JP3620680B2 - Exhaust gas purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purifying device provided in an exhaust passage for purifying exhaust particulates contained in exhaust discharged from a diesel engine.
[0002]
[Prior art]
As a conventional exhaust gas purifying device, for example, as shown in FIG. 11, there is one that aims to improve the NOx conversion rate by adding HC to the exhaust and improving the HC / NOx ratio in the exhaust ( JP, 7-19031, A).
[0003]
[Problems to be solved by the invention]
However, in such a conventional exhaust gas purification device, the NOx conversion rate of the catalyst is also affected by the space velocity SV (exhaust gas flow rate passing through the unit capacity of the catalyst), so the engine speed changes. When the exhaust gas recirculation device (EGR) is operated, the SV changes, and not only the NOx cannot be sufficiently reduced, but also HC may be supplied more than necessary, resulting in a significant deterioration in fuel consumption.
[0004]
The present invention has been made paying attention to such a conventional problem, and by supplying necessary HC into the exhaust gas according to the exhaust gas flow rate actually passing through the catalyst and the NOx concentration in the exhaust gas, the present invention has been made. The goal is to solve the problem.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an exhaust gas purification apparatus having a catalyst for purifying exhaust gas, which is interposed in an exhaust passage of an internal combustion engine, and determines the unit capacity of the catalyst from the engine speed and the EGR rate. Means for calculating the flow rate of exhaust gas passing through, means for determining the amount of nitrogen oxide in the exhaust gas, and the amount of reducing agent and the amount of nitrogen oxide corresponding to the flow rate of exhaust gas passing through the unit volume of the catalyst. A means for setting a ratio to the amount and a value of the ratio so as to increase as the flow rate of the exhaust gas passing through the unit volume of the catalyst increases, and when the exhaust gas temperature is in the active temperature range of the catalyst, According to the above ratio, there is provided a reducing agent supply means for supplying a necessary amount of a reducing agent for reducing nitrogen oxide in exhaust gas upstream of the catalyst.
[0011]
The present invention is characterized in that the fuel injection device for an internal combustion engine is used as a reducing agent supply means for exhaust gas.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 is a view showing a first embodiment of the present invention and corresponds to claim 6 (claims 1, 2, 5).
[0014]
First, the configuration will be described. The engine 101 includes an exhaust passage 102, an NOx catalyst 201 interposed in a catalyst case 203 located in the exhaust passage 102, and an upstream of the catalyst 201. Further, an NOx sensor 104, an HC supply injector 105 as a reducing agent supply means, and an engine control unit 106 that drives the HC supply injector 105 based on information from the NOx sensor 104 are provided.
[0015]
Next, the operation of the first exemplary embodiment of the present invention will be described.
When the exhaust temperature is determined to be within the catalyst active temperature range from the engine operating state (it may be detected by providing a temperature sensor at the catalyst inlet), the NOx emission amount is detected by the NOx sensor 104, and the engine speed, EGR SV is calculated from the rate. After obtaining the necessary HC / NOx ratio from the relationship between the SV and the HC / NOx ratio in FIG. 8, the necessary HC is supplied from the HC supply injector 105. As shown in FIG. 5, since the NOx conversion rate is affected by the HC / NOx ratio in the exhaust gas and the SV, in order to obtain the target NOx reduction effect, the amount of HC added can be set according to the SV as in the present invention. It is necessary to adjust.
[0016]
Next, the above operation will be described with reference to the flowchart shown in FIG.
In step S1 (hereinafter abbreviated as S1), signals such as engine speed and engine load are read.
In S2, it is determined whether the temperature of the exhaust gas is the activation temperature of the catalyst. As shown in the map of FIG. 7, the exhaust gas temperature is estimated from the engine speed and the load (a temperature sensor may be provided at the catalyst inlet).
In S3, the amount of NOx in the exhaust gas is measured by a NOx sensor.
In S4, the actual exhaust gas amount flowing to the catalyst is calculated from the engine speed and the EGR map shown in FIG. 6, and the actual SV (actual exhaust gas amount flowing to the catalyst / catalyst capacity) is calculated based on this.
In S5, the required HC / NOx ratio is searched from the relationship shown in FIG.
In S6, a required amount of HC is added to the exhaust gas from the reducing agent supply means according to the HC / NOx ratio.
[0017]
FIG. 2 is a diagram showing a second embodiment of the present invention, and corresponds to claim 6 (claims 1, 2, 4) of the present invention.
[0018]
First, the configuration will be described. The engine 101 includes an exhaust gas purification device, an exhaust passage 102, a NOx catalyst 201 interposed in a catalyst case 203 located in the exhaust passage 102, an HC supply injector 105, and an HC supply. An engine control unit 106 that drives the injector 105 is provided.
[0019]
Next, the operation of the second embodiment will be described.
When it is determined from the engine operating state that the exhaust temperature is within the catalyst active temperature range (it may be detected by providing a temperature sensor at the catalyst inlet), the NOx emission amount is searched from the NOx emission amount map (FIG. 9). Further, the SV is calculated from the engine speed and the EGR rate, the necessary HC supply amount is calculated from the relationship between the SV and the HC / NOx ratio shown in FIG. 8, and HC is supplied from the HC supply injector 105.
[0020]
