FR2923533A1 - EXHAUST GAS PURIFYING APPARATUS FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

When the amount of sulfur components left in the NOx catalyst is large, high temperature sulfur poisoning recovery control is performed, where the temperature of the catalytic bed is increased more than in the usual control of recovery of sulfur. Sulfur poisoning, whereby the sulfur components are removed from the NOx catalyst more effectively and therefore the amount of sulfur components left in the NOx catalyst decreases. Thus, the execution of the sulfur poisoning recovery command at high temperature reduces the amount of sulfur components left in the NOx catalyst while avoiding an excessive increase in the temperature of the catalyst bed, thereby removing a increased NOx emissions from the internal combustion engine that may be caused by the sulfur components left in the NOx catalyst.

Description

FIELD OF THE INVENTION 1. Field of the Invention The invention relates to an exhaust gas purifying apparatus for an internal combustion engine. BACKGROUND OF THE INVENTION 2. Description of the State of the Art

As an exhaust gas purification device, a catalytic converter carrying an absorption-reduction type NOx catalyst for removing nitrogen oxides (NOx) from the exhaust gas is often provided in the exhaust system. an internal combustion engine which is, for example, mounted in a motor vehicle.

In such an exhaust gas purification device, the NOx storage capacity of the NOx catalyst decreases as the amount of sulfur components (eg, sulfur oxides) absorbed in the NOx catalyst increases. Therefore, when such an exhaust purification device is used, typically, an amount S of the sulfur poisoning representing the amount of sulfur components absorbed (stored) in the NOx catalyst is determined, and if the amount S of the determined sulfur poisoning is greater than or equal to a threshold, a sulfur poisoning recovery control for removing the sulfur components from the NOx catalyst is performed to recover the NOx storage capacity NOx catalyst which has decreased due to the sulfur components absorbed therein as described in [0003], [0033], and [0037] of Japanese Patent Application Publication No. 2005-90253 (JP document -A-2005-90253). In the sulfur poisoning control described above, the NOx catalyst is heated to about 600 to 700 ° C by supplying the catalytic converter in the exhaust system with unburned fuel components. while carrying an atmosphere that surrounds the NOx catalyst at a fuel-rich condition (hereinafter referred to as a "fuel-rich combustion atmosphere") using heat, whereby the absorbed sulfur components in the NOx catalyst are removed from the latter and then reduced to recover the NOx storage capacity of the NOx catalyst. Sulfur poisoning recovery control is terminated when the sulfur poisoning amount S to the NOx catalyst decreases due to execution of the sulfur poisoning recovery control to a predetermined value. (eg 0) which is below the threshold.

According to the exhaust purification device described above, the amount of sulfur poisoning is estimated on the basis of the operational state of the internal combustion engine, etc. More specifically, when the sulfur poisoning recovery command is not executed, the amount of sulfur poisoning is calculated based on the amount of fuel that has been consumed since the end of the last order of sulfur. recovery of sulfur poisoning, and so on. On the other hand, when sulfur poisoning recovery control is performed, the amount of sulfur poisoning is calculated by estimating the amount of sulfur components that have been removed from the NOx catalyst by the control of the sulfur poisoning. recovery of sulfur poisoning.

As mentioned above, when ordering recovery of sulfur poisoning, the amount of sulfur poisoning of the NOx catalyst is calculated by estimating the amount of sulfur components that are removed from the NOx catalyst during Sulfur poisoning recovery control. However, the estimated amount of sulfur components removed may, in some cases, deviate from the actual amount.

Since some sulfur components are not removed from the NOx catalyst and remain in the latter. If a theoretical value is used as the amount of sulfur components removed, i.e., if said quantity is estimated instead of actually being detected, this value deviates from the amount of sulfur components actually removed from the NOx catalyst by the amount of sulfur components remaining in the NOx catalyst. The reason why some sulfur components remain in the NOx catalyst is that the temperature of the catalyst bed does not increase much at some parts of the catalytic converter such as the corresponding upstream end. That is, it is considered difficult to remove from the NOx catalyst the sulfur components absorbed therein at such portions of the catalytic converter, even if the NOx catalyst is heated and an atmosphere Fuel-rich combustion is created around the NOx catalyst in the recovery control of sulfur poisoning.

As such, some sulfur components can not be removed from the NOx catalyst by the sulfur poisoning recovery control and therefore they remain in the NOx catalyst, i.e. Residual sulfur exist in the NOx catalyst. For this reason, in a case where the amount of sulfur poisoning is estimated without taking into account the amount of sulfur components that can not be removed from the NOx catalyst, the amount of the estimated sulfur poisoning becomes lower. to the amount of effective sulfur poisoning.

Therefore, when sulfur poisoning recovery control is completed in response to the estimated amount of sulfur poisoning reaching 0, the amount of cumulative sulfur poisoning is not yet reduced to 0, c. that is, some sulfur components are still left in the NOx catalyst. As the NOx catalyst continues to be used, the amount of sulfur components left in the NOx catalyst increases, and hence the deviation of the amount S from the estimated sulfur poisoning from its value. Effective increases, that is, the amount of sulfur components that are left in the NOx catalyst at the end of the sulfur poisoning recovery control increases.

In particular, in the following cases (1) to (3), the deviation of the amount of the estimated sulfur poisoning from its actual value is considerably large, i.e. the amount of The estimated sulfur poisoning is considerably larger than its actual value.

(1) When a driver drives a motor vehicle only for a short time, the temperature of the exhaust gas from the internal combustion engine does not increase significantly, and therefore the temperature of the catalytic bed of the NOx catalyst tends to stay low. Therefore, the likelihood of performing the sulfur poisoning recovery command is relatively small, and even if the latter is executed, the temperature of the catalytic bed may not increase significantly in the recovery control of the poisoning. sulfur. As a result, the rate of removal of sulfur components from the NOx catalyst decreases, and a greater amount of sulfur components remain in the NOx catalyst.

(2) When a driver is used to driving a motor vehicle in a manner that consumes a large amount of fuel, such as the rapid acceleration of the motor vehicle, the amount of sulfur components entering the catalyst NOx as the fuel is consumed is large, and as a result, the amount of sulfur components that remain in the NOx catalyst is large. (3) When the sulfur concentration of the fuel used is higher than a standard value, a large amount of sulfur components tends to enter the NOx catalyst compared to the moment when fuel with a concentration of standard fuel. A larger amount of sulfur components is absorbed to the NOx catalyst, and therefore, a greater amount of sulfur components remain in the NOx catalyst.

As described above, in a state where a greater amount of sulfur components remains in the NOx catalyst, more than in a normal state, i.e., the amount of actual sulfur poisoning becomes more large than the estimated quantity, the NOx storage capacity of the NOx catalyst remains low due to the sulfur components left in the NOx catalyst even after the end of the sulfur poisoning recovery control, thus causing an increase in NOx emissions from the internal combustion engine. However, this problem can be solved by allowing more effective removal of sulfur components from the NOx catalyst by further increasing the temperature of the catalyst bed for recovery control of sulfur poisoning. Thus, the amount of sulfur components left in the NOx catalyst can decrease, in other words, the estimated value of the amount of sulfur poisoning can approach the amount of actual sulfur poisoning. However, if the temperature of the catalytic bed for sulfur poisoning recovery control increases further, the temperature of the catalyst bed may become too high compared to what can cause thermal deterioration, which often results in increased NOx emissions from the internal combustion engine. SUMMARY OF THE INVENTION The invention provides an exhaust purification apparatus for an internal combustion engine that reduces the amount of sulfur components left in the NOx catalyst while avoiding an excessive increase in the temperature of the catalytic bed. NOx catalyst, thus suppressing an increase in NOx emissions from the internal combustion engine that may be caused by the sulfur components left in the NOx catalyst.

The first aspect of the invention relates to an exhaust purification apparatus for an internal combustion engine, having an absorption-reduction type NOx catalyst provided in an exhaust system of the internal combustion engine and a estimation means for estimating an amount of sulfur poisoning representing the amount of sulfur components absorbed in the NOx catalyst, wherein when the amount of sulfur poisoning is greater than or equal to a threshold, components of sulfur are removed from the NOx catalyst by performing a sulfur poisoning recovery control in which a temperature of the catalytic bed increases to a target temperature of the catalyst bed by supplying the NOx catalyst to unburned fuel components while carrying an atmosphere around the NOx catalyst to a state for fuel-rich combustion, and recovery control Sulfur poisoning is complete when the amount of sulfur poisoning falls below a predetermined value that is below the threshold. This exhaust purification apparatus has a cumulative value calculating means for calculating a cumulative value of the high temperature duration as a value indicative of the degree of thermal deterioration of the NOx catalyst, which is a cumulative length of time. during which the temperature of the NOx catalyst is higher than a predetermined temperature; a standard value calculation means for calculating a standard value of the cumulative value of the high temperature duration, which corresponds to a total duration of the current operation of the internal combustion engine based on a total engine running time indicating the total duration of the current operation of the internal combustion engine; and control means for executing a high temperature sulfur poisoning recovery control in which the temperature of the catalyst bed increases to a target temperature of the catalyst bed which is above the target temperature of the catalyst bed according to the sulfur poisoning recovery command, when the cumulative value of the high temperature duration calculated by the cumulative value calculation means is less than or equal to the standard value calculated by the standard value calculation means.

