Exhaust gas purification device for an internal combustion engine

Abstract

An exhaust gas purification device for an internal combustion engine comprises an ammonia supply device which includes a storage unit configured to store a precursor of ammonia or ammonia (a reducing agent or the like), and a control device configured to perform a discharge limiting control such that the discharge of the internal combustion engine is limited to not exceeding a predetermined discharge, so that a NOx cleaning rate effected by the storage-reducing NOx catalyst is within an acceptable range if the quantity of the reducing agent or the like stored in the storage unit is less than a predetermined storage quantity.

Description

[Field of technology]

[0001] The present invention relates to an exhaust gas purification device for an internal combustion engine. [Technical background]

[0002] A selective catalytic reduction (SCR) system is known which is equipped with a NOx catalyst (hereinafter also referred to as an "SCR catalyst"), wherein NOx contained in the exhaust gas of an internal combustion engine is purified by using ammonia as a reducing agent. In some cases, an injection valve, which introduces an aqueous urea solution (urea-water solution) into the exhaust gas, is installed upstream of the SCR catalyst. The aqueous urea solution added to the exhaust gas is hydrolyzed by the heat of the exhaust gas and the heat of the SCR catalyst, and the aqueous urea solution is converted into ammonia, which is absorbed by the SCR catalyst. The aqueous urea solution is stored, for example, in a tank, and the aqueous urea solution is finite or...The tank capacity is limited. Therefore, it is necessary to refill the aqueous urea solution tank, for example, by a user. If the aqueous urea solution is consumed without being refilled, the reducing agent cannot be supplied to the SCR catalyst. Consequently, there is a risk that NOx could be released into the atmosphere.

[0003] In this context, a technique is known in which a warning is issued if the residual amount of aqueous urea solution is reduced, and the output or power output of an internal combustion engine is then gradually limited in response to the residual amount of aqueous urea solution (see, for example, JP 2013-160 104 A). Furthermore, the following technique is known. This involves the provision of an SCR catalyst and a NOx storage reduction catalyst (hereinafter also referred to as an "NSR catalyst"), which occludes NOx contained in the exhaust gas.absorbs, and which reduces NOx if the air-fuel ratio of the exhaust gas does not exceed the stoichiometric air-fuel ratio, wherein the NSR catalyst is mainly used if the residual amount of aqueous urea solution is reduced (see, for example, WO 2014 / 108619 A1). Further prior art includes JP 2007-321671A, JP 2002-371831A, JP 2001-123826A, and DE 102007059473A1. DE 102005022420A1 forms the basis for the preamble of claim 1. [Summary of the invention][Problems to be solved by the invention]

[0004] If the residual amount of aqueous urea solution is reduced, even if the internal combustion engine's output is restricted, the aqueous urea solution will gradually be depleted unless replenished. If the internal combustion engine is operated in a state where the aqueous urea solution is depleted, NOx removal may become difficult. Furthermore, in some cases, depending on the country or region, restarting the internal combustion engine may be prevented when the aqueous urea solution is depleted. In this case, the internal combustion engine may not be able to be restarted after being stopped until the aqueous urea solution is replenished.Furthermore, if the residual amount of aqueous urea solution is reduced, even if the control is designed to primarily use the NSR catalyst, it may be difficult to clean the NOx using only the NSR catalyst, depending on the amount of NOx emitted or released by the internal combustion engine.

[0005] The present invention was made taking into consideration the above problems, one object of which is to inhibit the release of NOx into the atmospheric air, even when a sufficient quantity of a reducing agent cannot be supplied to a NOx catalyst for selective catalytic reduction. [Means of solving the problems]

[0006] To solve the problem described above, an exhaust gas purification device comprises the features listed in claim 1. An advantageous embodiment is the subject of the dependent claim.

