JP2008111352A - Exhaust control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust control device of an internal combustion engine capable of improving purification performance, by realizing early activation by promoting a temperature rise in a catalyst, without increasing a noble metal carrying quantity of the catalyst, by supplying CO and O<SB>2</SB>of a proper quantity on the catalyst, by optimally controlling a variation state of the exhaust air-fuel ratio at this time, by performing forced modulation, after starting the engine. <P>SOLUTION: When a forced modulation starting condition is realized after starting the engine, the forced modulation is performed in response to a waveform pattern of the average air-fuel ratio 15.0 when the inlet temperature Tex of a three-way catalyst is less than 350°C (S14, and 16), and the forced modulation is performed in response to the waveform pattern of the average air-fuel ratio 14.0 when the inlet temperature Tex becomes 350 °C or more (S18, and 20), and control is switched to O<SB>2</SB>F/B control in response to the realization of a finishing condition of the forced modulation (S22). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust control device for an internal combustion engine (hereinafter referred to as an engine), and more particularly to an exhaust control device that promotes a catalytic reaction immediately after engine startup and improves exhaust purification performance by early activation.

Hazardous components emitted from the engine at the time of cold start where the catalyst has not yet been activated, such as THC (Total HC), etc., account for a considerable proportion of the total THC emission generated by each mode operation of the engine, It is known that measures at the cold start are important for improving the purification performance. As one of countermeasures for this, immediately after the engine is started, first, an open loop (hereinafter abbreviated as O / L) having characteristics that the exhaust gas concentration (especially HC) of the engine-out is low and combustion fluctuation is acceptable. ) When the exhaust air-fuel ratio is controlled to a substantially constant value on the rich side by control and the O ₂ sensor is activated thereafter, feedback to the theoretical air-fuel ratio based on the O ₂ sensor output (hereinafter abbreviated as O ₂ F / B) ) A method of switching to control is adopted.

However, this method has a drawback that the exhaust gas purification performance greatly depends on the amount of the noble metal supported by the three-way catalyst. In particular, in the process of shifting from O / L control to O ₂ F / B control, this tendency appears prominently, and the purification performance decreases significantly as the amount of noble metal supported decreases. Therefore, with this conventional method, if the amount of noble metal supported is insufficient, sufficient purification performance cannot be realized. Conversely, if the amount of noble metal supported is increased in order to ensure sufficient purification performance, the cost increases and the catalyst capacity increases. Another problem that caused an increase in pressure loss occurred.

  On the other hand, a technique for executing forced modulation of the air-fuel ratio has been proposed in order to suppress emission of harmful components immediately after engine startup (see, for example, Patent Document 1). The forced modulation is control for forcibly varying the engine exhaust air-fuel ratio alternately in a rich direction and a lean direction with a predetermined amplitude. In the technique of Patent Document 1, forced modulation is performed at the time of cold start, The reduction reaction is caused on the catalyst during the modulation in the direction, and the oxidation reaction is caused on the catalyst during the modulation in the lean direction, thereby promoting the temperature rise of the catalyst, thereby improving the purification performance.

In the technique of Patent Document 1, after the activation of the O ₂ sensor, switching from forced modulation to normal O ₂ F / B control is performed, but even after switching, the air-fuel ratio fluctuation is continued for a while, and the exhaust air-fuel ratio is reduced to the theoretical sky. In view of the fact that the fuel ratio cannot be quickly converged to the fuel ratio (that is, within the catalyst window), the higher the engine water temperature correlated with the catalyst active state, the smaller the amplitude of the exhaust air / fuel ratio at the time of forced modulation, thereby O ₂ F / B Convergence to the stoichiometric air-fuel ratio at the time of switching to control is improved.
Japanese Patent No. 3392197

