JP2013189870A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of sufficiently raising a temperature of a NOx trap catalyst while restraining a temperature rise of an oxidation catalyst.SOLUTION: A fuel injection amount of in-cylinder combustion when HC is not added is made smaller than an injection amount corresponding to a theoretical air-fuel ratio so as to have a lean air-fuel ratio as an air-fuel ratio. A fuel injection amount of in-cylinder combustion when HC is added is set to the injection amount corresponding to the theoretical air-fuel ratio or more by increasing an injection amount for combustion post injection so as to have an air-fuel ratio same with or larger than the theoretical air-fuel ratio. Then, in-cylinder post injection is carried out so as to have an injection amount required at catalyst rich time which is required for achieving a desired air-fuel ratio with a NOx trap catalyst (25), thus achieving a rich air-fuel ratio as the air-fuel ratio.

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly, to an S purge process for a NOx trap catalyst.

Conventionally, in a diesel engine or the like, a NOx trap catalyst for purifying nitrogen oxide (NOx) in exhaust gas is provided in an exhaust passage.
Such a NOx trap catalyst stores NOx in the exhaust gas when the exhaust gas flowing into the NOx trap catalyst has a lean air-fuel ratio, and reduces and purifies the stored NOx when the exhaust gas has a rich air-fuel ratio. doing.

Further, the fuel of the diesel engine contains sulfur, and the diesel engine generates not only NOx but also sulfur oxides (SOx) such as SO ₂ and SO ₃ at the same time.
However, SOx is stored in the NOx trap catalyst when the exhaust gas flowing into the NOx trap catalyst has a lean air-fuel ratio, like NOx. And such occlusion of SOx in the NOx trap catalyst leads to a decrease in NOx purification performance in the NOx trap catalyst.

  Therefore, a reducing agent such as fuel is added to the exhaust gas (HC addition), and the exhaust gas flowing into the NOx trap catalyst is made a rich air-fuel ratio at a high temperature to contain sulfur (S) components such as SOx stored in the NOx trap catalyst. A sulfur poisoning recovery process (hereinafter referred to as S purge process) for desorption is performed. In such S purge control, post-injection for HC addition is performed in addition to normal fuel injection, and the NOx trap catalyst is brought to a high temperature and rich state (Patent Document 1).

JP 2004-332743 A

In the exhaust purification device of Patent Document 1 described above, in the S purge process, in addition to normal fuel injection, post injection for HC addition is performed, and in-cylinder combustion with normal fuel injection regardless of the presence or absence of HC addition The amount is constant. The fuel injection amount in the post injection is controlled so as to be a temperature required for the S purge process by the NOx trap catalyst.
Thus, if the in-cylinder combustion amount in normal fuel injection is made constant regardless of the presence or absence of HC addition and the temperature of the NOx trap catalyst is controlled by the fuel injection amount in post injection, the heat generation of the oxidation catalyst Therefore, the temperature of the oxidation catalyst becomes a desired temperature.

  However, if the heat generation of the oxidation catalyst is not controlled in this way, for example, in the low load region where the air-fuel ratio of in-cylinder combustion in normal fuel injection is a lean air-fuel ratio, When the post-injection is performed and the rich air-fuel ratio exhaust gas is introduced into the oxidation catalyst, HC in the rich air-fuel ratio exhaust gas is oxidized by the residual oxygen in the in-cylinder combustion and the temperature of the oxidation catalyst rises. Become.

Therefore, when the air-fuel ratio of in-cylinder combustion in normal fuel injection is in a low load region where the lean air-fuel ratio becomes a lean air-fuel ratio, if the NOx trap catalyst is set to a temperature suitable for the S purge process, the oxidation catalyst is more than the NOx trap catalyst. However, there is a risk that the temperature of the oxidation catalyst will rise first and the temperature of the oxidation catalyst will exceed the allowable value.
Thus, in order to avoid the temperature of the oxidation catalyst from exceeding the allowable value, if the HC addition is interrupted, the NOx trap catalyst cannot be sufficiently heated to a temperature suitable for the S purge process, and the NOx trap catalyst. There is a risk that it will not be possible to sufficiently desorb sulfur.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an internal combustion engine capable of sufficiently raising the temperature of the NOx trap catalyst while suppressing the temperature rise of the oxidation catalyst. An object is to provide an exhaust emission control device.

