JP2009281176A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To immediately return the amount of oxygen storage of a catalyst to a neutral state while ensuring engine startability when restarting fuel supply accompanying with the automatic restart of an internal combustion engine. <P>SOLUTION: An exhaust emission control catalyst having an oxygen storage function is provided in an exhaust passage of the internal combustion engine. When the automatic restart is required (S11), a neutral air-fuel ratio λ1 on a rich side for neutralizing the amount of oxygen storage in the exhaust emission control catalyst is calculated based on the actual amount of oxygen storage (S13). Also, a limit air-fuel ratio λ0 on the rich side set from the combustion limit of the internal combustion engine is calculated (S14). When the neutral air-fuel ratio λ1 exceeds the limit air-fuel ratio λ0, a target air-fuel ratio is set to the limit air-fuel ratio λ0 (S16), and also the amount of air sucked is increased according to a difference between the neutral air-fuel ratio λ1 and the limit air-fuel ratio λ0 (S17). When the λ1 is less than the λ0, the target air-fuel ratio is set to the neutral air-fuel ratio λ1 without correcting a target amount of air sucked (S18). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine mounted on an idle stop vehicle that automatically stops and restarts the internal combustion engine.

As a conventional exhaust emission control device for an internal combustion engine, for example, there is one described in Patent Document 1. In this case, when the fuel supply is restarted from the state where the fuel supply is stopped during the deceleration operation, the fuel increase is performed so that the oxygen accumulation (storage) amount of the exhaust purification catalyst becomes a neutral state. Accordingly, the ignition timing is retarded and the intake air amount is increased, thereby suppressing the NOx (nitrogen oxide) emission amount without increasing the HC (hydrocarbon) emission amount.
JP-A-11-101150

  When the fuel supply is restarted from the fuel supply cut-off state, the amount of oxygen stored in the catalyst varies depending on the catalyst capacity, the amount of noble metal, the deterioration of the catalyst, etc., and the oxygen storage amount in the catalyst is appropriately neutralized. In order to achieve this, it is necessary to change the fuel increase amount at the time of resumption of fuel supply, that is, the rich degree of the target air-fuel ratio, according to the state of the catalyst. However, since the degree of richness of the target air-fuel ratio is limited from the combustion limit, if the target air-fuel ratio is excessively enriched, there is a possibility that the combustion stability at the time of resumption of fuel supply may be impaired.

  In particular, in the case of an idle stop vehicle that performs automatic stop and automatic restart of the internal combustion engine, when the fuel supply is restarted in the automatic restart, the internal combustion engine is stopped, that is, the rotation of the crankshaft is stopped. As in the general non-idle stop vehicle described in Patent Document 1 described above, the fuel is cut during deceleration, and the fuel supply is resumed during deceleration, that is, during rotation of the crankshaft of the internal combustion engine. In comparison with this, it is difficult to ensure the combustion stability, that is, the startability at the time of automatic engine restart, and the enrichment of the air-fuel ratio is greatly limited due to the combustion limit.

  The present invention has been made in view of such problems, and at the time of resumption of fuel supply accompanying automatic restart in an idle stop vehicle, the oxygen storage amount of the catalyst is quickly brought to a neutral state without impairing engine startability. The main purpose is to restore.

  In an exhaust purification device for an internal combustion engine of an idle stop vehicle that automatically stops and restarts the internal combustion engine, an exhaust purification catalyst having an oxygen storage function is provided in an exhaust passage of the internal combustion engine. The target air-fuel ratio and the target intake air amount are set according to the engine operating state, and the fuel injection amount and the intake air amount are controlled based on the target air-fuel ratio and the target intake air amount. When the fuel supply is resumed due to the automatic restart, the target intake air amount is corrected to the increase side based on the actual oxygen storage amount stored in the exhaust purification catalyst while setting the target air-fuel ratio to the rich side. To do.

  According to the present invention, when fuel supply is restarted due to automatic restart in an idle stop vehicle, the target intake air amount is corrected to the increase side based on the actual oxygen storage amount while setting the target air-fuel ratio to the rich side. In addition, the oxygen storage amount of the catalyst can be quickly returned to the neutral state without causing deterioration in engine startability due to excessive enrichment of the target air-fuel ratio.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an internal combustion engine 1 according to an embodiment of the present invention. The air sucked into the internal combustion engine 1 passes through the air cleaner 2, is then measured for the flow rate by the air flow meter 3, and is guided to the electric throttle valve 4. The electric throttle valve 4 controls the intake air amount according to the target intake air amount. Thereafter, the intake air passes through the intake collector 5 and the intake manifold 6 and is introduced into the combustion chamber 8 via the intake valve 7.

  The combustion injection valve 9 injects fuel to the intake air in the combustion chamber 8 to form an air-fuel mixture, and the spark plug 10 ignites and burns this air-fuel mixture. Then, the combustion exhaust is discharged to the exhaust passage 12 through the exhaust valve 11.

