Exhaust gas purification device for an internal combustion engine

Abstract

A situation in which exhaust emissions are suppressed due to NOx being flushed from an NSR catalyst can be minimized. An exhaust gas purification device for an internal combustion engine operating in lean-burn mode includes: an NSR catalyst; a downstream catalyst located on the NSR catalyst; a reducing agent supply device; an air-fuel ratio control unit to implement a rich-peak procedure; and a supply control unit to control the supply of reducing agent to the downstream catalyst, wherein, in cases where the temperature of the NSR catalyst falls below a predetermined temperature for at least part of a period, the supply control unit implements the supply control according to the current rich-peak procedure.and a NOx storage quantity calculation unit to calculate a NOx storage quantity in the NSR catalyst; wherein the feed control unit controls such that, in cases where the NOx storage quantity is the same, a feed quantity of the reducing agent in the feed control becomes larger when a period during which the temperature of the NSR catalyst is lower than the predetermined set temperature becomes longer.

Description

Technical field

[0001] The present invention relates to an exhaust gas purification device for an internal combustion engine. Description of the state of the art

[0002] A technology is known in which a NOx storage reduction catalyst (sometimes referred to below as an "NSR catalyst") is arranged as an exhaust gas purification catalyst in the exhaust manifold of an internal combustion engine operating in lean-burn mode, where the air-fuel ratio of the mixture is set to a leaner air-fuel ratio higher than the stoichiometric air-fuel ratio. The NSR catalyst has the function of storing NOx in the exhaust gas when the ambient air-fuel ratio is lean, and the function of reducing the stored NOx when the ambient air-fuel ratio is richer than the stoichiometric air-fuel ratio, provided a reducing agent is present.In this description, it should be noted that the term "storage" is used as such, including a mode of "adsorption".

[0003] Then, in the internal combustion engine equipped with such an NSR catalyst, the NOx stored in the NSR catalyst is reduced by implementing a rich-peak process, which temporarily changes the air-fuel ratio of the exhaust gas from a lean air-fuel ratio, which is higher than the stoichiometric air-fuel ratio, to a rich air-fuel ratio, which is lower than the stoichiometric air-fuel ratio.

[0004] In JP 2005-163590 A, a technology is disclosed in which a fat peak process is carried out when a quantity of NOx stored by a NOx storage catalyst reaches a predetermined quantity.

[0005] Additionally, JP 2016-186239 A discloses a technology in which, in an exhaust gas purification control device which performs a rich peak operation in cases where a NOx quantity stored in an NSR catalyst exceeds a first threshold, the rich peak operation is performed at an air-fuel ratio of the exhaust gas which is leaner than in the case where the NOx quantity is less than or equal to the second threshold. Summary

[0006] When the fat-peak process is carried out, the NOx stored in the NSR catalyst (the stored NOx) is released once from a storage material within the NSR catalyst and reacts with the reducing agent, such as CO, HC, etc., in the presence of a noble metal catalyst within the NSR catalyst. As a result, NOx is reduced to N2 within the NSR catalyst. It has been shown that even if the amount of stored catalyst (the NOx storage quantity) and the temperature of the NSR catalyst are the same at the time the fat-peak process is carried out, the ease of release when the stored NOx is released from the storage material via the fat-peak process changes due to the storage mode of the NOx within the NSR catalyst.

[0007] Additionally, some of the NOx released from the storage material by the fat-peak process can flow out of the NSR catalyst without being reduced by the reducing agent. In other words, even when the fat-peak process is carried out, some of the stored NOx can be flushed out of the NSR catalyst without being reduced.

[0008] Here, by providing a downstream catalyst capable of reducing NOx, the NOx flushed from the NSR catalyst can be further reduced by the downstream catalyst. However, as described above, given that the ease of releasing the stored NOx from the storage material changes due to the storage mode of the NOx in the NSR catalyst, even if the NOx storage quantity and the temperature of the NSR catalyst are the same at the time the fat-peak process is carried out, the amount of NOx flushed from the NSR catalyst by the fat-peak process (the NOx flushing quantity) can change due to the storage mode of the NOx in the NSR catalyst.If the NOx flushed from the NSR catalyst is reduced by the downstream catalyst, there is a risk that exhaust emissions may worsen if a difference in the NOx flushing quantity due to the NOx storage mode is not taken into account.

[0009] The present invention was made in view of the aforementioned problems and aims to prevent, as far as possible, the occurrence of a situation in which exhaust emissions worsen due to NOx flushed out of an NSR catalyst.

[0010] The present invention relates to an exhaust gas purification device for an internal combustion engine which operates in lean-burn mode, comprising: a first NOx storage reduction catalyst arranged in an exhaust gas channel of the internal combustion engine; a post-stage catalyst arranged in the exhaust gas channel downstream of the first NOx storage reduction catalyst and reducing NOx in an exhaust gas by means of a supplied reducing agent; a reducing agent supply device arranged in the exhaust gas channel between the first NOx storage reduction catalyst and the post-stage catalyst and supplying the reducing agent into the exhaust gas channel;an air-fuel ratio control unit configured to perform a rich-peak procedure to temporarily change the air-fuel ratio of exhaust gas flowing into the first NOx storage reduction catalyst from a lean air-fuel ratio higher than a stoichiometric air-fuel ratio to a rich air-fuel ratio lower than the stoichiometric air-fuel ratio; a feed control unit configured to perform feed control to supply the reducing agent to the downstream catalyst by using the reducing agent feed device; and a NOx storage quantity calculation unit configured to calculate a NOx storage quantity, which is a quantity of NOx stored in the first NOx storage reduction catalyst.

[0011] In such an exhaust gas purification device, a large proportion of the NOx emitted by the internal combustion engine can be stored in the first NOx storage reduction catalyst (hereinafter sometimes referred to as an "NSR catalyst"). When the rich-peak process is then carried out, the NOx stored in the first NSR catalyst (hereinafter sometimes referred to as "the stored NOx") can be reduced by the reducing agent present in the exhaust gas with a rich air-fuel ratio, such as CO, HC, etc. However, even when the rich-peak process is carried out, some of the stored NOx may be flushed from the first NSR catalyst without being reduced.

[0012] Even if NOx is flushed out of the first NSR catalyst in the exhaust gas purification system using the rich-peak method, the NOx can be reduced by the downstream catalyst located on the first NSR catalyst. Here, the downstream catalyst is, for example, a NOx selective reduction catalyst (SCR catalyst), which reduces the NOx in the exhaust gas using ammonia as a reducing agent, or a NOx storage reduction catalyst (NSR catalyst), which reduces the NOx in the exhaust gas using fuel as a reducing agent.

[0013] As a result of previous studies, the inventor of the present application has recently been able to show that, even if the NOx storage quantity and the temperature of the first NSR catalyst are the same at the time the fat-peak process is executed, the amount of NOx flushed from the first NSR catalyst by the current fat-peak process can change due to the temperature history of the first NSR catalyst during a period from the completion of the last fat-peak process to the requirement to execute the current fat-peak process (hereinafter sometimes referred to as a "determination period"). Accordingly, in cases where the temperature of the first NSR catalyst is relatively low, the NOx tends to be stored in a storage material as part of the first NSR catalyst in a simple release mode (hereinafter sometimes referred to as a "first mode").In cases where the temperature of the NSR catalyst is relatively high, the NOx tends to be stored in a mode with difficult release (sometimes referred to below as a "second mode"). Thus, the storage mode of the NOx in the first NSR catalyst changes according to the temperature history of the first NSR catalyst during the determination period.

[0014] The amount of NOx flushed from the first NSR catalyst by the rich-peak process (hereinafter referred to as the "NOx flushing quantity") can then change as a result of such a NOx storage mode. Even if the NOx storage mode is the same, the NOx flushing quantity tends to be larger the greater the amount of NOx from the first mode is in the stored NOx. Conversely, even if the NOx storage quantity is the same, the NOx flushing quantity tends to be smaller the greater the amount of NOx from the second mode is in the stored NOx. If the NOx flushed from the first NSR catalyst is then reduced by using the downstream catalyst, there is concern that exhaust emissions could worsen if this situation is not taken into account.

[0015] Accordingly, in an exhaust gas purification device for an internal combustion engine according to a first aspect of the present invention, in cases where the temperature of the first NOx storage reduction catalyst falls below a predetermined temperature for at least part of the determination period, the feed control unit executes the feed control according to the implementation of the current peak fuel trim method by the air-fuel ratio control unit. Furthermore, in cases where the NOx storage quantity calculated by the NOx storage quantity calculation unit is the same, the feed quantity control is executed such that the feed quantity of the reducing agent in the feed control increases when the period during which the temperature of the first NOx storage reduction catalyst is below the predetermined temperature becomes longer.

[0016] Here, the predetermined settling temperature is defined as the temperature at which NOx can transition to the second mode and be stored in the first NSR catalyst if the temperature of the first NSR catalyst becomes equal to or higher than the settling temperature. It should be noted that the NOx already stored in the first NSR catalyst in the first mode can change to the second mode if the temperature of the first NSR catalyst becomes equal to or higher than the predetermined settling temperature after NOx storage. Consequently, in the first NSR catalyst, whose temperature has become equal to or higher than the predetermined settling temperature, there is a tendency for the NOx to be stored in the first mode.On the other hand, in the first NSR catalyst, whose temperature has fallen below the predetermined determination temperature, there is a tendency for the NOx to be stored in the second mode. Then, in cases where the temperature of the first NSR catalyst falls below the predetermined determination temperature for at least part of the determination period, some of the stored NOx is flushed out of the first NSR catalyst when the fuel-fuel ratio control is executed. Consequently, in this case, as mentioned above, the feed control unit executes the feed control according to the fuel-fuel ratio control unit's instructions for the fuel-fuel ratio control. This allows the NOx flushed out of the first NSR catalyst by the fuel-fuel ratio control to be reduced in the downstream catalyst by the reducing agent supplied by the feed control unit.

