DE102008043895B4 - Exhaust control device - Google Patents

Abstract

An exhaust gas control apparatus for generating a reducing agent from an additive agent by using heat of an exhaust gas discharged from an internal combustion engine (1) and reducing nitrogen oxide contained in the exhaust gas by the reducing agent, the apparatus comprising: an exhaust pipe (2); which defines a passage for the exhaust air; a catalyst (3) disposed in the exhaust pipe (2), the catalyst (3) being capable of promoting a reduction reaction of the nitrogen oxide in the exhaust gas; supply means (5) for supplying the additive agent to an upstream side of the catalyst (3) in a flow direction of the exhaust gas air; a temperature detecting means (8) for detecting a temperature of the exhaust gas flowing through the exhaust pipe (2); and control means (10) for controlling the supply means (5) to regulate an amount of the additive agent supplied into the exhaust pipe (2), wherein: the control means (10) stops the supply of the additive means when the temperature of the exhaust gas passing through the temperature detecting means (8) is detected to be less than a generation temperature required to produce the reducing agent from the additive agent and to supply the additive agent when the temperature of the exhaust gas air is equal to or greater than the generation temperature; characterized in that, when a predetermined time elapses after a start of supply of the additive agent, the control means (10) reduces the amount of the additive agent to be supplied as compared with the amount of the additive agent supplied before the predetermined time has elapsed the predetermined time is set to a time equal to or shorter than a time in which an amount of the generated reducing agent exceeds an amount that can be adsorbed in the catalyst (3).

Description

The invention relates to an exhaust gas control device for reducing nitrogen oxide in an exhaust air of an internal combustion engine, such as a diesel engine. The invention is effectively applied to a vehicle.

According to an exhaust gas control apparatus for reducing nitrogen oxide (NOx) contained in an exhaust gas of an internal combustion engine such as a diesel engine, the nitrogen oxide is purified (reduced) by providing a catalyst in an exhaust pipe that promotes a reduction reaction, and by Additive agent, such as an aqueous urea solution, is injected into exhaust gas flowing into the catalyst (see, for example, US Pat JP 2003-293739 A ).

More specifically, urea (CO (NH 2) 2) injected into an exhaust air is hydrolyzed by an exhaust heat (CO (NH 2) 2 + H 2 O → 2NH 3 + CO 2) to generate ammonia (NH 3), which is a reducing agent. Then, the nitrogen oxide is reduced by a reaction between the nitrogen oxide and the ammonia through the catalyst.

An exhaust gas temperature must be equal to or greater than a temperature of 170 ° C to 175 ° C (hereinafter referred to as ammonia generation temperature) to hydrolyze the urea by the exhaust heat. Therefore, even if urea is added to the exhaust gas when the exhaust gas temperature is lower than the ammonia generation temperature, the nitrogen oxide can not be reduced by the ammonia and, moreover, the urea is discharged into the atmosphere without being hydrolyzed, so that the urea wastes wastefully becomes.

DE 10 2006 057 325 A1 discloses an exhaust gas purifying apparatus having a NOx catalyst for treating NOx contained in exhaust gas by using ammonia as a reducing agent, an ammonia supply device for supplying ammonia to the NOx catalyst, a catalyst temperature sensor for detecting the internal temperature of the NOx catalyst, and a control unit; the ammonia supply from the ammonia supply device stops, when the stop condition is satisfied, that the internal temperature (Ts) of the NOx catalyst becomes equal to or higher than a first prescribed temperature in the process in which ammonia is supplied from the ammonia supply device to the NOx catalyst becomes.

JP H06 129 238 A also relates to an exhaust emission control device, wherein an electronic control unit calculates a delivery volume of the reducing agent necessary for consuming the oxygen in the exhaust gas from a detected oxygen density and a reducing agent amount adhered to the wall surface of an exhaust system from a detected exhaust gas temperature, and Also controls the flow rate of the reducing agent, which is injected from a reducing agent injection valve in accordance with the values thus calculated. As a result, since a suitable volume of the reducing agent is always supplied to the NOx absorbent, it is possible to prevent the occurrence of insufficient or excessive delivery volume of the reducing agents. The invention addresses the above disadvantages. Therefore, it is an object of the invention to prevent an additive agent, such as urea, from being wastefully consumed, and to reliably reduce (purify) nitrogen oxide.

