygen storage amount of the catalyst is close to the maximum oxygen storage amount Cmax during a period from when the target air-fuel ratio lean rich is changed until a predetermined time elapses. Therefore, if the fluctuation of the air-fuel ratio due to the start of the evaporated fuel purge appears in the upstream air-fuel ratio in the period from the target air-fuel ratio lean rich change time until the predetermined time elapses, the oxygen storage amount of the catalyst is maximized. The possibility of reaching the oxygen storage amount Cmax increases.

  On the other hand, according to the above configuration, it is possible to prevent the execution of the evaporated fuel purge from being started for a period from when the target air-fuel ratio lean / rich change is performed until a predetermined time elapses. In other words, after the predetermined time has elapsed since the target air-fuel ratio lean-rich change time, that is, after the time when the oxygen storage amount of the catalyst has decreased to some extent, the air-fuel ratio caused by starting the evaporated fuel purge is reduced. The fluctuation can appear in the upstream air-fuel ratio. Therefore, since the possibility that the oxygen storage amount of the catalyst reaches the maximum oxygen storage amount Cmax can be reduced, the possibility that the emission deteriorates can be reduced.

in this case,
The evaporated fuel purge means includes
It is configured not to start the execution of the evaporated fuel purge in a period after the lean rich change, which is a period from the target air-fuel ratio lean rich change time to the passage of the first predetermined time as the predetermined time,
A first time (target air-fuel ratio lean continuation time) from the target air-fuel ratio rich-lean change time to the target air-fuel ratio lean-rich change time subsequent to the target air-fuel ratio rich-lean change time is correlated with at least the intake air amount of the engine Based on a value having
Predicting the next target air-fuel ratio lean rich change time point that is to come next based on the estimated first time;
It is preferable that the execution of the evaporated fuel purge is not started during a period from a time point before a predicted target air-fuel ratio lean-rich change time to a time point after the lean-rich change period.

  According to this, since the execution of the evaporated fuel purge is not started during a period from a time point before a predicted target air-fuel ratio lean-rich change time to a time point after the lean-rich change period, When the occlusion amount is close to the maximum oxygen occlusion amount Cmax, fluctuations in the air-fuel ratio caused by starting the evaporated fuel purge do not appear in the upstream air-fuel ratio. Therefore, it is possible to reduce the possibility of deterioration of emission due to the oxygen storage amount reaching the maximum oxygen storage amount Cmax.

The evaporated fuel purge means includes:
It is configured not to start the execution of the evaporated fuel purge in a period after the rich lean change, which is a period from the time when the target air-fuel ratio rich lean is changed until the second predetermined time as the predetermined time elapses.
A second time (target rich air-fuel ratio duration) from the target air-fuel ratio lean rich change time to the target air-fuel ratio rich lean change time following the target air-fuel ratio lean rich change time is correlated with at least the intake air amount of the engine Based on a value having
Predicting the next target air-fuel ratio rich lean change time to arrive next based on the estimated second time;
It is preferable that the evaporative fuel purge is not started during a period from a time before the predicted target air-fuel ratio rich lean change time to a time point after the rich lean change period.

  According to this, since the execution of the evaporative fuel purge is not started during a period from a time point a predetermined time before the predicted target air-fuel ratio rich-lean change time point to an elapsed time point after the rich-lean change time period, When the occlusion amount is close to “0”, the fluctuation of the air-fuel ratio due to the start of the evaporated fuel purge does not appear in the upstream air-fuel ratio. Therefore, it is possible to reduce the possibility of emission deterioration due to the oxygen storage amount reaching “0”.

  Other objects, other features and attendant advantages of the apparatus of the present invention will be readily understood from the description of each embodiment of the present invention described with reference to the following drawings.

1 is a schematic plan view of an internal combustion engine to which a control device according to each embodiment of the present invention is applied. 2 is a graph showing the relationship between the air-fuel ratio (upstream air-fuel ratio) of gas flowing into the catalyst shown in FIG. 1 and the output value of the upstream air-fuel ratio sensor shown in FIG. 2 is a graph showing the relationship between the air-fuel ratio (downstream air-fuel ratio) of gas flowing out from the catalyst shown in FIG. 1 and the output value of the downstream air-fuel ratio sensor shown in FIG. It is a time chart for demonstrating the action | operation of the control apparatus (1st control apparatus) which concerns on 1st Embodiment of this invention. It is the figure which showed the mode of the change of the upstream air-fuel ratio before and after evaporative fuel purge is started. It is the flowchart which showed the routine which CPU of a 1st control apparatus performs. It is the flowchart which showed the routine which CPU of a 1st control apparatus performs. It is the flowchart which showed the routine which CPU of a 1st control apparatus performs. It is the flowchart which showed the routine which CPU of a 1st control apparatus performs. It is a time chart for demonstrating the action | operation of the control apparatus (2nd control apparatus) which concerns on 2nd Embodiment of this invention. It is the flowchart which showed the routine which CPU of a 2nd control apparatus performs. 3 is a time chart showing the relationship between the upstream air-fuel ratio and the oxygen storage amount of a catalyst. 6 is a map showing a relationship among a fluctuation range of an upstream air-fuel ratio, an intake air amount, and a target air-fuel ratio switching cycle. It is the figure which showed the mode of the change of the upstream air-fuel ratio before and after evaporative fuel purge is started. It is the flowchart which showed the routine which CPU of the control apparatus (3rd control apparatus) concerning 3rd Embodiment of this invention performs. It is the figure which showed the mode of the change of the upstream air-fuel ratio before and after evaporative fuel purge is started. It is the flowchart which showed the routine which CPU of the control apparatus (4th control apparatus) which concerns on 4th Embodiment of this invention performs.

  Hereinafter, a control device for an internal combustion engine (hereinafter also simply referred to as “control device”) according to each embodiment of the present invention will be described with reference to the drawings. This control device is a part of an air-fuel ratio control device that controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (the air-fuel ratio of the engine). Further, the fuel injection amount control device that controls the fuel injection amount and the evaporation It is also a part of an evaporative fuel purge amount control device for controlling the fuel purge amount.

<First Embodiment>
(Constitution)
FIG. 1 shows a system in which a control device according to the first embodiment (hereinafter also referred to as “first control device”) is applied to a 4-cycle, spark ignition type, multi-cylinder (in-line 4-cylinder) internal combustion engine 10. The schematic structure of is shown.

  The internal combustion engine 10 includes an engine main body 20, an intake system 30, an exhaust system 40, and an evaporated fuel supply system 50.

  The engine body portion 20 includes a cylinder block portion and a cylinder head portion. The engine body 20 includes a plurality of cylinders (combustion chambers) 21. Each cylinder communicates with an “intake port and exhaust port” (not shown). A communicating portion between the intake port and the combustion chamber 21 is opened and closed by an intake valve (not shown). A communicating portion between the exhaust port and the combustion chamber 21 is opened and closed by an exhaust valve (not shown). Each combustion chamber 21 is provided with a spark plug (not shown).

  The intake system 30 includes an intake manifold 31, an intake pipe 32, a plurality of fuel injection valves 33, and a throttle valve 34.

  The intake manifold 31 includes a plurality of branch portions 31a and a surge tank 31b. One end of each of the plurality of branch portions 31a is connected to each of the plurality of intake ports. The other ends of the plurality of branch portions 31a are connected to the surge tank 31b.

  One end of the intake pipe 32 is connected to the surge tank 31b. An air filter (not shown) is disposed at the other end of the intake pipe 32.

  One fuel injection valve 33 is provided for each cylinder (combustion chamber) 21. The fuel injection valve 33 is provided at the intake port. That is, each of the plurality of cylinders includes a fuel injection valve 33 that supplies fuel independently of the other cylinders. The fuel injection valve 33 responds to the injection instruction signal, and when it is normal, “the fuel of the indicated fuel injection amount included in the injection instruction signal” in the intake port (therefore, the cylinder 21 corresponding to the fuel injection valve 33). It is supposed to be injected into.

  More specifically, fuel is supplied to the fuel injection valve 33 via a fuel supply pipe 57 connected to a fuel tank 51 described later. The pressure of the fuel supplied to the fuel injection valve 33 is controlled by a pressure regulator (not shown) so that the differential pressure between the pressure of the fuel and the pressure in the intake port becomes constant. The fuel injection valve 33 is opened for a time corresponding to the command fuel injection amount. Therefore, if the fuel injection valve 33 is normal, the fuel injection valve 33 injects an amount of fuel equal to the indicated fuel injection amount.

  The throttle valve 34 is rotatably disposed in the intake pipe 32. The throttle valve 34 has a variable opening cross-sectional area of the intake passage. The throttle valve 34 is rotationally driven in the intake pipe 32 by a throttle valve actuator (not shown).

  The exhaust system 40 includes an exhaust manifold 41, an exhaust pipe 42, an upstream catalyst 43 disposed in the exhaust pipe 42, and a “downstream catalyst (not shown) disposed in the exhaust pipe 42 downstream of the upstream catalyst 43. Is provided.

  The exhaust manifold 41 includes a plurality of branch portions 41a and a collecting portion 41b. One end of each of the plurality of branch portions 41a is connected to each of the plurality of exhaust ports. The other ends of the plurality of branch portions 41a are gathered in the gathering portion 41b. The collecting portion 41b is also referred to as an exhaust collecting portion HK because exhaust gas discharged from a plurality of (two or more, four in this example) cylinders gathers.

  The exhaust pipe 42 is connected to the collecting portion 41b. The exhaust port, the exhaust manifold 41 and the exhaust pipe 42 constitute an exhaust passage.

Each of the upstream side catalyst 43 and the downstream side catalyst is a so-called three-way catalyst device (exhaust purification catalyst) carrying an active component made of a noble metal (catalyst substance) such as platinum, rhodium and palladium. Each catalyst oxidizes unburned components such as HC, CO, and H ₂ when the air-fuel ratio of the gas flowing into each catalyst is “the air-fuel ratio within the window of the three-way catalyst (for example, the theoretical air-fuel ratio)”. In addition, it has a function of reducing nitrogen oxides (NOx). This function is also called a catalyst function.

