JP2011163197A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress NH<SB>3</SB>slip in a selective reduction catalyst supplying a reducing agent to an upstream side. <P>SOLUTION: This exhaust emission control device for an internal combustion engine includes: the selective reduction catalyst including a first selective reduction catalyst provided in an exhaust passage and a second selective reduction catalyst provided downstream of the first selective reduction catalyst; a reducing-agent supply means supplying the reducing agent to the upstream side of the selective reduction catalyst; a catalyst temperature detection means detecting the temperature of the first selective reduction catalyst; a means for setting the storable amount of NH<SB>3</SB>in the first selective reduction catalyst according to the temperature of the first selective reduction catalyst; a means for calculating the amount of NH<SB>3</SB>in the first selective reduction catalyst; a means for setting the correction amount of the amount of the reducing agent supplied so that the difference between the calculated amount of NH<SB>3</SB>and the storable amount of NH<SB>3</SB>in the first selective reduction catalyst is reduced; and a reducing-agent supplied amount setting means setting the amount of the reducing agent supplied by the use of the correction amount. A means for calculating the storable amount of NH<SB>3</SB>sets the storable amount of NH<SB>3</SB>at a predetermined temperature as the storable amount of NH<SB>3</SB>in the first selective reduction catalyst until the temperature of the first selective reduction catalyst reaches the predetermined temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an exhaust purifying apparatus for an internal combustion engine, and more particularly relates to an exhaust purifying apparatus for an internal combustion engine provided with a selective reduction catalyst for reducing NO _x in the exhaust passage in the presence of a reducing agent.

2. Description of the Related Art Conventionally, as one of exhaust purification apparatuses that purify NO _x in exhaust gas, an apparatus has been proposed in which a selective reduction catalyst that selectively reduces NO _x in exhaust gas by adding a reducing agent is provided in an exhaust passage. Yes. For example, urea addition type of the selective reduction catalyst using urea water as the reducing agent, the added urea is hydrolyzed to produce ammonia (NH _3), to selectively reduce NO _x in the exhaust by NH ₃ .

In such a selective reduction catalyst, if less than the injection amount is optimum amount of the reducing agent, the reduction rate of the NO _x by NH ₃ to be consumed in the reduction of the NO _x is insufficient is reduced, optimal When the amount is larger than the amount, NH ₃ surplus in the reduction of NO _x is discharged. For this reason, it is important to appropriately control the injection amount of the reducing agent in the exhaust emission control device including the selective reduction catalyst.

Patent Document 1 discloses an exhaust gas purification apparatus for an internal combustion engine using two selective reduction catalysts. In this exhaust purification apparatus, in accordance with the NH ₃ concentration NH ₃ sensor provided between two of the selective reduction catalyst is detected, feedback injection amount of the reducing agent on the upstream side of the selective reduction catalyst (F / B) control To do.

International Publication WO2009 / 128169

The selective reduction catalyst has an ability to adsorb NH ₃ , and this NH ₃ adsorptionable amount tends to decrease as the temperature of the selective reduction catalyst increases. In the exhaust purifying apparatus according to patent document 1 performs the F / B control the temperature is NH ₃ sensor from a low state (for example, 160 ° C.) according to the NH ₃ concentration detection of the selective reduction catalyst. Therefore, when the temperature of the selective reduction catalyst rises to a temperature that can exhibit purification performance to maximize (e.g. 250 ° C.), since the NH ₃ adsorption capacity of the selective reduction catalyst decreases, NH ₃ adsorption capacity higher There is a problem that a large amount of NH ₃ is discharged (slipped).

Accordingly, the present invention is, in the exhaust purification system for an internal combustion engine having a selective reduction catalyst, and an object thereof is to suppress the NH ₃ adsorption capacity more abundant NH ₃ slip from the selective reduction catalyst.