In order to achieve the object of the present invention, an exhaust gas control device according to claim 1 is provided. A further education is subject of the subclaim. In order to generate a reducing agent from an additive agent by using heat of an exhaust gas discharged from an internal combustion engine and to reduce nitrogen oxide contained in the exhaust gas by the reducing agent, the apparatus has an exhaust pipe, a catalyst, a supply device, a temperature detection device and a control device. The exhaust pipe defines a passage for the exhaust air. The catalyst is arranged in the exhaust pipe. The catalyst is capable of promoting a reduction reaction of the nitrogen oxide in the exhaust gas. The supply air serves to supply the additive agent to an upstream side of the catalyst in a flow direction of the exhaust gas air. The temperature detecting means is for detecting a temperature of the exhaust gas flowing through the exhaust pipe. The control means is for controlling the supply means to regulate an amount of the additive agent supplied into the exhaust pipe. The controller stops the supply of the additive agent when the temperature of the exhaust gas detected by the temperature detecting means is smaller than a generation temperature required to generate the reducing agent from the additive agent and supplies the additive agent when the temperature of the exhaust air is equal to or greater than the generation temperature. When a predetermined time has elapsed after a start of the supply of the additive agent, the control means reduces the amount of the additive agent supplied, compared with the amount of the additive agent supplied before the predetermined time has elapsed. The "predetermined time" may be a time equal to or shorter than a time in which an amount of the generated reducing agent exceeds an amount in the catalyst 3 can be adsorbed ".

Further, an exhaust gas control device is provided for generating a reducing agent from an additive agent by using heat of exhaust gas discharged from an internal combustion engine and reducing nitrogen oxide contained in the exhaust gas by the reducing agent. The apparatus has an exhaust pipe, a catalyst, a feeder, a temperature detector, a reductant detector, and a controller. The exhaust pipe defines a passage for the exhaust air. The catalyst is arranged in the exhaust pipe. The catalyst is capable of promoting the reduction reaction of nitrogen oxide in the exhaust gas. The supply means serves to supply the additive agent to an upstream side of the catalyst in a flow direction of the exhaust gas air. The temperature detecting means is for detecting a temperature of the exhaust gas flowing through the exhaust pipe. The reducing agent detecting means is disposed on a downstream side of the catalyst in the flow direction of the exhaust gas to detect the reducing agent. The control means is for controlling the supply means to regulate an amount of the additive agent supplied into the exhaust pipe. The controller stops the supply of the additive agent when the temperature of the exhaust gas detected by the temperature detecting means is smaller than a generation temperature required to generate the reducing agent from the additive agent and supplies the additive agent when the temperature of the exhaust air is equal to or greater than the generation temperature. When the reducing agent, which is equal to or greater than a predetermined value, is detected by the reducing agent detecting means after a start of supply of the additive agent, the controlling means reduces the amount of the supplied additive agent compared with the amount of the additive agent supplied before the reducing agent , which is equal to or greater than the predetermined value, is detected.

Further, to achieve the object of the present invention, an exhaust gas control device is provided for generating a reducing agent from an additive agent by using heat of an exhaust gas discharged from an internal combustion engine and reducing nitrogen oxide contained in the exhaust gas by the reducing agent. The apparatus has an exhaust pipe, a catalyst, a supply device, a temperature detection device and a control device. The exhaust pipe defines a passage for the exhaust air. The catalyst is arranged in the exhaust pipe. The catalyst is capable of promoting a reduction reaction of the nitrogen oxide in the exhaust gas. The supply means serves to supply the additive agent to an upstream side of the catalyst in a flow direction of the exhaust gas air. The temperature detecting means is for detecting a temperature of the exhaust gas flowing through the exhaust pipe. The control means is for controlling the supply means to regulate an amount of the additive agent supplied into the exhaust pipe. The controller stops the supply of the additive agent when the temperature of the exhaust gas detected by the temperature detecting means is smaller than a generation temperature required to produce the reducing agent from the additive agent, and supplies the additive agent when the temperature of the additive Exhaust gas is equal to or greater than the generation temperature. When the temperature of the exhaust gas is equal to or greater than a predetermined temperature, i. H. is higher than the generation temperature, the controller reduces the amount of the additive additive supplied as compared with the amount of the additive agent supplied when the temperature of the exhaust gas is equal to or greater than the generation temperature and less than the predetermined temperature.