Further, each catalyst has an oxygen storage function for storing (storing) oxygen. That is, each catalyst occludes oxygen and purifies NOx when excessive oxygen is contained in the gas flowing into the catalyst (catalyst inflow gas). When the catalyst inflow gas contains excessive unburned substances, each catalyst releases the stored oxygen and purifies the unburned substances. This oxygen storage function is provided by an oxygen storage material such as ceria (CeO ₂ ) supported on the catalyst. Each catalyst can purify unburned components and nitrogen oxides even if the air-fuel ratio shifts from the stoichiometric air-fuel ratio due to the oxygen storage function. That is, the window width is expanded by the oxygen storage function.

  The evaporated fuel supply system 50 includes a fuel tank 51, a canister 52, a vapor collection pipe 53, a purge flow path pipe 54, a purge control valve 55, and a fuel pump 56.

  The fuel tank 51 stores fuel that is injected and supplied from the fuel injection valve 33 to the engine 10.

  The canister 52 is a “well-known charcoal canister” that stores the evaporated fuel (evaporated fuel gas) generated in the fuel tank 51. The canister 52 includes a housing in which a tank port 52a, a purge port 52b, and an atmospheric port 52c exposed to the atmosphere are formed. The canister 52 accommodates (holds) an adsorbent (activated carbon or the like) 52d for adsorbing evaporated fuel in the casing.

  One end of the vapor collection pipe 53 is connected to the upper part of the fuel tank 51, and the other end of the vapor collection pipe 53 is connected to the tank port 52a. The vapor collection pipe 53 is a pipe for introducing the evaporated fuel generated in the fuel tank 51 from the fuel tank 51 to the canister 52.

  One end of the purge passage pipe 54 is connected to the purge port 52b, and the other end of the purge passage pipe 54 is connected to the surge tank 31b (that is, the intake passage downstream from the throttle valve 34). The purge flow path pipe 54 is a pipe for introducing the evaporated fuel desorbed from the adsorbent 52d of the canister 52 into the surge tank 31b. The vapor collection pipe 53 and the purge flow path pipe 54 constitute a purge passage (purge passage portion).

  The purge control valve 55 is interposed in the purge flow path pipe 54. The purge control valve 55 is configured to change the passage cross-sectional area of the purge passage pipe 54 by adjusting the opening degree (valve opening period) by a drive signal representing the duty ratio DPG which is an instruction signal. The purge control valve 55 is configured to completely close the purge flow path pipe 54 when the duty ratio DPG is “0”. Further, when the duty ratio DPG is larger than “0”, the purge control valve 55 is opened so that the passage sectional area becomes larger as the duty ratio DPG is larger.

  The fuel pump 56 supplies the fuel stored in the fuel tank 51 to the fuel injection valve 33 through the fuel supply pipe 57.

  In the evaporated fuel supply system 50 configured as described above, when the purge control valve 55 is completely closed, the evaporated fuel generated in the fuel tank 51 is occluded in the canister 52. When the purge control valve 55 is opened, the evaporated fuel occluded in the canister 52 is discharged to the surge tank 31b (the intake passage downstream of the throttle valve 34) through the purge passage pipe 54, and the combustion chamber 21 (engine 10). ). That is, when the purge control valve 55 is open, the fuel vapor purge (also referred to as “vapor fuel gas purge” or “purge”) is performed.

  This system includes a hot-wire air flow meter 61, a throttle position sensor 62, a water temperature sensor 63, a crank position sensor 64, an intake cam position sensor 65, an upstream air-fuel ratio sensor 66, a downstream air-fuel ratio sensor 67, and an accelerator opening sensor. 68.

  The air flow meter 61 outputs a signal corresponding to the mass flow rate (intake air flow rate) Ga of intake air flowing through the intake pipe 32. That is, the intake air amount Ga represents the intake air amount taken into the engine 10 per unit time.

  The throttle position sensor 62 detects the opening (throttle valve opening) of the throttle valve 34 and outputs a signal representing the throttle valve opening TA.

  The water temperature sensor 63 detects the temperature of the cooling water of the engine 10 and outputs a signal indicating the cooling water temperature THW. The coolant temperature THW is an operating state index amount that represents the warm-up state of the engine 10 (temperature of the engine 10).

  The crank position sensor 64 outputs a signal having a narrow pulse every time the crankshaft rotates 10 ° and a wide pulse every time the crankshaft rotates 360 °. This signal is converted into an engine speed NE by an electric control device 70 described later.

  The intake cam position sensor 65 outputs one pulse every time the intake cam shaft rotates 90 degrees, 90 degrees, and 180 degrees from a predetermined angle. The electric control device 70 described later acquires an absolute crank angle CA based on the compression top dead center of the reference cylinder (for example, the first cylinder) based on signals from the crank position sensor 64 and the intake cam position sensor 65. It has become. This absolute crank angle CA is set to “0 ° crank angle” at the compression top dead center of the reference cylinder, and increases to a 720 ° crank angle according to the rotation angle of the crankshaft. Set to

  The upstream air-fuel ratio sensor 66 is disposed in “one of the exhaust manifold 41 and the exhaust pipe 42” at a position between the collecting portion 41 b (exhaust collecting portion HK) of the exhaust manifold 41 and the upstream catalyst 43. .

  The upstream air-fuel ratio sensor 66 is disclosed in, for example, “Limit current type wide area air-fuel ratio including diffusion resistance layer” disclosed in JP-A-11-72473, JP-A-2000-65782, JP-A-2004-69547, and the like. Sensor ".

  The upstream air-fuel ratio sensor 66 corresponds to the air-fuel ratio of the exhaust gas flowing through the position where the upstream air-fuel ratio sensor 66 is disposed (the air-fuel ratio of the “catalyst inflow gas” that is the gas flowing into the catalyst 43, the upstream air-fuel ratio abyfs). Output the output value Vabyfs. As shown in FIG. 2, the output value Vabyfs increases as the air-fuel ratio (upstream air-fuel ratio abyfs) of the catalyst inflow gas increases (as the air-fuel ratio becomes leaner).

  The electric control device 70 stores an air-fuel ratio conversion table (map) Mapabyfs that defines the relationship shown in FIG. 2 between the output value Vabyfs and the upstream air-fuel ratio abyfs. The electric control device 70 detects the actual upstream air-fuel ratio abyfs (obtains the detected upstream air-fuel ratio abyfs) by applying the output value Vabyfs to the air-fuel ratio conversion table Mapabyfs.

  Referring to FIG. 1 again, the downstream air-fuel ratio sensor 67 is disposed in the exhaust pipe 42. The downstream air-fuel ratio sensor 67 is disposed downstream of the upstream catalyst 43 and upstream of the downstream catalyst (that is, the exhaust passage between the upstream catalyst 43 and the downstream catalyst). It is. The downstream air-fuel ratio sensor 67 is a known electromotive force type oxygen concentration sensor (a known concentration cell type oxygen concentration sensor using a solid electrolyte such as stabilized zirconia). The downstream air-fuel ratio sensor 67 generates an output value Voxs corresponding to the air-fuel ratio of the gas to be detected, which is a gas passing through a portion of the exhaust passage where the downstream air-fuel ratio sensor 67 is disposed. ing. In other words, the output value Voxs is a value corresponding to the air-fuel ratio of the gas flowing out from the upstream catalyst 43 and flowing into the downstream catalyst.

  As shown in FIG. 3, the output value Voxs becomes the maximum output value max (for example, about 0.9 V to 1.0 V) when the air-fuel ratio of the detected gas is richer than the stoichiometric air-fuel ratio. The maximum output value max is a value corresponding to a rich air-fuel ratio that is an air-fuel ratio smaller than the theoretical air-fuel ratio, and is also referred to as a rich-corresponding value. The output value Voxs becomes the minimum output value min (for example, about 0.1 V to 0 V) when the air-fuel ratio of the gas to be detected is leaner than the stoichiometric air-fuel ratio. The minimum output value min is a value corresponding to a lean air-fuel ratio that is an air-fuel ratio larger than the stoichiometric air-fuel ratio, and is also referred to as a lean-corresponding value.

  Further, the output value Voxs is a voltage Vst (median value Vmid, intermediate voltage Vst, for example, about 0.5 V) between the maximum output value max and the minimum output value min when the air-fuel ratio of the gas to be detected is the stoichiometric air-fuel ratio. ) The output value Voxs suddenly changes from the maximum output value max to the minimum output value min when the air-fuel ratio of the gas to be detected changes from an air-fuel ratio richer than the stoichiometric air-fuel ratio to a lean air-fuel ratio. Similarly, the output value Voxs suddenly changes from the minimum output value min to the maximum output value max when the air-fuel ratio of the detected gas changes from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to a rich air-fuel ratio.

  The accelerator opening sensor 68 shown in FIG. 1 outputs a signal representing the operation amount Accp (accelerator pedal operation amount, accelerator pedal AP opening amount) of the accelerator pedal AP operated by the driver. The accelerator pedal operation amount Accp increases as the operation amount of the accelerator pedal AP increases.

  The electric control device 70 includes: “a CPU, a program executed by the CPU, a ROM in which tables (maps, functions), constants, and the like are stored in advance, a RAM in which the CPU temporarily stores data as necessary, and a backup RAM (B− RAM), an interface including an AD converter, and the like ".

  The backup RAM is supplied with electric power from a battery mounted on the vehicle regardless of the position of an ignition key switch (not shown) of the vehicle on which the engine 10 is mounted (any one of an off position, a start position, an on position, etc.). It is like that. When receiving power from the battery, the backup RAM stores data according to an instruction from the CPU (data is written) and holds (stores) the data so that the data can be read. Therefore, the backup RAM can hold data even when the operation of the engine 10 is stopped.

  The backup RAM cannot retain data when the power supply from the battery is interrupted, for example, when the battery is removed from the vehicle. Therefore, when the power supply to the backup RAM is resumed, the CPU initializes (sets to the default value) data to be held in the backup RAM. The backup RAM may be a readable / writable nonvolatile memory such as an EEPROM.

  The electric control device 70 is connected to the above-described sensors and the like, and supplies signals from these sensors to the CPU. Furthermore, the electric control device 70 is responsive to an instruction from the CPU to provide a spark plug (actually an igniter) provided for each cylinder, a fuel injection valve 33 provided for each cylinder, a purge control valve. 55, and a drive signal (instruction signal) is sent to a throttle valve actuator or the like.