In the case of a driver who drives a motor vehicle only for a short time, the temperature of the exhaust gas from the internal combustion engine does not increase significantly, and therefore the temperature of the catalytic converter catalyst bed NOx tends to stay low. In such a case, the probability of executing the sulfur poisoning recovery command is relatively small, and even if the latter is executed, it is relatively difficult to increase the temperature of the catalytic bed during the recovery control. sulfur poisoning. As a result, the rate of removal of sulfur components removed from the NOx catalyst decreases, leaving a greater amount of sulfur components in the NOx catalyst. In particular, in a case where the fuel having a higher sulfur concentration than a standard sulfur concentration is used, the amount of sulfur components that enter the NOx catalyst is greater than it is when the fuel having the standard sulfur concentration is used, and therefore, a greater amount of sulfur components is absorbed to the NOx catalyst and thus a larger amount of sulfur components is left in the NOx catalyst.

As such, in a case where the driver often drives the motor vehicle for a short time, the increase in the cumulative value of the high temperature duration, which is a cumulative value of the time during which the temperature of the catalytic bed of the NOx catalyst is high, tends to remain small, and therefore, the possibility that the cumulative value of the high temperature time becomes less than or equal to the standard value is relatively large. As such, by executing the sulfur poisoning recovery command at high temperature when the cumulative value of the high temperature time becomes lower than or equal to the standard value, the sulfur components can be removed from the NOx catalyst of effectively and thus the amount of sulfur components left in the NOx catalyst can be effectively reduced.

As such, the exhaust purification apparatus according to the first aspect of the invention is capable of reducing the amount of sulfur component left in the NOx catalyst while avoiding an excessive increase in the temperature of the catalytic bed. NOx catalyst, thus suppressing an increase in NOx emissions from the internal combustion engine that may be caused by the sulfur components left in the NOx catalyst.

The exhaust gas purifying apparatus according to the first aspect of the invention may be such that, the smaller the cumulative value of the high temperature duration, the more the control means makes the target temperature of the catalytic bed used. in the recovery control of sulfur poisoning at high temperature, high.

When the cumulative value of the high temperature duration is less than the standard value, the greater the difference in the cumulative value of the high temperature duration compared to the standard value, the more sulfur components left in the the NOx catalyst. In this state, even if sulfur poisoning recovery control is performed, the temperature of the catalyst bed does not increase much, and therefore the sulfur components are not effectively removed from the NOx catalyst. In other words, it can be said that this state is a state in which it is unlikely that the temperature of the catalytic bed will increase excessively as the temperature of the catalyst bed increases by the control of recovery of sulfur poisoning. high temperature. According to the exhaust purification apparatus described above, because the maximum temperature of the target temperature of the catalytic bed, when the cumulative value of the high temperature time is lower than the standard value, increases the higher the deviation from the cumulative value of the high temperature duration is large compared to the standard value, an inhibition of an excessive increase in the catalyst bed temperature of the NOx catalyst and an effective removal of sulfur components from the NOx catalyst can both be made in desirable ways.

In addition, the exhaust gas purification apparatus according to the first aspect of the invention may be such that the control means increases the target temperature of the catalyst bed used in the recovery control of high sulfur poisoning. temperature at a predetermined optimum temperature. In addition, the exhaust gas purification apparatus according to the first aspect of the invention may be such that the standard value of the cumulative value of the high temperature time increases plus the value indicating the total duration of engine operation. The second aspect of the invention relates to an exhaust gas purification apparatus for an internal combustion engine, having an absorption-reduction type NOx catalyst provided in an engine exhaust system. internal combustion and estimation means for estimating an amount of sulfur poisoning representing the amount of sulfur components absorbed in the NOx catalyst, wherein when the amount of sulfur poisoning is greater than or equal to a threshold , the sulfur components are removed from the NOx catalyst by performing a sulfur poisoning recovery control in which a temperature of The catalytic bed increases to a target temperature of the catalyst bed by supplying the NOx catalyst to unburned fuel components while carrying an atmosphere around the NOx catalyst to a state for fuel-rich combustion, and recovery control. Sulfur poisoning is complete when the amount of sulfur poisoning falls below a predetermined value that is below the threshold. This exhaust gas purification apparatus has a means for calculating the amount of sulfur introduced to calculate a total amount of sulfur introduced indicating the total amount of sulfur components circulating in the NOx catalyst; standard value calculating means for calculating a standard value of the total quantity of sulfur introduced, which corresponds to a total duration of the current operation of the internal combustion engine, based on a total duration of engine operation indicating the duration total of the current operation of the internal combustion engine; and control means for executing a high temperature sulfur poisoning recovery control in which the temperature of the catalyst bed increases to a target temperature of the catalyst bed which is above the target temperature of the catalyst bed according to the sulfur poisoning recovery control, when the total quantity of sulfur introduced calculated by the value calculating means indicating the amount of sulfur introduced is greater than or equal to the standard value calculated by the standard value calculation means.

In a case where the driver is accustomed to driving a motor vehicle in a manner that consumes a large amount of fuel, such as the rapid acceleration of the motor vehicle, the amount of sulfur components that enter the catalytic converter NOx as the fuel is consumed is relatively large, and as a result a relatively large amount of sulfur components is left in the NOx catalyst. In particular, in a case where the sulfur concentration in the fuel used is higher than the standard sulfur concentration, a large amount of sulfur components tends to enter the NOx catalyst in comparison with the time when the fuel is used. fuel having the standard sulfur concentration. Therefore, in such a case, a larger amount of sulfur components is absorbed to the NOx catalyst, resulting in a considerable increase in the amount of sulfur components left in the NOx catalyst.

As such, in a case where the driver drives the motor vehicle often in a manner that consumes fuel, the value indicating the total quantity of sulfur introduced, which indicates the total amount of sulfur components that enter the catalyst of the fuel. NOx, increases at a relatively high rate, and therefore the possibility that the value indicating the total amount of sulfur introduced becomes greater than or equal to the standard value is relatively large. As such, by executing the sulfur poisoning recovery command at high temperature when the value indicating the total amount of sulfur introduced exceeds the standard value, sulfur components can be effectively removed from the NOx catalyst and thus the amount of sulfur components left in the NOx catalyst can be effectively reduced. As such, the exhaust gas purification apparatus according to the second aspect of the invention is capable of reducing the amount of sulfur components left in the NOx catalyst while avoiding an excessive increase in the temperature of the catalytic bed. NOx catalyst, thus suppressing an increase in NOx emissions from the internal combustion engine that may be caused by the sulfur components left in the NOx catalyst.

The exhaust gas purification apparatus according to the second aspect of the invention may be such that, the higher the value indicating the total amount of sulfur introduced compared to the standard value, the more the control means makes the temperature Catalytic bed target, used in high temperature, high temperature sulfur poisoning recovery control.

When the value indicating the total amount of sulfur introduced is greater than the standard value, the greater the difference in the cumulative value of the high temperature duration compared to the standard value, the more sulfur components left in the the NOx catalyst. In this state, even if sulfur poisoning recovery control is performed, the temperature of the catalyst bed does not increase significantly, and therefore, the sulfur components are not effectively removed from the NOx catalyst. In other words, it can be said that this state is a state in which it is unlikely that the temperature of the catalytic bed will increase excessively as the temperature of the catalyst bed increases by the control of recovery of sulfur poisoning. high temperature. According to the exhaust purification apparatus described above, because the maximum temperature of the target temperature of the catalytic bed, when the value indicating the total amount of sulfur introduced is greater than the standard value, increases more than deviation from the value indicating the total amount of sulfur introduced is large compared to the standard value, the prevention of an excessive increase in the catalyst bed temperature of the NOx catalyst and an effective removal of sulfur components from the NOx catalyst both can be done in desirable ways.

In addition, the exhaust gas purification apparatus according to the second aspect of the invention may be such that the control means increases the target temperature of the catalyst bed used in the recovery control of high sulfur poisoning. temperature at a predetermined optimum temperature.

In addition, the exhaust gas purification apparatus according to the second aspect of the invention may be such that the standard value of the total amount of sulfur introduced increases, plus the value indicating the total operating time of the engine becomes large. .

In addition, the exhaust gas purifying apparatus according to the second aspect of the invention may additionally have correction means for correcting the total quantity of sulfur introduced which corresponds to the total operating time of the engine to the value. standard, when the recovery command for high temperature sulfur poisoning is performed.

Since the execution of the sulfur poisoning recovery command at high temperature further reduces the amount of sulfur components left in the NOx catalyst, preferably the frequency of execution of the recovery control of the NOx catalyst. High temperature sulfur poisoning is reduced to prevent an excessive increase in the catalyst bed temperature of the NOx catalyst. According to the exhaust purification apparatus described above, because the total amount of sulfur introduced is corrected to the standard value when the high temperature sulfur poisoning recovery command is executed, the total quantity of sulfur introduced that corresponds to the value indicating the total running time of the engine changes to the standard value, thus reducing the possibility that the total amount of sulfur introduced will become greater than or equal to the standard value and thus reduce the chances of a excessive increase in the temperature of the catalytic bed.

