DE102008002326A1 - Addition amount control means for an exhaust gas purifying agent and exhaust emission control system - Google Patents

Abstract

In an exhaust quantity control device (40) for an exhaust gas purifying agent to be used for an exhaust emission control system of an engine, a mode based on satisfaction of an execution condition for each mode is executed from a plurality of control modes. The control modes include a purge control mode in which an addition amount of NH <SUB> 3 </ SUB> or an additive serving as a generation source of NH <SUB> 3 </ SUB> is determined according to a predetermined parameter designated by NO <SUB> x </ SUB> amount in the exhaust gas is linked, and a storage control mode in which the addition amount is set to be larger than that in the purification control mode. When it is determined that a rotational speed of an output shaft of the engine is being delayed from a higher-speed state than an allowable level, the execution condition of the memory control mode is satisfied after a predetermined non-satisfaction period from a start of the deceleration.

Description

FIELD OF THE INVENTION

The present invention relates to an addition amount control device for an exhaust gas purifying agent for controlling an addition amount of NH ₃ for purifying an exhaust gas by a reaction with NO _x in the exhaust gas. The invention also relates to an exhaust emission control system, for example a urea-SCR system, for purifying an exhaust gas by an exhaust gas purification reaction based on NH ₃ on a catalyst.

BACKGROUND OF THE INVENTION

In recent years, urea-SCR systems (urea selective reduction systems) have been developed in electric power plants, various factories, vehicles and the like. Particularly in the field of automobiles (especially in a diesel engine vehicle), exhaust gas aftertreatment techniques for purifying and reducing NO _x (nitrogen oxides) in the exhaust gas are classified in two important directions, the above-described urea SCR system and NO _x storage-reduction catalyst. The urea SCR system is already used in practice in large trucks and is known to have a high cleaning ratio with a maximum of about "90%". Currently, the general urea SCR systems now being investigated for use on diesel engines are being developed to reduce (purify) NO _x in the exhaust by means of NH ₃ (ammonia) consisting of a urea ((NH ₂ ) ₂ CO) -water solution is generated (hereinafter referred to as urea water).

Conventionally, this is in JP-A-2003-293739 disclosed system as a particular example of such a urea SCR system known. This system mainly has a catalyst for promoting a specific exhaust gas purifying reaction (reduction reaction of NO _x ), an exhaust pipe for guiding the exhaust gas discharged from an exhaust gas generation source (for example, an engine) to the catalyst, and a urea water addition valve at a middle point of the exhaust pipe for injecting and adding the aqueous urea solution (additive) to the exhaust gas flowing in the exhaust pipe. The system having this arrangement is configured to inject and add the urea aqueous solution into the exhaust gas through the urea water addition valve, and to supply the aqueous urea solution to the catalyst on the downstream side together with the exhaust gas, utilizing a flow of the exhaust gas. The aqueous urea solution supplied in this manner is hydrolyzed by exhaust heat or the like to produce NH ₃ (ammonia) as represented by the following chemical equation: (NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂ .

This results in a reduction reaction of NO _x by the NH ₃ on the catalyst, through which the exhaust gas is purified.

However, the catalyst used in such purification of the exhaust gas generally promotes the reduction reaction of NO _x in a temperature range exceeding an activation temperature (critical reaction temperature) attributable to the catalyst, that is, in a temperature range that is the activation temperature as the lower limit has. Thus, the system as it is in JP-A-2003-293739 is disclosed to have insufficient exhaust gas cleaning ability when the catalyst is at a low temperature below the activation temperature.

SUMMARY OF THE INVENTION

The inventors of the present application consider the fact that the general catalyst for purifying the exhaust gas used in a vehicle-mounted internal combustion engine or the like can store NH ₃ , and the larger the amount of NH ₃ stored, the lower is the activation temperature (critical reaction temperature) of the catalyst. Thus, the inventors are currently conducting various studies and have developed an additive control device for an exhaust gas purifying agent to improve an exhaust gas purification ability by utilizing a decrease in an activation temperature (critical reaction temperature) due to the storage of NH ₃ .

As a result, it has been found that an exhaust gas purifying ability largely changes according to a timing of storing NH ₃ by adding the exhaust gas purifying agent. For example, when the exhaust gas is purified by the vehicle internal combustion engine while a rotation speed of an output shaft of the internal combustion engine is sufficiently high, the temperature of portions around the internal combustion engine including the catalyst due to the combustion caused by previous acceleration of the engine becomes sufficiently high. Thus, even if the engine is decelerated, the temperature of the catalyst remains at a temperature above the activation temperature for a while. Even if storage of the NH _{3 is started} at the same time as the start of deceleration, the storage of the NH _{3 may} not be effective, and the remaining NH ₃ that is not rich stores may lead to a deterioration of the emission characteristics.

The The present invention is in view of the above facts and it is an object of the invention, an addition amount control device to provide for an exhaust gas cleaner, which is a high Emission control capability in response to multiple conditions and to provide an exhaust emission control system, the high exhaust gas purification capability by using the May have an addition amount control device.

According to the present invention, an addition amount control device for an exhaust gas purifying agent is constructed to be applied to an exhaust emission control system for purifying exhaust gas discharged from an internal combustion engine. The exhaust emission control system has a catalyst for promoting a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit and an adding valve for adding an NH ₃ (ammonia) additive or an additive serving as a generation source of the NH ₃ , to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, wherein the additive is adapted to purify NO _x (nitrogen oxides) in the exhaust gas by the exhaust gas purifying reaction on the catalyst. The addition amount control means is adapted to control an addition amount by the addition valve, and the catalyst has properties of storing NH ₃ and further reducing the critical reaction temperature as the amount of NH ₃ storage is increased.

According to a first aspect of the present invention, the addition amount control means has: a mode selector for selecting a mode to be executed at that time based on satisfaction of an execution condition for each mode from among a plurality of control modes, the control modes including a purge control mode in which the addition amount is determined by the addition valve according to a predetermined parameter associated with a NO _x amount in the exhaust gas and a storage control mode in which the addition amount through the addition valve is determined to be larger than that in the purge control mode; and condition determining means for determining whether a rotational speed of an output shaft of the internal combustion engine is being delayed from a higher-speed state than an allowable level. Further, the execution condition of the storage control mode is set to be satisfied after a predetermined non-satisfaction period from a start of deceleration when the condition determination means determines that the rotational speed is being retarded from the higher-speed state.

Alternatively, according to a second aspect of the present invention, the addition amount control means has: a mode selector for selecting a mode to be executed at that time based on satisfaction of an execution condition for each mode among a plurality of control modes, the control modes including a purge control mode wherein the amount of addition by the addition valve is determined according to a predetermined parameter associated with a NO _x amount in the exhaust gas and a storage control mode in which the amount of addition by the addition valve is set to be larger than that in the purification control mode ; and condition determining means for determining whether a fluctuation amount of a load on the output shaft of the internal combustion engine is greater than an allowable level to a negative side. Further, the execution condition of the storage control mode is set to be satisfied after a predetermined non-satisfaction period since the fluctuation, when the condition determination device determines that the fluctuation amount of the load toward the negative side is greater than the allowable level.

Alternatively, according to a third aspect of the present invention, the addition amount control means has: a mode selector for selecting a mode to be executed at that time based on satisfaction of an execution condition for each mode among a plurality of control modes, the control modes including a purge control mode wherein the amount of addition by the addition valve is determined according to a predetermined parameter associated with a NO _x amount in the exhaust gas and a storage control mode in which the amount of addition by the addition valve is set to be larger than that in the purification control mode ; and a condition determining means for determining whether a fluctuation amount of the rotational speed of the output shaft of the internal combustion engine toward the negative side is greater than an allowable level. Further, the execution condition of the storage control mode is set to be satisfied after a predetermined non-satisfaction period since the fluctuation, when the condition determination device determines that the fluctuation amount of the rotational speed toward the negative side is greater than the allowable level.

Alternatively, according to a fourth aspect of the present invention, the addition amount control a mode selector for selecting a mode to be executed at that time based on satisfaction of an execution condition for each mode among a plurality of control modes, the control modes including a purge control mode in which the addition amount by the addition valve is made according to a predetermined parameter determining that is associated with a NO _x amount in the exhaust gas, and include a storage control mode in which the addition amount by the addition valve is set to be larger than that in the purge control mode; and condition determining means for determining whether a fuel cut is being performed in the internal combustion engine. Further, the execution condition of the storage control mode is set to be satisfied after a predetermined non-satisfaction period from a start of the fuel cut, when the condition determination means determines that the fuel cut is being performed.

In general, the amount of NH ₃ for effectively purifying NO _x in the exhaust gas (and an addition amount through the addition valve) differs from an amount of NH ₃ appropriate for storage (and an addition amount by the addition valve that is suitable for storage) Save is appropriate). This is so because if NH ₃ is stored, the amount of NH _3, in addition to the amount of NH ₃ is required, the _x is used to clean the NO which is to further save. Each controller of the above first to fourth aspects of the invention takes this fact into account with the above-mentioned property of the catalyst that the larger the amount of stored NH ₃ , the lower the critical reaction temperature. Such a controller according to any one of the first to fourth aspects of the present invention can improve the purification ability of the catalyst at a low temperature by decreasing the critical reaction temperature of the catalyst by executing the above-mentioned storage control mode. Further, at the time of deceleration or the like, assuming that the catalyst is in a high-temperature state or the like, the mode selector does not start storing NH ₃ for cleaning immediately upon decelerating the internal combustion engine Load on the machine or a start of the fuel cut. However, the mode selecting means starts storing NH ₃ after a predetermined non-satisfaction period, which may be set by the time, the temperature of the catalyst, or the like, for example. Accordingly, the control device according to any one of the above first to fourth aspects of the present invention can appropriately suppress the deterioration of the emission characteristic while reducing the deterioration of the emission characteristic due to the execution of unnecessarily storing the NH ₃ .

