JP7192522B2 - Exhaust purification device for internal combustion engine and vehicle - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to an exhaust purification device for an internal combustion engine and a vehicle.

An SCR catalyst having a NOx selective catalytic reduction (hereinafter referred to as "SCR catalyst") that selectively reduces NOx in exhaust gas using ammonia (NH3) as a reducing agent as an exhaust purification device for an internal combustion engine. Exhaust gas purification systems are known (see, for example, Patent Literature 1).

In this SCR catalyst exhaust purification system, in order to effectively function the NOx reduction characteristics of the SCR catalyst, the amount of ammonia stored in the SCR catalyst (hereinafter referred to as "ammonia storage amount") is controlled to an appropriate amount. There is a need to. As a control method, the control unit sequentially predicts the amount of ammonia consumed by the SCR catalyst based on various sensor information, and supplies the insufficient amount of ammonia to the SCR catalyst as urea water, which is a precursor. method is common.

JP 2012-189007 A

However, the NOx purification reaction in the SCR catalyst is complicated, and it is difficult to accurately calculate the amount of ammonia consumed based on the NOx purification reaction. In addition, the predicted ammonia consumption amount includes errors caused by errors in the injection amount of the urea water injection device, detection errors of the NOx sensor, and the like.

Therefore, it is not uncommon for the estimated value of the ammonia storage amount estimated by the calculation of the control unit to deviate from the actual value. For example, when a state in which the amount of ammonia stored in the SCR catalyst is insufficient (hereinafter referred to as an "understorage state") occurs, the NOx purification rate of the SCR catalyst decreases due to the lack of ammonia that causes the NOx purification reaction. will do.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide an internal combustion engine exhaust purification device and a vehicle that enable highly accurate estimation of the ammonia storage amount in the SCR catalyst.

The main disclosure that solves the above-mentioned problems is
An exhaust purification device disposed in an exhaust passage of an internal combustion engine,
an SCR (Selective Catalytic Reduction) catalyst disposed in the exhaust passage;
a urea water injection device for injecting urea water upstream of the SCR catalyst in the exhaust passage;
a control device for estimating an ammonia storage amount in the SCR catalyst and controlling the urea water injection amount of the urea water injection device based on the estimated value of the ammonia storage amount;
with
The control device is
a first estimation unit that estimates the current amount of ammonia storage based on the transition of the urea water injection amount and the transition of the ammonia consumption amount in the SCR catalyst;
a second estimation unit that estimates the current amount of ammonia storage based on the NOx purification rate of the SCR catalyst, the temperature of the SCR catalyst, and the exhaust gas flow rate in the exhaust passage, which are detected at the current time. ,
It is an exhaust purification device.
In addition, the main disclosure that solves the above-mentioned problems is
An exhaust purification device disposed in an exhaust passage of an internal combustion engine,
an SCR (Selective Catalytic Reduction) catalyst disposed in the exhaust passage;
a urea water injection device for injecting urea water upstream of the SCR catalyst in the exhaust passage;
a control device for estimating an ammonia storage amount in the SCR catalyst and controlling the urea water injection amount of the urea water injection device based on the estimated value of the ammonia storage amount;
with
Based on the currently detected NOx purification rate of the SCR catalyst, the temperature of the SCR catalyst, and the exhaust gas flow rate in the exhaust passage, the control device uses the following formula (1) to determine the SCR estimating the current amount of ammonia storage in the catalyst;
It is an exhaust purification device.

Also, in other aspects,
A vehicle including the above exhaust purification device.

According to the exhaust purification device according to the present disclosure, the ammonia storage amount in the SCR catalyst can be estimated with high accuracy.

A diagram showing an example of the configuration of an exhaust purification device according to one embodiment. 1 is a block diagram showing an example of the configuration of an ECU according to one embodiment; FIG. FIG. 4 is a diagram showing an example of the relationship between the NOx purification rate of the SCR catalyst and the ammonia storage amount of the SCR catalyst; A diagram showing an example of a specific operation flow performed by the correction command unit In the exhaust purification device according to one embodiment, the behavior of the urea water injection amount in the urea water injection device (FIG. 5A), the behavior of the ammonia storage amount of the SCR catalyst (FIG. 5B), and the behavior of the NOx purification rate of the SCR catalyst ( Fig. 5C) Time chart showing an example Diagram for explaining the method of setting the frequency factor, storage order, and exhaust gas flow rate order in formula (1)

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functions are denoted by the same reference numerals, thereby omitting redundant description.