In addition, the exhaust purification apparatus described above may be such that, the smaller the amount of sulfur components left in the NOx catalyst, the more the correction means reduces the frequency of execution of the NOx catalyst. the control of recovery of sulfur poisoning at high temperature.

In addition, the exhaust gas purifying apparatus according to the second aspect of the invention may additionally have correction means for correcting the total quantity of sulfur introduced which corresponds to the value indicating the total operating time of the engine. to the standard value, when the recovery command for high temperature sulfur poisoning is executed.

The exhaust purification apparatus according to the first and second aspects of the invention may be such that the control means determines whether the degree of deterioration of the NOx catalyst due to heat and sulfur components left in the NOx catalyst is large on the basis of the temperature of the catalytic bed when the temperature of the catalyst bed increases or has increased. The control means may perform the high temperature sulfur poisoning recovery control if it is determined that the degree of deterioration of the NOx catalyst is large.

In addition, the exhaust purification apparatus according to the first and second aspects of the invention may be such that the value indicative of the total running time of the engine is calculated on the basis of a total mileage of one vehicle incorporating the internal combustion engine or on the basis of a cumulative value of a rotational speed of the internal combustion engine.

In addition, the exhaust gas purifying apparatus according to the first and second aspects of the invention may be such that increasing the temperature of the catalyst bed to the target temperature of the catalyst bed includes increasing the temperature of the catalyst bed to the target temperature of the catalyst bed. the average temperature of the catalytic bed to the target temperature of the catalyst bed.

When the degree of deterioration of the NOx catalyst due to the heat and sulfur components left in the NOx catalyst is great, the temperature of the catalyst bed does not increase much even if the recovery control of the sulfur poisoning is executed. Therefore, by executing the sulfur poisoning recovery command at high temperature only when the degree of deterioration of the NOx catalyst due to the heat and sulfur components left in the NOx catalyst is large, an excessive increase of the temperature of the NOx catalyst can be reliably avoided during the control of recovery of sulfur poisoning at high temperature.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned objects, features and advantages of the invention as well as the additional objects, features and advantages will become apparent from the following description of the preferred embodiments with reference to the accompanying drawings, wherein like numbers are used to represent like elements and where: FIG. 1 is a view illustrating the overall configuration of an internal combustion engine incorporating an exhaust gas purification apparatus according to the first exemplary embodiment of the invention;

FIG. 2A is a timing chart illustrating the manner in which the fuel addition pulses for actuating the fuel addition valve are controlled during sulfur poisoning recovery control;

FIG. 2B is a timing chart illustrating the manner in which the atmosphere around the NOx catalyst changes upon Sulfur poisoning recovery control; 2C is a timing chart illustrating how the catalyst bed T temperature of the NOx catalyst changes during sulfur poisoning recovery control; FIG. 2D is a timing chart illustrating how the cumulative values EQr, EQ change during the sulfur poisoning recovery command;

FIG. 2E is a timing chart illustrating the manner in which the fuel addition permission flag F is set during the sulfur poisoning recovery command;

FIG. 3 is a flowchart illustrating the procedure for selectively executing the usual sulfur poisoning recovery command or the high temperature sulfur poisoning recovery control in the exhaust gas purification apparatus of the first exemplary embodiment;

FIG. 4 is a graph illustrating how the cumulative value Et of the high temperature duration and the standard value Bh increase as the mileage of the motor vehicle increases; FIG. 5 is a graph illustrating the manner in which the total quantity ESU of sulfur introduced and the standard value Bsu increase as the mileage of the motor vehicle increases;

FIG. 6 is a flowchart illustrating the procedure for selectively executing the usual sulfur poisoning recovery control or high temperature sulfur poisoning recovery control in a second mode exhaust purification apparatus. exemplary achievement;

FIG. 7 is a flowchart illustrating a correction routine for correcting the total amount of sulfur ESU introduced after completion of the high temperature sulfur poisoning recovery command; and FIG. 8 is a graph illustrating the temperatures of the catalyst bed at respective positions of the NOx catalytic converter between the upstream and downstream ends thereof.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the first exemplary embodiment of the invention will be described with reference to FIG. 1 to FIG. 4. In the first exemplary embodiment, an exhaust purification apparatus according to the invention is incorporated in an internal combustion engine for motor vehicles.

FIG. 1 illustrates the configuration of an internal combustion engine incorporating the exhaust gas purification apparatus of the first exemplary embodiment of the invention. The internal combustion engine 10 is a diesel engine having a common rail fuel injection system. An intake passage 12 provided in the intake system of the internal combustion engine 10 and an exhaust passage 14 provided in the exhaust system of the internal combustion engine 10 are both connected to the combustion chambers 13 in the respective cylinders of the engine. An air flow meter 16 is provided in the inlet passage 12, and a NOx catalytic converter 25, a PM (Particles) filter 26, and an oxidizing catalytic converter 27 are provided in the exhaust passage 14 in this order on the upstream side of it.

The NOx catalytic converter comprises an absorption-reduction type NOx catalyst. The NOx catalyst absorbs (stores) the NOx contained in the exhaust gas when the oxygen concentration in the exhaust gas is high and releases the absorbed NOx when said concentration is low. If a sufficient amount of unburned fuel components, which serves as a reducing agent, is present around the NOx catalyst, the NOx removed from the NOx catalyst is reduced and thus removed from the exhaust gas. The PM 26 filter is made of a porous material and is used to trap particulate matter (PM) composed mainly of the soot contained in the exhaust gas. Like the NOx catalytic converter, the PM filter 26 also includes an absorption-reduction type NOx catalyst and removes the NOx contained in the exhaust gas as described above. In addition, particulate matter trapped in the PM filter 26 is burned (oxidized) and thus removed through reactions caused by the NOx catalyst that the PM filter 26 comprises.

The oxidizing catalytic converter 27 comprises oxidizing catalysts. The oxidizing catalysts remove hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gas by oxidizing them. In the exhaust passage 14, a gas inlet temperature sensor 28 is provided on the upstream side of the PM filter 26 to detect the temperature of the exhaust gas flowing in the PM filter 26. On the other hand a gas outlet temperature sensor 29 is provided on the downstream side of the PM filter 26 in the exhaust passage 14 to detect the temperature of the exhaust gas flowing out of the PM filter 26. A differential pressure sensor 30 is provided in the exhaust passage 14, which detects the differential pressure between the upstream side and the downstream side of the PM filter 26. In addition, an air / fuel ratio sensor 31 is provided upstream of the NOx catalytic converter in the exhaust passage 14, and an air-fuel ratio sensor 32 is provided between the PM filter 26 and the oxidizing catalytic converter 27 in the exhaust passage 14.

An injector 40 for injecting the fuel is provided in the combustion chamber 13 of each cylinder of the internal combustion engine 10. The injectors 40 in the respective cylinders are connected to a common rail 42 through pipes 41 for high fuel supply. pressure, respectively. The common rail 42 is supplied with high pressure fuel through a fuel pump 43. The pressure of the high pressure fuel in the common rail 42 is detected by a rail pressure sensor 44 provided with the common rail 42. In addition, the pump The fuel nozzle 43 sends low pressure fuel to the fuel addition valve 46 through a low pressure fuel supply pipe 45.

An electronic control unit 50 executes various commands to control the operation of the internal combustion engine 10. The electronic control unit 50 consists of a CPU (Central Unit) which performs various computer calculation and calculation processes to control the operation of the internal combustion engine. internal combustion engine 10; a ROM (Dead Memory) which stores various programs and data for controlling the internal combustion engine 10; a RAM (Memory Vive) which is used to temporarily store the results of computations and computations computed by the CPU, and so on; an inlet for introducing various signals externally; an output port for outputting various signals externally; and etc.

The inlet of the electronic control unit 50 is connected to various sensors, as well as those described above, such as a sensor NE 51 for detecting the speed of the engine, an accelerator sensor 52 for detecting the amount of actuation of the accelerator, an intake temperature sensor 54 for detecting the intake air temperature introduced into the internal combustion engine 10, and a coolant temperature sensor 55 for detecting the temperature of the coolant of the internal combustion engine 10. On the other hand, the outlet of the electronic control unit 50 is connected to the control circuits for the injectors 40, the fuel pump 43, the fuel addition valve 46, and so on.

The electronic control unit 50 outputs the control signals to the control circuits for the respective components, which are connected to the output port of the electronic control unit 50 as described above, on the basis of the operational state of the internal combustion engine 10 detected on the basis of the signals obtained from the sensors described above. That is, the electronic control unit 50 performs various commands such as fuel injection control to control the fuel injection amount, the fuel injection timing, and the fuel pressure. fuel injection, and the fuel addition control for adding the fuel from the fuel addition valve 46.

In the exhaust gas purification apparatus configured as described above, the electronic control unit 50 performs a sulfur poisoning recovery control to recover the NOx storage capacity of the NOx catalyst when the It has decreased because of the sulfur components (eg, sulfur oxides (SOx)) absorbed in the NOx catalyst. Sulfur poisoning recovery control begins when the amount of sulfur components absorbed in the NOx catalyst, which is calculated (estimated) based on logging of the operating state of the combustion engine. internal 10, reaches a threshold. The amount of sulfur components absorbed in the NOx catalyst will hereinafter be referred to as "S amount of sulfur poisoning".

