JP2003206791A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure excellent emission by controlling an air-fuel ratio considering the condition of a catalyst when an internal combustion engine is re-started after it is automatically stopped. <P>SOLUTION: The oxygen storage (adsorption and occlusion) of a three-way catalyst 13 immediately before the internal combustion engine 1 is automatically stopped is estimated based on the quantity of exhaust gas flowing into the three-way catalyst 3 and the air-fuel ratio by an air-fuel ratio sensor 25, and fuel is injected so that an equivalence ratio is the inverse of the air-fuel ratio when the internal combustion engine 1 is re-started after it is automatically stopped. The oxygen storage of the three-way catalyst 13 when the internal combustion engine 1 is re-started after it is automatically stopped can be rapidly returned to a neutral state, and excellent emission can be ensured. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, which can improve an exhaust gas purification rate by controlling an air-fuel ratio in consideration of a state of a catalyst.

[0002]

2. Description of the Related Art Conventionally, as a prior art document relating to an exhaust emission control system for an internal combustion engine, one disclosed in Japanese Patent Laid-Open No. 9-88688 is known. In this system, the internal combustion engine is automatically stopped when the vehicle is stopped for a long time, such as waiting for a signal to drive the city, and then the internal combustion engine is restarted without a start operation such as a key operation. The so-called idle stop mechanism for (i.e.) is mounted, and the air-fuel ratio feedback control in the air-fuel ratio control is preferably executed according to the active state of the oxygen concentration (air-fuel ratio) sensor that detects the air-fuel ratio of the exhaust gas. A technique has been disclosed that suppresses deterioration of emissions when the internal combustion engine is restarted by controlling the stoichiometric air-fuel ratio at an early stage.

[Patent Document] Japanese Patent Laid-Open No. 9-88688 (pages 2 to 3)

[0003]

By the way, in the vehicle equipped with the idle stop mechanism of the internal combustion engine and the hybrid vehicle equipped with the internal combustion engine and the electric motor, the vehicle equipped with the internal combustion engine has been wasted until then. In order to reduce the fuel consumption while the vehicle is stopped, the automatic stop and restart of the internal combustion engine are frequently repeated. At this time, the state of the catalyst that purifies the exhaust gas of the internal combustion engine is not taken into consideration at the time of restart or immediately after the restart, and the combustion is not performed at the air-fuel ratio that gives the optimum purification rate of the catalyst. There was a problem that the emission deteriorated at the time of starting and immediately after restarting.

Therefore, the present invention has been made in order to solve such a problem, and in a vehicle equipped with an idle stop mechanism of an internal combustion engine or a hybrid vehicle equipped with the internal combustion engine and an electric motor, after the internal combustion engine is automatically stopped. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can secure good emissions by controlling the air-fuel ratio in consideration of the state of the catalyst when the engine is restarted.

[0005]

According to the exhaust gas purifying apparatus for an internal combustion engine of claim 1, the catalyst state estimating means estimates the oxygen storage amount of the catalyst immediately before the automatic start / stop control means automatically stops the internal combustion engine. Instead of the air-fuel ratio control for controlling to a predetermined air-fuel ratio, fuel is injected by the fuel injection control means so as to have an air-fuel ratio according to the estimated oxygen storage amount of the catalyst at the time of restart after the automatic stop. As a result, when the internal combustion engine is restarted after being automatically stopped, the oxygen storage amount of the catalyst is quickly returned to the neutral state, and good emission is secured.

According to the second aspect of the exhaust gas purifying apparatus of the internal combustion engine, the catalyst state estimating means determines the amount of the exhaust gas flowing into the catalyst and the air-fuel ratio of the exhaust gas of the internal combustion engine detected by the air-fuel ratio sensor. Since the oxygen storage amount is estimated, the state of the catalyst can be accurately grasped.

In the catalyst state estimating means in the exhaust gas purifying apparatus for an internal combustion engine according to claim 3, the estimation of the oxygen storage amount of the catalyst is continued even during the automatic stop of the internal combustion engine, so that it is possible to accurately determine the amount of oxygen storage immediately after the automatic stop. The air-fuel ratio control can be performed according to the oxygen storage amount of various catalysts. As a result, when the internal combustion engine is restarted after being automatically stopped, the oxygen storage amount of the catalyst is quickly returned to the neutral state, and good emission is secured.

In the fuel injection control means in the exhaust gas purifying apparatus for an internal combustion engine according to claim 4, the temperature of the catalyst detected or estimated by the catalyst temperature estimating means is equal to or lower than a predetermined value when the internal combustion engine is restarted after being automatically stopped. Since the catalyst is not in the active state and cannot support the air-fuel ratio control according to the oxygen storage amount of the catalyst, the temperature raising control for activating the catalyst is preferentially executed. As a result, the catalyst is quickly returned to the active state, and emission deterioration is suppressed.

In the exhaust gas purification device for an internal combustion engine according to claim 5,
The temperature condition of the catalyst is estimated by using one or more of the outside air temperature introduced into the internal combustion engine, the stop time as the elapsed time from the automatic stop of the internal combustion engine, and the temperature of the exhaust gas. Is accurately estimated.

According to the exhaust purification system of the internal combustion engine of claim 6,
Since the air-fuel ratio sensor is kept active during the automatic stop of the internal combustion engine, accurate air-fuel ratio control can be performed immediately after restart after the automatic stop, and the oxygen storage amount of the catalyst is quickly returned to the neutral state. Good emissions are secured.