In addition, an exhaust gas control device is provided for generating a reducing agent from an additive agent by using heat of exhaust gas discharged from an internal combustion engine and reducing nitrogen oxide contained in the exhaust gas by the reducing agent. The apparatus has an exhaust pipe, a catalyst, a supply device, a temperature detection device and a control device. The exhaust pipe defines a passage for the exhaust air. The catalyst is arranged in the exhaust pipe. The catalyst is capable of promoting a reduction reaction of the nitrogen oxide in the exhaust gas. The supply means serves to supply the additive agent to an upstream side of the catalyst in a flow direction of the exhaust gas air. The temperature detecting means is for detecting a temperature of the exhaust gas flowing in the exhaust pipe. The control means is for controlling the supply means to regulate an amount of the additive agent supplied into the exhaust pipe. The controller stops the supply of the additive agent when the temperature of the exhaust gas detected by the temperature detecting means is smaller than a generation temperature required to produce the reducing agent from the additive agent, and supplies the additive agent when the temperature of the additive Exhaust gas is equal to or greater than the generation temperature. When at least one of the following conditions is satisfied, the controller reduces the amount of the additive additive supplied as compared with the amount of the additive agent supplied before the one of the following conditions is satisfied: the temperature of the exhaust gas is equal to or greater than a predetermined temperature ie higher than the generation temperature; and a predetermined time has elapsed since a start of supply of the additive agent.

The invention, together with additional objects, features and advantages thereof, will best be understood from the following description, the appended claims and the accompanying drawings, in which:

1 Fig. 10 is a schematic diagram illustrating an exhaust gas control device according to a first embodiment of the invention;

2 FIG. 10 is a flowchart illustrating characteristic processes of the exhaust gas control device according to the first embodiment; FIG.

3 FIG. 12 is a graph illustrating a relationship between an injection amount of an additive agent (urea), an exhaust gas temperature, and the time according to the first embodiment; FIG.

4 FIG. 15 is a diagram illustrating a relationship between the injection amount of the additive agent (urea) and the exhaust gas temperature according to the first embodiment; FIG.

5 Fig. 10 is a schematic diagram illustrating an exhaust gas control device according to a second embodiment of the invention; and

6 FIG. 10 is a flowchart illustrating characteristic processes of the exhaust gas control device according to the second embodiment. FIG.

Embodiments are uses of an exhaust gas control device of the invention in a urea SCR system (a selective catalytic reduction system) of a diesel engine for vehicles. The embodiments will be described below with reference to the drawings.

(First embodiment)

(Construction of an Exhaust Gas Control Device)

As it is in 1 is shown defines an exhaust pipe 2 a passage for an exhaust air coming from a diesel engine 1 is delivered. An SCR catalyst 3 (hereinafter referred to as catalyst 3 ), which promotes a reduction reaction of nitrogen oxide in the exhaust gas, and a DPF (Diesel Particulate Filter) 4 for trapping solids, such as soot, contained in the exhaust gas are in the exhaust pipe 2 arranged. The DPF 4 is located on an upstream side in an exhaust gas flow direction (machine side) of the catalyst 3 ,

A supply valve 5 is a supply means for supplying an additive agent used for a reduction reaction (aqueous urea solution in a first embodiment) into the exhaust pipe 2 on an upstream side of the catalyst in a flow direction of the exhaust gas air 3 , An additive tank 6 is a tank means for storing the additive agent, the exhaust pipe 2 is supplied.

