JP2009036117A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide both an improvement in exhaust emission purifying capability and reduction in fuel consumption in an internal combustion engine which performs enriching control at the time of recovery from fuel cutting. <P>SOLUTION: When an output of an O<SB>2</SB>sensor on a catalyst downstream side indicates a lean state in recovery from fuel cutting, enriching control is started and then when oxygen inside a catalyst has been judged to be consumed during implementing the enriching control, the enriching control is terminated. However, even if the judgment has been made in the course of consuming oxygen, when the output of the O<SB>2</SB>sensor at the catalyst downstream side changes to a rich side, the enriching control is terminated, thus permitting the enriching control at the time of the recovery from the fuel cutting to be timely terminated at all times. By performing such control, even if the fuel cutting for the purpose of improving fuel economy is frequently iterated, exhaust emission can be prevented from becoming more noxious. Regardless of catalyst deterioration due to repeated use over the years, consistently stable enriching control (increase in fuel volume) at the time of the recovery from the fuel cutting is realized. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus for an internal combustion engine that feedback-controls the air-fuel ratio based on the output of an O ₂ sensor provided in an exhaust passage.

  In an internal combustion engine (hereinafter also referred to as an engine) mounted on a vehicle, a harmful component (HC, CO, NOx, etc.) contained in the exhaust gas is usually generated by a catalyst (for example, a three-way catalyst) disposed in the exhaust passage of the engine. To purify. This purification action by the catalyst is most efficient when the air-fuel mixture is burned at the stoichiometric air-fuel ratio.

  The catalyst used for purifying exhaust gas can store an appropriate amount of oxygen inside, and when NOx is contained in the exhaust gas, the NOx is reduced by storing oxygen. Moreover, when HC and CO are contained in exhaust gas, these HC and CO can be oxidized by releasing oxygen. Therefore, by disposing the catalyst in the exhaust passage of the engine, the amount of NOx, HC, CO, etc. emitted can be suppressed sufficiently small.

In order for the catalyst disposed in the exhaust passage of the engine to exhibit an appropriate purification capacity, an appropriate amount of oxygen must be occluded in the catalyst, and there must be a surplus in the oxygen absorption capacity of the catalyst. is necessary. For this reason, in normal control of the engine, the oxygen concentration in the exhaust gas is detected by an O ₂ sensor arranged in the exhaust passage, and the actual exhaust air-fuel ratio obtained from the detected oxygen concentration is the stoichiometric air-fuel ratio (stoichiometric). The fuel injection amount is controlled so as to vibrate alternately between the lean side and the rich side. By executing such control, the oxygen occlusion state of the catalyst is always maintained in an appropriate state, so that a good purification ability is continuously exhibited.

  On the other hand, in an engine mounted on a vehicle, for the purpose of improving fuel efficiency, a fuel cut (fuel cut) for stopping fuel supply to the engine is performed during deceleration of the vehicle. Since air flows in the exhaust passage of the engine during the fuel cut, if the fuel cut is continued for a certain period of time, the catalyst is in a state of fully storing oxygen.

  When exhaust gas containing NOx is exhausted in a state where oxygen is fully stored in the catalyst, the NOx is blown through the catalyst without being reduced. Therefore, in the conventional control, in order to reduce such NOx emission, the enrichment control for forcibly enriching the air-fuel ratio of the air-fuel mixture over a predetermined period is executed immediately after the end of the fuel cut (for example, Patent Document 1). In the enrichment control, for example, the air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio by raising the air-fuel ratio feedback control correction value FAF.

  During the execution of the enrichment control, exhaust gas containing HC and CO is exhausted from the combustion chamber of the engine. Since oxygen is released from the catalyst to oxidize these HC and CO, the oxygen in the catalyst is consumed, and the catalyst returns to a state where oxygen can be stored. Then, after the catalyst returns to that state, if rich control is terminated and normal fuel injection amount control (stoichiometric control) is resumed, HC and CO are not discharged, including immediately after the fuel cut, Good exhaust emission characteristics can be maintained continuously.

  Here, there are techniques described in Patent Documents 2 to 4 below as techniques for enriching the air-fuel ratio when returning from a fuel cut (hereinafter also referred to as a fuel cut return).

  In the technique described in Patent Document 2, the NOx emission amount increases by enriching the air-fuel ratio according to the amount of oxygen stored in the catalyst at the time of fuel cut recovery and restarting the fuel supply from the cylinder having the largest exhaust passage volume. That is restrained.

  In the technology described in Patent Document 3, the air-fuel ratio is enriched when returning from the fuel cut, and after the output signal of the exhaust sensor becomes lean during execution of the enrichment control, a predetermined time has elapsed since the fuel cut return. By controlling to stoichiometric when it has elapsed, the deterioration of exhaust emission when returning from fuel cut is suppressed.