In the fuel injection control means in the exhaust gas purification apparatus for an internal combustion engine according to claim 7, under the condition that the air-fuel ratio control according to the oxygen storage amount of the catalyst is prohibited when the internal combustion engine is restarted after being automatically stopped. Since it is prohibited to maintain the active state of the air-fuel ratio sensor, power saving is achieved.

In the catalyst state estimating means in the exhaust gas purifying apparatus for an internal combustion engine according to claim 8, among the outside air temperature introduced into the internal combustion engine, the stop time as an elapsed time from the automatic stop of the internal combustion engine, and the temperature of the exhaust gas, By correcting the oxygen storage amount of the catalyst using one or more, the state of the catalyst can be accurately estimated.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below based on Examples.

FIG. 1 is a schematic configuration diagram showing an internal combustion engine and its peripheral equipment to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied.

In FIG. 1, an internal combustion engine 1 has an in-line 4-cylinder 4
It is configured as a spark ignition type of cycle, and its intake air passes from an upstream side through an air cleaner 2, an intake passage 3, a throttle valve 4, a surge tank 5 and an intake manifold 6, and an injector (fuel injection valve) 7 in the intake manifold 6. It is mixed with the fuel injected from and is distributed and supplied to each cylinder as an air-fuel mixture having a predetermined air-fuel ratio. Further, the high voltage supplied from the ignition circuit 9 is distributed and supplied by the distributor 10 to the spark plug 8 provided in each cylinder of the internal combustion engine 1, and the air-fuel mixture in each cylinder is ignited at a predetermined timing. The exhaust gas after combustion passes through the exhaust manifold 11 and the exhaust passage 12, and the exhaust passage 1
No. 3, which is a harmful component in the three-way catalyst 13 which carries a catalyst component such as platinum and rhodium and an additive such as cerium and lanthanum, and which is harmful component, such as CO (carbon monoxide), HC (hydrocarbon), and N.
Ox (nitrogen oxide) is purified and discharged into the atmosphere.

An automatic transmission (hereinafter simply referred to as "AT") 14 using a torque converter is provided on an output shaft (crank shaft) (not shown) of the internal combustion engine 1.
Are connected, and the vehicle is driven by the rotation of the output shaft (drive shaft) 15 extending from the AT 14.
A vehicle speed sensor 16 is provided on the output shaft 15 to detect a vehicle speed V as the vehicle speed.

An air flow meter 21 is provided in the intake passage 3 on the downstream side of the air cleaner 2. The air flow meter 21 detects the intake air amount QA passing through the air cleaner 2 per unit time. Further, the throttle valve 4 is provided with a throttle opening sensor 22. The throttle opening sensor 22 detects an analog signal corresponding to the throttle opening TA, and the throttle valve 4 is almost fully closed. It is detected by an "ON" / "OFF" signal from an idle switch (not shown). A water temperature sensor 23 is provided in the cylinder block of the internal combustion engine 1.
At 3, the cooling water temperature THW of the internal combustion engine 1 is detected.

The distributor 10 is provided with a rotation angle sensor 24, and the rotation angle sensor 24 detects the engine speed NE of the internal combustion engine 1. The rotation angle sensor 24 outputs 24 pulse signals every two rotations of the crankshaft of the internal combustion engine 1, that is, every 720 [° CA (Crank Angle)]. Further, the exhaust passage 12
An air-fuel ratio sensor 25 that outputs a linear current signal Is according to the equivalence ratio φ of the exhaust gas of the internal combustion engine 1 is provided on the upstream side of the three-way catalyst 13. This equivalence ratio φ indicates the fuel excess ratio based on the theoretical air-fuel ratio A / F, and is the reciprocal of the air excess ratio λ. Further, the air-fuel ratio sensor 25 is provided with a heater 26 for keeping the air-fuel ratio sensor 25 active.

ECU for controlling the operating state of the internal combustion engine 1
(Electronic Control Unit) 30
Is a CPU 31 as a central processing unit that executes various known arithmetic processes, a ROM 32 that stores control programs and control maps, a RAM 33 that stores various data, and a B / U.
(Backup) It is configured as a logical operation circuit centering on the RAM 34 and the like, and is connected via a bus 37 to an input port 35 for inputting detection signals from various sensors and an output port 36 for outputting control signals to various actuators. ing.

In the ECU 30, the vehicle speed V from the vehicle speed sensor 16 and the air flow meter 2 are input via the input port 35.
Various sensor signals such as the intake air amount QA from 1, the throttle opening TA from the throttle opening sensor 22, the cooling water temperature THW from the water temperature sensor 23, and the engine speed NE from the rotation angle sensor 24 are input to them. The fuel injection amount TAU, the ignition timing Ig, etc. are calculated based on the output port 36.
A control signal is output to each of the injector 7 and the ignition circuit 9 via the.

The equivalence ratio φ of the air-fuel mixture based on the exhaust gas is detected by the linear current signal Is from the air-fuel ratio sensor 25 input to the ECU 30. And EC
U30 is a target equivalence ratio φ set according to the oxygen storage amount during air-fuel ratio F / B (feedback) control described later.
In order to match ref with the actual equivalent ratio φ detected by the air-fuel ratio sensor 25, an air-fuel ratio F / B correction coefficient described later is calculated. It should be noted that this air-fuel ratio F / B control is not executed when the cooling water temperature THW of the internal combustion engine 1 is low or when the engine is running under high load and high rotation speed. Further, as will be described later, the ECU 30 obtains a basic fuel injection amount (basic fuel injection time) from the engine speed NE and the intake air amount QA, and based on this basic fuel injection amount, an air-fuel ratio F / B correction coefficient FAF or the like is used. Correction is performed to calculate the final fuel injection amount (fuel injection time) TAU, and the injector 7 is made to perform fuel injection at a predetermined injection timing.

