JP2946886B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine having an exhaust system provided with a lean NOx catalyst for reducing NOx in a lean exhaust gas and in the presence of a reducing agent .

[0002]

2. Description of the Related Art Conventionally, an exhaust system of an engine capable of operating in a lean air-fuel ratio range (lean burn engine) is composed of a catalyst in which a transition metal is ion-exchanged on a zeolite or a noble metal is supported on the zeolite. During the air-fuel ratio lean exhaust, a catalyst that reduces NOx in the presence of a reducing agent (hereinafter, referred to as
There has been proposed an exhaust gas purifying apparatus for an internal combustion engine provided with a lean NOx catalyst (for example, Japanese Patent Application No. 2-4).
No. 06183).

[0003] In order for a lean NOx catalyst to purify NOx, a reducing agent is required. In a conventional exhaust gas purifying apparatus, in order to improve the NOx purification rate, a target reducing agent amount is calculated according to an engine operating state, while an actual amount of the actual reducing agent in the exhaust gas is calculated.
The reducing agent amount detected or estimated actual reducing agent amount, the target
The feedback control was performed so that the amount of the reducing agent might be obtained.

[0004]

However, the conventional exhaust gas purifying apparatus has the following problems. (B) for an indirect NOx amount reduction control by controlling the amount of reducing agent, it is possible to control the amount of reducing agent, whether or not the amount of NOx to be finally controlled is made actually controlled below the target value do not know. (B) Since the control of the amount of the reducing agent does not include the influence of the deterioration of the catalyst, the accuracy of the exhaust gas purification control shifts when the catalyst deteriorates. For example, when the catalyst has deteriorated, a larger amount of the reducing agent should be required than in the initial stage where the catalyst has not deteriorated, but such control is not performed. (C) The NOx concentration in the exhaust gas from the engine changes depending on the use conditions (summer, winter, sunny, rainy), but it cannot cope with the change in NOx due to uniform control based on the amount of reducing agent .

An object of the present invention, instead of controlling the NOx purification by the supply amount of reducing agent control based on the reducing agent amount as in the prior art, the supply amount of reducing agent based on the amount of NOx to be finally controlled An object of the present invention is to provide an exhaust gas purification control for an internal combustion engine in which the NOx purification is controlled by controlling the NOx purification control.

[0006]

According to the present invention, the above object is achieved by the following apparatus for purifying exhaust gas of an internal combustion engine. That is, an exhaust system of the internal combustion engine, a lean NOx catalyst installed in the exhaust system of the internal combustion engine, for reducing NOx in the air-fuel ratio lean exhaust and in the presence of the reducing agent,
A reducing agent supply device that supplies a reducing agent to the exhaust system of the internal combustion engine at an upstream side of the lean NOx catalyst so that the supply amount of the reducing agent can be adjusted; and a portion of the exhaust system of the internal combustion engine downstream of the lean NOx catalyst. wherein provided from the lean NOx catalyst on the upstream side portion, it calculates a NOx sensor for detecting the NOx concentration in the exhaust gas, a basic reducing agent supply amount on the basis of the operating condition of the internal combustion engine, from the lean NOx catalyst under
The NOx concentration detected by the NOx sensor provided at the downstream side and the upstream side of the lean NOx catalyst
NO detected by the NOx sensor
x The correction amount of the basic reducing agent supply amount is calculated based on the concentration, and the reducing agent supply device is controlled such that the reducing agent supply amount obtained by correcting the basic reducing agent supply amount by the correction amount is supplied. An exhaust gas purification device for an internal combustion engine, comprising: a reducing agent supply control device.

[0007]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, NOx sensors are provided downstream and upstream of the lean NOx catalyst.
Detecting the actual NOx concentration, since corrects the reducing agent supply amount on the basis thereof, the actual NOx amount to the reducing agent supply <br/> supply amount control based, NOx purification control is performed and thus, the NOx purification control Accuracy is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings.
Figure 1 shows the basic structure of the present invention, FIG. 2, FIG. 4 relates to the actual施例of the present invention, FIG. 3 shows an example of a NOx sensor.