As described above, the technology of Patent Document 1 sets the amplitude of the exhaust air / fuel ratio with an emphasis on the switchability from forced modulation to O ₂ F / B control. It was difficult to say that it was an appropriate setting for improving purification performance.
That is, the reduction reaction and oxidation reaction on the catalyst obtained by forced modulation are closely related to the amount of CO and O ₂ supplied to the catalyst together with the exhaust gas, so these supply amounts must be optimally controlled. Appropriate reduction reaction and oxidation reaction, and hence sufficient temperature increase promotion cannot be expected. In the technique of Patent Document 1, since the amplitude of the exhaust air / fuel ratio is only controlled assuming switching to O ₂ F / B control, as a result, an appropriate amount of CO on the catalyst during forced modulation is obtained. And O ₂ could not be supplied, and the purification performance could not be improved by promoting the temperature rise of the catalyst.

The present invention has been made to solve such problems. The object of the present invention is to perform forced modulation after the engine is started and to optimally control the fluctuation state of the exhaust air-fuel ratio at this time to provide a catalyst. Exhaust control for internal combustion engines that can supply the appropriate amount of CO and O ₂ and improve the purification performance by realizing early activation by increasing the temperature of the catalyst without increasing the amount of noble metal supported on the catalyst To provide an apparatus.

  In order to achieve the above object, the invention of claim 1 is directed to a catalyst provided in an exhaust passage of an internal combustion engine, a catalyst temperature correlation value detecting means for detecting a parameter value correlated with the temperature of the catalyst, and immediately after starting the internal combustion engine. Air-fuel ratio fluctuation control means for forcibly changing the air-fuel ratio of the exhaust gas flowing into the catalyst between a lean air-fuel ratio and a rich air-fuel ratio. The central air-fuel ratio of the fluctuation in fuel ratio is set to a leaner air-fuel ratio side than stoichiometric, and then the central air-fuel ratio is made richer than stoichiometric as the detected value detected by the catalyst temperature correlation value detecting means changes in the temperature rising direction. It is configured to shift.

  Therefore, immediately after the internal combustion engine is started, the exhaust air-fuel ratio is forcibly changed by the air-fuel ratio fluctuation control means around the center air-fuel ratio set to the lean air-fuel ratio side from the stoichiometry, and detected by the catalyst temperature correlation value detection means. As the value changes in the temperature rising direction, the central air-fuel ratio is shifted to the rich air-fuel ratio side with respect to the stoichiometry, and the exhaust air-fuel ratio is forcibly changed around the shifted center air-fuel ratio.

FIG. 10 shows the amount of temperature increase ΔT (= catalyst bed temperature−inlet temperature) on the catalyst when the exhaust air / fuel ratio is varied between the average air / fuel ratio 14.0 (rich air / fuel ratio side) and 15.0 (lean air / fuel ratio side). It is the test result measured for every inlet temperature. According to this test result, when the inlet temperature is about 350 ° C., the average air-fuel ratio 15.0 has a larger temperature increase ΔT on the low temperature side, and the average air-fuel ratio 14.0 has a larger temperature on the high temperature side. A rise amount ΔT is obtained. From this test result, it is presumed that an appropriate amount of CO or O ₂ is supplied onto the catalyst in any temperature range by switching the central air-fuel ratio, thereby contributing to the temperature rise of the catalyst.

  The characteristics shown in FIG. 10 are only examples, and may change depending on factors such as the amount of precious metal in the catalyst, but as a basic characteristic, the central air-fuel ratio of the air-fuel ratio fluctuation is set to the lean air-fuel ratio side. In this case, a good catalyst temperature rising action can be obtained in a region where the catalyst temperature is low. There is no doubt that Therefore, as in this aspect of the present invention, the exhaust air-fuel ratio is changed based on the center air-fuel ratio on the lean air-fuel ratio side immediately after the start of the internal combustion engine, and the center air-fuel ratio is brought to the rich air-fuel ratio side as the catalyst temperature rises. By shifting, a good catalyst temperature rising action can be obtained regardless of the temperature range.