  An exhaust purification catalyst 13 is provided in the exhaust passage 12. The exhaust purification catalyst 13 includes, for example, platinum (Pt) -rhodium (Rh) or palladium (Pd) -rhodium-based noble metal (catalyst component), and additives (co-catalyst) such as ceria (CeO2) and lanthanum (La). ), And purifies CO, HC, and NOx, which are harmful components in the exhaust gas, with high efficiency at a stoichiometric air-fuel ratio (neutral state of oxygen storage equivalent to the stoichiometric air-fuel ratio). An oxygen concentration sensor 14 for detecting the oxygen concentration in the exhaust gas is provided upstream of the exhaust purification catalyst 13. When the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio, this oxygen concentration sensor 14 is used for fuel injection control. Air-fuel ratio feedback control based on the output signal is executed.

  The intake air amount by the electric throttle valve 4, the fuel injection amount by the fuel injection valve 9, the ignition timing by the spark plug 10, and the like are controlled by an engine control unit (hereinafter referred to as "ECU") 20 as a control unit. . In addition to the intake air amount Qa detected by the air flow meter 3 and the output signal of the oxygen concentration sensor 14, the ECU 20 includes the accelerator opening APO detected by the accelerator pedal sensor 21 and the engine rotational speed detected by the crank angle sensor 22. Ne, the engine coolant temperature Tw detected by the water temperature sensor 23, the intake pressure Pa detected by the intake pressure sensor 24, the vehicle speed V detected by the vehicle speed sensor 25, and the brake (not shown) detected by the brake sensor 26. Operation (ON / OFF), a shift lever position of an automatic transmission (not shown) detected by the shift lever position sensor 27, and the like are input.

  During normal operation, the ECU 20 calculates a required torque tTe of the internal combustion engine 1 mainly based on the accelerator opening APO, and based on the required torque tTe, the engine rotational speed Ne, the engine coolant temperature Tw, and the like. Then, a target equivalent ratio TFBYA corresponding to the target air-fuel ratio is calculated. This target equivalent ratio TFBYA is the reciprocal of the excess air ratio λ, and is 1.0 for the theoretical air-fuel ratio, a value smaller than 1 for the lean air-fuel ratio, and a value larger than 1 for the rich air-fuel ratio. Then, the electric throttle valve 4 is driven so as to obtain an air amount necessary for realizing the target equivalent ratio TFBYA. Further, the basic fuel injection amount Tp = K × Qa / Ne (K; constant) is calculated from the intake air amount Qa and the engine rotational speed Ne, and this is multiplied by the target equivalent ratio TFBYA to obtain the final fuel injection. The amount Ti = Tp × TFBYA × COEF (COEF; various correction coefficients) is calculated. The fuel injection valve 9 is driven by outputting a fuel injection pulse signal having a pulse width corresponding to the final fuel injection amount Ti. The ignition timing by the spark plug 10 is controlled based on the engine speed Ne, the required torque tTe, and the like.

  Further, the ECU 20 executes an idle stop for automatically stopping the internal combustion engine 1 when a predetermined idle stop condition is satisfied, and idles when a predetermined idle stop release condition is satisfied during the idle stop execution. A so-called idle stop (automatic stop / restart) control is performed in which the stop is released and the starter 15 is automatically driven to restart the internal combustion engine 1.

  FIG. 2 shows the vehicle speed, the air-fuel ratio (A / F), the engine speed, and the engine restart speed in the engine operation state that reaches the restart state A4 through the steady state A1, the deceleration state A2, the stop state A3 of the internal combustion engine. It is a timing chart which shows the mode of change of the amount of intake air.

  In the steady running state A1, the target equivalent ratio TFBYA corresponding to the target air-fuel ratio is set to 1.0 corresponding to the theoretical air-fuel ratio, and the above-described air-fuel ratio feedback control is performed. When shifting to the deceleration state A2, the fuel supply is stopped, so-called fuel cut is performed, and then the engine speed decreases as the vehicle speed decreases. When the vehicle stops, the engine speed becomes zero and the engine is automatically stopped. . In other words, in the idle stop vehicle of this embodiment, even if the engine speed drops below the idle speed during vehicle deceleration, the fuel supply is not resumed, and the engine automatically stops, so-called idle stop state. As described above, since the fuel cut is performed promptly when shifting to the deceleration state A2, the oxygen storage amount of the catalyst inevitably becomes leaner from the deceleration state A to the stop state A3.

  Therefore, in this embodiment, when the fuel supply is restarted due to the automatic engine restart from the engine automatic stop state A3 after the fuel cut accompanying the deceleration, the target air-fuel ratio is set to the rich side and the actual oxygen storage amount is set. Based on this, the target intake air amount is corrected to the increase side.