As described above, the actual equivalence ratio φ and the target equivalence ratio φre calculated by the target equivalence ratio φref calculation routine described later are described.
The fuel injection amount TAU is F / B so as to reduce the deviation from f.
Since the oxygen storage amount OS of the three-way catalyst 13, which will be described later, is corrected, the target oxygen storage amount OS is in a neutral state.
Controlled near ref.

In addition to the various sensors described above, the ECU 30 includes
SW (switch) signals from the following switches are input. An eco-run SW 41 operated by the driver based on the intention to implement an eco-run is provided on, for example, the operation panel in the vehicle compartment. Further, the AT 14 is provided with a neutral SW 42 for detecting the neutral position. The brake pedal (not shown) is provided with a brake SW 43 that turns “ON” when the brake pedal is depressed. Further, the ECU 30 automatically stops the internal combustion engine 1 or drives the starter 44 to restart the internal combustion engine 1 in response to an instruction from the eco-run SW 41 or a vehicle state.

Next, the ECU 3 used in the exhaust gas purification apparatus for an internal combustion engine according to an example of the embodiment of the present invention.
The air-fuel ratio control in the CPU 31 within 0 will be described with reference to FIGS. 2 to 13. Here, FIG. 12 shows various control amounts when the oxygen storage amount OS of the three-way catalyst 13 corresponds to the air-fuel ratio lean when the internal combustion engine 1 corresponding to the air-fuel ratio control of the present embodiment is restarted after being automatically stopped. It is a time chart showing the transition state of, showing the present embodiment with a solid line,
For comparison, a conventional example is shown by a broken line. Contrary to FIG. 12, FIG. 13 is a time chart showing transition states of various control amounts when the internal combustion engine 1 is restarted after being automatically stopped and the oxygen storage amount OS of the three-way catalyst 13 is equivalent to the air-fuel ratio rich. It is a chart, the present example is shown by a solid line, and the conventional example is shown by a broken line for comparison.

The fact that the oxygen storage amount OS is equivalent to lean air-fuel ratio is the amount of oxygen stored in the three-way catalyst 13 when the internal combustion engine is operated in a lean air-fuel ratio state.
That is, the air-fuel ratio lean equivalent means that the oxygen storage amount is larger than that in the neutral state. On the other hand, the fact that the oxygen storage amount OS is equivalent to the air-fuel ratio rich means that the oxygen storage amount is smaller than that in the neutral state.

<< Main Routine of Air-Fuel Ratio Control: See FIG. 2 >> The air-fuel ratio control routine will be described with reference to FIG. It should be noted that this air-fuel ratio control routine is executed by the CPU 31 at predetermined time intervals.
Is repeatedly executed at.

In FIG. 2, first, step S101.
Then, the internal combustion engine stop determination process described later is executed. Next, the process proceeds to step S102, and a catalyst temperature estimation process described later is executed. Next, the process proceeds to step S103, and the air-fuel ratio sensor heater control process described below is executed. Next, the process proceeds to step S104, and the oxygen storage amount calculation process described below is executed. Next, the process proceeds to step S105, and a target equivalent ratio φref calculation process described later is executed. Next, the process proceeds to step S106, and an air-fuel ratio F / B correction coefficient FAF calculation process described later is executed. Next, the routine proceeds to step S107, where a fuel injection amount TAU calculation process described later is executed, and this routine is ended.

<Subroutine for determination of stop of internal combustion engine: FIG. 3
Reference> The internal combustion engine stop determination routine will be described with reference to FIG.

In FIG. 3, first, step S201.
Then, it is determined whether the internal combustion engine 1 is stopped. When the determination condition of step S201 is not satisfied, that is, when the internal combustion engine 1 is operating, the process proceeds to step S202, and it is determined whether the eco-run SW41 is "ON". The determination condition of step S202 is satisfied, that is, the eco-run SW41.
Is ON, the process proceeds to step S203,
It is determined whether the neutral SW 42 is "ON". When the determination condition of step S203 is satisfied, that is, when the neutral SW 42 is "ON" and the gear position of the AT 14 is "N", the process proceeds to step S204, and it is determined whether other various eco-run conditions are satisfied.

As the eco-run condition, specifically, the cooling water temperature THW of the internal combustion engine 1 is equal to or higher than a predetermined temperature, the vehicle speed V is "0 [km / h]", a predetermined time has elapsed, and the brake SW43 is "ON". The turn signal lamp (not shown) on the right turn side is “OFF”, the internal combustion engine 1 is in the idle state, and the like.

When the determination condition of step S204 is satisfied, that is, when all of the above eco-run conditions are satisfied, the process proceeds to step S205, and after the fuel injection amount and the spark ignition stop process are performed to automatically stop the internal combustion engine 1 ( At time t01 shown in FIG. 12 or time t11 shown in FIG. 13, this routine ends. On the other hand, when the determination condition of step S202 is not satisfied, that is, when the eco-run SW41 is "OFF", or when the determination condition of step S203 is not satisfied, that is, when the neutral SW42 is "OFF", AT1
When the gear position of No. 4 is other than "N", or when the determination condition of step S204 is not satisfied, that is, when any one of the eco-run conditions is not satisfied, the internal combustion engine 1 is continuously operated, and Exit the routine.

