JP2004190549A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prove an exhaust emission control device of an internal combustion engine, which attains efficient and positive HC control. <P>SOLUTION: The exhaust emission control device includes a HC trap (20), a three-way catalyst (22), an oxygen feeders (30, 34), and a temperature-rise controller (40). The HC trap (20) having no catalytic function is provided in an exhaust-gas passage so that the exhaust gas is directly let in from an exhaust port of the internal combustion engine, performing the function of adsorbing HC in the exhaust gas and desorbing the adsorbed HC at a specified temperature or higher. The three-way catalyst (22) is provided to the position downstream of the exhaust gas of the HC trap, and capable of oxidizing CO at ordinary temperature. The oxygen feeders (30, 34) feed oxygen to the upstream side of the exhaust gas of the three-way catalyst. The temperature-rise controller (40) functions to shift the air-fuel ratio to the rich side to discharge HC and CO to the exhaust passage, and feeds oxygen by the oxygen feeders. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly, to an exhaust gas purification device that can surely purify HC (hydrocarbon) at the time of a cold start of the internal combustion engine or the like.
[0002]
[Related background art]
Generally, an exhaust gas purification device that purifies harmful substances (HC, CO, NOx, etc.) in exhaust gas using a three-way catalyst is provided in an exhaust passage of an engine (internal combustion engine). However, the three-way catalyst cannot sufficiently exhibit purification performance until the temperature reaches the activation temperature, and even if the three-way catalyst is arranged close to the engine body to achieve early activation, even when the engine is cold started, Has a problem that the exhausted HC cannot be sufficiently purified.
[0003]
In order to solve this problem, an HC trap having a function of adsorbing HC and desorbing the adsorbed HC at a constant temperature is provided downstream of the three-way catalyst disposed close to the engine body. On the side, a low-temperature activated three-way catalyst capable of oxidizing CO even at normal temperature is provided, and a secondary air pump for supplying oxygen to the three-way catalyst is provided. Oxygen from the secondary air pump and CO in exhaust gas are There has been proposed an apparatus configured to purify HC desorbed from the HC trap by using a three-way catalyst which has been heated and activated by the oxidation reaction (for example, see Non-Patent Document 1).
[0004]
[Non-patent document 1]
SAE Paper No. 980421
[0005]
[Problems to be solved by the invention]
However, the device proposed by the above-mentioned document still has a three-way catalyst (proximity catalyst) in close proximity to the engine main body, and if such a proximity catalyst is provided, much of the CO discharged from the cylinder is reduced. The oxidation reaction occurs in the proximity catalyst, and CO is not sufficiently supplied to the low-temperature activated three-way catalyst on the downstream side, and the activation of the low-temperature activated three-way catalyst is insufficient, resulting in sufficient HC. There is a problem that can not be purified.
[0006]
Furthermore, such a configuration is disadvantageous in the heat resistance and durability of the proximity catalyst, and the exhaust pressure on the upstream side of the proximity catalyst is increased, so that the output performance of the engine is inferior. is not.
The present invention has been made to solve such a problem, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can efficiently and reliably purify HC during a cold start of the internal combustion engine. To provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to claim 1 is provided such that exhaust gas from an exhaust port of the internal combustion engine flows directly into an exhaust passage, adsorbs HC in the exhaust gas and adsorbs the HC. An HC trap that has a function of releasing the discharged HC at a certain temperature or higher and does not have a catalytic function, a three-way catalyst that is provided downstream of the exhaust of the HC trap and that can oxidize CO at normal temperature, Oxygen supply means for supplying oxygen to the exhaust gas upstream of the three-way catalyst, and when the temperature of the three-way catalyst needs to be raised, the air-fuel ratio of the internal combustion engine is made rich and the oxygen supply means supplies oxygen. And a temperature raising control means.
[0008]
When a low-temperature activated three-way catalyst capable of oxidizing CO at room temperature is used as the three-way catalyst, the catalytic reaction rate of the low-temperature activated three-way catalyst increases as the concentration of CO in the exhaust gas increases. However, it is possible to oxidize CO as the amount of CO increases (see Non-Patent Document 1).