Next, description will be made with reference to the flowchart of FIG. 10 used in the first embodiment. The second embodiment is the same as in the first embodiment, differences are only S3 in FIG. 10, the contents of the S3, NOx emission map of FIG. 9 the amount of NOx in the exhaust gas It is a point to search by.
[0021]
FIG. 3 shows a third embodiment, which corresponds to claim 6 (claims 1, 2, 3, and 5) of the present invention.
First, the configuration will be described. There is an engine 101 provided with an intake air amount detection means 100. As an exhaust purification device, an exhaust passage 102, a catalyst 201 interposed in a catalyst case 203 located in the exhaust passage 102, An HC supply injector 105 and an engine control unit 106 for driving the HC supply injector 105 are provided.
[0022]
Next, the operation of the second embodiment will be described.
When the exhaust temperature is recognized as the catalyst active temperature range from the engine operating state (a temperature sensor may be provided at the catalyst inlet), the NOx emission amount is detected by the NOx sensor 104. Further, the SV of the catalyst is calculated from the signal from the intake air amount detection means 100, the engine speed, and the EGR rate. A required HC supply amount is calculated from the calculated SV and NOx emission amount, and HC is supplied from the HC supply injector 105.
[0023]
Next, a description will be given with reference to the flowchart of FIG.
Basically, it is the same as the first embodiment corresponding to claim 6 and the only difference is S4.
In S4, the actual exhaust gas amount flowing to the catalyst is calculated from the intake air amount detecting means, the EGR map and the engine speed shown in FIG. 6, and the actual SV (actual exhaust gas amount flowing to the catalyst / catalyst capacity) is calculated. To do.
[0024]
FIG. 4 shows a fourth embodiment, which corresponds to claim 7 (claims 1, 2, 5) of the present invention.
First, the configuration will be described. The engine 101 includes an exhaust passage 102, an NOx catalyst 201 interposed in a catalyst case 203 located in the exhaust passage 102, and an upstream of the catalyst 201. Further, a NOx sensor 104, a fuel injection device 107 also used as a reducing agent supply device, and an engine control unit 106 for driving the fuel injection device 107 are provided (as second and third embodiments of claim 7). In the second and third embodiments of the sixth aspect of the present invention, it is conceivable to search the NOx emission amount on a map or calculate the SV using the intake air amount detection means).
[0025]
Next, the operation of the fourth embodiment will be described.
When the exhaust temperature is determined to be within the catalyst active temperature range from the engine operating state (it may be detected by providing a temperature sensor at the catalyst inlet), the NOx emission amount is detected by the NOx sensor 104, and the engine speed, EGR SV is calculated from the rate. After obtaining the required HC / NOx ratio from the relationship between the SV and the HC / NOx ratio in FIG. 8, the required HC is injected into the combustion chamber from the fuel injection device 107 when the exhaust valve at the later stage of combustion is opened. HC is supplied to
[0026]
Next, description will be made with reference to the flowchart of FIG. 10 used in the above description.
Basically, it is the same as the first embodiment corresponding to claim 6 and the only difference is S6.
In S6, according to the required HC / NOx ratio, a required amount of HC is injected into the exhaust gas from the fuel injection device 107 in the later stage of combustion.
[0027]
【The invention's effect】
As described above, according to the present invention, by improving the HC / NOx ratio according to the actual SV, it is possible to suppress unnecessary fuel consumption deterioration and obtain a necessary NOx reduction effect.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of the present invention.
FIG. 2 is a block diagram showing a second embodiment of the present invention.
FIG. 3 is a block diagram showing a third embodiment of the present invention.
FIG. 4 is a configuration diagram showing a fourth embodiment of the present invention.
FIG. 5 is a graph showing the relationship between SV and the NOx conversion rate of the NOx catalyst.
FIG. 6 is a diagram showing a relationship between an EGR rate and an engine operating state.
FIG. 7 is a graph showing the relationship between exhaust gas temperature and engine operating state.
FIG. 8 is a diagram showing a relationship between SV and HC / NOx ratio necessary for obtaining sufficient NOx conversion performance.
FIG. 9 is a diagram showing the relationship between the NOx emission amount and the operating state of the engine.
FIG. 10 is a flowchart of the present invention.
FIG. 11 is a block diagram showing a conventional example.
[Explanation of symbols]
100 Intake air amount detection means 101 Engine 102 Exhaust passage 104 NOx sensor 105 HC supply injector 106 Engine control unit 107 Fuel injection device 201 Catalyst 203 Catalyst case

Claims (2)

In an exhaust gas purification apparatus having a catalyst that is disposed in an exhaust passage of an internal combustion engine and purifies exhaust gas,
Means for calculating an exhaust gas flow rate passing through a unit volume of the catalyst from the engine speed and the EGR rate;
Means for determining the amount of nitrogen oxides in the exhaust gas;
Corresponding to the exhaust gas flow rate passing through the unit volume of the catalyst, a ratio between the amount of reducing agent and the nitrogen oxide amount is set, and the value of this ratio is set to the exhaust gas flow rate passing through the unit volume of the catalyst. Means to set it to increase as the value increases,
When the exhaust gas temperature is in the active temperature range of the catalyst, it has a reducing agent supply means for supplying a necessary amount of a reducing agent for reducing nitrogen oxide in the exhaust gas upstream of the catalyst according to the ratio. A featured exhaust gas purifier. 2. The exhaust gas purifying apparatus according to claim 1, wherein the fuel injection device of the internal combustion engine is used as a reducing agent supply means into the exhaust gas.

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