  The electric control device 70 sends an instruction signal to the throttle valve actuator so that the throttle valve opening TA increases as the acquired accelerator pedal operation amount Accp increases. That is, the electric control device 70 changes the opening degree of the “throttle valve 34 disposed in the intake passage of the engine 10” according to the acceleration operation amount (accelerator pedal operation amount Accp) of the engine 10 changed by the driver. Throttle valve drive means is provided.

(Outline of operation of first control device)
Based on the output value Voxs of the downstream air-fuel ratio sensor 67, the first control device determines whether the state of the catalyst 43 (the state of oxygen storage of the catalyst 43, hereinafter also referred to as “catalyst state”) is an oxygen excess state and It is determined whether the state is an oxygen deficient state.

The oxygen excess state is also referred to as a lean state. The oxygen excess state is a state in which the oxygen storage amount of the catalyst 43 is close to the maximum oxygen storage amount Cmax. In other words, the oxygen excess state is a state in which the oxygen storage amount of the catalyst 43 should be reduced.
The oxygen-deficient state is also called a rich state. The oxygen-deficient state is a state where the oxygen storage amount of the catalyst 43 is a value close to “0”. In other words, the oxygen-deficient state is a state where the oxygen storage amount of the catalyst 43 should be increased.

  However, if the first control device determines that the catalyst state is an oxygen-deficient state, the first control device determines that the catalyst state is an oxygen-deficient state until it is next determined that the catalyst state is an oxygen-excess state. Similarly, when it is determined that the catalyst state is an oxygen-excess state, the first control device determines that the catalyst state is an oxygen-excess state until it is determined that the catalyst state is next an oxygen-deficient state.

  More specifically, the first control device is a case where it is determined that the state of the catalyst 43 is an oxygen excess state, and the change amount ΔVoxs per predetermined time of the output value Voxs is a positive value. When the magnitude | ΔVoxs | becomes larger than the rich determination threshold dRichth, it is determined that the state of the catalyst 43 has become an oxygen-deficient state. At this time, the first control device sets the value of the catalyst lean state display flag XCCROLean to “0”.

  Furthermore, when it is determined that the state of the catalyst 43 is in an oxygen-deficient state, the first control device has a negative change amount ΔVoxs and the magnitude | ΔVoxs | is less than the lean determination threshold dLeanth. Is also increased, it is determined that the state of the catalyst 43 has become an oxygen-excess state. At this time, the first control device sets the value of the catalyst lean state display flag XCCROLean to “1”.

  In the first control device, when it is determined that the state of the catalyst 43 is an excess oxygen state, and the output value Voxs is greater than the rich determination threshold VRichth, the state of the catalyst 43 is insufficient for oxygen. It may be determined that the state has been reached. Further, the first control device is a case where the state of the catalyst 43 is determined to be an oxygen-deficient state, and when the output value Voxs is smaller than the lean determination threshold value VLeanth, the state of the catalyst 43 is excessive oxygen. It may be determined that the state has been reached.

  When the catalyst 43 is in an oxygen-deficient state, excess oxygen should be allowed to flow into the catalyst 43. Therefore, the target air-fuel ratio abyfr (required air-fuel ratio, upstream target air-fuel ratio abyfr) that is the target value of the catalyst inflow gas. ) Should be set to “a target lean air-fuel ratio afLean larger than the stoichiometric air-fuel ratio”. Therefore, when the first control device determines that the state of the catalyst 43 is in an oxygen-deficient state, the first control device sets the target air-fuel ratio abyfr to the target lean air-fuel ratio afLean (time t1 to time t3, time t5 in FIG. 4). -See time t7).

  When the state of the catalyst 43 is an oxygen-excess state, excess unburned material should flow into the catalyst 43. Therefore, the target air-fuel ratio abyfr of the catalyst inflow gas is “a target rich air-fuel ratio afRich smaller than the stoichiometric air-fuel ratio”. Should be set. Therefore, when the first control device determines that the state of the catalyst 43 is an oxygen-excess state, the first control device sets the target air-fuel ratio abyfr to the target rich air-fuel ratio afRich (time t3 to time t5, time t7 in FIG. 4). -See time t9.).

  Hereinafter, the time when the target air-fuel ratio abyfr is changed from the target rich air-fuel ratio afRich to the target lean air-fuel ratio afLean (time t1, t5, t9 in FIG. 4) is referred to as “target air-fuel ratio rich-lean change time”. Further, the time point (time t3, t7 in FIG. 4) when the target air-fuel ratio abyfr is changed from the target lean air-fuel ratio afLean to the target rich air-fuel ratio afRich is referred to as “target air-fuel ratio lean rich change time”.

  On the other hand, when the predetermined purge execution request condition is not established, the first control device closes the purge control valve 55 and does not execute the evaporated fuel purge. Further, the first control device opens the purge control valve 55 and introduces the evaporated fuel into the intake passage, except in the following cases, when the purge execution request condition is changed from the state not satisfied to the state satisfied. (That is, the fuel vapor purge is started.)

  By the way, as shown after time t1 in FIG. 5, when the evaporated fuel purge is started and the influence of the evaporated fuel purge appears in the upstream air-fuel ratio abyfs, the amplitude of the upstream air-fuel ratio abyfs increases. This is because the concentration of the evaporated fuel contained in the gas introduced into the intake passage is not constant. Further, as understood from a comparison between time t1 to time t2 in FIG. 5 and after time t2, immediately after the influence of the evaporated fuel purge starts to appear in the upstream air-fuel ratio abyfs, the upstream air-fuel ratio abyfs is changed. The fluctuation range becomes large. This is due to a control delay of the main feedback control.

  Further, as shown after time t2 in FIG. 5, if the fuel vapor purge is continued, the amplitude of the upstream air-fuel ratio abyfs starts to appear in the upstream air-fuel ratio abyfs. It becomes smaller and almost constant than immediately after. Further, when the evaporated fuel purge is continued, the output value Voxs of the downstream air-fuel ratio sensor 67 reflects the influence of the evaporated fuel purge. In other words, if the fuel vapor purge is continued, the output value Voxs of the downstream air-fuel ratio sensor 67 is a value reflecting the catalyst state. Accordingly, even if the fuel vapor purge is continued, the possibility that the emission will deteriorate is low.

  Therefore, in the first control device, the time point when the purge execution request condition is not satisfied is changed to the satisfied state is within a period from when the target air-fuel ratio rich lean is changed until the first predetermined time Δta1 elapses. In this case, it is prohibited to start the fuel vapor purge (see time t1 to t2, time t5 to t6, time t9 to t10 in FIG. 4). If the purge execution request condition is satisfied when the first predetermined time Δta1 has elapsed from the time when the target air-fuel ratio rich lean is changed, the first control device starts the evaporated fuel purge.

  According to this, the evaporated fuel purge is started after the first predetermined time Δta1 has elapsed since the target air-fuel ratio rich lean change time, and the influence of the start of the evaporated fuel purge appears in the upstream air-fuel ratio abyfs. At the time when the first predetermined time Δta1 has elapsed from the time when the target air-fuel ratio rich lean is changed, the oxygen storage amount of the catalyst 43 is a value deviating from “0” (value D1 in FIG. 4). Further, the time when the influence of starting the evaporated fuel purge appears in the upstream air-fuel ratio abyfs is delayed from the time when the first predetermined time Δta1 has elapsed from the time when the target air-fuel ratio rich lean is changed. Accordingly, when the effect of starting the evaporated fuel purge appears in the upstream air-fuel ratio abyfs, the oxygen storage amount of the catalyst 43 is sufficiently deviated from “0”, so the effect of starting the evaporated fuel purge is affected. Even if it appears in the upstream air-fuel ratio abyfs, the possibility that the oxygen storage amount of the catalyst 43 reaches “0” is low. As a result, the “possibility of emission deterioration due to the evaporated fuel gas purge” can be reduced.

  Further, in the first control apparatus, the time point when the purge execution request condition is not satisfied is changed to the satisfied state is within a period from when the target air-fuel ratio lean rich change is elapsed until the second predetermined time Δta2 elapses. In this case, it is prohibited to start the fuel vapor purge (see times t3 to t4 and times t7 to t8 in FIG. 4). The first control device starts the evaporated fuel purge if the purge execution request condition is satisfied when the second predetermined time Δta2 has elapsed from the target air-fuel ratio lean rich change time.

  According to this, the evaporated fuel purge is started after the second predetermined time Δta2 has elapsed from the target air-fuel ratio lean rich change time, and the influence of the start of the evaporated fuel purge appears in the upstream air-fuel ratio abyfs. When the second predetermined time Δta2 has elapsed since the target air-fuel ratio rich-lean change time, the oxygen storage amount of the catalyst 43 deviates from the maximum oxygen storage amount Cmax (the value D2 in FIG. 4 is smaller than the maximum oxygen storage amount Cmax). Value). Furthermore, the time when the effect of starting the evaporated fuel purge appears in the upstream air-fuel ratio abyfs is delayed from the time when the second predetermined time Δta2 has elapsed from the time when the target air-fuel ratio lean rich change. Therefore, when the influence of starting the evaporated fuel purge appears in the upstream air-fuel ratio abyfs, the oxygen storage amount of the catalyst 43 is sufficiently deviated from the maximum oxygen storage amount Cmax, so the evaporated fuel purge is started. Even if the influence appears in the upstream air-fuel ratio abyfs, the possibility that the oxygen storage amount of the catalyst 43 reaches the maximum oxygen storage amount Cmax is low. As a result, the “possibility of emission deterioration due to the evaporated fuel gas purge” can be reduced.

(Actual operation)
Next, the actual operation of the first control device will be described.
<Fuel injection control>
The CPU of the first control device repeatedly executes the fuel injection control routine shown in FIG. 6 for each cylinder every time the crank angle of any cylinder reaches a predetermined crank angle before the intake top dead center. It has become. The predetermined crank angle is, for example, BTDC 90 ° CA (90 ° crank angle before intake top dead center). A cylinder whose crank angle coincides with the predetermined crank angle is also referred to as a “fuel injection cylinder”. The CPU calculates the commanded fuel injection amount (final fuel injection amount) Fi and instructs fuel injection by this fuel injection control routine.

  When the crank angle of an arbitrary cylinder matches the predetermined crank angle before the intake top dead center, the CPU starts the process from step 600, and in step 605, determines whether or not the value of the fuel cut flag XFC is “0”. judge. The value of the fuel cut flag XFC is set to “1” when the fuel cut start condition is satisfied, and is “0” when the fuel cut end condition is satisfied when the value of the fuel cut flag XFC is “1”. Set to The value of the fuel cut flag XFC is further set to “0” in the initial routine. The initial routine is a routine executed by the CPU when the ignition key switch of the vehicle on which the engine 10 is mounted is changed from OFF to ON.