Therefore, when the temperature of the three-way catalyst needs to be raised, such as at the time of a cold start, by the temperature raising control means, the air-fuel ratio is made rich and the HC and CO are discharged to the exhaust passage to reduce the concentration of CO. By supplying oxygen to the exhaust gas upstream of the three-way catalyst by the oxygen supply means, HC is adsorbed by the HC trap on the upstream side, while CO is supplied to the low-temperature active type at room temperature by the oxygen supply of the oxygen supply means. The oxidation reaction is favorably performed by the three-way catalyst, and the three-way catalyst is heated and heated by the reaction heat of the oxidation reaction and reaches the activation temperature (about 250 ° C. to 350 ° C.) early. In particular, since no proximity catalyst is provided on the exhaust passage, the HC trap has no catalytic function, and CO discharged from the internal combustion engine is directly supplied to the three-way catalyst, so that all of the CO The oxidation reaction is carried out by the three-way catalyst, and the temperature of the three-way catalyst rises efficiently.
[0009]
Therefore, the HC adsorbed in the HC trap is desorbed at a certain temperature (about 150 ° C.) or more and released toward the downstream three-way catalyst. At this point, the three-way catalyst has already reached the activation temperature. Therefore, the desorbed HC is reliably purified by the three-way catalyst.
In this case, since the proximity catalyst is not provided on the exhaust passage, there is no need to worry about the heat resistance and durability of the proximity catalyst, and there is no decrease in the output of the internal combustion engine due to an increase in the exhaust pressure.
[0010]
Further, in the exhaust gas purifying apparatus for an internal combustion engine according to claim 2, the oxygen supply means is configured to communicate a secondary air supply pump and the secondary air supply pump with an exhaust passage on the exhaust upstream side of the three-way catalyst. And an air supply passage.
In this way, even if the air-fuel ratio of the internal combustion engine is set to a rich air-fuel ratio, it is possible to reliably supply oxygen to the three-way catalyst while maintaining combustion stability. It is often possible to quickly activate the three-way catalyst and thereby improve the HC purification performance.
[0011]
Further, in the exhaust gas purifying apparatus for an internal combustion engine according to claim 3, the internal combustion engine includes two or more multi-cylinders, and the oxygen supply unit converts the air-fuel ratio of some of the multi-cylinders to a lean air-fuel ratio. Thus, oxygen is supplied to the exhaust gas upstream side of the three-way catalyst.
In this way, a large amount of oxygen is discharged from some of the cylinders having a lean air-fuel ratio, while HC and CO are discharged from the remaining cylinders having a rich air-fuel ratio. Oxygen can be reliably supplied to the three-way catalyst together with CO, and early activation of the three-way catalyst can be efficiently performed, and further, the purification performance of HC can be improved.
[0012]
Preferably, fuel injection in some cylinders is stopped, and intake air is discharged from some cylinders by pumping, so that oxygen and CO can be supplied to the three-way catalyst more easily and reliably.
Further, in the exhaust gas purifying apparatus for an internal combustion engine according to claim 4, the HC trap is made of β-type zeolite.
[0013]
That is, β-zeolite has a particularly high HC adsorbing ability, can sufficiently retain HC in the HC trap until the three-way catalyst is activated, and further improves HC purification performance.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an exhaust gas purification device for an internal combustion engine according to the present invention will be described based on examples with reference to the accompanying drawings.
First, a first embodiment will be described.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to a first embodiment of the present invention mounted on a vehicle. The configuration of the exhaust gas purification device will be described.
[0015]
As the internal combustion engine (hereinafter, simply referred to as an engine) 1, a spark-ignition gasoline engine of an intake pipe injection type is employed. Since the spark-ignition gasoline engine of the intake pipe injection type is known, the detailed description of the configuration is omitted here.
In the cylinder head of the engine 1, an intake port is formed for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. An exhaust port is formed for each cylinder in the cylinder head, and one end of the exhaust manifold 12 is connected to each of the exhaust ports so as to communicate with each exhaust port.
[0016]
An exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12. The exhaust pipe 14 is provided with an HC trap 20 located below the floor of the vehicle, and is located downstream of the HC trap 20. A low-temperature active three-way catalyst 22 is interposed.
The HC trap 20 has a porous monolith-type cordierite carrier composed of a large number of cells, and each cell is formed, for example, in a rectangular cross section.
