JP6179378B2 - Exhaust purification device - Google Patents

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.

If the urea water injection amount becomes excessive and exceeds the NH ₃ adsorption capacity of the SCR, excess NH ₃ slips from the SCR and is released to the atmosphere, which is not preferable. Therefore, the NH ₃ adsorption amount in the SCR is estimated based on the difference between the NH ₃ amount supplied to the SCR and the detection value of the NH ₃ sensor provided at the SCR outlet, and the estimated NH ₃ adsorption amount is A technique for appropriately adjusting the urea water injection amount accordingly is known (see, for example, Patent Document 1).

JP 2003-293737 A

However, NH ₃ sensor, etc. can not be provided directly in the interior in SCR, there is NH ₃ challenges can not be accurately grasped adsorption amount in SCR. Therefore, the sensor value of the NH ₃ sensor or, in the technique of estimating the adsorbed NH ₃ amount from the sensor value of the NOx sensor, the response of a chemical reaction delay or sensor in the SCR delay, by reaction of the NOx sensor and the NOx and NH _3, There is a possibility that optimum control of the urea water injection amount according to the actual NH ₃ adsorption amount cannot be performed depending on the operation region.

An object of the present invention is to detect the NH ₃ adsorption amount of the SCR with high accuracy and to optimize the urea water injection amount.

  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 Based on the electric capacity, the reducing agent adsorption amount calculating means for calculating the reducing agent adsorption amount of the selective reduction catalyst, and at least based on a predetermined reference injection amount set according to the operating state of the internal combustion engine, An injection control unit that controls urea water injection of the urea water injection unit, and an injection amount correction unit that corrects the reference injection amount based on the reducing agent adsorption amount input from the reducing agent adsorption amount calculation unit. Features To.

  The apparatus further comprises an internal temperature calculating means for calculating an internal temperature of the selective reduction catalyst based on the capacitance input from the capacitance detecting means, and the injection amount correcting means includes the reducing agent adsorption amount. The reference injection amount is corrected based on the difference between the reducing agent adsorption amount input from the calculating means and the reductant adsorbable amount of the selective reduction catalyst according to the internal temperature input from the internal temperature calculating means. You may do it.

  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 NH ₃ adsorption amount of the SCR can be detected with high accuracy, and the urea water injection amount can be optimized.

1 is a schematic overall configuration diagram showing an exhaust emission control device for an internal combustion engine according to an 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 a capacitance · NH ₃ adsorption amount map in the present embodiment. It is a diagram illustrating an example of the NH ₃ target adsorption amount map in the present embodiment. It is a flowchart which shows the control content of this embodiment.

  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 uses the SCR internal temperature calculation unit 51, the NH ₃ adsorption amount calculation unit 52, the urea water injection control unit 53, and the injection amount correction unit 54 as some functional elements. Have. 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 NH ₃ adsorption amount calculation unit 52 is an example of the reducing agent adsorption amount calculation means of the present invention. Based on the capacitance C between the electrodes 27, the NH ₃ adsorption amount ST _NH3 adsorbed on the SCR 22 is calculated. Calculate. Since NH ₃ has a high dielectric constant ε, the capacitance C between the electrodes 27 increases as NH ₃ adsorption proceeds in the SCR 22 (see Formula 1). That is, if the electrostatic capacitance C between the electrodes 27 is detected, the NH ₃ actual adsorption amount ST _NH3 of the SCR 22 can be calculated.

The ECU 50 stores a capacitance / NH ₃ adsorption amount map (see, for example, FIG. 4) that shows the relationship between the capacitance C and the NH ₃ actual adsorption amount obtained in advance through experiments or the like. The NH ₃ adsorption amount calculation unit 52 calculates the current NH ₃ actual adsorption amount ST _NH3 by reading a value corresponding to the capacitance C between the electrodes 27 from the capacitance / NH ₃ adsorption amount map. Note that the calculation of the NH ₃ actual adsorption amount ST _NH3 is not limited to a map, and may be obtained from 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 _SCR and the actual NH ₃ adsorption amount ST _NH3 input from the NH ₃ adsorption amount calculation unit 52.

