JP2021050605A - Exhaust purification device - Google Patents

Abstract

To provide an exhaust purification device which enables an NH3 absorption amount to be accurately estimated while preventing a model calculation from getting complicated.SOLUTION: An exhaust purification device 100 comprises: an SCR 9c which reduces NOx included in exhaust gas of an engine 1; an addition valve 9e which adds urea water to the SCR 9c; an upstream NOx sensor 23 which acquires an upstream NOx amount; a downstream NOx sensor 25 which acquires a downstream NOx amount; an exhaust temperature sensor 24 which acquires a temperature of the SCR 9c; and a reducing agent control section 12 which estimates an NH3 absorption amount using a predetermined model of the SCR 9c on the basis of the upstream NOx amount, the downstream NOx amount and the temperature of the SCR 9c. The reducing agent control section 12 estimates the NH3 absorption amount using the model including a reaction speed equation representing a reaction speed when NH3 undergoes absorption or desorption with respect to an absorption site of NH3 on the SCR 9c. The reaction speed equation includes a proportionality coefficient to be set in accordance with the temperature of the SCR 9c.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification device.

Conventionally, as an exhaust purification device that is provided with an addition valve that adds urea water to the exhaust gas and a selective reduction catalyst located downstream of the addition valve to purify nitrogen oxides (NOx) contained in the exhaust gas, for example, Patent Documents. The device described in 1 is known. In the apparatus described in Patent Document 1, the concentration of ammonia in the exhaust gas that has passed through the selective reduction catalyst is estimated using a model.

Japanese Unexamined Patent Publication No. 2018-100615

In the exhaust gas purifying apparatus as described above, may be calculated using the model estimates the adsorbed NH ₃ amount to the reducing catalyst. In _{order to improve the calculation accuracy of the estimated value of NH 3} adsorption amount, as a general method, a model in which the reaction formula is subdivided or added or a correction term of the reaction rate formula is added is used as a general method. Can be considered. However, in this method, the amount of calculation increases due to the complexity of model calculation.

An object of the present invention is to provide an exhaust gas purification device capable of accurately calculating an estimated value of _{NH 3 adsorption amount while suppressing the complexity of model calculation.}

The exhaust purification device according to one aspect of the present invention is provided in the exhaust passage of the internal combustion engine, has a reduction catalyst for reducing NOx contained in the exhaust gas of the internal combustion engine, and is provided on the upstream side of the reduction catalyst. An addition valve for adding water, an upstream NOx amount acquisition unit for acquiring the amount of NOx contained in the exhaust gas on the upstream side of the reduction catalyst, and an amount of NOx contained in the exhaust gas on the downstream side of the reduction catalyst. A downstream NOx amount acquisition unit that acquires a certain downstream NOx amount, a catalyst temperature acquisition unit that acquires the catalyst temperature of the reduction catalyst, and a preset reduction catalyst based on the upstream NOx amount, the downstream NOx amount, and the catalyst temperature. The adsorption amount estimation unit includes an adsorption amount estimation unit that estimates the _{NH 3} adsorption amount using a model, and the adsorption amount estimation unit represents the reaction rate at which _{NH 3} is adsorbed or desorbed from the adsorption site _{of NH 3 on the reduction catalyst. The NH 3} adsorption amount is estimated using a model including a reaction rate formula, and the reaction rate formula includes a proportional coefficient set according to the catalyst temperature.

In the exhaust gas purification device according to one embodiment of the present invention, by using a model including a rate equation that contains a proportionality coefficient set according to the catalyst temperature, NH ₃ adsorption amount is estimated. Therefore, by adjusting the proportionality coefficient according to the catalyst temperature, it is possible to appropriately set the reaction rate at which _{NH 3} is adsorbed or desorbed from the adsorption site _{of NH 3 on the reduction catalyst according to the catalyst temperature.} It becomes. As a result, it is possible to accurately calculate the estimated value of the _{NH 3} adsorption amount while suppressing the complexity of the model calculation as compared with the case where the proportionality coefficient is set regardless of the catalyst temperature.