[0017]
On the surface of the cordierite carrier of the HC trap 20, an HC adsorbent mainly composed of β-type zeolite is formed. β-type zeolite has a function of adsorbing HC, particularly olefinic HC, and desorbing and releasing the adsorbed HC when the temperature rises and reaches a certain temperature (about 150 ° C.). The β-type zeolite has a pore size of 7.6 to 7.8%, which is larger than other zeolites (MFI type, Y type, etc.), has a larger adsorption amount, has a higher desorption start temperature (about 150 ° C.), It has the characteristics that the desorption end temperature is high and the HC desorption ratio in the high temperature range is high. That is, by using β-type zeolite as the HC adsorbent of the HC trap 20, it is possible to increase the HC adsorbing ability and adsorb and hold HC as high as possible.
[0018]
Note that a catalyst layer is not formed in the HC trap 20, and CO and NOx are not purified in the HC trap 20.
Further, in the present embodiment, the HC trap as described above is used. However, the HC trap has a function of adsorbing HC in exhaust gas and releasing the adsorbed HC at a certain temperature or higher, and has no catalytic function. If it is a trap, an HC trap other than the above may be used.
[0019]
The three-way catalyst 22 is a low-temperature activated three-way catalyst capable of oxidizing CO even at normal temperature, and also has a porous monolith-type cordierite carrier 23 composed of a large number of cells. Is formed. Specifically, the three-way catalyst 22 includes at least one of platinum (Pt), rhodium (Rh), and palladium (Pd) as a noble metal similarly to a normal three-way catalyst, and the exhaust air-fuel ratio has a stoichiometric air-fuel ratio ( In addition to being able to satisfactorily purify the three components of HC, CO and NOx when it is in the vicinity of (stoichio), as described above, it has the property that the catalytic reaction rate increases as the concentration of CO in the exhaust gas increases. However, even at a low temperature such as room temperature, the larger the amount of CO, the more CO can be oxidized.
[0020]
In the present embodiment, the above-described three-way catalyst is used. However, any other three-way catalyst that can oxidize CO at room temperature may be used.
A secondary air passage 30 branches from an immediately upstream portion of the three-way catalyst 22, and the secondary air passage 30 is discharged from a secondary air pump (oxygen supply means) 34 via a check valve 31 and an air filter 32. Connected to the exit. That is, when the secondary air pump 34 operates, an amount of air corresponding to the operation amount of the secondary air pump 34 is supplied to the upstream portion of the three-way catalyst 22, and oxygen flows into the three-way catalyst 22 together with the exhaust gas.
[0021]
Further, the exhaust pipe 14 is provided with a linear air-fuel ratio sensor 16 that detects an exhaust air-fuel ratio by detecting an oxygen concentration contained in exhaust gas flowing into the HC trap 20. A temperature sensor 28 for detecting the temperature of the catalyst 22, that is, the catalyst temperature Tcat is provided.
Further, an electronic control unit (ECU) 40 including an input / output device, a memory, a CPU, and the like is provided. The ECU 40 controls the exhaust gas purifying apparatus for the engine 1 and the internal combustion engine according to the present invention. Is
[0022]
Various sensors such as the linear air-fuel ratio sensor 16 and the temperature sensor 28 described above are connected to an input side of the ECU 40, and detection information from these sensors is input.
On the other hand, various devices such as a fuel injection valve and an ignition coil (both not shown) of the engine 1 and the secondary air pump 34 are connected to an output side of the ECU 40. Optimal control signals such as a fuel injection amount and an ignition timing corresponding to the target air-fuel ratio calculated based on the detection information from the various sensors are output to the secondary air pump 34 based on the detection information from the various sensors. An optimal control signal such as a pump operation amount and a pump operation timing is output.
[0023]
Hereinafter, the operation of the exhaust gas purifying apparatus according to the first embodiment of the present invention configured as described above will be described.
Referring to FIG. 2, a control routine of the catalyst temperature increase control (temperature increase control means) according to the first embodiment is shown in a flowchart, and will be described below with reference to the flowchart.