  In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, an oxidation catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine, and provided downstream of the oxidation catalyst, at least the oxidation catalyst An NOx storage reduction catalyst having a larger oxygen storage capacity than the catalyst, a fuel injection means for injecting fuel into the cylinder of the internal combustion engine, a reducing agent supply means for supplying a reducing agent to the oxidation catalyst, and the storage reduction And controlling the fuel injection amount from the fuel injection means and the reducing agent supply amount from the reducing agent supply means so as to desorb the exhaust component stored in the NOx catalyst. Desorption processing control means for modulating the air-fuel ratio flowing into the NOx catalyst into a lean air-fuel ratio or a rich air-fuel ratio, and the desorption processing control means has an air-fuel ratio in the cylinder when supplying the reducing agent. Of the reducing agent Compared to the time supplied and sets the fuel injection quantity from said fuel injection means so that the rich air-fuel ratio side.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 2, the desorption processing control means according to claim 1 is configured so that the air-fuel ratio in the cylinder becomes equal to or higher than the stoichiometric air-fuel ratio when the reducing agent is supplied. The fuel injection amount from the fuel injection means is set.
Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 3, in the claim 1 or 2, the desorption processing control means sets the air-fuel ratio in the cylinder when the reducing agent is not supplied from the reducing agent supply means. The fuel injection amount from the fuel injection means is set so as to obtain a lean air-fuel ratio.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 4, in any one of claims 1 to 3, the desorption processing control means is configured so that the temperature of the NOx storage reduction catalyst becomes a predetermined value. The fuel injection unit and the reducing agent supply unit are controlled.
Further, in the exhaust emission control device for an internal combustion engine according to claim 5, in any one of claims 1 to 4, the fuel injection means is configured so that the fuel does not flow into the exhaust passage but burns in the cylinder. Combustion post injection for injecting the fuel in an expansion stroke can be performed, and the desorption processing control means controls the air-fuel ratio in the cylinder at the time of supplying or not supplying the reducing agent. The fuel injection amount from the means is set by increasing or decreasing the combustion post injection.

  Further, in the exhaust emission control device for an internal combustion engine according to claim 6, in claim 5, the reducing agent supply means is the fuel injection means, and the desorption processing control means supplies the reducing agent to the combustion post. It is characterized by performing in-cylinder post injection performed after injection.

  According to the first aspect of the present invention, for example, in the sulfur poisoning recovery process (S purge process) in which the sulfur component stored in the NOx storage reduction catalyst is desorbed, the exhaust gas flowing into the NOx storage reduction catalyst When the reducing agent is supplied from the reducing agent supply means in order to make the air-fuel ratio of the cylinder a rich air-fuel ratio, the reducing agent is set so that the air-fuel ratio in the cylinder is on the rich air-fuel ratio side compared to when the reducing agent is not supplied. By setting the fuel injection amount that is injected into the cylinder by the fuel injection means at the time of supply, the amount of oxygen contained in the exhaust gas flowing into the oxidation catalyst before the supply of the reducing agent can be reduced.

Therefore, even if the reducing agent is supplied from the reducing agent supply means to the oxidation catalyst, the temperature increase of the oxidation catalyst can be suppressed without oxidizing the reducing agent in the oxidation catalyst.
Therefore, it is possible to sufficiently raise the temperature of the NOx storage reduction catalyst without excessively raising the temperature of the oxidation catalyst during the S purge process in which the sulfur component stored in the NOx storage reduction catalyst is desorbed.

  According to the invention of claim 2, for example, in the sulfur poisoning recovery process (S purge process) in which the sulfur component stored in the NOx storage reduction catalyst is desorbed, the NOx catalyst flows into the NOx storage reduction catalyst. When supplying the reducing agent from the reducing agent supply means in order to make the air-fuel ratio of the exhaust gas rich, the fuel injection means before supplying the reducing agent so that the air-fuel ratio in the cylinder becomes equal to or higher than the theoretical air-fuel ratio. By setting the fuel injection amount to be injected into the cylinder, it is possible to reduce the amount of oxygen contained in the exhaust gas flowing into the oxidation catalyst before supplying the reducing agent.