On the other hand, when the determination condition of step S201 is satisfied, that is, when the internal combustion engine 1 is stopped, the process proceeds to step S206, and it is determined whether the brake SW 43 is "OFF". When the determination condition of step S206 is satisfied, that is, when the brake SW 43 is "OFF" and the driver releases the depression of the brake pedal and the driver intends to start traveling of the vehicle, the process proceeds to step S207 to restart the internal combustion engine 1. After the injection amount and spark ignition execution processing has been executed (time t02 shown in FIG. 12 or time t12 shown in FIG. 13), this routine is ended. on the other hand,
When the determination condition of step S206 is not satisfied, that is, when the brake SW 43 is "ON" and the driver fully depresses the brake pedal, the automatic stop of the internal combustion engine 1 is continued, and this routine ends.

<Catalyst Temperature Estimating Subroutine: See FIGS. 4 and 5> A catalyst temperature estimating routine will be described with reference to FIG.
Will be described with reference to. Here, FIG. 5 is a map for calculating the initial value Tini [° C.] of the catalyst temperature with respect to the intake air amount QA [g / sec] per unit time.

In FIG. 4, first, step S301.
Then, it is determined whether the internal combustion engine 1 is stopped. When the determination condition of step S301 is satisfied, that is, when the internal combustion engine 1 is stopped (time t01 to time t02 shown in FIG. 12 or time t11 to time t12 shown in FIG. 13), step 302 is executed.
Then, the catalyst temperature TMPcat of the three-way catalyst 13 is calculated by the following equation (1). Where k is the temperature decay coefficient, T
stop is a stop time after the internal combustion engine 1 is automatically stopped.
As shown in FIG. 5, the catalyst temperature initial value Tini is set to a larger value as the intake air amount QA increases.

[0035]

[Equation 1]   TMPcat = Tini-k · Tstop (1)

Next, in step S303, a guard process for the catalyst temperature TMPcat is executed. next,
In step S304, it is determined whether the catalyst temperature TMPcat is equal to or higher than a predetermined value. When the determination condition of step S304 is satisfied, that is, when the catalyst temperature TMPcat is higher than the predetermined value, this routine ends.

On the other hand, when the determination condition of step S304 is not satisfied, that is, when the catalyst temperature TMPcat is lower than the predetermined value, the process proceeds to step S305, the storage control at restart is prohibited, and this routine ends. On the other hand, when the determination condition of step S301 is not satisfied, that is, when the internal combustion engine 1 is operating, the process proceeds to step S306, and the catalyst temperature initial value Tini is updated to update the catalyst temperature initial value Tini.
After the catalyst temperature is set to TMPcat, this routine ends.

<Air-Fuel Ratio Sensor Heater Control Subroutine: See FIG. 6> FIG. 6 shows the air-fuel ratio sensor heater control routine.
It will be described based on.

In FIG. 6, first, step S401.
Then, it is determined whether the internal combustion engine 1 is stopped. When the determination condition of step S401 is satisfied, that is, when the internal combustion engine 1 is stopped, the process proceeds to step S402, and it is determined whether the oxygen storage control will be performed at the next startup. The determination condition of step S402 is satisfied, that is, when the oxygen storage control is performed at the next startup, or step S402.
When the determination condition of 401 is not satisfied, that is, when the internal combustion engine 1 is in operation, the process proceeds to step S403, normal heater control is performed, and then this routine ends.

On the other hand, when the determination condition of step S402 is not satisfied, that is, when the oxygen storage control is not performed at the next start, the process proceeds to step S404, the heater control is stopped for power saving, and then this routine is ended. .

<Subroutine for calculating oxygen storage amount:
7 and 8> The oxygen storage amount calculation routine will be described based on FIG. 7 and with reference to FIG. Here, FIG. 8 is a map for calculating the damping coefficient kcatos with respect to the catalyst temperature TMPcat [° C.].

In FIG. 7, first, step S501.
Then, it is determined whether the internal combustion engine 1 is stopped. When the determination condition of step S501 is not satisfied, that is, when the internal combustion engine 1 is operating, the process proceeds to step S502, and the change amount ΔOS (i) of the oxygen storage amount of the three-way catalyst 13 is calculated by the following equation (2). It is calculated. Here, φ is the actual equivalence ratio detected by the air-fuel ratio sensor 25 on the upstream side of the three-way catalyst 13, and φre
f is the target equivalence ratio, and QA is the amount of intake air flowing into the three-way catalyst 13 per unit time.

[0043]

[Equation 2]   ΔOS (i) ← (φ-φref) ・ QA (i-d) (2)

According to this equation (2), when the equivalence ratio φ matches the target equivalence ratio φref, the change amount ΔOS (i) of the oxygen storage amount of the three-way catalyst 13 is “0”. When the equivalence ratio φ becomes larger than the target equivalence ratio φref, that is,
When the excess fuel ratio is large (on the rich side), oxygen adsorbed on the three-way catalyst 13 is consumed. The change amount ΔOS (i) of the oxygen storage amount of the three-way catalyst 13 at this time is defined as a positive value. On the other hand, when the excess fuel ratio is small (on the lean side), the change amount ΔOS (i) of the oxygen storage amount of the three-way catalyst 13 is defined as a negative value.

The intake air amount QA takes into consideration the delay time d from the fuel injection to the detection of the exhaust gas equivalent ratio φ, and the past intake air amount Q before the delay time d before the present time i.
A (id) is used. At this time, the delay time d may be a fixed value in order to simplify the calculation process, but the delay time d may be changed according to the intake air amount QA. That is,
The larger the intake air amount QA, the faster the air flow rate and the shorter the actual delay time d. Therefore, the larger the intake air amount QA, the shorter the delay time d may be set.