In the technique described in Patent Document 4, return rich control after fuel cut for enriching the air-fuel ratio at the time of fuel cut return is started, and when the output value of the exhaust sensor exceeds a threshold value, the return rich control after fuel cut is performed. End and control the air-fuel ratio to stoichiometric. Further, the amount of reducing component flowing into the catalyst after completion of the return rich control after fuel cut is estimated, the threshold value set for the output value of the exhaust sensor is changed according to the estimated amount of reducing component, and the amount of estimated reducing component By changing the speed of change from rich to stoichiometric in response to this, exhaust emission deterioration due to execution of return rich control after fuel cut is suppressed.
JP 2003-166414 A JP 2005-180282 A JP 2005-036790 A JP 2006-233943 A

  By the way, the oxygen storage amount of the catalyst used for exhaust gas purification decreases as the catalyst deteriorates over time. However, in the conventional control (including the techniques described in Patent Documents 2 to 4 above), the oxygen storage amount due to catalyst deterioration is reduced. The change in the amount (occlusion performance) is not taken into consideration. For this reason, for example, when the control for performing enrichment control at the time of fuel cut return is always executed for a certain period of time, when the vehicle is new (when the catalyst is new) When the oxygen storage amount of the catalyst is large, the enrichment may be insufficient and NOx may be discharged. Conversely, when the oxygen storage amount of the catalyst is reduced due to catalyst deterioration, the enrichment becomes excessive and HC, There is a possibility that CO deterioration and fuel consumption (hereinafter also referred to as fuel efficiency) increase.

  In addition, in an engine mounted on a vehicle, the frequency (condition / time) of performing a fuel cut for increasing fuel efficiency tends to increase more and more, but the enrichment control time at the time of fuel cut return is appropriately controlled. If the frequency of fuel cuts increases in situations where there is no exhaust, there is a concern that exhaust emissions will deteriorate.

  The present invention has been made in view of such circumstances, and in an internal combustion engine that executes enrichment control at the time of return from a fuel cut, achieves both improvement in exhaust gas purification performance and reduction in fuel consumption. It is an object of the present invention to provide an air-fuel ratio control device capable of performing

-Solving principle-
The solution principle of the present invention taken in order to achieve the above object is to start the enrichment control when the output of the O ₂ sensor downstream of the catalyst is a value indicating lean at the time of return from the fuel cut, During the execution of the enrichment control, the amount of oxygen in the catalyst is estimated, and the enrichment control is performed when it is determined that the oxygen in the catalyst (specifically, oxygen corresponding to the allowable oxygen storage amount of the new catalyst) has been consumed. In addition, even if the determination is in the course of oxygen consumption, when the output of the O ₂ sensor on the downstream side of the catalyst changes to the rich side, the enrichment control is terminated and the air-fuel ratio is returned to stoichiometry. By such control, it is possible to always realize a stable enrichment (fuel increase) at the time of fuel cut recovery.

-Solution-
Specifically, the present invention relates to a catalyst disposed in an exhaust passage, an O ₂ sensor disposed in an exhaust passage downstream of the catalyst, and fuel to the internal combustion engine when a fuel cut condition is satisfied. An air-fuel ratio control device applied to an internal combustion engine provided with fuel cut control means for executing fuel cut for stopping supply is assumed.

In such an air-fuel ratio control apparatus for an internal combustion engine, when the output of the O ₂ sensor is a value indicating lean when the fuel cut is restored, the rich air-fuel ratio is made richer than the stoichiometric air-fuel ratio. Enrichment control starting means for starting the enrichment control, determination means for determining whether or not oxygen in the catalyst has been consumed after the enrichment control is started, and the determination after starting the enrichment control Enrichment control end means for ending the enrichment control when the means determines that “the oxygen in the catalyst has been consumed” or when the output of the O ₂ sensor changes to the rich side. It is characterized by being.

  As a specific configuration of the determination means, was the amount of oxygen equivalent to the allowable oxygen storage amount (upper limit of oxygen storage amount) when the catalyst was new during execution of the enrichment control at the time of fuel cut return being consumed? A configuration of determining whether or not is possible can be given.

  Further, as a specific configuration of the determination means, the intake air amount of the internal combustion engine is integrated from the time when the enrichment control at the time of fuel cut return is started, and the oxygen amount (remaining amount) in the catalyst is determined based on the integrated intake air amount. (Amount) can be estimated and it can be determined whether or not oxygen in the catalyst is consumed. Further, the fuel injection amount of the internal combustion engine is integrated from the time when the enrichment control at the time of fuel cut return is started, and the oxygen amount (remaining amount) in the catalyst is estimated based on the integrated fuel injection amount, A configuration in which it is determined whether or not oxygen is consumed.

  Due to the above specific matters, the enrichment control that is performed when the fuel cut is restored can always be terminated at an appropriate timing. This will be described below.