[0017] The stored NOx of the first mode then increases in the total stored NOx if the period during which the temperature of the first NSR catalyst within the determination period is lower than the predetermined determination temperature (hereinafter sometimes referred to as a "catalyst low-temperature period") is longer. Consequently, even if the NOx storage quantity is the same, the NOx discharge quantity will be greater in cases where the catalyst low-temperature period is long compared to cases where it is short. Thus, the feed control unit controls the feed rate of the reducing agent such that, in cases where the NOx storage quantity is the same, it increases when the catalyst low-temperature period is longer, according to the implemented feed control of the fat-peak method.The control mechanism for increasing the amount of reducing agent supplied in this way is referred to below as "supply rate control." The supply rate control unit then executes this control, supplying the reducing agent to the downstream catalyst in an amount corresponding to the NOx scavenged. As a result, the NOx scavenged from the first NSR catalyst by the "rich tip" process is adequately reduced by the reducing agent in the downstream catalyst. Consequently, a situation in which exhaust emissions worsen due to NOx scavenged from the first NSR catalyst is suppressed as effectively as possible.

[0018] Additionally, the downstream catalyst can be a NOx selective reduction catalyst (SCR catalyst), which reduces the NOx in the exhaust gas by means of supplied ammonia. In this case, the reducing agent supply device can supply an ammonia precursor or ammonia. If the temperature of the first NOx storage reduction catalyst falls below the predetermined temperature for at least part of the period between the completion of the last peak fuel trim process and the request for the current peak fuel trim process, the supply control unit can override the air-fuel ratio control before the current peak fuel trim process is executed. Therefore, before the NOx is purged from the first NOx storage reduction catalyst by the peak fuel trim process, the amount of ammonia adsorption in the NOx selective reduction catalyst can be increased in advance.If NOx is indeed flushed out of the first NSR catalyst by the fat tip method, one result is that the NOx can be reduced in a reasonable manner in the NOx selective reduction catalyst.

[0019] Furthermore, the feed control unit can execute feed rate control, so that the amount of ammonia adsorption in the NOx selective reduction catalyst (SCR catalyst) after the feed rate control is executed is less than the slip development adsorption amount at which ammonia slip occurs at the NOx selective reduction catalyst (SCR catalyst). Consequently, the NOx flushed from the first NOx catalyst by the fat tip process can be reduced, while the ammonia slip from the NOx selective reduction catalyst (SCR catalyst) is suppressed.

[0020] Additionally, the downstream catalyst can be a second NOx storage reduction catalyst, which reduces the NOx in the exhaust gas by adding fuel. In this case, the reducing agent supply device feeds fuel, and if the temperature of the first NOx storage reduction catalyst falls below the predetermined temperature for at least part of the period between the completion of the last fuel-fuel peaking process and the request for the current fuel-fuel peaking process, the supply control unit can execute the fuel feed simultaneously with the execution of the current fuel-fuel peaking process by the air-fuel ratio control unit. As a result, the NOx purged from the first NOx storage reduction catalyst by the fuel-fuel peaking process can be adequately reduced in the second NOx storage reduction catalyst.

[0021] Next, reference is made to an exhaust gas purification device for an internal combustion engine according to a second aspect of the present invention. It has been shown that, in the first mode described in the first aspect of the present invention, the NOx stored in the first NSR catalyst is nitrite, and that the nitrites are stored in the storage material of the first NSR catalyst by a relatively weak adsorption force. On the other hand, it has been shown that, in the second mode, the NOx stored in the first NSR catalyst is nitrate, and that the nitrates are stored in the storage material of the first NSR catalyst by an adsorption force that is stronger than that of the nitrites.Therefore, if the stored NOx is released from the storage material of the first NSR catalyst by the fat tip method, the nitrites stored in the storage material are released more easily than the nitrates stored in the storage material.

[0022] In view of this, if a ratio of the amount of nitrates stored in the first NSR catalyst (hereinafter sometimes referred to as a "nitrate storage quantity") to the NOx storage quantity is defined as a nitrate ratio, even if the NOx storage quantity is the same, the NOX discharge quantity may be greater in the case where the fat peaking process is carried out in a low nitrate ratio state compared to the case where the fat peaking process is carried out in a high nitrate ratio state.

[0023] Accordingly, the exhaust gas purification device for an internal combustion engine according to the second aspect of the present invention comprises: a first NOx storage reduction catalyst arranged in an exhaust gas channel of the internal combustion engine; a post-stage catalyst arranged in the exhaust gas channel on the downstream side of the first NOx storage reduction catalyst and reducing NOx in an exhaust gas by means of a supplied reducing agent; a reducing agent supply device arranged in the exhaust gas channel between the first NOx storage reduction channel and the post-stage catalyst and supplying the reducing agent to the exhaust gas channel;an air-fuel ratio control unit configured to perform a rich-peak procedure to temporarily change the air-fuel ratio of exhaust gas flowing into the first NOx storage reduction catalyst from a lean air-fuel ratio, higher than a stoichiometric air-fuel ratio, to a rich air-fuel ratio, lower than the stoichiometric air-fuel ratio; a feed control unit configured to perform feed control to supply the reducing agent to the downstream catalyst by means of the reducing agent feed device; a NOx storage quantity calculation unit configured to calculate a NOx storage quantity, which is a quantity of the NOx stored in the first NOx storage reduction catalyst;a nitrate storage quantity calculation unit, which is set up to calculate a storage quantity of nitrates based on a temperature of the first NOx storage reduction catalyst, which is a quantity of nitrates stored in the first NOx storage reduction catalyst;and a nitrate ratio calculation unit, which is configured to calculate a nitrate ratio based on the NOx storage quantity calculated by the NOx storage quantity calculation unit and the nitrate storage quantity calculated by the nitrate storage quantity calculation unit. This nitrate ratio is a ratio of the nitrate storage quantity to the NOx storage quantity. In cases where the nitrate ratio calculated by the nitrate ratio calculation unit is lower than a predetermined set ratio when the execution of the fat peak procedure is requested, the feed control unit then executes the feed control according to the execution of the fat peak procedure by the air-fuel ratio control unit and controls the feed quantity of the reducing agent during the feed control based on the nitrate ratio.

[0024] Whether NOx can be converted directly into nitrites and stored in the first NSR catalyst, or whether it can be converted directly into nitrates and stored in the first NSR catalyst, depends on the temperature of the first NSR catalyst. Consequently, the amount of nitrate stored will also change depending on the temperature of the first NSR catalyst. In cases where the amount of NOx stored remains the same when the temperature of the first NSR catalyst is relatively low and the amount of nitrate stored is small, the nitrate ratio will be lower compared to cases where the temperature of the first NSR catalyst is relatively high.During the period of determination described in the description of the aforementioned first aspect of the present invention, for example, in cases where the NOx storage quantity is the same, the nitrate ratio tends to be lower if a period during which the temperature of the first NSR catalyst is relatively low becomes longer.

[0025] In cases where the nitrate ratio is lower than the predetermined determination ratio when the fat peaking process is requested, the feed control unit then executes the feed control according to the fat peaking process and controls the feed rate of the reducing agent in the feed control based on the nitrate ratio. Here, the predetermined determination ratio is defined as a ratio at which the NOx flushed from the first NSR catalyst by the fat peaking process becomes extremely low when the nitrate ratio is equal to or higher than the predetermined determination ratio.In cases where the feed control is implemented according to the fat-peak method, the feed control unit can increase the amount of reducing agent supplied when the nitrate ratio is low compared to high, even if the NOx storage quantity is the same. As a result, the NOx flushed from the first NSR catalyst by the fat-peak method can be reduced more effectively when the fat-peak method is implemented at a low nitrate ratio than when it is implemented at a high nitrate ratio. In other words, it becomes possible to minimize the occurrence of a situation where exhaust emissions worsen due to NOx flushed from the first NSR catalyst.

[0026] According to the present invention, a situation in which exhaust emissions worsen due to NOx purged from a first NSR catalyst can be suppressed as effectively as possible. List of characters Fig. Figure 1 is a view showing the schematic construction of an intake system and an exhaust system of an internal combustion engine according to a first embodiment of the present invention. Fig. Figure 2 is a view which represents a NOx concentration in an exhaust gas discharged from the internal combustion engine and before entering a first NSR catalyst, a NOx concentration of an exhaust gas after the first NSR catalyst and before an SCR catalyst, and a NOx concentration of an exhaust gas after the SCR catalyst. Fig. 3A is a view to explain a NOx storage mode in the case where the temperature of the first NSR catalyst is relatively low. Fig. 3B is a view to explain a NOx storage mode in the case where the temperature of the first NSR catalyst is relatively high. Fig. Figure 4 is a schematic diagram representing an estimated NOx reduction mechanism in the first NSR catalyst. Fig. Figure 5 is a view which presents a comparison of the NOx concentration in the exhaust gas after the first NSR catalyst and before the SCR catalyst between a normal operation of the internal combustion engine and an operation in which NOx is purged from the first NSR catalyst according to the implementation of a rich peak process. Fig. Figure 6 is a time diagram showing the time changes of a NOx storage quantity, a request flag, an execution flag, an NSR catalyst temperature, a low-temperature counter, a setpoint of a urea-water solution addition quantity, an ammonia adsorption quantity and a urea-water solution addition flow rate according to the first embodiment of the present invention. Fig. Figure 7 is a flowchart that represents a control sequence according to the first embodiment of the present invention. Fig. Figure 8 is a view that shows a correlation between the target value of the urea-water solution addition quantity and the low-temperature counter. Fig. Figure 9 is a time diagram showing the time changes of a NOx storage quantity, a request flag, an execution flag, an NSR catalyst temperature, a high-temperature counter, a setpoint of a urea-water solution addition quantity, an ammonia adsorption quantity and a urea-water solution addition flow rate according to a modification of the first embodiment of the present invention. Fig. Figure 10 is a flowchart which represents a control sequence according to the modification of the first embodiment of the present invention. Fig. Figure 11 is a view which represents a correlation between the target value of the urea-water solution addition quantity and the high-temperature counter. Fig. Figure 12 is a view showing the schematic construction of an intake system and an exhaust system of an internal combustion engine according to a second embodiment of the present invention. Fig. Figure 13 is a flowchart which represents a control sequence according to the second embodiment of the present invention. Fig. Figure 14 is a view that represents a correlation between a target value of a fuel addition quantity and a low-temperature meter. Fig. Figure 15 is a flowchart which represents a control sequence according to a third embodiment of the present invention. Description of the exemplary implementations

[0027] Below, exemplary modes (or embodiments) for carrying out the present invention are described in detail with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of components described in the embodiments are not intended to limit the scope of protection of the present invention to these alone, particularly as long as there are no specific statements to the contrary. First embodiment: Design of an intake and exhaust system for an internal combustion engine

[0028] Fig. Figure 1 is a view illustrating the schematic construction of an intake system and an exhaust system of an internal combustion engine according to a first embodiment of the present invention. The Fig. 1 internal combustion engine shown 1is a self-igniting internal combustion engine (diesel engine). However, the present invention can also be applied to a lean-burn, spark-ignition internal combustion engine which uses gasoline or the like as fuel.