In one embodiment, the rate equation may include exponential parameters set according to the catalyst temperature. In this case, by adjusting the exponential parameter according to the catalyst temperature, the reaction rate can be calculated more appropriately according to the catalyst temperature.

In one embodiment, the rate equation _{may represent the rate at which NH 3} adsorbs or desorbs to a single adsorption site on a reduction catalyst. In this case, the complexity of the model calculation can be suppressed as compared with the case where the reaction rate in the reaction rate equation _{represents the adsorption or desorption of NH 3 to a plurality of adsorption sites.}

According to the present invention, while suppressing the complexity of the model calculation, it becomes possible to accurately calculate the estimated value of the adsorbed NH ₃ amount.

It is a schematic block diagram of the engine system provided with the exhaust gas purification device of embodiment. It is a figure which illustrates the internal structure of the catalytic converter of FIG. It is a conceptual diagram which shows the adsorption or desorption to the adsorption site in a model. (A) is a comparative example of a reaction equation and a reaction rate equation representing the reaction of adsorption or desorption to the adsorption site of FIG. (B) is an example of a reaction rate equation in the exhaust gas purification device of the embodiment. Is a diagram representing the adsorbed NH ₃ amount when the rate equations of FIG. 4 (a). It is a diagram representing the adsorbed NH ₃ amount when the reaction rate equation in Figure 4 (b).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicate description will be omitted.

[Engine system configuration]
FIG. 1 is a schematic configuration diagram of an engine system including the exhaust gas purification device of the embodiment. As shown in FIG. 1, the exhaust gas purification device 100 is mounted on a vehicle such as a truck and purifies the exhaust gas discharged from a diesel engine (hereinafter, simply referred to as an engine) 1 which is an internal combustion engine. The engine 1 has a plurality of injectors 2 that inject fuel into a plurality of cylinders. The vehicle on which the exhaust gas purification device 100 is mounted may be a large vehicle such as a tractor or a bus, a medium-sized vehicle, a small vehicle, and a light vehicle, in addition to a truck.

The intake passage 3 of the engine 1 is provided with an air cleaner 4, a turbocharger compressor 5, and an intercooler 6 in this order from the upstream side in the flow direction of the intake air. The engine 1 includes an EGR unit 7 that recirculates a part of the exhaust gas as EGR (exhaust gas recirculation) gas. An exhaust passage 8 for exhausting exhaust gas is connected to the engine 1. A catalytic converter 9 is provided in the exhaust passage 8.

FIG. 2 is a diagram illustrating the internal configuration of the catalytic converter 9 of FIG. As shown in FIGS. 1 and 2, in the catalyst converter 9, the oxidation catalyst [DOC: Diesel Oxidation Catalyst] 9a and the diesel exhaust particulate filter [DPF] are sequentially arranged from the upstream side to the downstream side in the exhaust gas flow direction. : Diesel Particulate Filter] 9b, selective reduction catalyst [SCR: Selective Catalytic Reduction] (reduction catalyst) 9c, and NH ₃ slip catalyst 9d are arranged.

DOC9a oxidizes and purifies HC, CO, etc. contained in the exhaust gas. DPF9b removes PM from the exhaust gas by collecting particulate matter [PM: Particulate Matter] contained in the exhaust gas. SCR9c reduces and purifies NOx contained in the exhaust gas. The NH ₃ slip catalyst 9d oxidizes and purifies _{NH 3} contained in the exhaust gas that has passed through the SCR 9c.

The exhaust gas purification device 100 includes an addition valve 9e arranged on the upstream side of the SCR9c, specifically, between the DPF9b and the SCR9c in the catalytic converter 9. The addition valve 9e is connected to the urea water tank via a supply pipe (not shown), and urea water is added to the SCR9c. When urea water is added to SCR9c by the addition valve 9e, the urea water becomes NH ₃ and is adsorbed on SCR 9c, and the NH ₃ reacts with NOx in the exhaust gas to reduce NOx.

