WO2011099051A1

WO2011099051A1 - Exhaust gas purification device for internal combustion engine

Info

Publication number: WO2011099051A1
Application number: PCT/JP2010/000792
Authority: WO
Inventors: 羽賀久夫; フィッシャーミハエル
Original assignee: 本田技研工業株式会社
Priority date: 2010-02-09
Filing date: 2010-02-09
Publication date: 2011-08-18
Also published as: DE112010005244T5

Abstract

Disclosed is an exhaust gas purification device for an internal combustion engine. The exhaust gas purification device is equipped with a selective reduction catalyst that is provided in the exhaust passage of the internal combustion engine, captures the reducing agent NH₃, and uses the captured NH₃ to reduce NO_x flowing through the aforementioned exhaust passage; a reducing agent supply means that supplies the reducing agent upstream of the selective reduction catalyst in the exhaust passage; and a reducing agent supply setting means that sets the amount of the reducing agent supplied by the reducing agent supply means. In cases in which it is necessary to set a shorter supply period than the minimum supply period that can be controlled by the reducing agent supply means, the reducing agent supply setting means sets the supplied amount of the reducing agent on the basis of said minimum supply period while lengthening the intervals between the supply of said reducing agent.

Description

Exhaust purification system for internal combustion engine

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.

Conventionally, as one of exhaust purification devices for purifying NO _x in exhaust, a device has been proposed in which a selective reduction catalyst for selectively reducing NO _x in exhaust by adding a reducing agent is provided in an exhaust passage. There is. For example, in a urea addition type selective reduction catalyst using urea water as a reducing agent, the added urea is hydrolyzed to form ammonia (NH ₃ ), and NH ₃ selectively reduces NO _x in exhaust gas. .

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 If the amount is larger than the amount, excess NH ₃ is exhausted for the reduction of NO _x . For this reason, in the exhaust gas purification apparatus provided with the selective reduction catalyst, it is important to appropriately control the injection amount of the reducing agent.

Japanese Patent Application Laid-Open No. 2001-323835 (Patent Document 1) discloses an exhaust gas purification apparatus for an internal combustion engine. In this exhaust gas control apparatus, the amount of HC supplied to the exhaust gas purification is controlled by controlling the interval between the main injection amount of fuel and the sub injection.

JP 2001-323835 A

When properly controlling the injection amount of the reducing agent, if the injection amount of the reducing agent reaches a flow rate lower than the injection resolution that can be controlled by the injector, specify the injection time that corresponds to the injection amount. Even injection as specified may not be guaranteed.

In addition, the selective reduction catalyst has an ability to adsorb NH ₃ , and the NH ₃ adsorbable amount tends to decrease depending on the temperature and the degree of deterioration of the selective reduction catalyst. For this reason, if the reducing agent is constantly injected at a constant interval, the reducing agent becomes excessive to exceed the NH ₃ adsorbable amount, and the NH ₃ slip from the exhaust pipe increases.

However, the exhaust gas purification apparatus described in Japanese Patent Application Laid-Open No. 2001-323835 (Patent Document 1) does not disclose a technique for controlling the injection amount of the reducing agent.

Therefore, in the exhaust gas purification apparatus for an internal combustion engine provided with a selective reduction catalyst, the present invention appropriately controls the injection amount of the reducing agent to suppress a large amount of NH ₃ slips larger than the NH ₃ adsorbable amount from the selective reduction catalyst. The purpose is to

The present invention provides an exhaust purification system of an internal combustion engine. The exhaust gas purification apparatus is provided in an exhaust gas passage of an internal combustion engine, and is configured to capture NH ₃ which is a reducing agent, and to reduce NO _x flowing in the exhaust gas passage using captured NH ₃ A reduction catalyst, reducing agent supply means for supplying a reducing agent to the upstream side of the selective reduction catalyst in the exhaust passage, and reducing agent supply amount setting means for setting the supply amount of reducing agent by the reducing agent supply means The agent supply amount setting means sets the supply amount of the reducing agent based on the minimum supply time and sets the supply amount of the reducing agent, when the supply time shorter than the controllable minimum supply time has to be set. Increase the feed interval.

According to the present invention, it is possible to precisely adjust (secure) the required amount of the reducing agent supplied by controlling the reducing agent supplying time and the supplying interval of the reducing agent by the reducing agent supplying means with high accuracy. As a result, it is possible to avoid the lack of purification of NO _x and the increase of the slip amount of NH ₃ .

