JP2007138882A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce emission by secondary air while preventing an excessive temperature rise in a catalyst regardless of an operation condition in an internal combustion engine mounted with a secondary air supply system. <P>SOLUTION: This exhaust emission control device is provided with an upstream side secondary air supply nozzle 17 for supplying the secondary air 13 delivered from an air pump 16 to the upstream side of the catalyst 13, a downstream side secondary air supply nozzle 18 for supplying the secondary air to the downstream side of the catalyst 13 and a supply destination switching valve 19 for switching a supply destination of the secondary air. When the temperature of the catalyst 13 is not raised to the active temperature, the secondary air is supplied to the upstream side of the catalyst 13. After the temperature of the catalyst 13 rises to the active temperature, the excessive temperature rise in the catalyst 13 is prevented by stopping supply of the secondary air to the upstream side of the catalyst 13. When increasing a quantity of high load fuel, a rich component unpurified by the catalyst 13 is purified by reacting with oxygen of the secondary air by oxidation on the downstream side of the catalyst 13 by supplying the secondary air to the downstream side of the catalyst 13. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine in which a catalyst is installed in an exhaust passage of the internal combustion engine and secondary air is supplied to the exhaust gas to promote exhaust gas purification and catalyst warm-up. It is.

  In recent years, in a vehicle using an internal combustion engine as a power source, as shown in Patent Document 1 (Japanese Patent Laid-Open No. 2004-11585), a secondary air pump is provided upstream of the exhaust gas purification catalyst in the exhaust passage. There are known techniques for supplying air to promote the purification (oxidation reaction) of exhaust gas HC and CO, and to promote the warm-up of the catalyst by the reaction heat.

Further, in a system in which two catalysts are installed in series in the exhaust passage, as shown in Patent Document 2 (Japanese Utility Model Publication No. 63-16825), secondary air is supplied to the upstream side of the upstream side catalyst, There is a type in which secondary air is supplied between an upstream catalyst and a downstream catalyst, and secondary air is also supplied to the downstream catalyst.
JP 2004-11585 A Japanese Utility Model Publication No. 63-16825

  All of the conventional secondary air supply systems described above promote the purification (oxidation reaction) of HC and CO in the exhaust gas flowing into the catalyst by supplying secondary air to the exhaust gas flowing into the catalyst. Or the heat of reaction promotes warming up of the catalyst.

  However, for example, during high-load operation, the temperature of the exhaust gas increases and the temperature of the catalyst rises, so the fuel injection amount is increased to reduce the air-fuel ratio from the viewpoint of preventing excessive catalyst temperature rise (catalyst melting damage prevention). Although the enrichment suppresses the temperature rise of the exhaust gas, when the secondary air is supplied to the upstream side of the catalyst during high load operation, the exhaust gas rich component (HC, CO) and the secondary air Since the exhaust gas temperature rises due to the oxidation reaction with oxygen and the catalyst may overheat, the secondary air supply to the upstream side of the catalyst is stopped during high-load operation . Therefore, during high load operation, the rich component of the exhaust gas that increases due to the enrichment of the air-fuel ratio cannot be purified by secondary air, so the rich component concentration of the exhaust gas flowing into the catalyst is the purification capacity (oxidation treatment) There was a problem that the emissions deteriorated.

  The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to reduce emissions by secondary air while preventing overheating of the catalyst regardless of the operating conditions of the internal combustion engine. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine.

  In order to achieve the above object, an invention according to claim 1 is directed to an exhaust gas purification apparatus for an internal combustion engine in which one or a plurality of catalysts are installed in an exhaust passage of the internal combustion engine to purify exhaust gas. An upstream secondary air supply section for supplying secondary air to the upstream side of the one or more catalysts in the exhaust passage (hereinafter simply referred to as “catalyst upstream side”); A downstream secondary air supply unit that supplies secondary air downstream of one or a plurality of catalysts (hereinafter simply referred to as “catalyst downstream side”), and the upstream side secondary air supply unit according to operating conditions of the internal combustion engine. The secondary air supply unit switches the supply of secondary air to the upstream side of the catalyst and the supply of secondary air to the downstream side of the catalyst by the downstream side secondary air supply unit by the secondary air supply control means or the secondary air The supply amount is controlled.