[0007] Even in the case of an SCR system equipped with a selective catalytic reduction (SCR) catalyst for NOx purification using ammonia, the system can also include a storage NOx reduction catalyst (NSR catalyst) as an additional catalyst. If the system incorporates the NSR catalyst alongside the SCR catalyst, it is possible to purify NOx using both the SCR and NSR catalysts. Therefore, even if the NOx purification rate is reduced in one of the catalysts, this reduction can be compensated for by the other catalyst. In this context, the reducing agent used to reduce NOx differs between the SCR catalyst and the NSR catalyst.Even if the reducing agent intended for the SCR catalyst is scarce, it can still be supplied to the NSR catalyst in some cases. For example, if the reducing agent is supplied to the NSR catalyst by ensuring that the air-fuel ratio of the internal combustion engine does not exceed the stoichiometric air-fuel ratio, the reducing agent can be supplied to the NSR catalyst as long as the internal combustion engine is operating. Conversely, if the reducing agent is supplied to the NSR catalyst by adding fuel for the internal combustion engine to the exhaust gas, the reducing agent can be supplied to the NSR catalyst as long as fuel for the internal combustion engine is present.

[0008] However, there is also a limit to the capacity of the NSR catalyst intended for the SCR system. Therefore, if the intention is to clean NOx using the NSR catalyst, NOx present in a quantity greater than the amount that the NSR catalyst can handle may flow into the catalyst. In such a situation, it is impossible to completely clean the NOx using the NSR catalyst. Conversely, the amount of NOx that cannot be completely cleaned by the NSR catalyst can be reduced by decreasing the amount of NOx emitted or released by the internal combustion engine. Accordingly, it is possible to reduce the amount of NOx released into the atmosphere without stopping the internal combustion engine.In this context, the combustion gas temperature can be lowered by reducing the engine's internal combustion output. It is therefore possible to reduce the amount of NOx produced. This means that the amount of NOx exiting the SCR catalyst can be reduced by lowering the engine's internal combustion output. Furthermore, the pre-determined storage quantity represents the lower limit for the amount of ammonia precursor or ammonia at which the NOx can be adequately cleaned by the SCR catalyst, even if the output limitation control is not activated. It should be noted that the pre-determined storage quantity can also represent the lower limit for the amount of ammonia precursor or ammonia at which the NOx cleaning rate of the SCR catalyst remains within the permissible range.The permissible range of the NOx cleaning rate of the NSR catalyst can be determined, for example, on the basis of laws and regulations.

[0009] Furthermore, the control device can execute the discharge limiting control if the amount of ammonia precursor or ammonia stored in the storage unit is less than the pre-determined storage amount, and the control device can enable or allow the air-fuel ratio of an exhaust gas flowing into the storage-reduction NOx catalyst to be no more than a stoichiometric air-fuel ratio in order to shorten an interval for executing a rich spike or temporary rich operation or rich peak to reduce the NOx occluded by the storage-reduction NOx catalyst, in the case where the discharge limiting control is executed, compared with the case where the discharge limiting control is not executed.

[0010] The interval for executing the transient rich operation, as referred to here, can be a period extending from the point in time at which transient rich operation is initiated to the point in time at which the next transient rich operation is initiated, or the interval can be a period extending from the point in time at which transient rich operation is terminated to the point in time at which the next transient rich operation is initiated. The transient rich operation is executed for the purpose of reducing the NOx occluded by the NSR catalyst. Shortening the interval for executing the transient rich operation results in a relatively small amount of NOx occluded by the NSR catalyst.Accordingly, the NOx occlusion rate in the NSR catalyst (the rate at which the amount of NOx is occluded by the NSR catalyst relative to the amount of NOx flowing into the NSR catalyst) is increased. Therefore, it is possible to inhibit, prevent, or suppress NOx from flowing out of the NSR catalyst, and thus to more reliably inhibit NOx release into the atmosphere, even if it is impossible to supply a sufficient amount of ammonia to the SCR catalyst. Furthermore, it is possible to increase the emission to a greater extent, even when the emission limiting control is in operation, by shortening the interval for operating in a temporarily rich mixture. Therefore, it is possible to mitigate the reduction in drivability.

[0011] Furthermore, the exhaust aftertreatment device for the internal combustion engine may also include an estimating unit configured to estimate the amount of NOx occluded by the storage-reduction NOx catalyst, wherein the control device may allow the air-fuel ratio of an exhaust gas flowing into the storage-reduction NOx catalyst to be no more than a stoichiometric air-fuel ratio in order to perform a temporarily rich operation to reduce the NOx occluded in the storage-reduction NOx catalyst whenever the amount of NOx estimated by the estimating unit is not less than a first occlusion quantity, provided that the amount of ammonia precursor or ammonia stored in the storage unit is not less than the pre-estimated storage quantity.and the control unit can execute the discharge limitation control, and it can execute the temporarily rich operation each time the amount of NOx estimated by the estimating unit is not less than a second occlusion quantity, which is a quantity smaller than the first occlusion quantity, if the quantity of the ammonia precursor or of ammonia stored in the storage unit is less than the pre-determined storage quantity.