More specifically, the ECU 50 has an NH ₃ target adsorption amount map (for example, a relationship between the internal temperature T _{SCR of the SCR} 22 and an NH ₃ adsorption possible amount (hereinafter referred to as a target adsorption amount ST _{NH3_TAG} ) created in advance by experiments or the like. (See FIG. 5).

The injection amount correction unit 54 reads an adsorption amount deviation ΔST _NH3 between the target adsorption amount ST _{NH3_TAG} corresponding to the current internal temperature T _SCR and the current NH ₃ actual adsorption amount ST _NH3 from the NH ₃ target adsorption amount map. Based on the injection correction amount ΔINJ corresponding to this adsorption amount deviation ΔST _NH3 , the basic injection amount INJ _{U_std} is corrected to increase or decrease (INJ _{U_exh} = INJ _{U_std} +/− ΔINJ). The corrected urea water injection is executed by increasing or decreasing the energization pulse width of each injection applied to the injector (not shown) of the urea water injection device 21 or increasing or decreasing the number of injections.

  Next, based on FIG. 6, 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 NH ₃ actual adsorption amount ST _{NH3 of the SCR} 22 is calculated based on the capacitance C between the electrodes 27. Is calculated.

In S130, the NH ₃ target adsorption amount map (FIG. 5), the target adsorption amount ST _{NH3_TAG} corresponding to the calculated internal temperature T _SCR and Oyobi in S110, the adsorption of NH ₃ actual adsorption amount ST _NH3 calculated in S120 A quantity deviation ΔST _NH3 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. When 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 increased or decreased 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.

Conventionally, as a technique for suppressing the NH ₃ slip of the SCR, the amount of NH ₃ supplied to the SCR and the detection value of the NH ₃ sensor at the SCR outlet are compared to estimate the amount of NH ₃ adsorption in the SCR, A technique for adjusting the urea water injection amount in accordance with the estimated NH ₃ adsorption amount is known. However, in the method of estimating from the sensor value of the NH ₃ sensor, the actual NH ₃ adsorption amount in the SCR cannot be accurately grasped, and the urea water injection amount may not be optimally controlled.

On the other hand, in the exhaust purification apparatus of the present embodiment, the actual NH ₃ adsorption amount in the SCR 22 is directly calculated based on the capacitance C between the electrodes 27, and the accurate NH ₃ actual adsorption amount and NH _{3 The} urea water injection amount is corrected in accordance with the difference from the target adsorption amount (adsorbable amount).

Therefore, according to the exhaust gas purification apparatus of the present embodiment, it is possible to accurately control the urea water injection amount in accordance with the actual NH ₃ adsorption amount of the SCR 22, and effectively prevent the NH ₃ slip of the SCR 22. it can. In addition, since the NH ₃ adsorption amount of the SCR 22 is effectively maintained at the target value (adsorbable amount), the NOx reduction and purification rate can be reliably improved. 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 NH ₃ adsorption amount 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;
Reducing agent adsorption amount calculating means for calculating the reducing agent adsorption amount of the selective reduction catalyst based on the capacitance input from the capacitance detecting 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 correcting unit that corrects the reference injection amount based on a reducing agent adsorption amount input from the reducing agent adsorption amount calculating unit. An internal temperature calculating means for calculating the internal temperature of the selective reduction catalyst based on the capacitance input from the capacitance detecting means;
The injection amount correction means includes a reducing agent adsorption amount input from the reducing agent adsorption amount calculation means, and a reducing agent adsorption possible amount of the selective reduction catalyst according to an internal temperature input from the internal temperature calculation means. The exhaust emission control device according to claim 1, wherein the reference injection amount is corrected based on a difference between the two. 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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