The present invention provides an exhaust emission control device for an internal combustion engine. The exhaust purification device is a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine, captures NH ₃ as a reducing agent, and reduces NO _x flowing through the exhaust passage using the captured NH ₃ . A selective reduction catalyst including a first selective reduction catalyst and a second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage, and a reducing agent upstream of the selective reduction catalyst in the exhaust passage. Reducing agent supply means to be supplied, catalyst temperature detection means for detecting the temperature of the first selective reduction catalyst, and means for setting the NH ₃ storage possible amount in the first selective reduction catalyst according to the temperature of the first selective reduction catalyst And the means for calculating the amount of NH _{3 in} the first selective reduction catalyst, and the supply of the reducing agent so that the difference between the calculated amount of NH ₃ and the NH ₃ storage capacity in the first selective reduction catalyst decreases. Correction amount setting for setting the amount of correction And a reducing agent supply amount setting means for setting the supply amount of the reducing agent by the reducing agent supply means using the correction amount, and the means for calculating the NH ₃ storage possible amount is a temperature of the first selective reduction catalyst. There is to a predetermined temperature to set the NH ₃ storage amount capable of at the predetermined temperature as a NH ₃ storage possible amount of the first selective reduction in catalyst.

According to the present invention, the temperature of the first selective reduction catalyst is to a predetermined temperature to set the NH ₃ storage amount capable of at the predetermined temperature as a NH ₃ storage possible amount of the first selective reduction in catalyst, the first It becomes possible to suppress and control the NH ₃ slip amount from the selective reduction catalyst.

According to an embodiment of the present invention, means for calculating the NH ₃ storage possible amount, if the temperature of the first selective reduction catalyst is equal to or higher than a predetermined temperature, said first selected according to the temperature detected by the catalyst temperature detecting means It sets so that NH ₃ storage possible amount in a reduction catalyst may become small.

According to one aspect of the present invention, it is possible to stably perform the suppression control of the NH ₃ slip amount from the first selective reduction catalyst even after the temperature of the first selective reduction catalyst becomes equal to or higher than the predetermined temperature. .

According to an embodiment of the present invention, the predetermined temperature, NO _x reduction capability of the first selective reduction catalyst is a temperature at which the maximum.

According to one aspect of the present invention, it is possible to suppress the supply of an unnecessarily reducing agent that is not consumed in the reduction reaction until the NO _x reduction capability of the first selective reduction catalyst is maximized. NH ₃ slip amount can be suppressed.

It is a mimetic diagram showing composition of an engine and its exhaust gas purification device according to one example of the present invention. And concentration of NO _x in the selective reduction catalyst, and NH ₃ concentration is a diagram showing the relationship between the NH ₃ storage amount. Is a graph showing the relationship between the temperature and the NH ₃ storage amount of the selective reduction catalyst. It is a block diagram which shows the structure (function) of ECU3 of FIG. NH ₃ is a diagram showing a flow of a first correction amount setting calculated reducing agent supply amount of the estimated value of the adsorption amount. It is a figure which shows the control flow which leads to calculation of the 1st and 2nd correction amount of urea water. And catalyst temperature, the urea water correction amount according to the estimated storage F / B, and NH ₃ concentration is a diagram showing the relationship between the NH ₃ storage amount.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an internal combustion engine (hereinafter referred to as “engine”) 1 and its exhaust purification device 2 according to an embodiment of the present invention. The engine 1 is a gasoline engine or a diesel engine, and is mounted on a vehicle (not shown).

The exhaust purification device 2 includes an oxidation catalyst 21 provided in the exhaust passage 11 of the engine 1 and a nitrogen oxide (hereinafter referred to as “hereinafter referred to as“ nitrogen oxide ”) provided in the exhaust passage 11 provided downstream of the oxidation catalyst 21 in the exhaust passage 11. NO _x ”) in the presence of a reducing agent, a selective reduction catalyst 23, a urea water injection device 25 for supplying urea water as a reducing agent to the upstream side of the selective reduction catalyst 23 in the exhaust passage 11, and electronic control A unit (hereinafter referred to as “ECU”) 3 is included.

  The ECU 3 is a computer that includes a central processing unit (CPU) and a memory. The memory can store a computer program for realizing various controls of the vehicle and data, tables, and maps necessary for executing the program. As will be described later, the ECU 3 receives data sent from each part (sensor or the like) of the vehicle, performs calculation, and generates a control signal for controlling each part of the vehicle.

