JP2015110922A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system which precisely controls a urea water injection amount to an optimum injection amount on the basis of a deterioration degree of an SCR.SOLUTION: An exhaust emission control system includes an SCR 22 which is provided in an exhaust system of an engine 10 and reductively purifies NOx contained in the exhaust gas with ammonia produced from urea water being used as a reductant agent; a urea water injection device 21 which injects the urea water to the SCR 22; an electrode 27 which detects the electrostatic capacitance of the SCR 22; an SCR internal temperature calculation unit 51 which calculates the internal temperature of the SCR 22 on the basis of the electrostatic capacitance input from the electrode 27; an SCR deterioration degree calculation unit 52 which calculates a deterioration degree of the SCR 22 on the basis of the internal temperature input from the SCR internal temperature calculation unit 51; a urea water injection control unit 53 which controls the injection of the urea water from the urea water injection device 21 on the basis of a predetermined reference injection amount; and an injection amount correction unit 54 which corrects the reference injection amount on the basis of the deterioration degree input from the SCR internal temperature calculation unit 52.

Description

  The present invention relates to an exhaust purification device, and more particularly to an exhaust purification device including an exhaust purification catalyst that reduces and purifies nitrogen compounds in exhaust gas.

As an exhaust purification catalyst provided in an exhaust system of a diesel engine or the like, selective reduction and purification of nitrogen compounds (NOx) in exhaust gas using ammonia (NH ₃ ) hydrolyzed from urea water as a reducing agent Reduction catalysts (Selective Catalytic Reduction: SCR) are known.

In general, the NH ₃ adsorption amount and NOx purification performance of the SCR vary depending on the internal temperature of the SCR. Therefore, in order to optimally control the urea water injection amount, it is important to accurately grasp the internal temperature of the SCR.

  As a technique for controlling the urea water injection amount based on the SCR temperature, for example, the internal temperature of the SCR is estimated from the detected values of the exhaust temperature sensors arranged before and after the SCR, and the urea water injection amount is set according to the estimated internal temperature. A technique for appropriately adjusting is known (for example, see Patent Document 1).

JP 2003-293736 A

By the way, since the exhaust temperature sensor cannot be provided directly inside the SCR, there is a problem that the internal temperature of the SCR cannot be accurately detected. Further, since the NH ₃ adsorption amount of the SCR changes depending on the internal temperature and the deterioration degree of the SCR, the technology for controlling the urea water injection amount based on the sensor value of the exhaust temperature sensor is optimal according to the internal temperature and the deterioration degree. May not be able to set the correct injection amount.

  An object of the present invention is to control the urea water injection amount with an optimal injection amount corresponding to the degree of deterioration of the SCR.

  In order to achieve the above-described object, an exhaust purification apparatus of the present invention is provided in an exhaust system of an internal combustion engine, and selectively reduces and purifies nitrogen compounds contained in exhaust using ammonia generated from urea water as a reducing agent. A catalyst, urea water injection means for injecting urea water to the selective reduction catalyst, electrostatic capacity detection means for detecting electrostatic capacity of the selective reduction catalyst, and static electricity input from the electrostatic capacity detection means An internal temperature calculation means for calculating the internal temperature of the selective reduction catalyst based on the electric capacity, and a deterioration for estimating the deterioration state of the selective reduction catalyst based on the internal temperature input from the internal temperature calculation means State estimation means, injection control means for controlling urea water injection of the urea water injection means based on at least a predetermined reference injection amount set according to the operating state of the internal combustion engine, and the deterioration state estimation Characterized in that it comprises a injection amount correction means for correcting the reference injection amount in accordance with the deterioration state of the selective reduction catalyst that is input from the stage.

  The injection amount correction means obtains the reducing agent adsorption capacity of the selective reduction catalyst based on the deterioration state input from the deterioration state estimation means, and uses an injection correction amount corresponding to the reducing agent adsorption capacity. The reference injection amount may be corrected.

  Further, the capacitance detection means may be composed of at least a pair of electrodes that are disposed opposite to each other with one or more partition walls in the selective reduction catalyst to form a capacitor.

  According to the exhaust emission control device of the present invention, the urea water injection amount can be controlled with an optimal injection amount corresponding to the degree of deterioration of the SCR.