When ordering recovery of sulfur poisoning, the NOx catalyst is heated, for example, to about 600-700 ° C by supplying the NOx catalyst to unburned fuel components while carrying the atmosphere. surrounding the NOx catalyst to a fuel-rich condition (hereinafter referred to as "fuel-rich combustion atmosphere") using heat, whereby the sulfur components absorbed in the NOx catalyst are removed and thus the NOx storage capacity of the NOx catalyst is recovered. Note that in the sulfur poisoning recovery control, the unburned fuel components can be delivered to the NOx catalyst by adding fuel from the fuel addition valve 46 to the exhaust gas. .

The sulfur poisoning recovery command stops when the sulfur poisoning amount S is reduced to a target value (for example, 0), which is below the threshold, through the execution of the command recovery of sulfur poisoning.

Then, the calculations performed to begin and end the sulfur poisoning recovery command will be described in detail.

The amount S of the sulfur poisoning is calculated using the following formula (1) each time the fuel is injected from the fuel injectors 40; (1) Si = Si-1 + SU - SD

where: "Si" represents the current amount S of sulfur poisoning S: "Si-1" represents the last amount S of sulfur poisoning S: "SU" represents the amount of sulfur components that have been newly absorbed to the NOx catalyst from the last fuel injection to the actual fuel injection (hereinafter referred to as "SU amount of newly absorbed sulfur components"): and "SD" represents the amount of components of sulfur that have been newly removed from the NOx catalyst since the last fuel injection to the actual fuel injection (hereinafter will be referred to as "SD amount of newly removed sulfur components").

The amount SU of newly absorbed sulfur components is calculated using a fuel injection control value Qf1 which is a control value identifying the amount of fuel to be injected through an injection from each injector 40. Note that the control value Qf1 of fuel injection is calculated before the fuel is injected from the injectors 40. More specifically, the amount of sulfur components contained in the fuel injected through an injection from each injector 40 is calculated by multiplying the fuel injection control value Qfin by the value obtained by dividing a concentration N of sulfur, which is the standard sulfur concentration of the fuel, by 100 (N / 100). The value Qfin • (N / 100) obtained through the multiplication described above is then multiplied by a parameter conversion factor K to convert the amount of sulfur components contained in the injected fuel to a quantity of sulfur components which are newly absorbed to the NOx catalyst from the injected fuel, whereby the amount SU of newly absorbed sulfur components is calculated. The parameter conversion factor K is established by applying the air-fuel ratio detected by the sensors 31, 32 of the air-fuel ratio and the temperature of the catalytic bed to a card. According to this map, the parameter conversion factor K is set to 0 when the air-fuel ratio detected by the air-fuel ratio sensors 31, 32 is equal to or below (richer) of the stoichiometric air-fuel ratio. (14.5 in this example). In addition, when the air-fuel ratio detected by the air-fuel ratio sensors 31, 32 is above (poorer) the stoichiometric air-fuel ratio, the parameter conversion factor K is larger plus the air ratio. -Fuel detected by the sensors 31, 32 of the air-fuel ratio is high (poorer) and the temperature of the catalyst bed is high.

The amount of sulfur components that are theoretically removed from the NOx catalyst at the actual temperature of the catalyst bed and the air-fuel ratio detected by the air-fuel ratio sensors 31, 32 is estimated to be an amount of SD of sulfur components. newly withdrawn in formula (1). When the air-fuel ratio detected by the sensors 31, 32 of the air-fuel ratio is lower (richer) than the stoichiometric air-fuel ratio, the estimated amount SD of newly removed sulfur components is greater than 0 and is larger. the temperature of the catalytic bed is high and the air-fuel ratio detected by the sensors 31, 32 of the air-fuel ratio is low (richer). The amount SD of newly removed sulfur components is kept at 0 when the air-fuel ratio detected by the air-fuel ratio sensors 31, 32 is larger (leaner) than the stoichiometric air-fuel ratio.

The amount S of the sulfur poisoning (current amount Si of sulfur poisoning), calculated using the formula (1) as described above, gradually increases by the amount SU of newly absorbed sulfur components as the fuel is consumed during the normal operation of the internal combustion engine 10, while it gradually decreases by the amount of SD newly removed sulfur components in the sulfur poisoning recovery control. As such, during normal operation of the internal combustion engine 10, the amount S of the sulfur poisoning increases as the sulfur components are newly absorbed by the NOx catalyst through the fuel consumption, and when In the sulfur poisoning recovery control, the sulfur poisoning amount S decreases as the sulfur components are removed from the NOx catalyst by said control.

Next, a detailed description of how the sulfur poisoning recovery control begins and ends in accordance with the amount S of sulfur poisoning will be made with reference to the timing chart shown in FIG. 2A in FIG. 2E. In the sulfur poisoning recovery control, the catalyst bed T temperature of the NOx catalyst increases to a target temperature Tt of the catalyst bed which increases, for example, up to about 700 ° C by feeding the NOx catalyst to unburned fuel components, through addition of fuel from the fuel addition valve 46 while the fuel-rich combustion atmosphere is created around the NOx catalyst using heat .

In the example illustrated in FIG. 2A in FIG. 2E, the addition of fuel from the fuel addition valve 46 starts in response to the fuel addition permission flag F (shown in FIG 2E) being set to 1 (allowed), for example in this case, at the time Tl. The fuel addition permission flag F is reset to 0 after being set to 1. After the start of the addition of fuel from the fuel addition valve 46, the fuel is added intermittently from the fuel addition valve 46 according to the fuel addition pulse shown in FIG. 2A in a concentrated manner.

During such an intermittent addition of concentrated fuel from the fuel addition valve 46, for example, each fuel addition time, each fuel addition suspension time, and the number of fuel additions, Once the fuel is added from the fuel addition valve 46 are adjusted so that the air-fuel ratio detected by the air-fuel ratio sensors 31, 32 approaches a target air-fuel AFt ratio. which is lower (richer) than the ratio ai-stoichiometric fuel. More specifically, the fuel addition suspension time (fuel addition interval) is shorter, and the air-fuel ratio detected by the air-fuel ratio sensors 31, 32 is large (poorer) than to the ratio AFt air-fuel target, and the duration of execution of fuel addition is longer plus the air-fuel ratio detected by the sensors 31, 32 air-fuel ratio is large (poorer) compared to AFt air-fuel target ratio. The number of fuel additions increases as the air-fuel ratio detected by the air-fuel ratio sensors 31, 32 is large (poorer) than the target air-fuel AFt ratio.

The intermittent addition of concentrated fuel from the fuel addition valve 46, which begins as described above, continues until the fuel is added to the number of times that has been determined on the basis of the ratio AFt air-fuel target as mentioned above. In the example illustrated in FIG. 2A to 2B, the addition of fuel from the fuel addition valve 46 is completed at time T2.

After the start of the addition of fuel from the fuel addition valve 46, a quantity Q of heat generating fuel is calculated repeatedly based on the operating state of the valve 46. addition of fuel to predetermined control cycles. The quantity Q of heat generating fuel is the amount of fuel added from the fuel addition valve 46 in each control cycle. In the example illustrated in FIG. 2A in FIG. 2E, the length of this control cycle is 16 milliseconds. The quantity Q of the calculated heat generation fuel is accumulated each time according to the formula (2) indicated below: (2) EQ + Q

where "EQ" represents the cumulative value of heat generation fuel Q amounts that have been accumulated to the last 16 millisecond control cycle and "Q" represents the Q amount of heat generating fuel calculated within 16 milliseconds current. As such, the cumulative value EQ of the heat generating fuel quantities representing the total amount of fuel that has been added from the fuel addition valve 46 since the start of the fuel addition (Ti), in other words, the total amount of fuel that has been used since the start of the fuel addition (T1) for an oxidation that generates heat is calculated. Referring to the continuous line in FIG. 2D, the cumulative EQ value of the heat generation fuel quantities, which is calculated as described above, increases significantly in a fuel addition run period A which is the period of time during which the fuel is added from the fuel addition valve 46 (T1 to T2), but it does not increase during a fuel addition suspension period B according to the fuel addition period A.

On the other hand, during the addition of fuel from the fuel addition valve 46, each time the next 16 millisecond control cycle begins, a quantity Qr of fuel required which is the amount of fuel to be added from the fuel addition valve 46 in the next 16 millisecond control cycle, i.e., the amount of fuel required to bring the catalytic bed temperature T of the NOx catalyst to the target temperature Tt of the catalytic bed, is calculated. The quantity Qr of fuel required is calculated on the basis of a difference At between the temperature T of the catalytic bed of the NOx catalyst and the target temperature Tt of the catalytic bed and a flow rate Ga of the exhaust gas from the internal combustion engine. 10. More specifically, the quantity Qr of fuel required is calculated so that the quantity Qr of fuel required is greater plus the temperature T of the catalytic bed of the NOx catalyst is low relative to the target temperature Tt of the catalytic bed and of so that the quantity Qr of fuel required is smaller, the temperature T of the catalytic bed of the NOx catalyst is higher than the target temperature Tt of the catalytic bed. The required quantity Qr of fuel required is accumulated according to the formula (3) given below, (3) EQr + Qr

where "EQr" represents the cumulative value of the Qr values of the required fuel quantities accumulated up to the last control cycle and "Qr" represents the required fuel quantity Qr calculated in the current control cycle. Through this accumulation, the cumulative value EQr of the required fuel quantities, representing the total amount of fuel required since the start of the addition of fuel from the fuel addition valve 46 (T 1) to bring the temperature The average catalytic bed of the NOx catalyst at the target temperature Tt of the catalytic bed is obtained. Since the cumulative value EQr of the required fuel quantities is calculated (updated) as described above, the increase in the cumulative value EQr of the required fuel quantities, which is indicated by the dashed line in FIG. . 2D, is light in comparison with the increase in the cumulative value EQ of the fuel quantities of heat generation, which is indicated by the solid line in FIG. 2D.