  The urea water injection device 25 includes a tank 251 and an injector 253. The tank 251 stores urea water, and is connected to the injector 253 via the urea water supply path 254 and a pump (not shown). The tank 251 is provided with a urea water level sensor 255. This sensor 255 detects the water level of the urea water in the tank 251 and outputs a detection signal corresponding to this water level to the ECU 3. The injector 253 is connected to the ECU 3 and injects urea water into the exhaust passage 11 in accordance with a control signal from the ECU 3. That is, the injector 253 injects a predetermined amount of urea water into the exhaust passage 11 at an injection time (seconds / shot) set by the ECU 3 and an injection interval (seconds, period (Hz)).

The oxidation catalyst 21 is provided on the upstream side of the selective reduction catalyst 23 and the injector 253 in the exhaust passage 11, and converts NO occupying most of the NO _{x in} the exhaust gas into NO ₂ , thereby the selective reduction catalyst. to promote the reduction of the NO _x in 23.

The selective reduction catalyst 23 includes a first selective reduction catalyst 231 and a second selective reduction catalyst 232 provided downstream of the first selective reduction catalyst 231 in the exhaust passage 11. The first and second selective reduction catalysts 231 and 232 selectively reduce NO _x in the exhaust gas in an atmosphere in which ammonia as a reducing agent exists. Specifically, when urea water is injected by the urea water injection device 25, ammonia (hereinafter referred to as “NH ₃ ”) is generated from urea by hydrolysis, and the NO _x in the exhaust gas in the selective reduction catalyst 23 is generated by this NH _3. (NO and NO ₂ ) are selectively reduced. The selective reduction catalyst 23 also has a function of storing NH _3, NO _x is reduced and purified by NH ₃ that is stored.

In addition to the NH ₃ sensor 26, the catalyst temperature sensor 27, and the NO _x sensor 28, the ECU 3 is connected with a crank angle position sensor 14, an accelerator opening sensor 15, and a urea water remaining amount warning lamp 16.

The NH ₃ sensor 26 detects the concentration of ammonia in the exhaust gas between the first selective reduction catalyst 231 and the second selective reduction catalyst 232 in the exhaust passage 11 (hereinafter referred to as “NH ₃ concentration”), and detects the detected NH A detection signal corresponding to the _three concentrations is sent to the ECU 3.

The catalyst temperature sensor 27 detects the temperature of the first selective reduction catalyst 231 (hereinafter referred to as “catalyst temperature”), and sends a detection signal corresponding to the detected catalyst temperature to the ECU 3. The NO _x sensor 28 detects the concentration of NO _{x in} the exhaust gas flowing into the first selective reduction catalyst 231 and sends a detection signal corresponding to the detected NO _x to the ECU 3.

  The crank angle position sensor 14 detects the rotation angle of the crankshaft of the engine 1, generates a pulse at every crank angle, and sends the pulse signal to the ECU 3. The ECU 3 calculates the rotational speed NE of the engine 1 based on this pulse signal. The crank angle position sensor 14 further generates a cylinder identification pulse at a predetermined crank angle position of the specific cylinder and sends it to the ECU 3.

  The accelerator opening sensor 15 detects the amount of depression of an accelerator pedal (not shown) of the vehicle (hereinafter referred to as “accelerator opening”), and sends a detection signal corresponding to the detected accelerator opening to the ECU 3. In the ECU 3, the required torque of the engine 1 is calculated according to the accelerator opening and the rotational speed.

  The urea water remaining amount warning lamp 16 is provided, for example, on a meter panel of the vehicle, and lights up when the remaining amount of urea water in the tank 251 is less than a predetermined remaining amount. As a result, the driver is warned that the remaining amount of urea water in the tank 251 has decreased.

FIG. 2 is a diagram illustrating the relationship among the NO _x concentration, the NH ₃ concentration, and the storage amount of NH ₃ in the selective reduction catalyst 23 of FIG. Graphs 30 and 31 in FIG. 2 indicate that as NO _x is reduced and the NO _x concentration decreases, NH ₃ of the selective reduction catalysts 231 and 232 is consumed and the NH ₃ concentration also decreases.