In general, the temperature of the catalyst has an influence on the property of the catalyst (for example, an NH ₃ storage amount or the like). Furthermore, it is known that the higher the temperature of the catalyst, the lower the limit storage amount of NH ₃ (NH ₃ storage amount). Thus, if the catalyst temperature is sufficiently low, a degree of permissibility up to the NH ₃ limit storage amount is large, which may require higher storage of NH ₃ . As mentioned above, when the catalyst is at a low temperature, it is highly required that the activation temperature (critical reaction temperature) of the catalyst be lowered. In this regard, the addition amount control means may further be provided with catalyst temperature determination means for determining whether the temperature of the catalyst at that time is lower than an allowable level. In this case, the predetermined non-satisfaction period has an end time at which the catalyst temperature determination means determines that the temperature of the catalyst is lower than the allowable level.

If For example, the temperature of the catalyst at this time in a predetermined temperature range which is the critical reaction temperature or a predetermined temperature that is less than the critical one Reaction temperature is determined as having an upper limit the catalyst temperature determining means that the temperature of the catalyst at this time lower than the allowable Level is.

alternative may be the execution condition of the cleaning control mode be set to be met if the execution condition Memory control mode is not met. In this case The mode selector switches between two types of control modes the cleaning control mode and the storage control mode according to a Fulfillment or non-fulfillment of the execution condition around.

According to a fifth aspect of the present invention, an addition amount control device for an exhaust gas purifying agent is constructed to be applied to an exhaust emission control system for purifying an exhaust gas discharged from an internal combustion engine. The exhaust emission control system has a catalyst for promoting a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit, and an addition valve for adding an NH ₃ (ammonia) additive or an additive serving as a generation source of the NH ₃ to the catalyst itself or the exhaust gas at one upstream side with respect to the catalyst, wherein the additive is adapted to purify NO _x (nitrogen oxides) in the exhaust gas by the exhaust gas purifying reaction on the catalyst. The addition amount control means is adapted to control an addition amount by the addition valve, and the catalyst has properties of storing NH ₃ and further reducing the critical reaction temperature as the amount of NH ₃ storage is increased. Further, the addition amount control means has: an operation mode determination means for determining whether the operation mode of the internal combustion engine is a preset operation mode in which a load on the output shaft of the internal combustion engine is controlled to be reduced when the catalyst has a high temperature which is the critical one Exceeds reaction temperature; and prohibiting means for prohibiting addition of NH ₃ or the additive serving as the generation source of NH ₃ by the addition valve to the catalyst in an NH ₃ storage amount for a predetermined period of time when the operation mode determination means determines that the operation mode is to this Time is the default operating mode.

In an operation mode in which the load applied to the output shaft of the internal combustion engine is controlled to be decreased, for example, in a deceleration operation, a fuel cut operation, or a reduced-cylinder operation, it is considered that the catalyst has a high temperature. In this regard, the storage of NH ₃ (specifically, an addition for the purpose of storing) is prevented for the predetermined period of time, for example, while the catalyst temperature is sufficiently high. This can suitably suppress a deterioration of the emission characteristic while decreasing a decrease in a purifying ratio of NO _x due to the execution of the unnecessary storage of NH ₃ .

For example, the addition valve may be adapted to inject and add an aqueous urea solution as the additive to the exhaust gas on the upstream side with respect to the catalyst. In this case, the aqueous urea solution is injected to the exhaust gas on the upstream side with respect to the catalyst and added so that the urea is hydrolyzed by exhaust heat or the like until the urea reaches the catalyst to form NH ₃ . This can perform ₃ (detergent) to the catalyst more NH.

BRIEF DESCRIPTION OF THE DRAWINGS

additional Objects and advantages of the present invention will be readily apparent from the following detailed description of preferred embodiments, when taken together with the accompanying drawings.

1 Fig. 10 is a schematic diagram showing an addition amount control means for an exhaust gas purifying agent and an exhaust emission control system with the addition amount control means according to an embodiment of the invention;

2 Fig. 10 is a flowchart showing a control process for controlling an addition amount of urea water;

3 FIG. 10 is a flowchart showing a control process for determining a start time of an engine delay time period; FIG.

4 FIG. 10 is a flowchart showing a control process for determining an end time of the engine delay time period; FIG.

5 Fig. 12 is a graph showing an example of a map used for calculating an NH ₃ margin amount;

6 Fig. 12 is a graph showing an example of a relationship between the critical reaction temperature of an SCR catalyst and the NH ₃ storage amount;

7 Fig. 10 is a graph showing an example of a purifying property of the SCR catalyst;

8A to 8C Fig. 10 is timing charts showing a form of urea water addition control according to the embodiment; and

9 FIG. 10 is a flowchart showing another example of a mode selection control process. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An addition amount control device for an exhaust gas purifying agent and an exhaust emission control system according to an embodiment of the invention will be described below with reference to FIG described on the accompanying drawings. For example, the exhaust emission control system of this embodiment has the basic structure used in a general urea-SCR system (urea selective reduction system). At the in 1 The structure shown reduces (purifies) NH ₃ (ammonia) produced from a urea ((NH ₂ ) ₂ CO) -water solution (hereinafter referred to as a urea water), NO _x in an exhaust gas.

Regarding 1 The structure of the exhaust emission control system will be described in detail below. 1 FIG. 15 is a diagram schematically showing the structure of a urea SCR system (exhaust gas purification device) according to this embodiment.

As in 1 is shown, this system is adapted to purify exhaust gas discharged from a diesel engine (exhaust generation source) installed, for example, in the four-wheeled vehicle (not shown). This system mainly has various actuators and sensors for purifying the exhaust gas and an ECU (Electronic Control Unit) 40 , The engine of this embodiment (engine of interest) is adopted as a multi-cylinder engine (for example, a four-cylinder in-line engine) mounted in a four-wheeled vehicle (for example, an automatic vehicle). Each cylinder is provided with an injector having a fuel injection valve. Fuel supplied to each cylinder through the injector burns in the corresponding cylinder. The engine is the so-called four-stroke (4 × piston stroke) piston diesel engine (internal combustion engine), which is designed to convert energy generated by combustion of the fuel into rotary motion to rotate an output shaft (crankshaft). In other words, in this engine, the cylinder of interest at that time is sequentially determined by a cylinder determination sensor (electromagnetic pickup) provided in a camshaft of an air intake and exhaust valve. A combustion cycle consisting of four strokes, namely, sucking, compressing, burning and discharging, is performed in a cycle of "720 ° CA" in each of four # 1 to # 4 cylinders. Specifically, for example, the respective combustion cycles for the four cylinders in cylinders # 1, # 3, # 4 and # 2 are sequentially executed by shifting the cycle between one cylinder and the next cylinder by "180 ° CA".

Specifically, various exhaust gas purification devices are arranged in the exhaust emission control system to form an exhaust gas purification system. The exhaust gas purification devices include a diesel particulate filter (DPF) 11 , an exhaust pipe (exhaust passage) 12 , an SCR catalyst 13 , an exhaust pipe (exhaust passage) 14 and an NH ₃ catalyst (for example, an oxidation catalyst) 15 that is located from the upstream side of the exhaust gas (on the engine side, which is an exhaust generation source) in this order. On a wall surface of the passage at a middle point of the exhaust pipe 12 is a urea water addition valve 16 arranged such that an injection port 16a opens to the downstream side of the exhaust gas. That's why it's very hard for the injection port 16a is polluted by the exhaust gas. The urea water addition valve 16 is adapted to the urea water entering a urea water tank 17a pressure to the downstream part with respect to the DPF 11 to add (inject and supply). In this embodiment, the urea water addition valve is 16 a so-called electromagnetically driven injection valve whose drive is electrically driven by the ECU 40 is controlled. The addition valve 16 is through the ECU 40 is controlled so that the urea water serving as an additive is injected and supplied to the exhaust gas with a desired addition amount in the exhaust pipe 12 between the DPF 11 and the SCR catalyst 13 flows. Thus, the added urea water (or NH ₃ after decomposition) becomes the SCR catalyst 13 supplied on the downstream side together with the exhaust gas by utilizing the flow of the exhaust gas (exhaust gas flow).

That is, in this system, the addition of urea water by the urea water addition valve produces 16 the NH ₃ (detergent) based on the urea water as shown by the following decomposition reaction reaction (formula 1) in the exhaust gas. The following NO _x reduction reaction (as represented by the following formula 2) is performed using NH ₃ on the SCR catalyst 13 performed, whereby the exhaust gas to be cleaned (NO _x ) is cleaned. (NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂ (Formula 1) NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (Formula 2)

The excess NH ₃ (excess NH ₃ ) that is not consumed in the above reduction reaction (shown in Formula 2) and the downstream side of the SCR catalyst 13 (Exhaust pipe 14 ) is caused by the reaction (represented by Formula 3) by the NH ₃ catalyst 15 cleaned, and thereby the amount of discharged into the atmosphere NH _{3 is} reduced. The temperature of the exhaust gas at the downstream side of the SCR catalyst 13 and the amount of NO _x (that is, the NO _x emission amount) contained in the exhaust gas may be caused by an exhaust gas sensor 14a (which is in an NO _x sensor and a temperature sensor receives) provided in an exhaust pipe 14 is intended to be recorded (in particular they can be detected by the ECU 40 calculated on the basis of outputs from the sensors). 4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (Formula 3)

When Next, each of the above-described exhaust gas purification devices, the exhaust purification system of the exhaust emission control system according to this embodiment, described in detail below.

First, the DPF 11 a continuously regenerating filter for particle removal or PM removal, that is, for collecting particulate matter (PM) in the exhaust gas. For example, the DPF may be continuously used by repeatedly burning and removing (corresponding to a regeneration process) of the collected PM in a post-injection or the like after a main injection for mainly generating a torque. The DPF 11 supports a platinum-based oxidation catalyst not shown (in this example, the DPF and the oxidation catalyst are integrally formed with each other, but they may be separately formed). This can remove HC and CO together with soluble organic compounds (SOF), which are PM components, and also oxidize a part of NO _x (when the ratio of NO to NO ₂ ("NO: NO ₂ ") closer to "1 Is 1 ", the purification ratio of NO _x becomes higher, as by the above reaction formula 2 is shown).

The SCR catalyst 13 is formed of a catalytic metal, such as vanadium oxide (V ₂ O ₅ ), which is supported for example on a honeycomb catalyst carrier. The SCR catalyst 13 has a catalytic action for promoting the reduction reaction (exhaust gas purification reaction) of NO _x , that is, the reaction represented by the above formula 2.