[Configuration of exhaust gas purification device]
Hereinafter, with reference to FIG. 1, the configuration of an exhaust purification system according to one embodiment will be described.

FIG. 1 is a diagram showing an example of the configuration of an exhaust purification device U according to this embodiment.

An exhaust purification device U according to this embodiment is mounted on a vehicle such as a truck, for example, and purifies NOx in the exhaust gas of the engine 10 .

The engine 10 includes, for example, a combustion chamber and a fuel injection device (not shown) that injects fuel into the combustion chamber. Engine 10 combusts and expands a mixture of fuel and air in a combustion chamber to generate power. The engine 10 includes an intake passage (for example, an intake pipe) 20 for introducing air into the combustion chamber, and an exhaust passage (for example, an exhaust pipe) 30 for discharging exhaust gas after combustion from the combustion chamber to the outside of the vehicle. and are connected.

Note that the engine 10 according to this embodiment is a four-cylinder engine, and an intake passage 20 branches into four combustion chambers via an intake manifold, and the four combustion chambers flow into an exhaust passage 30 via an exhaust manifold. It is configured to merge.

The exhaust purification device U includes an SCR catalyst 40 , an aqueous urea injection device 50 , various sensors 61 to 64 and an ECU (Electronic Control Unit) 100 .

The SCR catalyst 40 adsorbs ammonia hydrolyzed by the urea water supplied from the urea water injection device 50, and selectively reduces and purifies NOx from the exhaust gas with the adsorbed ammonia. As the SCR catalyst 40, a known SCR catalyst can be used. For example, a ceramic carrier having a NOx reduction catalyst such as Fe zeolite, Cu zeolite, or vanadium carried on the surface thereof can be used. As the SCR catalyst 40, a type that converts urea water into ammonia on the catalyst may be used.

The urea water injection device 50 injects urea water upstream of the SCR catalyst 40 in the exhaust passage 30 . The urea water injection device 50 includes, for example, a urea water addition valve 51 , a urea water tank 52 and a supply pump 53 .

In the urea water injection device 50 , urea water pressure-fed from the urea water tank 52 by the supply pump 53 is injected into the exhaust passage 30 from the urea water addition valve 51 . The urea water injected into the exhaust passage 30 from the urea water addition valve 51 is hydrolyzed by the high temperature of the exhaust gas, converted into ammonia, and supplied to the SCR catalyst 40 . Then, the ammonia is adsorbed on the SCR catalyst 40 and reacts with NOx by the action of the SCR catalyst 40 to reduce and purify NOx.

The amount of urea water injected from the urea water injection device 50 into the exhaust passage 30 is adjusted by adjusting the opening of the urea water addition valve 51 . The opening degree of the urea water addition valve 51 is controlled by a control signal output from the ECU 100 (urea water injection control section 103).

Various sensors 61 to 64 are provided to detect the state of the exhaust gas flowing through the exhaust passage 30, the state of the SCR catalyst 40, and the like. Specifically, the exhaust passage 30 is equipped with a first NOx sensor 61, a second NOx sensor 62, a temperature sensor 63, a flow rate sensor 64, and the like.

The first NOx sensor 61 is arranged upstream of the SCR catalyst 40 in the exhaust passage 30 and detects the amount of NOx flowing into the SCR catalyst 40 (that is, the NOx concentration). The second NOx sensor 62 is arranged downstream of the SCR catalyst 40 in the exhaust passage 30 and detects the amount of NOx flowing out from the SCR catalyst 40 (that is, the NOx concentration). A temperature sensor 63 detects the temperature of the exhaust gas discharged from the engine 10 . A flow rate sensor 64 detects the flow rate of exhaust gas discharged from the engine 10 . These various sensors 61 to 64 sequentially transmit sensor information obtained by detection to the ECU 100 .

The ECU 100 (corresponding to the "control device" of the present invention) controls the operation of the exhaust purification device U. The ECU 100 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, an output port, and the like. Each function of the ECU 100, which will be described later, is realized, for example, by the CPU referring to control programs and various data stored in ROM, RAM, or the like. However, the function is not limited to processing by software, and can of course be realized by a dedicated hardware circuit.

