JP2000240432A - Exhaust gas emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress emission of HC and CO in an unburnt state in the atmosphere during ignition of EGC. SOLUTION: This exhaust gas emission control device comprises a catalyst 6 disposed in the exhaust pipe 2 of an engine 1; a combustion chamber 5 disposed in the exhaust pipe 2 situated upper stream from the catalyst 6; a secondary air pump 3 to supply secondary air to the exhaust pipe 2 situated upper stream from the combustion chamber 5; and a control unit 8 to control a fuel feed amount such that, when the temperature of the catalyst 6 is increased, an air-fuel ratio of air-fuel mixture fed to the engine 1 is brought into the further rich side than a theoretical air-fuel ratio, and control a secondary air amount such that an air-fuel ratio on the combustion chamber 5 is brought into an air-fuel ratio being a combustible lean limit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to quickly activate the catalyst by using a combustor installed upstream of the catalyst immediately after starting the internal combustion engine to activate the catalyst quickly. The present invention relates to an exhaust gas purification device provided with the device.

[0002]

2. Description of the Related Art Catalysts carrying noble metals (platinum, rhodium, etc.) or other metals have been used for exhaust gas purification of automobiles. Such a catalyst purifies the exhaust gas by oxidizing or reducing HC, CO, NOx and the like, which are harmful components. The purification by the catalyst is strongly affected by the catalyst temperature, and is generally 350 to 40.
Requires temperatures above 0 ° C. Immediately after the start of the engine, the exhaust gas temperature is low, and the catalyst is activated (350 to 4).
(00 ° C. or higher), so that harmful components are hardly purified. Furthermore, during a cold state immediately after the start of the engine, the amount of HC and CO emissions is extremely large, and the amount of HC and CO released into the atmosphere may increase. In order to solve such a problem of the conventional exhaust gas purifying apparatus for an internal combustion engine, an exhaust gas combustor (Exhaust GasCombus) is provided upstream of a catalyst provided in an exhaust passage of the engine.
(hereinafter referred to as EGC) and rapidly heating the catalyst by the combustion energy (Japanese Patent Application Laid-Open No. 6-50 / 1990)
No. 8409) has been devised. In the above idea,
Immediately after the start-up of the catalyst, the air-fuel ratio (hereinafter, referred to as A / F) of the engine is maintained rich while the catalyst is not activated, and air is supplied by an air pump or the like to make the exhaust gas a combustible air-fuel mixture, which is burned by an ignition plug. Then, the catalyst is rapidly heated by the combustion energy to activate the catalyst early.

[0003]

However, in such an exhaust gas purifying apparatus for an internal combustion engine, when the EGC is ignited, the pressure in the exhaust pipe increases (FIG. 8), so that the supply amount of the secondary air decreases. In addition, there is a problem that the A / F in the EGC becomes temporarily rich and a part of HC and CO may be released to the atmosphere in an unburned state. The present invention has been made in view of such a conventional problem.
Even if the secondary air supply decreases during ignition of C, HC, CO
It is an object of the present invention to solve the above-mentioned problem by controlling the A / F of the engine and the supply amount of secondary air so that all the fuel burns.

[0004]

According to the first aspect of the present invention, an exhaust purification catalyst disposed in an exhaust passage of an engine and an exhaust combustor disposed in an exhaust passage upstream of the exhaust purification catalyst are provided. Secondary air supply means for supplying secondary air to an exhaust passage on the upstream side of the exhaust combustor; and, when the temperature of the exhaust purification catalyst is to be raised, the air-fuel ratio of the mixture supplied to the engine is stoichiometric. Control means for controlling the amount of fuel supplied so as to be richer than the fuel ratio and controlling the amount of secondary air so that the air-fuel ratio in the exhaust combustor becomes a lean-limit air-fuel ratio capable of burning. And According to the above configuration, even when the pressure in the exhaust passage increases at the start of combustion in the exhaust combustor and the secondary air supply amount temporarily decreases, the air-fuel ratio in the exhaust combustor is lower than the stoichiometric air-fuel ratio. It can be suppressed from becoming rich,
It is possible to suppress the release of C and CO into the atmosphere without burning. Further, when the temperature of the exhaust gas purifying catalyst is to be raised, the control means may control the air-fuel ratio of the air-fuel mixture supplied to the engine to a rich-limit air-fuel ratio capable of performing stable combustion. If it is configured to control the fuel supply amount so that
The difference between the amount of secondary air when the air-fuel ratio in the exhaust combustor reaches the stoichiometric air-fuel ratio and the amount of secondary air when the air-fuel ratio reaches the lean limit of combustible (the margin of secondary air) is maximized. The emission of HC and CO at the start of combustion of the exhaust combustor can be more effectively suppressed. Further, as in the third aspect of the present invention, there is provided an exhaust combustor ignition determining means for determining a timing at which combustion is started in the exhaust combustor, and the control means determines the start of combustion in the exhaust combustor. If the fuel supply amount is reduced and corrected only for a predetermined period after the start of the combustion, even when the enrichment in the exhaust combustor at the start of combustion cannot be avoided by the margin of the secondary air alone, HC and CO
Release can be suppressed. Further, as in the invention as set forth in claim 4, there is provided an exhaust combustor ignition determining means for determining a timing at which combustion is started in the exhaust combustor, and the control means determines that combustion in the exhaust combustor is started. Even if the secondary air supply amount is increased and corrected only for a predetermined period after the above operation, the same effect as that of the third aspect can be obtained.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention. A catalyst 6 is provided in the exhaust pipe 2 of the engine 1. The catalyst 6 is provided with a temperature sensor 7. Further, upstream of the catalyst 6, the EGC combustion chambers 5 and 2
A secondary air pump 3 and a spark plug 4 are provided. The control unit 8 drives the air-fuel ratio of the engine 1, the secondary air pump 3, and the ignition plug 4 with reference to the cooling water temperature of the engine 1, the output of the temperature sensor 7, and the like to control the exhaust combustor.