The construction of the urea water addition valve 16 is based on that of a fuel injection valve (injector) commonly used for supplying fuel to an engine for a vehicle (internal combustion engine). The construction of the urea water addition valve 16 is well known and will therefore be described only briefly below. That is, for convenience of explanation, an illustration of an internal structure of the adding valve will be made 16 omitted. The urea water addition valve 16 receives, in a valve body, a needle driving portion formed of an electromagnetic solenoid or the like and a needle driven by the needle driving portion and reciprocating in the valve body (housing). The needle is adapted to a necessary number of injection holes in an injection port 16a are formed at the end of the valve body, or to open and close a circulation route to these injection holes. When the electromagnetic solenoid is energized, the urea water addition valve moves 16 with this structure (each element) in the valve opening direction by driving the needle with the electromagnetic solenoid in accordance with an electrical signal from the ECU 40 (For example, a pulse signal by PWM (Pulse Width Modulation) control), that is, according to an injection command from the ECU 40 , Thus, the injection port 16a opened at the end of the valve body, and in particular, at least one of the injection holes at the injection port 16a opened so that the urea water is added (injected) in the direction of the exhaust gas, which through the exhaust pipe 12 flows. At this time, the amount of addition of the urea water (injection amount) is determined on the basis of an energization time of the electromagnetic solenoid (for example, according to a pulse width of the pulse signal from the ECU 40 ).

On the other hand, a urea water supply system for pressure-feeding the urea water to the urea water addition valve includes 16 mainly a urea water tank 17a and a pump 17b , That is, in the urea water tank 17a Stored urea water will pass through the tank 17a arranged pump 17b pumped and then to the urea water addition valve 16 pressure-fed. The pressure-fed urea water is passed through a pipe 17c for supplying the urea water sequentially to the urea water addition valve 16 fed.

At this time, foreign particles contained in the urea water pass through a barrier filter 17f located on the upstream side with respect to the addition valve 16 is provided before the urea water to the urea water addition valve 16 is supplied. The supply pressure of the urea water to the addition valve 16 is by a urea water pressure regulator 17d controlled. Specifically, when the supply pressure exceeds a predetermined value, a mechanical device using a spring or the like allows urea water in the pipe 17c to the urea water tank 17a can return. In the present system, the supply pressure of the urea water becomes based on the operation of the regulator 17d controlled to stay at the predetermined value (set pressure). The supply pressure of the urea water becomes even by the operation of such a regulator 17d not precisely controlled to stay at the set pressure. In this system, the supply pressure of the Urea water through the urea water pressure sensor 17e (in particular by the ECU 40 calculated on the basis of the sensor output) provided in a predetermined detection position (for example, is on the upstream side of the regulator 17d where a fuel pressure through the pressure control by the regulator 17d is stabilized).

A section for mainly performing a control associated with exhaust purification as an electronic control unit in such a system is the ECU 40 (For example, the ECU for controlling the purification of the exhaust gas, which is connected to an ECU for controlling the engine via a CAN or the like), that is, the addition amount control means for an exhaust gas purification means according to this embodiment. The ECU 40 has a known microcomputer (not shown) and operates various types of actuators, such as the urea water addition valve 16 , on the basis of detection signals from the various sensors to perform various kinds of control operations associated with the exhaust gas purification in the optimum form according to the condition at all times. The one in the ECU 40 built-in microcomputer mainly has a CPU (central processing unit) for performing various calculations, RAM (Random Access Memory) serving as a main memory for temporarily storing data in the middle of the calculation, the result of calculation or the like, and a ROM (read-only memory) serving as a program memory. The microcomputer also has an EEPROM (Electrically Erasable Programmable Read Only Memory, Electrically Erasable Programmable Nonvolatile Memory) serving as a memory for data storage, and a backup RAM (RAM operated by a backup power source such as in FIG a vehicle-mounted battery). Further, the microcomputer has signal processors including an A / D converter and a clock generating circuit, various calculating devices such as an input / output port for inputting and outputting signals to / from the external element, a memory device, a communication device, and a power supply circuit. The ROM stores in advance various programs and a control map associated with the control of exhaust gas purification, including a program associated with a control of an addition amount of the exhaust gas purifying agent. The memory for storing data (for example, the EEPROM) stores in advance various kinds of control data or the like, including design data for the machine.

In the above description, the structure of the exhaust emission control system of this embodiment has been described in detail. That is, in this embodiment with this structure, NH ₃ serving as the purifying agent becomes exhaust gas in the form of urea aqueous solution (urea water) through the addition valve 16 added for aqueous urea. Thus, the urea water in the exhaust gas is decomposed to form NH ₃ , and the NO _x reduction reaction (represented by the formula 2) becomes on the SCR catalyst 13 based on the NH ₃ produced in this way to purify the exhaust gas to be purified (exhaust gas from the engine). Furthermore, in this embodiment, the in 2 shown process performed as the control of an addition amount of urea water. This process can achieve the high exhaust gas purification ability in response to multiple conditions. The control of the addition amount of the urea water will be explained with reference to FIG 2 to 8th described.

2 FIG. 11 is a flowchart showing the addition amount control of the urea water. FIG. A series of control steps in the in 2 The process shown is basically repeated at intervals of a predetermined process time while a predetermined condition is satisfied by executing the program stored in the ROM by means of the ECU 40 performed, for example, during the time from the start of the machine to the stop of the machine. Values of various parameters included in the in 2 shown in the memory device, such as the RAM or the EEPROM, in the ECU 40 are mounted, stored on occasion, and updated whenever necessary.

As in 2 is shown, in the control of the urea water addition amount in step S10, it is determined whether the engine is being accelerated, that is, it is determined whether the timing at that time of the step S10 is an engine deceleration period.

The machine delay time period is determined by repeatedly executing a routine operation other than that in FIG 2 Process shown is, that is, the sequence of steps in the processes that are in 3 and 4 shown in the ROM of the ECU 40 are stored, at intervals of the predetermined process time.

As in 3 is shown, in determining the start timing in step S31, it is determined whether the engine is being driven at a high speed, and specifically, whether a rotational speed (engine rotational speed) of the output shaft of the engine is greater than a predetermined determination value (Engine speed> determination value). Further, in step S31, it is also determined whether the engine is decelerating, and specifically, whether an accelerator pedal is in a non-operating state (an accelerator pedal operation amount ≈ 0). The determination in step S31 is repeatedly performed. When it is determined in the same step S31 that the engine is driven at the high speed and the accelerator pedal is in the non-operating state (that is, the driver's foot releases the accelerator pedal), the timing at that time becomes the engine deceleration time period start timing determined subsequent step S32. The above-mentioned engine delay time period corresponds to a period from the time when the starting time is set in step S32 to the time when the end time is set. During the engine delay period, a fuel cut (stopping a process of fuel injection associated with generation of a torque) is performed in all cylinders of the engine.

In contrast, the process that serves in 4 is shown, to determine the end time of the machine delay time period.

As in 4 is shown, in the determination of the end time, first, in step S41, it is determined whether the engine is being decelerated, that is, whether the engine deceleration period start time has already been set in the previous step S32, which is in 3 is shown. Only when it is determined in step S41 that the engine is being decelerated, the processes in step S42 and the following steps are executed.

The means, if the machine is delayed, go the flow proceeds to step S42. In step S42, it is determined whether the engine speed at this time is lower than a permissible one Level is, and in particular, whether the engine speed is lower is a predetermined determination value (engine speed <determination value). The predetermined determination value in step S42 is not necessarily the same as the determination value in step S31. The determination process in step S42 is repeatedly performed. When in step S42 determines that the engine speed is lower than that permissible level is (predetermined determination value), becomes determines that the machine is at low speed, and in the subsequent step S43, the time becomes at this time as the end time of the engine delay period established. The machine delay time span above is determined in this way.

If in step S10, it is determined that the time is in the engine delay period is, the processes in step S11 and the following steps are executed. If it is determined in the same step S10 that the time is not is in the machine delay period, the process goes proceed to step S19a.

In this embodiment, the addition amount control means selects one of a purge control mode and a storage control mode to be executed. In the purification control mode, an addition amount of the urea water by the urea water addition valve is added 16 determined in accordance with a predetermined parameter with regard to an amount of _NOx in the exhaust gas, and more particularly according to the engine speed and the fuel injection amount. In the storage control mode, there is an addition amount of the urea water through the urea water addition valve 16 set to be larger than that in the cleaning control mode (specifically, only by increasing an amount required to meet a deficit with respect to a target value of the NH ₃ storage amount). That is, while one of the control modes is not performed, the other is performed. The selection of the control mode (that is, switching between these control modes) is performed on the basis of the result of determination by the processes in steps S10 and S13. Specifically, if it is determined in at least one of steps S10 and S13 that the necessary condition is not satisfied, it is determined that the storage of NH ₃ is unnecessary, and thus the purification control mode is performed by the processes in steps S19a and S20. On the other hand, if it is determined in both steps S10 and S13 that the necessary conditions are satisfied, the storage control mode is performed by the processes in steps S14 to S20 to control the NH ₃ on the SCR catalyst 13 save.

That is, when it is determined in S10 that the time is not in the engine delay period, the cleaning control mode is performed by the processes in steps S19a and S20. Specifically, in step S19a, an addition amount Q of the urea water is obtained in accordance with the engine speed and the fuel injection amount using a reference map (or a mathematical formula) for calculating a predetermined addition amount of the urea water. This reference map has appropriate values (optimum values) of the urea water addition amount Q determined in advance and written down by experiments or the like according to the respective optimum values of the engine speed and the fuel injection amount. The map is, for example, in the ROM or the like in the ECU 40 saved. This allows the high NO _x purification ratio he to hold. In the subsequent step S20, the urea water addition valve becomes 16 driven on the basis of the urea water addition amount Q thus obtained (energized only for a period of time according to the urea water addition amount Q).