Therefore, similarly to the first aspect, even if the reducing agent is supplied from the reducing agent supply means to the oxidation catalyst, the temperature increase of the oxidation catalyst can be suppressed without oxidizing the reducing agent by the oxidation catalyst.
Therefore, it is possible to sufficiently raise the temperature of the NOx storage reduction catalyst without excessively raising the temperature of the oxidation catalyst during the S purge process in which the sulfur component stored in the NOx storage reduction catalyst is desorbed.

  According to the invention of claim 3, for example, in the S purge process of the NOx storage reduction catalyst, the fuel injection is performed so that the air-fuel ratio in the cylinder becomes the lean air-fuel ratio when the reducing agent is not supplied from the reducing agent supply means. By setting the fuel injection amount injected into the cylinder from the means, the amount of oxygen flowing into the NOx storage reduction catalyst can be increased, and the amount of oxygen stored in the NOx storage reduction catalyst can be increased. .

Therefore, by storing a large amount of oxygen in the NOx storage reduction catalyst, when the reducing agent is supplied, the NOx storage reduction catalyst reacts with the reducing agent and oxygen to overheat the oxidation catalyst. In addition, the temperature of the NOx storage reduction catalyst can be reliably raised.
According to the invention of claim 4, the sulfur component is reliably desorbed from the NOx storage reduction catalyst by setting the temperature of the NOx storage reduction catalyst to a predetermined value suitable for the desorption of the sulfur component. Can do.

Further, according to the invention of claim 5, since the control of the in-cylinder air-fuel ratio at the time of supply or non-supply of the reducing agent is performed by increasing or decreasing the combustion post-injection that has little influence on the output torque of the internal combustion engine. The in-cylinder air-fuel ratio can be made equal to or higher than the theoretical air-fuel ratio while suppressing the influence on the output torque of the internal combustion engine.
According to the invention of claim 6, since the reducing agent is supplied by in-cylinder post injection performed after the combustion post injection by the fuel injection means, the cost can be increased by using the existing fuel injection means. Can be suppressed.

  Further, the theoretical air-fuel ratio correction is performed by increasing or decreasing the combustion post-injection, and the reducing agent is supplied by in-cylinder post-injection, for example, when the theoretical air-fuel ratio correction is performed and when the theoretical air-fuel ratio correction is performed. When the total supply amount of the reducing agent supplied to the NOx storage reduction catalyst necessary for setting the temperature and the air fuel ratio of the NOx storage reduction catalyst to the predetermined values is the same as the case of not performing, the stoichiometric air fuel ratio By performing the commutation correction by increasing or decreasing the combustion post injection, it is possible to reduce the amount of reducing agent supplied to the NOx storage reduction catalyst by in-cylinder post injection. Therefore, since the reducing agent adhering to the cylinder by the in-cylinder post injection can be reduced, the dilution of the lubricating oil by the reducing agent can be reduced.