[0029] An intake manifold 2 and an exhaust duct 3 are with the internal combustion engine 1 connected. An air mass meter 4 is in the intake manifold 2 arranged. The air mass meter 4 serves to measure a quantity of fuel in the internal combustion engine 1 drawn-in intake air. Also a throttle valve. 5 is in the intake manifold 2 downstream of the air mass meter 4 arranged. The throttle valve 5 It is used to control the amount of intake air into the internal combustion engine. 1 by changing the cross-sectional area of ​​the intake duct 2 .

[0030] In the exhaust duct 3are a first NOx storage reduction catalyst 6 (hereinafter sometimes also referred to as a "first NSR catalyst") 6 “” and a NOx selective reduction catalyst 8 (hereinafter sometimes also referred to as an "SCR catalyst") 8 These are referred to as exhaust gas purification catalysts. Then a fuel injection valve is installed. 7 in the exhaust duct 3 on the upstream side of the first NSR catalyst 6 arranged. The one from the fuel injection valve 7 The added fuel is fed to the first NSR catalyst. 6 It is supplied together with the exhaust gas. Additionally, a urea-water solution addition valve is installed. 9 in the exhaust duct 3 between the first NSR catalyst 6 and the SCR catalyst 8 arranged. The urea-water solution addition valve 9It serves to add the urea-water solution to the exhaust gas, and the urea-water solution added in this way is fed to the SCR catalyst. 8 supplied. In other words, urea, which is a precursor of ammonia, is fed to the SCR catalyst. 8 The urea is supplied. Then, ammonia, which is produced by the hydrolysis of the supplied urea, is adsorbed in the SCR catalyst. 8 The NOx in the exhaust gas is removed by using this in the SCR catalyst. 8 Adsorbed ammonia is reduced as a reducing agent. It should be noted that this is in place of the urea-water solution addition valve. 9 An ammonia addition valve, which serves to add ammonia gas to the exhaust gas, may be arranged. In this embodiment, the urea-water solution addition valve corresponds to this. 9or the ammonia addition valve of a reducing agent supply device in the present invention. Additionally, a filter for filtering fine dust particles (PM) in the exhaust gas can be provided in the exhaust duct. 3 be arranged.

[0031] Additionally, a first NOx sensor 13 and an air-fuel ratio sensor 14 in the exhaust duct 3 downstream of the fuel injection valve 7 and upstream of the first NSR catalyst 6 arranged. The first NOx sensor 13 detects the NOx concentration in the first NSR catalyst. 6 Flowing exhaust gas (hereinafter sometimes also referred to as an "inlet exhaust gas"). The air-fuel ratio sensor 14 It measures the air-fuel ratio of the incoming exhaust gas. In addition, a second NOx sensor is included. 15 and a temperature sensor 16 in the exhaust duct 3 between the first NSR catalyst 6and the SCR catalyst 8 arranged. The second NOx sensor 15 detects the NOx concentration in the material from the first NSR catalyst 6 flowing exhaust gas (hereinafter sometimes also referred to as "exhaust gas"). The temperature sensor 16 It measures the temperature of the exhaust gas. Furthermore, a third NOx sensor is included. 17 in the exhaust duct 3 on the downstream side of the SCR catalyst 8 arranged. The third NOx sensor 17 detects the NOx concentration in the exhaust from the SCR catalyst 8 flowing exhaust gas.

[0032] In the internal combustion engine 1 In combination with this, it is an electronic control unit (ECU) 10 for controlling the internal combustion engine 1 arranged. The air mass meter 4 , the first NOx sensor 13 , the air-fuel ratio sensor 14 , the second NOx sensor 15, the temperature sensor 16 and the third NOx sensor 17 are electrically connected to the ECU 10 connected. Furthermore, a crank angle sensor is included. 11 and an accelerator pedal opening sensor 12 electrically connected to the ECU 10 connected. The crank angle sensor 11 gives a signal with a correlation to a crank angle of the internal combustion engine 1 off. The accelerator pedal opening sensor 12 gives a signal with a correlation to the opening angle of an accelerator pedal of a vehicle at which the internal combustion engine 1 is mounted, off.

[0033] Then, the output values ​​and signals from these individual sensors are sent to the ECU. 10 entered. The ECU 10 derives based on the output value of the crank angle sensor. 11 the speed of the internal combustion engine 1 the ECU also derives 10based on the output value of the accelerator pedal opening angle sensor 12 the engine load of the internal combustion engine 1 off. Additionally, the ECU estimates 10 based on the output value of the air mass meter 4 the exhaust gas flow rate (hereinafter sometimes referred to as an "exhaust gas flow rate") and calculates based on the exhaust gas flow rate and the output value of the first NOx sensor. 13 the flow rate of the fluid entering the first NSR catalyst 6 flowing NOx (hereinafter sometimes referred to as a "NOx inflow flow rate") and calculated based on the exhaust gas flow rate and the output value of the second NOx sensor 15 the flow rate from the first NSR catalyst 6 flowing NOx (hereinafter sometimes referred to as a "NOx exhaust flow rate"). Furthermore, the ECU estimates 10 based on the output value of the temperature sensor 16the temperature of the first NSR catalyst 6 (hereinafter sometimes referred to as an "NSR catalyst temperature").

[0034] Furthermore, fuel injectors (not shown) of the internal combustion engine 1 , the throttle valve 5 , the fuel injection valve 7 and the urea-water solution addition valve 9 electrically connected to the ECU 10 connected. These parts are connected by the ECU. 10 controlled. Here the ECU takes the lead. 10 Method for temporarily changing the air-fuel ratio of the first NSR catalyst 6flowing exhaust gas from a lean air-fuel ratio, higher than a stoichiometric air-fuel ratio, to a rich air-fuel ratio, lower than the stoichiometric air-fuel ratio (hereinafter sometimes referred to as the "rich peak method"). In this embodiment, the ECU performs 10 the fat peak method by adding fuel to the internal combustion engine 1 discharged exhaust gas using the fuel addition valve 7 However, in this embodiment, there is no intention limited to such a case, and the ECU 10 The grease tip procedure can be performed using known technologies. For example, the ECU can 10The rich-fuel method is achieved by creating a rich mixture in one cylinder using a fuel injector (not shown) of the internal combustion engine and by burning the rich mixture in that cylinder. It should be noted that the ECU 10 as an air-fuel ratio control unit according to the present invention by performing the fat tip method.

[0035] In the exhaust gas purification device according to this embodiment, which includes the first NSR catalyst 6 and the SCR catalyst 8 The NOx concentrations measured by the first NOx sensor are shown here. 13 , the second NOx sensor 15 and the third NOx sensor 17 be recorded based on Fig. 2 explained. Fig. 2 is a view which shows the NOx concentration in the exhaust gas coming from the internal combustion engine 1is discharged and before flowing into the first NSR catalyst 6 is (detected by the first NOx sensor) 13 ), the NOx concentration of the exhaust gas after the first NSR catalyst 6 and in front of the SCR catalyst 8 (detected by the second NOx sensor) 15 ) and the NOx concentration of the exhaust gas after the SCR catalyst 8 (detected by the third NOx sensor) 17 ) in the case where the internal combustion engine 1 discharged exhaust gas through the exhaust duct 3 flows towards the downstream side, successively passing through the first NSR catalyst 6 and the SCR catalyst 8 traversed, represents.

[0036] As in Fig. As shown in section 2, most of the power is supplied by the internal combustion engine. 1 discharged NOx (a concentration C1 ) stored or by the first NSR catalyst 6reduced, so that the after the NSR catalyst 6 (and before the SCR catalyst) 8 ) measured NOx concentration at a concentration C2 decreases. This NOx is then further reduced by the SCR catalyst. 8 reduced, so that the NOx concentration in the exhaust gas after the SCR catalyst 8 (a concentration C3 ) becomes extremely small.

[0037] The ECU 10 Here, the urea-water solution is injected into the exhaust duct. 3 by using the urea-water solution addition valve 9 to and feeds into the SCR catalyst 8 Ammonia produced by the hydrolysis of urea is added. It should be noted that this control is referred to below as "feed control". This feed control is executed when a certain amount of ammonia adsorbed in the SCR catalyst is reached. 8(hereinafter sometimes referred to as an "ammonia adsorption quantity") by reducing NOx in the exhaust gas, for example by using the adsorbed ammonia in the SCR catalyst 8 as the reducing agent has decreased.

[0038] The ECU then performs the following action in the aforementioned exhaust gas purification device. 10 the feed control is switched off, so that the ammonia adsorption quantity is close to an adsorption quantity (a reference adsorption quantity) which is one of the concentrations mentioned above. C2 The corresponding amount of NOx can be reduced and maintained. NOx storage and NOx reduction mechanism in the NSR catalyst

[0039] When the fat tip process is carried out, the reducing agent, such as HC, CO, etc., is added to the first NSR catalyst. 6 supplied. Then this can happen in the first NSR catalyst. 6Stored NOx (hereinafter sometimes referred to as "stored NOx") is reduced by this reducing agent. For example, in cases where the fuel injection method is used by adding fuel from the fuel injection valve. 7 When this process is carried out, the stored NOx can be reduced primarily by HC. Additionally, for example, in cases where the rich-burn method is implemented by rich combustion in each cylinder, the stored NOx can be reduced primarily by CO and HC.

