ES2266971T3 - CATALYST CONTROL UNIT AND DETERMINATION DETERMINATION DEVICE OF INTERNAL COMBUSTION ENGINE CATALYST. - Google Patents

Abstract

Apparatus for controlling an exhaust purification catalyst, the catalyst being located in an exhaust system of an internal combustion engine (2), in which, during sulfur release control to allow the catalyst to recover from poisoning by sulfur, the apparatus repeats a period of enrichment and a period of non-enrichment, in which, in the period of enrichment, the apparatus intermittently supplies fuel to the exhaust gas in a section upstream of the catalyst, thus decreasing the air-fuel ratio of the exhaust gas that comes into contact with the catalyst to a value equal to or less than the stoichiometric air-fuel ratio, and in which, in the period of non-enrichment, the apparatus does not supply fuel to the exhaust gas, the apparatus by: means of detecting the degree of deterioration that detect the degree of deterioration of the exhaust purification catalyst; and means of change that change the ratio of the duration of the enrichment period with respect to the duration of the non-enrichment period according to the degree of deterioration of the exhaust purification catalyst detected by the means of detecting the degree of deterioration.

Description

Catalyst control apparatus and apparatus Determination of the deterioration of the combustion engine catalyst internal

Background of the invention

The present invention relates to an apparatus to control a facilitated exhaust purification catalyst in the exhaust system of an internal combustion engine and at a apparatus for determining the deterioration of such catalyst.

A usual exhaust purification catalyst, particularly, a NOx storage reduction catalyst, is poisoned with the sulfur components contained in the fuel. When the degree of sulfur poisoning increases, the NOx storage reduction performance of the catalyst degrades. Therefore, when a certain amount of sulfur components accumulates in the NOx storage reduction catalyst, a temperature increase process is performed to heat the catalyst. In addition, the air-comp ratio
Exhaust gas fuel is enriched to cause a sulfur release control in which the sulfur components are discharged from the NOx storage reduction catalyst.

However, if the air-fuel ratio is continuously enriches during the release control of sulfur, the sulfur components are intermittently discharged from the catalyst. Consequently, the concentration of components of Sulfur in the exhaust gas increases. This produces stink. So, Japanese patent publication open for public consultation number 2000-274232 (pages 4 to 5, figure 2) describes a technology to prevent the concentration of Sulfur components in the exhaust gas are excessive by the intermittent enrichment of the air-gas ratio escape Specifically, an execution period, in which enriches the air-fuel ratio, and a period of interruption, in which the air-fuel ratio is not enriched, they are repeated alternatively.

During the execution period, the fuel in the exhaust purification catalyst it oxidizes and heats up, which increases the temperature of the catalyst bed. For other part, during the interruption period, the heating the catalyst and the catalyst is cooled by exhaust gas, which lowers the bed temperature of the catalyst. That is, the air-fuel ratio is enriched intermittently so that the bed temperature of the Catalyst increases and decreases periodically. Therefore in some cases, even if the average bed temperature is adjusted of the catalyst to be an objective temperature, the catalyst bed temperature can be increased beyond the target temperature during the execution period. Although catalyst bed temperature is excessively high only temporarily, the exhaust purification catalyst degrades With the heat

Normally, to prevent the temperature of the catalyst bed increase excessively during the period of execution, the duration of the execution period is fixed so that the maximum value of the catalyst bed temperature due to the enrichment of the air - fuel is less than the temperature at which the catalyst begins to deteriorate exhaust purification due to heat.

However, the temperature of a catalyst of totally new exhaust purification and the temperature of a old exhaust purification catalyst increase in ways different even if the air-fuel ratio is enriched in The same conditions. Compared to a catalyst of old exhaust purification, the maximum temperature value of the catalyst bed of an exhaust purification catalyst brand new when the air-fuel ratio is enriched, is higher. Therefore, if the conditions of the execution period are designed for old catalysts, the bed temperature of catalyst will increase excessively by enriching the air-fuel ratio when the purification catalyst of exhaust is still new, which can cause the catalyst to deteriorate prematurely. On the other hand, if the conditions of runtime are designed for a catalyst completely new and the catalyst gradually wears out, the period of execution may end even when the bed temperature of the catalyst has not increased sufficiently. This makes it difficult to Efficient emission of sulfur components and degrades accuracy of sulfur release control. As a result, the issuance deteriorates and the period of sulfur poisoning is extended, which that degrades fuel economy.

Summary of the invention

Consequently, it is an objective of the present invention provide a catalyst control apparatus for a internal combustion engine, device that easily suppresses a excessive increase in a catalyst bed temperature and the degradation of sulfur release control accuracy. The present invention also relates to an apparatus of Determination of the deterioration of the catalyst used in the apparatus of catalyst control to determine the degree of deterioration of an exhaust purification catalyst.

To achieve the above and other objectives and according to the purpose of the present invention, an apparatus is provided to control an exhaust purification catalyst. He catalyst is located in an exhaust system of an engine internal combustion. During sulfur release control to allow the catalyst to recover from poisoning by sulfur, the device repeats an enrichment period and a period of non-enrichment In the enrichment period, the apparatus intermittently supplies fuel to the exhaust gas in a upstream section of the catalyst, thus decreasing the air ratio - exhaust gas fuel that comes into contact with the catalyst up to a value equal to or less than the ratio stoichiometric air - fuel. In the period of no enrichment, the device does not supply fuel to the gas escape. The apparatus includes means for detecting the degree of deterioration and means of change. The means of detecting the degree of deterioration detect the degree of deterioration of the catalyst of exhaust purification. The means of change change the reason for the duration of the enrichment period with respect to the duration of the period of non-enrichment according to the degree of deterioration of the exhaust purification catalyst detected by the means of Determination of the degree of deterioration.

The present invention also provides a apparatus for detecting a degree of deterioration of a catalyst of exhaust purification located in an engine exhaust system Internal combustion The apparatus includes means of supply of fuel, bed temperature sensing means of the catalyst, and means of determining the degree of deterioration. The fuel supply means supply fuel intermittently to the exhaust gas in a section upstream of the exhaust purification catalyst. The means of detecting the catalyst bed temperature detect a physical amount which represents a bed temperature of the actual catalyst of the exhaust purification catalyst. The determination of the degree of impairment means that the smaller a fluctuation interval of the physical quantity, fluctuation produced by the supply from fuel to exhaust gas and is detected by the means of Catalyst bed temperature detection, the higher the degree of deterioration of the exhaust purification catalyst.

Other aspects and advantages of the invention are will become apparent from the following description, taken together with the accompanying drawings, which illustrate by way of example the principles of the invention.

Brief description of the drawings

The invention, together with the objects and advantages of it, can be better understood by referring to the following description of the currently preferred embodiments, together with the attached drawings in which:

Figure 1 is a block diagram that illustrates a general configuration of a vehicle diesel engine and a control system according to a first embodiment, in which the control system works like a control device catalyst and an apparatus for determining the deterioration of the catalyst;

Figure 2 is a flow chart showing a sulfur release process according to the first embodiment;

Figure 3 is a flow chart showing a process of determining the degree of deterioration according to the first realization;

Figure 4 is a flow chart showing a sulfur emission process according to the first embodiment;

Figure 5 is a diagram showing a map f used to calculate the duration of an enrichment period R_ {t} based on an amplitude value A_ {mpin};

Figure 6 is a graph showing changes in the air - fuel ratio of the exhaust gas and temperature of the catalyst bed according to the first embodiment, when a NOx storage reduction catalyst is fully new;

Figure 7 is a graph showing changes in the air - fuel ratio of the exhaust gas and temperature of the catalyst bed according to the first embodiment, when a NOx storage reduction catalyst has deteriorated until a certain point;

Figure 8 is a flow chart showing a process of determining the degree of deterioration according to a second realization;

Figure 9 is a flow chart showing a sulfur emission process according to a second embodiment;

Figure 10 is a diagram showing a map h used to calculate a detection interval t_ {dt} based on an input flow rate GA;

Figure 11 is a diagram showing a map of the fuel purification rate used to obtain a fuel purification rate;

Figure 12 is a graph showing changes in the air-fuel ratio of the exhaust gas and the temperature of the catalyst bed according to the second embodiment, when a NOx storage reduction catalyst is fully new;

Figure 13 is a graph that shows changes in the air-fuel ratio of the exhaust gas and the temperature of the catalyst bed according to the first embodiment, when a NOx storage reduction catalyst has deteriorated until a certain point;

Figure 14 is a flow chart showing a sulfur emission process according to a third embodiment;

Figure 15 is a graph showing changes in the air-fuel ratio of the exhaust gas and the temperature of the catalyst bed according to the third embodiment, when a NOx storage reduction catalyst has deteriorated until a certain point;

Figure 16 is a flow chart showing a sulfur emission process according to a fourth embodiment;

Figure 17 is a diagram showing a map p used to calculate the duration of a period of R_ {t} enrichment based on a temperature difference ΔT in; Y

Figure 18 is a graph that shows changes in the air-fuel ratio of the exhaust gas and the temperature of the catalyst bed according to the fourth embodiment, when a NOx storage reduction catalyst has deteriorated until a certain point.