1 is a schematic configuration diagram of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied. It is a figure which shows the fuel injection quantity and oxygen amount in S purge process which ECU which concerns on this invention performs. It is a figure which shows the change of the injection signal at the time of HC addition in the S purge process which concerns on this invention, and the change of a cylinder pressure in time series.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied. FIG. 2 is a diagram showing the fuel injection amount and the oxygen amount in the S purge process executed by the ECU. The upper part of FIG. 2 shows the fuel injection amount, and the lower part shows the oxygen amount in the exhaust gas. The fuel injection amount and the oxygen amount are shown for each of the HC addition and non-HC addition during the S purge process. The broken line in the figure indicates the fuel injection amount when HC is added, and the solid line indicates the fuel injection amount during in-cylinder combustion. The stoichiometric air-fuel ratio equivalent injection amount in FIG. 2 is the fuel injection amount required to make the air-fuel ratio the stoichiometric air-fuel ratio, and the catalyst-rich required injection amount is the sulfur previously derived from experiments or analyzes. In the desorption process (S purge process), the fuel injection amount necessary for setting the temperature of the NOx trap catalyst to a predetermined temperature (predetermined value) is shown. FIG. 3 is a diagram showing, in time series, changes in the injection signal and the in-cylinder pressure when HC is added in the S purge process. Specifically, it is a diagram showing a change in in-cylinder pressure when an injection signal is generated and fuel is injected. That is, if there is no change in the in-cylinder pressure even if fuel injection is performed as in the combustion post injection or in-cylinder post injection in FIG. 3, this indicates that the fuel injection does not contribute to the output of the engine. Thus, the combustion post-injection is a fuel injection that does not contribute to the output of the engine 1 and is injected in the expansion stroke so that the fuel does not flow into the exhaust pipe but burns in the combustion chamber and the cylinder. The in-cylinder combustion in FIGS. 2 and 3 indicates fuel injection in which combustion is completed in the combustion chamber and the cylinder, and HC addition is not burned in the combustion chamber and the cylinder, but in the unburned fuel state in the exhaust pipe. The discharged fuel injection, so-called in-cylinder post injection is shown.

  As shown in FIG. 1, an engine (internal combustion engine) 1 is a multi-cylinder direct injection internal combustion engine (for example, a common rail type diesel engine), and more specifically, high pressure fuel (reducing agent) accumulated in the common rail. Is supplied to the fuel injection nozzle (fuel injection means, reducing agent supply means) 2 of each cylinder, and can be injected from the fuel injection nozzle 2 into the combustion chamber 3 of each cylinder at an arbitrary injection timing and injection amount. doing.

  Each cylinder of the engine 1 is provided with a piston 4 that can slide up and down. The piston 4 is connected to the crankshaft 6 via a connecting rod 5. Further, a flywheel (not shown) is provided at one end of the crankshaft 6, and a crank angle sensor 7 that detects the rotational speed of the crankshaft 6 is provided on the flywheel.

An intake port 8 and an exhaust port 9 are communicated with the combustion chamber 3.
The intake port 8 is provided with an intake valve 10 for communicating and blocking between the combustion chamber 3 and the intake port 8. In addition, the exhaust port 9 is provided with an exhaust valve 11 for performing communication and blocking between the combustion chamber 3 and the exhaust port 9.

  Upstream of the intake port 8, an air cleaner 12 that removes dust in the sucked fresh air, a compressor housing (not shown) of a turbocharger 13 that compresses the sucked fresh air using the energy of exhaust gas, and a compressed high temperature An intercooler 14 that cools the fresh air, an electronic control throttle valve 15 that adjusts the flow rate of the fresh air, and an intake manifold 16 that distributes the intake air to each cylinder are provided in communication with each other. The electronically controlled throttle valve 15 is provided with a throttle position sensor 17 for detecting the degree of opening of the throttle valve.

  An air flow sensor 18 for detecting the amount of fresh air sucked into the combustion chamber 3 is provided so as to protrude into the passage downstream of the air cleaner 12 and upstream of the compressor housing of the turbocharger 13. Further, a boost sensor 19 for detecting the pressure of intake air sucked into the combustion chamber 3 and an intake temperature sensor 20 for detecting the temperature of the intake air are provided so as to protrude into the intake manifold 16.

Downstream of the exhaust port 9, an exhaust manifold 21 that collects exhaust gas discharged from each cylinder, a turbine housing (not shown) that introduces exhaust gas into the turbocharger 13, and an exhaust pipe 22 are provided so as to communicate with each other. Yes.
The exhaust pipe 22 includes an oxidation catalyst 23 that sequentially oxidizes components to be oxidized in the exhaust gas from the upstream side, a diesel particulate filter 24 that collects and burns particulate matter mainly composed of graphite in the exhaust gas, and A NOx trap catalyst (occlusion reduction type NOx catalyst) 25 having an oxygen storage capacity and storing and reducing NOx in the exhaust gas is provided.