On the other hand, when it is determined in the previous step S10 that the time is in the engine delay time period, an exhaust gas temperature Tex is detected in the subsequent step S11. For example, the exhaust gas temperature Tex may actually be through the exhaust gas sensor 14a be measured. In the next step S12, the temperature of the SCR catalyst becomes 13 (Catalyst temperature Tc) calculated on the basis of the detected exhaust gas temperature Tex. The catalyst temperature Tc is calculated using, for example, a predetermined map (or a mathematical formula).

Then, in step S13, it is determined whether the catalyst temperature Tc calculated in the previous step S12 is smaller than a predetermined determination value Ts (Tc <Ts). The determination value Ts is variably set according to a corresponding critical reaction temperature of each time. If it is determined in step S13 that the catalyst temperature Tc is not smaller than the determination value Ts, the process proceeds to the next step S19a in which the cleaning control mode described above is performed. That is, even if the engine is decelerated, NH _{3 will} not be on the SCR catalyst 3 stored while the catalyst remains at the high temperature (Tc ≥ Ts).

In contrast, when it is determined in step S13 that the catalyst temperature Tc is smaller than the determination value Ts, the storage control mode is performed by the control processes in the following steps S14 to S20 to generate NH ₃ in the SCR catalyst 13 save.

Specifically, in step S14, first, a current NH ₃ storage amount ST1 is obtained, which is the NH ₃ storage amount of the SCR catalyst 13 at this time is. At this time, the current NH ₃ storage amount ST1 is calculated by another routine. Specifically, an amount of increase or decrease of an NH ₃ storage amount ΔNH _{3 of} the SCR catalyst becomes 13 at any time based on a difference between the amount of NH _{3 added} to the SCR catalyst 13 is supplied, and the consumption amount of NH ₃ to the SCR catalyst 13 certainly. Further, the amounts of increasing or decreasing the respective times are subsequently summed to be set as the above-described present NH ₃ storage amount ST1 (ST1 (current value) = ΣST1 (previous value) + ΔNH ₃ ). The above NH ₃ amount leading to the SCR catalyst 13 is supplied on the basis of, for example, the addition amount of urea water through the urea water addition valve 16 calculated. In contrast, the amount of NH ₃ consumed on the SCR catalyst 13 mainly based on the amount of NO _{x released} from the engine and the purifying power of the catalyst 13 calculated. Of these, the amount of NO _x discharged from the engine may be calculated based on the predetermined parameter (for example, the engine speed and the fuel injection amount) associated with the operating state of the engine. On the other hand, the cleaning power of the SCR catalyst 13 (Reaction rate of NH ₃ ), for example, using a control model of the SCR catalyst 13 be calculated. The control model for use may be, for example, one or a combination of the following models: a property model showing a relationship between parameters relating to a predetermined property; a transfer function showing a correspondence relationship between respective inputs and outputs in terms of a level ratio, a frequency-amplitude ratio, a phase difference, a proportional element, a differential element, an integral element and a delay element (= output signal / input signal); and a mathematical model in which a predetermined natural phenomenon is mathematically described.

Then, in step S15, an NH ₃ storage amount ST21 is calculated on the basis of the catalyst temperature Tc calculated in the previous step S12. 5 FIG. 14 shows an example of a map used for calculating the NH ₃ margin storage amount ST21. This map has appropriate values (optimum values) written down through experiments in advance. As in 5 4, the NH ₃ storage amount ST21 tends to decrease with an increase in the catalyst temperature Tc (an NH ₃ storage capacity tends to decrease).

Then, in step S16, a necessary NH ₃ storage amount (a required NH ₃ storage amount ST22, for example, a fixed value) is obtained by a desired temperature as the critical reaction temperature (activation temperature) of the SCR catalyst 13 to obtain. The required NH ₃ storage amount ST22 becomes based on the relationship between the critical reaction temperature of the SCR catalyst 13 and the NH ₃ storage amount is determined as in 6 is shown (an example, by the inventors through experiments or the like). As indicated by the solid line RT in 6 is shown, the critical reaction temperature of the SCR catalyst tends 13 to decrease with an increase in NH ₃ storage amount. In the example represented by the solid line RT, it is assumed that the desired temperature is a critical reaction temperature T1 with respect to the critical reaction temperature T0 when NH _{3 is} not stored. For example, the critical reaction temperature T1 is a temperature lower than "140 ° C", which is assumed as the catalyst temperature at an idling, and specifically, for example, a temperature in a range of "50 to 120 ° C". At this time, the critical reaction temperature (activation temperature) of the SCR catalyst is 13 an important parameter for determining the purifying property of the SCR catalyst 13 , 7 Fig. 10 is a graph showing an example of the purifying property of the SCR catalyst 13 shows. As in 7 is shown, the NO _x purification ratio of the SCR catalyst changes 13 to a large extent at the limit of the critical reaction temperature RT. That is, at the low temperature side with respect to the critical reaction temperature, the NO _x purification ratio is set to substantially "0", and the _NH3 storage amount is greater than the NH ₃ consumption amount, that is _x consumed by the cleaning reaction with NO , In contrast, the NO _x purification generally greater at the higher temperature side with respect to the critical reaction temperature, when a catalyst temperature is increased (in particular, the NO _x purification ratio changes drastically at a temperature close to the critical reaction temperature RT).

In the following step S17, by comparing the NH ₃ storage amount ST21 obtained in step S15 with the required NH ₃ storage amount ST22 obtained in step S16, it is determined whether the required NH ₃ storage amount ST22 is smaller than the NH ₃ limit storage amount ST21 is (ST21> ST22). If it is determined in step S17 that the relationship ST21> ST22 is met, then in the following step S171, the above required _NH3 storage amount ST22 as an NH ₃ -Zielspeichermenge ST2 is set. On the other hand, if it is determined in step S17 that the relationship ST21> ST22 is not satisfied, then in step S172, the above NH ₃ -limit amount ST21 is set as the NH ₃ target storage amount ST2.

Then, in step S18, a difference between the current NH ₃ storage amount ST1 and the NH ₃ target storage amount ST2 is calculated as a deficit of the NH ₃ storage amount ΔST (a storage amount that is absent compared to the NH ₃ target storage amount ST2) (ΔST = ST2 - ST1).

Then, in step S19b, a urea water addition amount Q is obtained by using the reference map for calculating the predetermined urea water addition amount (the same as that used in step S19a) and the NH ₃ storage amount deficit ΔST. Specifically, the urea water addition amount Q in the storage control mode is a urea water addition amount that is increased as compared with the urea water addition amount in the purge control mode to cover the NH ₃ storage amount deficit ΔST. In the following step S20, the urea water addition valve becomes 16 is driven (energized only for a time corresponding to the urea water addition amount Q) on the basis of the urea water adding amount Q thus obtained.

8A to 8C FIG. 15 is timing charts showing the urea water addition control by taking a case as an example where the vehicle equipped with the exhaust gas purification device and the exhaust emission control system of this embodiment is decelerated from a high-speed state. 8A shows the course of the engine speed. 8B shows the course of the temperature of the SCR catalyst 13 , 8C shows the occurrence or non-occurrence of execution of the memory control mode (ON = execute, OFF = non-execute). At this time, an apparatus for starting to store NH ₃ at the same time as the beginning of a delay (see, for example, FIG Japanese Patent Application No. 2000-556137 ) used as a comparative example. The operating form of the comparative example is indicated by the solid line L1 in FIG 8C and the operational form of this embodiment is represented by the solid line L2 in FIG 8C shown. The following description will be given by comparing both modes of operation with each other.

As in 8A to 8C 4, the vehicle is running in the steady state at high speed until the shown time t1 and starts to decelerate when the foot of a driver releases the accelerator pedal at the time t1. In step S31, which is in 3 2, it is determined that the accelerator pedal is in a non-operated state during the high-speed operation. Then, in the subsequent step S32, the timing of the determination is set as a start time of the engine delay time period.

In the comparative example (by the solid line in FIG 8C shown), a storage of NH _{3 is started} at this time t1. In contrast, in this embodiment (by the solid line L2 in FIG 8C shown) a storage of NH _{3 is} not started until in the in 2 In step S13, it is determined that the catalyst temperature Tc is smaller than the allowable level (Tc <Ts) (that is, for a predetermined non-satisfaction period). Therefore, the present embodiment (L2) can suppress the deterioration of the emission characteristic due to emission of NH ₃ as compared with the comparative example (L1).

At this time, the temperature of the SCR catalyst starts 13 at the time t2 slightly delayed from the above-described delay (time t1). In this embodiment, when the temperature of the SCR catalyst 13 decreases further and then becomes lower than the determination value Ts at a time t3, in step S13 which is in 2 is shown, determines that the catalyst temperature Tc is lower than the allowable level. At a time t3, the control mode of the purification control mode is switched to the memory control mode, so that the storage of NH ₃ in the SCR catalyst 13 is started. The end time of the engine delay time period (which, in step S43 in FIG 4 is set) is a time after the time t3.

In this way, in this embodiment, the series of control steps in the in 2 repeatedly performed, so that the execution of the storage control mode, the NH ₃ storage amount of the SCR catalyst 13 increased by the deficit.

Furthermore, the activation temperature of the catalyst 13 (critical reaction temperature) is controlled to a suitable temperature (for "ST21>ST22" to the critical reaction temperature T1). The execution of the memory control mode is not started immediately after the delay of the engine, but started after the predetermined non-satisfaction period. This can suitably suppress the deterioration of the emission characteristic while reducing the deterioration of the emission characteristic due to the execution of the unnecessary storage of the NH ₃ .