When the cumulative value EQr of the required fuel quantities exceeds the cumulative EQ value of the heat generating fuel quantities at time T3, the fuel addition permission flag F is set to 1 (allowed) and the intermittent addition of concentrated fuel from the fuel addition valve 46 begins. At this time, because the fuel of the cumulative value EQ of the amounts of heat generating fuel that have been accumulated since time T1 has previously been fed from the fuel addition valve 46, the cumulative EQ value of the The amount of heat generation fuel is subtracted from the cumulative value EQr of the required fuel quantities, and the cumulative value EQ of the heat generating fuel quantities is cleared (zeroed). Then, the intermittent addition of fuel from the fuel addition valve 46 starts again, i.e., the next fuel addition run period A begins, followed by the period B of fuel addition suspension as mentioned above. As such, the fuel addition period A and the fuel addition suspension period B are repeated during the sulfur poisoning recovery command.

When ordering the recovery of the sulfur poisoning, the higher the temperature T of the catalytic bed of the NOx catalyst is relative to the target temperature Tt of the catalytic bed, the greater the quantity Qr of fuel required, which is the the amount of fuel required to be added from the fuel addition valve 46 in each 16 millisecond control cycle, and therefore the more the cumulative value EQr of the required fuel quantities increases rapidly. This reduces the time required for the cumulative value EQr of the fuel quantities required to reach the cumulative value EQ of the heat generating fuel quantities and thereby shortens the fuel addition suspension period B. Therefore, the average amount of fuel added from the fuel addition valve 46 per unit time (which is the ratio of the length of the fuel addition period A to the length of the period A fuel addition performance + fuel addition suspension period B increases, thus accelerating the increase of the catalyst bed temperature T, which is lower than the target temperature Tt of the catalytic bed, towards target temperature Tt of the catalytic bed.

As the catalytic bed temperature T of the NOx catalyst approaches the target temperature Tt of the catalytic bed, the quantity Qr of fuel required for each control cycle of 16 milliseconds is reduced, whereby the increase in the value cumulative EQr of the required fuel quantities becomes lighter. As such, the time required for the cumulative value EQr of the fuel quantities required to reach the cumulative value EQ of the fuel quantities of heat generation becomes longer, whereby the period B of fuel addition suspension becomes longer. . As a result, the average amount of fuel added from the fuel addition valve 46 per unit time decreases. That is, thereby reducing the average amount of fuel supply, it is possible to prevent the catalytic bed temperature T of the NOx catalyst from excessively increasing beyond the target temperature Tt of the catalytic bed.

As described above, as the length of the fuel addition suspension period B changes according to the difference between the catalyst bed T temperature of the NOx catalyst and the target temperature Tt of the catalyst bed as described herein. above, the catalyst bed temperature T of the NOx catalyst fluctuates, for example, as indicated by the solid line in FIG. 2C, so that the center of fluctuation of the temperature T of the catalytic bed of the NOx catalyst (the average temperature T of the catalytic bed) coincides with the target temperature Tt of the catalytic bed. In this respect, during the sulfur poisoning recovery command, the NOx catalyst is fed with unburned fuel components to bring the temperature T of the catalyst to the target temperature Tt of the catalytic bed which increases continuously until at 700 ° C, whereby the catalyst bed T temperature of the NOx catalyst increases to about 700 ° C.

When the intermittent addition of concentrated fuel from the fuel addition valve 46 is effected in the fuel addition period A in a state where the temperature of the NOx catalyst is previously raised after the increase. from the average temperature T of the catalytic bed of the NOx catalyst to the target temperature Tt of the catalytic bed as described above, the fuel added from the fuel addition valve 46 creates, around the NOx catalyst, a fuel-rich combustion atmosphere having an air-fuel ratio equal to the target Aft air-fuel ratio which is lower (richer) than the stoichiometric air-fuel ratio. The fuel-rich combustion atmosphere thus created around the NOx catalyst facilitates the removal of the sulfur components from the NOx catalyst and their subsequent reduction. Thus, as the fuel addition period A and the fuel addition suspension period B are repeated, sulfur components (eg, SOx) are removed from the NOx catalyst and by the This reduces the amount of sulfur components absorbed in the NOx catalyst, thereby reducing the NOx storage capacity of the NOx. Sulfur poisoning recovery control is terminated when the amount S of the sulfur poisoning representing the amount of sulfur components absorbed in the NOx catalyst is reduced to the aforementioned target value ("0" in this example) .

According to formula (1), the amount S of the sulfur poisoning is calculated (estimated) by taking into account the quantity SD of newly removed sulfur components representing the amount of sulfur components removed from the NOx catalyst when ordering recovery of sulfur poisoning. However, the amount SD of newly removed sulfur components may be different from the amount of sulfur components that have actually been removed from the NOx catalyst. That is, the amount of SD newly removed sulfur components is calculated as an amount of sulfur components that are theoretically removed from the NOx catalyst when ordering recovery of sulfur poisoning. However, in reality, some sulfur components are not removed by sulfur poisoning recovery control and remain in the NOx catalyst. More specifically, even though the NOx catalyst has been heated and the atmosphere around the NOx catalyst has been enriched with fuel, sulfur components can not be removed from the NOx catalyst at parts of the NOx catalytic converter. where the temperature of the catalytic bed does not increase much, such as the upstream end portion of the NOx catalytic converter.

As such, the amount SD of newly removed sulfur components, which is used to calculate the amount S of sulfur poisoning, can deviate from the amount of sulfur components actually removed from the NOx catalyst by the amount of sulfur compounds. Sulfur components that are left in the NOx catalyst as described above. Specifically, the amount of SD of newly removed sulfur components may be smaller than the amount of the sulfur components that have actually been removed from the NOx catalyst when controlling sulfur poisoning recovery, and such a difference in the amount SD of newly removed sulfur components relative to the amount of the sulfur components actually removed causes a deviation of the amount S of the sulfur poisoning which is calculated from the amount of SD newly removed sulfur components.

Therefore, in a case where the amount S of the calculated (estimated) sulfur poisoning is smaller than the amount S of the accumulated sulfur poisoning, when the sulfur poisoning recovery control is completed in response with the amount S of the calculated (estimated) sulfur poisoning reaching 0, the amount S of the cumulative sulfur poisoning is always greater than 0, whereby some sulfur components are still left in the NOx catalyst. As the NOx catalyst continues to be used, the amount of sulfur components left in the NOx catalyst increases and hence the deviation of the amount S of the sulfur poisoning calculated from the S amount of effective sulfur poisoning becomes more important, increasing the amount of sulfur components left in the NOx catalyst and the end of sulfur poisoning recovery control. The cases (1) to (3) described in "Description of the State of the Art" are typical cases where a relatively large amount of sulfur components is left in the NOx catalyst for the reason mentioned above. As such, in a state where the amount of sulfur components left in the NOx catalyst is large, even when the sulfur poisoning recovery control has been completed, the NOx storage capacity of the NOx catalyst is still low due to the sulfur components left in the NOx catalyst as described above, and therefore NOx emissions from the internal combustion engine 10 can increase.

However, this problem can be solved by allowing more effective removal of the sulfur components of the NOx catalyst by further increasing the average temperature of the catalyst bed NOx catalyst temperature T when controlling the sulfur poisoning recovery. and this can be done by adjusting the target temperature Tt of the catalyst bed to above 700 ° C. That is, by allowing more effective removal of the sulfur components of the NOx catalyst, the amount of sulfur components left in the NOx catalyst can be smaller than in a normal state, in other words the amount S of the calculated sulfur poisoning may be closer to the amount S of the effective sulfur poisoning. However, when the target temperature Tt of the catalyst bed for the sulfur poisoning recovery control is high as mentioned above, the catalyst bed T temperature of the NOx catalyst can become excessively high, and it can cause deterioration. thermal NOx catalyst, increasing NOx emissions from the internal combustion engine 10.

Next, a sulfur poisoning recovery control execution routine, which is executed to avoid the problem described above, will be described in detail with reference to the flow chart of FIG. 3. This sulfur poisoning recovery control execution routine is executed repeatedly by the electronic control unit 50 at given time intervals as an interrupt.

In this subroutine, the probability that the amount of sulfur components left in the NOx catalyst is large is determined, if so, a high temperature sulfur poisoning recovery control is performed. In the recovery control of high temperature sulfur poisoning, the temperature of the catalytic bed increases more than it is in the sulfur poisoning recovery control described above (hereinafter referred to as by "usual control of sulfur poisoning recovery" to be distinguished from the high temperature sulfur poisoning recovery control). That is, by executing the sulfur poisoning recovery command at high temperature, it is possible to reduce the amount of sulfur components left in the NOx catalyst and thus suppress an increase in sulfur emissions. NOx from the internal combustion engine 10, which is caused by the sulfur components left in the NOx catalyst, without causing an excessive increase in the temperature of the NOx catalyst.

