JP4631680B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. The NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the stored NOx when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present.

By the way, the NOx catalyst is sulfur oxide (S
Ox) is also occluded by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning. Since the NOx purification rate in the NOx catalyst is reduced by this sulfur poisoning, it is necessary to perform a poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This poisoning recovery process is performed by causing the NOx catalyst to have a high temperature and the exhaust gas having a reduced oxygen concentration to flow through the NOx catalyst.

In this way, when the reduction of NOx and the recovery of sulfur poisoning are performed in a rich atmosphere, the reducing agent and H ₂ S may flow out downstream of the NOx catalyst. Here, a technique is known in which an oxidation catalyst is provided downstream of the NOx catalyst, air is supplied to the oxidation catalyst to form an oxygen-excess atmosphere, and a reducing agent and H ₂ S are oxidized (for example, Patent Documents). 1).
JP 2000-110552 A JP 2002-309929 A Japanese Patent Laid-Open No. 2004-076762

  Incidentally, an air pump for supplying secondary air is originally provided for promoting warm-up of the catalyst and HC purification immediately after the engine is started. Therefore, it is not considered to be used at the time of sulfur poisoning recovery processing in which secondary air needs to be sent for a long time during traveling. If an air pump is used for the sulfur poisoning recovery process, the frequency of use of the motor increases. Therefore, a design change or the like is required to extend the life of the motor. Therefore, there is a risk of increasing the cost. In addition, since the power consumption of the motor is increased, there is a possibility that the fuel consumption is deteriorated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of reducing the frequency of use of an air pump for supplying secondary air in an exhaust gas purification apparatus for an internal combustion engine. And

In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine of the present invention is
A NOx catalyst provided in the exhaust passage of the internal combustion engine for reducing NOx in the presence of a reducing agent;
Reducing agent supply means for supplying a reducing agent to the NOx catalyst;
A catalyst provided downstream of the NOx catalyst and having an oxidation function;
At least two secondary air sources for supplying secondary air to an exhaust passage between the NOx catalyst and the catalyst having an oxidizing function;
Secondary air supply source switching means for switching the secondary air supply source according to the load of the internal combustion engine;
It is characterized by comprising.

When the reducing agent is supplied to the NOx catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes a rich air-fuel ratio, and SOx is released from the NOx catalyst. However, at this time, a part of the reducing agent such as HC and CO may flow downstream. Further, at the time of recovery from sulfur poisoning, SOx released from the NOx catalyst tends to become H ₂ S. In this way, HC, CO, and H ₂ S flowing out from the NOx catalyst are oxidized by the downstream catalyst. Here, the catalyst having an oxidation function works effectively in an oxygen-excess atmosphere. However, when the sulfur poisoning is recovered, the oxygen concentration is lowered by the supply of the reducing agent. End up. Even in such a state, it is possible to improve the oxidation ability of the catalyst by supplying air from the secondary air supply source to the upstream side of the catalyst having an oxidation function.

  Then, by providing at least two secondary air supply sources and switching them according to the load of the internal combustion engine, the frequency of use of each secondary air supply source can be reduced. Thereby, since deterioration of components in each secondary air supply source can be suppressed, durability of each secondary air supply source can be improved.

  In the present invention, at least one of the secondary air supply sources is an air pump driven by an electric motor, and at least one is a means other than the air pump, and the secondary air supply source switching means is The air pump and other secondary air supply sources can be switched based on the operating state of the air pump.

  That is, the secondary air supply source can be switched based on the load of the internal combustion engine and the operating state of the air pump. Here, examples of the operating state of the air pump include the operating time of the air pump, the power consumption of the air pump, or the brush temperature of the electric motor. If the operation time of the air pump becomes long or the power consumption of the air pump increases, so-called battery exhaustion may occur. Further, the life of the motor is shortened when the brush temperature of the electric motor is increased. If this can occur, supplying secondary air from a secondary air supply source other than the air pump can reduce the frequency of air pump use while suppressing battery run-up and brush temperature increase of the electric motor. it can. Thereby, since the burden of the electric motor can be reduced, it is possible to improve the durability of the electric motor and reduce the power consumption. For example, even if it is necessary to switch from the air pump to another secondary air supply source due to the load of the internal combustion engine, the supply of secondary air by the air pump may be continued depending on the operating state of the air pump.

