JP2009174502A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a response delay when an increase in an engine load of an internal combustion engine is requested, in an exhaust emission control device for an internal combustion engine the temperature of which is increased by supplying a reducing agent to a front stage catalyst which is provided on an exhaust passage on the upstream side from the exhaust emission control device, has a smaller heat capacity than that of the exhaust emission control device, is formed to make exhaust gas flow between the outer peripheral face of the catalyst and the inner peripheral face of the exhaust passage, and also has an oxidation function. <P>SOLUTION: When the increase in the engine load of the internal combustion engine is requested (S102) while the reducing agent is being supplied to the front stage catalyst to increase the temperature of the exhaust emission control device, the amount of the reducing agent to be supplied to the front stage catalyst is reduced, or supply of the reducing agent to the front stage catalyst is stopped (S103). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is provided upstream of the exhaust purification device in the exhaust passage of the internal combustion engine, has a smaller heat capacity than the exhaust purification device, and is formed so that the exhaust flows between the outer peripheral surface thereof and the inner peripheral surface of the exhaust passage. The present invention relates to an exhaust gas purification system for an internal combustion engine having a pre-stage catalyst having an oxidation function.

  In an exhaust passage of an internal combustion engine, an exhaust purification device including an oxidation catalyst, an NOx storage reduction catalyst, and / or a particulate filter may be provided, and a pre-stage catalyst having an oxidation function may be further provided upstream thereof. In this case, by supplying the reducing agent to the upstream catalyst, the reducing agent is oxidized in the upstream catalyst, and the temperature of the exhaust emission control device can be raised by the oxidation heat.

  In the above case, a technique is known in which the pre-stage catalyst is formed so that the heat capacity is smaller than that of the exhaust purification device and the exhaust gas flows between the outer peripheral surface thereof and the inner peripheral surface of the exhaust passage.

  When the heat capacity of the pre-stage catalyst is relatively small, the temperature of the pre-stage catalyst rises more rapidly when the reducing agent is supplied to the pre-stage catalyst. As a result, it becomes possible to raise the temperature of the exhaust purification device more quickly.

  Further, when the front catalyst is formed so that the exhaust flows between the outer peripheral surface thereof and the inner peripheral surface of the exhaust passage, the cross-sectional area of the front catalyst in the direction perpendicular to the exhaust flow direction is relatively small. Therefore, the flow resistance of the exhaust when the exhaust passes through the front catalyst increases. As a result, it takes a long time for the reducing agent that has flowed into the upstream catalyst together with the exhaust gas to pass through the upstream catalyst, and the oxidation reaction of the reducing agent in the upstream catalyst is further promoted. Therefore, it is possible to further increase the temperature of the exhaust purification device.

Patent Document 1 describes a technique in which a reforming catalyst for reforming supplied fuel is provided upstream of the NOx catalyst in the exhaust passage. Patent Document 1 discloses a technique in which a reforming catalyst is disposed in the center of an exhaust passage, and a detour in which exhaust flows is formed on the outer periphery of the reforming catalyst.
JP 2005-127257 A

  In order to raise the temperature of the exhaust gas purification device, a reducing agent is supplied to a pre-stage catalyst that has a smaller heat capacity than the exhaust gas purification device and is configured such that exhaust gas flows between the outer peripheral surface and the inner peripheral surface of the exhaust passage. When the temperature of the front catalyst rises due to oxidation of the reducing agent, the flow resistance of the exhaust gas passing through the front catalyst further increases. As a result, the back pressure upstream of the upstream catalyst is likely to increase.

  When an increase in the engine load of the internal combustion engine is required in a state where the back pressure upstream of the upstream catalyst is excessively high, the engine load is difficult to increase and the response delay may increase.

The present invention has been made in view of the above problems, and is provided in an exhaust passage upstream of the exhaust purification device, has a smaller heat capacity than the exhaust purification device, and has an outer peripheral surface and an inner peripheral surface of the exhaust passage. In an exhaust gas purification apparatus for an internal combustion engine that raises the temperature of the exhaust gas purification apparatus by supplying a reducing agent to a pre-stage catalyst that has an oxidizing function and is configured so that exhaust gas flows between them, there is a demand to increase the engine load of the internal combustion engine. An object of the present invention is to provide a technique capable of suppressing a response delay when there is a problem.