  In short, depending on the operating conditions of the internal combustion engine, if secondary air is supplied to the upstream side of the catalyst, it may lead to excessive temperature rise of the catalyst. By supplying the secondary air, the rich component of the exhaust gas that has passed through the catalyst is purified by oxidizing the downstream side of the catalyst. In this way, the emission can be reduced by the secondary air while preventing excessive temperature rise of the catalyst regardless of the operating conditions of the internal combustion engine.

  Specifically, as in claim 2, when the operating condition is that the amount of fuel supplied to the internal combustion engine is increased to enrich the air-fuel ratio, the downstream side secondary air supply unit provides the secondary downstream to the catalyst. It is better to switch to air supply. This is because the rich component concentration of the exhaust gas flowing into the catalyst may exceed the purification capacity (oxidation capacity) of the catalyst under the operating conditions that enrich the air-fuel ratio, so the rich component that could not be purified by the catalyst Is purified by oxidizing the secondary air with oxygen in the downstream side of the catalyst.

  Further, as in the third aspect, it is preferable to switch to the supply of secondary air to the downstream side of the catalyst by the downstream side secondary air supply unit under the high load operation condition. This is because, under high load operating conditions, the temperature of the exhaust gas becomes high, so when the secondary air is supplied to the upstream side of the catalyst, the exhaust gas is oxidized by the oxidation reaction between the rich component of the exhaust gas and the oxygen of the secondary air. Since the temperature may increase further and the catalyst may overheat, the rich component that could not be purified by the catalyst is purified by oxidizing it with the oxygen in the secondary air on the downstream side of the catalyst.

  Further, as claimed in claim 4, there is provided means for determining whether or not the rich component concentration of the exhaust gas flowing into the catalyst exceeds the purification capacity (oxidation processing capacity) of the catalyst, and the rich exhaust gas flowing into the catalyst When it is determined that the component concentration exceeds the purification capacity of the catalyst, switching to secondary air supply to the catalyst downstream side by the downstream secondary air supply unit may be performed. Thereby, the rich component that could not be purified by the catalyst can be reliably purified by oxidizing the secondary component with oxygen in the downstream side of the catalyst.

  By the way, if the temperature of the exhaust gas on the downstream side of the catalyst is too low, even if the secondary air is supplied to the downstream side of the catalyst, the oxidation reaction between the rich component of the exhaust gas and the oxygen of the secondary air is not promoted. The exhaust gas on the downstream side is increasingly cooled by the secondary air, and the exhaust gas temperature required to cause the exhaust gas purification reaction (oxidation / reduction reaction) cannot be secured on the downstream side of the catalyst. There is an increasing concern.

  Accordingly, as in claim 5, the exhaust gas temperature determining means for detecting or estimating the exhaust gas temperature on the downstream side of the catalyst is provided, and the exhaust gas temperature on the downstream side of the catalyst detected or estimated by the exhaust gas temperature determining means is a predetermined temperature. At the time described above, switching to the supply of secondary air to the downstream side of the catalyst by the downstream side secondary air supply unit may be performed. In this way, when the exhaust gas temperature on the downstream side of the catalyst is in a temperature range that can promote the oxidation reaction between the rich component and the oxygen of the secondary air, the secondary air is supplied to the downstream side of the catalyst to reduce emissions. In a lower temperature range, it is possible to control to stop the supply of secondary air to the downstream side of the catalyst and avoid an increase in emission due to the cooling effect of the secondary air.

  Further, as in claim 6, there is provided catalyst temperature determination means for detecting or estimating the temperature of the catalyst, and when the catalyst temperature detected or estimated by the catalyst temperature determination means is equal to or higher than a predetermined temperature, downstream secondary air supply It may be switched to supply secondary air to the downstream side of the catalyst by the unit. In this way, in the catalyst temperature range where there is a concern about the excessive temperature rise of the catalyst due to the heat of the oxidation reaction between the rich component of the exhaust gas upstream of the catalyst and the oxygen of the secondary air, the secondary air is supplied downstream of the catalyst. By supplying it, emission can be reduced while preventing excessive temperature rise of the catalyst. In the lower catalyst temperature range, secondary air can be supplied upstream of the catalyst to promote warming up of the catalyst. It becomes.

  In addition, if the supply amount of secondary air is excessive with respect to the exhaust gas flow rate on the downstream side of the catalyst, the exhaust gas on the downstream side of the catalyst is cooled by the excess secondary air, and the purification reaction of the exhaust gas on the downstream side of the catalyst There is a concern that the exhaust gas temperature necessary to cause (oxidation / reduction reaction) cannot be secured, and the emission increases on the contrary.