• (1) Die Zugabemengensteuerungseinrichtung kann in geeigneter Weise auf das Abgasemissionssteuerungssystem zum Reinigen des Abgases angewendet werden, das von der Brennkraftmaschine (Maschine) abgegeben wird. In diesem Fall hat die Zugabemengensteuerungseinrichtung den SCR-Katalysator 13 mit den Eigenschaften des Speicherns von NH₃ und des Weiteren des Verringerns der kritischen Reaktionstemperatur (Aktivierungstemperatur), wenn die Menge einer NH₃-Speicherung erhöht wird (siehe 6). Der SCR-Katalysator 13 ist angepasst, um eine bestimmte Abgasreinigungsreaktion in einem Temperaturbereich zu fördern, der die kritische Reaktionstemperatur als die untere Grenze hat. Die Zugabemengensteuerungseinrichtung hat auch das Harnstoffwasserzugabeventil 16 zum Zugeben des Additivs (Harnstoffwasser), das als eine NH₃(Ammoniak)-Erzeugungsquelle dient, zu dem Abgas an der stromaufwärtigen Seite mit Bezug auf den SCR-Katalysator 13. Das Additiv ist angepasst, das Abgas durch die vorstehende Abgasreinigungsreaktion mit NO_x (Stickstoffoxide) in dem Abgas an dem Katalysator 13 zu reinigen. Des Weiteren ist die Zugabemengensteuerungseinrichtung angepasst, die Zugabemenge des Harnstoffwassers durch das Harnstoffwasserzugabeventil 16 zu steuern. Solch eine Zugabemengensteuerungseinrichtung für ein Abgasreinigungsmittel (ECU 40) hat ein Steuerungsprogramm (Modusauswahleinrichtung, entspricht Schritten S10 und S13 in 2) zum Auswählen eines Modus, der zu dieser Zeit auf der Basis einer Erfüllung der Ausführungsbedingung für jeden Modus auszuführen ist, aus einer Vielzahl von Steuerungsmodi, einschließlich eines Reinigungssteuerungsmodus und eines Speichersteuerungsmodus. In dem Reinigungssteuerungsmodus wird die Zugabemenge des Harnstoffwassers durch das Harnstoffwasserzugabeventil 16 gemäß einem vorbestimmten Parameter bestimmt, der mit der NO_x-Menge des Abgases verknüpft ist. In dem Speichersteuerungsmodus wird die Zugabemenge des Harnstoffwassers durch das Harnstoffwasserzugabeventil 16 festgelegt, um größer als die in dem Reinigungssteuerungsmodus zu sein. Die Zugabemengensteuerungseinrichtung hat auch ein Steuerungsprogramm (Bedingungsbestimmungseinrichtung, entspricht Schritt S31 in 3) zum Bestimmen, ob eine Drehzahl einer Abgabewelle der Maschine (Maschinendrehzahl) aus einem Zustand mit höherer Geschwindigkeit als ein zulässiges Niveau verzögert wird. Wenn durch den Prozess in Schritt S31 bestimmt wird, dass die Drehzahl aus dem Hochgeschwindigkeitszustand verzögert wird, ist die Ausführungsbedingung des Speichersteuerungsmodus nach einer vorbestimmten Nichterfüllungszeitspanne (die durch den Prozess in Schritt S13 festgelegt wird, der in 2 gezeigt ist) seit einem Start der Verzögerung erfüllt. Dies kann das Reinigungsvermögen des Katalysators durch Verringern der kritischen Reaktionstemperatur des Katalysators durch Ausführung des vorstehend genannten Speichersteuerungsmodus verringern. Bei der Verzögerungszeit, wenn angenommen wird, dass der Katalysator eine hohe Temperatur hat, wird das Speichern von NH₃ nicht unmittelbar nach dem Beginn einer Verzögerung gestartet, sondern nach der vorbestimmten Nichterfüllungszeitspanne (nach einer Zeitspanne, in der die Katalysatortemperatur niedriger als das zulässige Niveau wird). Dies kann in geeigneter Weise die Verschlechterung der Emissionscharakteristik unterdrücken, während die Verschlechterung der Emissionscharakteristik aufgrund der Ausführung der unnötigen Speicherung des NH₃ verringert wird.
• (2) In dem Speichersteuerungsmodus in Schritt S20, der in 2 gezeigt ist, wird die NH₃-Speichermenge des SCR- Katalysators 13 gesteuert, um die NH₃-Zielspeichermenge ST2 zu sein, durch Ausgleichen des Defizits der NH₃-Speichermenge, die einer Differenz zwischen der NH₃-Zielspeichermenge ST2 und der derzeitigen NH₃-Speichermenge ST1 entspricht (das heißt des NH₃-Speichermengendefizits ΔST), durch den Prozess in Schritt S19b. Somit wird in dem Speichersteuerungsmodus das Defizit der NH₃-Speichermenge (NH₃-Speichermengendefizit ΔST) ausgeglichen, sodass die NH₃-Speichermenge des SCR-Katalysators 13 auf die NH₃-Zielspeichermenge festgelegt werden kann.
• (3) In dem in 2 gezeigten Schritt S20 wird, während eine vorbestimmte Bedingung (Bedingungen in Schritten S10 und S13) erfüllt ist, die Steuerung der NH₃-Speichermenge in Schritten S14 bis S20, die vorstehend beschrieben sind, wiederholt durchgeführt. Mit diesem Aufbau kann die NH₃-Speichermenge des SCR-Katalysators 13 fortlaufend auf eine geeignete Menge mit hoher Genauigkeit gesteuert werden, während die vorbestimmte Bedingung in Schritten S10 und S13 erfüllt ist. Somit wird die Aktivierungstemperatur (das heißt die kritische Reaktionstemperatur) des Katalysators 13 auf eine geeignete Temperatur gesteuert.
• (4) Die Zugabemengensteuerungseinrichtung hat des Weiteren ein Steuerungsprogramm (Katalysatortemperaturbestimmungseinrichtung, Schritt S13, der in 2 gezeigt ist) zum Bestimmen, ob die Temperatur des SCR-Katalysators 13 zu dieser Zeit (Katalysatortemperatur Tc) niedriger als das zulässige Niveau ist. Der Zeitpunkt, wenn in Schritt S13 bestimmt wird, dass die Temperatur des SCR-Katalysators 13 niedriger als das zulässige Niveau ist (Zeitpunkt t3, der in 8 gezeigt ist) wird als der Endzeitpunkt der vorbestimmten Nichterfüllungszeitspanne festgelegt. Zu diesem Endzeitpunkt wird der Speichersteuerungsmodus begonnen. Demzufolge ist es möglich, das NH₃ in einer begrenzten Weise in der höhere Anforderung stellenden Bedingung zu speichern, das heißt, wenn die Katalysatortemperatur ausreichend niedrig ist (niedriger als das zulässige Niveau).
• (5) Der Bestimmungswert Ts, der in dem in 2 gezeigten Schritt S13 verwendet wird, kann variabel auf die kritische Reaktionstemperatur von jeder Zeit festgelegt sein. Das heißt in Schritt S13, wenn die Katalysatortemperatur Tc in einem vorbestimmten Temperaturbereich ist (Tc < Ts), in dem die kritische Reaktionstemperatur (Bestimmungswert Ts) der obere Grenzwert ist, wird bestimmt, dass die Katalysatortemperatur Tc niedriger als das zulässige Niveau ist. Auf diese Weise kann der Startzeitpunkt der NH₃-Speicherung, die vorstehend beschrieben ist (Zeitpunkt t3, der in 8A bis 8C gezeigt ist), auf eine günstigere Zeit festgelegt werden.
• (6) Die Ausführungsbedingung des Reinigungssteuerungsmodus ist erfüllt, wenn die Ausführungsbedingung des Speichersteuerungsmodus nicht erfüllt ist. Das heißt in den in 2 gezeigten Schritten S10 und S13 werden zwei Arten von Steuerungsmodi, und zwar der Reinigungssteuerungsmodus und der Speichersteuerungsmodus, gemäß der Erfüllung oder Nichterfüllung dieser Ausführungsbedingungen umgeschaltet. Dies kann die Steuerung der Abgasreinigung leichter und genauer erreichen.
• (7) In Schritt S14, der in 2 gezeigt ist, wird der Betrag einer Erhöhung oder einer Abnahme einer NH₃-Speichermenge des SCR-Katalysators 13 zu jeder Zeit auf der Basis der Differenz zwischen der NH₃-Menge, die zu dem SCR-Katalysator 13 zugeführt wird, und der NH₃-Verbrauchsmenge an dem Katalysator 13 bestimmt. Des Weiteren werden die Erhöhungs- oder Abnahmebeträge der jeweiligen Zeiten anschließend summiert (ST1 (Wert zu dieser Zeit) = ΣST1 (vorheriger Wert) + ΔNH₃), wodurch die derzeitige NH₃-Speichermenge ST1 erfasst wird, wie vorstehend beschrieben ist. Dieser Aufbau macht es möglich, den Betrag einer Erhöhung oder einer Abnahme der NH₃-Speichermenge zu jeder Zeit und die derzeitige NH₃-Menge ST1 durch Bestimmen, dass das verbleibende NH₃ an dem SCR-Katalysator 13 gespeichert ist, auf der Basis der Zunahme und der Abnahme der NH₃-Menge genau zu berechnen.
• (8) In dem in 2 gezeigten Schritt S14 wird die Verbrauchsmenge von NH₃ an dem SCR-Katalysator 13 auf der Basis eines vorbestimmten Parameters bestimmt, der mit dem Betriebszustand der Maschine verknüpft ist (beispielsweise der Maschinendrehzahl und der Kraftstoffeinspritzmenge). Mit diesem Aufbau kann die von der Maschine abgegebene NO_x-Menge und des Weiteren die NH₃-Verbrauchsmenge an dem SCR-Katalysator 13 leichter und genauer erfasst werden.
• (9) Die Zugabemengensteuerungseinrichtung hat auch ein Steuerungsprogramm (Grenzspeichermengenerfassungseinrichtung, entspricht Schritt S15, der in 2 gezeigt ist) zum Erfassen der Grenzspeichermenge von NH₃, die in dem SCR-Katalysator 13 zu dieser Zeit gespeichert werden kann (NH₃-Grenzspeichermenge ST21). Die Zugabemengensteuerungseinrichtung hat des Weiteren ein Steuerungsprogramm (Schritte S17, S171 und S172, die in 2 gezeigt sind) zum Festlegen eines variablen Bereichs der NH₃-Zielspeichermenge ST2 durch Verwenden der NH₃-Grenzspeichermenge ST21. Die NH₃-Grenzspeichermenge ST21 wird durch den Prozess in Schritt S15 erfasst und als der obere Grenzwert (Überwachungswert) festgelegt. Somit ist es möglich, die NH₃-Grenzspeichermenge ST21 als die obere Grenze festzulegen, um die Zufuhr des überschüssigen NH₃ zu verhindern (oder zu unterdrücken).
• (10) In dem in 2 gezeigten Schritt S15 wird die NH₃-Grenzspeichermenge ST21 auf der Basis der Abgastemperatur an der stromabwärtigen Seite mit Bezug auf den Katalysator 13 erfasst, die der Temperatur des SCR-Katalysators 13 entspricht. Somit kann die Temperatur des SCR-Katalysators 13 mit hoher Genauigkeit erfasst (geschätzt) werden.
• (11) Eine Temperatur, die niedriger als die Katalysatortemperatur von "140°C" ist und in einem Leerlauf angenommen wird, und eine NH₃-Speichermenge, die zu der Temperatur korrespondiert, sind als die kritische Reaktionstemperatur ST1 bzw. als die erforderte NH₃-Speichermenge ST22 (siehe 6 für beide) festgelegt. Dies kann das Abgas sicher reinigen, selbst wenn eine Beschleunigung aus dem Leerlaufzustand begonnen wird.
• (12) Das Harnstoffwasserzugabeventil 16 ist gestaltet, um die wässrige Harnstofflösung als das Additiv, das als die NH₃-Erzeugungsquelle wirkt, zu dem Abgas an der stromaufwärtigen Seite (Abgasrohr 12) mit Bezug auf den SCR-Katalysator 13 einzuspritzen und zuzugeben (das heißt, um das sogenannte Harnstoff-SCR-System zu schaffen). Somit wird die wässrige Harnstofflösung zu dem Abgas an der stromaufwärtigen Seite mit Bezug auf den SCR-Katalysator 13 eingespritzt und zugegeben. Deshalb wird der Harnstoff, bis das Harnstoffwasser den Katalysator 13 erreicht, durch Abgaswärme oder dergleichen hydrolisiert, um NH₃ zu bilden. Dadurch kann mehr NH₃ (Reinigungsmittel) zu dem SCR-Katalysator 13 zugeführt werden.
• (13) Das vorstehende Harnstoff-SCR-System ist in dem Fahrzeug installiert, das mit der Dieselmaschine ausgestattet ist (vierrädriges Fahrzeug in dieser Ausführungsform). Dies kann die Kraftstoffeffizienz verbessern und die PM durch Gestatten der Erzeugung von NO_x während des Verbrennungsprozesses verringern. Dadurch kann das sauberere Dieselfahrzeug mit dem hohen Abgasreinigungsvermögen erreicht werden.
• (14) Im Gegensatz dazu hat das Abgasemissionssteuerungssystem den SCR-Katalysator 13 und das Harnstoffwasserzugabeventil 16 zusammen mit jedem Programm (ECU 40) und eine Harnstoffwasserzufuhrvorrichtung (den Harnstoffwassertank 17a, die Pumpe 17b und dergleichen) zum Zuführen der wässrigen Harnstofflösung zu dem Zugabeventil 16. Das Abgasemissionssteuerungssystem mit diesem Aufbau schafft das Abgasreinigungssystem mit dem höheren Abgasreinigungsvermögen.