  Assume that the value of the fuel cut flag XFC is “0”. In this case, the CPU makes a “Yes” determination at step 605 to proceed to step 610, where “fuel” is based on “intake air amount Ga, engine rotational speed NE, and lookup table MapMc (Ga, NE)”. The amount of air sucked into the injection cylinder (that is, the in-cylinder intake air amount) Mc) ”is acquired. The in-cylinder intake air amount Mc may be calculated by a well-known air model (a model constructed according to a physical law simulating the behavior of air in the intake passage).

Next, the CPU proceeds to step 615 to determine whether or not the value of the feedback control flag XFB is “1”. The value of the feedback control flag XFB is set to “1” when the air-fuel ratio feedback control condition is satisfied, and is set to “0” when the feedback control condition is not satisfied. The feedback control condition is satisfied when, for example, all the following conditions are satisfied.
(A1) The upstream air-fuel ratio sensor 66 is activated.
(A2) The downstream air-fuel ratio sensor 67 is activated.
(A3) The engine load KL is equal to or less than the threshold load KLfbth.
(A4) The value of the fuel cut flag XFC is “0”.

The load KL is a load factor (filling rate) KL in this example, and is calculated based on the following equation (1). In this equation (1), ρ is the air density (unit is (g / l)), L is the displacement of the engine 10 (unit is (l)), and 4 is the number of cylinders of the engine 10. However, the load KL may be the in-cylinder intake air amount Mc, the throttle valve opening TA, the accelerator pedal operation amount Accp, and the like.

KL = {Mc (k) / (ρ · L / 4)} · 100 (%) (1)

  If the value of the feedback control flag XFB is not “1”, the CPU makes a “No” determination at step 615 to proceed to step 620 to set the target air-fuel ratio abyfr to the theoretical air-fuel ratio stoich (eg, 14.6). To do.

  Next, the CPU sequentially performs the processing from step 625 to step 640 described below, and proceeds to step 695 to end the present routine tentatively.

  Step 625: The CPU calculates the basic fuel injection amount Fbase by dividing the in-cylinder intake air amount Mc by the target air-fuel ratio abyfr. The basic fuel injection amount Fbase is a feed-forward amount of the fuel injection amount necessary for making the air-fuel ratio of the engine coincide with the target air-fuel ratio abyfr.

  Step 630: The CPU reads the main feedback amount KFmain separately calculated by a routine not shown. The main feedback amount KFmain is calculated based on known PID control so that the detected upstream air-fuel ratio abyfs matches the target air-fuel ratio abyfr. Therefore, the main feedback amount KFmain is increased when the detected upstream air-fuel ratio abyfs is larger than the target air-fuel ratio abyfr, and is decreased when the detected upstream air-fuel ratio abyfs is smaller than the target air-fuel ratio abyfr. The main feedback amount KFmain is set to “1” when the value of the feedback control flag XFB is “0”.

  Step 635: The CPU calculates the command fuel injection amount Fi by correcting the basic fuel injection amount Fbase with the main feedback amount KFmain. More specifically, the CPU calculates the command fuel injection amount Fi by multiplying the basic fuel injection amount Fbase by the main feedback amount KFmain.

  Step 640: The CPU sends to the fuel injection valve 33 an injection instruction signal for injecting “the fuel of the indicated fuel injection amount Fi” from the “fuel injection valve 33 provided corresponding to the fuel injection cylinder”. To do.

  As a result, an amount of fuel required to make the air-fuel ratio of the engine coincide with the target air-fuel ratio abyfr is injected from the fuel injection valve 33 of the fuel injection cylinder. That is, Steps 625 to 640 constitute command fuel injection amount control means for “controlling the command fuel injection amount Fi so that the air-fuel ratio of the engine matches the target air-fuel ratio abyfr”.

  On the other hand, if the value of the feedback control flag XFB is “1” at the time when the CPU performs the process of step 615, the CPU makes a “Yes” determination at step 615 to proceed to step 645 to display the catalyst lean state display. It is determined whether or not the value of the flag XCCROLean is “1”. The value of the catalyst lean state display flag XCCROLean is set by a routine described later. Determination of whether the value of the catalyst lean state display flag XCCROLean is “1” is synonymous with determination of whether the value of the rich air-fuel ratio request flag XRichreq is “1”. That is, in step 645, it is determined whether or not the oxygen storage state of the catalyst 43 is an excess oxygen state, in other words, a rich air-fuel ratio request that is an air-fuel ratio request for setting the target air-fuel ratio abyfr to the target rich air-fuel ratio afRich is generated. It is determined whether or not.

  If the value of the catalyst lean state display flag XCCROLean is “1”, the CPU makes a “Yes” determination at step 645 to proceed to step 650, where the target air-fuel ratio abyfr is set to “predetermined target rich air-fuel ratio afRich (theoretical air-fuel ratio). A constant air-fuel ratio smaller than the fuel ratio, for example, 14.2) ”is set. Thereafter, the CPU proceeds to step 625 and subsequent steps. Accordingly, the air-fuel ratio of the engine is made to coincide with the target rich air-fuel ratio afRich.

  In contrast, if the value of the catalyst lean state display flag XCCROLean is “0” at the time when the CPU executes the process of step 645, the CPU makes a “No” determination at step 645 to proceed to step 655. The target air-fuel ratio abyfr is set to “a predetermined target lean air-fuel ratio afLean (a constant air-fuel ratio larger than the theoretical air-fuel ratio, for example, 15.0)”. Thereafter, the CPU proceeds to step 625 and subsequent steps. Accordingly, the air-fuel ratio of the engine is made to coincide with the target lean air-fuel ratio afLean.

  On the other hand, if the value of the fuel cut flag XFC is “1” at the time when the CPU executes the process of step 605, the CPU makes a “No” determination at step 605 to directly proceed to step 695, and this routine Is temporarily terminated. In this case, fuel injection is not executed by the process of step 640, so fuel cut control is executed. That is, the operating state of the engine 10 is a fuel cut operating state.

<Catalyst state determination>
The CPU repeatedly executes the “catalyst state determination routine (required air-fuel ratio determination routine)” shown in the flowchart of FIG. 7 every elapse of a predetermined time ts. Accordingly, when the predetermined timing is reached, the CPU starts the process from step 700 and proceeds to step 710, from “current output value Voxs of downstream air-fuel ratio sensor 67” to “previous output value of downstream air-fuel ratio sensor 67. By subtracting “Voxsold”, the change amount ΔVoxs of the output value Voxs per predetermined time ts (unit time) is calculated. The previous output value Voxsold is a value that is updated in the next step 720, and is the output value Voxs at the time point a predetermined time ts before the current time (the output value Voxs when this routine was executed last time). The change amount ΔVoxs is also referred to as a change rate ΔVoxs. Next, the CPU proceeds to step 720 to store the current output value Voxs as “previous output value Voxsold”.

  Next, the CPU proceeds to step 730 to determine whether or not the value of the catalyst lean state display flag XCCROLean is “1”. The value of the catalyst lean state display flag XCCROLean is set to “1” in the above-described initial routine. Further, the value of the catalyst lean state display flag XCCROLean is determined when it is determined that the state of the catalyst 43 is in an oxygen-deficient state (rich state) based on the output value Voxs of the downstream air-fuel ratio sensor 67, as will be described later. It is set to “0”, and is set to “1” when it is determined that the state of the catalyst 43 is an oxygen excess state (lean state) based on the output value Voxs of the downstream air-fuel ratio sensor 67.

  Assume that the value of the catalyst lean state display flag XCCROLean is “1”. In this case, the CPU makes a “Yes” determination at step 730 to proceed to step 740 to determine whether or not the change speed ΔVoxs is positive. That is, the CPU determines whether or not the output value Voxs is increasing. At this time, if the change speed ΔVoxs is not positive, the CPU makes a “No” determination at step 740 to directly proceed to step 795 to end the present routine tentatively.

  Incidentally, when the value of the catalyst lean state display flag XCCROLean is “1”, the target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich. Therefore, the oxygen storage amount of the catalyst 43 gradually decreases, and unburned substances begin to flow out of the catalyst 43 from a certain point. As a result, the change rate ΔVoxs becomes a positive value. When the change speed ΔVoxs becomes a positive value, the CPU makes a “Yes” determination at step 740 to proceed to step 750 to determine whether or not the magnitude | ΔVoxs | of the change speed ΔVoxs is greater than the rich determination threshold dRichth. To do. At this time, if the magnitude | ΔVoxs | is equal to or smaller than the rich determination threshold dRichth, the CPU makes a “No” determination at step 750 to directly proceed to step 795 to end the present routine tentatively.

  If the magnitude | ΔVoxs | of the change speed ΔVoxs is larger than the rich determination threshold value dRichth at the time when the CPU executes the process of step 750, the CPU determines “Yes” in step 750 and proceeds to step 760. The value of the catalyst lean state display flag XCCROLean is set to “0”. That is, when the output value Voxs increases and the magnitude | ΔVoxs | of the change rate ΔVoxs is larger than the rich determination threshold value dRichth, the CPU determines that “the state of the catalyst 43 is an oxygen-deficient state”. The value of the catalyst lean state display flag XCCROLean is set to “0”.

  In this state (that is, in a state where the value of the catalyst lean state display flag XCCROLean is set to “0”), when the CPU starts again from step 700, the CPU proceeds to step 730 via step 710 and step 720. In step 730, “No” is determined, and the process proceeds to step 770.

  In step 770, the CPU determines whether or not the change speed ΔVoxs is negative. That is, the CPU determines whether or not the output value Voxs is decreasing. At this time, if the change rate ΔVoxs is not negative, the CPU makes a “No” determination at step 770 to directly proceed to step 795 to end the present routine tentatively.