An exhaust purification system for an internal combustion engine according to the present invention includes:
An exhaust purification device provided in the exhaust passage of the internal combustion engine;
An oxidation function provided in an exhaust passage upstream of the exhaust purification device, having a smaller heat capacity than the exhaust purification device and configured to allow exhaust to flow between an outer peripheral surface thereof and an inner peripheral surface of the exhaust passage. A pre-stage catalyst having
A reducing agent supply means for supplying a reducing agent to the preceding catalyst when raising the temperature of the exhaust gas purification device,
When there is a request to increase the engine load of the internal combustion engine when the reducing agent is supplied to the upstream catalyst by the reducing agent supply means, the amount of the reducing agent supplied to the upstream catalyst by the reducing agent supply means Or the supply of the reducing agent to the preceding catalyst by the reducing agent supply means is stopped.

  According to the present invention, when there is a request to increase the engine load of the internal combustion engine when the reducing agent is supplied to the upstream catalyst by the reducing agent supply means, the temperature increase of the upstream catalyst is suppressed. As a result, an increase in the flow resistance of the exhaust gas passing through the front catalyst is suppressed, so that it is possible to suppress an excessive increase in the back pressure upstream of the front catalyst. Therefore, the engine load of the internal combustion engine can be increased more quickly, and the response delay can be reduced.

  According to the present invention, the exhaust passage is provided in the exhaust passage upstream of the exhaust purification device, has a smaller heat capacity than the exhaust purification device, and is formed so that the exhaust flows between the outer peripheral surface and the inner peripheral surface of the exhaust passage. In addition, in an exhaust gas purification device for an internal combustion engine that raises the temperature of the exhaust gas purification device by supplying a reducing agent to a pre-stage catalyst having an oxidation function, it is possible to suppress a response delay when there is a request to increase the engine load of the internal combustion engine. I can do it.

  Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Example 1>
<Schematic configuration of internal combustion engine and intake / exhaust system thereof>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  An intake manifold 5 and an exhaust manifold 7 are connected to the internal combustion engine 1. An intake passage 4 is connected to the intake manifold 5. An exhaust passage 6 is connected to the exhaust manifold 7.

  A compressor housing 8 a of a turbocharger 8 is installed in the intake passage 4. A turbine housing 8 b of a turbocharger 8 is installed in the exhaust passage 6.

  An air flow meter 12 is provided in the intake passage 4 upstream of the compressor housing 8a. A throttle valve 13 is provided in the intake passage 4 downstream of the compressor housing 8a.

  An oxidation catalyst 9 is provided in the exhaust passage 6 on the downstream side of the turbine housing 8b. In addition, a particulate filter (hereinafter simply referred to as a filter) 10 that collects particulate matter (hereinafter referred to as PM) in the exhaust gas is provided downstream of the oxidation catalyst 9 in the exhaust passage 6. ing. The filter 10 carries an NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst) 11.

  The oxidation catalyst 9 according to the present embodiment has a cylindrical shape, and the outer diameter thereof is smaller than the inner diameter of the exhaust passage 6. That is, the cross-sectional area in the direction perpendicular to the direction in which the exhaust gas of the oxidation catalyst 9 flows is smaller than the cross-sectional area in the direction perpendicular to the direction in which the exhaust gas flows through the exhaust passage 6. With such a configuration, a bypass path 18 through which exhaust flows is formed between the outer peripheral surface of the oxidation catalyst 9 and the inner peripheral surface of the exhaust passage 6. Further, the heat capacity of the oxidation catalyst 9 is smaller than the heat capacity of the filter 10.

  In this embodiment, the filter 10 carrying the NOx catalyst 11 corresponds to the exhaust purification device according to the present invention. The exhaust emission control device according to the present invention is not limited to such a configuration. For example, a catalyst such as a NOx catalyst and a filter may be arranged in series, or a single catalyst or filter It may be a simple substance. In the present embodiment, the oxidation catalyst 9 corresponds to the former stage catalyst according to the present invention. The oxidation catalyst 9 may be any catalyst having an oxidation function, and may be, for example, a three-way catalyst or a NOx catalyst.

  A fuel addition valve 17 for adding fuel as a reducing agent is provided in the exhaust passage 6 upstream of the oxidation catalyst 9. The fuel addition valve 17 is disposed close to the oxidation catalyst 9 so that the fuel injection hole through which the fuel is injected faces the upstream end face of the oxidation catalyst 9. The fuel injected from the fuel injection hole of the fuel addition valve 17 is supplied to the oxidation catalyst 9 (in FIG. 1, the shaded area represents fuel spray). In this embodiment, the fuel addition valve 17 corresponds to the reducing agent addition valve according to the present invention.