The exhaust purification device 100 includes an air flow sensor 21, an engine state sensor 22, an upstream NOx sensor (upstream NOx amount acquisition unit) 23, an exhaust temperature sensor (catalyst temperature acquisition unit) 24, and a downstream NOx sensor (downstream NOx amount acquisition unit). A unit) 25 and an ECU [Electronic Control Unit] 10. The sensors 21 to 25 and the addition valve 9e are connected to the ECU 10.

The air flow sensor 21 is, for example, a detector provided in the intake passage 3 of the engine 1 to detect the intake air amount of the engine 1. The air flow sensor 21 transmits a detection signal of the detected intake air amount to the ECU 10.

The engine state sensor 22 is a sensor for acquiring the engine state. The engine state sensor 22 includes, for example, a detector that detects the rotation speed of the engine 1 (engine rotation speed), the load of the engine 1, and the like. The engine state sensor 22 transmits a detection signal regarding the detected engine state to the ECU 10.

The upstream NOx sensor 23 is a detector provided between the DPF 9b and the addition valve 9e in the catalytic converter 9 and detects the amount of upstream NOx. The upstream NOx amount is the NOx amount (for example, NOx concentration) contained in the exhaust gas upstream of the SCR9c. The upstream NOx sensor 23 transmits a detection signal of the detected upstream NOx amount to the ECU 10.

The exhaust temperature sensor 24 is a detector that detects the temperature of the exhaust gas between the DPF 9b and the SCR 9c in the catalytic converter 9. The exhaust temperature sensor 24 transmits the detected exhaust temperature detection signal to the ECU 10.

The downstream NOx sensor 25 is _{a detector provided downstream of the NH 3} slip catalyst 9d in the catalyst converter 9 (that is, on the downstream side of the SCR 9c) and detects the amount of downstream NOx. The amount of downstream NOx is the amount of NOx (NOx concentration) contained in the exhaust gas downstream of the _{NH 3 slip catalyst 9d.} The downstream NOx sensor 25 transmits a detection signal of the detected downstream NOx amount to the ECU 10.

The ECU 10 is an electronic control unit having a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a CAN [Controller Area Network] communication circuit, and the like. The ECU 10 realizes various functions by loading the program stored in the ROM into the RAM and executing the program loaded in the RAM in the CPU. The ECU 10 may be composed of a plurality of electronic control units.

The ECU 10 has an engine state acquisition unit (upstream NOx amount acquisition unit, catalyst temperature acquisition unit) 11 and a reducing agent control unit (adsorption amount estimation unit) 12 as functional configurations.

The engine state acquisition unit 11 acquires various engine states based on the detection signals of the airflow sensor 21, the engine state sensor 22, the upstream NOx sensor 23, the exhaust temperature sensor 24, and the downstream NOx sensor 25. The engine state acquisition unit 11 acquires, for example, the intake air amount of the engine 1 as the exhaust flow rate in the SCR 9c based on the detection signal of the air flow sensor 21.

The engine state acquisition unit 11 acquires the amount of upstream NOx, which is the amount of NOx contained in the exhaust gas on the upstream side of the SCR9c, based on the detection signal of the upstream NOx sensor 23. Alternatively, the engine state acquisition unit 11 may calculate the fuel injection amount from the engine rotation speed and the load, and acquire an estimated value of the upstream NOx amount from the fuel injection amount and the intake air amount. In this case, the upstream NOx sensor 23 may be omitted.

The engine state acquisition unit 11 acquires the amount of downstream NOx, which is the amount of NOx contained in the exhaust gas on the downstream side of the SCR9c, based on the detection signal of the downstream NOx sensor 25.

The engine state acquisition unit 11 acquires the temperature of the exhaust gas between the DPF 9b and the SCR 9c in the catalyst converter 9 as the temperature of the SCR 9c (catalyst temperature) based on the detection signal of the exhaust temperature sensor 24. Alternatively, the engine state acquisition unit 11 may calculate the fuel injection amount from the engine speed and the load, and acquire the estimated temperature (catalyst temperature) of the SCR 9c from the fuel injection amount and the intake air amount. In this case, the exhaust temperature sensor 24 may be omitted.