An additive pump 7 is a pumping means for pumping in the additive tank 6 stored additive agent to the supply valve 5 , An exhaust gas temperature sensor 8th is a temperature detecting means for detecting the temperature of exhaust air from the internal combustion engine 1 is delivered. A NOx sensor 9 is a NOx detecting means for detecting nitrogen oxide contained in an exhaust gas passing through the catalyst 3 has entered.

In the first embodiment, the exhaust air temperature becomes near the inlet of the catalyst 3 captures and releases the nitrogen oxide near the outlet of the catalyst 3 detected. Detection signals from the exhaust gas temperature sensor 8th and the NOx sensor 9 be in an electric control unit (hereinafter referred to as ECU) 10 entered. The ECU 10 controls the operation of the supply valve 5 and the operation of the additive pump 7 based on these detection signals from the exhaust gas temperature sensor 8th and the NOx sensor 9 and the same.

The ECU 10 is a well-known microcomputer with a central processing unit (CPU) 10A , a random access memory (RAM) 10B , a read-only memory (ROM) 10C and a timer (timer) 10D indicating the time. A program to control the supply valve 5 and the like is in the ROM 10C saved.

(Basic principles of the exhaust control device)

The exhaust gas control device hydrolyzes (CO (NH 2) 2 + H 2 O → 2NH 3 + CO 2) urea (CO (NH 2) 2), which is the additive agent injected into the exhaust air, by using exhaust heat to generate ammonia (NH 3) which is a reducing agent. Then, the exhaust gas control device causes through the catalyst 3 a reaction between the nitrogen oxide and the ammonia to purify (reduce) the nitrogen oxide.

Meanwhile, when the exhaust gas temperature is equal to or greater than a temperature of 170 ° C to 175 ° C (hereinafter referred to as ammonia generation temperature), urea is hydrolyzed to generate ammonia. However, if the exhaust gas temperature is lower than the Ammonia production temperature is, urea is released into the atmosphere without being hydrolyzed, and thus urea is wastefully consumed.

(Characteristic working principles of the exhaust gas control device)

As it is in 2 is shown, the exhaust gas control device (the supply valve 5 and the additive pump 7 ) at the same time as starting the internal combustion engine 1 started. The amount of the additive additive supplied is determined based on the temperature of the exhaust gas air (the detection temperature of the exhaust gas temperature sensor 8th ), by the internal combustion engine 1 is discharged, the amount of nitrogen oxide (detection value of the NOx sensor 9 ) contained in the exhaust gas and the like are normally controlled (hereinafter referred to as normal control).

The controller (hereinafter referred to as the reducing agent removal prevention control) shown in FIG 2 is started at the same time as the normal control and is performed independently of the normal control. The reducing agent removal prevention control is performed as follows.

That is, when the exhaust gas temperature sensor 8th detected exhaust gas temperature is lower than the ammonia production temperature, the supply of the additive agent (urea) to the exhaust pipe 2 stopped. On the other hand, when the exhaust gas temperature is equal to or greater than the ammonia generation temperature, the additive agent becomes the exhaust pipe 2 fed.

An amount of the additive agent entering the exhaust pipe 2 is such that a larger amount of the reducing agent is generated than an amount of the reducing agent required for reducing all of the nitrogen oxide contained in the exhaust gas discharged from the engine 1 is delivered.

Meanwhile, the reducing agent generated by the hydrolysis becomes in the catalyst 3 adsorbs and then generates a reduction reaction with the nitrogen oxide by the catalyst 3 , An excessively generated reducing agent becomes in the catalyst 3 kept adsorbed and when the exhaust gas temperature decreases to a temperature which is smaller than the ammonia generation temperature, and thereby stops supply of the additive agent, the reducing agent, which is generated excessively and in the catalyst 3 adsorbed in the reduction reaction consumed and thus the nitrogen oxide is purified.

However, if the exhaust gas temperature continues to be equal to or greater than the ammonia generation temperature for a long time, a total amount of the generated reducing agent exceeds a threshold of adsorption by the catalyst 3 and hence, the generated reducing agent is discharged without being used for the reduction reaction.