  An air-fuel ratio sensor 23 that detects the air-fuel ratio of exhaust gas and a temperature sensor 24 that detects the temperature of exhaust gas are provided downstream of the filter 10 in the exhaust passage 6.

  One end and the other end of an EGR passage 15 are connected to the exhaust manifold 7 and the intake manifold 5, respectively. A part of the exhaust discharged from the internal combustion engine 1 is introduced into the intake manifold 5 from the exhaust manifold 7 as EGR gas through the EGR passage 15. An EGR valve 16 is provided in the EGR passage 15. The EGR valve 16 controls the amount of EGR gas introduced into the intake manifold 5.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 20. The ECU 20 is a unit that controls the operating state of the internal combustion engine 1 and the like. An air flow meter 12, an air-fuel ratio sensor 23, a temperature sensor 24, a crank position sensor 21 and an accelerator opening sensor 22 are electrically connected to the ECU 20. The crank position sensor 21 detects the crank angle of the internal combustion engine 1. The accelerator opening sensor 22 detects the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted. Output signals from the sensors are input to the ECU 20.

  The ECU 20 derives the engine speed of the internal combustion engine 1 based on the detected value of the crank position sensor 21. Further, the ECU 20 derives the engine load of the internal combustion engine 1 based on the detection value of the accelerator opening sensor 22. Further, the ECU 20 derives the temperature of the filter 10 (that is, the temperature of the NOx catalyst 11) based on the detection value of the temperature sensor 18. Further, the ECU 20 derives the air-fuel ratio of the exhaust gas flowing into the filter 10 based on the detection value of the air-fuel ratio sensor 23 (that is, the air-fuel ratio in the atmosphere surrounding the NOx catalyst 11).

  In addition, each fuel injection valve 3, throttle valve 13, fuel addition valve 17, and EGR valve 16 are electrically connected to the ECU 20. These are controlled by the ECU 20.

<Temperature control>
When the PM collected by the filter 10 is oxidized and removed, or when the SOx stored in the NOx catalyst 11 is released and reduced, it is necessary to raise the temperature of the filter 10 (NOx catalyst 11). In the present embodiment, the temperature increase control for increasing the temperature of the filter 10 is performed by adding fuel from the fuel addition valve 17 and supplying the fuel to the oxidation catalyst 9.

  When fuel is supplied to the oxidation catalyst 9, the fuel is oxidized. The temperature of the exhaust gas is raised by the oxidation heat generated at this time, and the temperature of the filter 10 rises as the heated exhaust gas flows into the filter 10.

  At this time, in this embodiment, since the heat capacity of the oxidation catalyst 9 is relatively small, the temperature of the oxidation catalyst 9 rises more rapidly. Therefore, the temperature of the filter 10 can be raised more quickly.

  Further, as described above, in the present embodiment, the outer diameter of the oxidation catalyst 9 is smaller than the inner diameter of the exhaust passage 6. In this case, compared with the case where the outer diameter of the oxidation catalyst 9 is equal to or larger than the inner diameter of the exhaust passage 6, the exhaust flow resistance when the exhaust gas passes through the oxidation catalyst 9 is increased. Therefore, the flow rate of the exhaust gas flowing through the oxidation catalyst 9 is reduced. As a result, when fuel is supplied from the fuel addition valve 17, it takes a longer time for the fuel to pass through the oxidation catalyst 9, and the oxidation reaction of the fuel in the oxidation catalyst 9 is more facilitated. Therefore, the temperature rise of the filter 10 can be further promoted.

<Control of fuel addition when engine load increases>
By performing the temperature increase control as described above, when the temperature of the oxidation catalyst 9 rises, the flow resistance of the exhaust gas passing through the oxidation catalyst 9 further increases. As a result, the back pressure upstream of the oxidation catalyst 9 is likely to increase.

  Here, even when the temperature raising control is being executed, there is a case where an increase in the engine load of the internal combustion engine 1 is required as in the case of accelerating a vehicle on which the internal combustion engine 1 is mounted. In such a case, if the back pressure upstream of the oxidation catalyst 9 is excessively high for the reasons described above, the engine load is difficult to increase and the response delay may increase.