[0012] Such a condition, in which the NOx occlusion quantity of the NSR catalyst is relatively small and the NOx occlusion rate is increased, occurs when the temporarily rich operation is performed whenever the amount of NOx estimated by the estimating unit is not less than the second occlusion quantity, compared to when the temporarily rich operation is performed whenever the amount of NOx estimated by the estimating unit is not less than the first occlusion quantity. Therefore, the NOx occlusion rate of the NSR catalyst is increased. Even if a sufficient amount of ammonia cannot be supplied to the SCR catalyst, it is thus possible to more reliably inhibit NOx from flowing out of the NSR catalyst.

[0013] Furthermore, the total amount of NOx capable of being occluded per unit time by the storage-reduction NOx catalyst and the amount of NOx capable of being reduced per unit time by the selective catalytic reduction NOx catalyst can be a predetermined NOx amount if the amount of ammonia precursor or ammonia stored in the storage unit is not less than the predetermined storage amount in the exhaust aftertreatment device for the internal combustion engine, and a maximum NOx amount capable of being occluded per unit time by the storage-reduction NOx catalyst can be less than the predetermined NOx amount, and the predetermined emission can be an emission from the internal combustion engine in which an amount of NOx capable of being reduced per unit time by the internal combustion engine is emittednot exceeding the maximum NOx quantity.

[0014] If the amount of ammonia precursor or ammonia stored in the storage unit is not less than the pre-determined storage quantity, it is possible to supply a sufficient amount of reducing agent to the SCR catalyst. Therefore, it is possible to clean the NOx using both the SCR catalyst and the NSR catalyst. Similarly, if the amount of NOx emitted or released per unit of time by the internal combustion engine is the pre-determined NOx quantity, it is still possible to clean the NOx sufficiently. In this context, it is confirmed that the pre-determined NOx quantity is the amount of NOx that can be treated or processed by the SCR catalyst and the NSR catalyst, provided the amount of ammonia precursor or ammonia stored in the storage unit is not less than the pre-determined storage quantity.This means that if the amount of ammonia precursor or ammonia stored in the storage unit is less than the pre-determined storage amount, the pre-determined NOx quantity cannot be occluded by the NSR catalyst alone per unit time. If the amount of NOx emitted by the internal combustion engine per unit time exceeds the maximum NOx quantity capable of being occluded by the NSR catalyst per unit time, NOx will flow out of the NSR catalyst for this reason. If the amount of NOx emitted by the internal combustion engine does not exceed the maximum NOx quantity capable of being occluded by the NSR catalyst per unit time, then...Since the NOx output is not greater, it is on the contrary possible to adequately clean the NOx using the NSR catalyst, even if it is impossible to supply a sufficient amount of ammonia to the SCR catalyst. That is, when the output control is implemented, the pre-determined output is set such that the amount of NOx emitted by the internal combustion engine does not exceed the maximum amount of NOx capable of being occluded by the NSR catalyst per unit of time. Therefore, it is possible to inhibit the NOx from flowing out of the NSR catalyst. [Advantageous effects of the invention]

[0015] According to the present invention, it is possible to inhibit the release of NOx into the atmospheric air even when a sufficient amount of the reducing agent cannot be supplied to the NOx catalyst for selective catalytic reduction. [Brief description of the drawings] Fig. Figure 1 shows a schematic arrangement of an internal combustion engine according to one embodiment and an intake system and an exhaust system thereof. Fig. Figure 2 shows a relationship between the temperatures of an NSR catalyst and an SCR catalyst and the amounts of NOx that are able to be treated and processed by the respective catalysts. Fig. Figure 3 shows a flowchart illustrating the flow of the output limitation control according to the embodiment. Fig. Figure 4 shows a timing diagram that results when the output limitation control is implemented according to the embodiment. Fig. Figure 5 shows a relationship between the amount of NOx occlusion and the NOx occlusion rate of the NSR catalyst. Fig. Figure 6 shows a relationship between the distance along an exhaust pipe from the internal combustion engine and the amount of NOx per unit volume of exhaust gas. Fig. Figure 7 shows a flowchart illustrating a control flow of the temporarily rich operation according to a second embodiment. [Emphasis on the implementation of the invention]