According to one aspect of the present invention, the system further comprises means for calculating the purification rate of the selective reduction catalyst and means for determining the degree of deterioration of the selective reduction catalyst from the purification rate, and the reducing agent supply amount setting means And / or reducing the feed time of the reducing agent and / or increasing the feed interval.

According to one aspect of the present invention, it is possible to accurately adjust (secure) the necessary amount of the reducing agent supplied in consideration of the deterioration degree of the selective reduction catalyst.

According to one aspect of the present invention, the catalyst temperature detection means for detecting the temperature of the selective reduction catalyst, and the NH ₃ storage capacity in the selective reduction catalyst are set according to the temperature of the selective reduction catalyst and the degree of deterioration of the selective reduction catalyst. Means for calculating the amount of NH ₃ in the selective reduction catalyst, and the reducing agent supply amount setting means calculates the difference between the calculated amount of NH ₃ and the NH ₃ storage capacity in the selective reduction catalyst. The supply amount of the reducing agent by the reducing agent supply means is set based on the above.

According to one aspect of the present invention, it becomes possible to adjust (secure) the amount of supply of the reducing agent, which is necessary according to the temperature and the degree of deterioration of the selective reduction catalyst, with high accuracy and without excess or deficiency.

According to an embodiment of the present invention, means for setting the NH ₃ storage possible amount in the selective reduction catalyst to reduce the NH ₃ storage amount capable of the selective reduction the catalyst in accordance with the deterioration degree.

FIG. 1 is a schematic view showing a configuration of an engine and its exhaust gas purification apparatus according to one embodiment of the present invention. 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 showing composition (function) of ECU3. It is a figure which shows the example of control of injection time and injection interval of urea water. It is a figure which shows the example of injection control of the urea water corresponding to deterioration of the selective reduction catalyst. NH ₃ storage amount capable is a diagram illustrating a control flow of the injection time and the injection interval of urea water when reduced. It is a figure showing an example of control which secures a predetermined flow as an accuracy guarantee interval as injection time (opening time). It is an example of composition for controlling injection time (valve opening time) and injection interval. It is a figure which shows the flow of injection amount control of urea water.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a configuration of an internal combustion engine (hereinafter referred to as “engine”) 1 and an exhaust gas 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 is provided downstream of the oxidation catalyst 21 provided in the exhaust passage 11 of the engine 1 and the oxidation catalyst 21 of the exhaust passage 11, and nitrogen oxides in the exhaust flowing through the exhaust passage 11 (hereinafter Selective reduction catalyst 23 for purifying NO _x )) in the presence of a reducing agent, a urea water injection device 25 for supplying urea water as a reducing agent upstream 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 including a central processing unit (CPU) and a memory. The memory can store computer programs for realizing various control of the vehicle and data, tables, and maps necessary for the execution of the programs. As will be described later, the ECU 3 receives data sent from each part (sensor etc.) 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 passage 254 and a pump (not shown). The tank 251 is provided with a urea water level sensor 255. The sensor 255 detects the level of urea water in the tank 251, and outputs a detection signal corresponding to the 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 the injection time (second / one shot) and the injection interval (second, cycle (Hz)) set by the ECU 3.

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 the NO that occupies most of the NO _{x in} the exhaust into NO ₂ , thereby the selective reduction catalyst Promote the reduction of NO _x at 23

The selective reduction catalyst 23 includes at least one selective reduction catalyst 231. The selective reduction catalyst may further have two or more reduction catalysts downstream of the selective reduction catalyst 231. Selective reduction catalyst 231, in an atmosphere of ammonia as a reducing agent is present, to selectively reduce NO _x in the exhaust. Specifically, when urea aqueous solution is injected by the aqueous urea solution injector 25, ammonia (hereinafter referred to as "NH ₃ ") is generated from urea by hydrolysis, and this NH ₃ causes NO _x in exhaust gas in the selective reduction catalyst 23 (NO and NO ₂ ) are selectively reduced.

Selective reduction catalyst 231 also has a function of storing (adsorbing) the NH _3, NO _x is reduced and purified by NH ₃ that is stored. FIG. 2 is a view showing the relationship between the temperature of the selective reduction catalyst and the NH ₃ storage capacity. The NH ₃ storage capacity tends to be large at low temperatures and to decrease as the temperature is high. This NH ₃ storage capacity tends to further decrease as the selective reduction catalyst 231 degrades.