First, the basic configuration will be described with reference to FIG. The exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes an internal combustion engine 2 which is operated or operable in a lean air-fuel ratio, an exhaust system 4 thereof, and a lean NO installed in the exhaust system 4.
x catalyst 6 and the exhaust system 4 upstream of the lean NOx catalyst 6.
Reducing agent supply device 8 for supplying a reducing agent in an adjustable supply amount
When, a NOx sensor 10 for detecting the NOx concentration provided from the lean NOx catalyst 6 in the exhaust system downstream portion, reducing
And a reducing agent supply control device 12 for controlling the agent supply device 8. Reducing agent supply control unit 12 calculates a basic reducing agent supply amount on the basis of the operating condition of the internal combustion engine 2, the basic reduction based on the NOx concentration detected by the NOx sensor 10
It calculates a correction amount of the agent supply amount, a basic reducing agent supply amount as the correction amount by the correction by the reducing agent supply amount obtained is supplied to the exhaust system, comprising means for controlling the reducing agent supply device 8 .

[0010] The NOx sensor 10 (or NOx described later)
The x sensor 18) is known, for example, from Japanese Patent Application Laid-Open No. 2-252959 . For example, as shown in FIG.
2 and a sensing device 28 provided with an electrode 26 on the outer surface of one of the insulating plates. The NOx concentration is detected by a change in the resistance value of the semiconductor resistor in accordance with the amount of NOx in the exhaust gas that is contact-adsorbed on the surface of the sensing device 28.

[0011] Next, the configuration of the onset AkiraMinoru施例will be described with reference to FIG. The examples are, when rie emissions NOx sensor 10 downstream of the lean NOx catalyst 6 is provided DOO
The lean NOx catalyst is located upstream of the lean NOx catalyst 6.
This corresponds to the case in which the support 18 is provided . Further, in the present embodiment, the HC supply control device 12 described in FIG.
The program means 102-116 , 20 having the flowchart shown in FIG. 4 and stored in the control device 16 shown in FIG.
2-206 .

In FIG. 2, a control device 16 is composed of a microcomputer and executes a calculation, a central processor unit (CPU) 16a, a read-only memory (ROM) 16b which is a read-only memory, and a memory for temporary storage. Random access memory (RA
M) 16c and A for converting an analog quantity to a digital quantity
/ D converter 16d and input interface 1
6e and an output interface 16f.

Reference numeral 14 denotes an exhaust gas temperature sensor for measuring the temperature of the gas emitted from the lean NOx catalyst 6. Outputs of the NOx sensor 10 and the exhaust gas temperature sensor 14 are converted into digital signals by an A / D converter 16d, and are input to an input interface 16e.
Is input to T indicates an accelerator opening in the case of a diesel engine (a throttle opening in the case of a gasoline engine), and is similarly input to an input interface 16e via an A / D converter 16d. The engine speed signal Ne is directly input to the input interface 16e. The command based on the calculation result in the CPU 16a is sent to the control valve 8b of the HC supply device 8 via the output interface 16f. 8a is H of the HC supply device 8.
The C source is shown. The second NOx sensor 18 is an internal combustion engine
In the exhaust gas from the time until the lean NOx catalyst 6
Detect Ox concentration. The output of the second NOx sensor 18 is
Input interface via A / D converter 16d
Source 16e.

The program shown in FIG. 4 is stored in the ROM 16b, and is read out by the CPU 16a and executed. 4 is interrupted at regular intervals.
First, at step 102, the engine speed Ne, the accelerator opening T, and the NOx concentration N which is the output of the NOx sensor 10 are set.
_{1. The} exhaust temperature TE, which is the output of the exhaust temperature sensor 14, is read. In step 102, Ne, T, N ₁ , and TE
In addition, lean NOx which is the output of the second NOx sensor 18
NOx concentration N ₂ of the catalyst upstream side is read.