[0016] The following is a detailed explanation of one way of carrying out the present invention, based on an embodiment and using an example with reference to the drawings. However, it is not intended that, for example, the dimensions or size, the material, the shape, and the relative arrangement of the respective defining parts or components described in the embodiment limit the scope of protection of the present invention only to those specific parts or components, unless explicitly stated otherwise. <Erste Ausführungsform>

[0017] The Fig. Figure 1 shows a schematic arrangement of an internal combustion engine according to this embodiment and an intake system and an exhaust system or discharge system thereof. The internal combustion engine 1, which is located in the Fig. Figure 1 shows a diesel engine. An exhaust line 2 is connected to the internal combustion engine 1. A fuel injection valve 3, a storage-reduction NOx catalyst 4 (hereinafter also referred to as an "NSR catalyst 4"), a valve 52 for adding an aqueous urea solution (urea-water solution), and a selective catalytic reduction NOx catalyst 6 (hereinafter also referred to as an "SCR catalyst 6"), designated in this order from the upstream side, are provided at intermediate positions in the exhaust line 2.

[0018] The NSR catalyst 4 occludes NOx contained in the exhaust gas when the oxygen concentration of the incoming exhaust gas is high, whereas the NSR catalyst 4 releases and reduces occluded NOx when the oxygen concentration of the incoming exhaust gas is lowered and a reducing agent is present. It should be noted that the term "occlusion" is used here to encompass the temporary absorption of NOx.

[0019] The fuel injection valve 3 adds fuel (HC) for the internal combustion engine 1 to the exhaust gas. The fuel is used as a reducing agent to reduce NOx by means of the NSR catalyst 4. It should be noted that CO or HC, as unburned fuel emitted or released by the internal combustion engine 1, can also be used as the reducing agent to be supplied to the NSR catalyst 4. That is, the reducing agent can also be supplied to the NSR catalyst 4 by operating the internal combustion engine 1 at a rich air-fuel ratio. In this case, it is unnecessary to provide the fuel injection valve 3.

[0020] The SCR catalyst 6 selectively reduces NOx by using previously absorbed ammonia. The aqueous urea solution addition valve 52 adds the reducing agent (the ammonia) to the SCR catalyst 6 by adding the aqueous urea solution. The aqueous urea solution added by the aqueous urea solution addition valve 52 is hydrolyzed by the heat of the exhaust gas or the heat from the SCR catalyst 6, and the aqueous urea solution is converted into the ammonia, which is absorbed by or in the SCR catalyst 6. It should be noted that an addition valve that adds ammonia may be provided instead of the aqueous urea solution addition valve 52. This means that the ammonia precursor or the ammonia can be added to the exhaust gas at the position upstream of the SCR catalyst 6.

[0021] The valve 52 for adding the aqueous urea solution is part of a reducing agent supply device 5. The reducing agent supply device 5 is equipped with a tank 51, the valve 52 for adding the aqueous urea solution, a line 53 for the aqueous urea solution or an aqueous-urea solution line, a pump 54 and a residual quantity sensor 55.

[0022] Tank 51 stores the aqueous urea solution. The valve 52 for adding the aqueous urea solution is located on the exhaust line 2 upstream of the SCR catalyst 6. The line 53 for the aqueous urea solution connects tank 51 and the valve 52 for adding the aqueous urea solution, so that the aqueous urea solution flows through it. It should be noted that in this embodiment, tank 51 corresponds to the storage unit according to the present invention. Furthermore, in this embodiment, the reducing agent supply device 5 corresponds to the ammonia supply device according to the present invention.

[0023] Pump 54 is located inside tank 51 to transfer the aqueous urea solution from the side of tank 51 to the side of valve 52 for adding the aqueous urea solution. It should be noted that pump 54 can also be located in line 53 for the aqueous urea solution instead of inside tank 51. Pump 54 is an electric pump (a motor pump or electric motor pump) which is rotated by the supply of electrical energy. When pump 54 is operating and valve 52 for adding the aqueous urea solution is open, the aqueous urea solution is fed under pressure through line 53 for the aqueous urea solution and is added to the exhaust gas. Furthermore, residual quantity sensor 55 is attached to tank 51 and detects the residual quantity of aqueous urea solution in tank 51.