[0040] Even when the fat peak method is performed, some of the stored NOx can escape from the first NSR catalyst without being reduced. 6 be flushed. It was shown here that if the fluid from the first NSR catalyst... 6 Purged NOx using the SCR catalyst 8A situation can arise in which NOx cannot be reduced sufficiently because the amount of NOx flushed from the NSR catalyst by the fat-tip process (hereinafter sometimes referred to as the "NOx flushing quantity") changes. Based on previous studies, the present inventor was able to show that such a situation can occur as a result of a NOx storage mode in the first NSR catalyst. 6 occurs. This is explained below. It should be noted here that the first NSR catalyst 6 The stored amount of NOx (the stored NOx) is hereinafter referred to as the “NOx storage amount”.

[0041] A NOx storage mechanism in the first NSR catalyst 6 The estimated mechanism, newly considered by the present inventor, is based on Fig. 3A and Fig. 3B explained. Fig. 3A and Fig. 3B are views on explaining the NOx storage mode in the first NSR catalyst 6 .

[0042] Here, the NOx storage mode is explained by describing a case in which the first NSR catalyst 6 The use of aluminum oxide (Al2O3) as a support, Pt as a noble metal catalyst, and Ba as a NOx storage material is illustrated in the NSR catalyst. 6 NOx, which has been induced to react with oxygen in the presence of Pt (which promotes the reaction between NOx and oxygen), is stored in Ba. It has now been shown that when NOx is stored in Ba, its storage mode changes with the temperature of the first NSR catalyst. 6 changes.

[0043] Fig. 3A is a view to explain the NOx storage mode in the case where the temperature of the first NSR catalyst is relatively low (e.g., 250–300 °C). In a Fig. The example shown in 3A is the first NSR catalyst. 6 The incoming NOx is caused to react with oxygen in the presence of Pt. In this case, the NOx is converted to nitrite (NO2). - Then the nitrites are stored in Ba by a relatively weak adsorption force.

[0044] On the other hand, Fig. 3B presents a view explaining the NOx storage mode in the case where the temperature of the first NSR catalyst is relatively high (e.g., 350–400°C). In a Fig. The example shown in 3B is similar to the one in Fig. The example shown in 3A, also the one in the first NSR catalyst 6 The inflowing NOx causes it to react with oxygen in the presence of Pt to form nitrites (NO2). -to generate nitrites, and as a result, the nitrites thus produced are stored in Ba by a relatively weak adsorption force. It was shown here that in cases where the temperature of the first NSR catalyst is 6 The relatively high concentration of nitrites stored in Ba is caused to react with oxygen to form nitrate (NO3). - ) which is then stored in Ba by a relatively strong adsorption force. It should be noted that the reaction temperature at which the reaction of nitrites to nitrates occurs can change with the degradation of Pt, etc., which promotes the reaction of NOx with oxygen. If the Pt deteriorates, for example, the aforementioned reaction temperature tends to increase.

[0045] Thus, the NOx storage mode changes in the first NSR catalyst. 6 according to the temperature of the first NSR catalyst 6It should be noted here that the stored NOx (which was stored in the first NSR catalyst) 6 stored NOx), as described above, contains nitrates and nitrites. Therefore, the NOx storage quantity is the amount of stored NOx in the first NSR catalyst. 6 stored nitrites and nitrates.

[0046] When the stored NOx is then reduced by the execution of the fat peak process, the stored NOx is released once by the Ba and then reacts with the reducing agent in the presence of Pt, whereby the NOx in the first NSR catalyst 6 is reduced to N2. This is illustrated by schematic diagrams showing the estimated reduction mechanism of NOx in the first NSR catalyst. 6 at the time of the execution of the in Fig. The fat tip procedure shown in section 4 is illustrated. Fig. Figure 4 shows the schematic diagrams in the upper and lower rows, respectively, of the states before and during the execution of the grease tip procedure.

[0047] As in the top row of Fig. As shown in Figure 4, nitrites and nitrates are stored in the storage material Ba. If CO then acts as the reducing agent in such a first NSR catalyst... 6 When supplied, the nitrites are released once from the Ba and reduced to NO by the reducing agent, as shown in the bottom row of Fig. Figure 4 shows this. On the other hand, some of the nitrates are reduced to nitrites, which can be released from Ba, but the majority of the nitrates tend to remain stored in Ba. In other words, the nitrites are easily released from Ba, but the nitrates are difficult to release. Consequently, in cases where the amount of nitrites easily released from Ba is large in the stored NOx, the stored NOx is easily reduced; however, in cases where the amount of nitrates difficult to release from Ba is large in the stored NOx, the stored NOx becomes difficult to reduce.

[0048] Furthermore, as described above, even when the fat peak method is carried out, some of the stored NOx can escape from the first NSR catalyst without being reduced. 6 be purged. A comparison of the NOx concentration in the exhaust gas after the first NSR catalyst.6 and in front of the SCR catalyst 8 between a version of a normal operation of the internal combustion engine 1 (similar to the one mentioned above) Fig. 2 NOx concentration shown) and, if NOx from the first NSR catalyst 6 The process is carried out according to the execution of the grease tip procedure, and is in Fig. 5 shown. As in Fig. 5 shown, when the normal operation of the internal combustion engine 1 is carried out, the majority of which is powered by the internal combustion engine 1 discharged NOx (the concentration C1 ) through the first NSR catalyst 6 stored and in front of the SCR catalyst 8 on concentration C2 lowered. On the other hand, assuming that the fat peak method is used during idle operation of the internal combustion engine. 1 The concentration of the fuel from the internal combustion engine is determined. 1discharged NOx at this time C1' , which is smaller than C1 This is the case if NOx from the first NSR catalyst is released here. 6 According to the execution of the grease tip procedure, the area after the first NSR catalyst is flushed. 6 and in front of the SCR catalyst 8 measured NOx concentration C2' , which is larger than C2 is. In cases where the NOx concentration after the first NSR catalyst 6 and in front of the SCR catalyst 8 increases when the ammonia adsorption quantity is close to the adsorption quantity (the reference adsorption quantity), which corresponds to the concentration C2 While the corresponding amount of NOx can be reduced, there are concerns that this will be achieved with the first NSR catalyst. 6 NOx purged in the SCR catalyst 8 cannot be reduced sufficiently.

[0049] Even if the NOx storage volume is the same, the amount of nitrite in the stored NOx that is easily released by Ba tends to increase with increasing NOx discharge volume. Conversely, even if the NOx storage volume is the same, the amount of nitrate in the stored NOx that is difficult to release by Ba tends to increase with decreasing NOx discharge volume. Then, when the NOx discharged from the first NSR catalyst is used by the SCR catalyst... 8 While the reduction is being addressed, there are concerns that exhaust emissions could worsen if such a situation is not taken into account. Input quantity control

[0050] Here, the predetermined determination temperature is defined as a temperature at which NOx is converted into nitrates and enters the first NSR catalyst. 6NOx can be stored if the NSR catalyst temperature is equal to or higher than the determination temperature. In cases where the NSR catalyst temperature is lower than the determination temperature for at least part of the determination period, NOx is converted to nitrites and stored in the NSR catalyst. 6 NOx is stored. As a result, when the current peak-fat procedure is carried out, some of the stored NOx is released from the NSR catalyst. 6 flushed. Consequently, in this case the ECU leads 10 The feed control is based on the peak fat method. This allows the output from the first NSR catalyst to be used. 6 NOx flushed through the grease peak method is filtered through the feed control in the SCR catalyst. 8 The amount of ammonia supplied will be reduced.

[0051] The nitrite concentration in the total stored NOx will then increase if the period during which the NSR catalyst temperature is lower than the predetermined set temperature (sometimes referred to below as the "catalyst low-temperature period") is longer. Consequently, even if the total amount of NOx stored is the same, the amount of NOx scavenged will be greater when the catalyst low-temperature period is long compared to when it is short. Thus, the ECU controls 10so that in cases where the NOx storage quantity is the same, the supply quantity of the reducing agent in the feed control implemented according to the peak-load method increases when the catalyst low-temperature period becomes longer. It should be noted here that the control used to increase the supply quantity of the reducing agent in this way is referred to below as a "feed quantity control". In this embodiment, the ECU performs 10 The feed rate control is achieved by increasing the amount of urea (a urea-water solution feed rate) supplied by the urea-water solution feed valve. 9 It is admitted, out. As a result of this, the first NSR catalyst is used. 6 NOx flushed out by the grease tip method is appropriately removed by the hydrolysis of urea in the SCR catalyst. 8The amount of ammonia produced is reduced, which makes it possible to suppress the occurrence of a situation where exhaust emissions worsen as much as possible. It should be noted here that the ECU 10 as a feed control unit according to the present invention by performing feed control and feed quantity control.

[0052] Here, a brief discussion will be held using a [method of] in Fig. The timing diagram shown in section 6 is implemented by the ECU in this embodiment. 10 Executed tax procedures explained. Fig. Figure 6 is the time diagram, which shows the time changes of a NOx storage quantity NOxsum, a request flag flr, which is a flag to indicate whether the execution of the fat peak procedure has been requested, an execution flag fle, which is a flag to indicate whether the fat peak procedure has been executed, and a low-temperature counter. Mc , which is a counter for counting a time interval during which the NSR catalyst temperature falls below the set temperature, a setpoint Quad of the urea-water solution addition quantity (hereinafter sometimes referred to as a "urea-water solution addition quantity setpoint"), which is determined by the feed control implemented according to the fat tip method from the urea-water solution addition valve 9 to be added, an ammonia adsorption quantity Qan and an addition flow rate Fr of the urea-water solution addition valve 9 The amount of urea-water solution to be added (hereinafter sometimes referred to as a "urea-water solution addition rate") is important to note. It should be noted that in the Fig. In the control system shown in Figure 6 of this embodiment, when the NOx storage quantity reaches a reference quantity NOxth, an execution requirement of the peak grease procedure is met. Here, the reference quantity NOxth is a threshold value that determines the fulfillment of the execution requirement of the peak grease procedure.