Detailed description of the preferred embodiments

Figure 1 is a block diagram that illustrates a general configuration of a vehicle diesel engine and a control system according to a first embodiment. System control works as a catalyst control apparatus and a catalyst deterioration determination apparatus.

As shown in figure 1, the engine 2 Diesel has cylinders. In this embodiment, the number of cylinders It is four, and the cylinders are called No. 1, No. 2, No. 3 and No. 4. A combustion chamber 4 of each of the cylinders No. 1 to No. 4 includes an entrance hole 8. The combustion chambers 4 are connected to a compensation tank 12 through holes 8 input and an input manifold 10. Each entry hole 8 It is opened and closed by an inlet valve 6. Tank 12 of compensation is connected to outputs of an exchanger 14 of heat and supercharger through an inlet duct 13. In this embodiment, a compressor 16a of an exhaust turbocharger 16 It works like a supercharger. A compressor inlet 16a It is connected to an air cleaner 18. A conduit 20 of exhaust gas recirculation (referred to later in the This EGR document) is connected to compensation tank 12. An EGR gas supply port 20a of the EGR conduit 20 opens towards the compensation tank 12, so that the tank Compensation 12 and EGR conduit 20 communicate with each other. A regulating valve 22 is located in a section of the duct 13 inlet between compensation tank 12 and exchanger 14 heat An input flow rate sensor 24 and a Inlet temperature sensor 26 are located between the compressor 16a and air cleaner 18.

The combustion chamber 4 of each of the Cylinders No. 1 to No. 4 includes an exhaust port 30. The cameras 4 combustion are connected to an inlet of a turbine 16b of exhaust through the exhaust holes 30 and a manifold 32 of escape. Each exhaust port 30 is opened and closed by a exhaust valve 28. An outlet of the exhaust turbine 16b is connected to an exhaust duct 34. Exhaust gas is extracted towards the exhaust turbine 16b in a section of the manifold 32 of exhaust that is closed for the fourth cylinder No. 4.

Three catalytic converters 36, 38, 40 are located in the exhaust duct 34. The first catalytic converter 36 supports a NOx storage reduction catalyst 36a, which functions as an exhaust purification catalyst. When the exhaust gas is considered as an oxidizing (poor) atmosphere during normal operation of the diesel engine 2, the NOx storage reduction catalyst 36a occludes the nitrogen oxides (NOx) in the exhaust. When the exhaust gas is considered as a reducing atmosphere (air - compress ratio
stoichiometric fuel or lower), the NOx storage reduction catalyst 36a emits the occluded NOx in the form of nitrogen monoxide. The emitted nitrogen monoxide is reduced by hydrocarbon and carbon monoxide. In this way, the first catalytic converter 36 removes the NOx from the exhaust gas, thus purifying the exhaust gas.

The second catalytic converter 38, which is located downstream of the first catalytic converter 36, houses a filter 38a. The filter 38a has a monolithic wall. The wall has pores through which the exhaust gas passes. The areas of the wall that define the pores are coated with a layer that contains a NOx storage reduction catalyst, which It works as an exhaust purification catalyst. That is, the NOx occlusion reduction catalyst is supported by the filter 38a. Therefore, when the exhaust gas passes through the pores, the NOx in the exhaust gas is removed as described previously. In addition, when the exhaust gas passes through the pores, the particulate matter in the exhaust gas is trapped by the wall of the filter 38a. Trapped particulate matter begins to oxidized by the active oxygen generated when low NOx is occluded an oxidizing atmosphere at high temperature. The particulate matter is oxidizes completely through excessive ambient oxygen. This Thus, the second catalytic converter 38 eliminates the NOx and the particulate matter in the exhaust gas, thus purifying the gas from escape. In the first embodiment, the second converter 38 catalytic is integrated with the first converter 36 catalytic.

The third catalytic converter 40, which is located downstream of catalytic converters 36, 38 first and second, it supports an oxidation catalyst 40a. Catalyst Oxidation 40a oxidizes hydrocarbons and carbon monoxide in the exhaust gas to purify the exhaust gas.

A first exhaust temperature sensor 44 is located between the storage reduction catalyst 36a NOx and filter 38a. A second temperature sensor 46 of Exhaust and a sensor 48 of the air-fuel ratio are located between the filter 38a and the oxidation catalyst 40a. The second Exhaust temperature sensor 46 is closer to filter 38a, and the sensor 48 of the air-fuel ratio is located closer of oxidation catalyst 40a.

The air-fuel ratio sensor 48 detects the air-fuel ratio of the exhaust gas based on the exhaust gas components, and the signal outputs electric in linear proportion with the air-fuel ratio detected The first exhaust temperature sensor 44 detects an exhaust temperature T_ {exin} in the corresponding position. Also, the second exhaust temperature sensor 46 detects an exhaust temperature T_ {exout} in the position correspondent.

Pipes of a pressure sensor 50 differential are connected to a section upstream of the filter 38a and a section downstream of the filter 38a. The sensor 50 of the differential pressure detects the pressure difference ΔP between the upstream and downstream sections of filter 38a, detecting thus the degree of obstruction in the filter 38a, or the degree of accumulation of particulate matter.

In the exhaust manifold 32 a EGR gas inlet port 20b of the EGR conduit 20 which connect the exhaust manifold 32 with the EGR conduit 20. He EGR gas inlet hole 20b is located in a section of the exhaust manifold 32 that is closed to the first cylinder No. 1, section in front of a section of manifold 32 of exhaust in which the exhaust turbine 16b introduces gas from escape.

An iron-based EGR catalyst 52, a EGR refrigerator 54, and an EGR valve 56 are located in the EGR conduit 20 in this order from the inlet hole 20b from the EGR gas to the ERG gas supply port 20a. He iron-based EGR catalyst 52 works to reshape EGR gas and to prevent clogging of refrigerator 54 of EGR The EGR refrigerator 54 cools the EGR gas formed from new. By controlling the opening degree of the valve 56 EGR, the flow rate of the EGR gas supplied to the inlet system through gas supply hole 20a ERG

A fuel injection valve 58 is provides in each of the cylinders No. 1 to No. 4 to inject directly fuel in combustion chamber 4 correspondent. The fuel injection valves 58 are connected to a common rail 60 with supply lines 58a fuel. The common rail 60 is supplied with fuel by the variable displacement fuel pump 62, which is electrically controlled High pressure fuel supplied from the fuel pump 62 to the common rail 60 distributed to fuel injection valves 58 at through the fuel supply lines 58a. A detector 64 of the fuel pressure to detect the pressure of the fuel is attached to common rail 60.

Fuel pump 62 supplies low pressure fuel to a valve 68 for adding fuel through a fuel supply line 66. The fuel addition valve 68 is provided in the exhaust port 30 of the fourth cylinder No. 4 and injects fuel to the exhaust turbine 16b. In this way, the addition valve 68 of fuel adds fuel to the exhaust gas. The adition of fuel to the exhaust gas through the valve 68 for adding fuel is carried out in a control procedure of the catalyst, which is described below.

An electronic control unit 70 (ECU) is mainly composed of a digital computer that has a CPU, a ROM and a RAM, and drive circuits for operating other devices. The ECU 70 reads the signals from the sensor 24 of the inlet flow rate, the sensor 26 of the inlet temperature, the first sensor 44 of the exhaust temperature, the second sensor 46 of the exhaust temperature, the sensor 48 of reason
air-fuel, the differential pressure sensor 50, an EGR opening degree sensor on the EGR valve 56, the fuel pressure detector 64, and a 22a sensor of the regulator opening degree. In addition, the ECU 70 reads signals from a sensor 74 of the acceleration pedal that detects the degree of depression of an acceleration pedal 72, or a degree of depression of the ACCP acceleration pedal, a sensor 76 of the cooling temperature that detects the THW coolant temperature of the diesel engine 2, an engine speed sensor 80 that detects the number of revolutions NE of a crankshaft 78, and a cylinder differentiation sensor 82 that differentiates the cylinders by detecting the rotation phase of the crankshaft 78 or the rotation phase of the input cams.

Based on the signals received, ECU 70 obtains the operating state of the engine 2. Based on the state of the engine obtained, the ECU 70 controls the quantity and the measurement of fuel injection time by valves 58 fuel injection. In addition, ECU 70 controls the degree of opening of the EGR valve 56, the degree of opening of the regulator with motor 22b, and displacement of pump 62 of fuel. In addition, the ECU 70 executes the regeneration control of the filter and the control of sulfur release, which will describe later.

Depending on the operating status, the ECU 70 executes either a normal combustion mode and a mode of low temperature combustion. In low combustion mode temperature, a large amount of the exhaust gas is recirculated so that the combustion temperature increases slowly. This Simultaneously reduces NOx and smoke. In combustion mode a low temperature, a valve opening map is used EGR for low temperature combustion mode. In this embodiment, the low temperature combustion mode is executed in a region of medium to high rotation speed, low load. At this time, the feedback control is executed by adjusting an opening degree of the AR regulator based on an air ratio - AC fuel detected by the air ratio sensor 48 fuel. In normal combustion mode, control is performed normal EGR (including a case in which it is not recirculated no exhaust gas). In normal combustion mode, it is used An opening map of the EGR Valve for combustion mode normal.