  In the present invention, when the internal combustion engine is operated at a light load, air from the air pump can be supplied to the exhaust passage.

  When the internal combustion engine is operated at a light load, secondary air is supplied from the air pump, and at other loads, secondary air is supplied from a secondary air supply source other than the air pump. Can be reduced. Thereby, the durability of the air pump can be improved and the power consumption can be reduced.

In the present invention, a supercharger,
A secondary air supply pipe connecting an exhaust passage from the NOx catalyst to the catalyst having the oxidation function and an intake passage from the supercharger to the internal combustion engine;
Further comprising
At least one of the secondary air supply sources includes the supercharger, and the pressure in the intake passage between the supercharger and the internal combustion engine is between the NOx catalyst and the catalyst having the oxidation function. When the pressure is higher than the pressure in the exhaust passage, the air flowing through the intake passage can be supplied to the exhaust passage through the secondary air supply pipe.

The pressure of the air flowing through the intake passage is increased by the supercharger. When the pressure in the intake passage between the supercharger and the internal combustion engine is higher than the pressure in the exhaust passage between the NOx catalyst and the catalyst having the oxidation function, the inside of the secondary air supply pipe The air flows from the intake passage toward the exhaust passage. As a result, the air in the intake passage can be supplied to the catalyst having the oxidation function, so that the oxidation ability of the catalyst having the oxidation function can be improved. Moreover, when the supercharging pressure by the supercharger is not sufficient, secondary air can be supplied by the air pump. In this way, the load on the air pump can be reduced. And the durability of an air pump can be improved and the power consumption can be reduced.

The present invention further includes an intercooler for cooling the intake air between the supercharger and the internal combustion engine,
The secondary air supply pipe can connect an exhaust passage from the NOx catalyst to the catalyst having the oxidation function and an intake passage from the intercooler to the internal combustion engine.

  Here, the temperature of the air compressed by the supercharger rises. Thereafter, the temperature of the air can be lowered by passing the intercooler. And the temperature rise of this catalyst can be reduced by supplying the air which temperature fell to the catalyst. Therefore, since the reducing agent supply interval can be shortened, the effect of reducing agent supply can be enhanced.

  Since the exhaust gas purification apparatus for an internal combustion engine according to the present invention can switch the secondary air supply source, the frequency of use of the air pump for supplying secondary air can be reduced.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and its intake / exhaust passage. The internal combustion engine 1 shown in FIG. 1 is a four-cycle diesel engine having four cylinders 2.

  An intake branch pipe 3 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 3 communicates with a combustion chamber of each cylinder 2. The intake branch pipe 3 is connected to an intake pipe 4, and a compressor housing 5 a of a centrifugal supercharger (turbocharger) 5 that operates using the heat energy of exhaust gas as a drive source is provided in the middle of the intake pipe 4. Yes.

  An intake throttle valve 6 for adjusting the flow rate of the intake air flowing through the intake pipe 4 is provided at a portion of the intake pipe 4 located immediately upstream of the intake branch pipe 3. An intercooler 7 for lowering the intake air temperature is attached to the intake pipe 4 between the intake throttle valve 6 and the compressor housing 5a. When air is compressed by the compressor housing 5a, the temperature of the air rises. The intercooler 7 cools the intake air by exchanging heat between the intake air and the outside air. An intake pressure sensor 8 that outputs an electrical signal corresponding to the pressure of the flowing intake air is attached to the intake pipe 4 between the intake throttle valve 6 and the intercooler 7.