The reducing agent control unit 12 calculates the amount of urea water added by the addition valve 9e based on the amount of upstream NOx. The reducing agent control unit 12 acquires, for example, the amount of urea water added to purify the NOx contained in the exhaust gas upstream of the SCR9c according to the amount of upstream NOx. The reducing agent control unit 12 adds urea water to the addition valve 9e at a predetermined addition timing with the calculated addition amount of urea water. The reducing agent control unit 12 may perform feedback control by calculating a correction value of the amount of urea water added by the addition valve 9e based on the detection result of the downstream NOx sensor 25.

Here, the reducing agent control unit 12 calculates an estimated value of the _{NH 3} adsorption amount using a preset model of SCR9c based on the amount of upstream NOx, the amount of downstream NOx, and the temperature of SCR9c. The _{amount of NH 3} adsorbed may be, for example, the adsorption rate of _{NH 3 on SCR9c.} In the following description, it cites NH ₃ adsorption rate as an example and is not limited to this.

The model here is a model simulating the reaction related to the adsorption or desorption of _{NH 3 to SCR9c.} For example, the model is configured to include, for example, the exhaust flow rate derived from the results of experiments and simulations performed in advance, the temperature of SCR9c, the target addition amount, and the like as parameters. The model has _{a reaction rate formula that expresses the reaction rate of each chemical reaction of NH 3} adsorption reaction, NH ₃ elimination reaction, NH ₃ oxidation reaction, NO oxidation reaction, and NOx reduction reaction by the Arenius formula. are doing. That is, the reducing agent control unit 12 estimates the _{NH 3} adsorption rate using a model including a reaction rate equation representing the reaction rate at which _{NH 3} is adsorbed or desorbed from the adsorption site _{of NH 3 on SCR9c.}

For example, the _{rate equation representing the reaction rate at which NH 3} adsorbs or desorbs may represent the reaction rate at which NH ₃ adsorbs or desorbs to a single adsorption site on the SCR9c. FIG. 3 is a conceptual diagram showing adsorption or desorption to an adsorption site in the model. As shown in FIG. 3, the model M, a single adsorption site S are defined on SCR9c, NH ₃ and a reaction rate r _ad to adsorb for this adsorption sites S, in the adsorption sites S The reaction rate r _de in which the adsorbed NH ₃ is eliminated can be defined.

As shown in FIG. 4A, the reaction in _{which NH 3 is adsorbed on the adsorption site S is}
NH ₃ + S → NH ₃ (S)
It can be expressed as. _{The reaction in which NH 3} adsorbed on the adsorption site S is eliminated is
NH ₃ (S) → NH ₃ + S
It can be expressed as. In this case, the reaction rate _rad and the reaction rate rd _de can be generally expressed as shown in (Equation 1) and (Equation 2) of FIG. 4 (a), respectively. (Equation 1) and (Equation 2) _{represent the reaction rate at which NH 3} is adsorbed or desorbed on a single adsorption site S on SCR9c. In this case, as compared with the case where a plurality of adsorption sites S are defined and the NH ₃ adsorption rate is estimated, the calculation complexity of the model can be suppressed and the calculation load is lightened, so that the mountability on the ECU 10 is good. Can be done.

In FIGS. 4A and 4B, "S" in the reaction formula means the adsorption site S in FIG. 3, K means a frequency factor, E means an activation temperature, and C means an activation temperature. It means the concentration, θ means the NH ₃ adsorption rate, and ε means the correction coefficient. The subscript ad means that it is a parameter in the reaction [adsorption] in _{which NH 3} is adsorbed to the adsorption site S, _{and the subscript de means that NH 3} adsorbed on the adsorption site S is eliminated. It means that it is a parameter in the desorption reaction. Here, in the general (Equation 1) and (Equation 2), the frequency factor K and the activation temperature E are set to values that do not depend on the temperature of SCR9c.