ECU 70 also executes four procedures catalyst control, which include a regeneration mode of filter, a sulfur release control mode, a mode of NOx reduction and a normal mode.

In the filter regeneration mode, the particulate matter deposited in the filter 38a of the second catalytic converter 38 is heated, so that the particulate matter is burned and divided into carbon dioxide and water. In this mode, the addition of fuel from the fuel addition valve 68 is repeated in an air-to-air ratio.
fuel greater than the stoichiometric air-fuel ratio, so that the catalyst bed temperature rises to a high temperature which is, for example, in a range of from 600 ° C to 700 ° C. In the filter regeneration mode, a subsequent injection can be performed, in which fuel is injected from the fuel injection valve 58 into the combustion chambers 4 during the expansion stroke or the exhaust stroke.

In the release control mode of sulfur, the sulfur components are emitted from the catalysts NOx storage reduction of converters 36, 38 catalytic first and second, so that the ability to NOx occlusion of converters 36, 38, which has decreased due to sulfur poisoning, it is restored. In this mode, it runs a temperature rise process, in which it repeats adding fuel from the valve 68 adding fuel, so that the catalyst bed temperature it rises to a high temperature that is, for example, 650 ° C. In addition, a process of decreasing the air ratio is executed - fuel, in which the intermittent addition of fuel from the fuel addition valve 68, so that the air-fuel ratio changes to reason stoichiometric air - fuel or a slightly lower value than the stoichiometric air-fuel ratio. In the mode of sulfur release control, an injection can be performed rear using fuel injection valve 58.

In the NOx reduction mode, the occluded NOx by the NOx storage reduction catalysts of the first and second catalytic converters 36, 38 is reduced to nitrogen. As a byproduct, carbon dioxide and water are formed when NOx is reduced to nitrogen. In the reduction mode of NOx, a process is executed, in which the addition of fuel from the fuel addition valve 68 in a relatively long interval, so that the temperature of the catalyst bed increases to a temperature not too high high which is, for example, in a range of from 250 ° C to 500 ° C In addition, another process is executed, in which the air ratio - fuel changes to the stoichiometric air-fuel ratio or a lower value than the stoichiometric air ratio - fuel.

In normal mode, the addition of fuel from the fuel addition valve 68 or a subsequent injection by injection valves 58 fuel.

Next, the control of the Sulfur release executed by ECU 70.

Figure 2 is a flow chart of this control. The control is executed repeatedly by ECU 70 at a default interval. That is, the control of the release of Sulfur is a periodic routine of the interruption process.

When the control of the release of Sulfur, ECU 70 determines if the requirements for execute the sulfur release control in step S102. The Execution requirements for sulfur release control include that the amount of sulfur poisoning is not less at a predetermined amount, that the filter regeneration mode is not currently selected, and that the temperatures of the NOx storage reduction catalysts of the first and second catalytic converters 36, 38, which are calculated from the exhaust temperatures T_ {exin}, T_ {exout}, no they are significantly high or low, and are in a range of appropriate temperatures. When it is determined that the requirements for the control of sulfur release control, the ECU 70 ends this control.

When it is determined that the requirements for the control of sulfur release control, the ECU 70 continues to step S104 and determines if the requirements to start a sulfur emission process. He requirement for starting the sulfur emission process is that catalyst bed temperatures of the catalysts of NOx storage reduction of converters 36, 38 first and second catalysts have reached values close to the target temperature (e.g. 650 ° C), specifically, that a estimated catalyst bed temperature of the catalyst NOx storage reduction is not less than 600 ° C. The estimated catalyst bed temperatures of the catalysts NOx storage reduction of converters 36, 38 First and second catalytic can be calculated based on the operating status of motor 2 (for example, the number of NE revolutions of the engine 2) and the amount of fuel added. Alternatively, catalyst bed temperatures Estimates can be estimated from the exhaust temperature T_ {exin}.

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When it is determined that the requirements for starting the sulfur emission process, ECU 70 continue to step S106 and execute the increase control of the temperature. During the temperature rise control, it assumes that the NOx storage reduction catalyst 36a It is brand new, and a fuel of predetermined quantity is added intermittently to the exhaust of the valve 68 of adding fuel, so that the reduction catalyst 36a of NOx storage does not overheat and that the estimated catalyst bed temperature of catalyst 36a NOx storage reduction is not less than 600 ° C. In this moment, although the catalyst bed temperature of the NOx storage reduction catalyst of the second catalytic converter 38 is close to the bed temperature of catalyst of storage reduction catalyst 36a NOx of the first catalytic converter 36, the temperature of the catalyst bed of storage reduction catalyst NOx of the second catalytic converter 38 fluctuates less than the catalyst bed temperature of catalyst 36a of NOx storage reduction. Therefore, it is more likely that the NOx storage reduction catalyst 36a of the first Catalytic converter 36 is overheated, that the NOx storage reduction catalyst of the second Catalytic converter 38 during the sulfur emission process. Therefore, the following description will focus on the catalyst 36a NOx storage reduction.

Even if it is determined that the requirements for starting the sulfur emission process, the control of temperature rise is executed in step S106, and the requirement for commencement of the sulfur emission process will be satisfied Finally. Then, ECU 70 continues to step S108 in place of step S106, after step S104. So, as I know shown in figure 3, the ECU 70 executes the process of Determination of the degree of deterioration. Subsequently, on the stage S110, ECU 70 executes the sulfur emission process.

When the process of determining the degree of deterioration, the ECU 70 first determines whether the requirements to execute the process of determining the degree of deterioration in step S122, as shown in Figure 3. The execution requirements of the process of determining the degree of impairment include a state in which the temperature value of exhaust T_ {exin} detected by the first sensor 44 of the exhaust temperature changes periodically in a stable manner, that is, a state in which the operating state of the engine 2 (for example, and the load and engine speed E 2) They are stable.

When it is determined that the execution requirements of the process of determining the degree of deterioration, the ECU 70 completes the process of determining the grade of deterioration, and continues to the sulfur emission process shown in Figure 4

On the other hand, when it is determined that meet the execution requirements of the determination process of the degree of deterioration, ECU 70 continues to step S123 and determines if an amplitude value A_ {mpin} has been obtained in the current sulfur release routine. When it is determined that it has obtained the amplitude value A_ {mpin}, the ECU 70 ends the process of determining the degree of deterioration, and continues until sulfur emission process shown in figure 4. When determines that the amplitude value A_ {mpin} has not been obtained, the ECU 70 continues to step S124. In step S124, ECU 70 execute a process to obtain the maximum value T_ {inmax} of the exhaust temperature T_ {exin} detected by the first sensor 44 of the exhaust temperature. In addition, in step S126, ECU 70 execute a process to obtain the minimum value T_ {inmin} of the exhaust temperature T_ {exin}.

When the sulfur emission process of Figure 4 is executed, which will be discussed below, a period of enrichment R_ {t}, during which the air-fuel exhaust ratio is enriched, and a period of non-enrichment L_ { t}, during which the air-fuel ratio is not enriched, they are repeated as shown in the graph in the upper part of Figure 6. Accordingly, the actual bed temperature of the catalyst of the storage reduction catalyst 36a NOx increases repeatedly during the enrichment period R t and decreases during the non-enrichment period L t. The exhaust temperature T_exin detected by the first exhaust temperature sensor 44 represents the actual bed temperature of the NOx storage reduction catalyst 36a. Therefore, the maximum value T_ {inmax} of the exhaust temperature T_ {exin} represents the maximum value of the catalyst bed temperature during the enrichment period R_ {t}, and the minimum value T_ {inmin} of the Exhaust temperature T_ {exin} represents the minimum value of the catalyst bed temperature during the non-enrichment period L_ {t}. In step S124, the ECU 70 obtains the maximum value T_ {inmax}, if any, from the values of the exhaust temperature T_ {exin} detected by the first sensor 44 of the exhaust temperature during the process of sulfur emission. In step S126, the ECU 70 obtains the minimum value T_ {inmin}, if any, from the values of the exhaust temperature T_ {exin} detected by the first sensor of the exhaust temperature during the emission process from
sulfur.

In the next step S128, the ECU 70 determines sise has obtained both the maximum value T_ {inmax} and the value minimum T_ {inmin}. When it is determined that one or both of the maximum value T_ {inmax} and the minimum value T_ {inmin}, the ECU 70 finishes the process of determining the degree of deterioration, and continues until the sulfur emission process shown in the figure 4.

In an example shown by the graph at the bottom of Figure 6, the maximum value T_ {inmax} appears at time t0 when the air-fuel ratio of the exhaust gas is enriched during the enrichment period R_ {t}. Subsequently, the minimum value T_ {inmin} appears at time t1 when the enrichment of the air - com- ratio stops.
fuel from the exhaust gas during the non-enrichment period L_ {t}. In this case, the ECU 70 obtains the maximum value T_ {inmax} and the minimum value T_ {inmin} in steps S124 and S126, respectively. In step S128, the ECU 70 determines that both the maximum value T_ {inmax} and the minimum value T_ {inmin} have been obtained. Thereafter, ECU 70 continues to step S130 and calculates the amplitude value A_ {mpin} according to a formula 1:

A_ {mpin} \ leftarrow T_ {inmax} - T_ {inmin}

Then, ECU 70 ends the process of Determination of the degree of deterioration, and continues until the process of sulfur emission shown in figure 4. The calculated value of amplitude A_ {mpin} is stored in non-volatile memory in the ECU 70, and is maintained when ECU 70 is disconnected.

