JP6500636B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus provided with a NOx storage reduction catalyst that reduces and purifies nitrogen oxides (NOx) contained in exhaust gas of an engine.

  An exhaust gas purification device is provided in the middle of an exhaust path for the purpose of purifying exhaust gas discharged from an engine such as a car before opening to the atmosphere. As an exhaust gas purification device, for example, as shown in Patent Document 1, there is one equipped with a NOx storage reduction catalyst.

The NOx storage reduction type catalyst (storage material) is a catalyst active metal portion having a supported noble metal in contact with exhaust gas on a part of a catalyst support layer formed of alumina (Al ₂ O ₃ ) or the like, and as a NOx storage material And a NOx storage material portion having an alkali metal such as barium (Ba).

In the catalytically active metal part, nitric oxide (NO) is oxidized on the noble metal in combination with oxygen in the exhaust gas to form nitrogen dioxide (NO ₂ ). In particular, when the exhaust is in a lean atmosphere, such as during normal operation, such reaction is promoted because there is much oxygen in the exhaust. Then, the generated nitrogen dioxide chemically reacts with barium, which is a NOx storage material, to become nitrates such as barium nitrate (Ba (NO ₃ ) ₂ ) and stored in the NOx storage portion.

By supplying a reducing agent such as carbon monoxide (CO), hydrocarbon (HC), or hydrogen (H ₂ ) into the exhaust gas to create a rich atmosphere, barium nitrate is decomposed in the NOx storage material section, and nitrogen oxidation occurs. The thing is released. At this time, the nitrogen oxides are reduced at the catalytically active metal part and released to the atmosphere in a harmless manner such as nitrogen (N ₂ ), water (H ₂ O) or carbon dioxide (CO ₂ ). This release of nitrogen oxide from the NOx storage material portion is referred to as a NOx purge.

  In addition to the NOx storage reduction type catalyst having a function of storing nitrogen oxides as described above, there is also an exhaust gas purification apparatus provided with a NOx adsorption catalyst having a function of adsorbing nitrogen oxides.

The NOx adsorption catalyst (adsorbent) is provided with a catalytically active metal portion having a supported noble metal in contact with the exhaust gas on a part of a catalyst supporting layer formed of cerium oxide (CeO ₂ ) or the like.

In the catalytically active metal part, nitric oxide (NO) is oxidized on the noble metal in combination with oxygen in the exhaust gas to form nitrogen dioxide (NO ₂ ). In particular, when the exhaust is in a lean atmosphere, such as during normal operation, such reaction is promoted because there is much oxygen in the exhaust. Then, the produced nitrogen dioxide is adsorbed to the cerium oxide (not in a chemical reaction but in a state of being chemisorbed), but it is desorbed from the cerium oxide by an increase in temperature.

  The NOx storage reduction catalyst has an extremely low activity at a temperature at which the catalyst temperature is low, and can not exhibit a predetermined storage performance. For this reason, after the start of the engine, the control of raising the temperature of the exhaust gas early is performed to promote the activation of the catalyst.

  Further, since the NOx adsorption catalyst can exhibit the adsorption performance of nitrogen oxides even at a relatively low temperature, the atmosphere of nitrogen oxides can be obtained even when the temperature of the exhaust gas is low such that the NOx storage reduction catalyst is not activated. It can exert the effect of suppressing the release.

JP, 2006-83746, A

  In the NOx trap catalyst including the NOx storage reduction catalyst (storage material) and the NOx adsorption catalyst (adsorption material) in combination, the difficulty in releasing nitrogen oxides in the NOx storage reduction catalyst corresponds to the NOx adsorption catalyst. It is relatively larger than the difficulty of releasing nitrogen oxides in That is, the NOx adsorption catalyst can release the occluded or adsorbed nitrogen oxides more easily than the NOx storage reduction catalyst. For this reason, it is considered that most of the nitrogen oxides desorbed from the NOx adsorption catalyst, from which nitrogen oxides are relatively easily released, are stored in the adjacent NOx storage reduction catalyst.

  In this NOx trap catalyst, for example, there are many nitrogen oxides stored in the NOx storage reduction catalyst, and even if there is no or less storage capacity more than that, or temperature conditions where the NOx storage reduction catalyst is not activated Even under the condition where the NOx adsorption catalyst adsorbs nitrogen oxides, the emission of nitrogen oxides to the atmosphere can be suppressed. In addition, when there is a large amount of nitrogen oxides adsorbed to the NOx adsorption catalyst, the adsorbed nitrogen oxides are desorbed by the temperature rise control, and the desorbed nitrogen oxides are occluded by the adjacent NOx storage reduction catalyst. Can restore its adsorption capacity.