  By the way, when the value of the catalyst lean state display flag XCCROLean is “0”, the target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean. Accordingly, the oxygen storage amount of the catalyst 43 gradually increases, and oxygen begins to flow out of the catalyst 43 from a certain point. As a result, the change rate ΔVoxs becomes a negative value. When the change rate ΔVoxs becomes a negative value, the CPU makes a “Yes” determination at step 770 to proceed to step 780 to determine whether or not the magnitude | ΔVoxs | of the change rate ΔVoxs is greater than the lean determination threshold dLeanth. To do. At this time, if the magnitude | ΔVoxs | is equal to or smaller than the lean determination threshold value dLeanth, the CPU makes a “No” determination at step 780 to directly proceed to step 795 to end the present routine tentatively.

  On the other hand, when the magnitude | ΔVoxs | of the change speed ΔVoxs is larger than the lean determination threshold value dLeanth, the CPU makes a “Yes” determination at step 780 to proceed to step 790 to set the value of the catalyst lean state display flag XCCROLean. Set to “1”. That is, when the output value Voxs is decreasing and the magnitude | ΔVoxs | of the change speed ΔVoxs is larger than the lean determination threshold value dLeanth, the CPU determines that “the state of the catalyst 43 is an oxygen excess state”. The catalyst lean state display flag XCCROLean is set to “1”.

  The CPU sets the value of the catalyst lean state display flag XCCROLean to “0” when the value of the catalyst lean state display flag XCCROLean is “1” and the output value Voxs becomes larger than the rich determination threshold VRichth. May be. Similarly, when the value of the catalyst lean state display flag XCCROLean is “0” and the output value Voxs becomes smaller than the lean determination threshold value VLeanth, the value of the catalyst lean state display flag XCCROLean is set to “1”. Also good. In this case, the rich determination threshold value VRichth may be a value equal to or less than the median value Vmid. The lean determination threshold value VLeanth may be a value equal to or greater than the median value Vmid.

  As described above, the value of the catalyst lean state display flag XCCROLean is alternately set to one of “1” and “0” based on the output value Voxs of the downstream air-fuel ratio sensor 67. Then, the target air-fuel ratio abyfr is determined according to the catalyst lean state display flag XCCROLean (see step 645 to step 655 of the routine of FIG. 6), and the command fuel injection amount Fi is determined based on the target air-fuel ratio abyfr. (See step 625 to step 635 of the routine of FIG. 6).

<Evaporated fuel purge control>
The CPU executes the evaporative fuel purge control routine shown in FIG. 8 every elapse of a predetermined time. Accordingly, when the predetermined timing comes, the CPU starts the process from step 800 and proceeds to step 810 to determine whether or not the value of the purge execution flag XPG is “0”. The value of the purge execution flag XPG is set to “0” in the above-described initial routine. Further, as will be described later, the value of the purge execution flag XPG is set to “1” when the evaporated fuel purge is executed, and is set to “0” when the execution of the evaporated fuel purge is stopped.

  It is assumed that the evaporated fuel purge is not executed and the value of the purge execution flag XPG is “0”. In this case, the CPU makes a “Yes” determination at step 810 to proceed to step 820 to determine whether or not the value of the purge execution request flag XPGreq is “1”.

  The value of the purge execution request flag XPGreq is set to “1” when the purge execution request condition is satisfied, and is set to “0” when the purge execution request condition is not satisfied. Further, the value of the purge execution request flag XPGreq is set to “0” in the above-described initial routine.

This purge execution request condition is satisfied, for example, when all of the following conditions are satisfied. Of course, other conditions may be added to the conditions constituting the purge execution request condition.
(B1) The value of the feedback control flag XFB is “1” (air-fuel ratio feedback control is being executed).
(B2) The engine 10 is in a steady operation (for example, the amount of change per unit time of the throttle valve opening TA representing the engine load is equal to or less than a predetermined value).
(B3) The cooling water temperature THW is equal to or higher than the threshold cooling water temperature THWth.

  Now, it is assumed that the purge execution request condition is not satisfied, and therefore the value of the purge execution request flag XPGreq is “0”. In this case, the CPU makes a “No” determination at step 820 to directly proceed to step 830 to determine whether or not the value of the purge execution flag XPG is “1”. In this case, the value of the purge execution flag XPG is “0”. Therefore, the CPU makes a “No” determination at step 830 to proceed to step 840, where the purge control valve 55 is closed by setting the duty ratio DPG to “0”. That is, the CPU stops the evaporated fuel purge at step 840. At this time, since the evaporated fuel purge is not executed, the purge control valve 55 is kept closed. Thereafter, the CPU proceeds to step 895 to end the present routine tentatively.

  When the purge execution request condition is satisfied in this state, the value of the purge execution request flag XPGreq is set to “1” in a routine (not shown). In this case, the CPU makes a “Yes” determination at both steps 810 and 820 to proceed to step 850 to determine whether or not the value of the purge execution prohibition flag XPGkinshi is “0”.

  The value of the purge execution prohibition flag XPGkinshi is set to “0” in the above-described initial routine. Further, the value of the purge execution prohibition flag XPGkinshi is determined by the purge execution prohibition flag setting routine shown in FIG. 9, which will be described later, and the “period until the first predetermined time Δta1 elapses after the target air-fuel ratio rich lean change” and “target It is set to “1” in the “period from the time when the air-fuel ratio lean rich is changed until the second predetermined time Δta2 elapses”, and is set to “0” in other periods.

  Assume that the value of the purge execution prohibition flag XPGkinshi is “1”. In this case, the CPU makes a “No” determination at step 850 to directly proceed to step 830. Therefore, the value of the purge execution flag XPG is maintained at “0”. Therefore, the CPU makes a “No” determination at step 830 to proceed to step 840. As a result, the fuel vapor purge continues to be stopped. In other words, even if the purge execution request condition is satisfied, the evaporated fuel purge is not started if the value of the purge execution prohibition flag XPGkinshi is “1”. That is, the start of execution of the evaporated fuel purge is prohibited.

  On the other hand, if the value of the purge execution prohibition flag XPGkinshi is “0” at the time when the CPU executes the process of step 850, the CPU determines “Yes” in step 850 and proceeds to step 860. The value of the purge execution flag XPG is set to “1”.

  In this case, the CPU makes a “Yes” determination at subsequent step 830 to proceed to step 870, where the purge control valve 55 is opened to introduce the evaporated fuel into the intake passage. That is, the CPU starts the evaporated fuel purge. In practice, the CPU determines the duty ratio DPG based on the intake air amount Ga and the engine rotational speed NE, and transmits a signal corresponding to the duty ratio DPG to the purge control valve 55. Thereafter, the CPU proceeds to step 895 to end the present routine tentatively.

  Thus, when the CPU next starts the routine shown in FIG. 8 from step 800, the CPU makes a “No” determination at step 810 to proceed to step 880, where the value of the purge execution request flag XPGreq is “0”. It is determined whether or not there is. At this time, if the value of the purge execution request flag XPGreq is “1”, the CPU makes a “No” determination at step 880 to directly proceed to step 830. Therefore, since the value of the purge execution flag XPG is maintained at “1”, the process of step 870 is executed. As a result, the evaporated fuel purge is continuously executed.

  In contrast, if the purge execution request condition is not satisfied at the time when the CPU executes the process of step 880 and the value of the purge execution request flag XPGreq is “0”, the CPU proceeds to step 880. "Yes" is determined, the process proceeds to step 890, and the value of the purge execution flag XPG is set to "0". Thereafter, the CPU proceeds to step 830. Therefore, the CPU makes a “No” determination at step 830 to proceed to step 840, where the purge control valve 55 is closed by setting the duty ratio DPG to “0”. That is, the CPU stops the evaporated fuel purge at step 840.

<Purge execution prohibition flag setting>
The CPU executes the evaporated fuel purge control routine shown in FIG. 9 every elapse of a predetermined time. Therefore, when the predetermined timing comes, the CPU starts the process from step 900 and proceeds to step 910, and whether or not the current time is within the “period from when the target air-fuel ratio rich lean is changed until the first predetermined time Δta1 elapses”. Determine whether. The first predetermined time Δta1 is also referred to as a purge prohibition time (predetermined time).

  If the current time is within the “period from when the target air-fuel ratio rich lean is changed until the first predetermined time Δta1 elapses”, the CPU makes a “Yes” determination at step 910 to proceed to step 920 where the purge execution prohibition flag Set the value of XPGkinshi to “1”. Thereafter, the CPU proceeds to step 995 to end the present routine tentatively.

  On the other hand, at the time when the CPU executes the process of step 910, if the current time is not within the “period from when the target air-fuel ratio rich lean is changed until the first predetermined time Δta1 elapses”, the CPU proceeds to step 910. Then, the process proceeds to step 930, where it is determined whether or not the current time is within the “period from when the target air-fuel ratio lean / rich change occurs until the second predetermined time Δta2 elapses”. Similarly to the first predetermined time Δta1, the second predetermined time Δta2 is also called a purge prohibition time (predetermined time).

  If the current time is within the “period from when the target air-fuel ratio lean-rich change has elapsed until the second predetermined time Δta2 elapses”, the CPU makes a “Yes” determination at step 930 to proceed to step 920, where the purge execution prohibition flag Set the value of XPGkinshi to “1”. Thereafter, the CPU proceeds to step 995 to end the present routine tentatively.

  On the other hand, when the CPU executes the process of step 930, if the current time is not within the “period until the second predetermined time Δta2 elapses from the target air-fuel ratio lean rich change time”, the CPU proceeds to step 930. Then, the process proceeds to step 940 where the purge execution prohibition flag XPGkinshi is set to “0”. Thereafter, the CPU proceeds to step 995 to end the present routine tentatively.

  In this way, the value of the purge execution prohibition flag XPGkinshi is determined when the current time is within the “period from when the target air-fuel ratio rich lean is changed until the first predetermined time Δta1 elapses” and when the current time is “target air-fuel ratio lean It is set to “1” when it is within the “period from the rich change time point until the second predetermined time Δta2 elapses”, and is set to “0” otherwise.