  FIG. 3 is a flowchart showing the flow of processing for setting the target air-fuel ratio (target equivalent ratio TFBYA) and the target intake air amount when fuel supply is restarted due to such automatic engine restart. In step S11, it is determined whether or not there is an engine automatic restart request. For example, (1) the brake is turned off, or (2) the start operation (accelerator operation or the like) by the driver is a condition for the restart request. If it is determined that there is a restart request, the process proceeds to step S12 and subsequent steps.

  In this step S12, the actual oxygen storage amount (OSC) stored in the exhaust purification catalyst 13 is read. This actual oxygen storage amount is constantly detected and monitored based on the detection signal of the oxygen concentration sensor 14 by other routines (not shown). In step S13, based on the actual OSC, when the fuel supply is restarted due to the restart, the target air-fuel ratio necessary for making the oxygen storage amount in the catalyst neutral, that is, the correction amount to the rich side of the target air-fuel ratio. Is calculated.

  In step S14, the limit air-fuel ratio λ0, which is the rich limit of the target air-fuel ratio at the time of engine restart required from the combustion limit of the internal combustion engine, is read. This limit air-fuel ratio λ0 is basically a fixed value that is preset and stored in consideration of the combustion limit of the internal combustion engine and the variation in air-fuel ratio when the engine is restarted. However, when the catalyst temperature is high and the atmosphere in the catalyst is rich, the deterioration of the catalyst is likely to proceed. Therefore, the limit air-fuel ratio λ0 is preferably corrected according to the catalyst temperature. Specifically, the limit air-fuel ratio λ0 is corrected to the lean side as the catalyst temperature increases. The catalyst temperature can be estimated based on a detection signal of the oxygen concentration sensor 14 or the like, but may be detected directly by providing a temperature sensor.

  In step S15, the limit air-fuel ratio λ0 is compared with the neutral air-fuel ratio λ1. When the neutral air-fuel ratio λ1 exceeds the limit air-fuel ratio λ0, the process proceeds to step S16, and the target air-fuel ratio is set to the limit air-fuel ratio λ0. Then, in step S17, the target intake air amount is corrected to be increased, that is, increased in accordance with the difference (λ1-λ0) between the neutral air-fuel ratio λ1 and the limit air-fuel ratio λ0. A broken line portion indicated by an arrow Y1 in FIG. 2 corresponds to the increased amount.

  As a result, while the correction of the target air-fuel ratio to the rich side is limited to the limit air-fuel ratio λ0 corresponding to the combustion limit, the increase in the exhaust gas volume enriched by the increase in the intake air amount causes the combustion at the time of engine restart While ensuring stability, that is, startability, the inside of the catalyst can be quickly returned to the neutral state. Here, although the engine output increases due to an increase in the intake air amount, the engine restart from the vehicle automatic stop state is almost an acceleration state, so there is not much discomfort to the passengers, and it rebounds to engine operability. There are few.

  On the other hand, when the neutral air-fuel ratio λ1 is equal to or less than the limit air-fuel ratio λ0, the process proceeds from step S15 to step S18, and the target air-fuel ratio is set to the neutral air-fuel ratio λ1. That is, when the neutral air-fuel ratio λ1 is equal to or less than the limit air-fuel ratio λ0, the target intake air amount is not corrected, and only the correction on the rich side of the target air-fuel ratio is supported.

  Such characteristic configurations and operational effects of this embodiment will be listed below.

  (1) An exhaust purification catalyst 13 disposed in the exhaust passage 12 of the internal combustion engine 1 and having an oxygen storage function, a target air-fuel ratio (target equivalent ratio TFBYA) and a target intake air amount are set according to the engine operating state, An ECU (control unit) 20 that controls the fuel injection amount and the intake air amount based on the target air-fuel ratio and the target intake air amount, and can realize an idle stop that automatically stops and restarts the internal combustion engine. It is. Then, when the fuel supply is restarted due to the automatic restart (step S11), the actual oxygen storage amount stored in the exhaust purification catalyst 13 (step S12) while setting the target air-fuel ratio to the rich side (steps S16 and S18). ), The target intake air amount is corrected to the increase side (step S17).

  Due to idling of the main motion system including the crankshaft from the fuel cut to the engine automatic stop, the oxygen storage amount in the catalyst when the engine is stopped is made lean, and when the fuel supply is restarted due to the engine restart, the exhaust emission is reduced. It is necessary to promptly return the inside of the catalyst to the neutral state so as not to cause deterioration. However, when the fuel supply is restarted in the automatic restart, if the air-fuel ratio is excessively rich, combustion stability, that is, engine startability cannot be ensured. In this embodiment, while setting the target air-fuel ratio to the rich side, the target intake air amount is corrected to the increase side based on the actual oxygen storage amount, thereby reducing the combustion stability due to excessive enrichment of the target air-fuel ratio. Thus, the oxygen storage amount of the catalyst can be quickly returned to the neutral state. Although the engine output increases due to the increase in the target intake air amount, the engine is generally in an accelerated state when the engine is restarted, so that there is little rebound to drivability.