  First, the catalyst is fully occluded when the fuel cut is restored. The oxygen stored in the catalyst is consumed by the enrichment control. Specifically, oxygen is released from the catalyst to oxidize HC and CO contained in the exhaust gas discharged from the combustion chamber of the engine, and the stored oxygen in the catalyst is consumed. When the enrichment control is continued, all the oxygen stored in the catalyst is released. Therefore, the enrichment control is performed at that time, that is, “the oxygen in the catalyst has been consumed”. By terminating the process and returning the air-fuel ratio to stoichiometric, NOx emissions can be suppressed, and HC and CO emissions can also be suppressed.

  Next, a specific example of determination processing for determining whether or not oxygen in the catalyst has been consumed will be described.

  In the enrichment control at the time of fuel cut return, as described above, oxygen in the catalyst is consumed by HC and CO contained in the exhaust gas. Therefore, during the enrichment control execution period, oxygen in the catalyst (at the time of fuel cut return) Whether or not oxygen in the catalyst has been consumed can be determined based on whether or not sufficient amounts of HC and CO have been supplied.

  Here, if the degree of enrichment during execution of enrichment control is set (fixed) to a certain value, the amount of HC and CO during the enrichment control execution period correlates with the integrated amount of exhaust gas, that is, the integrated intake air amount. Therefore, the consumption state (remaining amount) of oxygen in the catalyst can be estimated by calculating the integrated intake air amount. Therefore, in the present invention, the intake air amount is integrated from the time when the enrichment control at the time of fuel cut recovery is started, and the integrated intake air amount is a specified value (specifically, HC that can consume all of the oxygen in the catalyst). , A value considering the amount of CO), it is determined that “the oxygen in the catalyst has been consumed”.

  However, the exhaust gas purifying catalyst has a different allowable oxygen storage amount when it is new and when it is deteriorated (when it is new> when it is deteriorated). For this reason, the actual amount of occluded oxygen at the time of fuel cut recovery is smaller for the deteriorated catalyst, but the amount of change in the oxygen occlusion amount due to the catalyst deterioration cannot be grasped. Therefore, in the present invention, the allowable oxygen storage amount of the new catalyst is the oxygen storage amount actually stored in the catalyst when returning from the fuel cut (the oxygen storage amount in the full state), and the oxygen corresponding to the allowable oxygen storage amount is stored. As a condition that all of the above has been consumed, the enrichment control is terminated.

  As with the intake air amount described above, the amount of HC and CO during the enrichment control execution period correlates with the fuel injection amount. Therefore, the fuel injection amount is integrated from the time when the enrichment control is started, and the accumulated fuel is obtained. You may make it determine whether the oxygen in a catalyst was consumed based on the injection amount.

  By the way, in the above determination process, that is, the process for estimating the consumption of oxygen in the catalyst and determining the end timing of the enrichment control, the determination is made based on the allowable oxygen storage amount of the new catalyst. When the current allowable oxygen storage amount is reduced due to catalyst deterioration), all of the oxygen actually stored in the catalyst is reduced before the above-described determination condition “oxygen in the catalyst is consumed” is satisfied. May be consumed. In such a situation, the enrichment control time becomes excessive, and there is concern about deterioration of HC and CO and an increase in fuel consumption.

Considering such points, in the present invention, after the enrichment control is started, even if the estimated oxygen consumption does not reach the allowable oxygen storage amount of the new catalyst, the O ₂ sensor on the downstream side of the catalyst The enrichment control is terminated when the output changes to the rich side. In this way, the enrichment control can always be terminated at an appropriate timing regardless of changes in the catalyst performance (oxygen storage amount) due to deterioration over time.

As described above, according to the present invention, enrichment is performed based on the consumption (estimated amount) of oxygen in the catalyst during execution of enrichment control at the time of fuel cut recovery and the output of the O ₂ sensor on the downstream side of the catalyst. Since the end timing of the control is determined, the enrichment control can always be ended at an appropriate timing according to the amount of oxygen actually stored in the catalyst when returning from the fuel cut. As a result, it is possible to suppress the deterioration of exhaust emission even if many fuel cuts aimed at improving fuel efficiency are repeated. Furthermore, it is possible to realize a stable enrichment (fuel increase) at the time of return from fuel cut regardless of catalyst deterioration due to aging. As a result, both improvement in exhaust gas purification performance and reduction in fuel consumption can be achieved.

Here, when determining the end timing of the enrichment control based on the output of the O ₂ sensor on the downstream side of the catalyst, the enrichment control at the time of returning from the fuel cut can be terminated at a timing according to the catalyst deterioration. When the catalyst is a new product, the enrichment control at the time of fuel cut return may not be properly terminated only by the determination based on the output of the O ₂ sensor (rich determination). This point will be described.

First, in recent years, there has been an increasing demand for reduction of exhaust gas, and in order to satisfy this requirement, improvement in catalyst purification performance has been attempted. As the catalyst purification performance increases, the oxygen storage performance of the catalyst also improves. For this reason, when the catalyst is new, the output of the O ₂ sensor on the downstream side of the catalyst may not show a rich value even if oxygen in the catalyst is consumed by the enrichment control at the time of fuel cut return. This has been confirmed by experiments of the present inventors.