[0024] Furthermore, a temperature sensor 11 for measuring the exhaust gas temperature and a first NOx sensor 12 for measuring the NOx concentration in the exhaust gas are installed on the exhaust pipe 2 at positions downstream of the NSR catalyst 4 and upstream of the valve 52 for adding the aqueous urea solution. It is possible to calculate the temperature of the NSR catalyst 4 or the temperature of the SCR catalyst 6 based on the reading of temperature sensor 11. In addition, the reading of temperature sensor 11 can be used as the temperature of the NSR catalyst 4 or the SCR catalyst 6. Furthermore, a second NOx sensor 13 for measuring the NOx concentration in the exhaust gas is installed on the exhaust pipe at a position downstream of the SCR catalyst 6. The NOx concentration in the exhaust gas flowing out of the SCR catalyst 6 is detected by the second NOx sensor 13.It should be noted that the NOx concentration in the exhaust gas flowing into the NSR catalyst 4 is related to the operating condition of engine 1 with internal combustion. It is therefore possible to estimate the NOx concentration in the exhaust gas flowing into the NSR catalyst 4 based on the operating condition of engine 1 with internal combustion. However, it is also possible to detect the NOx concentration in the exhaust gas flowing into the NSR catalyst 4 by providing a NOx sensor on the upstream side of the NSR catalyst 4.

[0025] Furthermore, a fuel injection valve 7 for supplying fuel to the internal combustion engine 1 is attached to the internal combustion engine 1. An intake manifold 8 is also connected to the internal combustion engine 1. A throttle 9 for adjusting the intake air volume of the internal combustion engine 1 is located at an intermediate position on the intake manifold 8. Additionally, an airflow meter 15 for measuring the intake air volume of the internal combustion engine 1 is attached to the intake manifold 8 upstream of the throttle 9.

[0026] An ECU 10, which is an electronic control unit for controlling the internal combustion engine 1, is provided in combination with the internal combustion engine 1, which is designed as described above. The ECU 10 controls the internal combustion engine 1 in response to the operating state of the internal combustion engine 1 and the driver's request. In addition to the sensors described above, those connected to the ECU 10 via electrical lines or wiring include an accelerator pedal opening degree sensor 17, which outputs an electrical signal corresponding to the amount of pedal travel of an accelerator pedal 16 operated by the driver to detect engine load, combustion engine load, or engine power, and a crankshaft position sensor 18, which detects the engine rotation speed. Output signals from various sensors, as described above, are input into the ECU 10.On the other hand, the fuel addition valve 3, the valve 52 for adding the aqueous urea solution, the fuel injection valve 7, and the throttle 9 are connected to the ECU 10 via electrical lines. These devices are controlled by the ECU 10. Furthermore, a display 20 is connected to the ECU 10. A warning or the like is displayed on the display 20, as described below, in accordance with the instruction from the ECU 10. It should be noted that in this embodiment, the warning or the like is displayed on the display 20. However, the warning can alternatively be given by means of an audible signal, and / or a warning lamp can be illuminated or switched on.

[0027] The exhaust gas purification device according to this embodiment incorporates the SCR system, in which NOx is purified by the SCR catalyst 6. The exhaust gas purification device also includes the NSR catalyst 4 in addition to the SCR catalyst 6. In the case of the SCR system, ammonia is pre-absorbed by the SCR catalyst 6 to reduce the NOx contained in the exhaust gas, which is then allowed to flow through the SCR catalyst 6. The ECU 10 enables the SCR catalyst 6 to absorb the ammonia by adding the aqueous urea solution from the valve 52.