As described above, the first control device
Catalyst state determination means (routine of FIG. 7) for determining whether the oxygen storage state of the catalyst 43 is an oxygen excess state or an oxygen shortage state based on the output value Voxs of the downstream air-fuel ratio sensor 67;
When it is determined that the oxygen storage state is the oxygen excess state, the target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich (step 645 and step 650 in FIG. 6), and the oxygen storage state is the oxygen shortage. The target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean when determined to be in the state (step 645 and step 655 in FIG. 6), target air-fuel ratio setting means,
A fuel injection amount Fi, which is the amount of fuel injected from the fuel injection valve 33, is determined according to the set target air-fuel ratio abyfr (and in-cylinder intake air amount Mc), and the fuel of the determined fuel injection amount Fi Fuel injection control means (steps 625 to 640 in FIG. 6) for injecting fuel from the fuel injection valve 33;
Evaporation fuel purge that introduces the evaporated fuel generated in the fuel tank 51 that stores the fuel supplied to the fuel injection valve 33 into the intake passage of the engine 10 is executed when a predetermined purge execution requirement is satisfied. Fuel purge means (evaporated fuel supply system 50 including the purge control valve 55, step 820, step 860, step 830 and step 870 in FIG. 8);
An internal combustion engine control apparatus comprising:
The evaporated fuel purge means includes
The target air-fuel ratio rich lean change time point when the target air-fuel ratio abyfr is changed from the target rich air-fuel ratio afRich to the target lean air-fuel ratio afLean, and the target air-fuel ratio abyfr is changed from the target lean air-fuel ratio afLean to the target rich air-fuel ratio afRich The purge execution requirement condition is a period until a predetermined time (first predetermined time Δta1, second predetermined time Δta2) elapses from at least one of the target air-fuel ratio lean rich change time, which is the time when the target air-fuel ratio is changed to Even if it is established (see the determination of “Yes” in step 820 in FIG. 8), the fuel vapor purge is not started (the routine in FIG. 9 and the routine in FIG. 8). (Refer to “No” in Step 850, Step 830 and Step 840).

  According to the first control apparatus, after the first predetermined time Δta1 has elapsed from the time when the target air-fuel ratio rich lean is changed, in other words, after the time when the oxygen storage amount of the catalyst 43 has increased to some extent, the evaporated fuel A change in the air-fuel ratio due to the start of the purge appears in the upstream air-fuel ratio. Therefore, since the possibility that the oxygen storage amount of the catalyst reaches “0” can be reduced, the possibility that the emission deteriorates can be reduced.

  Similarly, according to the first control device, after the second predetermined time Δta2 has elapsed since the target air-fuel ratio lean-rich change time, in other words, after the time when the oxygen storage amount of the catalyst becomes small to some extent, A change in the air-fuel ratio due to the start of the fuel purge appears in the upstream air-fuel ratio. Therefore, since the possibility that the oxygen storage amount of the catalyst reaches the maximum oxygen storage amount Cmax can be reduced, the possibility that the emission is deteriorated can be reduced.

Second Embodiment
Next, a control device for an internal combustion engine according to a second embodiment of the present invention (hereinafter also referred to as “second control device”) will be described.

  The first control device starts the evaporative fuel purge by “a period until the first predetermined time Δta1 elapses after the target air-fuel ratio rich lean change time” and “a second predetermined time Δta2 elapses from the target air-fuel ratio lean rich change time point”. "Period until" is prohibited. However, the oxygen storage amount OSA of the catalyst 43 is very close to “0” even immediately before the target air-fuel ratio rich lean change time. Therefore, in such a case, it is not preferable that “a large fluctuation in the upstream air-fuel ratio abyfs due to the start of execution of the evaporated fuel purge” occurs. Similarly, the oxygen storage amount OSA of the catalyst 43 is very close to the maximum oxygen storage amount Cmax immediately before the target air-fuel ratio lean rich change time. Therefore, in such a case, it is not preferable that “a large fluctuation in the upstream air-fuel ratio abyfs due to the start of execution of the evaporated fuel purge” occurs.

  Therefore, the second control device predicts the target air-fuel ratio rich-lean change time tRL, and the predicted target air-fuel ratio rich-lean from the time a third predetermined time Δtb1 before the predicted target air-fuel ratio rich-lean change time tRL. The evaporative fuel purge is prohibited from starting during the period from the lean change time to the time when the first predetermined time Δta1 elapses (see time t1 to t3, time t7 to t9, time t13 to t15 in FIG. 10). .

  Further, the second control device predicts the target air-fuel ratio lean-rich change time point tLR, and the predicted target air-fuel ratio lean time from a time point before the fourth predetermined time Δtb2 before the predicted target air-fuel ratio lean-rich change time point tLR. The evaporative fuel purge is prohibited from starting during the period from the rich change time tLR to the time when the second predetermined time Δta2 elapses (see times t4 to t6 and times t10 to t12 in FIG. 10).

(Actual operation)
The CPU of the second control device executes the routines shown in FIGS. 6, 7, and 8 in the same manner as the CPU of the first control device. Further, the CPU of the second control device executes a “purge execution prohibition flag setting routine shown by a flowchart in FIG. 11 instead of FIG. 9” every time a predetermined time elapses. Therefore, the operation of the second control device will be described below mainly with reference to FIG.

  When the predetermined timing is reached, the CPU starts the process from step 1100 in FIG. 11 and proceeds to step 1110 to estimate the “target rich air-fuel ratio duration TRL and target lean air-fuel ratio duration TLR” based on the intake air amount Ga. To do.

  The target rich air-fuel ratio duration TRL is “the time from when the target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich until the target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean (that is, the state of the catalyst 43 is The time from when it is determined that there is an oxygen excess state to when it is determined that there is an oxygen deficiency state).

  The target lean air-fuel ratio duration TLR is “the time from when the target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean to when the target rich air-fuel ratio afRich is set (that is, the state of the catalyst 43 is an oxygen-deficient state). The time from when it is determined that the oxygen excess state is determined).

  12A and 12B show the upstream air-fuel ratio (actually the target air-fuel ratio abyfr) and the oxygen storage amount of the catalyst 43 when the intake air amount Ga is the first intake air amount Ga1 that is relatively small. FIGS. 12C and 12D are time charts showing OSA, respectively. FIGS. 12C and 12D show the upstream air-fuel ratio (actually, the target air flow when the intake air amount Ga is a relatively large second intake air amount Ga2. FIG. 6 is a time chart showing the fuel ratio abyfr) and the oxygen storage amount OSA of the catalyst 43, respectively.

  As can be understood from FIG. 12, if the target rich air-fuel ratio afRich is a constant value and the target lean air-fuel ratio afLean is a constant value, the larger the intake air amount Ga is, the larger the target air-fuel ratio switching cycle T (accordingly, the target rich air-fuel ratio). Each of the air-fuel ratio duration TRL and the target lean air-fuel ratio duration TLR) becomes shorter. The target air / fuel ratio switching cycle T is the sum of the target rich air / fuel ratio duration TRL and the target lean air / fuel ratio duration TLR.

  FIG. 13 is a map showing the relationship between the fluctuation range ΔA / F of the upstream air-fuel ratio (= target lean air-fuel ratio afLean−target rich air-fuel ratio afRich), the intake air amount Ga, and the target air-fuel ratio switching period T. is there.

  As will be understood from FIG. 13, the target air-fuel ratio switching cycle T becomes shorter as the upstream air-fuel ratio fluctuation range ΔA / F becomes larger, and the target air-fuel ratio switching cycle T becomes shorter as the intake air amount Ga becomes larger.

  On the other hand, in the second control device, the target rich air-fuel ratio afRich is a constant value, and the target lean air-fuel ratio afLean is a constant value. Therefore, the electric control device 70 of the second control device stores a lookup table MapTRL (Ga) and a lookup table MapTLR (Ga) in advance in the ROM.

  The look-up table MapTRL (Ga) defines the relationship between the “intake air amount Ga” and the “target rich air-fuel ratio duration TRL”. This lookup table MapTRL (Ga) is formed based on data obtained in advance by experiments.

  Similarly, the look-up table MapTLR (Ga) defines the relationship between the “intake air amount Ga” and the “target lean air-fuel ratio duration TLR”. This lookup table MapTLR (Ga) is also formed based on data obtained in advance by experiments.

  In step 1110 of FIG. 11, the CPU estimates the target rich air-fuel ratio duration TRL by applying the actual intake air amount Ga to the lookup table MapTRL (Ga), and looks up the actual intake air amount Ga. The target lean air-fuel ratio duration TLR is estimated by applying to the table MapTLR (Ga). In this example, since the target rich air-fuel ratio afRich is a constant value and the target lean air-fuel ratio afLean is a constant value, the fluctuation range ΔA / F of the upstream air-fuel ratio is equal to the target rich air-fuel ratio duration TRL and the target lean. There is no need to consider the influence of each of the air-fuel ratio durations TLR.

  Further, a lookup table MapT (Ga) that defines the relationship between “intake air amount Ga” and “target air-fuel ratio switching cycle T = TLR + TRL” is stored in advance, and the actual intake air amount Ga is looked up in the lookup table MapT. (Ga) may be used to estimate the target air-fuel ratio switching period T, and half (T / 2) thereof may be adopted as the “target rich air-fuel ratio duration TRL and target lean air-fuel ratio duration TLR”. Good.

  Next, the CPU proceeds to step 1120 in FIG. 11, where the current time is “the actual target air-fuel ratio lean rich change time point (the target air-fuel ratio abyfr is actually changed from the target lean air-fuel ratio afLean to the target rich air-fuel ratio afRich). ] (See immediately after time t5 and immediately after time t11 in FIG. 10).

  If the current time point is immediately after the target air-fuel ratio lean-rich change time point, the CPU makes a “Yes” determination at step 1120 to proceed to step 1130, and the target rich air-fuel ratio predicted at step 1110 at the current time tnow. The time when the continuation time TRL is added (the time after the target rich air-fuel ratio continuation time TRL after the current time = tnow + TRL) is predicted as the “future target air-fuel ratio rich-lean change time tRL”. Thereafter, the CPU proceeds to step 1140.

  On the other hand, when the CPU executes the process of step 1120, if that time is not immediately after the target air-fuel ratio lean-rich change time, the CPU makes a “No” determination at step 1120 to directly proceed to step 1140.

  In step 1140, the CPU determines that the current time tnow is “from the future target air-fuel ratio rich lean change time point tRL from the time point (tRL−Δtb1) before the third predetermined time Δtb1 from the future target air-fuel ratio rich lean change time point tRL. It is determined whether or not it is within the “period until the time point (tRL + Δta1) after the first predetermined time Δta1”. If the current time tnow is within the “period from time (tRL−Δtb1) to time (tRL + Δta1)”, the CPU makes a “Yes” determination at step 1140 to proceed to step 1150, and purge execution prohibition flag The value of XPGkinshi is set to “1”, and the routine proceeds to step 1195 to end the present routine tentatively.