  Therefore, as described in claim 7, the flow rate of the secondary air supplied to the downstream side of the catalyst by the downstream side secondary air supply unit may be changed according to the exhaust gas flow rate or a parameter correlated therewith. In this way, an appropriate amount of secondary air corresponding to the exhaust gas flow rate can be supplied to the downstream side of the catalyst, and cooling of the exhaust gas by the secondary air is suppressed, while the effect of reducing emissions by the secondary air is achieved. You can definitely get it.

  Hereinafter, two Examples 1 and 2, which embody the best mode for carrying out the present invention, will be described.

A first embodiment of the present invention will be described with reference to FIGS. First, the configuration of the entire system will be described with reference to FIG.
A catalyst 13 such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas is installed in the exhaust passage 12 of the engine 11 which is an internal combustion engine. The catalyst 13 may be a single catalyst, or a plurality of catalysts connected in series. An air-fuel ratio sensor 14 (or oxygen sensor) for detecting the air-fuel ratio (or rich / lean) of the exhaust gas is provided upstream of the catalyst 13.

  Further, the exhaust passage 12 is provided with a secondary air supply system 15 for supplying secondary air. The secondary air supply system 15 includes an air pump 16 driven by an electric motor and secondary air discharged from the air pump 16 upstream of the catalyst 13 in the exhaust passage 12 (in the case of a plurality of catalysts, the most upstream). An upstream secondary air supply nozzle 17 (upstream secondary air supply unit) for supplying to the upstream side of the catalyst and secondary air discharged from the air pump 16 downstream of the catalyst 13 in the exhaust passage 12 ( In the case of a plurality of catalysts, the downstream secondary air supply nozzle 18 (downstream secondary air supply unit) that supplies to the downstream side of the most downstream catalyst and the supply destination of the secondary air discharged from the air pump 16 are upstream. It comprises a supply destination switching valve 19 that switches between the side secondary air supply nozzle 17 and the downstream side secondary air supply nozzle 18. The air pump 16 and the supply destination switching valve 19 of the secondary air supply system 15 are controlled by an engine control circuit (hereinafter referred to as “ECU”) 20. The ECU 20 reads output signals of various sensors (for example, a crank angle sensor, an intake pressure sensor, a water temperature sensor, an air-fuel ratio sensor 14 and the like) that detect the engine operating state, detects the engine operating state, and responds to the engine operating state. To control the fuel injection amount and ignition timing.

  Further, the ECU 23 controls the secondary air supply operation by the secondary air supply system 15 by executing the secondary air supply control routine of FIG. Hereinafter, the processing content of the secondary air supply control routine of FIG. 2 will be described.

  The secondary air supply control routine of FIG. 2 is repeatedly executed at a predetermined cycle during engine operation, and serves as secondary air supply control means in the claims. When this routine is started, first, at step 101, it is determined whether or not the temperature of the catalyst 13 is higher than a predetermined temperature T1 corresponding to the activity determination temperature. At this time, the temperature of the catalyst 13 may be detected by a temperature sensor (catalyst temperature determination means) installed in the catalyst 13, or the elapsed time after the engine start, the exhaust heat amount integrated value after the engine start, the fuel injection amount integrated You may make it estimate based on a value etc. Or you may make it estimate the temperature of the catalyst 13 based on the temperature of the exhaust gas detected with the temperature sensor installed in the upstream of the catalyst 13, and / or the downstream.

  If it is determined in step 101 that the temperature of the catalyst 13 is equal to or lower than the predetermined temperature T1, it is determined that the catalyst 13 has not risen to the activation temperature, the process proceeds to step 104, and the supply destination switching valve 19 is turned on the upstream side. Switching to the secondary air supply nozzle 17 side, secondary air discharged from the air pump 16 is supplied to the upstream side of the catalyst 13. Thereby, the rich components (HC, CO) in the exhaust gas flowing into the catalyst 13 and the oxygen in the secondary air are oxidized and the warming of the catalyst 13 is promoted by the reaction heat.