When the sulfur emission process begins, ECU 70 first determines whether the amplitude value has been obtained A_ {mpin} in the current control of sulfur release in the step S152, as shown in Figure 4. When determined that the amplitude value A_ {mpin} has not been obtained, ECU 70 continue to step S154, and set the duration of the period of enrichment R_ {t} at an initial value R_ {tint}. The value initial R_ {tint} is a value obtained through experiments. He initial value R_ {tint} is determined so that a catalyst 36a completely new NOx storage reduction is not deteriorate due to heat, even when enrichment continues with fuel added by the fuel addition valve 68 for the duration of the initial value R_ {tint}. A catalyst 36a completely new NOx storage reduction will will deteriorate due to heat if the bed temperature of the catalyst exceeds a predetermined temperature (for example, the upper temperature limit shown in figure 6).

In the next step S158, the ECU 70 calculates the duration of the non-enrichment period L_ {t}, which should determined to set the catalyst bed temperature of the NOx storage reduction catalyst 36a at a target bed temperature T_ {cat}. The calculation is executed using a map g, based on the initial value R_ {tint}, a heat value H ex obtained by adding fuel of a predetermined amount Q_ {add} to the exhaust gas from the Fuel addition valve 68, exhaust temperature T_ {ex} that comes into contact with the reduction catalyst 36a NOx storage, an escape quantity V_ {ex}, a C_ {ex} thermal capacity of the exhaust system, and the temperature of target bed T_ {cat}.

The default value Q_ {add} is a amount of fuel added to the exhaust valve 68 fuel addition when the duration of the period of enrichment R_ {t} is set to the initial value R_ {tint}. He heat value H_ {ex} is an amount of heat generated by the fuel oxidation of the default value Q_ {add} when a NOx storage reduction catalyst 36a is used brand new. The exhaust temperature T_ {ex} is estimated based on the operating state of the engine (the load and the engine speed NE 2). The amount of escape V_ {ex} represents the amount of escape that escapes during a period that includes the enrichment period R_ {t} and the non-enrichment period L_ {t}, and is calculated based on a GA input flow rate detected by sensor 24 of the input flow rate and the total time of the period of enrichment R_ {t} and the non-enrichment period L_ {t}. The thermal capacity C_ {ex} is a value that has been obtained at through previous experiments, and a fixed value determined by The type of engine.

In the next step S160, based on a first counter that shows the elapsed time since started enrichment, ECU 70 determines whether the time elapsed since enrichment has begun is equal to or greater than an enrichment period R_ {t}. When determined that the enrichment period R_ {t} has not elapsed, the ECU 70 continues to step S162, and causes the addition valve 68 of fuel add fuel to the exhaust. That is, on the stage S162, ECU 70 begins or continues to enrich the exhaust gas. In the next step S164, ECU 70 increases the value of the first accountant. Then, ECU 70 ends the issuance process of sulfur.

Thereafter, the addition of fuel by the fuel addition valve 68 is repeated every time the sulfur emission process is executed, provided that the time once the enrichment had begun, it was less than the enrichment period R_ {t}. Consequently, the value of First counter continues to increase. When time once that the enrichment had begun, reaches the period of R_ {t} enrichment, ECU 70 does not continue until step S162 after step S160, instead continue to step S166. In the step S166, the ECU 70 does not make the valve 68 adding fuel add fuel to the exhaust gas. That is, the enrichment stops at step S166. In the next stage S168, based on a second counter that shows the time elapsed since enrichment has stopped, ECU 70 determines whether the elapsed time since the enrichment is equal to or greater than a period of no enrichment L_ {t}. When it is determined that it has not elapsed the non-enrichment period L_ {t}, the ECU 70 continues until the step S170. In step S170, ECU 70 increases the second counter, and the sulfur emission process ends.

From then on, the value of the second counter continues to increase as long as the time once enrichment stopped be less than the period of no enrichment L_ {t}. When the time once it stopped the enrichment reaches the period of non-enrichment L_ {t}, the ECU 70 does not continue until step S170 after step S168, however Continue to step S172. In step S172, the ECU 70 deletes the value of the first value of the counter. In the next step S174, the ECU 70 deletes the value of the second counter. So, ECU 70 The sulfur emission process ends.

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If the amplitude value A_ {mpin} is not obtained in a subsequent execution of the sulfur emission process during the sulfur emission process, the ECU 70 sets the duration of the enrichment period R_ {t} to the initial value R_ {tint} in the step S154. In addition, in step S158, ECU 70 calculates the duration of the non-enrichment period L_ {t} using the map g, and continue to step 160. In this case, since the enrichment has not even begun, the time elapsed a once the enrichment period R_ {t} had begun has not reached the enrichment period R_ {t}. Therefore, the ECU 70 continues to step S162 and causes the addition valve 68 of fuel add fuel to the exhaust gas. In this way, the enrichment of the exhaust gas begins again.

If the maximum value T_ {inmax} is obtained and the minimum value T_ {inmin} and the amplitude value A_ {mpin} is calculates in the process of determining the degree of deterioration shown in figure 3, ECU 70 does not continue until step S154 after step S152, until stage 156 in the issuance process Sulfur In step S156, ECU 70 calculates the duration of the enrichment period R_ {t} to be set. The calculation is run using a map f shown in figure 5, based on the size of an amplitude value A_ {mpin}, which represents the degree of deterioration of catalyst 36a for reducing NOx storage The higher the value value of amplitude A_ {mpin}, the degree of deterioration of the NOx storage reduction catalyst 36a and greater se makes the oxidation efficiency for the fuel in the NOx storage reduction catalyst 36a (same as fuel purification rate). In this case, the period of enrichment R_ {t} is set to a short value to correspond with the temperature of the catalyst bed, which increases quickly once enrichment has begun. On the other hand, when the value of the amplitude value A_ {mpin} is smaller, the greater causes the degree of deterioration of catalyst 36a for reducing NOx storage and lower oxidation efficiency is made of the NOx storage reduction catalyst 36a. In this case, the enrichment period R_ {t} is set to a long value to correspond to the catalyst bed temperature, which increases slowly once enrichment has begun.

As described above, the duration of the period of non-enrichment L_ {t} to be fixed is calculate in the next step S158 based on the map g using the initial value R_ {tint}, the heat value H_ {ex}, the exhaust temperature T_ {ex}, the thermal capacity C_ {ex}, and the target bed temperature T_ {cat}. In the next step S160, when it is determined that the period of time from the beginning of the enrichment has not reached the enrichment period R_ {t}, ECU 70 performs the addition of fuel in the stage S162. Then in step S164, ECU 70 increases the value of the First counter

The next time the process is executed Determination of the degree of deterioration, since there will already be obtained the amplitude value A_ {mpin}, the ECU 70 will end by both the process of determining the degree of deterioration without continue to steps S124 to S130 after step S123. Therefore in the following executions of the sulfur emission process, the ECU 70 does not continue until step S154 after step S152, but Continue to step S156. In step S156, the ECU 70 sets the duration of the enrichment period R_ {t} based on the amplitude value A_ {mpin}.

When the reduction catalyst 36a of NOx storage is recovered from the sulfur-poisoned state, the ECU 70 determines that the requirements to execute are not met the sulfur release control in step S102, while run the sulfur release control shown in the figure 2. The ECU 70 then terminates the control of the release of sulfur. Thereafter, if the requirements of execution, for example, when the amount of poisoning by sulfur reaches the predetermined amount, the process of Determination of the degree of deterioration and the issuance process of sulfur. That is, the duration of the enrichment period R_ {t} is set to the initial value R_ {tint} in step S154, and the value of amplitude A_ {mpin} is calculated in steps S124 to S130. So, based on the calculated value of amplitude A_ {mpin}, the duration of the enrichment period R_t is set in step S156.

Figure 6 shows changes in the air ratio - exhaust gas fuel and bed temperature of catalyst in a case where the reduction catalysts NOx storage of catalytic converters 36, 38 First and second are completely new. In this case, the duration of the enrichment period R_ {t} calculated based in the amplitude value A_ {mpin} is the same as the initial value R_ {tint}.

On the other hand, Figure 7 is a graph that shows changes in the air-fuel ratio of the exhaust gas and the temperature of the catalyst bed in a case where the NOx storage reduction catalyst 36a has been deteriorated to some extent. In this case, the duration of the enrichment period R_ {t} calculated based on the value of amplitude A_ {mpin} is greater than the initial value R_ {tint}. By therefore, as in the case where catalyst 36a of NOx storage reduction is brand new, which is shown in figure 6, the catalyst bed temperature of the NOx storage reduction catalyst 36a increases to a value equal to or greater than the target temperature, so that the maximum value T_ {inmax} does not exceed the upper limit of temperature.