  On the other hand, if the current time tnow is not within the “period from time (tRL−Δtb1) to time (tRL + Δta1)”, the CPU makes a “No” determination at step 1140 to proceed to step 1160. It is determined whether or not it is immediately after the actual target air-fuel ratio rich lean change time (the target air-fuel ratio abyfr is actually changed from the target rich air-fuel ratio afRich to the target lean air-fuel ratio afLean) (time in FIG. 10). (See immediately after t2, immediately after time t8, and immediately after time t14.)

  If the current time is immediately after the target air-fuel ratio rich-lean change time, the CPU makes a “Yes” determination at step 1160 to proceed to step 1170, and the target lean air-fuel ratio predicted at step 1110 at the current time tnow. The time when the duration time TLR is added (time after the target lean air-fuel ratio duration time TLR = tnow + TLR) is predicted as the “future target air-fuel ratio lean rich change time point tLR”. Thereafter, the CPU proceeds to step 1180.

  On the other hand, when the CPU executes the process of step 1160 and that time is not immediately after the target air-fuel ratio rich lean change time, the CPU makes a “No” determination at step 1160 to directly proceed to step 1180.

  In step 1180, the CPU determines that the current time tnow is “from the future target air-fuel ratio lean rich change time point tLR from the time point (tLR−Δtb2) which is a fourth predetermined time Δtb2 before the future target air fuel ratio lean rich change time point tLR. It is determined whether or not it is within the “period until the time point (tLR + Δta2) after the second predetermined time Δta2”.

  If the current time tnow is within the “period from time (tLR−Δtb2) to time (tLR + Δta2)”, the CPU makes a “Yes” determination at step 1180 to proceed to step 1150, where the purge execution prohibition flag is set. The value of XPGkinshi is set to “1”, and the routine proceeds to step 1195 to end the present routine tentatively.

  On the other hand, if the current time tnow is not within the “period from time (tLR−Δtb2) to time (tLR + Δta2)”, the CPU makes a “No” determination at step 1180 to proceed to step 1190 to prohibit purge execution. The value of the flag XPGkinshi is set to “0”, the process proceeds to step 1195, and this routine is temporarily ended.

  As described above, the second control device predicts the future target air-fuel ratio rich lean change time point, and starts evaporative fuel purge in the period near the predicted future target air-fuel ratio rich lean change time point. Ban. Therefore, the possibility that the oxygen storage amount of the catalyst 43 reaches “0” can be reduced. Further, the second control apparatus predicts a future target air-fuel ratio lean-rich change time point and prohibits the start of the evaporated fuel purge in a period in the vicinity of the predicted future target air-fuel ratio lean-rich change time point. Therefore, the possibility that the oxygen storage amount of the catalyst 43 reaches the maximum oxygen storage amount Cmax can be reduced.

  The second control device may determine the end point of the period during which the start of the evaporated fuel purge is prohibited as in the first control device. More specifically, the second control device predicts a future target air-fuel ratio rich-lean change time tRL and “a time point that is a third predetermined time Δtb1 before the predicted target air-fuel ratio rich-lean change time tRL. From the time when the actual target air-fuel ratio rich lean change occurs to the time when the first predetermined time Δta1 elapses, the evaporative fuel purge may be prohibited from starting.

In this case, the evaporated fuel purge means is
It is configured not to start the execution of the evaporated fuel purge in the period after the rich lean change, which is a period from the time when the target air-fuel ratio rich lean is changed until the first predetermined time as the predetermined time elapses.
A second time (target rich air-fuel ratio duration) from the target air-fuel ratio lean rich change time to the target air-fuel ratio rich lean change time following the target air-fuel ratio lean rich change time is correlated with at least the intake air amount of the engine Based on a value having
Predicting the next target air-fuel ratio rich lean change time to arrive next based on the estimated second time;
The execution of the evaporated fuel purge is not started during a period from a time before the predicted target air-fuel ratio rich lean change time to a time point before the rich lean change time period from a predetermined time (third predetermined time). Can be said to have been.

  Similarly, the second control device predicts a future target air-fuel ratio lean-rich change time point tLR, and then “from a time point before the predicted target air-fuel ratio lean-rich change time point tLR to the fourth predetermined time Δtb2 next. The evaporative fuel purge may be prohibited from starting during the period from the actual target air-fuel ratio lean rich change time to the time when the second predetermined time Δta2 elapses.

That is, the evaporated fuel purge means
It is configured not to start the execution of the evaporated fuel purge in a period after the lean rich change that is a period from the target air-fuel ratio lean rich change time to a second predetermined time as the predetermined time.
A first time (target lean air-fuel ratio duration) from the target air-fuel ratio rich-lean change time to the target air-fuel ratio lean-rich change time following the target air-fuel ratio rich-lean change time is correlated with at least the intake air amount of the engine Based on a value having
Predicting the next target air-fuel ratio lean-rich change time tLR that is scheduled to arrive based on the estimated first time;
The execution of the evaporated fuel purge is not started during a period from a time point before the predicted target air-fuel ratio lean-rich change time to a predetermined time (fourth predetermined time) to a time point after the lean-rich change time period. Can be said to have been.

<Third Embodiment>
Next, a control device for an internal combustion engine according to a third embodiment of the present invention (hereinafter also referred to as “third control device”) will be described.

  In the first control device, the purge control valve 55 is changed from the closed state to the open state when the first predetermined time Δta1 has elapsed since the change of the target air-fuel ratio rich lean. Even when the execution is started, the first predetermined time Δta1 is set so that the oxygen storage amount OSA is sufficiently deviated from “0” when the influence of the start of the execution of the evaporated fuel purge appears in the upstream air-fuel ratio abyfs. It is set.

  Further, in the first control device, the evaporated fuel is changed by changing the state of the purge control valve 55 from the closed state to the open state when the second predetermined time Δta2 has elapsed since the change of the target air-fuel ratio lean rich. Even if the execution of the purge is started, the second operation is performed so that the oxygen storage amount OSA is sufficiently deviated from the maximum oxygen storage amount Cmax when the influence of the start of the execution of the evaporated fuel purge appears in the upstream air-fuel ratio abyfs. A predetermined time Δta2 is set.

  In other words, the first control device purges the evaporated fuel gas from the time t0 when the evaporated fuel gas transport delay time shown in FIG. 14 is changed (that is, from the time t0 when the state of the purge control valve 55 is changed from the closed state to the open state). It is constructed based on the premise that the time (td) until the time point t1 at which the influence of the execution start appears in the upstream air-fuel ratio abyfs is constant.

  However, since the evaporated fuel purge is performed by causing the engine 10 to suck the evaporated fuel using the intake pipe negative pressure, the transport delay time td of the evaporated fuel gas changes according to the “intake pipe negative pressure”. More specifically, as the intake pipe negative pressure becomes smaller (the absolute value of the intake pipe pressure approaches the atmospheric pressure), the transport delay time td of the evaporated fuel gas becomes longer. Therefore, the third control device acquires a value correlated with the intake pipe pressure (intake pipe pressure correlation value P), and based on the intake pipe pressure correlation value P, the first predetermined time Δta1 and the second predetermined time Δta2 To decide. Thereby, since the period during which the start of the evaporated fuel purge is prohibited can be shortened, the evaporated fuel can be purged more appropriately.

(Actual operation)
The CPU of the third control device executes the routines shown in FIGS. 6, 7 and 8 in the same manner as the CPU of the first control device. Further, the CPU of the third control device executes the “purge execution prohibition flag setting routine shown by the flowchart in FIG. 15 instead of FIG. 9” every time a predetermined time elapses. Therefore, the operation of the third control device will be described below mainly with reference to FIG. The flowchart shown in FIG. 15 is similar to the flowchart shown in FIG. Therefore, the steps shown in FIG. 15 and also shown in FIG. 9 are denoted by the same reference numerals as the steps shown in FIG. Detailed description of these steps will be omitted as appropriate.

  When the predetermined timing is reached, the CPU starts the process from step 1500 in FIG. 15 and proceeds to step 1510 to acquire the intake pipe pressure correlation value P. In this example, the intake pipe pressure correlation value P is acquired based on the intake air amount Ga and the engine speed NE. The intake pipe pressure correlation value P increases as the intake air amount Ga increases, and increases as the engine speed NE decreases. The intake pipe pressure correlation value P may be acquired based on a signal from a pressure sensor that detects the pressure in the intake pipe 32 downstream of the throttle valve 34. The intake pipe pressure correlation value P increases as the pressure in the intake pipe 32 downstream of the throttle valve 34 approaches atmospheric pressure, and decreases as the pressure approaches vacuum.

  Next, the CPU proceeds to step 1520 to acquire a first predetermined time Δta1 and a second predetermined time Δta2 based on the intake pipe pressure correlation value P acquired in step 1510. In this example, the first predetermined time Δta1 and the second predetermined time Δta2 have the same length. The first predetermined time Δta1 and the second predetermined time Δta2 are determined so as to be shorter as the intake pipe pressure correlation value P is larger. This is because the larger the intake pipe pressure correlation value P, the smaller the intake pipe negative pressure, and the larger the intake pipe pressure correlation value P, the longer the transport delay time td of the evaporated fuel gas.

  That is, as the transportation delay time td of the evaporated fuel gas is longer, the effect of the evaporated fuel purge even when the “shorter time” elapses from the time when the target air-fuel ratio rich lean is changed will affect the upstream target. This is because since it takes a long time to appear at the air-fuel ratio abyfr, the oxygen storage amount OSA sufficiently deviates from “0” when the influence appears at the upstream target air-fuel ratio abyfr.

  Similarly, the longer the evaporative fuel gas transport delay time td is, the more the effect of the evaporative fuel purge starts at the time when the “shorter time” has elapsed since the target air-fuel ratio lean-rich change time has elapsed. This is because since it takes a long time to appear at the target air-fuel ratio abyfr, the oxygen storage amount OSA is sufficiently deviated from the maximum oxygen storage amount Cmax when the effect appears at the upstream target air-fuel ratio abyfr.

  Next, the CPU executes an appropriate one of steps 910 to 940. The routine consisting of step 910 to step 940 is the same as the routine shown in FIG. As a result, the state of the purge control valve 55 is changed from the closed state to the open state during the period from when the target air-fuel ratio rich lean is changed until the first predetermined time Δta1 elapses (start of execution of evaporated fuel purge). ) Is prohibited and the state of the purge control valve 55 is changed from the closed state to the open state during the period from when the target air-fuel ratio lean rich is changed until the second predetermined time Δta2 elapses (evaporated fuel purge state). Execution start) is prohibited.