First, in the sulfur poisoning recovery control execution routine, a cumulative value Et of the high temperature duration and its standard value Bh are calculated (S 101, S102). The cumulative value Et of the high temperature duration and the standard value Bh are used in determining whether it is likely that the amount of sulfur components left in the NOx catalyst is large.

More specifically, in step S101, my cumulative value Et of the high temperature time is calculated, for example, by accumulating the time during which the catalyst bed T temperature of the NOx catalyst is above 600 ° C. Since the cumulative value Et of the high temperature duration corresponds to the degree of thermal deterioration of the NOx catalyst, the cumulative value Et of the high temperature duration is small when said degree is low, and increases as said degree increases.

In step S102, the standard value Bh corresponding to the current mileage of the motor vehicle is calculated. The mileage of the motor vehicle corresponds to the total running time of the internal combustion engine 10 (hereinafter referred to as "corresponding value of the total running time of the engine) and the mileage of the motor vehicle increases as the The total operating time of the internal combustion engine 10 increases.The standard value Bh is calculated, for example, using a card.

More specifically, a relationship between the mileage of the motor vehicle and the standard value Bh is empirically determined, and a map describing the determined relationship is formulated and stored in the ROM of the electronic control unit 50. In this case, the standard value Bh is calculated by applying the current mileage of the motor vehicle to the card. The calculated standard value Bh increases as the mileage of the motor vehicle increases, for example, as indicated by the dashed line in FIG. 4.

After calculating the cumulative value And the high temperature duration and the standard value Bh as described above, a request to execute the sulfur poisoning recovery command was made (S 103). This request is made when the amount S of the sulfur poisoning calculated by the formula (1) is greater than or equal to a threshold while all the predetermined conditions for performing the sulfur poisoning recovery command are satisfied. If "YES" is obtained in step S 103, then it is determined whether the cumulative value Et of the high temperature duration is less than or equal to the standard value Bh (S 104). This determination determines whether it is likely that the amount of sulfur components left in the NOx catalyst is large.

In the case of a driver who drives a motor vehicle only for a short time, the temperature of the exhaust gas from the internal combustion engine 10 does not increase much, and therefore the temperature T of the catalytic catalyst bed NOx tends to stay low. In such a case, the probability of executing the sulfur poisoning recovery command is relatively small, and even if the latter is executed, it is relatively difficult to increase the temperature T of the catalytic bed of the NOx catalyst during of the sulfur poisoning recovery command. As a result, the rate of removal of sulfur components removed from the NOx catalyst decreases, leaving a large amount of sulfur components in the NOx catalyst. In particular, in a case where the fuel having a higher sulfur concentration than a standard sulfur concentration (N concentration in sulfur in this example) is used, the amount of sulfur components that enter the NOx catalyst is more when the fuel with the standard sulfur concentration is used, and therefore a greater amount of sulfur components is absorbed to the NOx catalyst and so a larger amount of sulfur components is left in the NOx catalyst.

As such, in a case where the driver often drives the motor vehicle only for a short time, the increase in the cumulative value and the duration of the high temperature is slow, and therefore the cumulative value and the duration of the elevated temperature increases as indicated by the solid line in FIG. 4 as the mileage of the motor vehicle increases. In this case, the possibility that the cumulative value Et of the determined high temperature duration is less than or equal to the standard value Bh in step S104 in the routine shown in FIG. 3 is relatively large. If it is determined in step S104 that the cumulative value Et of the high temperature duration is greater than the standard value Bh, this indicates that it is unlikely that the amount of sulfur components left in the catalyst NOx is large, and therefore the usual control for sulfur poisoning recovery is performed (S 106). On the other hand, if it is determined in step S104 that the cumulative value Et of the high temperature duration is less than or equal to the standard value Bh, this indicates that it is likely that the amount of Sulfur components left in the NOx catalyst are large, and therefore, high temperature sulfur poisoning recovery control is performed (S 105) in place of the usual sulfur poisoning recovery control. .

In the high temperature sulfur poisoning recovery control, the maximum temperature of the target temperature Tt of the catalytic bed is greater than 700 ° C, i.e., the maximum temperature of the target temperature Tt of the catalytic bed used in the usual control of recovery of sulfur poisoning. When ordering recovery of sulfur poisoning at high temperature, the target temperature Tt of the catalytic bed increases in rate in the same manner as the usual control of recovery of sulfur poisoning. Then, even if the target temperature Tt of the catalytic bed reaches 700 ° C. (the maximum temperature of the target temperature Tt of the catalytic bed in the usual sulfur poisoning recovery control), the target temperature Tt of the catalytic bed continues to increase. increase above 700 ° C provided that the average temperature T of the catalytic bed of the NOx catalyst is not greater than 700 ° C. The amount by which the target temperature Tt of the catalytic bed increases above 700 ° C during the high temperature sulfur poisoning recovery control is sufficiently small to prevent heat damage (heat damage) at the high temperature. NOx catalytic converter 25, and said amount is larger plus a difference KA of the cumulative value and the high temperature time compared to the standard value Bh (refer to FIG 4) is large. As the target temperature Tt of the catalyst bed increases in the recovery control of high temperature sulfur poisoning, the average temperature T of the catalytic bed of the NOx catalyst is higher than it is in the control. The usual sulfur poisoning recovery method allows for more efficient removal of sulfur components from the NOx catalyst, and therefore the amount of sulfur components left in the NOx catalyst decreases.

Meanwhile, the high temperature sulfur poisoning recovery command and the usual sulfur poisoning recovery control are both terminated when the S amount of sulfur poisoning is reduced to the target value ( 0 in this example). Since the execution of the sulfur poisoning recovery command at high temperature facilitates the increase of the cumulative value And the high temperature duration, the cumulative value And the high temperature duration corresponding to the current mileage of the motor vehicle is close to the standard value Bh (indicated by the dashed line in Figure 4) at the end of the high temperature sulfur poisoning recovery command.

According to the exemplary embodiment described above, the following advantages are obtained.

(1) The high temperature sulfur poisoning recovery control is performed to allow more effective removal of sulfur components from the NOx catalyst only when the cumulative value Et of the high temperature duration is less than or equal to the Bh standard value, in other words, only in a case where the rate of removal of sulfur components that are removed from the NOx catalyst by the sulfur poisoning recovery control is low due to the way of driving the and so it is likely that the amount of sulfur components left in the sulfur catalyst is large. Thus, the amount of sulfur components left in the NOx catalyst can be reduced by the recovery control of high temperature sulfur poisoning. As such, through the recovery control of sulfur poisoning at high temperature, the amount of sulfur components left in the NOx catalyst is reduced while avoiding an excessive increase in the temperature T of the catalytic bed of the catalyst. NOx, and thus it is possible to suppress an increase in NOx emissions from the internal combustion engine that is caused by the sulfur components left in the NOx catalyst.

(2) When the cumulative value And the high temperature duration becomes lower than the standard value Bh by increasing the gap KA of the cumulative value And the high temperature duration compared to the standard value Bh, the sulfur components left in the NOx catalyst thereby increase. In this state, even though the catalytic bed temperature T of the NOx catalyst increases by feeding the NOx catalyst into unburned fuel components in the sulfur poisoning recovery control, the sulfur components left in the catalyst of NOx NOx may not be removed. In other words, it can be said that this state is a state in which it is unlikely that the catalyst bed T temperature of the NOx catalyst will increase excessively when the catalyst bed T temperature of the NOx catalyst increases by recovery control of sulfur poisoning at high temperature. Taking this into consideration, when ordering recovery of high temperature sulfur poisoning, when the cumulative value Et of the high temperature duration becomes lower than the standard value Bh, the maximum temperature of the target temperature Tt of the Catalytic bed is higher, the more the difference KA of the cumulative value And the high temperature time compared to the standard value Bh is large, and the higher the temperature T of the catalytic bed of the NOx catalyst increases. As such, in the high temperature sulfur poisoning recovery control, the prevention of an excessive increase in catalyst bed NOx catalyst temperature T and effective removal of sulfur components from the NOx catalyst. both can be done in desirable ways. (3) In a case where the sulfur concentration in the fuel used is higher than the standard value (sulfur concentration N), a relatively large amount of sulfur components tends to be left in the NOx catalyst. However, even such a case, the high temperature sulfur poisoning recovery control effectively removes the sulfur components left in the NOx catalyst while avoiding an excessive increase in the temperature T of the catalyst bed.

Next, the second exemplary embodiment of the invention will be described with reference to FIG. 5 to FIG. 7. The second exemplary embodiment is different from the first exemplary embodiment in the manner of determining whether it is likely that the amount of sulfur components left in the NOx catalyst is large. More specifically, in the second exemplary embodiment, if the probability that the amount of sulfur components left in the NOx catalyst is large is determined based on a total amount of ESU of introduced sulfur representing the total amount of components. sulfur entering the NOx catalyst since the start of operation of the internal combustion engine 10 and its standard value Bsu corresponding to the current mileage of the motor vehicle.