In the first embodiment, in at least one of a condition that the exhaust gas temperature is equal to or greater than a predetermined temperature (hereinafter referred to as supply stop temperature) higher than the ammonia generation temperature and a condition that a predetermined time (hereinafter referred to as Supply stop time) has elapsed since a start of supply of the additive agent reduces the supply amount of the additive agent compared with an amount of the additive agent discharged into the exhaust pipe 2 was fed before one of the two conditions is met.

"Before either of the two conditions is satisfied" is "if the exhaust gas temperature is equal to or higher than the ammonia generation temperature and less than the supply stop temperature" or "before the supply stop time has elapsed after the exhaust gas temperature becomes equal to or greater than the ammonia generation temperature". Therefore, the "amount of additive agent entering the exhaust pipe 2 is supplied before one of the two conditions is satisfied "such that, as described above, a larger amount of the reducing agent is generated than an amount of the reducing agent needed to reduce the total nitrogen oxide that is in the exhaust gas included is that of the internal combustion engine 1 is delivered.

A supply amount of the additive agent which can generate an amount of the reducing agent needed to reduce all the nitrogen oxide contained in the exhaust gas is hereinafter referred to as a normal amount, and a supply amount of the additive agent supplied before one of the If two conditions are met, it will be referred to as an over-normal amount (larger amount than the normal amount).

Details of the principles described above will be described below with reference to a flowchart in FIG 2 explained. When the reducing agent removal prevention control is started, it is determined whether the detection temperature (hereinafter referred to as exhaust gas temperature) of the exhaust gas temperature sensor 8th smaller than the ammonia generation temperature T1 is (S1).

When it is determined that the exhaust gas temperature is lower than the ammonia generation temperature T1 is (S1: YES), the timer is timed 10D started or continued (S7) after the supply (injection) of the reducing agent is stopped and will take a time by the timer 10D is measured, initialized (S2).

If it is determined that the exhaust gas temperature is not smaller than the ammonia generation temperature T1, that is, the exhaust gas temperature is equal to or greater than the ammonia generation temperature T1 (S1: NO), it is determined whether the time taken by the timer 10D is equal to or greater than the feed stop time (S3). If it is determined that the measured time is equal to or greater than the feed stop time (S3: YES), the time measurement is made by the timer 10D started or continued (S7) after the normal amount of the additive agent in the exhaust pipe 2 is supplied (S5).

If it is determined that the measured time is not equal to or longer than the supply stop time (S3: NO), it is determined whether the exhaust gas temperature is equal to or greater than the supply stop temperature T2 (S4). When it is determined that the exhaust gas temperature is equal to or greater than the supply stop temperature T2 (S4: YES), the time measurement is made by the timer 10D started or continued (S7) after the normal amount of the additive agent in the exhaust pipe 2 is supplied (S5).

When it is determined that the exhaust gas temperature is not equal to or greater than the supply stop temperature T2 (S4: NO), the time measurement is made by the timer 10D started or continued (S7) after the additive means with excessive amount in the exhaust pipe 2 is supplied (S6). Then, after the processing S7 has been performed, the processing S1 is repeatedly performed.

(Features of the exhaust gas control device)

In the first embodiment, when the exhaust gas temperature is lower than the ammonia generation temperature T1, the supply of the additive agent is stopped as shown in FIG 3 and 4 is shown. Consequently, the additive agent is prevented from being wasted wastefully.

When the exhaust gas temperature is equal to or greater than the ammonia generation temperature T1, the additive agent is supplied at an excessive amount. Consequently, the nitrogen oxide is reduced (purified) by the reducing agent generated from the additive agent and becomes a part of the generated reducing agent in the catalyst 3 adsorbed. When the exhaust gas temperature is lower than the ammonia generation temperature T1 and thereby the supply of the additive agent stops, the nitrogen oxide is reduced by the reducing agent contained in the catalyst 3 is adsorbed.