It is a typical whole lineblock diagram showing the exhaust-air-purification device concerning one embodiment of the present invention. It is a functional block diagram which shows ECU of this embodiment. It is a figure which shows an example of the electrostatic capacitance and temperature characteristic map of this embodiment. Is a diagram illustrating an example of the NH ₃ adsorption capacity map of the present embodiment. It is a flowchart which shows the control content of this embodiment. It is the figure which compared the electrostatic capacitance between electrodes with respect to an actual exhaust temperature change, and the sensor value of an exhaust temperature sensor.

  Hereinafter, an exhaust emission control device according to an embodiment of the present invention will be described with reference to the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 10 is provided with an intake manifold 10a and an exhaust manifold 10b. An intake passage 11 for introducing fresh air is connected to the intake manifold 10a, and an exhaust passage 12 for releasing exhaust gas to the atmosphere is connected to the exhaust manifold 10b.

  In the intake passage 11, an air cleaner 13, a compressor 15 a of the supercharger 15, an intercooler 17 and the like are provided in order from the intake upstream side. In the exhaust passage 12, a turbine 15 b of the supercharger 15, an exhaust aftertreatment device 20, and the like are provided in order from the exhaust upstream side. In FIG. 1, reference numeral 18 denotes an engine speed sensor, and reference numeral 19 denotes an accelerator opening sensor.

  The exhaust aftertreatment device 20 includes, in order from the exhaust upstream side, a urea water injection device 21 and an SCR 22 accommodated in the case 20a.

The urea water injection device 21 is an example of the urea water injection means of the present invention, and enters the exhaust passage 12 upstream of the SCR 22 in response to an instruction signal input from an electronic control unit (hereinafter, ECU) 50. Then, urea water in a urea water tank (not shown) is injected. The injected urea water is hydrolyzed by exhaust heat to generate NH ₃ and is supplied as a reducing agent to the downstream SCR 22.

The SCR 22 is formed, for example, by supporting zeolite or the like on the surface of a ceramic carrier such as a honeycomb structure, and includes a large number of cells partitioned by porous partition walls. The SCR 22 adsorbs NH ₃ supplied as a reducing agent and selectively reduces and purifies NOx from exhaust gas passing through the adsorbed NH ₃ .

  In addition, the SCR 22 of the present embodiment is provided with a plurality of electrodes 27 that are arranged to face each other with at least one partition wall therebetween to form a capacitor. The plurality of electrodes 27 are preferable as an example of the capacitance detection means of the present invention.

  The ECU 50 performs various controls of the engine 10, the urea water injection device 21, and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like.

  Further, as shown in FIG. 2, the ECU 50 includes an SCR internal temperature calculation unit 51, an SCR deterioration degree calculation unit 52, a urea water injection control unit 53, and an injection amount correction unit 54 as some functional elements. . Each of these functional elements will be described as being included in the ECU 50 which is an integral hardware, but any one of these may be provided in separate hardware.

The SCR internal temperature calculation unit 51 is an example of the internal temperature calculation means of the present invention, and calculates the internal temperature TSCR of the _SCR 22 based on the capacitance C between the electrodes 27. In general, the capacitance C between the electrodes 27 is expressed by the following mathematical formula 1, where the dielectric constant ε of the medium between the electrodes 27, the area S of the electrodes 27, and the distance d between the electrodes 27.

In Formula 1, the area S and the distance d of the electrode 27 are constant, and when the dielectric constant ε changes under the influence of the exhaust temperature, the capacitance C also changes accordingly. That is, if the electrostatic capacitance C between the electrodes 27 is detected, the internal temperature TSCR of the _SCR 22 can be calculated.

The ECU 50 stores a capacitance / temperature characteristic map (see, for example, FIG. 3) showing the relationship between the capacitance C and the SCR internal temperature T obtained in advance through experiments or the like. The SCR internal temperature calculation unit 51 calculates the internal temperature TSCR of the _SCR 22 by reading a value corresponding to the capacitance C between the electrodes 27 from the capacitance / temperature characteristic map. Note that the calculation of the internal temperature _TSCR is not limited to a map, and may be obtained from an approximate expression or the like created in advance through experiments or the like.