The graph of FIG. 5 illustrates the relationship between the mileage of the motor vehicle, the standard value Bsu, and the total amount ESU of sulfur introduced. The standard value Bsu increases as the mileage of the motor vehicle increases as indicated by the solid line in FIG. 5, and the total amount ESU introduced sulfur also increases as the mileage of the motor vehicle increases. However, in a case where the driver is used to driving a motor vehicle in a manner that consumes a large amount of fuel, such as the rapid acceleration of the motor vehicle, the amount of sulfur components that enter the vehicle NOx catalyst as the fuel is consumed (SU amount of sulfur introduced) is relatively large, and therefore a relatively large amount of sulfur components is left in the NOx catalyst. In particular, in a case where the sulfur concentration in the fuel used (N concentration in sulfur) is higher than the standard sulfur concentration, a large amount of sulfur components tends to enter the NOx catalyst in comparison with the moment when fuel having the standard sulfur concentration is used. Therefore, in such a case, a larger amount of sulfur components is absorbed to the NOx catalyst, resulting in a considerable increase in the amount of sulfur components left in the NOx catalyst. When the driver drives the motor vehicle in a manner that consumes fuel, as indicated by the solid line in FIG. 5, the total amount ESU of sulfur introduced increases at a relatively high rate as the mileage of the motor vehicle increases.

As such, when the total quantity ESU of sulfur introduced (indicated by the continuous line in FIG 5) is greater than or equal to the standard value Bsu corresponding to the current mileage of the motor vehicle (indicated by the dotted line in the 5), it is likely that the amount of sulfur components left in the NOx catalyst is large, and therefore the high temperature sulfur poisoning recovery control is performed provided that the request to execute said order has been made.

The flowchart of FIG. 6 illustrates the sulfur poisoning recovery command execution routine of the second exemplary embodiment. This routine is also repeatedly executed by the electronic control unit 50 as an interruption, for example, at corners of the crankshaft.

In this subroutine, firstly, the amount SU of newly absorbed sulfur components is accumulated each time it is calculated (each time the fuel is injected), by which the total amount ESU of sulfur introduced represents the cumulative value of the amount SU of newly absorbed sulfur components is calculated (S201). Then, the standard value Bsu corresponding to the current mileage of the motor vehicle is calculated. The calculated standard value Bsu increases as indicated by the dashed line in FIG. 5 as the mileage of the motor vehicle increases. After calculating the total quantity ESU of sulfur introduced and the standard value Bsu, it is then determined whether the request to execute the sulfur poisoning recovery command has been made (S203). If "YES" is obtained in step 5203, it is then determined whether the total quantity ESU of sulfur introduced is greater than or equal to the standard value Bsu (S204). This determination is made to determine whether it is likely that the amount of sulfur components left in the NOx catalyst is large.

If it is determined in step 5204 that the total quantity ESU of sulfur introduced is lower than the standard value Bsu, this indicates that it is unlikely that the amount of sulfur components left in the NOx catalyst will be big. Therefore, in this case, the usual control of sulfur poisoning recovery is performed (S206). On the other hand, if it is determined in step S204 that the total amount ESU of sulfur introduced is greater than or equal to the standard value Bsu, it is likely that the amount of sulfur components remaining in the catalyst NOx is great. Therefore, in this case, the high temperature sulfur poisoning recovery command is executed (S205).

When ordering recovery of sulfur poisoning at high temperature, the target temperature Tt of the catalytic bed increases at a temperature above 700 ° C, that is to say, the maximum temperature of the target temperature Tt of catalytic bed in the usual control of recovery of sulfur poisoning. The amount by which the target temperature Tt of the catalytic bed increases above 700 ° C during the high temperature sulfur poisoning recovery control is sufficiently small to prevent heat damage (heat damage) at the high temperature. NOx catalytic converter 25, and said amount is larger, the greater the Ka difference of the total amount of sulfur introduced from the standard value Bsu (see FIG. Thus, as the target temperature Tt of the catalyst bed increases, the average temperature T of the catalytic bed of the NOx catalyst increases accordingly, allowing more effective removal of sulfur components from the NOx catalyst and thus reducing the amount of components of the catalyst. sulfur left in the NOx catalyst.

The high temperature sulfur poisoning recovery command and the usual sulfur poisoning recovery control are both terminated when the sulfur poisoning amount S is reduced to the target value (0 in this example ). Since the execution of the sulfur poisoning recovery command at high temperature reduces the amount of sulfur components left in the NOx catalyst, preferably, the frequency of execution of the recovery control of the Sulfur poisoning at high temperature is accordingly reduced in order to prevent an excessive increase in the temperature T of the catalytic bed of the NOx catalyst. For this reason, in an introduced total sulfur amount correction routine illustrated in FIG. 7, when the recovery command for sulfur poisoning at high temperature has been completed (S301: YES), the total quantity ESU of sulfur introduced is corrected to the standard value Bsu (S302). At this time, the total amount of sulfur introduced is corrected by an optimal amount which has been empirically determined in advance. Through this correction, the total quantity ESU of sulfur introduced corresponding to the current mileage of the motor vehicle changes to the standard value Bsu, reducing the possibility that the total quantity ESU of sulfur introduced will be greater than or equal to the standard value Bsu and reducing thus the chances of an excessive increase in the temperature T of the catalytic bed of the NOx catalyst described above.

According to the second exemplary embodiment of the invention, the following advantages can be obtained in addition to the advantages (1) to (3) of the first exemplary embodiment.

(4) The high temperature sulfur poisoning recovery control is performed to allow more effective removal of sulfur components from the NOx catalyst only when the total amount ESU of sulfur introduced is greater than or equal to the standard value Bsu in other words, when the fuel consumption of the internal combustion engine 10 (the quantity SU of sulfur introduced) is important, due, for example, to the conduct of the driver and therefore the amount of sulfur components. left in the NOx catalyst is large. Thus, the amount of sulfur components left in the NOx catalyst can be reduced by the recovery control of high temperature sulfur poisoning. As such, through the recovery control of sulfur poisoning at high temperature, the amount of sulfur components left in the NOx catalyst is reduced while avoiding an excessive increase in the temperature T of the catalytic bed of the catalyst. NOx, and thus it is possible to suppress an increase in NOx emissions from the internal combustion engine that is caused by the sulfur components left in the NOx catalyst.

(5) When the total amount ESU of sulfur introduced is greater than the standard value Bsu, the greater the difference KA of the total quantity ESU of sulfur introduced compared to the standard value Bsu, the greater the quantity of sulfur components. left in the NOx catalyst is large. In this state, even though the catalytic bed temperature T of the NOx catalyst increases by feeding the NOx catalyst into unburned fuel components in the sulfur poisoning recovery control, the sulfur components left in the catalyst of NOx NOx may not be removed. In other words, it can be said that this state is a state in which it is unlikely that the catalyst bed T temperature of the NOx catalyst will increase excessively when the catalyst bed T temperature of the NOx catalyst increases by recovery control of sulfur poisoning at high temperature. Taking this into consideration, when ordering the recovery of sulfur poisoning at high temperature, when the total amount ESU of sulfur introduced becomes greater than the standard value Bsu, the maximum temperature of the target temperature Tt of the catalytic bed is larger, the greater the difference KA of the total amount ESU of sulfur introduced compared to the standard value Bsu is large, and the higher the temperature T of the catalytic bed of the NOx catalyst increases. As such, the control of recovery of sulfur poisoning at high temperature, the prevention of an excessive increase in the temperature T of the catalytic bed of the NOx catalyst and the effective removal of sulfur components from the NOx catalyst can both be made in a desirable way. (6) Since execution of the sulfur poisoning recovery command at high temperature further reduces the amount of sulfur components left in the NOx catalyst, preferably the frequency of execution of the control of Recovery of sulfur poisoning at high temperature is reduced to prevent an excessive increase in the catalyst bed T temperature of the NOx catalyst. By taking this into consideration, the total quantity of sulfur introduced is corrected to the standard value Bsu at the end of the recovery command for high temperature sulfur poisoning. Through this correction, the total quantity ESU of sulfur introduced corresponding to the current mileage of the motor vehicle changes to the standard value Bsu, reducing the possibility that the total quantity ESU of sulfur introduced will be greater than or equal to the standard value Bsu and reducing thus the chances of an excessive increase in the temperature T of the catalytic bed of the NOx catalyst described above.

The above exemplary embodiments of the invention can be modified as follows.

(a) In the first and second exemplary embodiments, the high temperature sulfur poisoning recovery control can be performed when the NOx catalyst has deteriorated due to heat and residual sulfur components. In this case, it can be determined whether the NOx catalyst has deteriorated due to heat and residual sulfur components based on the average temperature T of the catalytic bed of the NOx catalyst during the increase of the temperature T of the catalytic bed, for example, during the execution of the usual sulfur poisoning recovery command.