Then, the current oxygen storage amount OS (i) of the three-way catalyst 13 is calculated by the following formula (3) based on the change amount ΔOS (i) of the oxygen storage amount calculated by the above formula (2). To be done. Here, OS (i-1) is the previous oxygen storage amount calculation value of the three-way catalyst 13. Here, by adding the change amount ΔOS (i) of the oxygen storage amount of the three-way catalyst 13 calculated by the above equation (2), the oxygen storage amount has a positive value when the air-fuel ratio is lean. And becomes a negative value when the air-fuel ratio is rich. The three-way catalyst 13
Is in the neutral state, the amount of change in the oxygen storage amount ΔOS
(i) is defined as "0". As a result, in this embodiment, the amount of oxygen storage adsorbed on the three-way catalyst 13 can be estimated.

[0047]

[Equation 3]   OS (i) ← ΔOS (i) + OS (i-1) (3)

On the other hand, when the determination condition of step S501 is satisfied, that is, when the internal combustion engine 1 is stopped, the routine proceeds to step S503, where the current oxygen storage amount OS (i) of the three-way catalyst 13 is expressed by the following equation (4). Calculated at. Where kc
atos is the damping coefficient for the catalyst temperature TMPcat, and as shown in FIG. 8, the damping coefficient kcatos is the catalyst temperature TMPcat.
Becomes higher and smaller.

[0049]

[Equation 4]   OS (i) ← kcatos OS (i-1) (4)

Next, the routine proceeds to step S504, after the guard processing for the present oxygen storage amount OS (i) of the three-way catalyst 13 is executed, this routine is ended. As the guard process, guard values OSmin and OSmax corresponding to the lean side / rich side saturated oxygen storage amount of the three-way catalyst 13 with respect to the oxygen storage amount OS (i) are used. For example, the oxygen storage amount OS (i) is the guard value OS
Within the range of min and OSmax (OSmin ≤ OS (i) ≤ OSma
x), the oxygen storage amount OS (i) is used as it is, and the oxygen storage amount OS (i) is used as the guard value OSmin.
When (or guard value OSmax) is exceeded, the oxygen storage amount OS (i) is replaced by the guard value OSmin (or guard value OSmax), and OS (i) ← OSmin (or OS (i) ← OSmax). It At this time, the guard values OSmin and OSmax may be fixed values in order to simplify the calculation process, but as the flow velocity of the exhaust gas flowing in the three-way catalyst 13 becomes faster (the intake air amount QA becomes larger), the guard values OSmin and OSmax become three. There is a saturated oxygen storage characteristic that the saturated oxygen storage amount of the original catalyst 13 becomes small.

<Subroutine for calculating target equivalence ratio φref:
Referring to FIG. 9> The target equivalent ratio φref calculation routine will be described with reference to FIG. 9.

In FIG. 9, first, step S601.
Then, it is determined whether the internal combustion engine 1 is stopped. When the determination condition of step S601 is not satisfied, that is, when the internal combustion engine 1 is operating, the process proceeds to step S602, and the deviation between the target oxygen storage amount OSref of the three-way catalyst 13 and the current oxygen storage amount OS (i). OSerror is the following formula (5)
Calculated at.

[0053]

[Equation 5]   OSerror ← OSref-OS (i) (5)

On the other hand, when the determination condition of step S601 is satisfied, that is, when the internal combustion engine 1 is stopped, the process proceeds to step S603, and the starting initial value is set. After the process of step S602 or step S603, the process proceeds to step S604, and PID (Proportional Integral)
Differential: Proportional / integral / derivative control circuit (not shown)
A proportional gain kp, an integral gain ki, and a differential gain kd are set by a map or the like. At this time, each gain kp,
Ki and kd may be varied according to operating conditions of the internal combustion engine 1, such as the intake air amount QA or the intake pressure by an intake pressure sensor (not shown).

Next, in step S605, the gains kp, ki, kd set in step S604 and the calculation interval dt (for example, 180 [° CA (Crank Angle)) time required for rotation. ), PI
Control parameters A1, A2, B1, B of the D control circuit
2, B3 are calculated by the following equation (6).

[0056]

[Equation 6]   A1 ← 1   A2 ← 0   B1 ← kp ・ (1 + dt / ki + kd / dt)   B2 ← kp ・ (1 + 2 ・ kd / dt)   B3 ← kp ・ kd / dt (6)

Next, in step S606, the control parameters A1, A2, calculated in step S605 are calculated.
From B1, B2, B3, the deviation OSerror calculated in step S602, and the target equivalent ratio φref, the target equivalent ratio correction amount Δφref is calculated by the following equation (7).

[0058]

[Equation 7]   Δφref ← B1 ・ OSerror (i) -B2 ・ OSerror (i-1)             ＋ B3 ・ OS error (i-2)             + A1 ・ φref (i-1) -A2 ・ φref (i-2) ・ ・ ・ (7)

Then, the target equivalence ratio correction amount Δφref is added to the base value “1”, and the current target equivalence ratio φref on the upstream side of the three-way catalyst 13 is calculated by the following equation (8). finish.

[0060]

[Equation 8]   φref ← 1 + Δφref (8)

<Air-Fuel Ratio F / B Correction Coefficient FAF Calculation Subroutine: See FIG. 10> An air-fuel ratio F / B correction coefficient FAF calculation routine will be described with reference to FIG.