  On the other hand, if it is determined in step 101 that the temperature of the catalyst 13 is higher than the predetermined temperature T1, it is determined that the catalyst 13 has been heated to the activation temperature, the process proceeds to step 102, and a high load is applied. The fuel injection amount is increased to enrich the air-fuel ratio, and it is determined whether or not the high-load fuel increase for operating the engine 11 is in progress. If the high-load fuel increase is in progress, the exhaust gas flowing into the catalyst 13 is determined. It is determined that the rich component concentration exceeds the purification capability (oxidation treatment capability) of the catalyst 13 and the exhaust gas temperature downstream of the catalyst 13 is a temperature region in which an oxidation reaction between oxygen in the secondary air and the rich component occurs. In step 103, the supply destination switching valve 19 is switched to the downstream secondary air supply nozzle 18 side to supply the secondary air discharged from the air pump 16 to the downstream side of the catalyst 13. As a result, the rich component that could not be purified by the catalyst 13 is purified by oxidizing it with oxygen in the secondary air on the downstream side of the catalyst 13.

  If it is determined in step 102 that the amount of high load fuel is not increasing, it is determined that the rich component contained in the exhaust gas can be sufficiently purified by the catalyst 13, and this routine is immediately terminated. In this case, the air pump 16 is stopped and all the supply of secondary air is stopped.

  According to the first embodiment described above, in addition to the upstream secondary air supply nozzle 17 that supplies the secondary air to the upstream side of the catalyst 13, the downstream side secondary air that supplies the secondary air to the downstream side of the catalyst 13. The secondary air supply nozzle 18 is provided, and when the temperature of the catalyst 13 is not raised to the activation temperature, the secondary air is supplied to the upstream side of the catalyst 13, so that the exhaust gas flowing into the catalyst 13 It is possible to oxidize the rich component therein and the oxygen in the secondary air, and promote the warm-up of the catalyst 13 by the reaction heat.

  Then, after the temperature of the catalyst 13 has risen above the predetermined temperature T1 (activity determination temperature), the supply of secondary air to the upstream side of the catalyst 13 is stopped to prevent the catalyst 13 from being overheated. Since the secondary air is supplied to the downstream side of the catalyst 13 during the increase of the high-load fuel, the rich components that could not be purified by the catalyst 13 are oxidized and oxidized in the downstream air on the downstream side of the catalyst 13. It can be purified by reaction. Thereby, the emission can be reduced by the secondary air while preventing the catalyst 13 from being overheated regardless of the engine operating conditions.

  By the way, if the temperature of the exhaust gas on the downstream side of the catalyst 13 is too low, the oxidation reaction between the rich component of the exhaust gas and the oxygen of the secondary air is not promoted even if the secondary air is supplied to the downstream side of the catalyst 13. In addition, the exhaust gas downstream of the catalyst 13 is gradually cooled by the secondary air, and the exhaust gas temperature necessary to cause a purification reaction (oxidation / reduction reaction) of the exhaust gas downstream of the catalyst 13 is secured. There is a concern that it will be impossible to do so and the emission will increase.

  Further, if the supply amount of secondary air is excessive with respect to the exhaust gas flow rate on the downstream side of the catalyst 13, the exhaust gas on the downstream side of the catalyst 13 is cooled by excess secondary air, and the downstream side of the catalyst 13 As a result, the exhaust gas temperature necessary to cause the exhaust gas purification reaction (oxidation / reduction reaction) cannot be secured, and there is a concern that the emission increases.

  Therefore, in the second embodiment of the present invention, the secondary air supply control routine of FIG. 3 is executed to control the secondary air supply system 15 in consideration of the exhaust gas temperature and the exhaust gas flow rate downstream of the catalyst 13. To do.

  The secondary air supply control routine of FIG. 3 is also repeatedly executed at predetermined intervals during engine operation. First, in step 201, it is determined whether or not the temperature of the catalyst 13 is higher than a predetermined temperature T1 corresponding to the activity determination temperature. If the temperature of the catalyst 13 is equal to or lower than the predetermined temperature T1, the process proceeds to step 206 where secondary air is supplied to the upstream side of the catalyst 13 and secondary air is supplied to the upstream side of the catalyst 13 to Promote warm-up.

  Thereafter, after the temperature of the catalyst 13 has risen to a predetermined temperature T1 (activity determination temperature) or higher, the supply of secondary air to the upstream side of the catalyst 13 is stopped to prevent the catalyst 13 from being overheated. Proceeding to 202, it is determined whether or not the fuel is being increased (during rich control for enriching the air-fuel ratio). If not, the rich component of the exhaust gas flowing into the catalyst 13 is sufficiently removed. This routine is finished as it is. In this case, the air pump 16 is stopped and all the supply of secondary air is stopped.