The graph of FIG. Figure 8 illustrates the temperature of the catalyst bed throughout the NOx catalytic converter from the upstream end to the downstream end compared with the case where the aforementioned deterioration of the NOx catalyst occurred (indicated by the solid line) and the case where said deterioration has not occurred (indicated by the dashed line). As can be seen from the graph of FIG. 8, in a case where the deterioration of the NOx catalyst occurred, even if an attempt was made to increase the temperature T of the catalytic bed of the NOx catalyst by performing, for example, the usual control of recovery of the poisoning at In the case of sulfur, the catalyst bed T temperature of the NOx catalyst does not increase significantly at the respective positions of the NOx catalytic converter between the corresponding upstream and downstream ends. Therefore, it can be determined that the degree of deterioration of the NOx catalyst due to heat or residual sulfur components is important if the average temperature T of the catalytic bed of the NOx catalyst is always lower than the target temperature Tt of the catalytic bed. by a predetermined reference amount while the catalyst bed T temperature of the NOx catalyst increases, for example, by sulfur poisoning recovery control.

Thus, by executing the sulfur poisoning recovery command at high temperature only when it is determined that the degree of deterioration of the NOx catalyst due to heat and residual sulfur components is significant, an excessive increase in NOx catalyst temperature can be prevented more reliably.

(b) In the second exemplary embodiment, the mileage of the motor vehicle can be corrected to be larger at the end of the high temperature sulfur poisoning recovery command. Thus, the total quantity ESU of sulfur introduced corresponding to the mileage of the motor vehicle can be corrected towards the standard value Bsu. In this case, the same effect as the advantage (6) of the second exemplary embodiment can be obtained. (c) In the second exemplary embodiment, the cumulative value of the accumulated fuel injection command value Qf1 since the start of operation of the internal combustion engine 10 (cumulative fuel injection amount value) can be used instead of the total amount ESU of sulfur introduced. In this case, said cumulative value can be considered as an example of "corresponding value of the total quantity of sulfur introduced". In addition, the number of times that the sulfur poisoning recovery command has been executed since the start of the operation of the internal combustion engine 10 may be used instead of the total quantity ESU of sulfur introduced. In this case, it can be considered that said number is an example of "value indicating the total amount of sulfur introduced".

(d) In the first and second exemplary embodiments, the amount by which, in the recovery control of high temperature sulfur poisoning, the target temperature Tt of the catalyst bed increases beyond the maximum temperature of the target temperature Tt of the catalytic bed in the usual sulfur poisoning recovery control, is not necessarily greater as the gap KA increases. For example, said amount can be set to an optimum value (constant value) that has been empirically determined in advance. (e) in the first and second exemplary embodiments, the total operating time since the start of operation of the internal combustion engine 10 may be used instead of the mileage of the motor vehicle. In addition, the cumulative value of the rotational speed of the internal combustion engine 10 since the start of operation of the internal combustion engine 10 may be used instead of the mileage of the motor vehicle.

In this case, it can be considered that said cumulative value is an example of "value indicating the total duration of operation of the engine" corresponding to the total operating time of the internal combustion engine 10 since the beginning of its operation. (f) The NOx catalyst can be supplied with unburned fuel components by injecting fuel from the injectors 40 on an exhaust stroke.

While the invention has been described with reference to the corresponding exemplary embodiments, it should be understood that the invention is not limited to the constructions or embodiments described. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. On the other hand, while the various elements of the disclosed invention are shown in various exemplary combinations and configurations, other combinations and configurations, including more, less, or only a single element, are also within the scope of the attached claims.

Claims (14)

An exhaust gas purifying apparatus for an internal combustion engine (10), having an absorption-reduction type NOx catalyst provided in an exhaust system of the internal combustion engine (10) and an engine exhaust system. estimate (50) for estimating a quantity of sulfur poisoning representing the amount of sulfur components absorbed in the NOx catalyst, wherein when the amount of sulfur poisoning is greater than or equal to a threshold, the components of Sulfur are removed from the NOx catalyst by performing a sulfur poisoning recovery control in which a temperature of the catalyst bed is raised to a target temperature of the catalyst bed by supplying the NOx catalyst to unburned fuel components while carrying an atmosphere around the NOx catalyst in a state for fuel-rich combustion, and control of recovery of poisoning at sulfur is terminated when the amount of sulfur poisoning becomes less than a predetermined value which is below the threshold, the exhaust purification apparatus being characterized by comprising: calculating means (50) for cumulative value for calculating a cumulative value of the high temperature duration, such as a value indicating the degree of thermal deterioration of the NOx catalyst, which is a cumulative length of time during which the temperature of the NOx catalyst is greater than a predetermined temperature; a standard value calculating means (50) for calculating a standard value of the cumulative value of the high temperature duration, which corresponds to a current total running time of the internal combustion engine (10), on the basis of a total running time of the engine indicating the total running time of the internal combustion engine (10); and control means (50) for performing high temperature sulfur poisoning recovery control in which the temperature of the catalyst bed is increased to a target temperature of the catalyst bed which is above the target temperature of the bed according to the sulfur poisoning recovery command, when the cumulative value of the high temperature duration calculated by the cumulative value calculation means (50) is less than or equal to the standard value calculated by the calculation means (50). ) of standard value. An exhaust purification apparatus according to claim 1, wherein the higher the cumulative value of the high temperature time than the standard value, the more control means (50) makes the target temperature of the bed catalytic, used in the control of recovery of sulfur poisoning at high temperature, high. An exhaust purification apparatus according to claim 1, wherein the control means (50) increases the target temperature of the catalyst bed used in the high temperature sulfur poisoning recovery control at an optimum temperature. predetermined. An exhaust purification apparatus according to any one of claims 1 to 3, wherein the larger the value indicating the total running time of the engine, the larger the standard value of the cumulative value of the temperature duration. high increases. An exhaust purification apparatus for an internal combustion engine (10), having an absorption-reduction type NOx catalyst provided in an exhaust system of the internal combustion engine (10) and means for estimate (50) for estimating a quantity of sulfur poisoning representing the amount of sulfur components absorbed in the NOx catalyst, wherein when the amount of sulfur poisoning is greater than or equal to a threshold, components of Sulfur are removed from the NOx catalyst by performing a sulfur poisoning recovery control in which a temperature of the catalyst bed is raised to a target temperature of the catalyst bed by supplying the NOx catalyst to unburned fuel components while by carrying an atmosphere around the NOx catalyst to a state for fuel-rich combustion, and the control of recovery from the poisoning to the sulfur re is complete when the amount of sulfur poisoning becomes less than a predetermined value which is below the threshold, the exhaust purification apparatus being characterized by comprising: calculating means (50) for amount of sulfur introduced to calculate a total quantity of sulfur introduced indicating the total amount of sulfur components circulating in the NOx catalyst; a standard value calculating means (50) for calculating a standard value of the total quantity of sulfur introduced, which corresponds to a current total running time of the internal combustion engine (10), on the basis of a total duration of engine operation indicating the current total running time of the internal combustion engine (10); and control means (50) for performing high temperature sulfur poisoning recovery control in which the temperature of the catalyst bed is increased to a target temperature of the catalyst bed which is above the target temperature of the bed according to the sulfur poisoning recovery command, when the total quantity of sulfur introduced calculated by the sulfur amount calculation means (50) introduced is greater than or equal to the standard value calculated by the calculation means (50). ) of standard value. The exhaust gas purification apparatus according to claim 5, wherein the value of the total quantity of sulfur introduced is larger than the standard value, plus the control means (50) makes the target temperature of the bed catalytic, used in the control of recovery of sulfur poisoning at high temperature, high. An exhaust gas purification apparatus according to claim 5, wherein the control means (50) increases the target temperature of the catalyst bed used in the high temperature sulfur poisoning recovery control at an optimum temperature. predetermined. An exhaust purification apparatus according to any one of claims 5 to 7, wherein the larger the value indicating the total operating time of the engine, the more the standard value of the total amount of sulfur introduced increases. An exhaust purification apparatus according to any one of claims 5 to 8, further comprising correction means (50) for correcting the total amount of sulfur entering the engine which corresponds to the total operating time of the engine to the engine. standard value, when the recovery command for high temperature sulfur poisoning is performed. An exhaust purification apparatus according to any one of claims 5 to 9, wherein the smaller the amount of sulfur components left in the NOx catalyst, the more the correction means (50) reduces the frequency Execution of the recovery command for sulfur poisoning at high temperature. An exhaust purification apparatus according to any of claims 5 to 8, further comprising correction means (50) for correcting the total amount of sulfur introduced which corresponds to the total operating time of the engine to the standard value, when the recovery command for high temperature sulfur poisoning is executed. An exhaust purification apparatus according to any one of claims 1 to 11, wherein: the control means (50) determines whether the degree of deterioration of the NOx catalyst due to heat and sulfur components left in the NOx catalyst is large on the basis of the temperature of the catalyst bed when the temperature of the catalyst bed is or has been increased; and the control means (50) performs the high temperature sulfur poisoning recovery control if it is determined that the degree of deterioration of the NOx catalyst is large. An exhaust purification apparatus according to any one of claims 1 to 12, wherein the value indicating the total operating time of the engine is calculated on the basis of a total mileage of a vehicle incorporating the engine. internal combustion engine (10) or on the basis of a cumulative value of rotational speed of the internal combustion engine (10). An exhaust purification apparatus according to any one of claims 1 to 13, wherein increasing the temperature of the catalytic bed at a target temperature of catalytic dulit includes increasing the average temperature of the catalytic bed in temperature. target of the catalytic bed.