  However, when there is a large amount of adsorbed nitrogen oxides and a large amount of absorbed nitrogen oxides, the action of the desorption of the adsorbed nitrogen oxides and the storage of the eliminated nitrogen oxides into the NOx storage reduction type catalyst Can not exert enough. For this reason, even if NOx purge is performed in that state, there is a risk that nitrogen oxides that can not be purified slip and are released to the atmosphere.

  Therefore, an object of the present invention is to prevent atmospheric emission of nitrogen oxides which can not be purified, in the NOx trap catalyst including the NOx storage reduction type catalyst and the NOx adsorption catalyst in combination.

  In order to solve the above problems, the present invention relates to an NOx trap catalyst provided in an intake passage and an exhaust passage connected to a combustion chamber of an engine, an occluding material and an adsorbing material provided in the exhaust passage, and the NOx Exhaust gas temperature control means for controlling the temperature of the exhaust gas to a temperature necessary for activation of the trap catalyst; reducing agent supply control means for supplying a reducing agent to the exhaust gas in the NOx trap catalyst; A storage amount estimation means for estimating the storage amount of nitrogen oxides stored in the material; and an adsorption amount estimation means for estimating the adsorption amount of the nitrogen oxides adsorbed on the adsorbent, wherein the storage amount is predetermined When the adsorption amount is less than the storage amount and the adsorption amount is the predetermined adsorption amount or more, the exhaust gas temperature control means performs the temperature rise control to desorb the nitrogen oxides adsorbed to the adsorbent, and the desorption thereof. Nitrogen acid Things were the engine exhaust purification device to be occluded in the occluding member.

  In this configuration, the reducing agent supply control means can adopt a configuration for releasing the nitrogen oxide stored in the storage material by supplying the reducing agent.

  Further, when the storage amount is equal to or more than a second predetermined storage amount set to a value larger than the predetermined storage amount, the reducing agent supply control unit supplies the reducing agent to store the storage material in the storage material. It is possible to adopt a configuration for releasing the nitrogen oxide.

  In the case where the exhaust passage is provided with a catalyst device for suppressing emission of exhaust particulates, hydrocarbons, or carbon monoxide into the atmosphere, and the NOx trapping catalyst is on the upstream side of the catalyst device, the temperature rise control is performed by the intake passage. By throttling the throttle valve provided in the valve to increase the temperature to a first predetermined temperature at which desorption of nitrogen oxides and storage of the desorbed nitrogen oxides are possible, and the amount of fuel stored is increased. A configuration may be employed in which the temperature is raised to a second predetermined temperature at which the oxide can be released.

  In the case where the exhaust passage is provided with a catalyst device for suppressing atmospheric emission of exhaust particulates, hydrocarbons, or carbon monoxide, and the NOx trap catalyst is on the downstream side of the catalyst device, the temperature rise control is performed by: If the temperature of the catalytic converter is lower than the catalyst activation temperature, the first predetermined valve is capable of desorbing nitrogen oxides and storing desorbed nitrogen oxides by throttling a throttle valve provided in the intake passage. The temperature is raised to the temperature, and if the temperature of the catalyst device is equal to or higher than the catalyst activation temperature, the fuel is increased to raise the temperature to the second predetermined temperature at which the stored nitrogen oxide can be released. It can be adopted.

  According to the present invention, the temperature of the exhaust gas is less than the predetermined temperature, and the storage amount of nitrogen oxides of the NOx storage reduction catalyst (storage material) provided in the NOx trap catalyst is less than the predetermined storage amount, and the NOx adsorption catalyst When the adsorption amount of nitrogen oxides of (adsorbent) is equal to or more than a predetermined adsorption amount, temperature rise control of exhaust gas is performed. By this temperature rise control, the nitrogen oxides adsorbed to the NOx adsorption catalyst are desorbed, and the desorbed nitrogen oxides are absorbed by the NOx storage reduction type catalyst, so that the adsorption performance of the NOx adsorption catalyst can be promptly enhanced. Can. This can prevent atmospheric emission of nitrogen oxides that can not be purified.

  In addition, when the temperature of the exhaust gas is less than the predetermined temperature, the storage amount of nitrogen oxides of the NOx storage reduction catalyst is the predetermined storage amount or more, and the adsorption amount is the predetermined adsorption amount or more, the exhaust gas While performing temperature rise control of (1), a reducing agent is supplied. By the temperature increase control and the supply of the reducing agent, the nitrogen oxides adsorbed on the NOx adsorption catalyst are desorbed, and the desorbed nitrogen oxides are absorbed in the NOx storage reduction type catalyst, and are stored in the NOx storage reduction type catalyst Nitrogen oxides are released to the atmosphere as harmless substances. This can prevent atmospheric emission of nitrogen oxides that can not be purified.