Next, the routine proceeds to step 104, where the exhaust gas temperature TE
Is 350 ° C. or more. If the exhaust gas temperature, that is, the catalyst bed temperature is lower than 350 ° C., since the catalyst is not activated, it is meaningless to perform the control in steps 106 to 114, and the process returns as it is. Step 104
If TE is determined to be equal to or higher than 350 ° C. in step 10
Proceed to 6.

In step 106, based on the accelerator opening T and the engine speed Ne, that is, based on the operating conditions of the internal combustion engine, the basic reducing agent supply amount HCB is determined using, for example, a two-dimensional map. Step 106 in FIG.
In the map inside, when T and Ne are large, HCB takes a large value, and when T and Ne are small, HCB takes a small value. After steps 104 and 106, step 202
Where it is detected by the NOx sensors 10 and 18.
The difference DEL between the obtained NOx concentrations N ₁ and N ₂ , that is, NOx
Is purified by the lean NOx catalyst 6
The difference in NOx concentration is calculated. Then to step 204
To determine whether the NOx concentration difference DEL is smaller than a predetermined value DELD.
Is determined. DEL is determined to be smaller than DELD
The basic reducing agent depends on the catalyst deterioration and operating conditions.
Assuming that the supply amount HCB needs to be increased by a certain amount M,
Proceed to step 206 to replace HCB + M with HCB.
To step 108. In step 204, DEL
NOx purification by lean NOx catalyst 6 if DELD or higher
Rate is considered to be sufficient and the basic reductant supply amount HCB
The process proceeds to step 108 without performing the correction.

Subsequently, the routine proceeds to steps 108-114, where N
The basic reducing agent supply amount HCB is corrected based on the NOx concentration detected by the Ox sensor 10 to reduce the reducing agent supply amount H.
Calculate C. For example, in step 108, it is determined whether or not the NOx concentration N is higher than a predetermined concentration ND1, and N> ND
NOx concentration is 1 if the catalyst deterioration is progressed assumes that there was a great, the process proceeds to step 110, a basic reducing agent supply amount HCB was increased by I _1, obtaining the reducing agent supply amount HC.

In step 108, the NOx concentration N is set to a predetermined value N
If D1 or less, it is considered that catalyst deterioration has not progressed and the amount of reducing agent is sufficient, and the process proceeds to step 112, where NO
x The density N is in the predetermined range ND1-ND2 or ND
2 (a value smaller than ND1). Reducing agent supply amount if the predetermined range is regarded as may remain basic reducing agent subjected <br/> supply amount HCB. Also, if N is ND2 hereinafter regarded as be reduced by the amount of the reducing agent is too large the flow proceeds to step 114 to determine the reducing agent supply amount HC and reduced the basic reducing agent supply amount HCB only I _2. Step 11
0, 112, or 114, the process proceeds to step 116, and the control valve 8b is controlled so that the amount of the reducing agent supplied from the reducing agent supply device 8 to the exhaust system 4 becomes the above-obtained HC. Control the opening. Then return.

[0019] Next, a description will be given of the operation of this onset AkiraMinoru施例.
Exhaust gas from the internal combustion engine 2 is changed from the reducing agent supply device 8
The base agent is supplied, reduced to N ₂ by a reducing agent in the lean NOx catalyst 6, made harmless, and released to the atmosphere.

The amount of NOx in the exhaust gas from the internal combustion engine 2 is basically determined by the operating conditions of the internal combustion engine, for example, the load and the number of revolutions, but is also affected by the deterioration of the catalyst and the operating conditions (season and weather). Is done. Therefore, the amount of the reducing agent to be supplied changes.

For this reason, the basic reducing agent supply amount HCB is determined based on the accelerator opening T and the engine speed Ne (step 106). The correction based on the catalyst deterioration and the use conditions is performed by detecting the actual NOx amount downstream of the lean NOx catalyst by the NOx sensor 10, and based on the detected NOx amount, the reducing agent correction amount I ₁
Seeking I _2, the HCB I _1, I ₂ by a correction to obtain the reducing agent supply <br/> supply amount (step 108-114).