[0024]
In step S10, it is determined whether or not the exhaust system is cold. Specifically, when the engine 1 is cold started, for example, the catalyst temperature Tcat of the three-way catalyst 22 detected by the temperature sensor 28 is equal to or lower than a predetermined low temperature, and it is necessary to raise the temperature of the three-way catalyst 22. Determine whether or not. The determination may be made based on the cooling water temperature, oil temperature, exhaust gas temperature, or the like of the engine 1 instead of the catalyst temperature Tcat.
[0025]
If the determination result of step S10 is false (No) and it is determined that the exhaust system is not in a cold state, the process exits the routine without performing the temperature increase control, while the determination result is true (Yes) and the exhaust system is not. Is determined to be cold, the process proceeds to step S12.
In step S12, the target air-fuel ratio of the engine 1 is set to a rich air-fuel ratio (for example, a value of 10 to 12). That is, the target air-fuel ratio is changed to the rich air-fuel ratio, thereby increasing the amount of HC and CO discharged to the exhaust pipe 14.
[0026]
In step S14, the secondary air pump 34 is operated simultaneously with the enrichment of the rich air-fuel ratio. That is, oxygen is supplied to the three-way catalyst 22 by operating the secondary air pump 34. At this time, the supply amount of oxygen is set so that, for example, the air-fuel ratio downstream of the three-way catalyst 22 becomes a predetermined value (for example, values 15 to 17) according to the target air-fuel ratio (for example, values 10 to 12). Then, the operation of the secondary air pump 34 is controlled to secure the supply amount.
[0027]
As described above, when the emission amount of HC and CO is increased by increasing the target air-fuel ratio to a rich air-fuel ratio and oxygen is supplied to the three-way catalyst 22, HC is adsorbed by the HC trap 20, while CO is , Pass through the HC trap 20 having no catalyst layer without being purified and reach the three-way catalyst 22 directly from the engine 1, and the CO concentration increases, so that the three-way catalyst 22 Oxidation reaction rate is increased and oxidation is performed well. When CO is oxidized in the three-way catalyst 22 in this manner, the temperature of the three-way catalyst 22 rapidly rises due to reaction heat, and the temperature of the three-way catalyst 22 rises early. As a result, the temperature Tcat of the three-way catalyst 22 easily reaches the activation temperature (about 250 ° C. to 350 ° C.), and early activation of the three-way catalyst 22 is achieved.
[0028]
In step S16, it is determined whether or not the temperature Tcat of the three-way catalyst 22 has reached the activation temperature lower limit T1 (for example, about 250 ° C.) (Tcat> T1). Note that the temperature of the three-way catalyst 22 may be estimated from the exhaust gas temperature. If the determination result is false (No) and the catalyst temperature Tcat is still below the activation temperature lower limit T1, the rich air-fuel ratio and oxygen supply are continued in steps S12 and S14. On the other hand, if the determination result is true (Yes) and it is determined that the catalyst temperature Tcat has reached the activation temperature lower limit value T1, the process proceeds to step S18.
[0029]
In step S18, in response to the activation of the three-way catalyst 22, the target air-fuel ratio that has been changed to the rich air-fuel ratio is returned to the normal air-fuel ratio setting. Then, in step S20, the operation of the secondary air pump 34 is stopped, and the oxygen supply is terminated.
While the temperature raising control is being performed in this way, on the other hand, the warm-up of the engine 1 proceeds, the exhaust gas temperature rises, and the temperature of the HC trap 20 gradually rises. When the temperature of the HC trap 20 rises, the HC adsorbed on the HC trap 20 starts to be desorbed when the HC trap 20 reaches a certain temperature (about 150 ° C.) as described above, and is released from the HC trap 20. The resulting HC flows into the three-way catalyst 22 on the downstream side.
[0030]
However, since the temperature of the three-way catalyst 22 is rapidly increased by the temperature increase control as described above, the three-way catalyst 22 is already activated at the time when the HC starts to be desorbed from the HC trap 20, HC discharged from the HC trap 20 and flowing into the three-way catalyst 22 is reliably purified by the three-way catalyst 22.
As a result, even during the cold start of the engine 1, the HC discharged from the engine 1 is efficiently and reliably purified, and the purification performance of the HC is improved. Regarding CO and NOx, CO is oxidized well by the three-way catalyst 22 of the normal temperature to low temperature activation type, and NOx is satisfactorily purified by the early activation of the three-way catalyst 22. Exhaust gas purification efficiency at the time of a cold start is improved as a whole.