When the exhaust gas temperature is equal to or greater than the ammonia generation temperature T1 as described above, a part of the generated reducing agent becomes in the catalyst 3 adsorbed without being used for the reduction reaction, and is then used for the reduction reaction when the exhaust gas temperature is lower than the ammonia generation temperature T1. However, if the amount of reductant produced exceeds an amount that is greater than that of the catalyst 3 can be adsorbed, the generated reducing agent is discharged without being used for the reduction of the nitrogen oxide. As a result, the additive agent is wastefully consumed.

In the first embodiment, as in 3 is shown, when the supply stop time has elapsed since the start of supply of the additive agent, the supply amount of the additive agent is reduced compared to a supply amount before the predetermined time has elapsed. Consequently, the amount of the reducing agent produced is prevented from exceeding the amount produced by the catalyst 3 can be adsorbed.

In addition, when the reducing agent is continuously generated from the additive agent, the exhaust gas temperature gradually increases over time. Accordingly, by reducing the supply amount of the additive agent when the exhaust gas temperature becomes equal to or greater than the supply stop temperature T2, the amount of the generated reducing agent is prevented from exceeding the amount that is generated by the catalyst 3 can be adsorbed.

In addition, as apparent from the above description, the supply stop temperature T2 is a temperature corresponding, for example, to an exhaust gas temperature at the time when the supply stop time elapses after the ammonia generation temperature T1 is reached. The feed stop time and the feed stop temperature T2 become suitable based on configurations of the catalyst 3 or embodiments of the internal combustion engine 1 certainly.

As described above, in the first embodiment, the additive agent is prevented from being wastefully consumed, and the nitrogen oxide is reliably reduced (purified). In the first embodiment, the supply valve corresponds 5 the "supply device", corresponds to the exhaust gas temperature sensor 8th the "temperature detecting device" and corresponds to the ECU 10 a "controller".

Second Embodiment

(General Description of an Exhaust Control Device According to a Second Embodiment)

In the second embodiment, as in 5 is shown is an ammonia sensor 11 for detecting ammonia, which is a reducing agent, on a downstream side of a catalyst in a flow direction of the exhaust gas air 3 arranged. A larger amount of an additive agent than a normal amount is supplied until the ammonia sensor 11 Ammonia having a predetermined value or above detected after an exhaust gas temperature becomes equal to or greater than an ammonia generation temperature T1. The normal amount of the additive agent is supplied until the exhaust gas temperature becomes smaller than the ammonia generation temperature T1 after the ammonia sensor 11 Ammonia detected.

The principles described above will be described in detail with reference to FIG 6 explained.

(Characteristic Working Principles of the Exhaust Gas Control Device of the Second Embodiment)

When a reducing agent removal prevention control is started, it is first determined whether the exhaust gas temperature is lower than the ammonia generation temperature T1 (S11).

When it is determined that the exhaust gas temperature is smaller than the ammonia generation temperature T1 (S11: YES), supply (injection) of the reducing agent is stopped and becomes a time determined by a timer 10D is measured, initialized (S12). Then, when a predetermined time has elapsed after the time measurement by the timer 10D was started or continued (S16), the processing S11 is performed again.

On the other hand, when it is determined that the exhaust gas temperature is not smaller than the ammonia generation temperature T1, that is, the exhaust gas temperature is equal to or greater than the ammonia generation temperature T1 (S11: NO), it is determined whether the ammonia sensor 11 Ammonia is detected at the predetermined value or above (S13). When it is determined that ammonia is detected at or above the predetermined value (S13: YES), the normal amount of the additive agent becomes the exhaust pipe 2 supplied (S14). Then, the processing S11 is repeatedly performed when the predetermined time has elapsed (S16).

When it is determined that ammonia is not detected at the predetermined value or above (S13: NO), the excess amount additive (having more than the normal amount) is added to the exhaust pipe 2 supplied (S15).

Then, the processing S11 is repeatedly performed when the predetermined time has elapsed (S16).

(Characteristics of the exhaust gas control device of the second embodiment)

Also in the second embodiment, similar to the embodiment described above, the supply of the additive agent is stopped, and the nitrogen oxide is reduced by the reducing agent contained in the catalyst 3 is adsorbed when the exhaust gas temperature is less than the ammonia production temperature T1. Therefore, the additive agent is prevented from being wasted wastefully.