The invention of claim 2 further comprises feedback control means for performing feedback control so that the actual air-fuel ratio of the internal combustion engine approaches the target air-fuel ratio in claim 1, wherein the air-fuel ratio fluctuation control means makes the center air-fuel ratio richer than the stoichiometric ratio. After shifting to the air-fuel ratio side, the feedback control means starts operating.
Therefore, after the air-fuel ratio fluctuation control means shifts the central air-fuel ratio to the rich air-fuel ratio side, the feedback control of the feedback control means is started.

According to a third aspect of the present invention, in the first or second aspect, the air-fuel ratio fluctuation control means shifts the central air-fuel ratio to the rich air-fuel ratio side from the stoichiometric range when the catalyst temperature is in the range of about 300 ° C to about 400 ° C. It is composed of.
Therefore, the central air-fuel ratio is shifted to the rich air-fuel ratio side when the temperature of the catalyst is in the range of about 300 ° C to about 400 ° C.

As described above, according to the exhaust control device for an internal combustion engine of the first to third aspects of the invention, forced modulation is executed after the engine is started, and the central air-fuel ratio of the exhaust air-fuel ratio at this time is increased as the catalyst temperature increases. As a result, the appropriate amount of CO or O ₂ is supplied onto the catalyst to accelerate the temperature rise of the catalyst without increasing the amount of noble metal supported on the catalyst. Realization can improve purification performance.

[First Embodiment]
Hereinafter, a first embodiment of an engine exhaust control system embodying the present invention will be described.
FIG. 1 is an overall configuration diagram schematically showing an engine and an exhaust control device thereof according to the present embodiment, which is configured for an in-cylinder injection type in-line four-cylinder gasoline engine 1. The engine 1 employs a DOHC 4-valve type valve operating mechanism, and an intake camshaft 3 and an exhaust camshaft 4 provided on the cylinder head 2 are rotationally driven by a crankshaft (not shown). 4, the intake valve 5 and the exhaust valve 6 are opened and closed at a predetermined timing.

  The cylinder head 2 is provided with an electromagnetic fuel injection valve 8 together with an ignition plug 7 for each cylinder, and high-pressure fuel supplied from a fuel pump (not shown) is directly fed into the combustion chamber 9 according to the opening and closing of the fuel injection valve 8. Be injected. An intake port 10 is formed in the cylinder head 2 so as to pass between the camshafts 3 and 4 in a substantially upright direction. As the intake valve 5 is opened, intake air flows from the air cleaner 11 to the throttle valve 12 and the surge tank 13. Then, it is introduced into the combustion chamber 9 through the intake manifold 14 and the intake port 10. The exhaust gas after combustion is discharged from the combustion chamber 9 to the exhaust port 15 as the exhaust valve 6 is opened, and further discharged to the atmosphere through the exhaust passage 16 and the three-way catalyst 17.

In the vehicle compartment, an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs and control maps, a central processing unit (CPU), an ECU (engine control unit) equipped with a timer counter, etc. ) 21 is installed and performs overall control of the engine 1. On the input side of the ECU 21, there are a water temperature sensor 22 for detecting the coolant temperature Tw of the engine 1, a throttle sensor 23 for detecting the throttle opening θth, and an exhaust gas temperature (hereinafter referred to as inlet temperature) Tex flowing into the three-way catalyst 17. Various sensors such as a temperature sensor 24 (catalyst temperature correlation value detecting means) to detect and an O ₂ sensor 25 for changing the output according to the O ₂ concentration of the exhaust gas are connected, and the fuel injection valve is connected to the output side of the ECU 21. 8. Various devices such as an igniter 26 for driving the spark plug 7 are connected.

The ECU 21 determines the ignition timing, the fuel injection amount, and the like based on the detection information from each sensor, and controls the operation of the engine 1 by drivingly controlling the igniter 26 and the fuel injection valve 8 based on these control amounts.
When the engine 1 is cold-started, the ECU 21 performs O ₂ F / B control to a target air-fuel ratio (for example, theoretical air-fuel ratio) based on the output of the O ₂ sensor 25 (feedback control means), and O 2 ₂ Forced modulation by O / L control is executed prior to F / B control (air-fuel ratio fluctuation control means). In forced modulation, the central air-fuel ratio of air-fuel ratio fluctuation is switched according to the inlet temperature Tex. The amount of CO and the amount of O ₂ supplied to the original catalyst 17 are optimized. Hereinafter, the exhaust control at the time of cold start will be described in detail.