In addition to the NH ₃ sensor 26, the catalyst temperature sensor 27, and the NO _x sensors 28, 29, the crank angle position sensor 14, the accelerator opening sensor 15, and the urea water remaining amount warning light 16 are connected to the ECU 3.

The NH ₃ sensor 26 detects the concentration of ammonia in the exhaust after the selective reduction catalyst 231 in the exhaust passage 11 (hereinafter referred to as “NH ₃ concentration”), and sends a detection signal corresponding to the detected NH ₃ concentration to the ECU 3 .

The catalyst temperature sensor 27 detects the temperature of the 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 sensors 28, 29 detect the concentration of NO _{x in} the exhaust flowing into or out of the selective reduction catalyst 231, and send 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 every one 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 a specific cylinder and sends it to the ECU 3.

The accelerator opening sensor 15 detects a depression amount 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. The ECU 3 calculates the required torque of the engine 1 according to the accelerator opening degree and the rotation speed.

The urea water remaining amount warning light 16 is provided, for example, on a meter panel of the vehicle, and lights up in response to the remaining amount of urea water in the tank 251 becoming smaller than a predetermined remaining amount. This warns the driver that the remaining amount of urea water in the tank 251 has decreased.

FIG. 3 is a block diagram showing the configuration (function) of the ECU 3 of FIG. The function of each block is realized by the CPU of the ECU 3 reading out and executing a control program stored in a memory (not shown). The NH ₃ amount calculation means 301 of the selective reduction catalyst calculates the NH ₃ amount (estimated amount) to be stored (adsorbed) on the selective reduction catalyst 231 of FIG. It means for setting the NH ₃ storage amount capable 302 sets the NH ₃ storage possible amount in the selective reduction catalyst depending on the temperature and the degree of degradation of the selective reduction catalyst 231.

The reducing agent supply amount setting unit 303 supplies the reducing agent (urea water) supplied amount (injection amount) by the urea water injection device 25 based on the difference between the calculated NH ₃ amount and the NH ₃ storage possible amount in the selective reduction catalyst. Set At that time, the reducing agent supply amount setting unit 303 injects urea water by the minimum injection time when the injection time shorter than the minimum injection time controllable by the injector 253 of the urea water injection device 25 has to be set. At the same time, the injection interval of urea water is extended to adjust the supply amount of urea water.

FIG. 4 is a diagram showing an example of control of injection time and injection interval of urea water by the reducing agent supply amount setting means 303. As shown in FIG. (A) is a conventional example shown for comparison, (b) is an example of the present invention.

In the conventional example shown in FIG. 4A, it is assumed that an injection command amount 41 smaller than the lower limit injection amount for securing the accuracy of the injector 253 is set. The injector 253 injects urea water at an injection time (opening time) T1 shorter than the accuracy ensuring interval (opening time) T0 and at a predetermined injection interval T2 in order to satisfy the injection instruction amount 41. However, since the injection time (opening time) T1 can not be sufficiently controlled, the actual injection amount per shot varies. In this case, as shown in the figure, the fluctuation of the NH ₃ storage amount at the selective reduction catalyst 231 becomes large, and the NH ₃ storage amount becomes extremely small relative to the NH ₃ storable amount, or conversely becomes excessive. It passes by. As a result, NH ₃ strips of the downstream side of the exhaust pipe (T / P) NO _x amount increases or exiting, or the exhaust pipe to the (T / P) of the selective reduction catalyst 23 is increased.

In the embodiment of the present invention shown in FIG. 4 (b), even when the injection instruction amount 41 smaller than the lower limit injection amount for securing the accuracy of the injector 253 is indicated, the reducing agent supply amount setting means 303 Control is made to inject urea water at accuracy guarantee interval (opening time) T0. At this time, the injection interval of urea water is set to T3 (> T2), which is longer than T2 in (a), in order to prevent the injection amount of urea water from increasing as a whole. As a result, the variation in the injection amount per shot by the injector 253 becomes smaller, and as shown in the drawing, the variation in the NH ₃ storage amount in the selective reduction catalyst 231 becomes relatively smaller. As a result, it is an increase in NH ₃ strips of the amount of NO _x increases and the exhaust pipe exiting from the downstream side of the exhaust pipe (T / P) of the selective reduction catalyst 23 (T / P) inhibition, to avoid.