  Therefore, in the present embodiment, when there is a request for increasing the engine load of the internal combustion engine 1 while the temperature raising control is being performed, the fuel addition valve 17 is used to suppress a delay in response to the increase in the engine load. Control the amount of fuel added. Hereinafter, the fuel addition amount control routine when the engine load is increased according to this embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, the ECU 20 first determines in S101 whether or not the temperature increase control is being executed. If an affirmative determination is made in S101, the ECU 20 proceeds to S102, and if a negative determination is made, the ECU 20 once ends the execution of this routine.

  In S102, the ECU 20 determines whether or not there is a request to increase the engine load of the internal combustion engine 1. This can be determined based on, for example, the detection value of the accelerator opening sensor 22 or the like. If an affirmative determination is made in S102, the ECU 20 proceeds to S103, and if a negative determination is made, the ECU 20 once ends the execution of this routine.

  In S103, the ECU 20 decreases the amount of fuel added from the fuel addition valve 17, that is, the amount of fuel supplied to the oxidation catalyst 9, from the point before the request for increasing the engine load. At this time, the amount of fuel added from the fuel addition valve 17 may be decreased to a predetermined amount or less, and based on the requested increase amount of the engine load, the flow rate of the exhaust gas, the temperature of the oxidation catalyst 9, and the like. It may be reduced below a fixed amount. Thereafter, the ECU 20 once terminates execution of this routine.

  According to the routine described above, when there is a request to increase the engine load of the internal combustion engine 1 while the temperature raising control is being performed, the amount of fuel supplied to the oxidation catalyst 9 decreases. When the amount of fuel supplied to the oxidation catalyst 9 decreases, the temperature rise of the oxidation catalyst 9 is suppressed. As a result, an increase in the flow resistance of the exhaust gas passing through the oxidation catalyst 9 is suppressed, so that an excessive increase in the back pressure upstream of the oxidation catalyst 9 can be suppressed.

  Therefore, according to the present embodiment, the engine load of the internal combustion engine 1 can be increased more quickly even when there is a request for an increase in the engine load of the internal combustion engine 1 when the temperature raising control is being executed. The response delay can be reduced. As a result, deterioration of drivability is suppressed.

  In the present embodiment, when there is a request to increase the engine load of the internal combustion engine 1 while the temperature raising control is being executed, the fuel addition from the fuel addition valve 17 may be stopped. According to this, an excessive increase in the back pressure upstream of the oxidation catalyst 9 can be further suppressed.

  In the present embodiment, the temperature increase control may be executed to increase the temperature of the NOx catalyst 11 when the internal combustion engine 1 is cold-started. In this case, the warming up of the internal combustion engine 1 is further promoted by increasing the back pressure upstream of the oxidation catalyst 9.

The figure which shows schematic structure of the intake / exhaust system of the internal combustion engine which concerns on an Example. The flowchart which shows the routine of fuel addition amount control at the time of the engine load increase which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Intake passage 5 ... Intake manifold 6 ... Exhaust passage 7 ... Exhaust manifold 8 ... Turbocharger 8a Compressor housing 8b Turbine housing 9 Oxidation catalyst 10 Particulate filter 11 Occlusion reduction type NOx catalyst 12 Air flow meter 13 Throttle valve 15 EGR passage 16 EGR valve 17 -Fuel addition valve 17-Air-fuel ratio sensor 18-Bypass passage 20-ECU
21 .. Crank position sensor 22 .. Accelerator opening sensor 23 .. Air-fuel ratio sensor 24 .. Temperature sensor

Claims (1)

An exhaust purification device provided in the exhaust passage of the internal combustion engine;
An oxidation function provided in an exhaust passage upstream of the exhaust purification device, having a smaller heat capacity than the exhaust purification device and configured to allow exhaust to flow between an outer peripheral surface thereof and an inner peripheral surface of the exhaust passage. A pre-stage catalyst having
A reducing agent supply means for supplying a reducing agent to the preceding catalyst when raising the temperature of the exhaust gas purification device,
When there is a request to increase the engine load of the internal combustion engine when the reducing agent is supplied to the upstream catalyst by the reducing agent supply means, the amount of the reducing agent supplied to the upstream catalyst by the reducing agent supply means Or reducing the supply of the reducing agent to the pre-stage catalyst by the reducing agent supply means.

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