Here, when estimating the NH ₃ adsorption rate by using a general formula (1) and the reaction rate _{r ad} and reaction rate _{r de} (Formula 2), at a temperature of a portion of SCR9c, other SCR9c compared with the temperature conditions, the estimated value of the NH ₃ adsorption rate may not be accurately calculated. For example, as shown in FIG. 5, when the temperature of SCR9c is 100 ° C., _{the estimated value of NH 3} adsorption rate (white circle in FIG. 5) is higher than that when the temperature of SCR9c is 200 ° C. to 500 ° C. It _{may happen that the NH 3} adsorption rate is not calculated accurately with respect to the measured value (black square mark in FIG. 5). Such estimation result, in the estimation method of particular estimate NH ₃ adsorption rate defines a single adsorption sites S, common when employing (Equation 1) and (Equation 2), the actual It can be considered that the adsorption reaction or elimination reaction of NH _{3 has not been properly described.} However, in the estimation method in which a plurality of adsorption sites S are defined and the NH ₃ adsorption rate is estimated, the calculation of the model becomes complicated and the calculation load is large. Therefore, _{the estimation accuracy of the NH 3} adsorption rate is improved and the NH 3 adsorption rate is mounted on the ECU 10. There is a possibility that it is incompatible with sex.

Therefore, in the exhaust purification device 100 of the present embodiment, _{while adopting an estimation method in which a single adsorption site S is defined and the NH 3} adsorption rate is estimated, (Equation 3) and (Equation 4) of FIG. 4 (b) are adopted. as shown in), the reaction rate _{r ad} and reaction rate _{r de} of the right side, the frequency factor K (Tc) is a function of the temperature of the SCR9c. That is, the reaction rate equations (Equation 3) and (Equation 4) include a frequency factor K (Tc) which is a proportional coefficient set according to the temperature of SCR9c.

Thus, since the frequency factor K (Tc) is variable depending on the temperature of SCR9c, at a temperature of a portion of SCR9c, compared to the temperature of the other SCR9c, an estimate of the NH ₃ adsorption rate It is possible to suppress that the calculation is not accurate. For example, previously performed from the results of experiments or simulations by setting the frequency factor K (Tc) in accordance with the temperature of SCR9c, adsorption or desorption reaction kinetics r _ad and reaction rate r _de a reality NH ₃ It becomes possible to approach. As a method of setting the frequency factor K (Tc) according to the temperature of the SCR9c, a predetermined temperature threshold value is set, and the value of the frequency factor K (Tc) depends on whether or not the temperature of the SCR9c is equal to or higher than the temperature threshold value. May be changed, or a pre-stored map with the temperature of SCR9c as an argument may be read out. As a result, for example, as shown in FIG. 6, even when the temperature of SCR9c is 100 ° C., _{the estimated value of NH 3} adsorption rate (FIG. 6) is the same as when the temperature of SCR9c is 200 ° C. to 500 ° C. (White circle mark) can _{be calculated accurately with respect to the measured value of NH 3} adsorption rate (black square mark in FIG. 6).

Incidentally, the reaction rate equation of the right side of the reaction rate r _ad and reaction rate r _de may comprise an activation temperature E (Tc) is an index parameter that is set according to the temperature of SCR9c. The activation temperature E (Tc) can be set according to the temperature of SCR9c by changing the value using the temperature threshold value or reading the map in the same manner as the method for setting the frequency factor K (Tc) described above. it can.

[Action and effect]
As described above, according to the exhaust gas purification device 100 according to the present embodiment, the model M including the reaction rate equations (Equation 3) and (Equation 4) including the frequency factor K (Tc) set according to the temperature of the SCR9c is used. Therefore, the amount of NH _{3 adsorbed is estimated.} Therefore, by adjusting accordingly the frequency factor K a (Tc) to a temperature of SCR9c, the reaction rate _{r ad} and reaction rate _{r de} of NH ₃ is adsorbed or desorbed against adsorption site S of NH ₃ on SCR9c It is possible to set appropriately according to the temperature of SCR9c. As a result, compared to the case where the frequency factor K is set regardless of the temperature of SCR9c, while suppressing the complexity of the model calculation, it becomes possible to accurately calculate the estimated value of the adsorbed NH ₃ amount ..