[0053] In the Fig. In the control system shown in Figure 6, the feed rate is controlled similarly to conventional technology, so that the ammonia adsorption quantity is kept close to the reference adsorption quantity Qanb. The feed rate control is achieved in particular by adding the urea-water solution at a flow rate Fr1 at a specific time. t1 The experiment, in which the ammonia adsorption quantity becomes a lower limiting adsorption quantity Qanth, is performed for a predetermined time period. In this case, the ammonia adsorption quantity is increased and can be kept close to the reference adsorption quantity Qanb.

[0054] Then at a time t2 When the NOx storage quantity becomes the reference quantity NOxth, the execution requirement of the grease injection procedure is fulfilled and the requirement flag is set to ON. During a period of time before this point in time t2 The NSR catalyst temperature did not fall below the target temperature Tcth. Therefore, the low-temperature counter was deactivated at that time. t2 to 0. In other words, the catalyst low-temperature time interval becomes 0. It should be noted here that the determination temperature Tcth is defined as the temperature at which NOx is converted to nitrates and in the first NSR catalyst. 6The system can be stored if the NSR catalyst temperature, as mentioned above, becomes equal to or higher than the target temperature Tcth. In this case, the feed control is not executed according to the peak fat method. For this reason, the execution flag is set at that time. t2 , at which the requirement flag is set to ON, is also set to ON and the fat peak procedure is initiated from that point in time t2 up to a certain point t3 The process is executed. It should be noted that the NOx storage quantity will be close to 0 once the fat peak procedure is complete.

[0055] Focusing on a specific time period (i.e., a period of time from the point in time) t3 up to a certain point t6 ) from the completion of the at that time t2 started execution of the fat peak procedure (i.e. the last fat peak procedure) up to the point at a time t6The fulfilled implementation requirement of the fat peak method (i.e., the current fat peak method) is here the NSR catalyst temperature during a time period of a time point t4 up to a certain point t5 , as in Fig. 6 shown, lower than the determination temperature Tcth In this case, at the time t4 the timer was started by the low-temperature counter and at that time t5 The low-temperature counter will be used M1 If the value of the low-temperature counter is then increased, e.g., if the catalyst low-temperature period becomes longer, the urea-water solution addition setpoint is increased from 0 and becomes Quad1 at that time t5 It should be noted here that during a period of time from that point in time t5 until that time t6the NSR catalyst temperature is equal to or higher than the target temperature Tcth and the timer is not being executed by the low-temperature counter.

[0056] Then at a certain point in time t6 , where the request flag is set to ON, the low-temperature counter M1 , i.e., the NSR catalyst temperature is lower than the specified temperature Tcth at least during part of the determination period, so that the feed control is carried out according to the fat peak method. In this embodiment, the feed control is carried out immediately before the fat peak method is executed, and the ammonia adsorption quantity is increased in advance before the fat peak method is executed. The feed control is achieved in particular by adding the urea-water solution at the flow rate Fr1 for a period of time Δt1 from that point on t6 executed as in Fig. Figure 6 shows that this time interval Δt1 is fixed in such a way that the amount of urea-water solution added is... Quad1 will. Then at a certain point in time t7 , in which the urea-water solution is added in the amount of Quad1 Once completed, the execution flag is set to ON and the fat peak process is executed. In this fat peak process, NOx, as mentioned above, is removed from the first NSR catalyst. 6 rinsed, but the amount of ammonia adsorption was, as in Fig. 6 shown, increased in advance before the execution of the fat peak procedure, so that the NOx is adequately reduced by the SCR catalyst. 8 Adsorbed ammonia can be reduced. It should be noted that once the grease peak process is complete, the low-temperature counter is initialized to 0 and the urea-water solution addition setpoint is also initialized to 0 accordingly.

[0057] Focusing on a timeframe from the completion of the work at that time t7 Starting the execution of the fat peak procedure until a fulfillment requirement of the fat peak procedure at a point in time t10 (i.e., a period of time from a point in time) t8 until that time t10 ) is, on the other hand, the NSR catalyst temperature during a period of time from a point in time t9 up to a certain point t10 , as in Fig. 6 shown, lower than the determination temperature Tcth. In this case, at time t9 the timer was started by the low-temperature counter and at that time t10 The low-temperature counter will be used M2 Then at that time t2 The target value for the urea-water solution addition quantity should be adjusted accordingly. Quad2 .

[0058] Then at that time t10, where the request flag is set to ON, the low-temperature counter M2 , so that the supply control is achieved by adding the urea-water solution to the flow rate Fr1 for a period of time Δt2 from that point on t10 is executed. This time period Δt2 is determined in such a way that the amount of urea-water solution added Quad2 will. Then at a certain point in time t11 , in which the urea-water solution is added in the amount of Quad2 Once completed, the execution flag is set to ON and the grease tip procedure is executed. Here is the value M2 of the low-temperature counter at that time t10 greater than the value M1 of the low-temperature counter at that time t6 In other words, the catalyst low-temperature period within a specified time period from the point in time t8 until that time t10is longer than the period of determination from the time t3 until that time t6 Therefore, within the determination period from the point in time t8 until that time t10 Nitrates more easily in the NSR catalyst 6 stored as within the specified time period from that point in time t3 until that time t6 In other words, even if the amount of NOx stored is the same, the amount of NOx discharged at that time will be different. t11 The initiated fat peak process was greater than the NOx flushing quantity at that time. t7 The fat peak procedure has been initiated. Accordingly, the amount of urea-water solution added will be... Quad2 at that time t10 The started feed control is greater than the amount of urea-water solution added. Quad1 at that time t6The feed control has been initiated. In other words, the feed rate control is being executed. As a result, it becomes possible to extract NSR from the first catalyst. 6 To adequately reduce flushed NOx.

[0059] In this embodiment, therefore, in cases where the NOx storage quantity is the same, the supply quantity of the reducing agent in the supply control implemented according to the peak-load method increases when the catalyst low-temperature period becomes longer. As a result, the amount of NOx stored in the first NSR catalyst is increased. 6 The purged NOx is reduced in an appropriate manner, thus suppressing a situation in which exhaust emissions worsen as much as possible.

[0060] Next, a control sequence or routine executed in this embodiment is based on Fig. 7 described. Fig. Figure 7 is a flowchart illustrating the control sequence or routine according to this embodiment. In this embodiment, this routine is repeated at a predetermined operating interval or time period. Δt through the ECU 10 during the operation of the internal combustion engine 1 executed.

[0061] In this routine, the first step is... S101 The NSR catalyst temperature Tc is obtained. At step S101 The NSR catalyst temperature is determined based on the output value of the temperature sensor. 16 calculated. Alternatively, the NSR catalyst temperature Tc can be calculated at step S101 based on the engine speed and engine load of the internal combustion engine 1 can be estimated. At this point, in cases where fuel is supplied by the fuel injection valve, it can be estimated. 7 The NSR catalyst temperature is added. Tc taking into account the amount of heat generated by the added fuel.

[0062] Then, in step S102 the exhaust gas flow rate Ga received. At step S102 will the exhaust gas flow rate Ga based on the output value of the air mass meter 4 calculated.

[0063] Then, at step S103 a change in NOx in the first NSR catalyst 6 (sometimes referred to simply as a "set of changes" below) NOxch is calculated up to the present time after this routine was last executed. At step S103 The NOx inflow flow rate is determined based on the value in step S102 obtained exhaust gas flow rate Ga and the output value of the first NOx sensor 13The NOx exhaust flow rate is calculated based on the exhaust gas flow rate Ga and the output value of the second NOx sensor. 15 Furthermore, the rate of change of NOx in the first NSR catalyst is calculated. 6 The NOx inflow flow rate is calculated per unit of time by adding the NOx outflow flow rate. Then, the rate of change of NOx (NOxch) is calculated by multiplying the rate of change of NOx per unit of time by the operating time. Δt calculated.

[0064] Then at step S104 The NOx storage quantity NOxsum is calculated. In step S104 The NOx storage quantity NOxsum is determined by adding the values ​​from step S103 The calculated change quantity NOxch is compared to the NOx storage quantity NOxsum. Additionally, the ECU works 10 as a NOx storage quantity calculation unit according to the present invention by carrying out the process steps S103 and S104 .

[0065] Then, in step S105 determines whether the step S101 calculated NSR catalyst temperature Tc lower than the specified temperature Tcth It should be noted that the determination temperature Tcth is defined as mentioned above. Then the ECU routine proceeds. 10 in cases where at step S105 a positive decision will lead to the next procedural step S106 , whereas in cases where at step S105 If a negative decision is made, the ECU routine 10 to the procedural step S107 goes.

[0066] In cases where at step S105 If a positive decision is reached, then step S106 the low-temperature counter Mc increased by 1. In other words, at step S106 a period of time during which the NSR catalyst temperature Tc The temperature below the set temperature Tcth is counted.

[0067] Then, in step S107 determines whether the step S104 The calculated NOx storage quantity NOxsum is compared to the reference quantity NOxth. Here, the reference quantity NOxth is a threshold value that determines whether the execution requirement of the peak-load procedure, as mentioned above, is met. Then the ECU routine proceeds. 10 in cases where at step S107 a positive decision will lead to the next procedural step S108 , whereas in cases where at step S107 If the decision is negative, the execution of this routine will be terminated.

[0068] In cases where at step S107 If a positive decision is reached, then step S108 determines whether the low-temperature counter Mc greater than 0. In other words, it determines whether the catalyst low-temperature time is longer than 0. This is the case when, at step S108 A positive decision is reached in a case where the NSR catalyst temperature is lower than the determination temperature Tcth for at least part of the determination period, and the ECU routine 10 goes to the procedural step S109 In cases where at step S108 On the other hand, if the decision is negative, this is a case in which the NSR catalyst temperature is equal to or higher than the determination temperature throughout the entire determination period. Tcth will, and the ECU routine 10 goes to the procedural step S112 .