On the other hand, an exhaust branch pipe 9 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 9 leads to a combustion chamber of each cylinder 2. The exhaust branch pipe 9 is connected to the turbine housing 5 b of the turbocharger 5. The turbine housing 5 b is connected to the exhaust pipe 10.
A particulate filter (hereinafter simply referred to as a filter) 11 carrying an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) 11 is provided in the middle of the exhaust pipe 10. The filter 11 collects particulate matter (hereinafter referred to as PM) in the exhaust gas. The NOx catalyst has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have An oxidation catalyst 12 having an oxidation function is provided downstream of the filter 11. Further, an exhaust pressure sensor 13 that outputs an electrical signal corresponding to the pressure of the exhaust gas flowing is attached between the filter 11 and the oxidation catalyst 12.

  A secondary air supply nozzle 20 for supplying secondary air into the exhaust pipe 10 is attached to the exhaust pipe 10 between the filter 11 and the oxidation catalyst 12. Two secondary air supply pipes are connected to the secondary air supply nozzle 20. One is an intake side supply pipe 21 connected to the intake pipe 4 between the intercooler 7 and the intake throttle valve 6. The other is a pump side supply pipe 23 connected to the air pump 22. The air pump 22 includes an electric motor, and discharges air according to the number of rotations.

  The intake-side supply pipe 21 and the pump-side supply pipe 23 are connected to a switching valve 24 provided along with the secondary air supply nozzle 20. With this switching valve 24, either the intake side supply pipe 21 or the pump side supply pipe 23 is selected and connected to the secondary air supply nozzle 20. That is, when the intake side supply pipe 21 is selected, the intake pipe 4 and the secondary air supply nozzle 20 are communicated with each other. Further, when the secondary air supply nozzle 20 is opened, the intake pipe 4 and the exhaust pipe 10 are communicated with each other. At this time, if the pressure in the intake pipe 4 is higher than that in the exhaust pipe 10, a part of the intake air flowing through the intake pipe 4 flows into the intake side supply pipe 21 and passes through the secondary air supply nozzle 20. Supplied to the exhaust pipe 10.

  Moreover, the air pump 22 and the secondary air supply nozzle 20 are connected by selecting the pump side supply pipe 23. Further, when the secondary air supply nozzle 20 is opened, the air pump 22 and the exhaust pipe 10 are communicated with each other. At this time, the air pump 22 operates and discharges air, so that air flows into the pump-side supply pipe 23. Then, this air is supplied to the exhaust pipe 10 via the secondary air supply nozzle 20.

  The air supplied to the exhaust pipe 10 in this way flows into the oxidation catalyst 12 while being mixed with the exhaust gas flowing from the upstream side of the exhaust pipe 10. In this embodiment, the turbocharger 5 and the air pump 22 correspond to the secondary air supply source in the present invention. In the present embodiment, the intake side supply pipe 21 corresponds to the secondary air supply pipe in the present invention.

Further, in this embodiment, a reducing agent addition valve 14 is provided for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust branch pipe 9. The reducing agent addition valve 14 is opened by a signal from the ECU 10 described later to inject fuel. The fuel injected from the reducing agent addition valve 14 into the exhaust branch pipe 9 enriches the air-fuel ratio of the exhaust and reduces NOx stored in the NOx catalyst. During NOx reduction, so-called rich spike control is performed in which the air-fuel ratio of the exhaust gas flowing into the filter 11 is made rich in a spike (short time) with a relatively short cycle. In this embodiment, the reducing agent addition valve 14 corresponds to the reducing agent supply means in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 15 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 15 controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

Various sensors are connected to the ECU 15 via electric wiring, and output signals of the various sensors described above are input to the ECU 15. On the other hand, the intake throttle valve 6, the reducing agent addition valve 14, the secondary air supply nozzle 20, the air pump 22, the switching valve 24, and the like are connected to the ECU 15 through electrical wiring, and the ECU 15 can control them. It has become. For example, the ECU 15 can adjust the valve opening amount of the secondary air supply nozzle 20 and thereby can control the supply amount of the secondary air. Further, the ECU 15 operates the switching valve 24 to connect either the intake side supply pipe 21 or the pump side supply pipe 23 to the secondary air supply nozzle 20. The ECU 15 stores various application programs and various control maps.