As described above, the addition amount control means for an exhaust gas purifying agent and the exhaust emission control system according to this embodiment achieve the following excellent effects and advantages.

• (1) The addition amount control means may be suitably applied to the exhaust emission control system for purifying the exhaust gas discharged from the internal combustion engine (engine). In this case, the addition amount controller has the SCR catalyst 13 with the properties of storing NH ₃ and further reducing the critical reaction temperature (activation temperature) when the amount of NH ₃ storage is increased (see 6 ). The SCR catalyst 13 is adapted to promote a particular exhaust gas purification reaction in a temperature range having the critical reaction temperature as the lower limit. The addition amount controller also has the urea water addition valve 16 for adding the additive (urea water) serving as an NH ₃ (ammonia) generation source to the exhaust gas on the upstream side with respect to the SCR catalyst 13 , The additive is adapted to the exhaust gas by the above exhaust gas purifying reaction with NO _x (nitrogen oxides) in the exhaust gas on the catalyst 13 to clean. Further, the addition amount control means is adapted, the addition amount of the urea water by the urea water addition valve 16 to control. Such an addition amount control device for an exhaust gas purifying means (ECU 40 ) has a control program (mode selector, corresponds to steps S10 and S13 in FIG 2 ) for selecting a mode to be executed at that time based on fulfillment of the execution condition for each mode, among a plurality of control modes including a cleaning control mode and a memory control mode. In the purge control mode, the addition amount of the urea water by the urea water addition valve becomes 16 determined according to a predetermined parameter, which is linked to the NO _x amount of the exhaust gas. In the storage control mode, the addition amount of the urea water by the urea water addition valve becomes 16 set to be greater than that in the cleaning control mode. The addition amount control means also has a control program (condition determination means, which corresponds to step S31 in FIG 3 ) for determining whether a rotational speed of an output shaft of the engine (engine rotational speed) is being retarded from a higher speed state than an allowable level. When it is determined by the process in step S31 that the rotational speed is being decelerated from the high-speed state, the execution condition of the storage control mode is after a predetermined non-satisfaction period (which is set by the process in step S13 that is in FIG 2 shown) has been met since a start of the delay. This can reduce the purifying ability of the catalyst by reducing the critical reaction temperature of the catalyst by executing the aforementioned storage control mode. In the delay time, when it is assumed that the catalyst has a high temperature, is the storage of NH _{3 is} not started immediately after the start of a delay, but after the predetermined non-satisfaction period (after a period in which the catalyst temperature becomes lower than the allowable level). This can suitably suppress the deterioration of the emission characteristic while reducing the deterioration of the emission characteristic due to the execution of the unnecessary storage of the NH ₃ .
• (2) In the memory control mode in step S20 included in 2 is shown, the NH ₃ storage amount of the SCR catalyst 13 controlled to be the NH ₃ target storage amount ST2 by offsetting the deficit of the NH ₃ storage amount corresponding to a difference between the NH ₃ target storage amount ST2 and the current NH ₃ storage amount ST1 (that is, the NH ₃ storage amount deficit ΔST ), through the process in step S19b. Thus, in the storage control mode, the deficit of the NH ₃ storage amount (NH ₃ storage amount deficit ΔST) is compensated, so that the NH ₃ storage amount of the SCR catalyst 13 can be set to the NH ₃ target amount.
• (3) In the in 2 As shown in step S20, while a predetermined condition (conditions in steps S10 and S13) is satisfied, the control of the NH ₃ storage amount in steps S14 to S20 described above is repeatedly performed. With this construction, the NH ₃ storage amount of the SCR catalyst 13 are continuously controlled to an appropriate amount with high accuracy while the predetermined condition is satisfied in steps S10 and S13. Thus, the activation temperature (that is, the critical reaction temperature) of the catalyst becomes 13 controlled to a suitable temperature.
• (4) The addition amount control means further has a control program (catalyst temperature determination means, step S13 shown in FIG 2 shown) for determining whether the temperature of the SCR catalyst 13 at this time (catalyst temperature Tc) is lower than the allowable level. The time when it is determined in step S13 that the temperature of the SCR catalyst 13 is lower than the allowable level (time t3, which is in 8th is shown) is set as the end time of the predetermined non-satisfaction period. At this end time, the memory control mode is started. Accordingly, it is possible to store the NH ₃ in a limited manner in the higher requirement condition, that is, when the catalyst temperature is sufficiently low (lower than the allowable level).
• (5) The determination value Ts, which in the in 2 shown step S13 may be variably set to the critical reaction temperature of each time. That is, in step S13, when the catalyst temperature Tc is in a predetermined temperature range (Tc <Ts) in which the critical reaction temperature (determination value Ts) is the upper limit, it is determined that the catalyst temperature Tc is lower than the allowable level. In this way, the starting time of the NH ₃ storage described above (time t3, which is in FIG 8A to 8C shown) to be set at a more favorable time.
• (6) The execution condition of the cleaning control mode is satisfied when the execution condition of the storage control mode is not satisfied. That is in the in 2 As shown in steps S10 and S13, two kinds of control modes, the cleaning control mode and the storage control mode, are switched according to the fulfillment or non-fulfillment of these execution conditions. This can more easily and accurately achieve control of exhaust gas purification.
• (7) In step S14, which is in 2 is shown, the amount of an increase or decrease of a NH ₃ storage amount of the SCR catalyst 13 at any time based on the difference between the amount of NH _{3 added} to the SCR catalyst 13 and the amount of NH ₃ consumed on the catalyst 13 certainly. Further, the increment or decrement amounts of the respective times are then summed (ST1 (value at this time) = ΣST1 (previous value) + ΔNH ₃ ), thereby detecting the current NH ₃ storage amount ST1 as described above. This structure makes it possible to determine the amount of increase or decrease of the NH ₃ storage amount at each time and the current NH ₃ amount ST1 by determining that the remaining NH ₃ on the SCR catalyst 13 is calculated accurately based on the increase and decrease in NH ₃ amount.
• (8) In the 2 As shown in step S14, the consumption amount of NH ₃ on the SCR catalyst 13 determined on the basis of a predetermined parameter associated with the operating state of the engine (for example, the engine speed and the fuel injection amount). With this structure, the output from the engine NO _x amount and further the NH ₃ consumption amount of the SCR catalyst 13 be detected more easily and accurately.
• (9) The addition amount control means also has a control program (limit storage amount detecting means, corresponding to step S15 shown in FIG 2 is shown) for detecting the limit storage amount of NH ₃ in the SCR catalyst 13 can be stored at this time (NH ₃ limit storage amount ST21). The addition amount controller has Further, a control program (steps S17, S171 and S172, which are described in US Pat 2 are shown) for setting a variable range of the NH ₃ target storage amount ST2 by using the NH ₃ limit storage amount ST21. The NH ₃ storage amount ST21 is detected by the process in step S15 and set as the upper limit value (guard value). Thus, it is possible to set the NH ₃ storage amount ST21 as the upper limit to prevent (or suppress) the supply of the excess NH ₃ .
• (10) In the 2 As shown in step S15, the NH ₃ storage amount ST21 becomes based on the exhaust gas temperature at the downstream side with respect to the catalyst 13 recorded the temperature of the SCR catalyst 13 equivalent. Thus, the temperature of the SCR catalyst 13 recorded (estimated) with high accuracy.
• (11) A temperature lower than the catalyst temperature of "140 ° C" and assumed to be idling and an NH ₃ storage amount corresponding to the temperature are referred to as the critical reaction temperature ST1 and the required NH, respectively ₃ storage amount ST22 (see 6 for both). This can purify the exhaust gas safely even if acceleration from the idling state is started.
• (12) The urea water addition valve 16 is designed to the aqueous urea solution as the additive, which acts as the NH ₃ generation source, to the exhaust gas on the upstream side (exhaust pipe 12 ) with respect to the SCR catalyst 13 Inject and add (that is, to create the so-called urea-SCR system). Thus, the aqueous urea solution becomes the exhaust gas on the upstream side with respect to the SCR catalyst 13 injected and added. Therefore, the urea, until the urea water is the catalyst 13 is hydrolyzed by exhaust heat or the like to form NH ₃ . This allows more NH ₃ (cleaning agent) to the SCR catalyst 13 be supplied.
• (13) The above urea SCR system is installed in the vehicle equipped with the diesel engine (four-wheeled vehicle in this embodiment). This can improve the fuel efficiency and reduce the PM by allowing the generation of NO _x during the combustion process. As a result, the cleaner diesel vehicle can be achieved with the high emission of exhaust gas.
• (14) In contrast, the exhaust emission control system has the SCR catalyst 13 and the urea water addition valve 16 together with each program (ECU 40 ) and a urea water supply device (the urea water tank 17a , the pump 17b and the like) for supplying the aqueous urea solution to the addition valve 16 , The exhaust emission control system having this structure provides the exhaust gas purification system having the higher exhaust gas purification ability.