The ECU 100 communicates with the engine 10, the urea water injection device 50, and the like to control them and obtain state information thereof. The ECU 100 also acquires sensor information from various sensors 61 to 64 to detect the state of the exhaust gas flowing through the exhaust passage 30, the state of the SCR catalyst 40, and the like.

[Detailed Configuration of ECU 100]
Next, an example of the detailed configuration of the ECU 100 will be described with reference to FIGS. 2 to 5. FIG.

FIG. 2 is a block diagram showing an example of the configuration of the ECU 100 according to this embodiment.

The ECU 100 includes a NOx purification rate detection section 101 , an ammonia storage amount estimation section 102 , a urea water injection control section 103 , a correction coefficient setting section 104 and a correction command section 105 .

<Regarding NOx Purification Rate Detector 101>
NOx purification rate detector 101 detects the NOx purification rate of SCR catalyst 40 and sends it to correction command section 105 . The NOx purification rate detection unit 101 detects, for example, the sensor signal of the first NOx sensor 61 (ie, the amount of NOx flowing into the SCR catalyst 40) and the sensor signal of the second NOx sensor 62 (ie, the amount of NOx flowing out of the SCR catalyst 40). Based on this, the NOx purification rate of the SCR catalyst 40 is detected.

When detecting the NOx purification rate of the SCR catalyst 40 , the NOx purification rate detection unit 101 may use a value estimated from the operating state of the engine 10 for the amount of NOx flowing into the SCR catalyst 40 .

<Regarding Ammonia Storage Amount Estimating Unit 102>
Ammonia storage amount estimation unit 102 estimates the amount of ammonia storage in SCR catalyst 40 . The ammonia storage amount estimating unit 102 includes a first estimating unit 102a that estimates the current ammonia storage amount based on the transition of the urea water injection amount of the urea water injection device 50 and the transition of the ammonia consumption amount in the SCR catalyst 40; a second estimation unit 102b for estimating the current amount of ammonia storage based on the NOx purification rate of the SCR catalyst 40, the temperature of the SCR catalyst 40, and the exhaust gas flow rate in the exhaust passage 30 detected at the current time; .

Typically, the first estimating unit 102a calculates the adsorption amount of ammonia newly adsorbed in the SCR catalyst 40 based on the urea water injection amount of the urea water injection device 50, and calculates the adsorption amount of the newly adsorbed ammonia. Accumulate quantity. Also, the first estimator 102a calculates the amount of ammonia consumed in the SCR catalyst 40 per unit time based on the amount of NOx arriving at the SCR catalyst 40 . Then, the first estimation unit 102a estimates the current ammonia storage amount in the SCR catalyst 40 by subtracting the ammonia consumption amount from the ammonia adsorption amount.

That is, the ammonia storage amount estimating unit 102 compares the transition of the urea water injection amount of the urea water injection device 50 (that is, the adsorption amount of ammonia newly adsorbed to the SCR catalyst 40) and the consumption of ammonia consumed in the SCR catalyst 40. The current amount of ammonia storage in the SCR catalyst 40 is estimated from the transition of the amount.

The amount of ammonia consumed in the SCR catalyst 40 is, for example, the amount of NOx arriving at the SCR catalyst 40 (for example, sensor information from the first NOx sensor 61), the exhaust gas temperature (for example, sensor information from the temperature sensor 63), and the exhaust gas flow rate. (For example, sensor information of the flow sensor 64) and the amount of ammonia storage in the SCR catalyst 40 at the present time.

Ammonia storage amount estimating unit 102 normally (meaning when the NOx purification rate of SCR catalyst 40 is in the vicinity of the target value; hereinafter the same) estimates the ammonia storage amount estimated by first estimating unit 102a. , is output to the urea water injection control unit 103 as the current ammonia storage amount. However, the estimated value of the ammonia storage amount estimated by the first estimator 102a may deviate from the actual value over time. Therefore, when there is a discrepancy between the estimated value of the ammonia storage amount estimated by the first estimation unit 102a and the actual value, the estimated value of the ammonia storage amount estimated by the second estimation unit 102b is used for the first estimation The unit 102a corrects the estimated value of the current ammonia storage amount stored in the storage unit (for example, RAM).