By the way, the NOx catalyst is sulfur oxide (S
Ox) is also occluded by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning. Since the NOx purification rate in the NOx catalyst is reduced by this sulfur poisoning, it is necessary to perform a poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This poisoning recovery process is performed by causing the NOx catalyst to have a high temperature and the exhaust gas having a reduced oxygen concentration to flow through the NOx catalyst. In the sulfur poisoning recovery process, the ECU 15 executes fuel addition control (so-called rich spike control) in which the oxygen concentration in the exhaust gas flowing into the filter 11 is lowered in a spike manner with a relatively short period.

  In the fuel addition control, the ECU 15 controls the reducing agent addition valve 14 so as to inject fuel as a reducing agent in a spike manner from the reducing agent addition valve 14, thereby temporarily setting the air-fuel ratio of the exhaust gas flowing into the filter 11. A predetermined target rich air-fuel ratio is set. In the filter 11, SOx is released from the NOx catalyst as the temperature rises. This makes it possible to recover the sulfur poisoning of the NOx catalyst carried on the filter 11.

By the way, when fuel is supplied to the NOx catalyst in order to recover the sulfur poisoning of the NOx catalyst, SOx is released from the NOx catalyst as described above, and this released SOx is H ₂ S in a rich atmosphere. It is easy to become. If the amount of fuel added is too large, reducing components such as HC and CO will be N
May flow downstream through the Ox catalyst.

  On the other hand, it is conceivable to provide an oxidation catalyst downstream to oxidize hydrocarbons (HC) and the like. However, since the atmosphere is reduced when sulfur poisoning is restored, the oxidation ability of the oxidation catalyst is significantly reduced.

Therefore, in this embodiment, the secondary air is supplied upstream of the oxidation catalyst 12 to make the exhaust gas flowing into the oxidation catalyst 12 an oxidizing atmosphere so that the oxidation ability of the oxidation catalyst 12 is enhanced. Thereby, it becomes possible to oxidize HC, CO, H ₂ S and the like by the oxidation catalyst 12.

  Therefore, in this embodiment, the pressure in the intake pipe 4 between the intercooler 7 and the intake throttle valve 6 and the pressure in the exhaust pipe 10 between the filter 11 and the oxidation catalyst 12 are detected. When the pressure in the intake pipe 4 is higher than the pressure in the exhaust pipe 10, the intake side supply pipe 21 is selected, and when the pressure in the intake pipe 4 is lower than the pressure in the exhaust pipe 10. The pump side supply pipe 23 is selected. Thereafter, the selected supply pipe and the secondary air supply nozzle 20 are communicated with each other by the switching valve 24, and when the secondary air supply nozzle 20 is further opened, the secondary air is supplied into the exhaust pipe 10. .

  Next, the flow of secondary air supply control according to the present embodiment will be described.

  FIG. 2 is a flowchart showing a flow of secondary air supply control according to the present embodiment. This routine is repeatedly executed at predetermined time intervals during execution of the sulfur poisoning recovery control.

  In step S101, it is determined whether rich control is being performed. In the sulfur poisoning recovery control, the air-fuel ratio of the exhaust gas flowing into the filter 11 is temporarily set to a predetermined target rich air-fuel ratio. Since secondary air is required during the period when the filter 11 is at the target rich air-fuel ratio, it is determined in this step whether or not this period is set. If an affirmative determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, this routine is temporarily terminated.

  In step S102, it is determined whether the pressure in the intake pipe 4 is higher than the pressure in the exhaust pipe 10. The pressure in the intake pipe 4 is the pressure in the intake pipe 4 between the intercooler 7 and the intake throttle valve 6, and is the pressure detected by the intake pressure sensor 8. The pressure in the exhaust pipe 10 is a pressure in the exhaust pipe 10 between the filter 11 and the oxidation catalyst 12 and is a pressure detected by the exhaust pressure sensor 13.