It is a schematic diagram of the exhaust gas purification device of the engine of one embodiment of this invention. It is a schematic diagram which shows the modification of FIG. It is a graph which shows control of the exhaust gas purification device of the engine of this invention. It is a flowchart which shows control of the exhaust gas purification device of the engine of this invention.

  Hereinafter, an embodiment of the present invention will be described based on the drawings. FIG. 1 is a schematic view conceptually showing the structure of an exhaust purification system of an engine of this embodiment. FIG. 2 is a modification of FIG.

  The type and arrangement of the catalyst or the like for purifying the exhaust gas are different from the example of FIG. 1 and the example of FIG. Hereinafter, first, the configuration of the exhaust gas purification apparatus of the engine of the present invention and the control method thereof will be described in the order of FIG. 1 and FIG.

  First, as shown in FIG. 1, an intake passage 11 and an exhaust passage 5 are connected to a combustion chamber of the engine 1. Air is supplied to the combustion chamber through the intake passage 11. Further, fuel is injected into the combustion chamber by the fuel injection device. Exhaust gas from the combustion chamber is discharged to the atmosphere through the exhaust passage 5.

  In the intake passage 11, from the upstream side to the downstream side, an air cleaner, a throttle valve 12 that changes the passage cross-sectional area to control the flow rate of intake air, an air flow sensor 13 that detects the amount of intake air, etc. .

  A NOx trap catalyst 2 provided with a diesel oxidation catalyst 4, a diesel particulate filter 3, a NOx storage reduction catalyst (storage material) and a NOx adsorption catalyst (adsorbent material) in the exhaust passage 5 from the upstream side toward the downstream side , Mufflers as a silencer, etc. are sequentially provided.

  The diesel oxidation catalyst 4 oxidizes carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas to suppress their release to the atmosphere.

  The diesel particulate filter 3 captures diesel particulates (PM) contained in the exhaust gas and suppresses the release of the diesel particulates into the atmosphere.

The NOx trapping catalyst 2 is a catalytically active metal portion having a supported noble metal in contact with exhaust gas on a part of a catalyst supporting layer formed of alumina (Al ₂ O ₃ ) or the like as a NOx storage reduction type catalyst (storage material) And a NOx storage material portion having an alkali metal such as barium (Ba) as a NOx storage material.

In the catalytically active metal part, nitric oxide (NO) is oxidized on the noble metal in combination with oxygen in the exhaust gas to form nitrogen dioxide (NO ₂ ). In particular, when the exhaust is in a lean atmosphere, such as during normal operation, such reaction is promoted because there is much oxygen in the exhaust. Then, the generated nitrogen dioxide chemically reacts with barium, which is a NOx storage material, to become nitrates such as barium nitrate (Ba (NO ₃ ) ₂ ) and stored in the NOx storage portion. Thus, the NOx storage reduction type catalyst stores nitrogen oxides (NOx) contained in the exhaust gas, and suppresses the release of nitrogen oxides to the atmosphere.

In addition, the NOx trapping catalyst 2 has a catalytically active metal portion having a supported noble metal in contact with exhaust gas on a part of a catalyst supporting layer formed of cerium oxide (CeO ₂ ) or the like as a NOx adsorption catalyst (adsorbent). Have.

In the catalytically active metal part, nitric oxide (NO) is oxidized on the noble metal in combination with oxygen in the exhaust gas to form nitrogen dioxide (NO ₂ ). In particular, when the exhaust is in a lean atmosphere, such as during normal operation, such reaction is promoted because there is much oxygen in the exhaust. And although the produced nitrogen dioxide is in the state where it is adsorbed to cerium oxide, it is desorbed from the cerium oxide by the rise of temperature. Thus, the NOx adsorption catalyst adsorbs nitrogen oxides (NOx) contained in the exhaust gas, and suppresses the release of nitrogen oxides to the atmosphere. Also, the adsorbed nitrogen oxide is appropriately desorbed, and the desorbed nitrogen oxide is transferred to a NOx storage reduction type catalyst that can be more stably held (occluded).

  Exhaust gas temperature detection means for detecting the temperature of the exhaust gas is provided in the exhaust passage 5. In this embodiment, exhaust temperature sensors 4a, 3a and 2a are provided in the diesel oxidation catalyst 4, the diesel particulate filter 3 and the NOx trap catalyst 2, respectively, as exhaust gas temperature detection means. The exhaust gas temperature detection means may be provided in a place other than the purification device, for example, in the exhaust passage 5 between the diesel oxidation catalyst 4 and the engine 1 or between the diesel particulate filter 3 and the NOx trap catalyst 2.