  (2) More specifically, the rich side necessary for the oxygen storage amount in the exhaust purification catalyst to be in a neutral state equivalent to the stoichiometric air-fuel ratio based on the actual oxygen storage amount when the fuel supply is restarted in the automatic restart. The neutral air-fuel ratio λ1 is calculated (step S13), and the rich limit air-fuel ratio λ0 determined from the combustion limit of the internal combustion engine at the time of this automatic restart is calculated (step S14). The limit air-fuel ratio λ0 is compared (step S15). If the neutral air-fuel ratio λ1 exceeds the limit air-fuel ratio λ0, the target air-fuel ratio is set to the limit air-fuel ratio λ0 (step S16), and the neutral air-fuel ratio λ1 is set. The target intake air amount is corrected to the increasing side according to the difference between the air-fuel ratio and the limit air-fuel ratio λ0 (step S17). As a result, the amount of increase in the target intake air amount can be obtained with high accuracy while returning the oxygen storage amount to the neutral state, and the increase in the intake air amount can be minimized.

  (3) Further, when the neutral air-fuel ratio λ1 is equal to or less than the limit air-fuel ratio λ0, the target air-fuel ratio is set to the neutral air-fuel ratio λ1 without correcting the target intake air amount (step S18). In other words, if the air / fuel ratio can be dealt with only by enrichment, the intake air amount is not increased as if rebounding to drivability is caused.

  (4) The limit air-fuel ratio λ0 is corrected in accordance with the catalyst temperature of the exhaust purification catalyst 13, and more specifically, the catalyst is more likely to deteriorate as the catalyst temperature increases, so the limit air-fuel ratio is corrected to the lean side. The catalyst can be satisfactorily prevented from being deteriorated.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, in the above embodiment, the present invention is applied to an idle stop vehicle in which the power source is only an internal combustion engine, but the present invention can be similarly applied to a hybrid vehicle using both an electric motor and an internal combustion engine. In the above-described embodiment, the description has been given of the automatic engine restart from the automatic engine stop after the fuel cut due to the deceleration. However, the present invention is not limited to this. For example, the engine automatic from the idle state and the automatic engine stop from the engine automatic stop. The same applies when restarting.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows schematic structure of the internal combustion engine which concerns on one Example of this invention. The timing chart which shows the change of the various parameters in the engine automatic stop and automatic restart state from vehicle deceleration in a present Example. The flowchart which shows the flow of control at the time of the engine restart of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Electric throttle valve 9 ... Fuel injection valve 12 ... Exhaust passage 13 ... Exhaust purification catalyst 14 ... Oxygen concentration sensor 20 ... Engine control unit (control part)

Claims (4)

An exhaust purification catalyst disposed in an exhaust passage of the internal combustion engine and having an oxygen storage function;
A control unit configured to set a target air-fuel ratio and a target intake air amount in accordance with an engine operating state and control a fuel injection amount and an intake air amount based on the target air-fuel ratio and the target intake air amount, and an internal combustion engine In an exhaust purification device for an internal combustion engine of an idle stop vehicle that performs automatic stop / automatic restart of
The control unit increases the target intake air amount based on the actual oxygen storage amount stored in the exhaust purification catalyst while setting the target air-fuel ratio to the rich side when the fuel supply is resumed due to the automatic restart. Correct to the side,
An exhaust emission control device for an internal combustion engine. The control unit
When the fuel supply is restarted in the automatic restart, the neutral air-fuel ratio on the rich side necessary for the oxygen storage amount in the exhaust purification catalyst to be in a neutral state equivalent to the theoretical air-fuel ratio is calculated based on the actual oxygen storage amount And
Compare this neutral air-fuel ratio with the rich limit air-fuel ratio determined from the combustion limit of the internal combustion engine at the time of automatic restart,
When the neutral air-fuel ratio exceeds the limit air-fuel ratio, the target air-fuel ratio is set to the limit air-fuel ratio, and the target intake air amount is corrected to increase according to the difference between the neutral air-fuel ratio and the limit air-fuel ratio. ,
The exhaust emission control device for an internal combustion engine according to claim 1.   3. The control unit according to claim 2, wherein the control unit sets the target air-fuel ratio to the neutral air-fuel ratio without correcting the target intake air amount when the neutral air-fuel ratio is equal to or lower than the limit air-fuel ratio. Exhaust gas purification device for internal combustion engine.   The exhaust purification device for an internal combustion engine according to claim 2 or 3, wherein the control unit corrects the limit air-fuel ratio in accordance with a catalyst temperature of the exhaust purification catalyst.

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