  That is, in this step, it is determined whether or not the air in the intake pipe 4 can be supplied into the exhaust pipe 10 because the pressure in the intake pipe 4 is higher than the pressure in the exhaust pipe 10. The pressure in the exhaust pipe 10 may be estimated from the operating state of the internal combustion engine 1. Further, when the pressure in the intake pipe 4 cannot be increased, for example, during deceleration, idling, or even during light load operation, the pressure in the intake pipe 4 can be detected without actually detecting the pressure. May be determined to be lower than the pressure in the exhaust pipe 10. That is, the secondary air supply source may be switched according to the load of the internal combustion engine 1. Further, for example, the relationship between the rotational speed of the internal combustion engine, the load, and the switching point of the switching valve 24 may be obtained in advance through experiments or the like and mapped, and the switching valve 24 may be controlled based on the map. If an affirmative determination is made in step S102, the process proceeds to step S103, whereas if a negative determination is made, the process proceeds to step S104.

  In step S <b> 103, the intake side supply pipe 21 and the secondary air supply nozzle 20 are connected by the switching valve 24. If the air pump 22 is operating at this time, the air pump 22 is stopped.

  In step S <b> 104, the pump side supply pipe 23 and the secondary air supply nozzle 20 are connected by the switching valve 24. At the same time, the air pump 22 is operated.

  In step S105, the supply amount of secondary air is controlled by adjusting the valve opening amount of the secondary air supply nozzle 20.

Since oxygen can be supplied to the oxidation catalyst 12 in this way, CO, HC, H ₂ S and the like flowing out from the NOx catalyst 11 at the time of sulfur poisoning recovery can be oxidized. In this embodiment, the pressures of the intake pipe 4 and the exhaust pipe 10 are compared (step S102), and the switching valve 24 is switched (steps S103 and 104). The ECU 15 and the switching valve 24 provide the secondary air supply in the present invention. This corresponds to the source switching means.

  Thus, when the pressure in the intake pipe 4 is higher than the pressure in the exhaust pipe 10, the air in the intake pipe 4 is supplied as secondary air; otherwise, the air from the air pump 22 is supplied. Can be supplied as secondary air. Thereby, the use frequency of the air pump 22 can be reduced. Therefore, power consumption can be reduced, and fuel efficiency can be improved. Moreover, since the wear of the air pump 22 can be reduced, the life of the air pump 22 can be extended.

If secondary air is supplied during recovery from sulfur poisoning, HC is oxidized by the oxidation catalyst 12, and the temperature of the oxidation catalyst 12 rises. If sulfur poisoning recovery is performed during traveling, the energy of the exhaust at this time is large, so that the temperature of the oxidation catalyst 12 may further rise and overheat. At this time, the temperature of the exhaust gas upstream of the oxidation catalyst 12 can be reduced by supplying the low-temperature air after passing through the intercooler 7 as the secondary air, thereby suppressing overheating of the oxidation catalyst 12. can do.

  By the way, when the reducing agent is added, a period in which the reducing agent is not added is provided in order to suppress overheating of the catalyst. However, since the temperature rise of the oxidation catalyst 12 can be suppressed by supplying the secondary air, the period during which this reducing agent is not added can be shortened. Thereby, the sulfur component can be easily released from the oxidation catalyst 12. In addition, since the time required for recovery from sulfur poisoning can be shortened, the release of harmful components can be suppressed. Moreover, fuel consumption can be improved.

  Furthermore, since it is not necessary to supply secondary air from the air pump 22 when the load of the internal combustion engine 1 is high, the maximum discharge amount of the air pump 22 can be reduced, so that the air pump 22 can be downsized.

  In the first embodiment, the switching valve 24 is controlled according to the load of the internal combustion engine 1, but in this embodiment, the switching valve 24 is controlled based on the operating state of the air pump 22 instead of or together with this. To do. For example, the switching valve 24 is controlled based on the operating time of the air pump 22, the power consumption of the air pump 22, or the brush temperature of the electric motor provided in the air pump 22.