The first exhaust temperature sensor 44 corresponds to the bed temperature detection means of the catalyst that detect a physical quantity that represents the actual catalyst bed temperature of the catalyst exhaust purification. The ECU 70 functions as the means of detection of the degree of deterioration that detects the degree of deterioration of the exhaust purification catalyst, and the medium of change that change the reason for the duration of the enrichment period with regarding the duration of the non-enrichment period according to the degree of deterioration of the exhaust purification catalyst detected by the means of detecting the degree of deterioration. The ECU 70 also functions as the means of fuel supply that intermittently supplies fuel to the exhaust gas in a upstream section of the exhaust purification catalyst, and as the means of determining the degree of deterioration. How much more narrow is the range of fluctuation of the physical quantity detected by the catalyst bed temperature as the fuel supply means supply fuel to the Exhaust gas, the greater the degree of deterioration of the catalyst exhaust purification that is determined by the means of Determination of the degree of deterioration.

In this embodiment, the determination process of the degree of deterioration shown in Figure 3 and in steps S152, S154 of the sulfur emission process shown in Figure 4 corresponds to a process executed by the detection means of the degree of deterioration Step S156 of the sulfur emission process It corresponds to a process executed by the means of change. He sulfur emission process corresponds to a process executed by The means of fuel supply. The determination process of the degree of deterioration and step S156 of the issuance process of Sulfur correspond to a process executed by the means of Determination of the degree of deterioration.

The first embodiment has the following advantages.

(1) During the execution of the control of the sulfur release, the enrichment period R_ {t}, in the that the air-fuel ratio of the exhaust gas is enriched, and the non-enrichment period L_ {t}, in which the air-fuel ratio, repeated alternately. Everytime that the enrichment period R_ {t} or the period of no enrichment L t, the catalyst bed temperature of the NOx storage reduction catalyst 36a increases and decreases repeatedly. The amplitude value A_ {mpin} reflects the fluctuation (amplitude) of the catalyst bed temperature. The more damaged the reduction catalyst 36a is NOx storage, smaller is the magnitude of the amplitude value A_ {mpin}, or the magnitude of the temperature fluctuation of the catalyst bed. Therefore, the amplitude value A_ {mpin} indicates the degree of deterioration of catalyst 36a for reducing NOx storage

In the first embodiment, when the value of amplitude A_ {mpin} is large as shown on map f of the Figure 5, that is, in a case in which the deterioration of the NOx storage reduction catalyst 36a has not been significantly developed, the duration of the period of R_ {t} enrichment is set relatively short. When the value of amplitude A_ {mpin} is small as shown on the map f of Figure 5, that is, in a case in which the deterioration of the NOx storage reduction catalyst 36a has been developed considerably, the duration of the period of enrichment R_t is fixed relatively long. Therefore with Changes in the degree of deterioration of catalyst 36a for reducing NOx storage, prevents an increase in the temperature of the  catalyst bed of catalyst 36a reducing NOx storage is excessive or too small. Thus prevents deterioration of catalyst 36a for reducing NOx storage due to excessive temperature rise of the catalyst bed and a decrease in the effectiveness of sulfur emission due to insufficient temperature increase from the catalyst bed. This prevents the decrease of the sulfur emission efficiency. As a result, the emission deterioration due to the decrease in the accuracy of the control of sulfur release and a decrease in the economy of the fuel, due to an extended period of control of the sulfur release

(2) The amplitude value A_ {mpin} is calculated in a state in which the duration of the enrichment period R_ {t} is set to the initial value R_ {tint}. Based on value of amplitude A_ {mpin} thus calculated, the degree of deterioration of the NOx storage reduction catalyst 36a. In this way, since the duration of the period of enrichment R_ {t} has a constant value (the initial value R_ {tint}) when calculating the amplitude value A_ {mpin}, the calculated value of amplitude A_ {mpin} corresponds exactly to degree of deterioration of catalyst 36a for reducing NOx storage When the duration of the period of enrichment R_ {t} is set to the initial value R_ {tint}, the amount of fuel added by valve 68 adding fuel during the enrichment period R_ {t} is the minimum value. Therefore, when the degree of deterioration is determined of the NOx storage reduction catalyst 36a by calculating the amplitude value A_ {mpin}, the catalyst is not likely 36a NOx storage reduction is heated excessively.

A second embodiment of the present invention with reference to the drawings.

In the second embodiment, the degree of deterioration of the exhaust purification catalyst is not determined based in the amplitude value A_ {mpin}, but is determined based on at the rate of increase of the exhaust temperature T_ {exin}. Also, in the second embodiment, the duration of the period does not change of enrichment R_ {t}, but the duration of the period of no enrichment L t, according to the degree of deterioration of the catalyst of exhaust purification.

In the second embodiment, a process is executed for determining the degree of deterioration in Figure 8, instead of process of determining the degree of deterioration of figure 4, and executes a sulfur emission process of figure 9 instead of sulfur emission process of figure 4. Other processes and the Hardware settings are the same as those of the first realization.

When the process of determining the degree of deterioration of Figure 8, ECU 70 first determines whether meet the requirements to execute the determination process of the degree of deterioration in step S202. The requirements for execute the process of determining the degree of deterioration are the same as those of the process of determining the degree of deterioration of figure 3.

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When it is determined that the execution requirements of the process of determining the degree of deterioration, the ECU 70 completes the process of determining the grade of deterioration, and continues until the sulfur emission process shown in Figure 9. On the other hand, when it is determined that meet the execution requirements of the determination process of the degree of deterioration, ECU 70 continues to step S204 and calculates a detection interval t_dt of the temperature of escape T_ {exin}. The calculation is done using a map h shown in figure 10 based on the flow rate of GA input. ECU 70 detects the exhaust temperature T_ {exin} at a time point at which the interval of detection t_ {dt} from when the valve 68 adding fuel added fuel to the exhaust gas in the process of sulfur emission shown in figure 9, which will be treated more ahead. When the fuel addition valve 68 adds fuel to the exhaust gas, increases the bed temperature of the catalyst of storage reduction catalyst 36a NOx, and the exhaust temperature T_ {exin} increases accordingly. The rate of increase of the exhaust temperature T_ {exin} changes according to the degree of deterioration of catalyst 36a for reducing NOx storage and GA input flow rate. Specifically, the greater the degree of deterioration of the NOx storage reduction catalyst 36a, the smaller the rate of increase of the exhaust temperature T_ {exin}. The older is the input flow rate GA, the higher the rate of increase of the exhaust temperature T_ {exin}. The detection interval t_ {dt} is calculated and fixed using the map h shown in the Figure 10, so that the rate of temperature rise of escape T_ {exin} always be constant, regardless of value of the input flow rate GA, provided the degree of deterioration of NOx storage reduction catalyst 36a be the same.

In the next step S206, the ECU 70 determines if the time elapsed since when the valve 68 of adding fuel started adding fuel to the exhaust gas being counting currently. The count begins at step S212, which is Will try later. When it is determined that the count is being currently carrying out, ECU 70 continues to step S208 and determine if now is the time to start adding fuel by the fuel addition valve 68. The ECU 70 determines that now is the time to start adding fuel if ECU 70 determined that the period from when there was started enrichment did not reach the period of R_ {t} enrichment in step S240 of the issuance process of sulfur shown in figure 9 in the previous execution of the control of sulfur release. Otherwise, ECU 70 determines Now is not the time to start adding fuel.

When it is determined that now is not the time If fuel addition begins, ECU 70 ends the process of determination of the degree of deterioration, and continues until the process of sulfur emission shown in Figure 9. On the other hand, when it is determined that now is the time to start adding fuel, the ECU 70 sets the exhaust temperature T_ {exin} detected at the time of the initial exhaust temperature T_ {a}. Then, in the next step S212, ECU 70 begins counting of the time since when the addition of fuel from the fuel addition valve 68. Starting thereafter, ECU 70 completes the process of determining the degree of deterioration, and continues until the sulfur emission process shown in figure 9.

In the case where the time count elapsed since when the fuel addition started from the fuel addition valve 68 will begin during execution previous of the process of determining the degree of deterioration, the ECU 70, in the subsequent execution of the degree determination process of deterioration, does not continue until step S208 after step S206, It continues until step S214. Then, in step S214, ECU 70 determines whether the time elapsed since when it began fuel addition has reached the detection interval t_ {dt}. When it is determined that the time elapsed since started adding fuel has not reached the interval of detection t_ {dt}, ECU 70 completes the determination process of the degree of deterioration, and continues until the process of issuing sulfur shown in figure 9.

On the other hand, when it is determined that the time elapsed since the addition of fuel began reached the detection interval t_ {dt}, the ECU 70 in the stage S216 calculates a temperature difference ΔT_ {in} between the exhaust temperature T_ {exin} detected at the moment and the initial exhaust temperature T_a according to a formula 2:

ΔT_ {in} \ leftarrow T_ {exin} - T_ {a}

The temperature difference ΔT_ {in} corresponds to the rate of increase of the exhaust temperature T_ {exin} in an exhaust flow velocity state of reference when the detection interval is used as a unit t_ {dt}. In the next step S218, ECU 70 stops counting of the time since when the addition of fuel. Thereafter, ECU 70 ends the process of Determination of the degree of deterioration, and continues until the process of sulfur emission shown in figure 9.