In this way, when the catalyst is new and the catalyst purification performance is high, the enrichment control is continued for a long time or the enrichment control does not end only by the determination based on the output of the O ₂ sensor on the downstream side of the catalyst. In the present invention, as described above, since it is determined whether or not oxygen corresponding to the allowable oxygen storage amount of the new catalyst has been consumed, the O ₂ sensor on the downstream side of the catalyst is Even if the output does not become rich, the enrichment control is terminated when oxygen corresponding to the allowable oxygen storage amount of the new catalyst is consumed. Therefore, even when the catalyst is new, the enrichment control at the time of returning from the fuel cut can be terminated at an appropriate timing. As a result, it is possible to realize richness (fuel increase) when returning from a fuel cut, which is stable from a new car to an aged car.

  In the present invention, when the enrichment control at the time of fuel cut return is terminated, the raised value of the air-fuel ratio feedback correction value at the time of execution of the enrichment control is gradually attenuated to return the air-fuel ratio to stoichiometry. Also good. By adopting such a configuration, it is possible to prevent the operating state of the internal combustion engine from changing suddenly at the end of the enrichment control, and to suppress a shock.

  According to the present invention, in an air-fuel ratio control apparatus for an internal combustion engine that performs enrichment control when returning from a fuel cut, the enrichment control can always be terminated at an appropriate timing. Even if this frequency increases, it is possible to suppress the deterioration of exhaust emission. Furthermore, even if the catalyst purification performance changes due to catalyst deterioration due to aging, regardless of this, it is possible to always realize a stable enrichment at the time of fuel cut recovery. As a result, both improvement in exhaust gas purification performance and reduction in fuel consumption can be achieved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, an engine (internal combustion engine) to which the present invention is applied will be described.

-Engine-
FIG. 1 is a diagram showing a schematic configuration showing an example of an engine 1 to which the present invention is applied. FIG. 1 shows only the configuration of one cylinder of the engine 1.

  The engine 1 in this example is, for example, a four-cylinder gasoline engine, and includes a piston 1b that forms a combustion chamber 1a and a crankshaft 15 that is an output shaft. The piston 1b is connected to the crankshaft 15 via the connecting rod 16, and the reciprocating motion of the piston 1b is converted into rotation of the crankshaft 15 by the connecting rod 16.

  A signal rotor 17 having a plurality of protrusions (teeth) 17 a on the outer peripheral surface is attached to the crankshaft 15. A crank position sensor (engine speed sensor) 24 is disposed near the side of the signal rotor 17. The crank position sensor 24 is, for example, an electromagnetic pickup, and generates a pulsed signal (output pulse) corresponding to the protrusion 17a of the signal rotor 17 when the crankshaft 15 rotates. Further, a water temperature sensor 21 that detects the temperature of the cooling water of the engine 1 is disposed in the cylinder block 1 c of the engine 1.

  A spark plug 3 is disposed in the combustion chamber 1 a of the engine 1. The ignition timing of the spark plug 3 is adjusted by the igniter 4. The igniter 4 is controlled by an ECU (Electronic Control Unit) 100.

  An intake passage 11 and an exhaust passage 12 are connected to the combustion chamber 1 a of the engine 1. An intake valve 13 is provided between the intake passage 11 and the combustion chamber 1a. By opening and closing the intake valve 13, the intake passage 11 and the combustion chamber 1a are communicated or blocked. Further, an exhaust valve 14 is provided between the exhaust passage 12 and the combustion chamber 1a. By opening and closing the exhaust valve 14, the exhaust passage 12 and the combustion chamber 1a are communicated or blocked. The opening / closing drive of the intake valve 13 and the exhaust valve 14 is performed by each rotation of the intake camshaft and the exhaust camshaft to which the rotation of the crankshaft 15 is transmitted.

  In the intake passage 11, an air cleaner 7, a hot-wire air flow meter 22 that detects the intake air amount, an intake air temperature sensor 23 (built in the air flow meter 22), and an electronically controlled throttle that adjusts the intake air amount of the engine 1. A valve 5 is arranged. The throttle valve 5 is driven by a throttle motor 6. The opening degree of the throttle valve 5 is detected by a throttle opening degree sensor 25.

A three-way catalyst 8 is disposed in the exhaust passage 12 of the engine 1. A front O ₂ sensor (main O ₂ sensor) 27 is disposed in the exhaust passage 12 upstream of the three-way catalyst 8. The front O ₂ sensor 27 is a sensor that exhibits linear characteristics with respect to the air-fuel ratio. A rear O ₂ sensor (sub O ₂ sensor) 28 is disposed in the exhaust passage 12 on the downstream side of the three-way catalyst 8. The rear O ₂ sensor 28 generates an electromotive force in accordance with the oxygen concentration in the exhaust gas. When the output is higher than a voltage (comparison voltage) corresponding to the theoretical air-fuel ratio, the rear O ₂ sensor 28 determines that the output is rich. When the output is lower than the comparison voltage, it is determined as lean.