This suppresses the continuation of a state in which the estimated value of the ammonia storage amount in the SCR catalyst 40 deviates from the actual value. Such correction processing is executed based on a correction command from the correction command unit 105. FIG.

Unlike the first estimating unit 102a, the second estimating unit 102b does not refer to the estimated ammonia storage amount of the SCR catalyst 40 at the previous point in time. , to estimate the ammonia storage amount of the SCR catalyst 40 at the present time.

Specifically, the second estimator 102b determines the current SCR catalyst 40 based on the NOx purification rate of the SCR catalyst 40, the temperature of the SCR catalyst 40, and the exhaust gas flow rate in the exhaust passage 30 detected at the current time. to estimate the amount of ammonia storage in At this time, the second estimating unit 102b more preferably uses the following equation (1) derived from the reaction rate equation of the NOx purification reaction in the SCR catalyst 40 to estimate the current ammonia storage amount of the SCR catalyst 40: Estimate (derivation process will be described later).

The second estimating unit 102b may calculate the ammonia storage amount of the SCR catalyst 40 directly by arithmetic processing using equation (1). Further, a control map corresponding to the calculation result of formula (1) is stored in advance in a storage unit (eg, ROM), and the second estimation unit 102b uses the control map to store the ammonia storage of the SCR catalyst 40. amount may be calculated.

Here, the reason why the ammonia storage amount estimating unit 102 normally estimates the ammonia storage amount by the first estimating unit 102a is that when the NOx purification rate of the SCR catalyst 40 is high, This is because the amount of change in the NOx purification rate is small, and the accuracy in estimating the amount of ammonia storage by the second estimator 102b is low.

FIG. 3 is a diagram showing an example of the relationship between the NOx purification rate of the SCR catalyst 40 and the ammonia storage amount of the SCR catalyst 40. As shown in FIG. 3, it is assumed that the temperature of the SCR catalyst 40 and the exhaust gas flow rate in the exhaust passage 30 are constant.

Generally, the NOx purification rate of the SCR catalyst 40 increases as the ammonia storage amount of the SCR catalyst 40 increases, as shown in FIG. The NOx purification rate of the SCR catalyst 40 varies greatly depending on the ammonia storage amount of the SCR catalyst 40 until the ammonia storage amount of the SCR catalyst 40 reaches a predetermined value (for example, 50%). In other words, the process of estimating the ammonia storage amount by the second estimating unit 102b is performed when the NOx purification rate of the SCR catalyst 40 is decreasing (that is, when the amount between the estimated value and the actual value of the ammonia storage amount of the SCR catalyst 40 is High estimation accuracy can be ensured only when there is a divergence, and estimation accuracy deteriorates when the NOx purification rate of the SCR catalyst 40 increases.

In addition, the calculation load on the second estimator 102b tends to be larger than the calculation load on the first estimator 102a.

From this point of view, the ammonia storage amount estimation unit 102 according to the present embodiment normally estimates the ammonia storage amount by the first estimation unit 102a, and the NOx purification rate of the SCR catalyst 40 decreases. The ammonia storage amount is estimated by the second estimation unit 102b only when the amount of ammonia is stored.

<Regarding the urea water injection control unit 103>
The urea water injection control unit 103 controls the urea water injection from the urea water injection device 50 by outputting an opening command signal to the urea water addition valve 51 . At this time, the urea water injection control unit 103 causes the urea water injection device 50 to inject the urea water so that the estimated value of the ammonia storage amount of the SCR catalyst 40 estimated by the ammonia storage amount estimation unit 102 becomes the target value. control the amount. As a result, the SCR catalyst 40 is maintained at a high NOx purification rate.

Note that the target value of the ammonia storage amount of the SCR catalyst 40 may be appropriately changed depending on the current exhaust gas temperature.

The urea water injection control unit 103 temporarily adjusts the urea water injection amount based on, for example, a control map that associates the current difference between the estimated ammonia storage amount of the SCR catalyst 40 and the target value with the urea water injection amount. Calculate Then, the urea water injection control unit 103 adds the urea water injection correction coefficient (for example, any value between 0.5 and 1.5) set in the correction coefficient setting unit 104 to the provisionally calculated urea water injection amount. value) to determine the urea water injection amount.