In FIG. 10, first, step S701.
Then, in step S701, it is determined whether the air-fuel ratio F / B control condition is satisfied. The air-fuel ratio F / B control condition is satisfied because the cooling water temperature THW of the internal combustion engine 1 is equal to or higher than a predetermined temperature, the engine speed NE, and the load are not high.
The determination condition of step S701 is satisfied, that is, the air-fuel ratio F /
When all the B control conditions are satisfied, the routine proceeds to step S702, where the target equivalent ratio φref calculated in the above-mentioned target equivalent ratio φref calculation routine is read.

Next, the routine proceeds to step S703, where it is judged if the detected value of the air-fuel ratio sensor 25 is within a predetermined range capable of maintaining the air-fuel ratio control. When the determination condition of step S703 is satisfied, that is, when the detection value of the air-fuel ratio sensor 25 is within the predetermined range, the process proceeds to step S704 and the ROM
Optimal F / B of state F / B system stored in advance in 32
The gain IKn (n = 1, 2, 3, 4, A) is selectively read.

On the other hand, when the determination condition of step S703 is not satisfied, that is, the detected value of the air-fuel ratio sensor 25 is outside the predetermined range, the process proceeds to step S705 and the ROM 32
Of the F / B gains of the state F / B system stored in advance, the lower F / B gain IKn '(n = 1, 2,
3, 4, A) are selectively read. Next in step S7
Then, the process proceeds to step S704 or step S7.
F / B gain IKn (n =
1, 2, 3, 4) or IKn '(n = 1, 2, 3,
4) is substituted into the following equation (9) to calculate the integral term ZI (K). Here, Ka is an integration constant and φ (K) is an actual equivalence ratio.

[0065]

[Equation 9]   ZI (K) ← ZI (K-1) + Ka ・ (φref −φ (K)) ・ ・ ・ (9)

Next, the routine proceeds to step S707, the air-fuel ratio F / B correction coefficient FAF is calculated by the following equation (10), and this routine ends. Here, FAF (K-1) is the air-fuel ratio F / B correction coefficient one time before, FAF (K-2) is the air-fuel ratio F / B correction coefficient two times before, and FAF (K-3) is three times. Previous air-fuel ratio F / B
The correction coefficients K1, K2, K3 and K4 are F / B constants.

[0067]

[Equation 10]   FAF (K) ← ZI (K) + K1 · φ (K) + K2 · FAF (K-3)               ＋ K3 ・ FAF (K-2) ＋ K4 ・ FAF (K-1) ・ ・ ・ (10)

On the other hand, when the determination condition of step S701 is not satisfied, that is, even when one of the air-fuel ratio F / B control conditions is not satisfied, the routine proceeds to step S708, where the air-fuel ratio F /
The B correction coefficient FAF is set to "1.0", and this routine ends.

<Fuel injection amount TAU calculation subroutine:
Refer to FIG. 11> The fuel injection amount TAU calculation routine will be described with reference to FIG.

In FIG. 11, first, step S801.
Then, the basic fuel injection amount Tp is calculated based on the engine speed NE and the intake air amount QA. Next, the routine proceeds to step S802, where the air-fuel ratio F / B correction coefficient FAF calculated by the above-mentioned air-fuel ratio F / B correction coefficient FAF calculation routine is read. Next, the routine proceeds to step S803, where the final fuel injection amount TAU is calculated by the following equation (11), and this routine ends. Here, FALL is a correction coefficient for correcting the fuel injection amount by an element other than the air-fuel ratio control.

[0071]

[Equation 11]   TAU ← FAF ・ Tp ・ FALL ・ ・ ・ (11)

Therefore, the oxygen storage amount OS of the three-way catalyst 13 is controlled by the conventional air-fuel ratio control (see FIG. 12 or FIG. 13).
(Indicated by a broken line), the internal combustion engine 1 is restarted after being automatically stopped (time t02 shown in FIG. 12 or time t12 shown in FIG. 13).
Although it is difficult to return to the neutral state from the state corresponding to the lean air-fuel ratio or the state corresponding to the air-fuel ratio rich of the above, according to the air-fuel ratio control (solid line shown in FIG. 12 or FIG. 13) of the above-described embodiment, the internal combustion engine 1 is automatically operated. It can be seen that when restarting after the stop (time t02 shown in FIG. 12 or time t12 shown in FIG. 13), the state corresponding to the lean air-fuel ratio or the state corresponding to the air-fuel ratio rich is quickly returned to the neutral state.

In this embodiment, the air-fuel ratio is feedback-controlled based on the equivalence ratio φ. However, the air-fuel ratio is feedback-controlled by using the excess air ratio λ and the air-fuel ratio A / F instead of the equivalence ratio φ. You may.

As described above, the exhaust gas purifying apparatus for an internal combustion engine of this embodiment is disposed in the exhaust passage 12 of the internal combustion engine 1,
A three-way catalyst 13 for purifying exhaust gas of the internal combustion engine 1, automatic start / stop control means achieved by an ECU 30 for controlling automatic stop of the internal combustion engine 1 under predetermined operating conditions and automatic start thereafter, and The catalyst state estimation means achieved by the ECU 30 that estimates the oxygen storage amount OS of the three-way catalyst 13 immediately before the automatic stop of the internal combustion engine 1 by the automatic start / stop control means, and a predetermined air-fuel ratio for the internal combustion engine 1. The ECU 30 injects fuel, and at the time of restarting the internal combustion engine 1 after automatic stop, injects fuel so that the air-fuel ratio becomes the air-fuel ratio according to the oxygen storage amount OS of the three-way catalyst 13 estimated by the catalyst state estimating means. Fuel injection control means.