[0031]
Further, when the low-temperature activated three-way catalyst 22 is provided under the floor as described above, it is not necessary to separately provide a three-way catalyst in the engine 1 as a proximity catalyst, so that there is no need to worry about the heat resistance and durability of the proximity catalyst. And the output of the engine 1 is prevented from decreasing due to an increase in the exhaust pressure.
Further, when oxygen is supplied from the outside using the secondary air pump 34 in this way, even if the target air-fuel ratio is made rich, the oxygen is reliably supplied to the three-way catalyst 22 while maintaining the combustion stability. As a result, there is an advantage that the three-way catalyst 22 can be activated early while preventing combustion instability of the engine 1 and the HC purification performance can be improved.
[0032]
In the first embodiment, air is supplied immediately upstream of the three-way catalyst 22. However, air is supplied upstream of the HC trap 20 within a range that does not affect HC adsorption performance. Is also good. When air is supplied upstream of the HC trap 20 in this way, the temperature of the HC trap 20 is suppressed because the outside air is lower in temperature than the exhaust gas, and the desorption of HC from the HC trap 20 is prevented. The effect of being able to delay is obtained.
[0033]
Next, a second embodiment will be described.
Referring to FIG. 3, there is shown a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to a second embodiment of the present invention mounted on a vehicle. The configuration of the exhaust gas purification device will be described. Note that the configuration is basically the same as that in the first embodiment, and here, only the portions different from the first embodiment will be described.
[0034]
In the second embodiment, a spark-ignition gasoline engine of an intake pipe injection type is adopted as the engine 1 as in the first embodiment, but here, in particular, a multi-cylinder engine (for example, a four-cylinder engine) is used. Limited.
That is, the cylinder head of the engine 1 is formed with an intake port and an exhaust port for each of the multi-cylinder cylinders, and one end of the intake manifold 10 is branched and connected so as to communicate with each intake port. In addition, one end of the exhaust manifold 12 is branched and connected so as to communicate with the exhaust port.
[0035]
More specifically, here, all the cylinders are divided into two cylinder groups, and as shown in the figure, correspond to a cylinder group composed of some cylinders (for example, two cylinders of a four-cylinder engine) in the branch pipe of the exhaust manifold 12. The branch pipes are grouped as a branch pipe group 12a, and the branch pipes corresponding to the cylinder group including the remaining cylinders (two cylinders other than the above) are grouped as a branch pipe group 12b.
[0036]
In the second embodiment, unlike the first embodiment, the secondary air passage 30, the check valve 31, the air filter 32, and the secondary air pump 34 are not provided.
On the other hand, in the second embodiment, the ECU 40 is configured such that a target air-fuel ratio (fuel injection amount) can be set for each of the two cylinder groups based on detection information from various sensors. The target air-fuel ratio is set to the lean air-fuel ratio for the cylinder group consisting of: and the target air-fuel ratio is set to the rich air-fuel ratio for the cylinder group consisting of the remaining cylinders, or the fuel injection is stopped for the cylinder group consisting of some cylinders. It is possible to set the fuel injection amount to zero and set the target air-fuel ratio to the rich air-fuel ratio for the cylinder group including the remaining cylinders.
[0037]
Hereinafter, the operation of the thus configured exhaust gas purification apparatus according to the second embodiment of the present invention will be described.
Referring to FIG. 4, a control routine of the catalyst temperature raising control (temperature raising control means) according to the second embodiment is shown in a flowchart, and will be described below with reference to the flowchart. Here, only portions different from FIG. 2 in the first embodiment will be described.
[0038]
If the result of the determination in step S10 is true (Yes) and it is determined that the exhaust system is in a cold state, the process proceeds to step S12 '.
In step S12 ', the target air-fuel ratio is set to the lean air-fuel ratio for the cylinder group including a part of the cylinders. Alternatively, for a group of cylinders composed of a part of cylinders, fuel injection is stopped, the fuel injection amount is set to zero, and only pumping by the piston is performed. Then, in step S14 ', the target air-fuel ratio is set to the rich air-fuel ratio for the cylinder group including the remaining cylinders.