The The embodiment described above can be seen in the following Be changed way.

In the above embodiment, when the catalyst temperature Tc is in the predetermined temperature range (Tc <Ts) using the critical reaction temperature (determination value Ts) as the upper limit value, it is determined that the catalyst temperature Tc is lower than the allowable level (FIG. Step S13, which is in 2 is shown), but the invention is not limited thereto. A predetermined temperature (a temperature that is lower than the critical reaction temperature only by a predetermined temperature lower than the critical reaction temperature at all times or a sufficiently low fixed value) may be set as the determination value Ts. Even in this case, when the catalyst temperature Tc is in a predetermined temperature range ("Tc <Ts" or "Tc ≦ Ts") using the determination value Ts as the upper limit value, it may be determined in the above-described step S13 that the catalyst temperature Tc is lower than the allowable level. In such a case, an effect based on the effect described in paragraph (5) can be obtained.

According to the applications of the exhaust emission control system, the control process in step S15, S17, S171 or S172 shown in FIG 2 are shown to be omitted. In this case, in step S18, the required NH ₃ storage amount ST22 is effectively set to the NH ₃ target storage amount ST2 as it is.

In the aforementioned embodiment, the non-satisfaction period (the non-execution period of the storage control mode) is set when the rotational speed of the output shaft of the engine (engine rotational speed) is decelerated from the high-speed state where the rotational speed is higher than the allowable level, but the invention is not limited thereto , For example, when larger fluctuations of the load occurring on the output shaft of the engine toward the negative side (take-off side) compared to an allowable level, the non-satisfaction time interval can be set. That is, in this case, for example, it is determined in step S31 whether the fluctuation amount of an accelerator pedal operation amount (corresponding to a requested torque) toward the negative side (non-operation side) is greater than a predetermined determination value. Here is the fluctuation amount, for example, the amount of change per unit time. If it is determined in step S31 that the fluctuation amount of the accelerator operation amount is larger (it is determined that the amount of depression of the accelerator pedal is rapidly decreasing), the flow proceeds to step S32. Not only an estimated value based on such accelerator pedal operation amount but also, for example, a value actually measured by an in-cylinder pressure sensor may be used as the detection value of the load on the engine.

Alternatively, if larger fluctuations in the speed of the output shaft the machine to the negative side (delay side) can occur in comparison to the permissible level the default time interval are set. The In this case, it is determined, for example, whether the fluctuation amount the engine speed to the negative side (deceleration side) greater than the predetermined determination value is. When it is determined in step S31 that the fluctuation amount the machine speed is greater, the process goes proceed to step S32.

Altnernativ the non-compliance period can be set if the fuel for the machine is interrupted. This means, In this case, it is determined, for example, in step S31, whether the fuel cut is carried out. If it is determined in step S31 that the fuel cut is done, the goes Proceed to step S32.

Of Furthermore, these structures can have an effect based of the effect described in paragraph (1).

The addition amount control means has a control program (operation mode determination means) for determining whether the operation mode of the engine (internal combustion engine) at this time is a preset operation mode. The default operation mode is a mode in which the load applied to the output shaft of the engine is controlled to be decreased when the temperature of the SCR catalyst 13 in the high-temperature state exceeding the critical reaction temperature (activation temperature). In particular, in the in 3 Step S31 shown determines whether the operating mode at this time is the aforementioned preset operating mode. With this configuration, if it is determined, for example, that the operation mode at this time is the preset operation mode, the process proceeds to step S32. Thus, in the preset mode of operation, the addition of urea water through the urea water addition valve 16 (Storage control mode) for the purpose of storing NH ₃ on the SCR catalyst 13 in the amount, the amount of added through the valve 16 is prohibited for a predetermined period of time (that is, a period of time until the catalyst temperature becomes lower than the allowable level). Also, this structure can obtain an effect based on the effect described in paragraph (1). It is effective that the preset operation mode set may include, for example, the deceleration operation, the fuel cut operation, the reduced cylinder operation, and the like.

The set default period is not limited to the time period associated with the catalyst temperature, but may be any other period of time. For example, the non-satisfaction period may be set based on the time. Specifically, the time point after a predetermined time since the start of the delay may be set as the end time of the non-satisfaction period. Here, the end time of the non-satisfaction period corresponds to the start time of NH ₃ storage.

Even though in the embodiment described above, two control modes the cleaning control mode and the storage control mode switched are, the invention is not limited thereto. An add another control mode to these control modes allows a selection of one to perform at this time is based on three or more types of control modes Fulfillment of the execution condition of each mode.

For example, a mode selection may be performed by the process as exemplified in the flowchart of FIG 9 is shown. In this example, the use of a value of a urea water addition control flag F ("0 to 2") selects one of three types of the purge control mode, the storage control mode, and the urea water mistaking mode.

As in 9 is shown, in this example, it is determined in step S101 whether a predetermined execution condition associated with the storage control mode (storage control execution condition) is satisfied. If it is determined in step S101 that the storage control execution condition is satisfied, the urea water addition control flag is set to "2" in subsequent step S103.

In contrast, when it is determined in step S101 that the storage control execution condition is not satisfied, it is determined in the subsequent step S102 whether a predetermined execution condition is satisfied with the cleaning is connected (cleaning control execution condition). If it is determined in step S102 that the purge control execution condition is satisfied, the urea water addition control flag F is set to "1" in subsequent step S105. On the other hand, when it is determined in step S102 that the purge control execution condition is not satisfied, in the subsequent step S104, the urea water addition control flag is set to "0".

This can one of the three to be carried out at this time or select more types of control modes.

Although in the above-described embodiment, the NH ₃ storage amount corresponding to the predetermined critical reaction temperature T 1, which is lower than the idle-running catalyst temperature of "140 ° C," is the required NH ₃ storage amount ST22 for use in determining the NH ₃ target accumulation amount ST2, the invention is not limited thereto. For example, the required NH ₃ storage amount ST22 can be effectively set to a threshold (convergence point) at which the critical reaction temperature itself increases by increasing the NH ₃ storage amount of the SCR catalyst 13 is not reduced. This structure can suitably prevent (or suppress) the excessive storage of NH ₃ which does not contribute to the critical reaction temperature.

In the above-described embodiment, the required NH ₃ storage amount ST22 is set as the fixed value, but the invention is not limited thereto. The required NH ₃ storage amount ST22 may be variably set according to the condition of each time. For example, the amount of memory may be set to be different between the start time of the machine and the idle time. Alternatively, the required NH ₃ storage amount ST22 may be variably set in accordance with a target value of the critical reaction temperature or a target value of the NO _x purification ratio on the SCR catalyst 13 be determined.

In In the embodiment described above, the catalyst temperature becomes Tc determined on the basis of the exhaust gas temperature. However, the temperature becomes the catalyst itself is not determined, and the exhaust gas temperature can be used as a replacement for the catalyst temperature become.

The amount of _NOx in the exhaust gas can be determined not only by estimating the engine operation state, but may, for example, by the actually measured value (sensor output) can be determined by a NO _x sensor or the like. Further, for example, the amount of NO _x in the exhaust gas may be estimated based on the state of the exhaust gas (eg, exhaust gas temperature detected by the exhaust temperature sensor or the like) or components (for example, an oxygen concentration detected by an oxygen concentration sensor or the like ).

The Type of exhaust gas generation source to be cleaned or system design can be arbitrary according to the used Conditions or the like to be changed.

If for example, the exhaust gas from the engine for a vehicle is an object to be cleaned, the invention can not only on one Compression ignition diesel engine, but also to a spark ignition gasoline engine or the like. Because the compression ignition engine, like the diesel engine, the low exhaust temperature compared to the in the spark ignition machine has, the invention effectively applied to the compression ignition engine, whereby the cleaning power is increased, if the catalyst temperature is low. The invention is also applicable a lathe or the like can be applied differently as a piston engine. Furthermore, the invention can also to be applied to a purification of exhaust gas from sources that unlike the vehicle, that is, for example on a purification of exhaust gas from an electric power plant, from various factories or the like.

On the other hand, the system configuration may be changed in the following manner. Such as in 1 is shown, the additive (urea water) becomes the exhaust gas on the upstream side with respect to the catalyst 13 added to the additive through the exhaust control to the catalyst 13 to promote, but the invention is not limited thereto. Alternatively, the additive can be added directly to the catalyst itself (for example, injected). For example, if the amount of emission of NH ₃ in the in 1 is sufficiently reduced, the NH ₃ catalyst 15 be omitted from the structure.