That is, the oxygen storage amount OS of the three-way catalyst 13 immediately before the automatic stop of the internal combustion engine 1 is estimated, and at the time of restart after the automatic stop, the air-fuel ratio according to the estimated oxygen storage amount OS of the three-way catalyst 13. Equivalence ratio φ which is the reciprocal of
Fuel is injected so that This makes it possible to quickly return the oxygen storage amount OS of the three-way catalyst 13 to the neutral state when the internal combustion engine 1 is restarted after being automatically stopped, and ensure good emissions.

Further, the exhaust gas purification apparatus for an internal combustion engine of this embodiment is equipped with an air-fuel ratio sensor 25 for detecting a signal corresponding to the air-fuel ratio of the exhaust gas of the internal combustion engine 1, and the catalyst state estimating means achieved by the ECU 30. However, the oxygen storage amount OS of the three-way catalyst 13 is estimated based on the amount of exhaust gas flowing into the three-way catalyst 13 and the air-fuel ratio by the air-fuel ratio sensor 25.
That is, the oxygen storage amount OS of the three-way catalyst 13 is the exhaust gas amount flowing into the three-way catalyst 13, that is, the intake air amount QA.
The state of the three-way catalyst 13 can be accurately grasped by being estimated on the basis of the amount of delay corresponding to 1 and the air-fuel ratio detected by the air-fuel ratio sensor 25.

The catalyst state estimating means achieved by the ECU 30 of the exhaust gas purifying apparatus for the internal combustion engine of this embodiment continues estimating the oxygen storage amount OS of the three-way catalyst 13 while the internal combustion engine 1 is automatically stopped. It is a thing. That is, the estimation of the oxygen storage amount OS of the three-way catalyst 13 is continued even during the automatic stop of the internal combustion engine 1, so that the oxygen storage amount OS of the three-way catalyst 13 can be immediately determined at the time of restart after the automatic stop. Air-fuel ratio control can be implemented. This makes it possible to quickly return the oxygen storage amount OS of the three-way catalyst 13 to the neutral state when the internal combustion engine 1 is restarted after being automatically stopped, and ensure good emissions.

Further, the exhaust gas purifying apparatus for an internal combustion engine of the present embodiment is provided with a catalyst temperature estimating means which is achieved by the ECU 30 which estimates the temperature of the three-way catalyst 13, and a fuel injection control means which is achieved by the ECU 30. When the temperature of the three-way catalyst 13 is equal to or lower than a predetermined value when the internal combustion engine 1 is restarted after being automatically stopped, the air-fuel ratio control according to the oxygen storage amount OS of the three-way catalyst 13 is prohibited, and the three-way catalyst 13 rises. The temperature control is prioritized. That is, when the temperature of the three-way catalyst 13 is equal to or lower than the predetermined value when the internal combustion engine 1 is restarted after being automatically stopped, the three-way catalyst 13
Is not in the active state and cannot support the air-fuel ratio control, so the temperature increase control for activating the three-way catalyst 13 is preferentially performed. As a result, the three-way catalyst 13 is quickly returned to the active state, and the emission deterioration can be suppressed.

Furthermore, in the exhaust gas purifying apparatus for an internal combustion engine of this embodiment, the temperature of the three-way catalyst 13 is set to the stop time T of the internal combustion engine 1.
It is estimated using stop. That is, three-way catalyst 1
Since the temperature of 3 changes according to the elapsed time after the automatic stop of the internal combustion engine 1, the temperature of the three-way catalyst 13 can be accurately estimated by using the stop time Tstop.

In addition, the exhaust gas purifying apparatus for an internal combustion engine of this embodiment keeps the air-fuel ratio sensor 25 active even when the internal combustion engine 1 is automatically stopped. That is, the air-fuel ratio sensor 2
If 5 is maintained in the active state even during the automatic stop of the internal combustion engine 1, an accurate air-fuel ratio control can be immediately performed at the time of restart after the automatic stop, so that the oxygen storage amount O of the three-way catalyst 13
S can be quickly returned to the neutral state and good emission can be secured.

Further, the fuel injection control means achieved by the ECU 30 of the exhaust purification system of the internal combustion engine of the present embodiment responds to the oxygen storage amount OS of the three-way catalyst 13 when the internal combustion engine 1 is restarted after being automatically stopped. When prohibiting the air-fuel ratio control, the holding of the active state of the air-fuel ratio sensor 25 is prohibited. That is, under the condition that the lean control of the air-fuel ratio is prohibited when the internal combustion engine 1 is restarted after being automatically stopped, the power supply to the heater 26 for keeping the active state of the air-fuel ratio sensor 25 is stopped. It is possible to save power.

Then, the catalyst state estimating means achieved by the ECU 30 of the exhaust purification system of the internal combustion engine of the present embodiment corrects the oxygen storage amount OS of the three-way catalyst 13 by using the stop time Tstop of the internal combustion engine 1. It is a thing. That is, since the oxygen storage amount OS of the three-way catalyst 13 changes according to the elapsed time from the time when the internal combustion engine 1 automatically stops, the correction of the oxygen storage amount OS of the three-way catalyst 13 using the stop time Tstop may be performed. If so, the state of the three-way catalyst 13 can be accurately estimated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an internal combustion engine and peripheral equipment to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied.