Returning to FIG. 3, the means 304 for calculating the purification rate of the selective reduction catalyst uses the NO _x concentration outputs N 1, N 2 of the NO _x sensors 28, 29 when the engine 1 is in a predetermined operation state. Calculate R from equation (1). Concentration of NO _x output N2 of the NO _x sensor downstream of the catalyst increases as the selective reduction catalyst deteriorates.
R = (N1-N2) / N1 (1)

The means 305 for determining the degree of deterioration of the selective reduction catalyst determines the degree of deterioration of the selective reduction catalyst based on the calculated purification rate R. The determination is performed as follows, for example. When the purification rate R is (i) a predetermined value R1 or less (R <R1), the deterioration degree is determined to be "large", and (ii) a predetermined value R2 or more larger than R1 (R> R2) The degree of deterioration is judged to be "small", and (iii) it is judged that the degree of deterioration is "medium" when R1 and R2 (R2> R> R1).

The reducing agent supply amount setting unit 303 injects urea water by shortening the injection time (opening time) of the urea water by the injector 253 or prolonging the injection interval according to the determined degree of deterioration. Control the quantity. For example, as the above-mentioned degree of deterioration progresses from "small"-> "medium"-> "large", the injection time (opening time) of urea water is shortened stepwise and the degree of deterioration is "large". When the accuracy guarantee interval (opening time) T0 is set. Similarly, as the degree of deterioration progresses from "small"-> "medium"-> "large", the injection interval (period) of urea water is gradually lengthened.

FIG. 5 is a view showing an example of injection control of urea water corresponding to the deterioration of the selective reduction catalyst. As shown in (a), the purification rate R represented by the equation (1) decreases with the passage of time, and the catalyst is deteriorated. Depending on the progress of the deterioration, as shown in (b), the injection time (opening time) of urea water is shortened, and finally the accuracy guarantee interval (opening time) when the degree of deterioration is "large" ) Make it to be T0. In addition, the injection interval of urea water is gradually increased from T2 to T3. As a result, the injection amount of urea aqueous solution is suppressed, and as shown in (c), the actual NH ₃ storage amount can be reduced to correspond to the NH ₃ storage possible amount which decreases with the deterioration of the catalyst. . At the same time, it is possible to suppress (avoid) the increase in the amount of NH ₃ stripping to the exhaust pipe (T / P).

FIG. 6 is a diagram showing a control flow of injection time and injection interval of urea water when the NH ₃ storable amount in the catalyst decreases due to deterioration or the like. The NH ₃ storage capacity V1 is calculated according to the degree of deterioration of the catalyst. At that time, the NH ₃ storage capacity map A stored in the memory of the ECU ₃ is used. As already mentioned, the NH ₃ storage capacity V 1 decreases as the catalyst temperature rises (FIG. 2) and as the deterioration progresses (c in FIG. 5). 1 shot (injection) injection amount of each of the urea solution in terms of the amount of NH ₃ with the formula B of hydrolysis determines the supply amount of NH ₃ V2.

The amount of NH ₃ V ₃ 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 concentration of NO _x detected by the NO _x sensor 28 is stored in advance in ECU3 memory. Similarly, the 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. The reduced NO amount and the reduced NO ₂ amount are calculated by respectively multiplying the NO amount and the NO ₂ amount by F 1 and F ₂ . From each of the reduction reaction formulas C ((1) to (3)) in FIG. 6, the amount of NH ₃ corresponding to the amount of reduced NO and the amount of reduced NO ₂ is determined. The total amount of NH ₃ obtained for each formula is the amount of NH ₃ V ₃ consumed in the NO _x reduction reaction.

Amount NH ₃ which remaining by subtracting the consumption amount of NH ₃ V3 from the supply NH ₃ amount V2 (V2-V3) and by adding over a predetermined injection period (number of shots), the catalyst at a predetermined injection period (number of shots) Calculate the NH ₃ amount V4 stored inside. The correction amount T1 of the injection time of the urea water is calculated from the magnitude of the difference (V1-V4) between the NH ₃ storage possible amount V1 and the storage NH ₃ amount V4 previously obtained. That is, for example, when the difference (V1-V4) is large, the correction amount T1 is set large so as to increase the injection amount, and conversely, when the difference is small (including minus), the correction amount is decreased. Set T1 small.

The injection amount for each shot (injection) of urea water is multiplied by a predetermined conversion factor, and an injection period (opening period) T2 corresponding to the injection amount is calculated. The correction amount T1 is subtracted from the injection period (opening period) T2 to determine the injection injection period (T2-T1) after correction. The injector 253 is instructed to perform this injection period (T2-T1). The injection interval (T3 × T2 / T1) obtained by multiplying the ratio (T2 / T1) to the injection interval T3 before correction is instructed to the injector 253 as the injection interval after correction. This ratio (T2 / T1) corresponds to a coefficient that decreases the injection interval in accordance with the increase or decrease of the injection injection period (T2-T1) after correction in order to secure (maintain) a predetermined injection flow rate.