  A fuel injection injector 2 is disposed in the intake passage 11. Fuel of a predetermined pressure is supplied from the fuel tank to the injector 2 by a fuel pump, and the fuel is injected into the intake passage 11. This injected fuel is mixed with intake air to form an air-fuel mixture and introduced into the combustion chamber 1a of the engine 1. The air-fuel mixture (fuel + air) introduced into the combustion chamber 1a is ignited by the spark plug 3 and burns and explodes. The piston 1b reciprocates due to combustion / explosion of the air-fuel mixture in the combustion chamber 1a, and the crankshaft 15 rotates. The operation state of the engine 1 described above is controlled by the ECU 100.

-ECU-
As shown in FIG. 2, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like.

  The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

  The CPU 101, the ROM 102, the RAM 103, and the backup RAM 104 are connected to each other via the bus 107, and are connected to the input interface 105 and the output interface 106.

The input interface 105 includes a water temperature sensor 21, an air flow meter 22, an intake air temperature sensor 23, a crank position sensor 24, a throttle opening sensor 25, an accelerator opening sensor 26 that outputs a detection signal corresponding to the depression amount of the accelerator pedal, a front An O ₂ sensor 27, a rear O ₂ sensor 28, and the like are connected. On the other hand, the output interface 106 is connected to the injector 2, the igniter 4 of the spark plug 3, the throttle motor 6 of the throttle valve 5, and the like.

The above-described injector 2, air flow meter 22, front O ₂ sensor 27, rear O ₂ sensor 28, ECU 100, and the like realize an air-fuel ratio control device. ,
Then, ECU 100 executes various controls of engine 1 based on the detection signals of the various sensors described above.

For example, the main air-fuel ratio feedback control is executed based on the output of the front O ₂ sensor 27 arranged in the exhaust passage 12 (upstream of the three-way catalyst 8) of the engine 1. Further, the sub air-fuel ratio feedback control is executed based on the output of the rear O ₂ sensor 28 disposed in the exhaust passage 12 (downstream of the three-way catalyst 8) of the engine 1.

In the main air-fuel ratio feedback control, the amount of fuel injected from the injector 2 to the intake passage 11 is controlled so that the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 8 matches the control target air-fuel ratio. Further, in the sub air-fuel ratio feedback control, more specifically, the rear disposed on the downstream side of the three-way catalyst 8 so that the air-fuel ratio of the exhaust gas flowing out downstream of the three-way catalyst 8 becomes the stoichiometric air-fuel ratio. The content of the main air-fuel ratio feedback control is corrected so that the output of the O ₂ sensor 28 becomes stoichiometric. By executing these air-fuel ratio feedback control, the air-fuel ratio on the downstream side of the three-way catalyst 8 can be accurately maintained at a value close to the stoichiometric air-fuel ratio, and excellent emission characteristics can be realized.

  Further, the ECU 100 executes a fuel cut (F / C) for stopping fuel injection from the injector 2 when a predetermined fuel cut start condition is satisfied. As the fuel cut start condition, for example, the accelerator opening detected by the accelerator opening sensor 26 indicates 0% (fully closed state), and the engine read from the output signal of the crank position sensor 24 is used. For example, the rotational speed is higher than a fuel cut reference rotational speed for executing the fuel cut.

  If such fuel cut is continued, basically only air passes through the exhaust passage 12, so that the three-way catalyst 8 in the exhaust passage 12 is oxygenated immediately after returning from the fuel cut. When exhaust gas containing NOx is exhausted in this state, the NOx is blown through the three-way catalyst 8 without being reduced.

  In order to prevent this, in this example, NOx emission is reduced by executing enrichment control that forcibly enriches the air-fuel ratio of the air-fuel mixture when returning from the fuel cut. The enrichment control is control for raising the air-fuel ratio feedback correction value FAF (see FIGS. 4 and 5). The rich air-fuel ratio in the enrichment control at the time of fuel cut recovery is calculated based on the operating state such as the engine speed and the accelerator opening, and the fuel is calculated based on the calculated air-fuel ratio and the intake air amount. An injection amount (fuel injection time) is calculated.

  In this example, the enrichment control at the time of fuel cut return starts at step ST203 in the flowchart of FIG. 3 described later, and ends at step ST206.

  Further, the ECU 100 executes the following “start / end control of the enrichment control at the time of fuel cut return”.

-Start / end control of enrichment control when returning from fuel cut-
First, as described above, the oxygen storage amount of the three-way catalyst 8 used for purifying the exhaust gas decreases as the catalyst deteriorates over time. However, in the conventional control, changes in the oxygen storage amount (storage performance) due to catalyst deterioration are not taken into consideration. For this reason, for example, the enrichment control at the time of fuel cut return is always executed for a certain time. In this case, when the oxygen storage amount of the three-way catalyst 8 is large at the time of a new vehicle (when the catalyst is new), there is a possibility that the enrichment is insufficient and NOx is discharged. When the oxygen storage amount is reduced, the enrichment becomes excessive, which may cause deterioration of HC and CO and increase in fuel consumption.