[0022] In this control, instead of obtaining a supply reducing agent correction amount based on the reducing agent <br/> amount in the exhaust gas, obtaining a supply reducing agent correction amount based on the NOx amount to be finally controlled Therefore, the NOx amount can be accurately controlled to a predetermined value or less, and the required amount of the reducing agent can be reduced to a minimum. For example, if the amount of NOx N is greater than ND1, instead
The amount of the base agent supplied is corrected by increasing the amount of I ₁ per interruption,
If less than the amount of NOx N is ND2, the reducing agent supply a single dose of I ₂ at a time weight loss corrected for each interrupt, the minimum required amount of
Supplying a reducing agent to reduce NOx to ND1-ND below the regulation value
2 can be maintained. Also, on the lean NOx catalyst 6,
NOx concentration is detected both in the stream and downstream
From the difference, the NOx purification rate of the lean NOx catalyst 6 itself
Can be known exactly, and the steps 202-20
By incorporating it into the routine as shown in Fig. 6, the NOx purification system
Control accuracy, responsiveness, and response to catalyst deterioration
be able to.

[0023]

According to the present invention, a lean NOx catalyst is provided in the exhaust system of an internal combustion engine, and NOx is provided downstream and upstream of the catalyst.
The x sensor is provided, the reducing agent supply control, along with determining the basic supply amount of reducing agent based on the engine operating condition, the lean NO
x NOx concentration detected by a NOx sensor provided downstream of the catalyst and upstream of the lean NOx catalyst
NO detected by the NOx sensor provided at the site
x The concentration of the supplied reducing agent is corrected based on the concentration , so that the NOx
The control based on the concentration can be performed, and the NOx purification control can be performed in consideration of catalyst deterioration and use conditions, which cannot be performed by the conventional control based on the reducing agent. Also,
Since the NOx concentration is detected both upstream and downstream of the lean NOx catalyst, it is possible to accurately know the NOx purification rate of the lean NOx catalyst itself from the difference, and to determine the NOx concentration.
x Accuracy of purification control, responsiveness, and response to catalyst deterioration can be further improved.

[Brief description of the drawings]

FIG. 1 is a system diagram of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.

2 is a system diagram of an exhaust gas purification system of an internal combustion engine according to the present onset AkiraMinoru施例.

FIG. 3 is a schematic configuration diagram of an example of a NOx sensor.

4 is a flowchart of the reducing agent supply control in this onset AkiraMinoru施例.

[Explanation of symbols]

Reference Signs List 2 internal combustion engine 4 exhaust system 6 lean NOx catalyst 8 reducing agent supply device 10 NOx sensor (first NOx sensor) 12 reducing agent supply control device 14 exhaust temperature sensor 16 control device 18 NOx sensor (second NOx sensor)

Claims (1)

(57) [Claims] 1. An exhaust system of an internal combustion engine, and a lean N installed in the exhaust system of the internal combustion engine for reducing NOx in an exhaust at a lean air-fuel ratio and in the presence of a reducing agent.
An Ox catalyst, a reducing agent supply device that supplies a reducing agent to the exhaust system of the internal combustion engine upstream of the lean NOx catalyst so that the supply amount thereof can be adjusted, provided from the lean NOx catalyst and the downstream portion to the upstream portion, calculates a NOx sensor for detecting the NOx concentration in the exhaust gas, a basic reducing agent supply amount on the basis of the operating condition of the internal combustion engine, wherein Installed downstream of the lean NOx catalyst
NOx concentration detected by the NOx sensor and
The above-mentioned catalyst provided upstream of the lean NOx catalyst.
A correction amount of the basic reducing agent supply amount is calculated based on the NOx concentration detected by the NOx sensor, and the reducing agent supply amount obtained by correcting the basic reducing agent supply amount by the correction amount is supplied. An exhaust gas purification device for an internal combustion engine, comprising: a reducing agent supply control device that controls the reducing agent supply device.