  When the operating time of the air pump 22 becomes longer than a predetermined time, when the power consumption of the air pump becomes higher than a predetermined value, or when the brush temperature of the electric motor becomes higher than the predetermined temperature, the ECU 15 24 is operated to make the intake side supply pipe 21 and the secondary air supply nozzle 20 communicate with each other, and the air pump 22 is stopped. Thereby, it is possible to prevent the battery from running out and to extend the life of the air pump 22. Further, since the burden on the electric motor can be reduced, it is possible to improve the durability of the electric motor and reduce the power consumption.

  Further, the switching valve 24 may be controlled in consideration of the load of the internal combustion engine. Here, in the first embodiment, when the pressure in the intake pipe 4 is higher than the pressure in the exhaust pipe 10, the secondary air supply nozzle 20 and the intake side supply pipe 21 are communicated by the switching valve 24. On the other hand, in the present embodiment, even if the pressure in the intake pipe 4 becomes higher than the pressure in the exhaust pipe 10, the switching valve 24 is not switched by this alone, and the operating state of the air pump 22 may cause the above-mentioned battery to rise. Alternatively, the switching valve 24 may be switched in a state where the life of the air pump 22 may be shortened. That is, considering only the load of the internal combustion engine 1, even if the air from the intake pipe 4 is supplied to the exhaust pipe 10, the air from the air pump 22 may be exhausted depending on the operating state of the air pump 22. May be supplied.

  Even if it does in this way, since the working time of the air pump 22 can be shortened, the effect similar to Example 1 can be acquired.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its intake and exhaust passage. It is the flowchart which showed the flow of the secondary air supply control which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Intake branch pipe 4 Intake pipe 5 Turbocharger 5a Compressor housing 5b Turbine housing 6 Intake throttle valve 7 Intercooler 8 Intake pressure sensor 9 Exhaust branch pipe 10 Exhaust pipe 11 Filter (Occlusion reduction type NOx catalyst)
12 Oxidation catalyst 13 Exhaust pressure sensor 14 Reducing agent addition valve 15 ECU
20 Secondary Air Supply Nozzle 21 Intake Side Supply Pipe 22 Air Pump 23 Pump Side Supply Pipe 24 Switching Valve

Claims (4)

A NOx catalyst provided in the exhaust passage of the internal combustion engine for reducing NOx in the presence of a reducing agent;
Reducing agent supply means for supplying a reducing agent to the NOx catalyst;
A catalyst provided downstream of the NOx catalyst and having an oxidation function;
At least two secondary air sources for supplying secondary air to an exhaust passage between the NOx catalyst and the catalyst having the oxidation function;
Secondary air supply source switching means for switching the secondary air supply source according to the load of the internal combustion engine;
Equipped with,
At least one of the secondary air supply sources is composed of an air pump driven by an electric motor, and at least one is composed of means other than the air pump, and the secondary air supply source switching means is in an operating state of the air pump. An exhaust gas purification apparatus for an internal combustion engine, wherein the air pump and another secondary air supply source are switched based on the air pump . 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein when the internal combustion engine is operated at a light load, air from the air pump is supplied to an exhaust passage. A turbocharger,
A secondary air supply pipe connecting an exhaust passage from the NOx catalyst to the catalyst having the oxidation function and an intake passage from the supercharger to the internal combustion engine;
Further comprising
At least one of the secondary air supply sources includes the supercharger, and the pressure in the intake passage between the supercharger and the internal combustion engine is between the NOx catalyst and the catalyst having the oxidation function. 3. The exhaust gas of the internal combustion engine according to claim 1, wherein when the pressure in the exhaust passage is higher, the air flowing through the intake passage is supplied to the exhaust passage through the secondary air supply pipe. Purification equipment. An intercooler for cooling the intake air between the supercharger and the internal combustion engine;
The secondary air supply pipe, to claim 3, characterized in that to connect the intake passage between the said NOx catalyst to the internal combustion engine from the intercooler and the exhaust passage until the catalyst having the oxidizing function An exhaust gas purification apparatus for an internal combustion engine as described.

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