  In addition, in the engine 1 mounted on the vehicle, the frequency (condition / time) of performing the fuel cut for increasing the fuel efficiency tends to increase more and more, but the enrichment control time when the fuel cut is restored is appropriately controlled. If the frequency of fuel cuts increases in a situation where it is not done, there is a concern that exhaust emissions will deteriorate.

In consideration of such points, in this example, the timing for ending the enrichment control upon returning from the fuel cut is based on the oxygen storage amount (estimated amount) of the three-way catalyst 8 and the output of the rear O ₂ sensor 28. By controlling, it is characterized in that the enrichment (fuel increase) at the time of stable fuel cut recovery is realized at all times. An example of the specific control will be described with reference to FIGS.

  FIG. 3 is a flowchart showing an example of a control routine for start / stop control of enrichment control upon return from fuel cut. The control routine of FIG. 3 is repeatedly executed in the ECU 100 at predetermined intervals.

  In step ST201, it is determined whether or not it is at the time of fuel cut return (at the time of F / C return). If the determination result is negative, this routine is temporarily exited. If the determination result of step ST201 is affirmative, the process proceeds to step ST202.

In step ST202, it is determined whether or not the output of the rear O ₂ sensor 28 on the downstream side of the three-way catalyst 8 is a value indicating lean, and if the determination result is negative (rich or stoichiometric). ) Once exits this routine.

When the determination result of step ST202 is affirmative (when the rear O ₂ sensor output is lean), the process proceeds to step ST203, and the above-described enrichment control at the time of fuel cut return is started. Furthermore, at the same time as the enrichment control at the time of fuel cut recovery is started, the integration of the intake air amount detected by the air flow meter 22 is started to calculate the integrated intake air amount TGa (step ST204). The integrated intake air amount TGa is returned to the initial value (0) every time the fuel cut is performed.

  The processing of steps ST201 to ST204 will be described with reference to the timing charts of FIGS. 4 and 5. When the fuel cut is being performed (F / C: ON), the fuel cut end condition (for example, accelerator ON, engine speed is The enrichment control (air-fuel ratio feedback correction value FAF raising control) is started at the time ta (at the time of F / C recovery) when the fuel cut reference rotational speed or less is established. Simultaneously with the start of the enrichment control, the integration of the intake air amount Ga is started, and the integrated intake air amount TGa increases with time.

  Next, in step ST205, it is determined whether or not the cumulative intake air amount TGa has become larger than a specified value A. If the determination result in step ST205 is affirmative, that is, it is determined that oxygen in the three-way catalyst 8 has been consumed at time tb (see FIG. 4) when [integrated intake air amount TGa> A]. Proceed to ST206. If the determination result in step ST205 is negative, it is determined that oxygen remains in the three-way catalyst 8, and the process proceeds to step ST207. The determination process in step ST205 will be specifically described.

  First, in the enrichment control at the time of fuel cut return, as described above, oxygen in the three-way catalyst 8 is consumed by HC and CO contained in the exhaust gas. Whether or not the oxygen in the three-way catalyst 8 has been consumed is determined by whether or not the amount of HC and CO that can consume all of the oxygen in the catalyst 8 (the oxygen in the catalyst full state when the fuel cut is restored) has been supplied. be able to.

  Here, when the enrichment degree of the enrichment control at the time of fuel cut recovery is set (fixed) to a certain value, the amount of HC and CO during the enrichment control execution period is equal to the integrated amount of exhaust gas, that is, the integrated intake air amount TGa. Since there is a correlation, the amount of oxygen in the three-way catalyst 8 (oxygen consumption state) can be estimated by calculating the integrated intake air amount TGa. That is, it can be determined (estimated) whether or not all of the oxygen in the three-way catalyst 8 has been consumed from the integrated intake air amount TGa. Therefore, in this example, as shown in FIG. 4, the integration of the intake air amount is started from the time ta when the enrichment control at the time of fuel cut return is started, and the integrated intake air amount TGa is a specified value A (specifically, Is determined (TGa> A) when the amount of HC and CO that can consume all of the oxygen in the three-way catalyst 8 is reached (TGa> A), it is determined that the oxygen in the three-way catalyst 8 has been consumed.

  The specified value A used for the above oxygen consumption determination is based on the allowable oxygen storage amount (upper limit of the oxygen storage amount) of the three-way catalyst 8 at the time of a new product, and the allowable oxygen storage amount (full oxygen storage amount). The amounts of HC and CO that can consume all of oxygen are obtained in advance by experiments and calculations, etc., and based on the HC and CO amounts and the enrichment degree of enrichment control (FAF raising value), the three-way catalyst 8 It is only necessary to calculate an integrated intake air amount that can consume all of the oxygen stored in a full state and to set it based on the calculated value.