<Regarding Correction Coefficient Setting Unit 104>
The correction coefficient setting unit 104 sets a urea injection correction coefficient, which is a correction coefficient when the urea water injection control unit 103 determines the urea water injection amount.

The urea injection correction coefficient is mainly set to calibrate the device error of the urea water injection device 50 (for example, the error of the actual valve opening of the urea water addition valve 51 with respect to the valve opening indicated by the opening command signal). be done. In other words, the urea water injection amount actually injected by the urea water injection device 50 may deviate from the command value from the urea water injection control unit 103 due to the device error of the urea water injection device 50. The device U calibrates the device error with the urea injection correction coefficient.

The urea injection correction coefficient is set to, for example, "1.0" in the initial state, and is increased stepwise to "1.1", "1.2", . . . be done. Further, the urea injection correction coefficient is decreased stepwise to "0.9", "0.8", .

Then, the urea water injection control unit 103 adds the urea water injection correction coefficient (for example, between 0.5 and 1.5) set by the correction coefficient setting unit 104 to the urea water injection amount temporarily calculated from the control map. ) to determine the final urea water injection amount. As a result, the urea water injection amount according to the command value from the urea water injection control unit 103 is brought closer to the urea water injection amount actually injected by the urea water injection device 50 .

Appropriately setting the urea injection correction coefficient also leads to an improvement in the estimation accuracy of the ammonia storage amount estimation unit 102, and reduces the frequency of occurrence of a state in which the estimated value of the ammonia storage amount deviates from the actual value. It also contributes to

<Regarding Correction Command Unit 105>
Correction command unit 105 monitors the occurrence of an ammonia understorage state in SCR catalyst 40 , and sends a correction command to ammonia storage amount estimation unit 102 and correction coefficient setting unit 104 when the understorage state is detected. That is, in the correction command unit 105, with the occurrence of ammonia understorage in the SCR catalyst 40 as a trigger, there is a deviation between the estimated value of the ammonia storage amount estimated by the first estimation unit 102a and the actual value. detect that

As a method for the correction command unit 105 to detect the occurrence of the understorage state in the SCR catalyst 40, for example, the NOx purification rate detected by the NOx purification rate detection unit 101 is used. For example, when the NOx purification rate of the SCR catalyst 40 drops below a threshold value (for example, 70%), the correction command unit 105 assumes that an understorage state has occurred, and the ammonia storage amount estimation unit 102 and A correction command is sent to the correction coefficient setting unit 104 .

Specific correction processing in the ammonia storage amount estimation unit 102 and the correction coefficient setting unit 104 is as follows.

When the ammonia storage amount estimation unit 102 receives the correction command from the correction command unit 105, the second estimation unit 102b estimates the ammonia storage amount. Then, the ammonia storage amount estimating unit 102 uses the estimated value of the ammonia storage amount calculated by the second estimating unit 102b as the current ammonia storage stored in the storage unit (for example, RAM) that is sequentially updated by the first estimating unit 102a. Override the volume estimate. As a result, the current estimated value of the ammonia storage amount stored in the storage unit (eg, RAM) is brought closer to the current actual value of the ammonia storage amount.

Further, when receiving a correction command from the correction command unit 105, the correction coefficient setting unit 104 increases the urea injection correction coefficient stored in the storage unit (for example, RAM). For example, the correction coefficient setting unit 104 increases the currently set urea injection correction coefficient by one step (for example, 0.1).

FIG. 4 is a diagram showing an example of a specific operation flow performed by the correction command unit 105. As shown in FIG. The flowchart shown in FIG. 4 is, for example, executed by the ECU 100 at predetermined intervals (for example, every 100 ms) according to a computer program.

5 shows the behavior of the urea water injection amount (FIG. 5A), the behavior of the ammonia storage amount of the SCR catalyst 40 (FIG. 5B), and the NOx purification rate of the SCR catalyst 40 in the exhaust purification device U according to the present embodiment. Fig. 5C is a time chart showing an example of behavior (Fig. 5C);

In FIG. 5, there is a discrepancy between the estimated ammonia storage amount of the SCR catalyst 40 (solid line in FIG. 5B) and the actual value (dotted line in FIG. 5B), and the SCR catalyst 40 is in an understorage state. The behavior of each value in the case is shown. Here, the ECU 100 controls the urea water injection amount of the urea water injection device 50 so that the estimated value of the ammonia storage amount of the SCR catalyst 40 is 90% of the storable amount of the SCR catalyst 40. ing. Also, T1 in FIG. 5 indicates the timing when the correction command unit 105 issues a correction command.