[0028] Normally, the aqueous urea solution is added by valve 52, so the amount of ammonia absorbed by the SCR catalyst 6 is a predetermined amount. In this case, the amount of aqueous urea solution added by valve 52 is determined as a function of the amount of NOx flowing into the SCR catalyst 6, as follows. It should be noted that the term "normally" refers to the situation in which the remaining amount of aqueous urea solution in tank 51 is sufficient. The amount of NOx flowing into the SCR catalyst 6 is equal to the amount of NOx flowing out of the NSR catalyst 4.The amount of NOx flowing into the SCR catalyst 6 can be calculated based on the readings from the first NOx sensor 12 and the airflow meter 15. As described above, the aqueous urea solution is added by the valve 52, such that the amount of ammonia absorbed by the SCR catalyst 6 is the pre-determined absorption amount. This pre-determined absorption amount is such that the NOx removal rate achieved by the SCR catalyst 6 remains within an acceptable range, and the amount of ammonia flowing out of the SCR catalyst 6 remains within an acceptable range. The NOx cleaning rate achieved by the SCR catalyst 6 is the ratio of the amount of NOx reduced by the SCR catalyst 6 to the amount of NOx flowing into the SCR catalyst 6.The amount of reduction in the absorption rate of ammonia by the SCR catalyst 6 can be calculated based on the amount of NOx flowing into the SCR catalyst 6. Therefore, aqueous urea solution is added from valve 52 to compensate for the reduction in ammonia absorption rate. The relationship between the amount of reduction in ammonia absorption rate by the SCR catalyst 6 and the amount of aqueous urea solution added from valve 52 can be determined in advance, for example, by experiment or simulation.

[0029] The Fig. Figure 2 shows a relationship between the temperatures of the NSR catalyst 4 and the SCR catalyst 6 and the amounts of NOx that can be treated or processed by the respective catalysts. The area indicated by "SCR" is the range of NOx amounts that can be processed or treated by the SCR catalyst 6, and the area indicated by "NSR" is the range of NOx amounts that can be processed or treated by the NSR catalyst 4. In this embodiment, the SCR system is used, in which NOx is primarily cleaned by the SCR catalyst 6. Therefore, the capacity of the NSR catalyst 4 is small compared to the SCR catalyst 6, and the NSR catalyst 4 cleans the NOx in a secondary manner.For this reason, the amount of NOx that is able to be treated or processed by the NSR catalyst 4 is small compared to the SCR catalyst 6.

[0030] Furthermore, the ECU 10 controls, for example, the fuel injection valve 7, so that the air-fuel ratio in the cylinder is the target air-fuel ratio. The target air-fuel ratio is the air-fuel ratio that is set depending on the operating state of the internal combustion engine 1. It should be noted that, according to this embodiment, the internal combustion engine 1 operates at a lean air-fuel ratio. Therefore, the target air-fuel ratio in the cylinder is set to a lean air-fuel ratio. However, the so-called rich peak or peak isA temporarily rich mixture is achieved by temporarily reducing the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 4 to no more than the stoichiometric air-fuel ratio. This is done to reduce the NOx occluded by the NSR catalyst 4 by adding fuel from the fuel injection valve 3 while the NOx reduction is being carried out. It should be noted that the temporarily rich mixture can also be achieved by temporarily lowering the target air-fuel ratio in the cylinder to no more than the stoichiometric air-fuel ratio by adjusting the amount of fuel injected by the fuel injection valve 7 instead of adding fuel from the fuel injection valve 3.

[0031] Normally, the system operates in a temporarily rich mixture, so that NOx is reduced in the first occlusion quantity when the NOx occlusion quantity in the NSR catalyst 4 is the first occlusion quantity. The term "normally," which refers here, describes a situation in which the residual amount of aqueous urea solution in tank 51 is sufficient, i.e., a situation in which the NOx is also adequately removed by the SCR catalyst 6. The NOx occlusion quantity in the NSR catalyst 4 can be determined, for example, by adding the value obtained by subtracting the amount of NOx flowing out of the NSR catalyst 4 and the amount of NOx reduced by the NSR catalyst 4 from the amount of NOx flowing into the NSR catalyst 4.The amount of NOx flowing into the NSR catalyst 4 is estimated based on the operating condition of the engine 1 with internal combustion. The amount of NOx flowing out of the NSR catalyst 4 can be determined based on the readings of the first NOx sensor 12 and the airflow meter 15. The amount of NOx reduced by the NSR catalyst 4, i.e., the NOx occlusion amount reduced by the temporarily rich operating mixture, depends on the temperature of the NSR catalyst 4, the reading of the airflow meter 15, and the air-fuel ratio of the exhaust gas.If the relationship between these factors is determined in advance, for example by means of an experiment or a simulation, it is therefore possible to calculate the amount of NOx reduced by the NSR catalyst 4 based on the temperature of the NSR catalyst 4, the reading of the airflow meter 15, and the air-fuel ratio of the exhaust gas. It should be noted that the NOx occlusion quantity of the NSR catalyst 4 can be calculated by any other known or well-known method, without being limited to the method described above. In this embodiment, the ECU 10 calculates the NOx occlusion quantity of the NSR catalyst 4, and therefore the ECU 10 functions as the estimation unit according to the present invention. In the following description, the NOx occlusion quantity calculated by the ECU 10 is also referred to as an "estimated NOx occlusion quantity".