An exhaust temperature sensor 26 for detecting the temperature of the exhaust gas is provided so as to protrude into the exhaust pipe 22 downstream of the turbocharger 13 of the exhaust pipe 22 and upstream of the oxidation catalyst 23.
Between the diesel particulate filter 24 and the NOx trap catalyst 25 in the exhaust pipe 22, an A / F sensor 27 that detects an oxygen concentration that is an oxygen ratio of the exhaust gas flowing into the NOx trap catalyst 25 is provided in the exhaust pipe 22. It is provided to protrude.

Further, an A / F sensor 29 that detects an oxygen concentration that is an oxygen ratio of exhaust gas flowing out from the NOx trap catalyst 25 is provided downstream of the NOx trap catalyst 25 in the exhaust pipe 22 so as to protrude into the exhaust pipe 22. It has been.
The intake manifold 16 and the exhaust manifold 21 are provided with an EGR passage 30 for returning a part of the exhaust gas to the intake air so as to communicate with each other. The EGR passage 30 is provided with an EGR valve 31 that adjusts the amount of exhaust gas returning to the intake air, that is, an EGR amount, and an EGR cooler 32 that cools the exhaust gas returning to the intake air.

  The fuel injection nozzle 2, the crank angle sensor 7, the electronic control throttle valve 15, the throttle position sensor 17, the air flow sensor 18, the boost sensor 19, the intake air temperature sensor 20, the exhaust gas temperature sensor 26, the A / F sensors 27 and 29, and Various devices such as the EGR valve 31 and various sensors are control devices for performing overall control of the engine 1, and are input / output devices, storage devices (ROM, RAM, nonvolatile RAM, etc.), timers, and central processing units. It is electrically connected to an electronic control unit (ECU) (detachment processing control means) 40 that includes a processing device (CPU) and the like, and the ECU 40 controls various devices based on information from various sensors. Control the operation.

Sensors such as a crank angle sensor 7, a throttle position sensor 17, an air flow sensor 18, a boost sensor 19, an intake air temperature sensor 20, an exhaust gas temperature sensor 26, and A / F sensors 27 and 29 are electrically connected to the input side of the ECU 40. The detection information from these various devices and various sensors is inputted.
On the other hand, the fuel injection nozzle 2, the electronic control throttle valve 15, and the EGR valve 31 are electrically connected to the output side of the ECU 40.