In FIG. 2, NH ₃ is almost saturated in the first selective reduction catalyst 231, that is, a state of maximum NH ₃ storage amount (reference numeral 32). The broken line indicated by reference numeral 35 indicates the minimum NH ₃ storage amount (lower limit storage amount) required to reduce NO _x in a low load (low rotation) operation state such as idling. In the second selective reduction catalyst 232, NH ₃ slipped from the first selective reduction catalyst 231 is stored (adsorbed) by an amount indicated by reference numeral 33. A broken line 34 indicates that this storage amount varies depending on the catalyst temperature.

FIG. 3 is a diagram showing the relationship between the temperature in the selective reduction catalyst and the NH ₃ storage capacity. The amount of NH ₃ storage that can be stored tends to increase at low temperatures and decrease with increasing temperatures. In the present invention, a predetermined temperature, for example, up to about 250 ° C. purification performance of the first selective reduction catalyst (NO _x reducing ability) is maximized, NH ₃ storage amount capable of NH ₃ storage amount capable W1 at the predetermined temperature Use as Above the predetermined temperature, the NH ₃ storage capacity W (T) that changes (decreases) in accordance with the temperature T detected by the catalyst temperature detecting means 27 is used.

FIG. 4 is a block diagram showing a configuration (function) of the ECU 3 in FIG. The function of each block is realized by the CPU included in the ECU 3 reading and executing a control program stored in a memory (not shown). The NH ₃ amount calculation means 301 of the first selective reduction catalyst calculates the amount of NH ₃ (estimated amount) captured (adsorbed) by the first selective reduction catalyst 231 in FIG. NH ₃ means 302 for setting a storage amount capable sets the NH ₃ storage possible amount of the first selective reduction in catalyst according to the temperature of the first selective reduction catalyst 231. At this time, until the temperature of the first selective reduction catalyst reaches a predetermined temperature, it sets the NH ₃ storage amount capable of at the predetermined temperature as a NH ₃ storage possible amount of the first selective reduction in catalyst.

The reducing agent supply amount first correction amount setting means 303 adjusts the reducing agent supply amount so that the difference between the calculated NH ₃ amount and the NH ₃ storage possible amount in the first selective reduction catalyst becomes zero. 1 Set the correction amount.

FIG. 5 is a diagram illustrating an example of the flow of calculating the estimated value of the NH ₃ adsorption amount and setting the first correction amount of the reducing agent supply amount. The estimated value Vs of the NH ₃ adsorption amount is based on the supplied NH ₃ amount V1, the NH ₃ amount V2 consumed in the NO _x reduction reaction, and the NH ₃ amount V3 slipping the first selective reduction catalyst 231. It is calculated by the following formula. The symbol Σ in the following equation means that the estimated value Vs is obtained as an integrated value per unit time. In FIG. 5, the loop 37 of the block “1 / Z” means that this integration is performed.

Vs = Σ [V1-V2-V3]

The supplied NH ₃ amount V1 is calculated from the amount of urea water injected from the injector 253 using the hydrolysis reaction equation shown in FIG. The NH ₃ amount V2 consumed in the NO _x reduction reaction is determined as follows. It is converted into the amount of NO and NO ₂ amount using the NO _x conversion map the amount of NO _x detected by the NO _x sensor 28 is stored in advance in ECU3 memory. Similarly, purification (reduction) rates F1 and F2 for NO and NO ₂ are obtained from the NO _x purification rate map stored in the memory of the ECU 3. F1, F2 and NO amount, by multiplying each of the NO ₂ amount, and calculates the reduced amount of NO and reducing NO ₂ amount. The amount of NH ₃ corresponding to the amount of reduced NO and the amount of reduced NO ₂ is determined from each of the three reduction reaction formulas (1) to (3) in FIG. The total amount of NH ₃ obtained for each formula is the NH ₃ amount V2 consumed in the NO _x reduction reaction.

The NH ₃ amount V3 slipping the first selective reduction catalyst 231 is obtained as the NH ₃ weight by multiplying the NH ₃ concentration detected by the NH ₃ sensor 26 by a parameter such as the volume of the selective reduction catalyst obtained in advance.