Before the difference in the temperature difference ΔT in in step S216, the Tin temperature difference is set to an initial value ΔT_ {inint} corresponding to when a catalyst is used 36a completely new NOx storage reduction.

The process of issuance of sulfur with reference to figure 9. When the process of sulfur emission, the ECU 70 first executes a calculation process k (\ DeltaT_ {in}, \ DeltaT_ {inint}, \ DeltaT_ {ine}, T_ {ex}) based on the temperature difference ΔT_ {in}, the value initial \ DeltaT_ {inint}, a temperature difference ΔT_ {ine}, and the exhaust temperature T_ {ex}, calculating thus a fuel purification rate K_ {ex}. The difference of temperature ΔT_ {ine} will be discussed later. At calculation process k (\ DeltaT_ {in}, \ DeltaT_ {inint}, ΔT_ {ine}, T_ {ex}), a purification rate of K_ {exs} fuel for a case where a undamaged catalyst and a fuel purification rate K_ {exe} for a case where a catalyst is used deteriorated, using a fuel purification map shown in figure 11, which is related to the rate of K_ {exs} fuel purification and purification rate of K_ {exe} fuel. Then, the purification rates of calculated fuel K_ {exs}, K_ {exe} are prorated by the temperature difference ΔT_ {in}, ΔT_ {ine} and the initial value \ DeltaT_ {inint}. As a result, you get the fuel purification rate K_ {ex}. More specifically, the fuel purification rate K_ {ex} is calculated according to a formula 3:

K_ {ex} \ leftarrow K_ {exs} - \ {(K_ {exs} - K_ {exe}) x (\ Delta T_ {inint} - ΔT_ {in}) / (ΔT_ {inint} - \ Delta T_ {ine}) \}

The fuel purification rate K_ {exs} is obtained through experiments in which it is used as parameter the temperature T_ {ex} of the exhaust gas entering contact with the storage reduction catalyst 36a NOx In addition, the fuel purification rate K_ {exs} is a fuel purification rate by a catalyst 36a of completely new NOx storage reduction, that is, a NOx storage reduction catalyst 36a no deteriorated. The K_ {exe} fuel purification rate it is also obtained through experiments in which it is used as a parameter the exhaust temperature T_ {ex}. The rate of K_ {exe} fuel purification is a purification rate of fuel by a storage reduction catalyst 36a of Old NOx, that is, a catalyst 36a for reducing NOx storage somewhat deteriorated. Temperature difference ΔT ine is a value obtained through experiments and corresponds to the temperature difference ΔT_ {in} that calculates when a reduction catalyst 36a is used NOx storage somewhat deteriorated.

In the next step S234, the ECU 70 sets the duration of enrichment period R_ {t} at initial value R_ {tinit}. This process is the same as the process of step S154 in the sulfur emission process shown in figure 4. In the Next step S236, ECU 70 calculates the heat value H_ {ex} of a single fuel addition according to a formula 4:

H_ {ex} \ leftarrow (K_ {ex} / K_ {exs}) x H_ {exint}

A constant H_ {exint} in formula 4 is a heat value of a single fuel addition when used a NOx storage reduction catalyst 36a brand new.

Thereafter, ECU 70 calculates the non-enrichment period L_ {t} using the g map in the step S238. Map g is the same map g used in the stage S158 of the sulfur emission process shown in Figure 4. The stages 240, S242, S244, S246, S248, S250, S252, and S254 in the figure 9, which are executed by ECU 70 after step S238 are each equal to steps S160, S162, S164, S166, S168, S170, S172, and S174 of the sulfur emission process shown in Figure 4.

As described above, the degree of deterioration of NOx storage reduction catalyst 36a It is reflected in the temperature difference ΔT_ {in}. How much smaller is the temperature difference ΔT_ {in}, more deteriorated is determined to be the deterioration of catalyst 36a of NOx storage reduction. Temperature difference ΔT_ {in}, which reflects the degree of deterioration of the catalyst 36a NOx storage reduction, is reflected in the duration of the period of non-enrichment L_ {t} through the rate of fuel purification K_ {ex} and heat value H_ {ex}. Therefore, the more deteriorated the catalyst 36a of NOx storage reduction, shorter the duration is set of the non-enrichment period L_ {t}, so that the catalyst bed temperature reaches the temperature of target bed

Figure 12 is a graph showing changes in the air - fuel ratio of the exhaust gas in the second embodiment when the storage reduction catalyst 36a NOx is brand new. Figure 13 is a graph that shows changes in the air-fuel ratio of the exhaust gas and the catalyst bed temperature in the second embodiment when the NOx storage reduction catalyst 36a is It has deteriorated to some extent. As shown in the figure 12, when the NOx storage reduction catalyst 36a It is brand new, the temperature difference ΔT in between the catalyst bed temperature in the time points t20, t22, at which the addition valve 68 of fuel begins to add fuel to the exhaust gas, and the catalyst bed temperature at time points t21, t23, in which the detection period t_ {dt} has elapsed from time points t20, t22, it is relatively large. So, the duration of the non-enrichment period L_ {t} is fixed relatively long, so that the bed temperature of the Catalyst reaches the target bed temperature. For other part, as shown in figure 13, when the catalyst 36a NOx storage reduction has deteriorated to certain point, the temperature difference ΔT_ {in} between the catalyst bed temperature at time points t30, t32, in which the fuel addition valve 68 begins to add fuel to the exhaust gas, and the bed temperature of the catalyst at time points t31, t33, in which the detection period t_ {dt} has elapsed from the points of Time t30, t32, is relatively small. Thus, the duration of non-enrichment period L_ {t} is set relatively short, so that the catalyst bed temperature reaches the target bed temperature.

In this embodiment, the determination process of the degree of deterioration shown in Figure 8 corresponds to a process executed by the means of detecting the degree of deterioration. Stages S232, S236, S238 of the issuance process of Sulfur shown in Figure 9 correspond to an executed process by the means of change. The sulfur emission process corresponds to a process executed by the means of supply of fuel. The process of determining the degree of deterioration and the step S232 of the sulfur emission process corresponds to a process executed by the means of determining the degree of deterioration.

The second embodiment has the following advantage.

(1) As in the first embodiment, during the execution of the sulfur release control, the enrichment period R_ {t} and the period of no enrichment L_ {t} are repeated alternately. Every time I know run the enrichment period R_ {t} or the period of no enrichment L t, the catalyst bed temperature of the NOx storage reduction catalyst 36a increases and decreases repeatedly. The more damaged the catalyst is 36a of NOx storage reduction, the smaller the temperature difference ΔT_ {in}, which corresponds to the rate of increase in catalyst bed temperature due at the beginning of the enrichment period R_ {t}. That is, the degree of deterioration of catalyst 36a for reducing NOx storage is reflected in the temperature difference ΔT_ {in}. Therefore, the degree of catalyst deterioration 36a NOx storage reduction is easily determined based on the temperature difference ΔT_ {in}.

When ECU 70 determines that the catalyst 36a NOx storage reduction has barely deteriorated since the temperature difference ΔT_ {in} is large enough, a high value of the rate of K_ {ex} fuel purification based on the map of fuel purification of figure 11 to maintain the catalyst bed temperature at bed temperature objective. As a result, the duration of the period of no enrichment L_ {t} is set relatively long. In consequently, an excessive increase in the temperature of the catalyst bed due to the enrichment of the air ratio - exhaust gas fuel. From then on, when the ECU 70 determines that the storage reduction catalyst 36a NOx has deteriorated to some extent, since the temperature difference ΔT_ {in} is small, a low value of the fuel purification rate K_ {ex} based on the fuel purification map of figure 11 to keep the catalyst bed temperature at target bed temperature. As a result, the duration of Non-enrichment period L_ {t} is set relatively short. Consequently, a decrease in the effectiveness of fuel emission due to insufficient increase in catalyst bed temperature. In this way, even when the degree of deterioration of catalyst 36a for reducing NOx storage, catalyst bed temperature not increases excessively, and the sulfur release control is Run accurately.

A third embodiment of the present invention with reference to the drawings.

In the third embodiment, the duration is changed of the non-enrichment period L_ {t} based on the value of amplitude A_ {mpin}, which is calculated through the process of Determination of the degree of deterioration shown in Figure 3. In the third embodiment, a sulfur emission process is executed shown in figure 14 instead of the sulfur emission process shown in figure 4. Other processes and configuration of Hardware are the same as those of the first embodiment.

When the sulfur emission process begins shown in figure 14, the ECU 70 first sets the duration of the enrichment period R_ {t} to the initial value R_ {tint} in the step S302. The process of step S302 is the same as the process of step S154 in the sulfur emission process shown in the figure 4.