  The temperature of the exhaust gas obtained by the exhaust gas temperature detection means is the temperature of the portion where the exhaust gas temperature detection means is provided, that is, the purification devices such as the diesel oxidation catalyst 4, the diesel particulate filter 3 and the NOx trap catalyst 2 The temperature information is transmitted to a control means provided in an Electronic Control Unit 20 that controls the engine 1 through a cable. Alternatively, exhaust gas temperature detection means may be provided at only one place in the exhaust passage 5, and the temperature of the exhaust gas detected at the one place may be positioned equivalent to the temperature of each purification device.

  Further, an air-fuel ratio sensor 14 is provided at the downstream end of the NOx trapping catalyst 2. Information on the air-fuel ratio obtained by the air-fuel ratio sensor 14 is similarly transmitted to the control means of the electronic control unit 20.

  The intake valve, the exhaust valve, the fuel injection device, and other devices necessary for the operation of the engine are controlled by control means provided in the electronic control unit 20 through cables.

  An exhaust gas recirculation passage 6 is connected between the exhaust gas passage 5 upstream of the diesel oxidation catalyst 4 which is the most upstream purification device and the intake gas passage 11 downstream of the throttle valve 12. The exhaust gas recirculation passage 6 is opened and closed by the exhaust gas recirculation valve 6a, and a part of the exhaust gas is recirculated into the intake passage 11 as a reflux gas. The opening and closing of the exhaust gas recirculation valve 6a is also controlled by the control means of the electronic control unit 20 according to the operating condition.

  The electronic control unit 20 includes a driving state determination unit 21 that determines the driving state of the engine 1 mounted on the vehicle.

  The operating state determination means 21 acquires information on the temperature of the cooling water, the number of revolutions of the engine, information on the engine load, and the like from the engine 1 and utilizes the information for controlling the engine 1. In addition to the information on the exhaust temperature described above, the operating state determination means 21 can also acquire information on whether the engine 1 is cold or after being warmed up, etc. It is used for control.

  The purification devices such as the diesel oxidation catalyst 4, the diesel particulate filter 3, and the NOx trap catalyst 2 have temperature conditions that are effective for purification of the exhaust gas. If the temperature of the catalyst or the filter is equal to or higher than the activity temperature specific to the catalyst or the filter, the purification of the harmful substance is satisfactorily performed unless it is an abnormally high temperature which is not a normal operating condition.

  The lowest temperature at which both the diesel oxidation catalyst 4 and the diesel particulate filter 3 can properly exhibit the purification action is referred to as a catalyst activation temperature. If it is above the catalyst activation temperature, the diesel oxidation catalyst 4 and the diesel particulate filter 3 can exhibit the purifying action well. When only one of the diesel oxidation catalyst 4 and the diesel particulate filter 3 is provided as the purification device, the lowest temperature at which one of the diesel oxidation catalyst 4 and the diesel particulate filter 3 can exhibit a good purification action is referred to as catalyst activation temperature. When both the diesel oxidation catalyst 4 and the diesel particulate filter 3 are provided as the purification device, the relatively lower minimum temperature can be referred to as a catalyst activation temperature.

  In addition, the temperature at which the NOx adsorption catalyst of the NOx trap catalyst 2 can satisfactorily desorb nitrogen oxides and the NOx storage reduction type catalyst of the NOx trap catalyst 2 can exhibit the NOx oxide storage function favorably It is called the predetermined temperature of. If the temperature is equal to or higher than the first predetermined temperature, the NOx adsorption catalyst can satisfactorily desorb the nitrogen oxide, and the NOx storage reduction catalyst can exhibit the nitrogen oxide storage function well. The adsorption of nitrogen oxides by the NOx adsorption catalyst is possible even at a relatively low temperature.

  Furthermore, the minimum temperature at which the nitrogen oxides stored in the NOx storage reduction type catalyst of the NOx trap catalyst 2 are released, that is, can be purged is referred to as a second predetermined temperature. If the temperature is higher than the second predetermined temperature, the stored nitrogen oxides can be released quickly if other environmental conditions are satisfied. Here, the relationship of second predetermined temperature> first predetermined temperature is established.

  The electronic control unit 20 includes the exhaust gas temperature control means 22 for performing control to raise the temperature of the exhaust gas to the temperature necessary for activating each purification device when it is determined that the operating state determination means 21 is necessary. . The exhaust gas temperature control means 22 can adjust the temperature of the exhaust gas by increasing and decreasing fuel into the combustion chamber, increasing and decreasing the amount of supplied air, controlling the fuel injection timing, and the like.