Thus, the ECU 40 optimally controls the fuel injection amount and injection timing from the fuel injection nozzle 2 and the opening degrees of the electronic control throttle valve 15 and the EGR valve 30 based on the detection values of the sensors.
The ECU 40 has a function of performing a desorption process of sulfur stored in the NOx trap catalyst 25, that is, a so-called S purge process (sulfur desorption process) every time the engine 1 is operated for a predetermined period. In the S purge process, as shown in FIG. 2, HC addition (corresponding to the supply of the reducing agent of the present invention) and non-HC addition (corresponding to the non-supplying of the reducing agent of the present invention) are repeated, and the NOx trap catalyst 25 The temperature is set to a predetermined temperature (predetermined value) at which the sulfur content stored in the NOx trap catalyst 25 can be desorbed. Specifically, at the time of non-HC addition in FIG. 2, the fuel injection amount in the combustion post injection shown in FIG. 3 is reduced to make the fuel injection amount in the in-cylinder combustion smaller than the theoretical air-fuel ratio equivalent injection amount. Thereby, the air-fuel ratio in the cylinder becomes a lean air-fuel ratio. That is, as shown in FIG. 2, the amount of oxygen in the cylinder when non-HC is added increases. In the in-cylinder combustion at the time of non-HC addition, a lean air-fuel ratio exhaust gas, that is, an exhaust gas with a large amount of oxygen is supplied to the oxidation catalyst 23 and the NOx trap catalyst 25. In the NOx trap catalyst 25, oxygen in the exhaust gas is occluded in the catalyst. Thereafter, at the time of addition of HC in FIG. 2, the fuel injection amount in the combustion post injection shown in FIG. 3 is increased so that the fuel injection amount in the in-cylinder combustion becomes equal to or greater than the theoretical air-fuel ratio equivalent injection amount. Thereby, the air-fuel ratio in the cylinder becomes equal to or higher than the theoretical air-fuel ratio. In the in-cylinder combustion at the time of HC addition, the exhaust gas with the oxygen amount equal to or higher than the theoretical air-fuel ratio is supplied to the oxidation catalyst 23 and the NOx trap catalyst 25. Thereafter, in order to set the temperature of the NOx trap catalyst 25 to a predetermined temperature (predetermined value) at which the sulfur content stored in the NOx trap catalyst 25 can be desorbed, the fuel injection amount of in-cylinder combustion at the time of HC addition and HC addition The in-cylinder post injection (HC addition) shown in FIG. 3 is performed in which the fuel injection amount is set so that the total fuel injection amount combined with the fuel injection amount becomes the required injection amount when the catalyst is rich in FIG. As a result, the air-fuel ratio in the cylinder becomes a rich air-fuel ratio. Then, the rich air-fuel ratio exhaust gas is supplied to the oxidation catalyst 23 and the NOx trap catalyst 25. In the NOx trap catalyst 25, the oxygen stored in the catalyst reacts with the rich air-fuel exhaust gas to reach a predetermined temperature. Then, the sulfur content stored in the NOx trap catalyst 25 is combusted and removed.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine of the present invention, when non-HC is added in the S purge process, the fuel injection amount for in-cylinder combustion is made smaller than the stoichiometric air-fuel ratio equivalent injection amount to theoretically calculate the air-fuel ratio in in-cylinder combustion. The lean air-fuel ratio is less than the air-fuel ratio. When HC is added, the combustion post injection is increased so that the fuel injection amount in the in-cylinder combustion is greater than or equal to the theoretical air-fuel ratio equivalent injection amount, and the air-fuel ratio in the in-cylinder combustion is the stoichiometric air-fuel ratio or rich air-fuel ratio. Then, in-cylinder post-injection of the fuel injection amount in which the total fuel injection amount that combines the fuel injection amount of in-cylinder combustion at the time of HC addition and the fuel injection amount by the addition of HC becomes the required injection amount at the time of catalyst rich is performed, The temperature of the NOx trap catalyst 25 is set to a predetermined temperature.

Therefore, by setting the fuel injection amount of in-cylinder combustion performed at the time of HC addition so that the in-cylinder air-fuel ratio becomes equal to or higher than the stoichiometric air-fuel ratio, the oxidation catalyst before HC addition (in-cylinder post injection) is performed. It is possible to reduce the amount of oxygen in the exhaust gas flowing into the air outlet 23.
For this reason, even if HC addition (in-cylinder post injection) is performed, the temperature increase of the oxidation catalyst 23 can be suppressed without oxidizing the fuel added by the oxidation catalyst 23.

Therefore, the NOx trap catalyst 25 can be sufficiently heated without increasing the temperature of the oxidation catalyst during the S purge process.
Further, when non-HC is added in the S purge process, the fuel injection amount for in-cylinder combustion is set so that the in-cylinder air-fuel ratio is less than the stoichiometric air-fuel ratio, that is, the lean air-fuel ratio, thereby flowing into the NOx trap catalyst 25. The amount of oxygen can be increased, and the amount of oxygen stored in the NOx trap catalyst 25 can be increased.

Therefore, by storing a large amount of oxygen in the NOx trap catalyst 25, the NOx trap catalyst 25 reacts with the added HC and oxygen at the next HC addition, and without raising the temperature of the oxidation catalyst 23, The temperature of the NOx trap catalyst 25 can be reliably raised.
Further, the total fuel injection amount, which is the sum of the fuel injection amount of in-cylinder combustion at the time of HC addition in the S purge process and the fuel injection amount of HC addition (in-cylinder post injection), is set as the required injection amount at the time of catalyst rich, and NOx trap The temperature of the catalyst 25 is set to a predetermined temperature.

Therefore, the NOx trap catalyst 25 can be brought to a temperature suitable for desorption of the sulfur component, so that the desorption of the sulfur component from the NOx trap catalyst 25 can be performed reliably.
In addition, when HC is added in the S purge process, the air-fuel ratio of in-cylinder combustion is set to be equal to or higher than the theoretical air-fuel ratio by adding combustion post-injection. Can be greater than or equal to the theoretical air-fuel ratio.