Thereafter, ECU 70 determines whether the amplitude value A_ {mpin} has already been obtained in execution current of the sulfur release process in step S304. When it is determined that the amplitude value A_ {mpin} has not been obtained, ECU 70 continues to step S306, and sets the duration of the non-enrichment period L_ {t} to the initial value L_ {tint}. The initial value L_ {tint} is set so that the temperature of the average catalyst bed of catalyst 36a reducing NOx storage when the fuel addition valve 68 is adding fuel to the exhaust in a case where the value initial R_ {tint} is set as the duration of the period of enrichment R t, and catalyst 36a for reducing NOx storage is brand new, it becomes the target bed temperature.

Stages 314, S316, S318, S320, S322, S324, S326, and S328 in Figure 14, which are executed by ECU 70 after the step S306 are each equal to stages S160, S162, S164, S166, S168, S170, S172, and S174 of the sulfur emission process shown in Figure 4. In this way, the initial values R_ {tint} and L_ {tint} are set as the duration of the enrichment period R_ {t} and the duration of the non-enrichment period L_ {t}, respectively, and through the degree determination process of deterioration shown in figure 3, the maximum value is obtained T_ {inmax} and the minimum value T_ {inmin} and the value of amplitude A_ {mpin}.

When the amplitude value is calculated A_ {mpin} in this way, ECU 70, in the following process of Sulfur emission, continue to step S308, instead of the step S306, after step S304. In step S308, the ECU 70 performs a calculation process m (A_ {mpin}, A_ {mpinint}, A_ {mpe}, T_ {ex}) based on the amplitude value A_ {mpin}, a value initial A_ {mpinint}, and an amplitude value A_ {mpe} for calculate the fuel purification rate K_ {ex}.

In the calculation process m (A_ {mpin}, A_ {mpinint}, A_ {mpe}, T_ {ex}), you get a rate of K_ {exs} fuel purification for a case where uses an undamaged catalyst and a purification rate of K_ {exe} fuel for a case where a deteriorated catalyst using a purification map of fuel shown in figure 11 based on the temperature of escape T_ {ex}. So, fuel purification rates calculated K_ {exs}, K_ {exe} are apportioned by the values of amplitude A_ {mpin}, A_ {mpe} and the initial value A_ {mpinint}. As a result, the fuel purification rate is obtained K_ {ex}. More specifically, the purification rate of Fuel K_ {ex} is calculated according to a formula 5:

K_ {ex} \ leftarrow K_ {exs} - \ {(K_ {exs} - K_ {exe}) x (A_ {mpinint} - A_ {mpin}) / (A_ {mpinint} - A_ {mpe}) \}

The initial value A_ {mpinint} corresponds to amplitude value A_ {mpin} obtained when using a NOx storage reduction catalyst 36a no deteriorated. The amplitude value A_ {mpe} corresponds to the value of amplitude A_ {mpin} obtained when a catalyst 36a of NOx storage reduction deteriorated.

In the next step S310, the ECU 70 calculates the heat value H ex of a single fuel addition according to the formula 4. In addition, in the next step S312, ECU 70 calculates the non-enrichment period L_ {t} using the map g. He process of step S312 is the same as the process of step S158 in the sulfur emission process shown in figure 4. From then, ECU 70 ends the sulfur emission process after execute the steps described above from S314 to the S328

As described above, the degree of deterioration of NOx storage reduction catalyst 36a It is reflected in the amplitude value A_ {mpin}. The smaller the amplitude value A_ {mpin}, the more deteriorated is determined to be the NOx storage reduction catalyst 36a. The value of amplitude A_ {mpin}, which reflects the degree of deterioration of the NOx storage reduction catalyst 36a, is reflected in the duration of the non-enrichment period L_ {t} through the K_ {fuel} purification rate and heat value H_ {ex}. Therefore, the more deteriorated the catalyst 36a is NOx storage reduction, shorter the duration is set of the non-enrichment period L_ {t}, so that the catalyst bed temperature reaches the temperature of the target bed

Figure 15 is a graph showing changes in the air-fuel ratio of the exhaust gas and the temperature of the catalyst bed according to the third embodiment, when the NOx storage reduction catalyst 36a has been deteriorated to some extent. In the third embodiment, the changes in the air - fuel ratio of the exhaust gas and the catalyst bed temperature when catalyst 36a of NOx storage reduction is brand new are same as those of the first embodiment shown in figure 6. As shown in Figure 15, when catalyst 36a of NOx storage reduction has deteriorated to some extent point, the duration of the non-enrichment period L_ {t} is fixed shorter than the initial value L_ {tint}, so that the catalyst bed temperature reaches the temperature of the target bed

In this embodiment, the determination process of the degree of deterioration shown in Figure 3 and steps S304, S306 of the sulfur emission process shown in Figure 14 correspond to a process executed by the detection means of the degree of deterioration Stages S308 to S312 of the issuance process of Sulfur correspond to a process executed by the means of exchange. The sulfur emission process corresponds to an executed process by means of fuel supply. The process of Determination of the degree of deterioration and step S308 of the process of Sulfur emission corresponds to a process executed by the media Determination of the degree of deterioration.

The third embodiment has the following advantage.

(1) As in the first and first embodiments second, during the execution of the release control of sulfur, the enrichment period R_ {t} and the period of no enrichment L_ {t} are repeated alternately. Every time I know run the enrichment period R_ {t} or the period of no enrichment L t, the catalyst bed temperature of the NOx storage reduction catalyst 36a increases and decreases repeatedly. The amplitude value A_ {mpin}, which represents the amplitude of the exhaust temperature T_ {exin} detected by the first exhaust temperature sensor 44, reflects the fluctuation (amplitude) of the bed temperature of the catalyst. When the catalyst 36a of NOx storage reduction, the smaller the magnitude of the amplitude value A_ {mpin}, that is, the magnitude of fluctuation of catalyst bed temperature. So, the amplitude value A_ {mpin} indicates the degree of deterioration of the NOx storage reduction catalyst 36a.

In the third embodiment, when the value of amplitude A_ {mpin} is large, that is, in a case where the deterioration of NOx storage reduction catalyst 36a has not developed significantly, the duration of the period of no enrichment L_ {t} is fixed relatively long through the processes of steps S308, S310, and S312. When the value of amplitude A_ {mpin} is small, that is, in a case where the deterioration of NOx storage reduction catalyst 36a has developed considerably, the duration of the period of no enrichment L_ {t} is set relatively long. In this way, in the third embodiment, the duration of the period of no change enrichment L_ {t}, not the duration of the period of R_ {t} enrichment. Consequently, an increase in the catalyst bed temperature of catalyst 36a of NOx storage reduction is excessive or too small with changes in the degree of deterioration of the reduction catalyst 36a NOx storage Thus, the deterioration of the catalyst is avoided 36a NOx storage reduction due to an increase excessive catalyst bed temperature and a decrease in sulfur emission efficiency due to an increase insufficient in catalyst bed temperature.

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(2) The amplitude value A_ {mpin} is calculated in a state in which the duration of the non-enrichment period L_ {t} is set to the initial value L_ {tint}. Based on value of amplitude A_ {mpin} thus calculated, the degree of deterioration of the NOx storage reduction catalyst 36a. In this way, since the duration of the period of no enrichment L_ {t} has a constant value (the initial value L_ {tint}) when calculating the amplitude value A_ {mpin}, the calculated value of amplitude A_ {mpin} exactly corresponds to degree of deterioration of catalyst 36a for reducing NOx storage

Now a fourth embodiment of the present invention with reference to the drawings.

In the fourth embodiment, the duration of the enrichment period R_ {t} changes based on the difference of temperature ΔT_ {pin}, which is calculated through the process of determining the degree of deterioration shown in the Figure 8. In the fourth embodiment, an issuance process is executed of sulfur shown in Figure 16, instead of the emission process of sulfur shown in figure 9. Other processes are the same as those of the second embodiment, and the hardware configuration is same as the first embodiment.

When the sulfur emission process begins shown in Figure 16, ECU 70 first calculates the duration of the enrichment period R_ {t} to be set in the stage S402 The calculation is executed using a p map shown in the Figure 17 based on temperature difference ΔT_ {in}, which reflects the degree of deterioration of the catalyst 36a NOx storage reduction. The older the temperature difference ΔT_ {in}, less deteriorated is NOx storage reduction catalyst 36a and greater is the oxidation efficiency for the fuel in the catalyst 36a NOx storage reduction (as is the rate of fuel purification). In this case, the period of enrichment R_ {t} is set to a short value to correspond with the temperature of the catalyst bed, which increases quickly once enrichment has begun. On the other hand, The smaller the temperature difference ΔT_ {in}, the more deteriorated is the storage reduction catalyst 36a of NOx and lower is the oxidation efficiency of catalyst 36a of NOx storage reduction. In this case, the period of enrichment R_ {t} is set to a long value to correspond to the temperature of the catalyst bed, which slowly increases a Once enrichment has begun.

In the next step S404, the ECU 70 calculates the non-enrichment period L_ {t} using the map g. He process of step S404 is the same as the process of step S158 in the sulfur emission process shown in figure 4. The stages 406, S410, S412, S414, S416, S418, and S420 in Figure 16, which are run by ECU 70 after step S404, are each equal to stages S160, S162, S164, S166, S168, S170, S172, and S174 of the Sulfur emission process shown in Figure 4.