Next, the operation of the embodiment will be described with reference to the flowchart shown in FIG. Here, the fuel injection control and the secondary air amount control when the EGC is used, which are the main features of the present invention, will be described. In step 1 (hereinafter, step is referred to as S), it is determined whether the condition is the EGC use condition, that is, whether the catalyst 6 is in an inactive state. This is a use condition when the cooling water temperature at the time of starting is equal to or lower than a predetermined value or the catalyst temperature is equal to or lower than a predetermined value. EGC
If it is not the use condition, normal air-fuel ratio control is performed in S3, and the process is terminated. If it is the EGC use condition, the process proceeds to S2. In S2, in order to set the A / F of the engine 1 to the rich limit at which the engine 1 stably burns, the fuel injection pulse width TI of the injector is set to TI = RLEGC, and E
In order to set the A / F in the GC to the combustible lean limit of the EGC, the drive signal KAP of the secondary air pump 3 is set to KAP = L.
The condition of the point A in FIG. 3 is set as the LAP. As a result, the routine is terminated with a sufficient margin for the secondary air amount.

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the EGC is burned under the conditions shown at point A in FIG. Even if the secondary air amount decreases with the rise, the A / F in the EGC does not become rich and the emission of HC and CO to the atmosphere is suppressed because the secondary air amount has a sufficient margin. Is done.

(Embodiment 2) The configuration of this embodiment is the same as that of Embodiment 1. Next, the operation of the present embodiment will be described. In the present embodiment, the amount of decrease in the secondary air amount at the time of the EGC ignition is large, and the A / F in the EGC at the time of the EGC ignition is shifted to the rich side from the stoichiometric air-fuel ratio only by the measure of the first embodiment. Applicable when HC and CO may be emitted.

The operation of this embodiment will be described with reference to the flowchart shown in FIG. Here, the fuel injection control and the secondary air amount control when the EGC is used, which are the main features of the present invention, will be described. First, at the time of IGN on, a flag FEGC described later is cleared to 0. In S21, it is determined whether the condition is the EGC use condition, that is, whether the catalyst 6 is in an inactive state. This is a use condition when the cooling water temperature at the time of starting is equal to or lower than a predetermined value or the catalyst temperature is equal to or lower than a predetermined value. If it is not the EGC use condition, the normal air-fuel ratio control is performed in S23, and the process ends. E
If the condition is the GC use condition, the flag FE is set in S22.
It is determined whether GC is 0. The flag FEGC indicates whether the EGC is burning. As will be described later, when the EGC is burning, FEGC = 1. FEG at S22
If C = 1, the process proceeds to S28, which will be described later, and it is determined whether the exhaust pipe pressure increased by the ignition of the EGC returns to the original level. If FEGC = 0, the process proceeds to S24 to burn EGC. In S24, in order to set the A / F of the engine 1 to the rich limit at which the engine 1 stably burns, the fuel injection pulse width TI of the injector is set to TI = RL.
The drive signal KA of the secondary air pump 3 is used to set the A / F in the EGC to the EGC combustible lean limit.
Let P be KAP = LLAP (point A in FIG. 5). In S25, it is determined whether or not the EGC ignition timing has come. EG
C normally fires after a certain delay time from the start of the engine 1. This ignition delay time is always constant if the engine 1 and the exhaust system are the same, and can be experimentally determined. Therefore, it may be determined whether the elapsed time from the start of the engine 1 has reached the predetermined ignition delay time. Or
As another embodiment, a pressure sensor is provided in the EGC or immediately upstream of the EGC, and when the pressure sensor output rises, the EG is detected.
The ignition of C may be determined. Based on these determinations, EGC
If it is determined that the ignition timing has come, S26
Proceed to. If the ignition timing of EGC has not come, the routine ends as it is. In S26, EGC
The A / F of the engine 1 is made lean in response to the decrease in the amount of secondary air due to the pressure increase at the time of ignition. Since the secondary air amount decrease at the time of EGC ignition is constant as long as the engine 1 is operated under the same conditions, the lean A / F of the engine 1 can be experimentally obtained. Therefore S
At 26, the fuel injection pulse width TI of the injector is reduced by a predetermined value RAP to be TI = RLEGC-RAP,
The condition is set to the point B in FIG. In S27, the flag FEGC indicating that the EGC is igniting and burning is set to 1 and S2
Proceed to 8. In S28, it is determined whether or not the pressure increased by the ignition of the EGC returns to the original level. This may be determined based on whether a predetermined time has elapsed since the EGC was ignited. Alternatively, when a pressure sensor is provided, the determination may be made based on whether the output of the pressure sensor has become equal to or less than a predetermined value. If it is determined that the pressure has not returned to the original level, the routine ends. If it is determined that the pressure has returned to the original level, the process proceeds to S29, where the A / F of the engine 1 and 2
In order to set the next air amount to a normal setting (point C in FIG. 5), the fuel injection pulse width TI of the injector is set to TI = LLEGC,
The drive signal KAP of the secondary air pump 3 is calculated as KAP = STAP
And terminate the routine.