The SCR deterioration degree calculation unit 52 is an example of a deterioration state estimation unit of the present invention, and is based on the internal temperature T _SCR (actual heat of reaction in the _SCR 22) input from the SCR internal temperature calculation unit 51. Calculate degree DEG _LEVEL . More specifically, the ECU 50 stores a normal SCR (for example, new) reference reaction heat obtained in advance through experiments or the like. The SCR deterioration degree calculation unit 52 calculates the deterioration degree DEG _LEVEL of the _SCR 22 by comparing the reference reaction heat with the actual reaction heat obtained from the internal temperature TSCR. Note that the degree of degradation DEG _LEVEL may be obtained from a map, an approximate expression, or the like created in advance by experiments or the like.

The urea water injection control unit 53 is an example of the injection control means of the present invention, and controls the urea water injection amount of the urea water injection device 21 based on the operating state of the engine 10 and the like. More specifically, the urea water injection control unit 53 calculates the NOx discharge amount of the engine 10 from the engine speed Ne and the accelerator opening Q, and the urea water basic injection amount INJ that is required according to the NOx discharge amount. Set _{U_std} . This basic injection amount INJ _{U_std} is corrected as necessary by an injection amount correction unit 54 described later.

The injection amount correction unit 54 is an example of the injection amount correction means of the present invention, and the basic injection amount INJ _{U_std} set by the urea water injection control unit 53 is used as the internal temperature T input from the SCR internal temperature calculation unit 51. Correction is performed based on the degradation degree DEG _LEVEL input from the _SCR and the SCR degradation degree calculation unit 52.

More specifically, the ECU 50, normal SCR (e.g., new) created in advance by experiments or the like NH ₃ showing the internal temperature T _SCR and NH ₃ adsorption capacity (hereinafter, reference adsorption capacity ST _{NH3 - MAX)} the relationship between A suckable amount map (for example, see FIG. 4) is stored. Furthermore, the relationship between the internal temperature T _{SCR for} each degree of deterioration and the NH ₃ adsorbable amount after deterioration (hereinafter referred to as the post-degradation adsorbable amount ST _{NH3_n} ) is also defined on this NH ₃ adsorbable amount map. .

The injection amount correction unit 54 reads the adsorption amount deviation ΔST _NH3 between the reference adsorbable amount ST _{NH3_MAX} corresponding to the current internal temperature T _SCR and the post-degradation adsorbable amount ST _{NH3_n} from the NH ₃ adsorbable amount map. Based on the injection correction amount ΔINJ corresponding to the adsorption amount deviation ΔST _NH3 , the basic injection amount INJ _{U_std} is corrected to decrease (INJ _{U_exh} = INJ _{U_std−} ΔINJ). The urea water injection after correction is executed by shortening the energization pulse width of each injection applied to the injector (not shown) of the urea water injection device 21 or reducing the number of injections.

  Next, based on FIG. 5, the control flow by the exhaust emission control device of the present embodiment will be described. Note that this control starts simultaneously with the ON operation of the ignition key.

In step (hereinafter, step is simply referred to as S) 100, the basic injection amount INJ _{U_std of} urea water is set according to the NOx emission amount of the engine 10 calculated from the engine speed Ne and the accelerator opening Q. .

In S110, the internal temperature TSCR of the _SCR 22 is calculated based on the capacitance C between the electrodes 27. Further, in S120, the degradation degree DEG _{LEVEL of the SCR} 22 is calculated based on the internal temperature TSCR calculated in S110. Is done.

In S130, NH ₃ adsorption capacity map (FIG. 4), the reference adsorption capacity ST _{NH3 - MAX} and corresponding to the internal temperature T _SCR calculated in S110, the post-adsorption deterioration corresponding to the deterioration degree the DEG _LEVEL calculated in S120 The possible amount ST _{NH3_n} is read, and an adsorption amount deviation ΔST _NH3 between the reference adsorbable amount ST _{NH3_MAX} and the post- _degradable adsorbable amount ST _{NH3_n} is calculated.

In S140, it is determined whether or not the adsorption amount deviation ΔST _NH3 calculated in S130 is larger than a predetermined threshold value. If the adsorption amount deviation ΔST _NH3 is larger than the predetermined threshold (Yes), the process proceeds to S150, and the basic injection amount INJ _{U_std} is corrected to decrease based on the injection correction amount ΔINJ corresponding to the adsorption amount deviation ΔST _NH3 (INJ). _{U_exh} = INJ _{U_std−} ΔINJ). Further, in S160, the urea water injection of the urea water injection device 21 is executed based on the corrected injection amount INJ _{U_exh} .