  That is, the exhaust gas temperature control means 22 increases the amount of fuel and air supplied to the combustion chamber in order to raise the temperature of the exhaust gas at an early stage, if necessary, when the engine 1 is started in cold weather or the like. Then, control is performed to increase the exhaust temperature by securing a high exhaust temperature or retarding the fuel injection timing. The control of the exhaust gas temperature rise by the exhaust gas temperature control means 22 is hereinafter referred to as temperature increase control. The control by the exhaust gas temperature control means 22 is based on the information from the operating state determination means 21.

In addition, the electronic control unit 20 includes a reducing agent supply control unit 23 for supplying a reducing agent to the exhaust gas in the NOx trap catalyst 2. The reducing agent supply control means 23 supplies reducing agents such as carbon monoxide (CO), hydrocarbons (HC) and hydrogen (H ₂ ) to the exhaust gas in the NOx trap catalyst 2 to make the exhaust gas a rich atmosphere. As a result, in the NOx storage material portion, barium nitrate is decomposed and nitrogen oxides are released. At this time, nitrogen oxides are released into the atmosphere in a harmless manner such as nitrogen (N ₂ ), water (H ₂ O) or carbon dioxide (CO ₂ ), and NOx purge is performed.

  The electronic control unit 20 estimates storage amount estimation means 24 for estimating the storage amount of nitrogen oxides by the NOx storage reduction type catalyst of the NOx trap catalyst 2, and estimates the adsorption amount of nitrogen oxides by the NOx adsorption catalyst of the NOx trap catalyst 2. And an adsorption amount estimation unit 25.

  The adsorption amount estimating means 25 calculates the adsorption amount of nitrogen oxide in the NOx adsorption catalyst and the NOx adsorption amount (n) on the basis of information such as the air-fuel ratio in the exhaust passing through the exhaust passage 5 and its temperature and elapsed time. It can be calculated. Based on the air-fuel ratio in the exhaust gas and the temperature thereof, it is also possible to determine the adsorption amount of these nitrogen oxides and the NOx adsorption amount (n) using a map. Also, even when the adsorbed nitrogen oxide is desorbed, the desorbed amount (desorbed amount) is calculated based on information such as the air-fuel ratio in exhaust gas, its temperature, elapsed time, etc., and the remaining nitrogen oxide The amount of adsorption of

As a specific calculation method, for example, the NOx adsorption amount is
It can be calculated by calculation of NOx adsorption amount (n) = NOx adsorption amount (n-1) + adsorbed NOx amount-desorbed NOx amount.

  First, the saturated NOx adsorption amount is calculated from the type and capacity of the adsorption material, and the temperature of the NOx trap catalyst 2, and the NOx adsorption saturation rate is calculated by dividing the NOx adsorption amount (n-1) by the saturated NOx adsorption amount. .

  Next, how to determine the amount of adsorbed NOx will be described. The adsorption / desorption rate is calculated from the NOx adsorption saturation rate. The adsorption / desorption rate indicates the increase rate by adsorption with the sign + and the decrease rate by desorption with the sign −. When the NOx adsorption saturation rate <1, the inflow NOx amount is calculated from the map of the rotational speed and the torque of the engine 1, and the adsorbed NOx amount is calculated by multiplying the adsorption / desorption rate. In the case of the NOx adsorption saturation ratio = 1, both the adsorbed NOx amount and the desorbed NOx amount are zero. In the case where the NOx adsorption saturation rate is more than 1, the desorbed NOx amount can be calculated by multiplying the NOx adsorption amount (n-1) by the adsorption / desorption rate.

  The storage amount estimation means 24 stores the storage amount of nitrogen oxide and the NOx storage amount (n) in the NOx storage reduction type catalyst based on information such as the air fuel ratio in the exhaust passing through the exhaust passage 5, its temperature, elapsed time and the like. It can be calculated by calculation. It is also possible to determine the storage amount of these nitrogen oxides and the storage amount of NOx (n) using a map based on the air-fuel ratio in the exhaust gas and the temperature thereof. In addition, even when the stored nitrogen oxide is released, the released amount (decomposed amount) is calculated based on the information such as the air-fuel ratio in exhaust gas, its temperature, elapsed time, and storage of remaining nitrogen oxide. You can figure out the amount.

As a specific calculation method, for example, the NOx storage amount is
It can be calculated by calculation of NOx storage amount (n) = NOx storage amount (n-1) + stored NOx amount-decomposed NOx amount.

  First, how to determine the NOx storageable amount will be described. The saturated NOx occluded amount is calculated from the type and capacity of the occluding material, and the NOx occludable amount is calculated from the NOx occluded amount (n-1).