When the exhaust gas temperature is equal to or greater than the ammonia generation temperature T1, the additive agent is supplied and the nitrogen oxide is reduced (purified) by the reducing agent generated from the additive agent. Further, part of the generated reducing agent becomes in the catalyst 3 adsorbed.

When ammonia (a reducing agent) with a predetermined amount or more through the ammonia sensor 11 is detected after the supply of the additive agent has been started, the supply amount of the additive agent compared to the supply amount is reduced before the reducing agent was detected. Thus, the amount of reducing agent produced is prevented from exceeding the amount produced by the catalyst 3 can be adsorbed.

Therefore, in the second embodiment, too, the additive agent is prevented from being wastefully consumed and the nitrogen oxide is reliably reduced (purified). In the second embodiment, the ammonia sensor corresponds 11 a "reducing agent detection device".

(Further embodiments)

In the above embodiments, urea is used as the additive agent. However, the invention is not limited to the above. That is, a reducing agent other than ammonia or an additive agent which produces this reducing agent may be used.

According to the invention, the first embodiment and the second embodiment can be combined.

In addition, benefits and modifications will easily attract attention. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.

An exhaust gas control device has an exhaust pipe ( 2 ), a catalyst ( 3 ) in the pipe, which promotes a reduction reaction of nitrogen oxide in an exhaust air, a supply device ( 5 ) for supplying an additive agent to an upstream side of the catalyst, a temperature detection device ( 8th ) for detecting an exhaust air temperature and a control device ( 10 ) for controlling the feeding device to regulate the amount of additive agent supplied into the pipe. The controller stops supply of the additive agent when an exhaust air temperature is lower than a generation temperature required for generating the reducing agent from the additive agent, and supplies the additive agent when an exhaust air temperature is equal to or greater than a generation temperature. When a predetermined time has passed since a start of supply of the additive agent, the controller reduces the amount of additive agent supplied, compared with the amount of additive agent supplied before the predetermined time has elapsed.

Claims (2)

Exhaust gas control device for generating a reducing agent from an additive agent by using a heat of an exhaust air from an internal combustion engine ( 1 ), and for reducing nitrogen oxide contained in the exhaust air by the reducing agent, the apparatus comprising: an exhaust pipe (Fig. 2 ) defining a passage for the exhaust air; a catalyst ( 3 ), which in the exhaust pipe ( 2 ), wherein the catalyst ( 3 ) is capable of promoting a reduction reaction of the nitrogen oxide in the exhaust air; a feeder ( 5 ) for supplying the additive agent to an upstream side of the catalyst in a flow direction of the exhaust gas ( 3 ); a temperature detection device ( 8th ) for detecting a temperature of the exhaust gas passing through the exhaust pipe (16) 2 ) flows; and a control device ( 10 ) for controlling the feeder ( 5 ) into the exhaust pipe ( 2 ) control amount of the additive agent, wherein: the control device ( 10 ) the supply of the additive agent stops when the temperature of the exhaust gas, which by the temperature detecting means ( 8th ) is less than a generation temperature required to generate the reducing agent from the additive agent, and supplies the additive agent when the temperature of the exhaust gas air is equal to or greater than the generation temperature; characterized in that the control device ( 10 ), when a predetermined time has elapsed after a start of supply of the additive agent, the amount of the additive agent to be supplied is reduced as compared with the amount of the additive agent supplied before the predetermined time has elapsed, the predetermined time being set to a time which is equal to or shorter than a time in which an amount of the generated reducing agent exceeds an amount in the catalyst ( 3 ) can be adsorbed. Exhaust gas control device according to claim 1, wherein the control device ( 10 ), when the temperature of the exhaust gas is equal to or greater than a predetermined temperature, that is, higher than the generation temperature, the amount of the additive agent supplied is reduced as compared with the amount of the additive agent supplied when Temperature of the exhaust gas is equal to or greater than the generation temperature and is less than the predetermined temperature.

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