FIG. 2 is a flowchart showing a start-up exhaust control routine executed by the ECU 21. The ECU 21 executes the routine at predetermined control intervals when the engine is started.
First, an engine start mode is executed in step S2. As the start mode, the start-up increase correction from the cranking start to the complete explosion determination, the post-start-up increase correction after the complete explosion determination, and the like are appropriately executed by O / L control, and a smooth engine start is achieved. The contents of the engine start mode are general, and the fuel control by the increase correction after the start at this time is executed before the activation of the O ₂ sensor described in [Background Art], and the O / L control by the rich air-fuel ratio is executed. It corresponds to.

Thereafter, the cooling water temperature Tw at step S4, the throttle opening [theta] th, captures various sensor information such as the inlet temperature Tex, it calculates the elapsed time from start completion (complete explosion judgment) in the subsequent step S6, O ₂ sensor in step S8 25 activation conditions are determined, and the catalyst temperature Tcat is estimated based on the inlet temperature Tex in step S10. The catalyst temperature Tcat is calculated from a map that defines a relationship between a preset inlet temperature Tex and the catalyst temperature Tcat. However, the method for calculating the catalyst temperature Tcat is not limited to this, and for example, the catalyst temperature Tcat is calculated from the inlet temperature Tex. Instead of the estimation, the bed temperature of the three-way catalyst 17 may be directly detected, or the catalyst temperature Tcat may be simply obtained based on the cooling water temperature Tw and the elapsed time from the completion of starting.

In a succeeding step S12, it is determined whether or not a forced modulation start condition is satisfied. The forced modulation start condition is set as an engine operating state that does not hinder the execution of forced modulation for forcibly changing the exhaust air-fuel ratio of the engine 1. For example, the requirements shown in the following 1) to 5) It is determined based on.
1) Engine load, specifically throttle opening θth, volumetric efficiency, etc. 2) Elapsed time after completion of engine start 3) Cooling water temperature Tw
4) Elapsed time after activation of the O ₂ sensor 5) Catalyst temperature Tcat
If it is determined in step S14 that the forced modulation start condition is not satisfied based on these requirements, the routine is terminated as it is. Therefore, in this case, in the engine start mode in step S2, the O / L control with the substantially constant rich air-fuel ratio is continuously executed as in the conventional control.

  Also, if the determination of Yes (Yes) is made in step S12 because the forced modulation start condition is satisfied, the forced modulation of the exhaust air-fuel ratio for the low temperature region and the high temperature region is divided into two stages by the processing after step S14. Execute. Although the execution conditions of these forced modulations are set in advance, the setting process will be described later, and the actual execution status of forced modulation will be described continuously.

  In this embodiment, the forced modulation for the low temperature region and the high temperature region is executed under the condition that the waveform pattern itself is common and the setting of the average air-fuel ratio is different. FIG. 3 is a time chart showing a waveform pattern applied to the forced modulation for the low temperature range, and FIG. 4 is a time chart showing a waveform pattern applied to the forced modulation for the high temperature range. A waveform pattern in which both the amount of fluctuation of the exhaust air-fuel ratio in the rich direction and the lean direction and the fluctuation period in the rich direction and the lean direction in one cycle are set equal is applied, the amplitude is set to 1.0, and the cycle is 1.0 sec. Is set to In the waveform pattern for the low temperature region in FIG. 3, the center air-fuel ratio (which matches the average air-fuel ratio from the above waveform characteristics) is set to 15.0 on the lean air-fuel ratio side of the stoichiometric, and in the waveform pattern for the high temperature region in FIG. The central air-fuel ratio (same as the average air-fuel ratio) is set to 14.0 on the rich air-fuel ratio side of the stoichiometric ratio.