If various modifications to the constructions in the preceding Embodiments are made, the details of the various processes (programs) described above preferably to the respective optimum shapes according to the actual structure changed if necessary is.

In fact, the main demand comes after the invention of the urea SCR system (urea selective reduction system). However, the invention may be used for other applications as long as the exhaust gas is purified on a catalyst using the same purifying agent (NH ₃ ) for purifying the same component of interest.

In the above-described and modified examples are assumed that different types of software (programs) are used but hardware, such as a dedicated line, can be used to achieve the same function.

It It should be understood that such changes and modifications within the scope of the present invention are as defined by the appended claims are defined.

In an addition amount control device ( 40 ) for an exhaust gas purifying agent to be used for an exhaust emission control system of an engine, a mode based on satisfaction of an execution condition for each of a plurality of control modes is executed. The control modes include a purge control mode in which an addition amount of NH ₃ or an additive serving as a generation source of the NH ₃ is determined according to a predetermined parameter associated with a NO _x amount in the exhaust gas and a storage control mode. in which the addition amount is set to be larger than that in the cleaning control mode. When it is determined that a rotational speed of an output shaft of the engine is being delayed from a higher-speed state than an allowable level, the execution condition of the memory control mode is satisfied after a predetermined non-satisfaction period from a start of the deceleration.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 2003-293739 A [0003, 0005]
• JP 2000-556137 [0064]

Claims (11)

Addition amount control device ( 40 ) for an exhaust gas purification means, wherein the control means is applied to an exhaust emission control system for purifying an exhaust gas discharged from an internal combustion engine, the exhaust emission control system comprising a catalyst ( 13 ) for conveying a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit and an addition valve ( 16 ) for adding an NH ₃ (ammonia) additive or an additive serving as a generation source of the NH ₃ to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, the additive being adapted, NO _x (Nitrogen oxides) in the exhaust gas to be purified by the exhaust gas purifying reaction on the catalyst, wherein the addition amount control means is adapted to control an addition amount by the addition valve, the catalyst having properties of storing NH ₃ and further reducing the critical reaction temperature the NH ₃ storage amount is increased, wherein the addition amount control means comprises: a mode selecting means for selecting a mode to be executed at that time based on satisfaction of an execution condition for each mode from among a plurality of control modes, the control modes including a purification control mode; in which the addition amount d the addition valve is determined according to a predetermined parameter associated with a NO _x amount in the exhaust gas and a storage control mode in which the addition amount through the addition valve is set to be larger than that in the purge control mode; and a condition determining means for determining whether a rotational speed of an output shaft of the internal combustion engine is decelerated from a higher-speed state than an allowable level, the execution condition of the storage control mode being set to be satisfied after a predetermined non-satisfaction period from a start of the deceleration, when Condition determining means determines that the speed is being delayed from the higher speed state. Addition amount control device ( 40 ) for an exhaust gas purification means, wherein the control means is applied to an exhaust emission control system for purifying an exhaust gas discharged from an internal combustion engine, the exhaust emission control system comprising a catalyst ( 13 ) for conveying a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit and an addition valve ( 16 ) for adding an NH ₃ (ammonia) additive or an additive serving as a generation source of the NH ₃ to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, the additive being adapted, NO _x (Nitrogen oxides) in the exhaust gas to purify by the exhaust gas purifying reaction on the catalyst, wherein the addition amount control means is adapted to control an addition amount by the addition valve, wherein the catalyst has properties of storing NH ₃ and further reducing the critical reaction temperature NH ₃ storage amount is increased, wherein the addition amount control means comprises: a mode selector for selecting a mode to be executed at that time based on fulfillment of an execution condition for each mode among a plurality of control modes, the control modes including a purge control mode the amount to be added durc h the addition valve is determined according to a predetermined parameter associated with an amount of _NOx in the exhaust gas, and include a memory control mode, in which the addition amount is determined by the addition valve so as to be larger than that in the purification control mode; and a condition determining means for determining whether a fluctuation amount of a load on the output shaft of the internal combustion engine is greater than an allowable level to a negative side, the execution condition of the storage control mode being set to be satisfied after a predetermined non-satisfaction period since the fluctuation, when the Condition determination means determines that the fluctuation amount of the load toward the negative side is greater than the allowable level. Addition amount control device ( 40 ) for an exhaust gas purification means, wherein the control means is applied to an exhaust emission control system for purifying an exhaust gas discharged from an internal combustion engine, the exhaust emission control system comprising a catalyst ( 13 ) for conveying a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit and an addition valve ( 16 ) for adding an NH ₃ (ammonia) additive or an additive serving as a generation source of the NH ₃ to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, the additive being adapted, NO _x (Nitrogen oxides) in the exhaust gas to be purified by the exhaust gas purifying reaction on the catalyst, wherein the addition amount control means is adapted to control an addition amount by the addition valve, the catalyst having properties of storing NH _3, and further reducing the critical reaction temperature when the NH ₃ storage amount is increased, the addition amount controller comprising: a mode selector for selecting a mode to execute at that time based on satisfaction of an execution condition for each mode is one of a plurality of control modes, wherein the control modes include a purge control mode in which the addition amount is determined by the addition valve according to a predetermined parameter associated with a NO _x amount in the exhaust gas, and a storage control mode in which the addition amount is set by the addition valve to be larger than that in the cleaning control mode; and condition determining means for determining whether a fluctuation amount of a rotational speed of the output shaft of the internal combustion engine toward the negative side is greater than an allowable level, the execution condition of the storage control mode being set to be satisfied after a predetermined non-satisfaction period since the fluctuation, when the condition determining means determines that the fluctuation amount of the rotational speed to the negative side is greater than the allowable level. Addition amount control device ( 40 ) for an exhaust gas purification means, wherein the control means is applied to an exhaust emission control system for purifying an exhaust gas discharged from an internal combustion engine, the exhaust emission control system comprising a catalyst ( 13 ) for conveying a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit and an addition valve ( 16 ) for adding an NH ₃ (ammonia) additive or an additive serving as a generation source of the NH ₃ to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, the additive being adapted, NO _x (Nitrogen oxides) in the exhaust gas to be purified by the exhaust gas purifying reaction on the catalyst, wherein the addition amount control means is adapted to control an addition amount by the addition valve, the catalyst having properties of storing NH ₃ and further reducing the critical reaction temperature the NH ₃ storage amount is increased, wherein the addition amount control means comprises: a mode selecting means for selecting a mode to be executed at that time based on satisfaction of an execution condition for each mode from among a plurality of control modes, the control modes including a purification control mode; in which the addition amount d the addition valve is determined according to a predetermined parameter associated with a NO _x amount in the exhaust gas and a storage control mode in which the addition amount through the addition valve is set to be larger than that in the purge control mode; and a condition determination means for determining whether a fuel cut is performed in the internal combustion engine, wherein the execution condition of the storage control mode is set to be satisfied after a predetermined non-satisfaction period from start of the fuel cut, when the condition determination means determines that the fuel cut is being performed. Addition amount control means for an exhaust gas purifying agent according to one of claims 1 to 4, which further comprises a Catalyst temperature determining means for determining whether the temperature of the catalyst at this time lower than one permissible level, the predetermined non-satisfaction period has an end time at which the catalyst temperature determination means determines that the temperature of the catalyst is lower than that permissible level is. Addition amount control means for an exhaust gas purifying agent according to claim 5, wherein, when the temperature of the catalyst to this time is in a predetermined temperature range, which is the critical reaction temperature or a predetermined temperature, which is less than the critical reaction temperature, than one upper limit value, the catalyst temperature determination means determines that the temperature of the catalyst at this time lower than the allowed level. Addition amount control means for an exhaust gas purifying agent according to one of claims 1 to 6, wherein the execution condition the cleaning control mode is set to met to be when the execution condition of the memory control mode is not met, and wherein the mode selector between two types of control modes of the cleaning control mode and the memory control mode according to a fulfillment or non-fulfillment of the execution condition switches. An exhaust gas purifying substance addition amount control device according to any one of claims 1 to 4, further comprising: operation mode determining means for determining whether the operation mode of the internal combustion engine is a preset operation mode in which a load on the output shaft of the internal combustion engine is controlled to be decreased; when the catalyst has a high temperature exceeding the critical reaction temperature; and a prohibition device for prohibiting an access adding NH ₃ or the additive serving as the generation source of NH ₃ through the addition valve to the catalyst in an NH ₃ storage amount during a predetermined period of time when the operation mode determination means determines that the operation mode is the preset operation mode at that time. Addition amount control device ( 40 ) for an exhaust gas purification means, wherein the control means is applied to an exhaust emission control system for purifying an exhaust gas discharged from an internal combustion engine, the exhaust emission control system comprising a catalyst ( 13 ) for conveying a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit and an addition valve ( 16 ) for adding an NH ₃ (ammonia) additive or an additive serving as a generation source of the NH ₃ to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, the additive being adapted, NO _x (Nitrogen oxides) in the exhaust gas to be purified by the exhaust gas purifying reaction on the catalyst, wherein the addition amount control means is adapted to control an addition amount by the addition valve, the catalyst having properties of storing NH ₃ and further reducing the critical reaction temperature the NH ₃ storage amount is increased, wherein the addition amount control means comprises: an operation mode determining means for determining whether the operation mode of the internal combustion engine is a preset operation mode in which a load on the output shaft of the internal combustion engine is controlled to be reduced when the catalyst is a high temperature has that exceeds the critical reaction temperature; and prohibiting means for prohibiting addition of NH ₃ or the additive serving as the generation source of NH ₃ by the addition valve to the catalyst in an NH ₃ storage amount only during a predetermined period of time when the operation mode determination means determines that the operation mode is increasing This time is the default operating mode. Addition amount control means for an exhaust gas purifying agent according to any one of claims 1 to 9, wherein the addition valve adapted to an aqueous urea solution as the additive to the exhaust gas at an upstream one Inject page with respect to the catalyst and add. An exhaust emission control system comprising: the addition amount control device according to claim 10; the catalyst and the addition valve; and a urea water supply device ( 17a - 17f ) for supplying the aqueous urea solution to the addition valve.