In FIG. 5, the NH ₃ storage capacity Va of the first selective reduction catalyst is obtained from the NH ₃ storage capacity map stored in the memory of the ECU ₃ . This NH ₃ storage possible amount map corresponds to, for example, the relationship diagram between the catalyst temperature and the NH ₃ storage amount in FIG. As already described in the description of FIG. 3, the NH ₃ storage capacity at the predetermined temperature is used as the NH ₃ storage capacity Va when the catalyst temperature is before the predetermined temperature, and changes according to the catalyst temperature above the predetermined temperature ( Use (reduced) NH ₃ storage capacity.

The difference (Va−Vs) between the NH ₃ storage capacity Va and the calculated NH ₃ adsorption amount estimated value Vs becomes zero, in other words, the NH ₃ adsorption amount estimated value Vs can be stored in NH _3. A first correction amount (first FB correction amount) of the urea water supply amount is calculated as a control input for feedback (PI) control so as to converge to the amount Va. In FIG. 5, the corrected urea water amount is calculated.

Returning to FIG. 4, the second correction amount setting means 304 of the reducing agent supply amount, so that the difference between the NH ₃ concentration and the target NH ₃ concentration detected by the NH ₃ sensor 26 of FIG. 1 is zero, the reduction A second correction amount of the agent supply amount is set. More specifically, as is detected NH ₃ concentration converges to a preset target NH ₃ concentrations were, as a control input to the feedback control, the second correction amount of the supply amount of the urea water (second FB correction amount).

  The means 305 for setting the reducing agent supply amount from the first and second correction amounts is the first correction amount by using the urea water supply amount by the reducing agent supply means, that is, the urea water amount injected from the injector 253 of FIG. And the second correction amount.

  FIG. 6 is a diagram illustrating an example of a control flow for calculating the first and second correction amounts of the urea water supply amount according to the present invention. This control flow is executed every predetermined control cycle by calling a control program stored in the memory by the ECU 3.

  In step S1, it is determined whether or not the failure flag of the urea water injection device 25 is “1”. This failure flag is set to “1” when it is determined in the determination process (not shown) that the urea water injection device has failed, and is set to “0” otherwise. If this determination is Yes, the process moves to step S14, and the urea water injection amount is set to “0”, and then this process ends. If this determination is No, the process proceeds to step S2.

  In step S2, it is determined whether or not the deterioration flag of the selective reduction catalyst is “1”. This catalyst deterioration flag is set to “1” when it is determined in the determination process (not shown) that one of the first selective reduction catalyst 231 and the second selective reduction catalyst 232 in FIG. 1 has failed, and otherwise. Set to “0”. If this determination is Yes, the process moves to step S14, and the urea water injection amount is set to “0”, and then this process ends. If this determination is No, the process proceeds to step S3.

  In step S3, it is determined whether or not the urea water remaining amount is less than a predetermined value. The remaining amount of urea water indicates the remaining amount of urea water in the urea water tank 251 in FIG. 1, and is calculated based on the output of the level sensor. If this determination is Yes, the process moves to step S4, and if No, the process moves to step S5.

  In step S4, a warning light for the remaining amount of urea water is turned on, the process proceeds to step S14, and after the urea water injection amount is set to “0”, this process is terminated.

  In step S5, it is determined whether or not the warm-up timer value of the oxidation catalyst 21 in FIG. 1 is greater than a predetermined value. This catalyst warm-up timer value measures the warm-up time of the oxidation catalyst 21 after the engine is started. If this determination is Yes, the process proceeds to step S6. When this determination is No, the process proceeds to step S14, and after setting the urea water injection amount to “0”, this process is terminated.

In step S6, it is determined whether or not the sensor failure flag is “0”. This sensor failure flag is set to “1” when it is determined that at least one of the NH ₃ sensor 26 and the catalyst temperature sensor 27 in FIG. 1 has failed in a determination process (not shown), and “0” otherwise. "Is set. If this determination is Yes, the process proceeds to step S7. When this determination is No, the process proceeds to step S14, and after setting the urea water injection amount to “0”, this process is terminated.

In step S7, it is determined whether or not the activation flag of the NH ₃ sensor 26 is 1. The NH ₃ sensor activation flag is set to “1” when it is determined in the determination process (not shown) that the NH ₃ sensor 26 has reached the active state, and is set to “0” otherwise. If this determination is Yes, the process proceeds to step S8. When this determination is No, the process proceeds to step S14, and after setting the urea water injection amount to “0”, this process is terminated.