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the A / A
F and the secondary air amount are set to the condition of the point A in FIG. 5 in order to allow a margin for the secondary air amount, and the A / F of the engine 1 is made lean at the same time as the ignition according to the rise in the exhaust pipe pressure. Therefore, the A / F in the EGC is not enriched, and the emission of HC and CO into the atmosphere is suppressed.

(Embodiment 3) The configuration of this embodiment is the same as that of Embodiment 1. Next, the operation of the present embodiment will be described. In the present embodiment, the secondary air amount is increased instead of making the A / F of the engine 1 lean at the moment of ignition of the EGC in the second embodiment, and only the portions different from the second embodiment are described. This will be described with reference to the flowchart shown in FIG. If it is determined in S25 that the EGC ignition timing has come, the process proceeds to S36, and in response to the decrease in the secondary air amount due to the increase in pressure at the time of EGC ignition, 2
Increase the amount of secondary air. Since the secondary air amount decrease at the time of EGC ignition is constant as long as the engine 1 is operated under the same conditions, the secondary air increase amount can be experimentally obtained. Therefore, in S36, the secondary air amount pump drive signal KAP is increased by a predetermined value LAP, KAP = LLAP +
LAP is set as the condition of point B in FIG.

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the A / A
F and the amount of secondary air are set to the condition of point A in FIG. 7 in order to allow a margin for the amount of secondary air, and at the same time as ignition, the amount of secondary air is increased according to the rise in the exhaust pipe pressure. Since it is set at point B, the A / F in the EGC does not become rich, and HC,
Release of CO into the atmosphere is suppressed.

[0013]

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, even if the supply amount of secondary air decreases at the time of ignition of the EGC, the engine is designed so that HC and CO are all burned. By controlling the A / F and the secondary air supply amount, it is possible to suppress HC and CO from being released to the atmosphere in an unburned state.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a flowchart of the first embodiment.

FIG. 3 is a diagram illustrating a relationship between an engine A / F and a secondary air supply amount according to the first embodiment.

FIG. 4 is a flowchart according to the second embodiment.

FIG. 5 is a diagram illustrating a relationship between an engine A / F and a secondary air supply amount according to the second embodiment.

FIG. 6 is a flowchart according to the third embodiment.

FIG. 7 is a diagram illustrating a relationship between an engine A / F and a secondary air supply amount according to a third embodiment.

FIG. 8 is a diagram showing a problem of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust pipe 3 Secondary air pump 4 Spark plug 5 Combustion chamber 6 Catalyst 7 Temperature sensor 8 Control unit

Continued on the front page (72) Inventor Taro Yokoi 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. F-term (reference) 3G091 AB01 AB16 BA03 BA17 CA01 CA22 CB02 DA01 DA02 DB07 DB10 DC01 EA16 EA18 EA32 FA01 HA35 HA38

Claims (4)

[Claims] 1. An exhaust purification catalyst disposed in an exhaust passage of an engine, an exhaust combustor disposed in an exhaust passage upstream of the exhaust purification catalyst, and an exhaust passage upstream of the exhaust combustor. A secondary air supply unit for supplying secondary air; and a fuel supply amount such that an air-fuel ratio of the air-fuel mixture supplied to the engine becomes richer than a stoichiometric air-fuel ratio when the temperature of the exhaust gas purification catalyst is to be raised. Control means for controlling and controlling the amount of secondary air so that the air-fuel ratio in the exhaust combustor becomes the air-fuel ratio at the lean limit at which combustion is possible. 2. The control means controls a fuel supply amount such that when the temperature of the exhaust gas purifying catalyst is to be raised, the air-fuel ratio of the air-fuel mixture supplied to the engine has a rich-limit air-fuel ratio that enables stable combustion. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein: 3. An exhaust combustor ignition determining means for determining a timing at which combustion is started in the exhaust combustor, wherein the control means controls the fuel for a predetermined period after the start of combustion in the exhaust combustor is determined. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the supply amount is reduced. 4. An exhaust combustor ignition determining means for determining a timing at which combustion is started in the exhaust combustor, wherein the control means determines that the combustion has started in the exhaust combustor for a predetermined period of time. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the secondary air supply amount is increased and corrected.