  In addition, you may apply what is shown to FIG.5, 6 as another example of a waveform pattern. In these waveform patterns, the amplitude is set to 1.5 and the cycle is set to 1.0 sec. However, the fluctuation amount of the exhaust air-fuel ratio in the rich direction and the lean direction with respect to the central air-fuel ratio, and the rich direction and the lean in one cycle The fluctuation period in the direction is different, the fluctuation amount with respect to the central air-fuel ratio is set to +0.5 (lean side), -1.0 (rich side), and the fluctuation period is set to lean: rich = 2: 1 ing. The setting of the central air-fuel ratio is the same as that in FIGS. 3 and 4. The low-temperature waveform pattern in FIG. 5 is 15.0 (matches the average air-fuel ratio), and the high-temperature waveform pattern in FIG. The waveform pattern of FIG. 5 may be applied instead of FIG. 3, and the waveform pattern of FIG. 6 may be applied instead of FIG. Thus, when the waveform pattern of FIG. 5 is applied instead of FIG. 3 and the waveform pattern of FIG. 6 is applied instead of FIG. 4, the catalytic reaction is improved and the exhaust gas purification performance is improved. .

On the other hand, when returning to the processing of the ECU 21, the ECU 21 executes the forced modulation for the low temperature region in step S14 of FIG. 2 according to the waveform pattern of FIG. 3 or 5 and whether the inlet temperature Tex is 350 ° C. or higher in the subsequent step S16. If it is No, it is considered that the three-way catalyst 17 has not reached the light-off temperature, and the process returns to Step S14. When the determination is Yes, the process proceeds to step S18 to execute high temperature forced modulation in accordance with the waveform pattern of FIG. 4 or FIG. 6, and then, in step S20, it is determined whether the forced modulation termination condition is satisfied. If No, the process returns to step S18. The forced modulation end condition is that the exhaust gas purification performance does not deteriorate even when the forced modulation is finished and the normal 0 ₂ F / B control is shifted (in other words, the three-way catalyst 17 is already activated). For example, it is determined based on the catalyst temperature Tcat or the like.

  Therefore, at the time of engine cold start, forced modulation for the low temperature region in step S14 is executed until the three-way catalyst 17 reaches the light-off temperature, and when the three-way catalyst 17 reaches the light-off temperature, the high temperature in step S18. It is switched to the forced modulation for the area. Note that the threshold for the inlet temperature Tex is not limited to 350 ° C., and may be arbitrarily changed within a range of 300 ° C. to 400 ° C., for example, depending on the catalyst type, oxygen storage capacity, deterioration degree, and the like. In step S16, the determination may be made based on the catalyst temperature Tcat estimated in step S10 instead of the inlet temperature Tex.

If the determination in step S20 becomes Yes due to the establishment of the forced modulation termination condition, the routine proceeds to step S22 and the routine is terminated after switching to the 0 ₂ F / B control to the theoretical air-fuel ratio based on the O ₂ sensor output. When switching from forced modulation to 0 ₂ F / B control, a transition period (shown in FIG. 7) is set to prevent sudden changes in the operating state, and the amplitude and period are gradually reduced during the transition period. Consideration to shift to 0 ₂ F / B control.

Next, the setting process of the execution conditions for the low temperature region and high temperature forced modulation will be described.
The waveform pattern of each forced modulation shown in FIGS. 3, 4 or 5, 6 is determined based on the required O ₂ concentration and the required CO concentration obtained as the optimum exhaust gas characteristics for the degree of activity of the three-way catalyst 17. It has been done. That is, the optimum amount of O ₂ and CO to be supplied onto the catalyst 17 for raising the temperature in accordance with the temperature range of the three-way catalyst 17 with the light-off temperature as a boundary, in other words, the optimum O ₂ concentration of the exhaust gas. The execution conditions are determined from the viewpoints that the execution conditions of the forced modulation that can achieve the O ₂ concentration and the CO concentration are also different.