[0069] In cases where at step S108 If a positive decision is reached, then step S109The target value for the urea-water solution addition quantity (quad) is calculated. At step S109 is based on the low-temperature counter Mc the target value for the amount of urea-water solution added Quad calculated. In particular, the target value for the urea-water solution addition quantity has been determined. Quad and the low-temperature meter Mc a correlation with each other, as in Fig. 8 shown. This correlation was previously stored in a ROM of the ECU. 10 stored as a function or characteristic map and at step S109 The urea-water solution addition target value Quad is based on the correlation and the value obtained at step S106 counted value of the low-temperature meter Mc calculated. If the value of the low-temperature counter Mc is equal to 0, the urea-water solution addition setpoint Quad calculated in this way, as shown in Fig. 8 shown, to 0. Then the urea-water solution addition quantity setpoint Quad is increased when the value of the low-temperature counter Mc greater than 0. In other words, in cases where the NOx storage quantity NOxsum equals the reference quantity NOxth, the urea-water solution addition setpoint Quad becomes larger when the catalyst low-temperature period is longer.

[0070] Then, in step S110 the urea-water solution from the urea-water solution addition valve 9 added. This increases the amount of ammonia adsorption in advance, before the fat tip removal process is carried out. Then, in step S111 determines whether the addition of the urea-water solution is controlled by the urea-water solution addition valve. 9 is completed. In particular, step S111 determines whether the addition of the urea-water solution in the amount specified in step S109calculated urea-water solution addition quantity target value Quad is completed. Then the ECU routine begins. 10 in cases where at step S111 a positive decision will lead to the next procedural step S112 , whereas in cases where at step S111 If a negative decision is made, the ECU routine 10 to the procedural step S110 returns.

[0071] In cases where at step S111 a positive decision is made, or in cases where, at step S108 If a negative decision is made, then in step S112 The fat tip procedure was performed. At step S112 The fat peak method is achieved by adding fuel to the mixture supplied by the internal combustion engine. 1 discharged exhaust gas via the fuel injection valve 7However, as mentioned above, the fat tip method can also be carried out by performing fat combustion in a cylinder.

[0072] Then, in step S113 the NOx storage quantity NOxsum and the value of the low-temperature counter Mc initialized with 0. Then, after the process step S113 The execution of this routine has ended.

[0073] In this example, the ECU performs 10 the aforementioned control sequence, whereby even if NOx from the first NSR catalyst 6 The execution of the fat peak procedure is accompanied by flushing, which reduces the NOx in the SCR catalyst. 8 is reduced in an appropriate manner. As a result, a situation in which exhaust emissions worsen can be suppressed as effectively as possible. Modification of the first embodiment

[0074] Next, a modification of the aforementioned first embodiment is described. It should be noted that in this modification, a detailed explanation of the essentially identical construction and control method compared to the first embodiment is omitted.

[0075] It will briefly refer to the ECU. 10 The tax procedure implemented in this modification uses a [unclear] Fig. The time diagram shown in section 9 is indicated. Fig. 9 is the time diagram, which shows the time changes of a NOx storage quantity NOxsum, a request flag flr , of an execution flag fle, of an NSR catalyst temperature Tc , a high-temperature meter Nc , which is a counter for counting a time period during which the NSR catalyst temperature is equal to or higher than a setpoint temperature, a urea-water solution addition quantity setpoint Quad, an ammonia adsorption quantity Qan and a urea-water solution addition flow rate Fr according to this modification of the first embodiment. In this modification, in contrast to the one mentioned above, Fig. In the first embodiment, a time period during which the NSR catalyst temperature is equal to or higher than a set temperature Tcth is counted. Then the target urea-water solution addition quantity is calculated based on the high-temperature counter reading.

[0076] In the Fig. The control shown in 9 is the NSR catalyst temperature during the entire determination period from the completion of the execution of the last fat peak process until a fulfillment requirement of the fat peak process at a time point. t2 (current fat peak method) equal to or higher than the determination temperature. Thus, in cases where the NSR catalyst temperature is equal to or higher than the determination temperature throughout the entire determination period, Tcth The high-temperature counter is set to Nmax. When the high-temperature counter is set to Nmax, the urea-water solution addition setpoint becomes 0. Therefore, at that time... t2 , in which the request flag is set to ON, the execution flag is also set to ON and the grease tip procedure is initiated from that point onwards. t2 up to a certain point t3The process is executed. It should be noted that once the grease peaking procedure is complete, the high-temperature counter is initialized to 0, and the urea-water solution addition setpoint is accordingly initialized with a maximum addition setpoint (Quadmax). Here, the maximum addition setpoint is... Quadmax A target value for the urea-water solution addition quantity is reached when the NSR catalyst temperature remains below the target temperature Tcth for the entire determination period. This maximum target value, Quadmax, is the urea-water solution addition quantity at which the ammonia adsorption quantity, according to the feed control implemented using the fat peak method, is set to a maximum within a range lower than the adsorption quantity (a slip development adsorption quantity) at which ammonia slip from the SCR catalyst is reduced. 8starts. Accordingly, in cases where the NSR catalyst temperature is assumed to be lower than the determination temperature Tcth throughout the entire determination period, the urea-water solution addition setpoint is set to the maximum addition setpoint Quadmax, whereby the ammonia adsorption quantity can be maximized before the fat peak method is carried out, while the ammonia slip from the SCR catalyst 8 is suppressed.

[0077] Focusing on a determination period from a point in time t3 at a time t6 is as in Fig. Figure 9 shows the NSR catalyst temperature during a period of time from the time t3 up to a certain point t4 and a period of time from a point in time t5 until that time t6equal to or higher than the set temperature Tcth. In this case, the time is recorded by the high-temperature counter during these time periods and at the specified time. t6 will the high-temperature counter N1 If the value of the high-temperature counter is then increased, the urea-water solution addition setpoint is reduced from the maximum addition setpoint Quadmax, and the urea-water solution addition setpoint becomes Quad1 at that time t6 Then the supply control is achieved by adding the urea-water solution to the flow rate. Fr1 for a period of time Δt1 from that point on t6 executed and at a time t7 , in which the addition of the urea-water solution in the amount of Quad1 Once completed, the execution flag is set to ON, so that the grease tip procedure is executed.

[0078] Focusing on a determination period from a point in time t8 up to a certain point t10 , is the NSR catalyst temperature Tc on the other hand, during a period of time from that point in time t8 up to a certain point t9 , as in Fig. 9 shown, equal to or higher than the determination temperature Tcth. In this case, at that time t8 the timer was started by the high-temperature counter and at that time t9 The high-temperature counter will be used N2 Then at that time t9 Therefore, the target value for the urea-water solution addition quantity is... Quad2 . The supply is then controlled by adding the urea-water solution to the flow rate. Fr1 for a period of time Δt2 from that point on t10 executed and at a time t11 , in which the addition of the urea-water solution in the amount of Quad2 Once completed, the execution flag is set to ON, so that the grease tip procedure is executed.

[0079] As described above, in this embodiment, in cases where the NOx storage quantity is the same, the urea-water solution addition quantity setpoint is larger if the time period in which the NSR catalyst temperature Tc equal to or higher than the specified temperature Tcth The catalyst high-temperature period is longer. In other words, in cases where the NOx storage quantity is the same, the target urea-water solution addition rate will be higher if the catalyst high-temperature period is longer. As a result, it becomes possible to use the first NSR catalyst 6 To adequately reduce flushed NOx.

[0080] Next, a control sequence or routine executed in this modification will be based on Fig. 10 described. Fig. Figure 10 is a flowchart illustrating the control sequence or routine according to this modification. In this modification, this routine is repeated at a predetermined operating interval or time period. Δt through the ECU 10 during the operation of the internal combustion engine 1 executed. It should be noted here that in the respective, in Fig. The procedures shown in section 10 use the same reference numerals and essentially the same procedural steps as those mentioned above. Fig. The 7 items shown are assigned to the items shown, and the detailed explanation of them is omitted.

[0081] In the Fig. The control sequence or routine shown in step 10 is carried out after the process step S104 at step S205 determines whether the step S101 The obtained NSR catalyst temperature Tc is equal to or higher than the determination temperature Tcth. It should be noted that the determination temperature Tcth as mentioned above. Then the ECU routine proceeds. 10 in cases where at step S205 a positive decision will lead to the next procedural step S206 , whereas in cases where at step S205 If a negative decision is made, the ECU routine 10 to the procedural step S107 goes.

[0082] In cases where at step S205 If a positive decision is reached, the next step will be... S206 The high-temperature counter Nc increases by 1. In other words, a period of time during which the NSR catalyst temperature Tc equal to or higher than the specified temperature Tcth will be at step S206 counted or to the high-temperature counter Nc added. Then the ECU routine begins. 10 after the procedural step S206 to the procedural step S107 .

[0083] Then, in cases where at step S107A positive decision is made at step S208 determines whether the high-temperature counter Nc to Nmax will be. It should be noted here that Nmax is as mentioned above. Then, in cases where at step S208 If the decision is positive, this is a case in which the NSR catalyst temperature Tc at least during part of the determination period lower than the determination temperature Tcth will, and the ECU routine 10 goes to the procedural step S209 In cases where at step S208 If the decision is negative, this is, on the other hand, a case in which the NSR catalyst temperature Tc throughout the entire determination period, the temperature must be equal to or higher than the determination temperature. Tcth will, and the ECU routine 10 goes to the procedural step S112 .