[0039]
That is, in the second embodiment, the exhaust gas discharged through the branch pipe group 12a corresponding to the cylinder group including a part of the cylinders includes a large amount of oxygen, and the branch corresponding to the cylinder group including the remaining cylinders. A large amount of HC and CO is contained only in the exhaust gas discharged through the tube group 12b. In particular, when only pumping is performed for a cylinder group including a part of cylinders, it is possible to make the exhaust gas contain much more oxygen.
[0040]
With this configuration, a simple structure is used, and oxygen is well mixed together with HC and CO in the exhaust pipe 14. HC is adsorbed in the HC trap 20, while CO is formed in the catalyst layer. The HC trap 20 does not pass through the HC trap 20 without being purified and reaches the three-way catalyst 22 directly from the engine 1 and the CO concentration increases. Oxidation reaction rate is increased and oxidation is performed well. Then, the temperature of the three-way catalyst 22 rapidly rises due to the heat of the oxidation reaction of CO, and the temperature Tcat of the three-way catalyst 22 easily reaches the activation temperature (about 250 ° C. to 350 ° C.) as described above. Early activation of the catalyst 22 is achieved.
[0041]
If the determination result of step S16 is true (Yes) and it is determined that the catalyst temperature Tcat has reached the activation temperature lower limit value T1, the process proceeds to step S18 '.
In step S18 ', in response to the activation of the three-way catalyst 22, the target air-fuel ratio in which the lean air-fuel ratio or the fuel injection is stopped in some cylinders and the target air-fuel ratio in which the rich air-fuel ratio is set in the remaining cylinders Return the air-fuel ratio to the normal air-fuel ratio setting.
[0042]
Thus, as in the first embodiment, also in the second embodiment, when the HC trap 20 reaches a certain temperature (about 150 ° C.) and starts desorption of HC, the three-way catalyst 22 is already activated. Thus, the HC discharged from the HC trap 20 and flowing into the three-way catalyst 22 is reliably purified by the three-way catalyst 22.
Therefore, even during the cold start of the engine 1, the HC discharged from the engine 1 is efficiently and reliably purified, and the purification performance of HC as well as the purification performance of CO and NOx is improved.
[0043]
That is, in the second embodiment, the lean air-fuel ratio operation is performed in some cylinders, or the fuel injection is stopped and only the pumping is performed to supply oxygen to the three-way catalyst 22. In addition, CO and oxygen can be reliably supplied to the three-way catalyst 22, so that the three-way catalyst 22 can be simply and efficiently activated at an early stage, and the purification performance of HC can be improved.
[0044]
The description of the embodiment of the present invention is finished above, but the present invention is not limited to the above embodiment.
For example, in the above-described embodiment, particularly, the cold start of the engine 1 has been described as an example. However, the present invention is not limited to the cold start, and even during the normal operation of the engine 1, It is preferable that the above-mentioned catalyst temperature increase control is performed whenever temperature increase is required without the active state of the three-way catalyst 22. Thereby, the same effect as described above is always obtained, and the exhaust gas purification efficiency is further improved.
[0045]
Further, in the above embodiment, the case where the engine 1 is an intake pipe injection type gasoline engine has been described as an example, but the engine 1 may be a direct injection type gasoline engine or a diesel engine. In this case, as the oxygen supply means, after performing the fuel injection corresponding to the lean air-fuel ratio in the compression stroke, and performing the two-stage injection in which the fuel is injected again (sub-injection) after the expansion stroke, HC, Oxygen can be discharged together with CO, and the three-way catalyst 22 can be easily and efficiently activated at an early stage.
[0046]
【The invention's effect】
As described above in detail, according to the exhaust gas purifying apparatus for an internal combustion engine of the first aspect of the present invention, a low-temperature active three-way catalyst capable of oxidizing CO at room temperature is provided as a three-way catalyst downstream of the HC trap. When the temperature of the three-way catalyst needs to be raised, such as at the time of a cold start, the air-fuel ratio is made rich and the HC and CO are discharged into the exhaust passage to increase the concentration of CO, thereby increasing the oxygen concentration. By supplying oxygen to the exhaust gas upstream side of the three-way catalyst by the supply means, HC is adsorbed by the HC trap on the upstream side, while CO is favorably oxidized by the low-temperature active type three-way catalyst at room temperature while being at room temperature. The temperature of the three-way catalyst can be increased by heating with the reaction heat of the oxidation reaction to quickly reach the activation temperature (about 250 ° C. to 350 ° C.). At this time, the proximity catalyst is not provided on the exhaust passage, the HC trap does not have a catalytic function, and the CO discharged from the internal combustion engine is directly supplied to the three-way catalyst, so that the discharged CO Can be oxidized by a three-way catalyst, and the temperature of the three-way catalyst can be raised efficiently without inconvenience such as a decrease in output due to the provision of a proximity catalyst.