  On the other hand, if it is determined in step 202 that the amount of fuel is being increased, it is determined that the rich component concentration of the exhaust gas flowing into the catalyst 13 exceeds the purification capacity (oxidation capacity) of the catalyst 13, and the step Proceeding to 203, it is determined whether or not the exhaust gas temperature downstream of the catalyst 13 is higher than the predetermined temperature T2. At this time, the exhaust gas temperature on the downstream side of the catalyst 13 may be detected by a temperature sensor (exhaust gas temperature determining means) installed on the downstream side of the catalyst 13 or detected by a temperature sensor installed on the catalyst 13. The exhaust gas temperature on the downstream side of the catalyst 13 may be estimated based on the temperature of the catalyst 13 that has been performed. Further, the predetermined temperature T2 is set to an exhaust gas temperature necessary for oxidizing the rich component of the exhaust gas downstream of the catalyst 13 and the oxygen of the secondary air.

  If it is determined in step 203 that the exhaust gas temperature downstream of the catalyst 13 is equal to or lower than the predetermined temperature T2, it is determined that the rich component of the exhaust gas cannot be purified even if secondary air is supplied to the downstream side of the catalyst 13. Then, this routine is finished as it is. In this case, the air pump 16 is stopped and all the supply of secondary air is stopped.

  On the other hand, if it is determined in step 203 that the exhaust gas temperature on the downstream side of the catalyst 13 is higher than the predetermined temperature T2, the secondary air is supplied to the downstream side of the catalyst 13 to enrich the exhaust gas. It is determined that the component can be purified, and the process proceeds to step 204, where the target secondary air flow rate is set according to the current exhaust gas flow rate (or a parameter correlated therewith). At this time, the exhaust gas flow rate may be calculated based on engine operating conditions (engine speed, fuel injection amount, air-fuel ratio, etc.). The target secondary air flow rate is set so as to increase as the current exhaust gas flow rate increases.

Thereafter, the process proceeds to step 205 where the supply destination switching valve 19 is switched to the downstream side secondary air supply nozzle 18 side, and the rotational speed of the air pump 16 is controlled according to the target secondary air flow rate. Air is supplied to the downstream side of the catalyst 13 at a flow rate corresponding to the target secondary air flow rate. As a result, the rich component that could not be purified by the catalyst 13 is purified by oxidizing it with the appropriate amount of secondary air oxygen corresponding to the exhaust gas flow rate.
The secondary air flow rate supplied to the upstream side of the catalyst 13 may also be set according to the exhaust gas flow rate.

  In the second embodiment described above, when the exhaust gas temperature on the downstream side of the catalyst 13 is in a temperature range equal to or higher than the predetermined temperature T2 that can promote the oxidation reaction between the rich component and the oxygen of the secondary air, the downstream side of the catalyst 13. The secondary air is supplied to reduce the emission, and in the lower temperature range, the supply of the secondary air to the downstream side of the catalyst 13 is stopped to avoid an increase in the emission due to the cooling effect of the secondary air. be able to. Moreover, since the flow rate of the secondary air supplied to the downstream side of the catalyst 13 is changed according to the exhaust gas flow rate (or a parameter correlated therewith), an appropriate amount of secondary air corresponding to the exhaust gas flow rate is converted to the catalyst. 13 can be supplied downstream, and the emission reduction effect by the secondary air can be reliably obtained while suppressing the cooling of the exhaust gas by the secondary air.

  In place of the process of step 101 of FIG. 2 (step 201 of FIG. 3), it is determined whether or not the warm-up control of the catalyst 13 is completed, and before the warm-up control of the catalyst 13 is completed (during the warm-up control being executed). If so, the process may proceed to step 104 in FIG. 2 (step 206 in FIG. 3), and secondary air may be supplied to the upstream side of the catalyst 13 to promote warming up of the catalyst 13.