FIG. 7 is an example of a time chart showing the switching state of the exhaust control with respect to the inlet temperature Tex at the time of engine cold start and the transition of the required O ₂ concentration and the required CO concentration. As a result of the above-described processing of the ECU 21, at the time of engine start and immediately after start-up, the engine start mode is subjected to start-up increase correction and post-start-up increase correction by O / L control, followed by forced modulation for the low temperature range, Forcible modulation is performed, and then the control is switched to 0 ₂ F / B control through the transition period.

For forced modulation for the low temperature range that is executed in the temperature range below the light-off temperature, 1.1% is set as the required O ₂ concentration and 0.3% is set as the required CO concentration. For forced modulation for the high temperature range executed in the temperature range, 0.6% is set as the required O ₂ concentration, and 0.9% is set as the required CO concentration. Based on these required O ₂ concentration and required CO concentration, the common waveform pattern shown in FIGS. 3 and 4 is set in both the low temperature range and the high temperature range, and in the low temperature range where the required CO concentration is relatively low. The center air-fuel ratio is set to 15.0, and the center air-fuel ratio is set to 14.0 in the high temperature range where the required CO concentration is relatively high.

Thus, the waveform pattern and the center A / F of the forcible modulation of the low temperature region and high temperature region is required O ₂ concentration and the required CO concentration previously determined by tests in advance a guide, the actual control of the ECU21 request O ₂ The center air-fuel ratio is selected according to the temperature range without considering the concentration and the required CO concentration, and the selected center air-fuel ratio is applied to the waveform pattern to execute forced modulation.
FIG. 8 shows the temperature rise of the catalyst according to the control of the exhaust air / fuel ratio, assuming the average air / fuel ratio of 15.0, the waveform pattern for the low temperature range shown in FIG. 3 (shown as 1 Hz ± 0.5 in the figure), the above Waveform pattern for low temperature range shown in Fig. 5 (displayed as 1Hz + 0.5 / -1.0 in the diagram), O / L control in engine start mode (displayed as O / L in the diagram), 0 ₂ F / B control This compares the temperature rise status (shown as 0 ₂ F / B in the figure). In this way, when the average air-fuel ratio is set to 15.0 on the lean side, the bed temperature rapidly rises with respect to the inlet temperature at an early stage after engine startup in any exhaust control, and the catalyst temperature rise state is the average air-fuel ratio. It can be assumed that there is a high possibility of depending on

  In view of this point, the temperature rise of the catalyst when the average air-fuel ratio is made different is measured, and the test result is shown in FIG. This figure compares the application of the average air-fuel ratio 15.0 waveform pattern shown in FIGS. 3 and 5 and the application of the average air-fuel ratio 14.0 waveform pattern shown in FIGS. As for the increase, the waveform pattern shown in FIG. 5 of the average air-fuel ratio 15.0 is good immediately after the start (low temperature range of the three-way catalyst 17), and after a certain amount of time has passed since the start (high temperature range of the three-way catalyst 17). It can be seen that the waveform pattern shown in FIG. 6 of 14.0 is good.

Therefore, the temperature rise ΔT (= catalyst bed temperature−inlet temperature) on the catalyst when forced modulation is executed at the average air-fuel ratios 14.0 and 15.0 is measured, and the test results are shown in FIG. According to the test results of FIG. 10, with the boundary when the inlet temperature is about 350 ° C., the average air-fuel ratio 15.0 has a larger temperature increase ΔT on the low temperature side, and the average air-fuel ratio 14.0 on the high temperature side. A large temperature increase ΔT is obtained. From this test result, it is presumed that an appropriate amount of CO or O ₂ is supplied onto the catalyst in any temperature range by switching the central air-fuel ratio, thereby contributing to the temperature rise of the catalyst.