  If the determination result in step ST205 is affirmative (TGa> A), that is, if it is determined that oxygen in the three-way catalyst 8 has been consumed, the enrichment control is terminated, and at the end of the enrichment control, As shown in FIG. 4, the damping control of the raised value of the air-fuel ratio feedback correction value FAF is executed (step ST206), the air-fuel ratio is returned to stoichiometric, and the normal air-fuel ratio feedback control (stoichiometric control) is resumed.

  The reason for executing the attenuation control of the increase value of the air-fuel ratio feedback correction value FAF at the end of the enrichment control is that the increase value of the air-fuel ratio feedback correction value FAF is increased to the normal value (stoichiometric control value) at the end of the enrichment control. This is to suppress such a shock in view of the fact that when the engine speed is lowered, the operating state of the engine 1 changes suddenly and a shock may occur.

On the other hand, when the determination result of step ST205 is negative (when it is determined that oxygen remains in the three-way catalyst 8), the process proceeds to step ST207. In step ST207, it is determined whether or not the output of the rear O ₂ sensor 28 on the downstream side of the three-way catalyst 8 has changed to the rich side. If the determination result is a negative determination, the process returns to step ST204 to return to the integrated intake air. The calculation of the amount TGa is continued.

If the determination result in step ST207 is affirmative (when the output of the rear O ₂ sensor 28 has changed to the rich side), the process proceeds to step ST206, where the rich control ends when the fuel cut returns and the rich control is performed. Attenuation control of the raised value of the air-fuel ratio feedback correction value FAF at the end is executed.

As described above, the enrichment control at the time of fuel cut return is completed by ending the enrichment control at the time of fuel cut return by the determination based on the output of the rear O ₂ sensor 28, even when the three-way catalyst 8 is deteriorated. Can be terminated at an appropriate timing. This point will be described.

  First, in the determination process of step ST205, that is, the process of estimating the consumption of oxygen in the three-way catalyst 8 and determining the end of the enrichment control, the determination is performed based on the allowable oxygen storage amount of the new three-way catalyst 8. Therefore, when the allowable oxygen storage amount of the three-way catalyst 8 changes (decreases) due to aging (catalyst deterioration), before the above-described determination condition [integrated intake air amount TGa> A] is satisfied. All of the oxygen actually stored in the three-way catalyst 8 is consumed. In such a situation, the enrichment control time becomes excessive, and there is concern about deterioration of HC and CO and an increase in fuel consumption.

Considering such points, in this example, as shown in FIG. 5, after the enrichment control at the time of fuel cut return is started, the above-described determination condition [integrated intake air amount TGa> A] is not satisfied. However, when the output of the rear O ₂ sensor 28 changes to the rich side, NOx is not exhausted, so at the time tc, the enrichment control at the time of fuel cut return is terminated and returned to stoichiometry. By doing so, the enrichment control at the time of returning from the fuel cut can always be terminated at an appropriate timing regardless of the change in the performance (oxygen storage amount) of the three-way catalyst 8 due to catalyst deterioration.

Incidentally, the time (end time) tc to end the enrichment control based on the output of the rear O ₂ sensor 28 may but if when the output of the rear O ₂ sensor 28 has changed from lean to rich side, the rear O the amount of change from the lean to the rich side of the output of the _second sensor 28 [Delta] S (Figure 5) it is desirable to when it becomes larger than a predetermined threshold value Th. The threshold value Th set for the change amount ΔS may be determined in consideration of the output characteristics of the rear O ₂ sensor 28 and the like.

As described above, in the control of this example, the oxygen amount in the three-way catalyst 8 is estimated based on the integrated intake air amount during execution of the enrichment control at the time of fuel cut return, and “the oxygen in the three-way catalyst 8 is The enrichment control ends when it is determined that it has been consumed, and the enrichment control ends when the output of the rear O ₂ sensor 28 changes to the rich side even when the oxygen consumption is determined. The enrichment control at the time of fuel cut return can always be terminated at an appropriate timing.

Specifically, as shown in FIGS. 4 and 5, first, when the three-way catalyst 8 is new, all of the oxygen stored in the three-way catalyst 8 in a full state when returning from the fuel cut is The enrichment control ends at the time when it is estimated that the consumption is performed by the enrichment control (the time tb when the integrated intake air amount TGa> A is satisfied). Next, when the three-way catalyst 8 deteriorates and the oxygen storage amount decreases, before the integrated intake air amount TGa> A, all of the oxygen in the three-way catalyst 8 is consumed, and downstream of the three-way catalyst 8. When HC and CO start to be discharged to the side, the output of the rear O ₂ sensor 28 changes to the rich side, and the enrichment control ends at this time tc. As the catalyst deterioration progresses and the oxygen storage amount of the three-way catalyst 8 decreases, the time during which all of the oxygen in the three-way catalyst 8 is consumed is shortened. Since the time (riching control time) from when the output of the rear O ₂ sensor 28 changes to the rich side becomes short (riching control time), the riching control ends at a timing according to the deterioration state of the three-way catalyst 8.