[0084] In cases where at step S208If a positive decision is reached, then step S209 The target value for the urea-water solution addition quantity (quad) is calculated. At step S209 The urea-water solution addition quantity setpoint Quad is based on the value of the high-temperature meter. Nc calculated. In particular, the urea-water solution addition quantity setpoint Quad and the high-temperature counter Nc one in Fig. The 11 correlations shown are related to each other. This correlation was predefined in the ECU's ROM. 10 stored as a function or characteristic map and at step S209 The urea-water solution addition target value Quad is based on the correlation and the value obtained at step S206 counted value of the high-temperature meter Nc calculated. If the value of the high-temperature counter Nc 0The calculated urea-water solution addition rate target value Quad becomes the maximum addition rate target value Quadmax, as in Fig. 11 shown. If then the value of the high-temperature counter Nc If the value is greater than 0, the urea-water solution addition quantity setpoint quad becomes smaller, and if the value of the high-temperature counter Nc even Nmax If this occurs, the urea-water solution addition quantity setpoint Quad becomes 0. After the process step S209 The ECU routine 10 then to the procedural step S110 .

[0085] Following this process step S112 the NOx storage quantity NOxsum and the value of the high-temperature counter Nc at step S213 initialized with 0. Then, after the process step S213 The execution of this routine has ended.

[0086] Also through the execution of the aforementioned control sequence or routine by means of the ECU. 10 The NOx is removed in an appropriate manner in the SCR catalyst. 8 reduced, which makes it possible to suppress a situation in which exhaust emissions worsen as much as possible. Second embodiment

[0087] Next, a second embodiment of the present invention will be described, based on Fig. 12 to Fig. 14 described. It should be noted that in this second embodiment, a detailed explanation of the essentially identical construction and control method as in the first embodiment mentioned above is omitted.

[0088] Fig. Figure 12 is a view illustrating the schematic construction of an inlet system and an exhaust system of an internal combustion engine according to a second embodiment of the present invention. In an exhaust duct 3 the internal combustion engine 1 According to the second embodiment, a second NOx storage reduction catalyst is used. 60 (hereinafter sometimes also referred to as a "second NSR catalyst") 60 “ referred to) instead of the above in Fig. 1 SCR catalyst shown 8 arranged. In other words, two NOx storage reduction catalysts are located in the exhaust manifold. 3 arranged. An upstream NOx storage reduction catalyst is the first NSR catalyst. 6 and a downstream NOx storage reduction catalyst is the second NSR catalyst 60 Then it is in the exhaust duct 3 between the first NSR catalyst 6and the second NSR catalyst 60 instead of the above, in Fig. 1 shown urea-water solution addition valve 9 a downstream fuel injection valve 70 arranged. The downstream fuel injection valve 70 It serves to add fuel to an exhaust gas, so that the added fuel, together with the exhaust gas, passes into the second NSR catalyst. 60 is supplied. It should be noted that in this second embodiment, the downstream fuel supply valve is... 70 corresponds to a reducing agent supply device in the present invention.

[0089] In such an exhaust gas purification device, the ECU 10 a first fat peak method to temporarily increase the air-fuel ratio of the first NSR catalyst 6to change the flowing exhaust gas from a lean air-fuel ratio, higher than the stoichiometric air-fuel ratio, to a rich air-fuel ratio, lower than the stoichiometric air-fuel ratio. Additionally, the ECU performs... 10 a second fat peak process to temporarily adjust the air-fuel ratio of the second NSR catalyst 60 to change the flowing exhaust gas from a lean air-fuel ratio, higher than the stoichiometric air-fuel ratio, to a rich air-fuel ratio, lower than the stoichiometric air-fuel ratio. Here, the ECU can 10 a control system for supplying fuel to the second NSR catalyst 60 using the downstream fuel addition valve 70 execute (sometimes referred to below as "fuel supply control"). Then the ECU can 10Perform the second fat peak procedure by executing the fuel supply control.

[0090] Then the ECU 10 the fuel supply control according to the first rich peak method, whereby the air-fuel ratio of the second NSR catalyst 60 The flowing exhaust gas temporarily results in a rich air-fuel ratio. In other words, the ECU causes this. 10 The second fat peak process is carried out according to the first fat peak process. This allows the process from the first NSR catalyst to be carried out. 6 The NOx flushed out by the first grease peak process is reduced by the second grease peak process. It should be noted that in this second embodiment, the second grease peak process is carried out simultaneously with the first grease peak process.

[0091] Furthermore, in cases where the NOx storage quantity is the same as for the ECU 10The fuel delivery quantity in the fuel delivery control implemented according to the first rich-peak method is greater when the catalyst low-temperature period becomes longer. In other words, in cases where the NOx storage quantity is the same, the ECU increases the fuel delivery quantity. 10 The richness of the rich air-fuel ratio, which is achieved by carrying out the second rich-peak process according to the first rich-peak process, when the catalyst low-temperature period is extended. As a result, even if the NOx scavenging quantity increases when the catalyst low-temperature period is extended, the first NSR catalyst can be used. 6 The purged NOx is reduced appropriately, making it possible to suppress a situation in which exhaust emissions worsen as effectively as possible. It should be noted that in this second embodiment, the ECU 10the fuel supply quantity, as mentioned above, is increased, whereby the supply quantity control is carried out.

[0092] Here, a control sequence or a routine executed in this second embodiment is based on Fig. 13 described. Fig. Figure 13 is a flowchart illustrating the control sequence or routine according to this second embodiment. In this second embodiment, this routine is repeated at a predetermined operating interval or time period. Δt through the ECU 10 during the operation of the internal combustion engine 1 executed. It should be noted that in the respective in Fig. The procedures shown in section 13 use the same reference numerals as those in the aforementioned procedure, which are essentially the same procedure. Fig. The 7 images shown are attached, and the detailed explanation of them is omitted.

[0093] In the Fig. The control sequence shown in step 13 is used in cases where, at step 13, the following occurs: S108 If a positive decision is reached, then step S309 The fuel supply quantity setpoint Qfad is calculated. Here, the fuel supply quantity setpoint Qfad is a setpoint for the supply quantity from the downstream fuel injection valve. 70 Fuel supplied by the second fat peak procedure, which is carried out according to the first fat peak procedure. At step S309 The fuel delivery setpoint Qfad is calculated based on the value of the low-temperature meter Mc. The fuel delivery setpoint Qfad and the low-temperature meter Mc have a particular relationship in Fig. The 14 correlations shown are related to each other. This correlation was then pre-programmed into the ECU's ROM. 10 stored as a function or characteristic map and at step S309 The fuel supply quantity setpoint Qfad is determined based on the correlation and the value obtained at stepS106 counted value of the low-temperature meter Mc calculated. If the value of the low-temperature counter Mc 0 The fuel supply quantity setpoint Qfad calculated in this way, as in Fig. As shown in Figure 14, the fuel delivery setpoint Qfad increases when the low-temperature counter value exceeds 0. In other words, in cases where the NOx storage quantity NOxsum is a reference quantity NOxth, the fuel delivery setpoint Qfad increases when the catalyst low-temperature period is longer.

[0094] Then, after the procedural step S309 The first fat tip procedure and the second fat tip procedure at the same time at step S310 executed. After the process step S310 Then the ECU routine begins 10 to the procedural step S113 .

[0095] Additionally, in cases where at step S108 If the decision is negative, then proceed to step S311 The first fat tip procedure was carried out. After the procedure step S311 Then the ECU routine begins 10 to the procedural step S113 .

[0096] By executing the aforementioned control sequence or routine by means of the ECU 10 can this be from the first NSR catalyst 6 NOx flushed by the first grease peak process is adequately reduced by the second grease peak process, making it possible to suppress a situation in which exhaust emissions worsen as much as possible. Third example

[0097] Next, a third embodiment of the present invention will be described, based on Fig. 15 described. It should be noted that in this third embodiment, a detailed explanation of the essentially identical construction and control method as in the first embodiment mentioned above is omitted.

[0098] In this third embodiment, the ECU calculates 10 a lot of in the first NSR catalyst 6 Stored nitrates (hereinafter sometimes referred to as a "nitrate storage quantity") based on the NSR catalyst temperature. Here, a ratio of the nitrate storage quantity to the NOx storage quantity is defined as a nitrate ratio, and a predetermined determination ratio is defined as a ratio at which the nitrate stored from the first NSR catalyst is... 6The NOx purged by the fat peaking process becomes extremely small when the nitrate ratio is equal to or higher than the predetermined settling ratio. In this case, if the nitrate ratio is lower than the predetermined settling ratio at the time the fat peaking process is requested, when the current fat peaking process is executed, a portion of the stored NOx from the first NSR catalyst is removed. 6Flushed. Then, in this case, even if the NOx storage quantity is the same, when the fat peaking procedure is executed in a low nitrate ratio state, the NOx flushing quantity will be greater compared to a state where the nitrate ratio is high when the fat peaking procedure is executed. Consequently, in cases where the nitrate ratio is lower than the predetermined setpoint when the fat peaking procedure is requested, the feed control is executed according to the fat peaking procedure, and the feed rate of the reducing agent in the feed control is controlled based on the nitrate ratio. In particular, the ECU can 10Control the system so that, even if the NOx storage quantity is the same, the amount of reducing agent supplied in the feed control system implemented according to the peak-fat method is greater when the nitrate ratio is low than when it is high. As a result, even when the peak-fat method is implemented in the state where the nitrate ratio is low, the amount of NOx released from the first NSR catalyst can be reduced. 6 NOx flushed by the fat peak method is reduced compared to the case where the fat peak method is carried out in the state where the nitrate ratio is high.

[0099] Here, a control sequence or a routine executed in this third embodiment is based on Fig. 15 described. Fig. Figure 15 is a flowchart illustrating the control sequence or routine according to this third embodiment. In this third embodiment, this routine is repeated at a predetermined operating interval or time period. Δt through the ECU 10 during the operation of the internal combustion engine 1 executed. It should be noted that in the respective in Fig. The procedures shown in section 15 use the same reference numerals as those in the aforementioned procedure, which are essentially the same procedure. Fig. The 7 images shown are attached, and the detailed explanation of them is omitted.

[0100] In the Fig. The control sequence shown in 15 is carried out after the process step S101 at step S401 An oxygen concentration (O2con) of an incoming exhaust gas is obtained. At step S401The oxygen concentration O2con of the incoming exhaust gas is determined based on the output value of the air-fuel ratio sensor. 14 calculated. Then, after the next step in the process... S401 the ECU routine 10 to the procedural step S102 .