Based on the above test results, execution conditions of forced modulation for low temperature range and high temperature range are set. Based on these execution conditions, the average air-fuel ratio of 15.0 shown in FIGS. When the inlet temperature Tex becomes 350 ° C. or higher, the waveform pattern of the average air-fuel ratio 14.0 shown in FIGS. 4 and 6 is applied to the forced modulation. Therefore, regardless of the temperature range, an appropriate amount of CO or O ₂ is supplied onto the three-way catalyst 17, so that the three-way catalyst 17 can be activated and purified early by promoting the temperature rise without depending on the amount of noble metal supported on the catalyst. The performance can be improved.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the execution conditions of the forced modulation for the low temperature region and the high temperature region are set under the condition that the waveform pattern itself is common and the setting of the average air-fuel ratio is different, but for the low temperature region and the high temperature region. The waveform pattern may be changed with. Specifically, the waveform pattern shown in FIG. 3 is applied for the low temperature region, the waveform pattern shown in FIG. 6 is applied for the high temperature region, or the waveform pattern shown in FIG. 5 is applied for the low temperature region. However, the waveform pattern shown in FIG. 4 may be applied to the high temperature region.

In each of the above embodiments, only the three-way catalyst 17 is provided in the exhaust passage 16 of the engine 1, but a proximity catalyst, a NOx catalyst, or the like may be arbitrarily added.
Further, the present invention is not limited to a direct injection type engine, but can be applied to an intake pipe injection type engine. Furthermore, an A / F target value may be controlled by mounting an O ₂ sensor downstream of the catalyst.

1 is an overall configuration diagram schematically showing an engine and an exhaust control device thereof in an embodiment. It is a flowchart which shows the start time exhaust control routine which ECU performs. It is a time chart which shows the waveform pattern applied to the forced modulation for low temperature regions. It is a time chart which shows the waveform pattern applied to the forced modulation for high temperature regions. It is a time chart which shows another example of the waveform pattern applied to the forced modulation for low temperature regions. It is a time chart which shows another example of the waveform pattern applied to the forced modulation for high temperature regions. Is a time chart showing changes in the switching status and request O ₂ concentration and requests CO concentration of the exhaust control for the inlet temperature at the time of engine cold start. It is a figure which shows the catalyst temperature rising condition according to control of an exhaust air fuel ratio. It is a figure which shows the catalyst temperature rising condition when making an average air fuel ratio differ. FIG. 6 is a diagram comparing temperature rise amounts on a catalyst when forced modulation is executed at average air-fuel ratios of 14.0 and 15.0.

Explanation of symbols

1 engine (internal combustion engine)
16 Exhaust passage 17 Three-way catalyst 21 ECU (feedback control means, air-fuel ratio fluctuation control means)
24 Temperature sensor (catalyst temperature correlation value detection means)

Claims (3)

A catalyst provided in the exhaust passage of the internal combustion engine;
A catalyst temperature correlation value detecting means for detecting a parameter value correlated with the temperature of the catalyst;
Air-fuel ratio fluctuation control means that operates immediately after starting the internal combustion engine and forcibly varies the air-fuel ratio of the exhaust gas flowing into the catalyst between a lean air-fuel ratio and a rich air-fuel ratio,
The air-fuel ratio fluctuation control means sets the central air-fuel ratio of the air-fuel ratio fluctuation to a lean air-fuel ratio side with respect to stoichiometry at the initial stage of its operation, and then in the direction of temperature rise of the detection value detected by the catalyst temperature correlation value detection means An exhaust control device for an internal combustion engine, characterized in that the central air-fuel ratio is shifted to a richer side than the stoichiometric with the change of the engine. Feedback control means for performing feedback control so that the actual air-fuel ratio of the internal combustion engine approaches the target air-fuel ratio,
2. An exhaust control apparatus for an internal combustion engine according to claim 1, wherein said feedback control means starts operating after said air-fuel ratio fluctuation control means shifts said central air-fuel ratio to a rich air-fuel ratio side from stoichiometry.   The temperature of the catalyst is in the range of about 300 ° C to about 400 ° C, and the air-fuel ratio fluctuation control means is configured to shift the central air-fuel ratio to a rich air-fuel ratio side from stoichiometry. Item 3. An exhaust control device for an internal combustion engine according to Item 1 or 2.

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