  Further, when HC is added in the S purge process, the in-cylinder operation is performed so that the air-fuel ratio in the in-cylinder combustion is equal to or higher than the stoichiometric air-fuel ratio by adding combustion post-injection, and then becomes the required injection amount when the NOx trap catalyst 25 is rich. Since the injection amount in the post injection can be reduced, the amount of fuel adhering to the cylinder can be reduced, so that the dilution of the lubricating oil by the fuel can be reduced.

In addition, the stoichiometric air-fuel ratio of the in-cylinder combustion at the time of HC addition in the S purge process and the lean air-fuel ratio of the in-cylinder combustion at the time of non-HC addition are made by increasing or decreasing the combustion post injection. Therefore, by using the existing fuel injection nozzle 2 of the engine 1, it is not necessary to newly add a device, and an increase in cost can be suppressed.
This is the end of the description of the embodiment of the present invention. However, the embodiment of the present invention is not limited to the above embodiment.

In the above embodiment, the engine 1 is a common rail diesel engine. However, the present invention is not limited to this, and it can be applied to a lean combustion gasoline engine having an exhaust system to which the NOx trap catalyst 25 is attached. Nor.
Further, the theoretical air-fuel ratio of the in-cylinder combustion at the time of HC addition in the S purge process and the lean air-fuel ratio of the in-cylinder combustion at the time of non-HC addition are made by increasing or decreasing the combustion post injection. However, the present invention is not limited to this, and the fuel post injection may be added or reduced.

  Further, HC addition in the S purge process is performed by in-cylinder post injection, but the present invention is not limited to this, and a fuel addition nozzle may be provided in the exhaust pipe 22 to perform HC addition.

1 engine (internal combustion engine)
2 Fuel injection nozzle (fuel injection means, reducing agent supply means)
23 Oxidation catalyst 25 NOx trap catalyst (NOx storage reduction catalyst)
28 Exhaust temperature sensor (temperature detection means)
40 ECU (detachment control means)

Claims (6)

An oxidation catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine;
An NOx storage reduction catalyst that is provided downstream of the oxidation catalyst and has at least a larger oxygen storage capacity than the oxidation catalyst;
Fuel injection means for injecting fuel into the cylinder of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent to the oxidation catalyst;
Controlling the fuel injection amount from the fuel injection means and the reducing agent supply amount from the reducing agent supply means so as to desorb the exhaust components stored in the NOx storage reduction catalyst, and Desorption treatment control means for modulating the air-fuel ratio flowing into the NOx storage reduction catalyst into a lean air-fuel ratio or a rich air-fuel ratio,
The desorption processing control means is configured to inject the fuel from the fuel injection means so that when the reducing agent is supplied, the air-fuel ratio in the cylinder is on the rich air-fuel ratio side compared to when the reducing agent is not supplied. An exhaust emission control device for an internal combustion engine, wherein the amount is set.   The desorption processing control means sets the fuel injection amount from the fuel injection means so that an air-fuel ratio in the cylinder is equal to or higher than a theoretical air-fuel ratio when the reducing agent is supplied. Item 6. An exhaust emission control device for an internal combustion engine according to Item 1.   The desorption processing control means sets the fuel injection amount from the fuel injection means so that the air-fuel ratio in the cylinder becomes a lean air-fuel ratio when the reducing agent is not supplied from the reducing agent supply means. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, characterized by the above.   The desorption processing control means controls the fuel injection means and the reducing agent supply means so that the temperature of the NOx storage reduction catalyst becomes a predetermined value. The exhaust gas purification apparatus for an internal combustion engine according to any one of the above. The fuel injection means can perform a combustion post injection for injecting the fuel in an expansion stroke so that the fuel does not flow into the exhaust passage and burns in the cylinder;
The desorption processing control means controls the air-fuel ratio in the cylinder when the reducing agent is supplied or not, and sets the fuel injection amount from the fuel injection means by increasing or decreasing the combustion post injection. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust gas purification device is an internal combustion engine. The reducing agent supply means is the fuel injection means;
6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the desorption processing control means performs in-cylinder post injection that supplies the reducing agent after the combustion post injection.

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