The control method of the injection time (opening time) and the injection interval of the injector 253, which are used in the above-described examples of FIGS. 4 to 6, will be described using FIGS. 7 and 8. FIG. FIG. 7 shows an example of control for securing a predetermined flow rate with the injection time (opening time) as the accuracy guarantee interval. FIG. 8 is a configuration example for controlling the injection time (opening time) and the injection interval.

In FIG. 7, (a) is an example of securing the instructed flow rate of 0.26 g / min by injecting it for 1 minute in a 1 Hz cycle with an accuracy ensuring interval of 10 ms. (B) is an example in which when the indicated flow rate becomes 0.13 g / min which is half of (a), the indicated flow rate is secured by injecting for 1 minute in 0.5 Hz cycle of accuracy guarantee interval 10 ms. . In (b), the divided injection cycle (interval) in which the indicated flow rate is half of (a) is twice as large as (a). (C) is secured by injecting the indicated flow rate for 1 minute in a 0.1 Hz cycle with a precision guarantee interval of 10 ms, when the indicated flow rate reaches 0.026 g / min, which is one-tenth of (a). This is an example of In (c), the injection period (interval) is 10 times as large as (a), as the indicated flow rate becomes 1/10 of (a). As described above, even when the injection time (the valve opening time) is the accuracy guarantee interval, it is possible to secure the necessary injection flow rate by adjusting the injection interval.

In FIG. 8, it is assumed that the ECU 3 instructs the valve opening time of the injection valve of the injector 253 as the energization period TA (ms). The TA is set in units of 1 ms (TA = n (ms), n is an arbitrary integer). The comparator 43 compares whether TA (ms) is greater than 10 ms. 10 ms is the accuracy guarantee interval (opening time) of the injection valve of the injector 253. If TA is greater than 10 ms, the TA value is selected by the selector 44 and is output as it is as the energization period. When TA is 10 ms or less, 10 ms is selected in the selector 44, and is output as an energization period.

Furthermore, in the comparator 45, it is determined whether TA is equal to each value of 1 ms to 10 ms every 1 ms. If TA is equal to any value between 1 ms and 10 ms, then the period 46 corresponding to that value is selected. For example, in the case of TA = 1 ms, 0.1 Hz is selected. When TA is 10 ms or more, 1 Hz is selected as the period. The selected cycle is sent to the selector 47, where it is output as the energization interval, ie, the injection interval.

FIG. 9 is a diagram showing a flow of injection amount control of urea water. The control flow is executed at predetermined control cycles by calling a control program stored in the memory by the ECU 3.

In step S1, it is determined whether the failure flag of the urea water injection device 25 is "1". The failure flag is set to “1” when it is determined that the urea water injection device has failed in a determination process not shown, and is set to “0” otherwise. If the determination is Yes, the process proceeds to step S16, and after the urea water injection amount is set to "0", the process ends. If the determination is No, the process proceeds to step S2.

In step S2, it is determined whether the deterioration flag of the selective reduction catalyst is "1". The catalyst deterioration flag is set to “1” when it is determined that the selective reduction catalyst 231 of FIG. 1 has failed in the determination process (not shown), and is set to “0” otherwise. If the determination is Yes, the process proceeds to step S16, and after the urea water injection amount is set to "0", the process ends. If the determination is No, the process proceeds to step S3.

In step S3, it is determined whether the residual amount of urea water 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 of FIG. 1 and is calculated based on the output of the level sensor. If the determination is Yes, the process proceeds to step S4, and if the determination is No, the process proceeds to step S5.

In step S4, the warning light for the urea water remaining amount is turned on, and the process proceeds to step S16. After the urea water injection amount is set to "0", this process is ended.

In step S5, it is determined whether the warm-up timer value of the oxidation catalyst 21 of FIG. 1 is larger than a predetermined value. The catalyst warm-up timer value measures the warm-up time of the oxidation catalyst 21 after the engine start. If this determination is Yes, the process proceeds to step S6. If the determination is No, the process proceeds to step S16, and after the urea water injection amount is set to "0", the process ends.