  Next, how to determine the amount of stored NOx will be described. The NOx storage ratio is calculated from the temperature of the NOx trap catalyst 2 and the map of the intake quantity, and the NOx storage ratio is corrected by correcting the NOx storage capacity with the NOx storage capacity. The change in the NOx storage ratio tends to have a peak at approximately 300 ° C., and the storage ratio tends to decrease if the intake amount is large.

  The amount of nitrogen oxides flowing into the NOx trap catalyst 2 is calculated from the map of the rotational speed and torque of the engine 1, the amount of nitrogen oxides desorbed from the NOx adsorption catalyst is added, and the corrected amount of inflow NOx is calculated calculate. By multiplying the after-correction inflow NOx amount by the after-correction NOx storage rate, it is possible to calculate the amount of nitrogen oxide to be newly stored, that is, the storage NOx amount. If the stored NOx amount> the NOx storable amount, the stored NOx amount = the NOx storable amount is corrected.

  Next, how to determine the amount of decomposed NOx will be described. The amount of decomposed NOx can be determined based on the air-fuel ratio in the exhaust gas and the temperature thereof, using a map to determine the amount of decomposition of these nitrogen oxides. When the amount of decomposed NOx> the amount of absorbed NOx is corrected, the amount of decomposed NOx is corrected to zero.

  The example of FIG. 2 is different from that of FIG. 1 in the type and arrangement of a purification device such as a catalyst that purifies exhaust gas. Specifically, the NOx trap catalyst 2 and the diesel particulate filter 3 are provided in order from the upstream side to the downstream side of the exhaust passage 5 as the purification device. The other configuration is the same as the description of FIG. 1 described above.

  The operation of the control device of the engine and the control method thereof will be described based on the diagram of FIG. 3 and the flowchart of FIG.

  First, in step S1, the electronic control unit 20 estimates the storage amount of nitrogen oxide by the NOx storage reduction catalyst of the NOx trap catalyst 2 and the adsorption amount of nitrogen oxide by the NOx adsorption catalyst of the NOx trap catalyst 2. The estimation is performed by the above-described calculation method.

  Next, at step S2, it is judged if the estimated storage amount is equal to or more than a predetermined storage amount a set in the NOx storage reduction type catalyst. If the storage amount 所 定 predetermined storage amount a, the process proceeds to step S3, and if the storage amount <predetermined storage amount a, the process proceeds to step S10.

  In step S3, it is determined whether the estimated storage amount is equal to or greater than a second predetermined storage amount b (b> a) set in the NOx storage reduction type catalyst. The second predetermined storage amount b is set to a value larger than the predetermined storage amount a, as shown in FIG. 3B, and is set to a value close to the saturation storage amount. Here, if the storage amount 第 the second predetermined storage amount b, the process proceeds to step S4, and it is determined whether or not the forced NOx purge (see the signs # 1, # 2, and # 3 in FIG. 3) is performed. . If the storage amount is less than the second predetermined storage amount b, the process proceeds to step S20.

A condition under which the forced NOx purge can be performed is that the exhaust gas temperature is equal to or higher than a predetermined temperature. If it is determined in step S4 that the exhaust gas temperature is equal to or higher than the predetermined temperature, the process proceeds to step S6 to execute NOx purge. If the exhaust temperature is lower than the predetermined temperature, the NOx purge is not ready to be performed. Therefore, the process proceeds to step S5, and the temperature rise control is performed to achieve the catalyst temperature at which the NOx purge can be performed. After the determination in step S4 again, the NOx purge is performed. Note that the determination based on the water temperature may be used instead of the determination based on the exhaust temperature. The same applies to the following steps.

  The forced NOx purge in step S6 is continued until the storage amount <second predetermined storage amount b (see step S7). If the storage amount <the second predetermined storage amount b, the control is ended (see step S14).

  In step S20, it is determined whether the estimated amount of adsorption is equal to or greater than a predetermined amount of adsorption c set for the NOx adsorption catalyst. Here, if the adsorption amount 所 定 predetermined adsorption amount c, the process proceeds to step S21. If the exhaust gas temperature does not reach the predetermined temperature, the process proceeds to step S22 to control the temperature rise of the exhaust gas, and adsorbed nitrogen oxides Desorption, storage of the desorbed nitrogen oxides, and NOx purge (refer to reference numerals # 4 and # 5 in FIG. 3). If the amount of adsorption is smaller than the predetermined amount of adsorption c, there is a margin for the amount of adsorption, and therefore, the process proceeds to step S14, and the control of purification is ended (see symbol # 6 in FIG. 3).

  The temperature increase control in step S22, desorption / storage, and NOx purge are continued until the amount of adsorption <predetermined amount of storage c (see step S23). If it becomes adsorption amount <predetermined storage amount c, the control is ended (see step S14).