  As described above, the third control device, based on the knowledge that the transport delay time td of the evaporated fuel gas changes according to the intake pipe pressure correlation value P, the first predetermined time Δta1 and the second predetermined time Δta2 Is changed according to the intake pipe pressure correlation value P. Therefore, it can be avoided that the period during which the start of the evaporated fuel purge is prohibited is set longer than necessary.

<Fourth embodiment>
Next, a control device for an internal combustion engine according to a fourth embodiment of the present invention (hereinafter also referred to as “fourth control device”) will be described.

  Fuel volatility is not constant. When the evaporated fuel purge is not performed, the higher the fuel volatility, the greater the amount of evaporated fuel that is adsorbed and accumulated in the canister. Therefore, for example, when the volatility of the fuel is relatively low, as shown in FIGS. 16A and 16B, the maximum amplitude of the fluctuation in the upstream air-fuel ratio accompanying the start of the evaporated fuel purge becomes the value af1. On the other hand, when the volatility of the fuel is relatively high, as shown in FIGS. 16C and 16D, the maximum amplitude of the fluctuation of the upstream air-fuel ratio accompanying the start of the evaporated fuel purge is larger than “value af1”. Value af2 ". As is clear from this, each of the “first predetermined time Δta1 and second predetermined time Δta2” should be longer as the volatility of the fuel is higher.

  Therefore, the fourth control device increases the “first predetermined time Δta1 and second predetermined time Δta2” for determining the period during which the start of the evaporated fuel purge is prohibited, as the volatility of the fuel increases. As a result, the period during which the start of the evaporative fuel purge is prohibited becomes an appropriate length according to the volatility of the fuel, so that the evaporative fuel can be purged more appropriately.

(Actual operation)
The CPU of the fourth control device executes the routines shown in FIGS. 6, 7, and 8 in the same manner as the CPU of the first control device. Further, the CPU of the fourth control device executes the “purge execution prohibition flag setting routine shown by the flowchart in FIG. 17 instead of FIG. 9” every time a predetermined time elapses. Accordingly, the operation of the fourth control apparatus will be described below mainly with reference to FIG. The flowchart shown in FIG. 17 is similar to the flowchart shown in FIG. Therefore, the steps shown in FIG. 17 and also shown in FIG. 9 are denoted by the same reference numerals as the steps shown in FIG. Detailed description of these steps will be omitted as appropriate.

  When the predetermined timing is reached, the CPU starts processing from step 1700 in FIG. 17 and proceeds to step 1710 to acquire the fuel volatility correlation value F. The fuel volatility correlation value F is acquired by a known method. In this example, the fuel volatility correlation value F is acquired based on the output of an alcohol concentration sensor (not shown) provided in the fuel tank. In general, the higher the alcohol concentration, the lower the volatility. The fuel volatility correlation value F is acquired as a value that increases as the volatility of the fuel increases.

  Next, the CPU proceeds to step 1720 to acquire a first predetermined time Δta1 and a second predetermined time Δta2 based on the fuel volatility correlation value F acquired in step 1710. In this example, the first predetermined time Δta1 and the second predetermined time Δta2 have the same length. The first predetermined time Δta1 and the second predetermined time Δta2 are determined so as to increase as the fuel volatility correlation value F increases. This is because when the fuel volatility is higher, the fluctuation range of the upstream air-fuel ratio resulting from the start of the evaporated fuel purge becomes larger, and therefore the upstream air-fuel ratio fluctuation starts to become larger due to the start of the evaporated fuel purge. This is because the oxygen storage amount OSA of the catalyst 43 needs to be further away from each of “0” and the maximum oxygen storage amount Cmax.

  Next, the CPU executes an appropriate one of steps 910 to 940. The routine consisting of step 910 to step 940 is the same as the routine shown in FIG. As a result, the state of the purge control valve 55 is changed from the closed state to the open state during the period from when the target air-fuel ratio rich lean is changed until the first predetermined time Δta1 elapses (start of execution of evaporated fuel purge). ) Is prohibited and the state of the purge control valve 55 is changed from the closed state to the open state during the period from when the target air-fuel ratio lean rich is changed until the second predetermined time Δta2 elapses (evaporated fuel purge state). Execution start) is prohibited.

As described above, the evaporated fuel purge means of the fourth control device is
The evaporative fuel purge is performed even when the purge execution request condition is satisfied during a period until a predetermined time elapses from at least one of the target air-fuel ratio rich-lean change time and the target air-fuel ratio lean-rich change time. (Steps 910 to 940 in FIG. 17, determination of “No” in step 850 in FIG. 8, steps 830 and 840), and
Based on the fuel volatility correlation value F, the predetermined time is determined such that the higher the fuel volatility, the longer the predetermined time is (step 1720 in FIG. 17).

  That is, the fourth control device changes the first predetermined time Δta1 and the second predetermined time Δta2 according to the fuel volatility correlation value F. Therefore, it can be avoided that the period during which the start of the evaporated fuel purge is prohibited is set longer than necessary.

  As described above, according to the embodiments of the control device for an internal combustion engine according to the present invention, the start timing of the evaporated fuel purge is limited, so that the deterioration of the emission due to the start of the evaporated fuel purge is avoided. be able to.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, the first predetermined time Δta1 and the second predetermined time Δta2 may be different from each other. Similarly, the third predetermined time Δtb1 and the fourth predetermined time Δtb2 may be different from each other.

Further, the command fuel injection amount Fi is obtained by correcting the basic fuel injection amount Fbase based on not only the main feedback amount KFmain but also the main feedback learning value KG and the purge correction coefficient FPG as shown in the following equation (2). May be.

Fi = FPG / KG / KFmain / Fbase (2)

  In this case, “learning of the main feedback learning value KG” may be included as one of the purge execution request conditions. That is, when the learning of the main feedback learning value KG is not completed, the evaporated fuel purge is not executed.

The evaporative fuel purge is not executed because the learning of the main feedback learning value KG is not completed, and the air-fuel ratio feedback control is executed (when the value of the feedback control flag XFB is “1”). ),
(1) When the average value of the main feedback amount KFmain is larger than “1 + α”, the value of the main feedback learning value KG is increased by a value ΔKG per predetermined time,
(2) When the average value of the main feedback amount KFmain is smaller than “1-α”, the value of the main feedback learning value KG is decreased by a value ΔKG per predetermined time.
Note that the value α is a value larger than 0 and smaller than 1 (for example, 0.02), and the initial value of the main feedback learning value KG is “1”.

  Thereafter, when the feedback control is continued and the duration of the state where the average value of the feedback amount KFmain is a value between “1 + α” and “1−α” becomes equal to or longer than the threshold time, the main feedback It is determined that learning of the learning value KG has been completed.

Further, the purge correction coefficient FPG is obtained according to the following (3). In the equation (3), FGPG is an evaporative fuel gas concentration learning value. PGT is a target purge rate.

FPG = 1 + PGT (FGPG-1) (3)

  The evaporative fuel gas concentration learning value FGPG is a predetermined time when the average value FAFAV of the main feedback amount KFmain is not a value between “1 + β” and “1-β” in the period during which the purge of evaporative fuel is executed. Increased by (FAFAV-1) / PGT. The target purge rate PGT is determined based on the load KL, the engine speed NE, and the like. The target purge rate PGT may be a constant value. The value β is a value larger than 0 and smaller than 1 (for example, 0.02).

  In each of the above embodiments, the target rich air-fuel ratio afRich may be a value that changes according to the intake air amount Ga, for example, or the target lean air-fuel ratio afLean may be a value that changes according to the intake air amount Ga, for example. There may be.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 21 ... Combustion chamber, 32 ... Intake pipe, 33 ... Fuel injection valve, 34 ... Throttle valve, 41 ... Exhaust manifold, 41b ... Collecting part, 42 ... Exhaust pipe, 43 ... Upstream catalyst (catalyst, three (Original catalyst), 50 ... evaporated fuel supply system, 51 ... fuel tank, 52 ... canister, 55 ... purge control valve, 61 ... hot-wire air flow meter, 66 ... upstream air-fuel ratio sensor, 67 ... downstream air-fuel ratio sensor, 70 ... electric control device.

Claims (1)

A catalyst disposed in an exhaust passage of the internal combustion engine and having an oxygen storage function;
A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
The oxygen storage state of the catalyst is an excessive oxygen state in which the amount of oxygen stored in the catalyst is excessive because the amount of oxygen stored in the catalyst is excessive, or stored in the catalyst. Catalyst state determining means for determining, based on an output value of the downstream air-fuel ratio sensor, whether or not an oxygen deficient state in which the amount of oxygen to be increased because the amount of oxygen present is insufficient ,
Setting the target air-fuel ratio, which is the target value of the air-fuel ratio of the gas flowing into the catalyst when the oxygen storage state is determined to be the oxygen excess state, to a target rich air-fuel ratio smaller than the theoretical air-fuel ratio; Target air-fuel ratio setting means for setting the target air-fuel ratio to a target lean air-fuel ratio larger than the stoichiometric air-fuel ratio when it is determined that the oxygen storage state is the oxygen-deficient state;
A fuel injection valve for injecting fuel to the engine;
Fuel injection control means for determining a fuel injection amount, which is the amount of fuel injected from the fuel injection valve, in accordance with the set target air-fuel ratio and for injecting the fuel of the determined fuel injection amount from the fuel injection valve When,
Evaporated fuel that performs evaporative fuel purge that introduces evaporative fuel generated in a fuel tank that stores fuel supplied to the fuel injection valve into the intake passage of the engine when a predetermined purge execution requirement condition is satisfied Purge means;
An internal combustion engine control apparatus comprising:
The evaporated fuel purge means includes
The target air-fuel ratio is changed from the target rich air-fuel ratio to the target lean air-fuel ratio, and the target air-fuel ratio is changed from the target lean air-fuel ratio to the target rich air-fuel ratio. The evaporative fuel purge is executed even when the purge execution request condition is satisfied during a period until a predetermined time elapses from at least one of the target air-fuel ratio lean-rich change time, which is the time when the target is changed to A control device for an internal combustion engine configured not to start the engine.

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