On the other hand, if the adsorption amount deviation ΔST _NH3 is less than the predetermined threshold value in S140 (No), the process proceeds to S170, and the correction of the urea water injector 21 is performed based on the basic injection amount INJ _{U_std} set in S100 without correction. Urea water injection is executed. Thereafter, each control step of S100 to S170 described above is repeatedly executed until the ignition key is turned off.

  Next, functions and effects of the exhaust emission control device according to the present embodiment will be described.

As shown in FIG. 6, the capacitance C between the electrodes 27 has a characteristic that shows a faster response to a change in the exhaust temperature (SCR internal temperature) than the sensor value of the exhaust temperature sensor. That is, if the capacitance C between the electrodes 27 arranged directly in the _SCR 22 is used, the internal temperature T _SCR of the _SCR 22 can be detected more accurately than the sensor value of the exhaust temperature sensor provided before and after the _SCR 22. It becomes possible.

NH in the exhaust gas purification apparatus of the present embodiment, while calculating the deterioration degree the DEG _LEVEL of SCR22 based on the internal temperature T _SCR of SCR22 which is calculated from the capacitance C between the electrodes 27, in accordance with the degree of deterioration the DEG _{LEVEL 3 The} urea water injection amount is corrected based on the adsorbable amount. That is, by correcting the urea water injection amount based on the NH ₃ adsorptionable amount considering the degradation level DEG _{LEVEL of the} SCR 22, compared with the conventional technology considering only the internal temperature estimated from the exhaust temperature sensors before and after the SCR, The water injection amount is configured to be optimized with certainty.

Therefore, according to the exhaust gas purification apparatus of the present embodiment, the urea water injection amount can be optimally controlled according to the degree of deterioration of the SCR 22, and the NOx purification performance of the SCR 22 can be effectively improved. Further, by optimizing the urea water injection amount, NH ₃ slip from the SCR 22 can be effectively suppressed. Furthermore, it is not necessary to arrange an oxidation catalyst or the like for oxidizing and removing excess NH ₃ on the downstream side of the SCR 22, and the cost, weight, size, etc. of the entire apparatus can be effectively reduced.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, the number of the electrodes 27 may be at least a pair, and is not limited to the illustrated example. Further, the engine 10 is not limited to a diesel engine, and can be widely applied to other internal combustion engines such as a gasoline engine.

DESCRIPTION OF SYMBOLS 10 Engine 12 Exhaust passage 18 Engine speed sensor 19 Accelerator opening degree sensor 20 Exhaust after-treatment apparatus 21 Urea water injection apparatus 22 SCR
27 electrodes 50 ECU
51 SCR internal temperature calculation unit 52 SCR deterioration degree calculation unit 53 urea water injection control unit 54 injection amount correction unit

Claims (3)

A selective reduction catalyst that is provided in an exhaust system of an internal combustion engine and that reduces and purifies nitrogen compounds contained in the exhaust gas using ammonia generated from urea water as a reducing agent;
Urea water injection means for injecting urea water to the selective reduction catalyst;
A capacitance detecting means for detecting a capacitance of the selective reduction catalyst;
Internal temperature calculation means for calculating the internal temperature of the selective reduction catalyst based on the capacitance input from the capacitance detection means;
A deterioration state estimation means for estimating a deterioration state of the selective reduction catalyst based on the internal temperature input from the internal temperature calculation means;
Injection control means for controlling urea water injection of the urea water injection means based on at least a predetermined reference injection amount set in accordance with the operating state of the internal combustion engine;
An exhaust emission control device comprising: an injection amount correction unit that corrects the reference injection amount in accordance with a deterioration state of the selective reduction catalyst input from the deterioration state estimation unit. The injection amount correction means obtains the reducing agent adsorption capacity of the selective reduction catalyst based on the deterioration state input from the deterioration state estimation means, and uses the injection correction amount according to the reducing agent adsorption capacity as the reference. The exhaust emission control device according to claim 1, wherein the injection amount is corrected. 3. The exhaust emission control device according to claim 1, wherein the capacitance detection unit includes at least a pair of electrodes that are disposed to face each other with one or more partition walls in the selective reduction catalyst to form a capacitor.

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