  In step S10, it is determined whether the estimated amount of adsorption is equal to or greater than a predetermined amount of storage c set in the NOx adsorption catalyst. Here, if the adsorption amount 所 定 predetermined storage amount c, the process proceeds to step S11, and if the exhaust gas temperature does not reach the predetermined temperature, the process proceeds to step S12, and the temperature rise control of the exhaust gas is performed (FIG. 3) (See # 7 and # 8 of). If the amount of adsorption is less than the predetermined amount of adsorption c, there is a margin for the amount of adsorption, and therefore, the process proceeds to step S14, and the control of purification is ended (see symbol # 9 in FIG. 3).

  The temperature rise control in step S12 is continued until the adsorption amount <predetermined storage amount c (see step S13). If the amount of adsorption <the predetermined amount of occlusion c, then the process proceeds to S14, and the control of purification is ended.

  The second predetermined adsorption amount d may be set separately from the predetermined adsorption amount c set for the NOx adsorption catalyst. As shown in FIG. 3B, the second predetermined adsorption amount d is set to a value larger than the predetermined adsorption amount c, and is set to a value close to the saturated adsorption amount. If the adsorption amount 第 second predetermined adsorption amount d, the temperature rise control of the exhaust gas performed in step S 8 or S 12 than in the case of the second predetermined adsorption amount d 吸着 adsorption amount 所 定 predetermined adsorption amount c, adsorbed nitrogen Control may be performed to perform each of the functions such as removal of oxides, storage of released nitrogen oxides, and NOx purge more rapidly.

  With regard to the above-described predetermined temperature that is a reference for determining whether temperature increase control is to be performed, the predetermined temperature may be a first predetermined temperature set for the NOx adsorption catalyst of the NOx trap catalyst 2, or NOx The second predetermined temperature may be set to the NOx storage reduction type catalyst of the trap catalyst 2. Further, the predetermined temperature may be set to one of the first predetermined temperature and the second predetermined temperature, whichever is lower.

  As described above, the temperature of the exhaust gas detected by the exhaust gas temperature detecting means 2a, 3a, 4a is less than the predetermined temperature, and the storage amount of the NOx storage reduction type catalyst of the NOx trap catalyst 2 is less than the predetermined storage amount a. And, when the adsorption amount of the NOx adsorption catalyst of the NOx trap catalyst 2 is equal to or more than the predetermined adsorption amount c, the exhaust gas temperature control means 22 adsorbs the NOx adsorption catalyst by performing temperature rise control of the exhaust gas. The desorbed nitrogen oxides are desorbed, and most of the desorbed nitrogen oxides are stored in the NOx storage reduction type catalyst. As a result, the adsorbable amount of the NOx adsorption catalyst can be rapidly increased, and the release of nitrogen oxides to the atmosphere can be prevented when the exhaust gas temperature is low.

  The temperature of the exhaust gas is less than a predetermined temperature, the storage amount of the NOx storage reduction type catalyst of the NOx trap catalyst 2 is a predetermined storage amount a or more, and the adsorption amount of the NOx adsorption catalyst of the NOx trap catalyst 2 is a predetermined adsorption When the amount c or more, the exhaust gas temperature control means 22 desorbs nitrogen oxides adsorbed on the NOx adsorption catalyst by performing temperature rise control of the exhaust gas, and most of the desorbed nitrogen oxides are removed. The NOx storage and reduction type catalyst is used for storage. Furthermore, the reducing agent supply control means 23 releases the nitrogen oxide stored in the NOx storage reduction catalyst as a harmless substance to the atmosphere by supplying the reducing agent. As a result, the adsorbable amount of the NOx adsorption catalyst and the storable amount of the NOx storage reduction catalyst are increased to cope with the release of nitrogen oxides to the atmosphere when the exhaust gas temperature is low.

  Further, if the storage amount of the NOx storage reduction type catalyst of the NOx trap catalyst 2 is equal to or greater than the second predetermined storage amount b set to a value larger than the predetermined storage amount a, there is no storage possible amount at all, Alternatively, since the reducing agent supply control means 23 forcibly supplies the reducing agent regardless of the other conditions, the nitrogen oxide stored in the NOx storage reduction catalyst is harmless because the state is very small. Release as a substance to increase the storable amount.

  Here, a method of temperature rise control will be described.