In step S6, it is determined whether 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, the catalyst temperature sensor 27 and the NO _x sensor 28, 29 in FIG. 1 has failed in the determination process not shown. Otherwise, it is set to "0". If this determination is Yes, the process proceeds to step S7. If the determination is No, the process proceeds to step S16, and after the urea water injection amount is set to "0", the process ends.

In step S7, it is determined whether the activation flag of the NH ₃ sensor 26 is one. The NH ₃ sensor activation flag is set to “1” when it is determined that the NH ₃ sensor 26 has reached the active state in a determination process not shown, and is set to “0” otherwise. If this determination is Yes, the process proceeds to step S8. If the determination is No, the process proceeds to step S16, and after the urea water injection amount is set to "0", the process ends.

In step S8, it is determined whether or not the aqueous urea solution is hydrolyzed to generate NH ₃ . Specifically, it is determined whether the temperature of the selective reduction catalyst 23 is equal to or higher than a predetermined hydrolyzable temperature (for example, about 160 ° C.) of urea water. When this determination is Yes, it is judged that urea aqueous solution is hydrolyzed and that NH ₃ can be generated, and the process moves to step S9. If the determination is No, the process proceeds to step S16, the urea water injection amount is set to "0", and the process ends.

In step S9, calculation of the urea water injection amount is started. First, in step S10, it is determined whether the urea water injection amount is equal to or more than a predetermined amount. Here, the predetermined amount refers to the flow rate injected at the accuracy guarantee interval (for example, 10 ms) of the injector 253 already described. If the determination is Yes, the process proceeds to step S11, where the degree of deterioration of the selective reduction catalyst 231 is determined. The determination method is as described above. Then, in the next step S12, the injection time and injection interval of the injector 253 are set in accordance with the determined degree of deterioration. The setting method is as described above with reference to FIGS.

If the determination in step S10 is No, that is, if an injection time shorter than the accuracy guarantee interval (for example, 10 ms) is set, then in step S13, the accuracy guarantee interval (for example, 10 ms) is set as the injection time. Thereby, the error of the actual injection amount by the injector 253 is suppressed. In the next step S14, the injection interval required to secure a predetermined injection flow rate is determined. The determination method is as described above with reference to FIGS. Finally, in step S15, the injector 253 is instructed of the urea water injection time (opening period) and injection interval (cycle) determined in step S12, S13, or S14.

The embodiment described above is an example and is not limited thereto. The invention is applicable to engines having any number of cylinders. The present invention is also applicable to an engine such as a direct injection gasoline engine. Furthermore, the present invention is applicable not only to the aqueous urea solution supply according to the above-described embodiment as the reducing agent supply but also to the case where gaseous NH ₃ is directly supplied. 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

An exhaust gas purification apparatus for an internal combustion engine
Provided in an exhaust passage of an internal combustion engine, as well as capturing the NH 3 as a reducing agent, a selective reduction catalyst for reducing NO x flowing through the exhaust passage by using the NH 3 was captured,
Reductant supply means for supplying the reductant upstream of the selective reduction catalyst in the exhaust passage;
A reducing agent supply amount setting unit configured to set a supply amount of the reducing agent by the reducing agent supply unit;
When the reducing agent supply amount setting means has to set a supply time shorter than the minimum supply time controllable by the reducing agent supply means, the reducing agent supply amount is set based on the minimum supply time, An exhaust gas purification apparatus for an internal combustion engine, which extends the supply interval of the reducing agent.
A means for calculating a purification rate of the selective reduction catalyst;
Means for determining the degree of deterioration of the selective reduction catalyst from the purification rate;
The exhaust gas purification apparatus according to claim 1, wherein the reducing agent supply amount setting means performs at least one of shortening the supply time of the reducing agent and prolonging the supply interval according to the degree of deterioration. .
Catalyst temperature detection means for detecting the temperature of the selective reduction catalyst;
A means for setting the NH 3 storable amount in the selective reduction catalyst according to the temperature of the selective reduction catalyst and the deterioration degree of the selective reduction catalyst;
And means for calculating the amount of NH 3 in the selective reduction catalyst,
The reducing agent supply amount setting means sets the supply amount of the reducing agent by the reducing agent supply means based on the difference between the calculated NH 3 amount and the NH 3 storable amount in the selective reduction catalyst. The exhaust purification device described in.
It said means for setting the NH 3 storage amount capable of selective reduction in catalyst decreases the NH 3 storage amount capable of the selective reduction the catalyst according to the deterioration degree, the exhaust purifying apparatus according to claim 3.