FIG. 2 is a main routine showing a processing procedure of air-fuel ratio control in a CPU in an ECU used in an exhaust gas purification apparatus for an internal combustion engine according to an example of an embodiment of the present invention.

FIG. 3 is a subroutine showing a processing procedure of an internal combustion engine stop determination in FIG.

FIG. 4 is a subroutine showing a processing procedure of catalyst temperature estimation in FIG.

5 is a map for calculating an initial catalyst temperature value using the intake air amount in FIG. 4 as a parameter.

FIG. 6 is a subroutine showing a processing procedure of air-fuel ratio sensor heater control in FIG.

FIG. 7 is a subroutine showing a processing procedure of an oxygen storage amount calculation in FIG.

FIG. 8 is a map for calculating an attenuation coefficient using the catalyst temperature in FIG. 7 as a parameter.

9 is a subroutine showing a processing procedure of a target equivalent ratio calculation in FIG.

FIG. 10 is a subroutine showing a processing procedure of air-fuel ratio F / B correction coefficient calculation in FIG.

FIG. 11 is a subroutine showing a processing procedure of a fuel injection amount calculation in FIG.

FIG. 12 is an oxygen storage amount of the three-way catalyst at the time of restart after the automatic stop of the internal combustion engine corresponding to the air-fuel ratio control of the exhaust purification system of the internal combustion engine according to one example of the embodiment of the present invention. 5 is a time chart showing transition states of various control amounts when is equal to lean air-fuel ratio.

FIG. 13 is an oxygen storage amount of the three-way catalyst at the time of restart after the automatic stop of the internal combustion engine corresponding to the air-fuel ratio control of the exhaust purification system of the internal combustion engine according to one example of the embodiment of the present invention. 6 is a time chart showing transition states of various control amounts when is corresponding to the air-fuel ratio rich.

[Explanation of symbols]

1 Internal combustion engine 7 injector (fuel injection valve) 12 Exhaust passage 13 three-way catalyst 25 Air-fuel ratio sensor 30 ECU (electronic control unit)

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3G091 AA02 AA17 AA28 AB03 BA01                       BA14 BA15 BA19 CB02 DA01                       DA02 DB04 DB05 DB06 DB07                       DB08 DB10 DB11 DB13 DC03                       EA01 EA05 EA07 EA16 EA34                       EA39 EA40 FA01 GB05W                       GB06W HA36                 3G093 AA05 BA20 BA21 BA22 CA02                       CA04 DA01 DA05 DA06 DA09                       DA11 DB00 DB05 DB12 DB15                       EA04 EC01 FA05 FA07 FA10                       FA11 FB01 FB02 FB05                 3G301 HA01 JA21 JA25 JA26 KA04                       MA01 NA03 NA04 NA05 NA08                       NA09 ND02 ND03 ND04 ND05                       ND06 ND15 NE13 NE15 NE23                       PA01Z PA11Z PD04A PE01Z                       PE08Z PF00Z PF01Z PF05Z                       PF10Z

Claims (8)

[Claims] 1. A catalyst disposed in the exhaust passage of an internal combustion engine, for purifying exhaust gas of the internal combustion engine, and an automatic control for controlling automatic stop and predetermined automatic start of the internal combustion engine. A start / stop control means, a catalyst state estimation means for estimating the amount of oxygen storage (Storage: adsorption and storage) of the catalyst immediately before the automatic stop of the internal combustion engine by the automatic start / stop control means, and a predetermined state for the internal combustion engine. Fuel injection control for injecting fuel to have an air-fuel ratio and for injecting fuel to have an air-fuel ratio according to the oxygen storage amount of the catalyst estimated by the catalyst state estimating means at the time of restart after the automatic stop of the internal combustion engine An exhaust gas purifying apparatus for an internal combustion engine, comprising: 2. An air-fuel ratio sensor for outputting a signal according to an air-fuel ratio of exhaust gas of the internal combustion engine, wherein the catalyst state estimating means comprises an amount of exhaust gas flowing into the catalyst and an air-fuel ratio by the air-fuel ratio sensor. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the oxygen storage amount of the catalyst is estimated based on 3. The exhaust gas purification of an internal combustion engine according to claim 1 or 2, wherein the catalyst state estimating means continues to estimate the oxygen storage amount of the catalyst even during the automatic stop of the internal combustion engine. apparatus. 4. A catalyst temperature estimating means for detecting or estimating the temperature of the catalyst, wherein the fuel injection control means has a temperature of the catalyst equal to or lower than a predetermined value when the internal combustion engine is restarted after being automatically stopped. 4. The internal combustion engine according to claim 1, wherein the air-fuel ratio control according to the oxygen storage amount of the catalyst is prohibited and the temperature increase control of the catalyst is prioritized. Exhaust purification device. 5. The exhaust gas of the internal combustion engine according to claim 4, wherein the temperature of the catalyst is estimated by using one or more of an outside air temperature, a stop time of the internal combustion engine, and a temperature of exhaust gas. Purification device. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio sensor is kept in an active state even during automatic stop of the internal combustion engine. . 7. The fuel injection control means holds the active state of the air-fuel ratio sensor when prohibiting the air-fuel ratio control according to the oxygen storage amount of the catalyst when the internal combustion engine is restarted after being automatically stopped. The exhaust emission control device for an internal combustion engine according to claim 6, which is prohibited. 8. The catalyst state estimating means corrects the oxygen storage amount of the catalyst by using one or more of a temperature of the catalyst, an outside air temperature, a stop time of the internal combustion engine, and a temperature of exhaust gas. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 7, characterized in that