  In this way, when returning from the fuel cut, the enrichment control can always be terminated at an appropriate timing in accordance with the amount of oxygen actually stored in the three-way catalyst 8, so that the fuel consumption can be improved. Even if many fuel cuts are repeated, deterioration of exhaust emission can be suppressed. Furthermore, even when the catalyst purification performance changes due to catalyst deterioration due to aging, regardless of this, stable enrichment (fuel increase) at the time of fuel cut recovery can be realized. As a result, both improvement in exhaust gas purification performance and reduction in fuel consumption can be achieved.

Here, when the three-way catalyst 8 is new and the catalyst purification performance is high, as described above, even if oxygen stored in the three-way catalyst 8 is consumed by the enrichment control at the time of fuel cut return, the rear The output of the O ₂ sensor 28 may not change to the rich side. In this case, there is a concern that the enrichment control is continued for a long time only by the determination based on the output of the rear O ₂ sensor 28, or the enrichment control does not end. When it is determined that the oxygen corresponding to the allowable oxygen storage amount of the new three-way catalyst 8 has been consumed during the execution of the enrichment control, the enrichment control is terminated. Therefore, when the three-way catalyst 8 is new However, the enrichment control at the time of returning from the fuel cut can be terminated at an appropriate timing. As a result, it is possible to realize richness (fuel increase) when returning from a fuel cut, which is stable from a new car to an aged car.

-Other embodiments-
In the above example, the accumulation of the intake air amount is started simultaneously with the start of the enrichment control at the time of fuel cut recovery, and the oxygen consumption amount in the catalyst is estimated based on the accumulated intake air amount. Instead, the integration of the fuel injection amount may be started simultaneously with the start of the enrichment control at the time of fuel cut recovery, and the oxygen consumption amount in the catalyst may be estimated based on the integrated fuel injection amount. The integrated fuel injection amount may be obtained from, for example, a fuel injection amount command value that is calculated according to the operating state of the engine 1.

  In the above example, the present invention is applied to the air-fuel ratio control of the port injection type gasoline engine. However, the present invention is not limited to this, and is also applied to the air-fuel ratio control of the in-cylinder direct injection type gasoline engine. Is possible. In addition to the in-line multi-cylinder gasoline engine, the present invention can be applied to air-fuel ratio control of a V-type multi-cylinder gasoline engine.

It is a schematic block diagram which shows an example of the engine (internal combustion engine) to which this invention is applied. It is a block diagram which shows the structure of control systems, such as ECU. It is a flowchart which shows an example of the start / end control of the enrichment control at the time of fuel cut return. It is a timing chart which shows an example of the start / end control of the enrichment control at the time of fuel cut return. It is a timing chart which shows an example of the start / end control of the enrichment control at the time of fuel cut return.

Explanation of symbols

1 Engine 8 Three-way catalyst 11 Intake passage 12 Exhaust passage 2 Injector 22 Air flow meter 24 Crank position sensor 25 Throttle opening sensor 26 Accelerator opening sensor 27 Front O ₂ sensor 28 Rear O ₂ sensor 100 ECU

Claims (5)

A catalyst disposed in the exhaust passage, an O ₂ sensor disposed in the exhaust passage on the downstream side of the catalyst, and a fuel cut that stops fuel supply to the internal combustion engine when a fuel cut condition is satisfied. An air-fuel ratio control device applied to an internal combustion engine comprising a fuel cut control means,
Enrichment control start means for starting enrichment control to make the air-fuel ratio richer than the stoichiometric air-fuel ratio when the output of the O ₂ sensor is a value indicating lean at the time of return from the fuel cut; and the enrichment After starting the control, a determination unit that determines whether or not oxygen in the catalyst is consumed, and after the enrichment control is started, the determination unit determines that "the oxygen in the catalyst has been consumed" Or an enrichment control end means for terminating the enrichment control when the output of the O ₂ sensor changes to the rich side. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
The air-fuel ratio control apparatus for an internal combustion engine, wherein the determination means determines whether or not an amount of oxygen corresponding to an allowable oxygen storage amount when the catalyst is new is consumed. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2,
The determination means integrates the intake air amount of the internal combustion engine from the time when the enrichment control is started, estimates the oxygen amount in the catalyst based on the integrated intake air amount, and the oxygen in the catalyst is An air-fuel ratio control apparatus for an internal combustion engine, wherein it is determined whether or not it has been consumed. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2,
The determination means integrates the fuel injection amount of the internal combustion engine from the time when the enrichment control is started, estimates the oxygen amount in the catalyst based on the integrated fuel injection amount, and the oxygen in the catalyst An air-fuel ratio control apparatus for an internal combustion engine, wherein it is determined whether or not it has been consumed. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4,
An air-fuel ratio control apparatus for an internal combustion engine, wherein the increase value of the air-fuel ratio feedback correction value at the time of execution of the enrichment control is gradually attenuated when the enrichment control is terminated.

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