In step S8, it is determined whether the urea water is hydrolyzed and NH ₃ can be generated. Specifically, it is determined whether or not the temperature of the selective reduction catalyst 23 is equal to or higher than a predetermined temperature at which urea water can be hydrolyzed (for example, about 160 ° C.). When this determination is Yes, it is determined that the urea water is hydrolyzed and NH ₃ can be generated, and the process proceeds to step S9. When this determination is No, the process proceeds to step S14, and the urea water injection amount is set to “0”, and then this process ends.

In step S9, calculation of the urea water injection amount is started. First, in step S10, it is determined whether or not the temperature of the first selective reduction catalyst 231 is equal to or lower than a predetermined temperature. The predetermined temperature is, for example, a temperature (for example, 250 ° C.) at which the NO _x reduction ability (purification performance) of the first selective reduction catalyst is maximized. This predetermined temperature can be arbitrarily set basically according to the nature (type, composition, etc.) of the catalyst.

When the determination in step S10 is Yes (below the predetermined temperature), in step S11, as already described in the description of FIGS. 3 and 5, the NH ₃ storage possible amount at the predetermined temperature is set to the first selective reduction catalyst. This is set as the NH ₃ storage capacity of H.231. If the decision in step S10 is No (larger than a predetermined temperature), in step S12, NH ₃ storage amount capable of NH ₃ storage possible quantity varying according to the catalyst temperature (decreasing) the first selective reduction catalyst 231 Set as.

In step S13, a first corrected supply amount of urea water is calculated. At that time, the estimated storage NH ₃ amount captured by the first selective reduction catalyst 231 is calculated first. This calculation method is as described in the description of the calculation of the estimated amount Vs in FIG. Then, the first corrected supply amount of urea water is calculated using either the NH ₃ storage possible amount set in step S11 or S12 and the calculated estimated storage NH ₃ amount. The calculation method of the first correction supply amount is as described in the calculation of the corrected urea water (first FB correction amount) in FIG.

In step S14, it is determined whether or not the NH ₃ concentration that is the output of the NH ₃ amount sensor 26 is obtained. If this determination is Yes, it is determined that NH ₃ has been stored up to the maximum storage NH ₃ amount (for example, reference numeral 32 in FIG. 2) in the first selective reduction catalyst 231, and the process proceeds to step S15. If this determination is No, this process ends. That is, until the NH ₃ is stored up to the maximum storage NH ₃ amount in the first selective reduction catalyst 231, only the calculated first corrected supply amount of urea water is used as a control input for the urea water supply amount.

In step S <b> 15, the second corrected supply amount of urea water is calculated using the NH ₃ concentration that is the output of the NH ₃ amount sensor 26. The calculation method of the second correction supply amount is as described in the description of the calculation of the second FB correction amount by the second correction amount setting unit 303 of the reducing agent supply amount in FIG. Thus, in the present invention, after the NH ₃ concentration is detected, in other words, after the NH ₃ is stored up to the maximum storage NH ₃ amount in the first selective reduction catalyst 231, the second corrected supply amount is calculated. Therefore, after the maximum storage, both the second correction supply amount and the first correction supply amount can be used as a control input for the urea water supply amount.

FIG. 7 is a diagram showing the relationship between the catalyst temperature, the urea water correction amount based on the estimated storage F / B, the NH ₃ concentration, and the NH ₃ storage amount. (A) is an example shown for comparison, and is a case where the NH ₃ target amount is set as a storage-capable amount regardless of the catalyst temperature. (B) is an example of the present invention, in which the NH ₃ target amount is set to a storageable amount at a predetermined temperature when the catalyst temperature is equal to or lower than the predetermined temperature.

In FIG. 7A, when the catalyst temperature rises and reaches a temperature at which urea water can be hydrolyzed (for example, 160 ° C.), supply of urea water from the injector 253 is started. In response to the start of supply of urea water, urea water correction by NH ₃ sensor F / B control, that is, correction by the above-described first FB correction amount is started. The supply amount of urea water is corrected until an NH ₃ sensor reaction, that is, NH ₃ full (maximum) storage in the first selective reduction catalyst 231 is obtained (1). At this time, since the NH ₃ storage target value (possible amount) is large, the supply amount correction input also becomes large, and a large amount of excessively supplied urea water is generated.