  Further, instead of the process of step 102 in FIG. 2 (step 202 in FIG. 3), the air-fuel ratio on the upstream side of the catalyst 13 detected by the air-fuel ratio sensor 14 on the upstream side of the catalyst 13 (or the air on the downstream side of the catalyst 13). It is determined whether or not the air-fuel ratio downstream of the catalyst 13 detected by the fuel ratio sensor has become rich beyond a predetermined rich degree, and when the air-fuel ratio has become rich beyond a predetermined rich degree, It may be determined that the rich component concentration of the exhaust gas flowing into the catalyst 13 exceeds the purification ability (oxidation treatment ability) of the catalyst 13. Then, the secondary air may be supplied to the downstream side of the catalyst 13 only based on this determination result, or the exhaust gas temperature on the downstream side of the catalyst 13 is higher than the predetermined temperature T2 as in step 203 of FIG. Only when it is high, secondary air may be supplied to the downstream side of the catalyst 13.

  In the first and second embodiments, the supply destination of the secondary air discharged from the air pump 16 is set between the upstream side secondary air supply nozzle 17 and the downstream side secondary air supply nozzle 18 by the supply destination switching valve 19. Although switched, the ratio of the secondary air flow rate supplied to the upstream side and the downstream side of the catalyst 13 may be changed according to the engine operating conditions.

It is a figure which shows the structure of the whole secondary air supply system which shows Example 1 of this invention. 4 is a flowchart illustrating a process flow of a secondary air supply control routine according to the first embodiment. 6 is a flowchart showing a flow of processing of a secondary air supply control routine of Embodiment 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Exhaust passage, 13 ... Catalyst, 14 ... Air-fuel ratio sensor, 15 ... Secondary air supply system, 16 ... Air pump, 17 ... Upstream secondary air supply nozzle (Upstream secondary air) Supply part), 18 ... downstream side secondary air supply nozzle (downstream side secondary air supply part), 19 ... supply destination switching valve, 20 ... ECU (secondary air supply control means)

Claims (7)

In an exhaust gas purification apparatus for an internal combustion engine in which one or a plurality of catalysts are installed in an exhaust passage of the internal combustion engine to purify exhaust gas,
An upstream secondary air supply section for supplying secondary air to the upstream side of the one or more catalysts in the exhaust passage (hereinafter simply referred to as “catalyst upstream side”);
A downstream secondary air supply section for supplying secondary air to the downstream side of the one or more catalysts in the exhaust passage (hereinafter simply referred to as “catalyst downstream side”);
Switching between the supply of secondary air to the upstream side of the catalyst by the upstream side secondary air supply unit and the supply of secondary air to the downstream side of the catalyst by the downstream side secondary air supply unit according to the operating conditions of the internal combustion engine Or a secondary air supply control means for controlling the supply amount of the secondary air.   The secondary air supply control means is configured to increase the amount of fuel supplied to the internal combustion engine and to enrich the air-fuel ratio, so that the secondary air supplied to the downstream side of the catalyst by the downstream secondary air supply unit 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the apparatus is switched to supply.   The said secondary air supply control means switches to the supply of the secondary air to the catalyst downstream by the said downstream secondary air supply part at the time of high load operation conditions, The Claim 1 or 2 characterized by the above-mentioned. Exhaust gas purification device for internal combustion engine.   The secondary air supply control means comprises means for determining whether or not the rich component concentration of the exhaust gas flowing into the catalyst exceeds the purification capacity of the catalyst, and the rich component concentration of the exhaust gas flowing into the catalyst 4 is switched to supply of secondary air to the downstream side of the catalyst by the downstream side secondary air supply unit when it is determined that the amount exceeds the purification capacity of the catalyst. 2. An exhaust gas purifying device for an internal combustion engine according to 1. An exhaust gas temperature determining means for detecting or estimating the exhaust gas temperature downstream of the catalyst,
When the exhaust gas temperature detected or estimated by the exhaust gas temperature determination means is equal to or higher than a predetermined temperature, the secondary air supply control means is connected to the downstream side of the catalyst by the downstream secondary air supply unit. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the apparatus is switched to supply of secondary air. Comprising a catalyst temperature determining means for detecting or estimating the temperature of the catalyst;
The secondary air supply control means switches to the supply of secondary air to the downstream side of the catalyst by the downstream side secondary air supply unit when the catalyst temperature detected or estimated by the catalyst temperature determination means is equal to or higher than a predetermined temperature. 6. An exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the exhaust gas purifying device is an internal combustion engine.   The secondary air supply control means changes the flow rate of secondary air supplied to the downstream side of the catalyst by the downstream secondary air supply unit in accordance with an exhaust gas flow rate or a parameter correlated therewith. The exhaust gas purifying device for an internal combustion engine according to any one of 1 to 6.

Images