In step S1, the correction command unit 105 determines whether or not the NOx purification rate of the SCR catalyst 40 has decreased to a threshold value (for example, 70%) or less. Here, if the NOx purification rate of the SCR catalyst 40 has not decreased to the threshold value or less (step S1: NO), the correction command unit 105 ends the processing of the flowchart of FIG. 4 without executing any particular processing. On the other hand, if the NOx purification rate of the SCR catalyst 40 has fallen below the threshold (step S1: YES), the correction command unit 105 advances the process to step S2.

In this step S1, the correction command section 105 may determine whether or not the NOx purification rate of the SCR catalyst 40 has decreased based on the integrated value of the NOx purification rate. As a result, it is possible to avoid a situation in which unnecessary correction processing is performed due to noise or the like.

In step S2, the correction command unit 105 sends a correction command to the ammonia storage amount estimation unit 102 to cause the ammonia storage amount estimation unit 102 to execute correction processing.

In step S2, the ammonia storage amount estimation unit 102 (second estimation unit 102b) estimates the current ammonia storage amount of the SCR catalyst 40 using the above equation (1). Then, the ammonia storage amount estimation unit 102 corrects the current estimated value of the ammonia storage amount stored in the storage unit (eg, RAM) using the estimated value of the ammonia storage amount calculated using the above formula (1). Let

In step S3, correction command unit 105 sends a correction command to correction coefficient setting unit 104 to increase the urea injection correction coefficient. Accordingly, for example, the correction coefficient setting unit 104 increases the currently set urea injection correction coefficient by one step (for example, increases from 1.0 to 1.1).

It should be noted that after steps S2 and S3 are executed, it is desirable to prohibit the execution of the process of the flowchart of FIG. 4 for a predetermined time (for example, 10 minutes). As a result, it is possible to prevent repeated execution of the process of correcting the estimated value of the ammonia storage amount of the SCR catalyst 40 and the urea injection correction coefficient before the NOx purification rate of the SCR catalyst 40 recovers.

Through the above processing, the deviation between the estimated value and the actual value of the ammonia storage amount of the SCR catalyst 40 is eliminated. Then, the first estimator 102a can calculate the subsequent transition of the ammonia storage amount of the SCR catalyst 40 using the corrected current ammonia storage amount. In other words, as a result, the urea water injection amount of the urea water injection device 50 increases from before the correction process, and the NOx purification rate of the SCR catalyst 40 recovers rapidly (see FIG. 5C). .

In addition, since the urea injection correction coefficient is also appropriately set, the frequency of deviation between the estimated value and the actual value of the ammonia storage amount of the SCR catalyst 40 can be suppressed from a long-term perspective. become.

[Regarding the derivation process of formula (1)]
The derivation process of the above formula (1) will be described below.

Equation (1) is obtained by converting the following equation (2) obtained from the NOx purification reaction.

Here, as NOx purification reactions, for example, two chemical reactions of the following equations (3) and (4) are considered.

When this is put together as a reaction formula of NOx, it becomes like the following Formula (5).

Considering the detailed chemical reaction process of the above reaction formula (5), if it is assumed that NOx is purified when the reaction of NOx, which is a reactant, starts, then there is no O2 in the elementary reaction at the start of the reaction. Assume that its effect is negligible. At this time, the NOx reaction rate formula is expressed as the following formula (6).

Assuming that the reaction time dt is constant except for [NOx], this reaction can be regarded as a first-order reaction with respect to the NOx concentration [NOx]. Therefore, when the reaction rate constant k is set as in Equation (7) in Equation (6), Equation (6) is expressed as Equation (8).

Here, rearranging by [NOx] yields the following equation (9).

When Equation (9) is subjected to indefinite integration to obtain an analytical solution, [NOx] is obtained by Equations (10) to (12).

Assuming that the upstream NOx concentration at t=0 is [NOx] ₀ , equation (13) is obtained, and the downstream NOx concentration [NOx] in equation (12) is expressed as equation (14).

Now, the purification rate η _NOx is obtained.

Reverting K, Equation (15) is expressed as the following Equation (16).