NH ₃ from the sensor response was obtained, although the detected NH ₃ concentration is in the F / B control to converge to a preset target NH ₃ concentrations were, NH ₃ in the first selective reduction catalyst 231 full ( (Maximum) Since the supply amount of urea water was corrected to the maximum extent to the storage, the NH ₃ concentration greatly exceeded the target NH ₃ concentration (2). That is, a large amount of NH ₃ slip occurs as the NH ₃ storage capacity of the first selective reduction catalyst 231 decreases as the temperature of the catalyst increases (3).

In FIG. 7B, as in the case of FIG. 7A, when the catalyst temperature reaches a temperature at which urea water can be hydrolyzed (for example, 160 ° C.), supply of urea water from the injector 253 is started. In response to the start of supply of urea water, urea water correction by NH ₃ sensor F / B control, that is, correction by the above-described first FB correction amount is started. However, unlike the case of (a), the NH ₃ storage target value (possible amount) is the storable amount when the catalyst temperature is a predetermined temperature (for example, 250 ° C.), that is, the NH ₃ storage target value (possible amount). ) Is relatively small, the supply amount correction input becomes small and excessive supply of urea water can be suppressed (1). That is, in this case, the NH ₃ storage amount in the first selective reduction catalyst 231 increases at a slower storage speed than in the case of (a) (1).

After the NH ₃ sensor reaction is obtained, urea water correction by the NH ₃ sensor F / B control (correction by the second FB correction amount) is started. NH ₃ storage amount in order to have increased moderately, NH ₃ concentration without exceed greatly the target NH ₃ concentration, is rapidly controlled such that it converges to the target NH ₃ concentration (2). As a result, the NH ₃ slip amount decreases and converges more quickly than in the case of (a) (3).

The above-described embodiment is an example, and the present invention is not limited to this. The present invention is applicable to an engine having an arbitrary number of cylinders. The present invention can also be applied to an engine such as a direct injection gasoline engine. Furthermore, the present invention can be applied not only to the urea water supply that is the above-described embodiment but also to the case where gaseous NH ₃ is directly supplied as the reducing agent supply. For example, when using the embodiment of FIG. 1, NH ₃ gas can be directly supplied by using an NH ₃ gas supply device instead of the urea water injection device 25.

Claims (3)

An exhaust purification device for an internal combustion engine,
A selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine, captures NH ₃ as a reducing agent, and reduces NO _x flowing through the exhaust passage using the captured NH _3. A selective reduction catalyst including a second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage;
Reducing agent supply means for supplying the reducing agent to the upstream side of the selective reduction catalyst in the exhaust passage;
Catalyst temperature detection means for detecting the temperature of the first selective reduction catalyst;
Means for setting the NH ₃ storage possible amount in the first selective reduction catalyst according to the temperature of the first selective reduction catalyst;
Means for calculating the amount of NH ₃ in the first selective reduction catalyst;
Correction amount setting means for setting a correction amount of the reducing agent supply amount so that a difference between the calculated NH ₃ amount and the NH ₃ storage possible amount in the first selective reduction catalyst decreases;
A reducing agent supply amount setting means for setting a reducing agent supply amount by the reducing agent supply means using the correction amount;
Said NH ₃ means for calculating the storage possible amount available NH ₃ storage of the first selective reduction temperature NH ₃ storage amount capable the first selective reduction in catalyst in the predetermined temperature until a predetermined temperature of the catalyst An exhaust purification device for an internal combustion engine, which is set as a quantity. Means for calculating the NH ₃ storage possible amount, if the temperature of the first selective reduction catalyst is equal to or higher than a predetermined temperature, NH of the first selective reduction in catalyst according to the temperature detected by the catalyst temperature detecting means _3. The exhaust emission control device according to claim 1, wherein the exhaust gas purifying device is set so that the storage capacity is small. Wherein the predetermined temperature, NO _x reduction capability of the first selective reduction catalyst is a temperature at which the maximum exhaust gas purification device according to claim 1 or 2.

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