[0047]
Therefore, even if HC adsorbed from the HC trap is desorbed at a certain temperature (about 150 ° C.) or more and released toward the downstream three-way catalyst, the three-way catalyst can be kept activated at this time. , HC can be reliably purified by the three-way catalyst.
According to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, the secondary air supply pump is used as the oxygen supply means, so that the combustion stability is ensured even if the air-fuel ratio of the internal combustion engine is made rich. Oxygen can be reliably supplied to the three-way catalyst as it is, and the early activation of the three-way catalyst can be efficiently performed while preventing combustion instability of the internal combustion engine, and the HC purification performance can be improved.
[0048]
According to the exhaust gas purifying apparatus for an internal combustion engine of the third aspect, oxygen is supplied to the exhaust gas upstream side of the three-way catalyst by making the air-fuel ratio of some of the multiple cylinders a lean air-fuel ratio. Therefore, while a large amount of oxygen can be discharged from some cylinders having a lean air-fuel ratio, HC and CO can be discharged from the remaining cylinders having a rich air-fuel ratio. Can be supplied to the three-way catalyst, and the early activation of the three-way catalyst can be efficiently performed, and the purification performance of HC can be efficiently improved.
[0049]
In this case, the fuel injection in some cylinders is stopped, and the intake air is discharged from some cylinders by pumping, so that oxygen and CO can be more easily and reliably supplied to the three-way catalyst.
Further, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, the HC trap is made of β-type zeolite having a high HC adsorption capacity, so that the HC is sufficiently held in the HC trap until the three-way catalyst is activated. As a result, the purification performance of HC can be further improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to a first embodiment of the present invention mounted on a vehicle.
FIG. 2 is a flowchart illustrating a control routine of catalyst temperature increase control according to the first embodiment.
FIG. 3 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to a second embodiment of the present invention mounted on a vehicle.
FIG. 4 is a flowchart illustrating a control routine of catalyst temperature increase control according to a second embodiment.
[Explanation of symbols]
1 engine 14 exhaust pipe 16 linear air-fuel ratio sensor 20 HC trap 22 three-way catalyst (low temperature activation type)
28 temperature sensor 30 secondary air passage (oxygen supply means)
34 Secondary air pump (oxygen supply means)
40 ECU (electronic control unit)

Claims (4)

An HC trap that is provided so that exhaust gas from an exhaust port of an internal combustion engine flows directly into an exhaust passage, has a function of adsorbing HC in the exhaust gas and releasing the adsorbed HC at a certain temperature or higher, and has no catalytic function. When,
A three-way catalyst that is provided on the exhaust gas downstream side of the HC trap and can oxidize CO at normal temperature;
Oxygen supply means for supplying oxygen to the exhaust upstream side of the three-way catalyst,
When the temperature of the three-way catalyst is required, while increasing the air-fuel ratio of the internal combustion engine to a rich air-fuel ratio, and a temperature increase control unit that supplies oxygen by the oxygen supply unit,
An exhaust gas purifying apparatus for an internal combustion engine, comprising: The said oxygen supply means comprises a secondary air supply pump and a secondary air supply passage which connects the secondary air supply pump to an exhaust passage on the exhaust upstream side of the three-way catalyst. An exhaust purification system for an internal combustion engine according to claim 1. The internal combustion engine consists of two or more cylinders,
2. The oxygen supply device according to claim 1, wherein the oxygen supply unit supplies oxygen to an exhaust gas upstream side of the three-way catalyst by changing an air-fuel ratio of a part of the multi-cylinder to a lean air-fuel ratio. 3. An exhaust gas purification device for an internal combustion engine. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the HC trap is made of β-type zeolite.

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