Here, when the reaction rate constant k is expressed by the Arrhenius equation, the following equation (17) is obtained.

Substituting k for η _NOx yields the following equation (18).

Assuming that the reaction time t is equal to the time the exhaust gas passes through the SCR catalyst 40, the reaction time t is expressed by the following equation (19).

The exhaust gas density ρ _T is given by the following equation (20) from the ideal gas equation of state.

Here, assuming P _EXh = 106.325 × 10 ³ [Pa] (constant), Mw _EXh = 29 × 10 ^-3 [kg/mol] (constant), R = 8.31 [J/(K mol )]. Substituting ρ _T into the equation (19) yields the following equation (21).

Also, the NH3 concentration [NH3] can be expressed by the following formula (22) when the unit is [mol/cm3].

Here, in the above formula (22), NH3 is the amount of ammonia storage, Mw _NH3 is the molecular weight of NH3, and Mw _NH3 =17.01 [g/mol]. Substituting the reaction time t and the NH3 concentration [NH3] into the equation (18) representing the estimated purification rate η _NOx yields the following equation (23).

The derivation of the basic physical formula is now complete, but we will also add unit conversion and engineering adjustments. The unit of the catalyst temperature is [°C], the ammonia storage amount NH3 is provided with an index α (for example, 0<α<3) for sensitivity adjustment, and the exhaust gas flow rate dmEG is also provided with an index β for sensitivity adjustment (for example, 0<β When <3) is provided, the following formula (24) is obtained.

In Equation (24) above, if the constant 12.73 is included in the frequency factor A, Equation (2) above is derived.

FIG. 6 is a diagram illustrating a method of setting the frequency factor A, the storage order α, and the exhaust gas flow rate order β in Equation (1). In the above formula (1) (and formula (24)), the frequency factor A, the storage order α, and the exhaust gas flow rate order β are set by experiments on a test bench, for example.

Specifically, first, on a test bench, the NOx purification rate in the SCR catalyst 40, the temperature of the SCR catalyst 40, the flow rate of the exhaust gas, and the amount of ammonia storage in the SCR catalyst 40 are detected under various conditions. to obtain the relationship between these detected values. Then, when the temperature of the SCR catalyst 40, the flow rate of the exhaust gas, and the detected value of the ammonia storage amount in the SCR catalyst 40 are substituted into the above formula (24), the NOx purification rate calculated by the above formula (24) The frequency factor A, the storage order α, and the exhaust gas flow rate order β are adjusted so that the estimated value of and the actual value of the NOx purification rate according to the experimental data are most compatible (in FIG. 6, the index indicating the NOx purification rate , the amount of downstream NOx is used).

The activation energy E in the above formula (24) is the activation energy in the above chemical reaction formula (5), but is adjusted together with the frequency factor A, the storage order α, and the exhaust gas flow rate order β as necessary. may

By appropriately setting the frequency factor A, the storage order α, and the exhaust gas flow rate order β in this way, it is possible to suppress deterioration in the estimation accuracy due to individual differences in the exhaust purification devices U and the like.

[effect]
As described above, according to the ECU 100 according to the present embodiment, based on the NOx purification rate of the SCR catalyst 40, the temperature of the SCR catalyst 40, and the exhaust gas flow rate in the exhaust passage 30 detected at the present time, It is possible to estimate the amount of ammonia storage. This makes it possible to estimate the current ammonia storage amount in the SCR catalyst 40 with high accuracy.

In particular, the ECU 100 according to the present embodiment includes a first estimating unit 102a that estimates the current ammonia storage amount based on changes in the urea water injection amount and changes in the ammonia consumption amount in the SCR catalyst 40, and the currently detected ammonia storage amount. It also has a second estimator 102 b that estimates the current ammonia storage amount based on the NOx purification rate of the SCR catalyst 40 , the temperature of the SCR catalyst 40 , and the exhaust gas flow rate in the exhaust passage 30 . Therefore, even when the estimated value of the ammonia storage amount sequentially updated by the first estimating unit 102a diverges from the actual value (that is, when the NOx purification rate decreases), the estimation processing by the second estimating unit 102b It is useful in that the estimated value can be corrected.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and various modifications are conceivable.