According to the exhaust gas purification device 100, the reaction rate equations (Equation 3) and (Equation 4) include an activation temperature E (Tc) set according to the temperature of the SCR9c. Thus, by adjusting accordingly the activation temperature E and (Tc) to a temperature of SCR9c, it is possible to calculate more appropriate reaction rate _{r ad} and reaction rate _{r de} according to the temperature of SCR9c.

According to the exhaust purification apparatus 100, the reaction rate equation (Equation 3) and (Equation 4), NH ₃ represents the reaction rate _{r ad} and reaction rate _{r de} adsorption or desorption into a single adsorption sites on SCR9c .. As a result, the complexity of the calculation of the model can be suppressed as compared with the case where the reaction rate in the reaction rate equation _{represents the adsorption or desorption of NH 3 to a plurality of adsorption sites.}

[Modification example]
Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments.

In the above embodiment, since the mountability to the ECU 10 is relatively emphasized, the reaction rate equations (Equation 3) and (Equation 4) are reactions in which NH ₃ is adsorbed or desorbed on a single adsorption site on the SCR9c. The rate _rad and the reaction rate r _de were shown. However, even when, for example, a model in which adsorption or desorption to a plurality of adsorption sites is already used and a model in which the frequency factor K and the activation temperature E are set to values independent of the temperature of SCR9c is used, the frequency is also used. Factor K (Tc) may be adjusted according to the temperature of SCR9c. In this case, as compared with the case where the number of multiple adsorption sites of the model is further increased to _{improve the calculation accuracy of the estimated value of the NH 3 adsorption amount, the NH 3} adsorption is suppressed while suppressing the complexity of the model calculation. The estimated value of the quantity can be calculated accurately.

In the above embodiment, the catalyst converter 9 in which the DOC9a, the DPF9b, the SCR9c, and the NH ₃ slip catalyst 9d are integrally arranged has been exemplified, but the present invention is not limited thereto.

In the above embodiment, the diesel engine 1 is exemplified as the internal combustion engine, but other internal combustion engines such as a gasoline engine may be used.

8 ... Exhaust passage, 9c ... SCR (reduction catalyst), 9e ... Addition valve, 12 ... Reducing agent control unit (adsorption amount estimation unit), 23 ... Upstream NOx sensor (upstream NOx amount acquisition unit), 24 ... Exhaust temperature sensor ( catalyst temperature acquiring unit), 25 ... downstream NOx sensor (downstream NOx amount acquiring unit), 100 ... exhaust gas purifying apparatus, M ... _{model, r} ad, r _{de ...} reaction rate, S ... adsorption sites.

Claims (3)

A reduction catalyst provided in the exhaust passage of the internal combustion engine to reduce NOx contained in the exhaust gas of the internal combustion engine, and
An addition valve provided on the upstream side of the reduction catalyst and adding urea water to the reduction catalyst.
An upstream NOx amount acquisition unit that acquires an upstream NOx amount, which is the amount of NOx contained in the exhaust gas on the upstream side of the reduction catalyst, and an upstream NOx amount acquisition unit.
A downstream NOx amount acquisition unit that acquires a downstream NOx amount, which is the amount of NOx contained in the exhaust gas on the downstream side of the reduction catalyst, and a downstream NOx amount acquisition unit.
A catalyst temperature acquisition unit that acquires the catalyst temperature of the reduction catalyst,
Wherein the upstream NOx amount based on downstream NOx amount and said catalyst temperature, and an adsorption amount estimating unit for estimating the adsorbed NH ₃ amount using the model of a preset the reducing catalyst,
The adsorption amount estimation unit is
_{The amount of NH 3} adsorbed was estimated using the model including the reaction rate equation representing the reaction rate at which _{NH 3} is adsorbed or desorbed from the adsorption site _{of NH 3} on the reduction catalyst.
The reaction rate equation is an exhaust gas purification device including a proportional coefficient set according to the catalyst temperature. The exhaust gas purification device according to claim 1, wherein the reaction rate equation includes an exponential parameter set according to the catalyst temperature. The exhaust gas purification apparatus according to claim 1 or 2, wherein the reaction rate equation represents a reaction rate at which NH _{3 is adsorbed or desorbed from a single adsorption site on the reduction catalyst.}

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