[0101] Additionally, in the Fig. 15 control sequence shown at step S402 after the procedural step S104 a production quantity of nitrates (hereinafter sometimes referred to as a "current production quantity") NO3now, which is in a current state of the first NSR catalyst 6 (i.e., the amount of NOx stored, the NSR catalyst temperature, and the oxygen concentration) produced is calculated. At step S402 A nitrate production rate will be determined based on the data in step S104 calculated NOx storage quantity NOxsum, which is used in step S101 obtained NSR catalyst temperature Tcand the step 401 The oxygen concentration O2con of the incoming exhaust gas is calculated. This nitrate production rate is calculated using the following equation 1. N 03 r e a c = A ⋅ e x p ( − E a R ⋅ T c ) × N 02 s u m a × 02 c o n b NO3reac: the nitrate production rate, Tc: the NSR catalyst temperature, NO2sum: the amount of nitrite stored, O2con: the oxygen concentration, R: a gas constant and A, Ea, a, b: empirical constants

[0102] The current production quantity NO3now is then calculated by multiplying the nitrate production rate NO3reac by the operating time period Δt.

[0103] Here, the nitrite storage quantity NO2sum is a quantity in the first NSR catalyst. 6 stored nitrite and is calculated using the following equation 2. NO 2 sum = NO 2 old + NOxch NO2sum: the amount of nitrite stored, N02old: the last nitrite storage quantity and NOxch: a set of changes

[0104] In other words, the first NSR catalyst 6 Flowing NOx can be converted to nitrite once and in the first NSR catalyst 6 be stored so that the change in NOx in the first NSR catalyst 6 up to the present time, after this routine was last executed, when the nitrite change is assumed. Then the nitrite storage quantity NO2sum is calculated by adding the last quantity of NO2 in the first NSR catalyst. 6 The stored nitrites were calculated as the amount of change NOxch.

[0105] Then, in step S403 The nitrate storage quantity NO3sum is calculated. In step S403 The nitrate storage quantity NO3sum is determined by adding the values ​​obtained in step S402 The calculated current production quantity NO3now is compared to the nitrate storage quantity NO3sum. It should be noted that the ECU 10as a nitrate storage quantity calculation unit according to the present invention by carrying out the process steps S402 and S403 works.

[0106] Then at step S404 The nitrate ratio (NO3rate) is calculated. At step S404 The nitrate ratio NO3rate is determined by dividing the values ​​obtained in step S403 calculated nitrate storage amount NO3sum by the at step S104 Calculated NOx storage quantity NOxsum calculated. After the process step S404 The ECU routine 10 then to the procedural step S107 It should be noted here that the ECU 10 as a nitrate ratio calculation unit according to the present invention by carrying out the process step S404 works.

[0107] Then, in cases where at step S107 A positive decision is made at step S408 determines whether this occurs at step S404The calculated nitrate ratio (NO3rate) is lower than the determined ratio (NO3rateth). Here, the determined ratio (NO3rateth) is as stated above. Then the ECU routine proceeds. 10 in cases where at step S408 a positive decision will lead to the next procedural step S409 In cases where at step S408 If the decision is negative, the ECU's routine continues. 10 on the other hand to the procedural step S112 .

[0108] In cases where at step S408 If a positive decision is reached, then step S409 The target value for the urea-water solution addition quantity (quad) is calculated. At step S409 The urea-water solution addition setpoint Quad is based on the value obtained at step S404The calculated nitrate ratio NO3rate is used. In particular, in cases where the NOx storage quantity NOxsum is the reference quantity NOxth, the urea-water solution addition setpoint Quad is larger when the nitrate ratio NO3rate is low than when it is high. After the process step S409 Then the ECU routine begins 10 to the procedural step S110 .

[0109] Following this process step S112 at step S413 The NOx storage quantity NOxsum and the nitrate storage quantity NO3sum are initialized to 0. After the process step S413 The routine will then end.

[0110] By executing the aforementioned control sequence or routine by means of the ECU 10 NOx is removed in an appropriate manner in the SCR catalyst. 8reduced, which makes it possible to suppress a situation in which exhaust emissions worsen as much as possible.

[0111] In summary, it can be stated that a situation in which exhaust emissions due to NOx purged from an NSR catalyst can be suppressed as effectively as possible. An exhaust gas purification device for an internal combustion engine operating in lean-burn mode includes: an NSR catalyst; a downstream catalyst located on the NSR catalyst; a reducing agent supply device; an air-fuel ratio control unit to implement a rich-peak procedure; and a supply control unit to control the supply of reducing agent to the downstream catalyst, whereby in cases where the temperature of the NSR catalyst falls below a predetermined temperature for at least part of a period, the supply control unit implements the supply control according to the current rich-peak procedure.and a NOx storage quantity calculation unit to calculate a NOx storage quantity in the NSR catalyst; wherein the feed control unit controls such that, in cases where the NOx storage quantity is the same, a feed quantity of the reducing agent in the feed control becomes larger when a period during which the temperature of the NSR catalyst is lower than the predetermined set temperature becomes longer. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2005163590 A

[0004] JP 2016186239 A

[0005]

Claims

[1] Exhaust gas purification device for an internal combustion engine which operates in lean combustion mode, comprising: a first NOx storage reduction catalyst located in an exhaust channel of the internal combustion engine; a downstream catalyst located in the exhaust gas channel downstream of the first NOx storage reduction catalyst, which reduces NOx in an exhaust gas by means of an supplied reducing agent; a reducing agent supply device which is arranged in the exhaust gas channel between the first NOx storage reduction catalyst and the post-stage catalyst and supplies the reducing agent to the exhaust gas channel; an air-fuel ratio control unit configured to perform a rich peak procedure to temporarily change the air-fuel ratio of an exhaust gas flowing into the first NOx storage reduction catalyst from a lean air-fuel ratio higher than a stoichiometric air-fuel ratio to a rich air-fuel ratio lower than the stoichiometric air-fuel ratio; a feed control unit configured to perform feed control to supply the reducing agent to the downstream catalyst by using the reducing agent feed device, wherein, in cases where the temperature of the first NOx storage reduction catalyst falls below a predetermined temperature for at least part of a period of time from the completion of the execution of the last fat peak process until a request is made to execute the current fat peak process, the feed control unit performs the feed control in accordance with the execution of the current fat peak process by the air-fuel ratio control unit; and a NOx storage quantity calculation unit that is set up to calculate a NOx storage quantity which is a quantity of NOx stored in the first NOx storage reduction catalyst; wherein in cases where the NOx storage quantity calculated by the NOx storage quantity calculation unit is the same, the feed control unit performs a feed quantity control to increase a feed quantity of the reducing agent in the feed control if a period during which the temperature of the first NOx storage reduction catalyst is lower than the predetermined determination temperature becomes longer. [2] Exhaust gas purification device for an internal combustion engine according to claim 1, wherein The post-stage catalyst is a NOx-SCR catalyst that reduces the NOx in the exhaust gas by adding ammonia; the reducing agent supply device supplies a precursor of ammonia or ammonia; and In cases where the temperature of the first NOx storage reduction catalyst falls below the predetermined temperature at least during part of the determination period from the completion of the execution of the last fat peak process until the request to execute the current fat peak process, the feed control unit executes the feed control before the current fat peak process is executed by the air-fuel ratio control unit. [3] Exhaust gas purification device for an internal combustion engine according to claim 2, wherein the feed control unit performs the feed quantity control, so that the amount of ammonia adsorption in the NOx-SCR catalyst after the execution of the feed quantity control becomes lower than a slip development adsorption amount at which ammonia slip occurs at the NOx-SCR catalyst. [4] Exhaust gas purification device for an internal combustion engine according to claim 1, wherein The post-stage catalyst is a second NOx storage reduction catalyst that reduces the NOx in the exhaust gas by adding fuel; the reducing agent supply device supplies fuel; and In cases where the temperature of the first NOx storage reduction catalyst falls below the predetermined temperature at least during part of the determination period from the completion of the execution of the last fat peak process until the request to execute the current fat peak process, the feed control unit executes the feed control simultaneously with the execution of the current fat peak process by the air-fuel ratio control unit. [5] Exhaust gas purification device for an internal combustion engine which operates in lean combustion mode, comprising: a first NOx storage reduction catalyst located in an exhaust channel of the internal combustion engine; a downstream catalyst located in the exhaust gas channel downstream of the first NOx storage reduction catalyst, which reduces NOx in an exhaust gas by means of an supplied reducing agent; a reducing agent supply device which is arranged in the exhaust gas channel between the first NOx storage reduction catalyst and the post-stage catalyst and supplies the reducing agent to the exhaust gas channel; an air-fuel ratio control unit configured to perform a rich peak procedure to temporarily change the air-fuel ratio of an exhaust gas flowing into the first NOx storage reduction catalyst from a lean air-fuel ratio higher than a stoichiometric air-fuel ratio to a rich air-fuel ratio lower than the stoichiometric air-fuel ratio; a feed control unit which is set up to perform feed control in order to supply the reducing agent to the downstream catalyst by using the reducing agent feed device; a NOx storage quantity calculation unit that is set up to calculate a NOx storage quantity which is a quantity of NOx stored in the first NOx storage reduction catalyst; a nitrate storage quantity calculation unit, which is set up to calculate a nitrate storage quantity based on a temperature of the first NOx storage reduction catalyst, which is a quantity of nitrate stored in the first NOx storage reduction catalyst; and a nitrate ratio calculation unit that is set up to calculate a nitrate ratio, which is a ratio of the nitrate storage quantity to the NOx storage quantity, based on the NOx storage quantity calculated by the NOx storage quantity calculation unit and the nitrate storage quantity calculated by the nitrate storage quantity calculation unit; wherein in cases where the nitrate ratio calculated by the nitrate ratio calculation unit is lower than a predetermined determination ratio, when the execution of the fat peak procedure is requested, the feed control unit executes the feed control in accordance with the execution of the fat peak procedure by the air-fuel ratio control unit and controls a feed quantity of the reducing agent in the feed control based on the nitrate ratio.

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