In the above embodiment, as an example of the ammonia storage amount estimation unit 102 of the ECU 100, the current ammonia storage amount is calculated based on the transition of the urea water injection amount of the urea water injection device 50 and the transition of the ammonia consumption amount of the SCR catalyst 40. The current ammonia storage amount is estimated based on the first estimation unit 102a that estimates, the NOx purification rate of the SCR catalyst 40, the temperature of the SCR catalyst 40, and the exhaust gas flow rate in the exhaust passage 30 detected at the current time. A mode having both the second estimation unit 102b is shown. However, the ammonia storage amount estimation unit 102 according to the present invention may have only a configuration corresponding to the second estimation unit 102b. Further, the ammonia storage amount estimation unit 102 according to the present invention may be configured to switch between estimation processing by the first estimation unit 102a and estimation processing by the second estimation unit 102b according to the current NOx purification rate of the SCR catalyst 40. good.

Further, in the above embodiment, as an example of the configuration of the ECU 100, the functions of the NOx purification rate detection unit 101, the ammonia storage amount estimation unit 102, the urea water injection control unit 103, the correction coefficient setting unit 104, and the correction command unit 105 are Although described as being implemented by a single computer, it may of course be implemented by a plurality of computers. For example, the function of the ammonia storage amount estimation unit 102 and the function of the urea water injection control unit 103 may be installed in separate ECUs.

Moreover, in the above embodiment, as an example, a mode in which the exhaust purification device is applied to a diesel engine will be described. However, the exhaust purification device according to the present embodiment can be applied not only to diesel engines but also to gasoline engines.

Further, in the above embodiment, a vehicle is shown as an example of an application target of the exhaust purification device U, but the application target of the exhaust purification device U is not limited to this. For example, the exhaust purification device U may be applied to generators, construction machinery, ships, and the like.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

According to the exhaust purification device according to the present disclosure, the ammonia storage amount in the SCR catalyst can be estimated with higher accuracy.

U Exhaust purification device 10 Engine 20 Intake passage 30 Exhaust passage 40 SCR catalyst (NOx selective reduction catalyst)
50 Aqueous urea injection device 51 Aqueous urea addition valve 52 Aqueous urea tank 53 Supply pump 61 First NOx sensor 62 Second NOx sensor 63 Temperature sensor 64 Flow rate sensor 100 ECU (control device)
101 NOx purification rate detection unit 102 ammonia storage amount estimation unit 102a first estimation unit 102b second estimation unit 103 urea water injection control unit 104 correction coefficient setting unit 105 correction command unit

Claims (4)

An exhaust purification device disposed in an exhaust passage of an internal combustion engine,
an SCR (Selective Catalytic Reduction) catalyst disposed in the exhaust passage;
a urea water injection device for injecting urea water upstream of the SCR catalyst in the exhaust passage;
a control device for estimating an ammonia storage amount in the SCR catalyst and controlling the urea water injection amount of the urea water injection device based on the estimated value of the ammonia storage amount;
with
The control device is
a first estimation unit that estimates the current amount of ammonia storage based on the transition of the urea water injection amount and the transition of the ammonia consumption amount in the SCR catalyst;
a second estimation unit that estimates the current amount of ammonia storage based on the NOx purification rate of the SCR catalyst, the temperature of the SCR catalyst, and the exhaust gas flow rate in the exhaust passage, which are detected at the current time. ,
Exhaust purification device. When the NOx purification rate of the SCR catalyst decreases, the control device corrects the ammonia storage amount sequentially updated by the first estimation unit to the ammonia storage amount estimated by the second estimation unit.
The exhaust purification device according to claim 1 . An exhaust purification device disposed in an exhaust passage of an internal combustion engine,
an SCR (Selective Catalytic Reduction) catalyst disposed in the exhaust passage;
a urea water injection device for injecting urea water upstream of the SCR catalyst in the exhaust passage;
a control device for estimating an ammonia storage amount in the SCR catalyst and controlling the urea water injection amount of the urea water injection device based on the estimated value of the ammonia storage amount;
with
Based on the currently detected NOx purification rate of the SCR catalyst, the temperature of the SCR catalyst, and the exhaust gas flow rate in the exhaust passage, the control device controls the SCR using the following formula (1): estimating the current amount of ammonia storage in the catalyst ;
Exhaust purification device.

A vehicle comprising the exhaust emission control device according to any one of claims 1 to 3 .

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