As described above, the degree of deterioration of NOx storage reduction catalyst 36a is reflected in the temperature difference ΔT_ {in}, and the temperature difference ΔT_ {in} is reflected in the duration of the enrichment period R_ {t} using the map p. By therefore, the more deteriorated the reduction catalyst 36a is NOx storage, the longer the period duration is set of enrichment R_ {t}.

Figure 18 is a graph that shows changes in the air-fuel ratio of the exhaust gas and the temperature of the catalyst bed according to the fourth embodiment, when the NOx storage reduction catalyst 36a has been deteriorated to some extent. In the fourth embodiment, the changes in the air - fuel ratio of the exhaust gas and the catalyst bed temperature when catalyst 36a of NOx storage reduction is brand new are same as those of the second embodiment shown in figure 12. As shown in Figure 18, when catalyst 36a of NOx storage reduction has deteriorated to some extent point, the duration of the enrichment period R_ {t} is fixed shorter than the initial value L_ {tint} as the temperature difference ΔT_ {in}, so that the catalyst bed temperature reaches the temperature of target bed and that catalyst 36a reducing NOx storage does not overheat.

In this embodiment, the determination process of the degree of deterioration shown in Figure 8 corresponds to a process executed by the means of detecting the degree of deterioration. Stages S402, S404 of the sulfur emission process shown in figure 16 correspond to a process executed by the means of change The sulfur emission process corresponds to a process executed by means of fuel supply. He process of determining the degree of deterioration and step S402 of the sulfur emission process correspond to a process executed by the means of determining the degree of deterioration.

The fourth embodiment has the following advantage.

(1) As in the first to third, during the execution of the release control of sulfur, the enrichment period R_ {t} and the period of no enrichment L_ {t} are repeated alternately. Every time I know run the enrichment period R_ {t} or the period of no enrichment L t, the catalyst bed temperature of the NOx storage reduction catalyst 36a increases and decreases repeatedly. The more damaged the catalyst is 36a of NOx storage reduction, the smaller the temperature difference ΔT_ {in}, which corresponds to the rate of increase of the exhaust temperature T_ {exin} due to beginning of the enrichment period R_ {t}. That is, the degree of deterioration of the storage reduction catalyst 36a of NOx is reflected in the temperature difference ΔT_ {in}. By therefore, the degree of deterioration of catalyst 36a for reducing NOx storage is easily determined based on the temperature difference ΔT_ {in}.

When ECU 70 determines that the catalyst 36a NOx storage reduction has barely deteriorated since the temperature difference ΔT_ {in} is sufficiently large, the duration of the enrichment period R_ {t} is set relatively short based on the p map of the Figure 17. Consequently, an excessive increase in the catalyst bed temperature of catalyst 36a of NOx storage reduction due to enrichment of the air - fuel ratio of the exhaust gas. Since then, when ECU 70 determines that the reduction catalyst 36a of NOx storage has deteriorated to some extent that the temperature difference ΔT_ {in} has decreased, the duration of the enrichment period R_ {t} is set relatively long based on the p map in figure 17. In consequently, a decrease in emission efficiency is suppressed of fuel due to insufficient temperature rise from the catalyst bed. In this way, even when the degree of deterioration of catalyst 36a for reducing NOx storage, catalyst bed temperature not increases excessively, and the sulfur release control is Run accurately.

It must be evident to experts in the technique that the present invention can be performed in many others specific forms without departing from the spirit of the scope of invention. In particular, it should be understood that the invention can be done in the following ways.

(a) In the second and fourth embodiments, the durations of the non-enrichment period L_ {t} and the period enrichment R_ {t} is not set to initial values when the temperature difference ΔT_ {in} is calculated, but they are set to values that correspond to the state in that moment. However, as in the first and third, the duration of the non-enrichment period L_ {t} and the enrichment period R_ {t} can be set to values initials when sulfur release control begins, and the sulfur emission process can be executed once the durations are set at values that correspond to the difference of temperature ΔT_ {in} once the difference in temperature ΔT_ {in}.

In addition, in the second and fourth embodiment, the initial exhaust temperature T_ a immediately detects a once the enrichment of the air ratio has begun - exhaust gas fuel during the enrichment period R_ {t}. However, in consideration of the fact that the Exhaust temperature T_ {exin} increases after a short delay, the initial exhaust temperature T_ {a} can be detected when after a waiting period, which corresponds to the speed of input flow GA, once the period of R_ {t} enrichment.

(b) In the illustrated embodiments, the reason air - exhaust gas fuel is enriched causing the fuel addition valve 68 add fuel to the exhaust. However, the air-fuel ratio of the exhaust gas can Get rich by other means. The air-fuel ratio of Exhaust gas can be enriched, for example, after injection, in the fuel injected into the combustion chambers from the fuel injection valve 58 during a run of expansion or escape run.

(c) In the illustrated embodiment, the duration of one of the non-enrichment period L_ {t} and the period of enrichment R_ {t} is changed according to the degree of deterioration of the exhaust purification catalyst. However, the durations of both can be changed.

(d) The present invention is not limited to diesel engines, but can be applied to gasoline engines of poor combustion

The present examples and embodiments should be considered illustrative and not limiting and the invention should not be limited to the details provided in this document, but that can be modified within the scope and equivalence of attached claims.

Claims (10)

1. Apparatus for controlling an exhaust purification catalyst, the catalyst being located in an exhaust system of an internal combustion engine (2), in which, during sulfur release control to allow the catalyst to recover from the sulfur poisoning, the apparatus repeats a period of enrichment and a period of non-enrichment, in which, in the period of enrichment, the apparatus intermittently supplies fuel to the exhaust gas in a section upstream of the catalyst, thus decreasing the air ratio - exhaust gas fuel that comes into contact with the catalyst up to a value equal to or less than the stoichiometric air-fuel ratio, and in which, in the period of non-enrichment, the apparatus does not supply fuel to the exhaust gas, being characterized by: means of detecting the degree of deterioration that detect the degree of deterioration of the purification catalyst of escape; Y means of change that change the reason for the duration of the enrichment period with respect to the duration of the period of non-enrichment according to the degree of deterioration of the exhaust purification catalyst detected by the means of Determination of the degree of deterioration. 2. Apparatus according to claim 1, characterized in that the exchange means change the ratio of the duration of the enrichment period with respect to the duration of the non-enrichment period so that the greater the degree of deterioration of the exhaust purification catalyst detected by the means of detecting the degree of deterioration, the higher the rate is made. 3. Apparatus according to claim 1 or 2, characterized in that a temperature of the catalyst bed of the exhaust purification catalyst is calculated based on an exhaust gas temperature that comes into contact with the exhaust purification catalyst and a heat value obtained from the amount of fuel supplied to the exhaust gas and a fuel purification rate in the exhaust purification catalyst, in which the rate of the duration of the enrichment period with respect to the duration of the non-enrichment period changes to control the estimated catalyst bed temperature, and in which the means of change correct the rate of fuel purification according to the degree of deterioration of the exhaust purification catalyst detected by the means of detection of the degree of deterioration, thus changing the reason for the duration of the enrichment period with respect to the duration of the period of non-enrichment accordingly. 4. Apparatus according to any one of claims 1 to 3, characterized in that it comprises means for detecting the temperature of the catalyst bed to detect a physical quantity representing a temperature of the actual catalyst bed of the exhaust purification catalyst, and in which the detection means of the degree of impairment determines that the smaller a fluctuation interval of the physical quantity produced by the fuel supply to the Exhaust gas, the greater the degree of deterioration of the catalyst exhaust purification. 5. Apparatus according to any one of claims 1 to 3, characterized in that it comprises means for detecting the temperature of the catalyst bed to detect a physical quantity representing a temperature of the actual catalyst bed of the exhaust purification catalyst, and in which the detection means of the degree of impairment determine that the lower the rate of increase in physical quantity produced by the supply of fuel to the gas of exhaust, the greater the degree of deterioration of the catalyst of exhaust purification. 6. Apparatus according to claim 4 or 5, characterized in that the means of detecting the degree of deterioration detect the degree of deterioration based on a physical quantity that is detected by the means of detecting the temperature of the catalyst bed when the fuel supply The exhaust gas is carried out in a state in which the rate of the duration of the enrichment period with respect to the duration of the non-enrichment period is set to correspond to a case in which an exhaust purification catalyst is used which It has not deteriorated. An apparatus according to any one of claims 4 to 6, characterized in that the means for detecting the temperature of the catalyst bed is a sensor (44) of the exhaust temperature located downstream of the exhaust purification catalyst, in which The physical amount detected by the catalyst bed temperature detection means is an exhaust temperature detected by the exhaust temperature sensor. 8. Apparatus according to any one of claims 1 to 7, characterized in that the exhaust purification catalyst is a NOx storage reduction catalyst.

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9. Apparatus according to any one of claims 1 to 8, characterized in that the internal combustion engine is a diesel engine. An apparatus according to any one of claims 1 to 9, characterized in that the supply of fuel to the exhaust gas is carried out either by adding fuel to the exhaust gas from a fuel addition valve provided in the internal combustion engine or by injecting fuel in a combustion chamber provided in the internal combustion engine during an expansion stroke or an exhaust stroke.