  In the case of the configuration of FIG. 1, the NOx trapping catalyst 2 is located downstream of the catalyst device such as the diesel oxidation catalyst 4 or the diesel particulate filter 3. In this case, if the temperature of the catalyst device is lower than the catalyst activation temperature, the temperature rise control of the exhaust gas decelerates the nitrogen oxides in the NOx adsorption catalyst by throttling the throttle valve 12 provided in the intake passage 11. The temperature is raised to a first predetermined temperature at which the desorbed nitrogen oxide can be stored in the NOx storage reduction type catalyst. If the temperature of the catalytic converter is equal to or higher than the catalyst activation temperature, the second predetermined temperature is capable of purging (releasing) the stored nitrogen oxides by increasing the fuel by post injection performed before main injection. Control can be performed to gradually increase the temperature. The post injection makes it possible to burn the fuel in the vicinity of the diesel oxidation catalyst 4 and the diesel particulate filter 3 which are purification devices in the former stage, thereby oxidizing and generating heat, thereby minimizing the heat radiation loss.

In the case of the configuration of FIG. 2, the NOx trapping catalyst 2 is on the upstream side of the catalyst device such as the diesel particulate filter 3. In this case, the temperature rise control of the exhaust gas is performed by throttling the throttle valve 12 provided in the intake passage 11 to desorb the nitrogen oxide in the NOx adsorption catalyst and the NOx storage reduction type catalyst of the desorbed nitrogen oxide. The temperature is raised to a first predetermined temperature at which storage in the air can be performed. Thereafter, by increasing the amount of fuel, control can be performed to raise the temperature to a second predetermined temperature at which the nitrogen oxides stored in the NOx storage reduction catalyst can be purged (released). Since the air intake throttle also reduces the _{space velocity} , storage of nitrogen oxides can be promoted.
In addition, although the exhaust gas of diesel was described in the present Example, it is not restricted to diesel and can be used for exhaust gas purification of a general internal combustion engine.

1 engine 2 NO _X trap catalyst 3 diesel particulate filter (diesel particulate filter)
4 Diesel oxidation catalyst 2a, 3a, 4a Exhaust gas temperature detection means 5 Exhaust passage 6 Exhaust gas recirculation device 11 Intake passage 12 Throttle valve 13 Air flow sensor 20 Electronic control unit 21 Operation condition judgment means 22 Exhaust gas temperature control means 23 Reductant Supply control means 24 Storage amount estimation means 25 Adsorption amount estimation means

Claims (5)

An intake passage and an exhaust passage connected to a combustion chamber of the engine;
A NOx trap catalyst provided in the exhaust passage and provided with a storage material and an adsorbent;
Exhaust gas temperature control means for controlling the temperature of the exhaust gas to a temperature necessary for activating the NOx trapping catalyst;
Reductant supply control means for supplying a reductant to the exhaust gas in the NOx trap catalyst;
Storage amount estimation means for estimating the storage amount of nitrogen oxides stored in the storage material;
An adsorption amount estimation means for estimating the adsorption amount of nitrogen oxides adsorbed by the adsorbent;
When the storage amount is less than a predetermined storage amount and the adsorption amount is a predetermined adsorption amount or more,
The exhaust gas temperature control means is an engine exhaust purification device for desorbing nitrogen oxides adsorbed on the adsorbent by performing temperature rise control, and storing the desorbed nitrogen oxides in the storage material. The engine exhaust gas purification device according to claim 1, wherein the reducing agent supply control means releases the nitrogen oxide stored in the storage material by supplying a reducing agent. When the storage amount is equal to or more than a second predetermined storage amount set to a value larger than the predetermined storage amount,
3. The exhaust gas purification apparatus for an engine according to claim 1, wherein the reducing agent supply control means releases the nitrogen oxide stored in the storage material by supplying a reducing agent. The exhaust passage is provided with a catalyst device that suppresses atmospheric emission of exhaust particulates, hydrocarbons, or carbon monoxide,
When the NOx trapping catalyst is on the upstream side of the catalytic converter, the temperature raising control is performed by throttling a throttle valve provided in the intake passage to desorb nitrogen oxides and desorbed nitrogen oxides. The temperature is raised to a first predetermined temperature at which storage is possible, and the fuel is increased to raise the temperature to a second predetermined temperature at which released nitrogen oxides can be released. The exhaust gas purification device of the engine as described in a term. The exhaust passage is provided with a catalyst device that suppresses atmospheric emission of exhaust particulates, hydrocarbons, or carbon monoxide,
When the NOx trap catalyst is on the downstream side of the catalyst device, the temperature raising control is performed by throttling a throttle valve provided in the intake passage if the temperature of the catalyst device is less than the catalyst activation temperature. The temperature is raised to a first predetermined temperature at which desorption of nitrogen oxides and storage of the desorbed nitrogen oxides are possible, and if the temperature of the catalyst device is equal to or higher than the catalyst activation temperature, the fuel is increased The exhaust gas purification apparatus for an engine according to any one of claims 1 to 3, wherein the temperature is raised to a second predetermined temperature at which the stored nitrogen oxide can be released.

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