[0032] There is a limit to the amount of aqueous urea solution stored in tank 51. Therefore, the residual amount of aqueous urea solution is progressively reduced each time it is added from valve 52, unless tank 51 is being refilled. When the residual amount of aqueous urea solution in tank 51 is low, and it becomes impossible to add a sufficient amount from valve 52, it becomes impossible to supply a sufficient amount of ammonia to the SCR catalyst 6. Even when the engine 1 is started with internal combustion, if the residual amount of aqueous urea solution is low, it is difficult to clean the NOx through the SCR catalyst 6 during operation.It is therefore to be feared that NOx can pass through the SCR catalyst 6 and be released into the atmosphere. For example, even if the amount of NOx that can be removed per unit time by the NSR catalyst 4 and the SCR catalyst 6 is the pre-determined amount, then, if the residual amount of aqueous urea solution is sufficiently large, the amount of NOx that can be removed per unit time will be less than the pre-determined amount. This is because the NOx is removed by only the NSR catalyst 4 when the residual amount of aqueous urea solution is small. That is, if the residual amount of aqueous urea solution is insufficient, the NOx is processed or treated using only the NSR catalyst 4.Therefore, the amount of NOx that can be processed per unit time when the temporarily rich operating mode is not used is the maximum amount of NOx capable of being occluded per unit time by the NSR catalyst 4. This maximum amount of NOx is less than the previously determined NOx amount described above. Furthermore, it is likely that the internal combustion engine 1 cannot be started until tank 51 is refilled with the aqueous urea solution if the ECU 10 is designed in such a way that the internal combustion engine 1 cannot be started in a state where a sufficient amount of ammonia cannot be supplied to the SCR catalyst 6 and the NOx cleaning rate is reduced. It will therefore be difficult for the vehicle to operate.

[0033] In light of the foregoing, in this embodiment, if the residual quantity of the aqueous urea solution is less than the pre-determined storage quantity, then the discharge limiting control for the internal combustion engine 1 is implemented as described later, and therefore the amount of NOx emitted by the internal combustion engine 1 is set by the ECU 10. The pre-determined storage quantity is the lower limit of the aqueous urea solution quantity at which it is possible to adequately clean the NOx by the SCR catalyst 6, even if the discharge limiting control for the internal combustion engine 1 is not implemented as described later, or the lower limit of the aqueous urea solution quantity at which the NOx cleaning rate of the SCR catalyst 6 is within an acceptable range.If the remaining quantity of the aqueous urea solution is less than the pre-determined storage quantity, and the output limiting control for engine 1 with internal combustion is not executed as described later, it will be difficult to adequately clean the NOx emitted by engine 1 with internal combustion. In light of the above, and to limit the amount of NOx emitted by engine 1 with internal combustion, ECU 10 executes the output limiting control, thus restricting the output of engine 1 with internal combustion to no more than the pre-determined output. The pre-determined output is the output at which the NOx cleaning rate of the NSR catalyst 4 is within an acceptable range.It should be noted that the output of engine 1 with internal combustion may be limited such that the amount of NOx emitted per unit time by engine 1 with internal combustion does not exceed the maximum amount of NOx capable of being occluded per unit time by the NSR catalyst 4. The NOx cleaning rate of the NSR catalyst 4 is the ratio of the amount of NOx reduced by the NSR catalyst 4 to the amount of NOx flowing into the NSR catalyst 4 during the interval for performing the temporarily rich operation, i.e.,during the period from the start of a period of temporarily rich operation to the start of the next period of temporarily rich operation, or from the end of a period of temporarily rich operation to the start of the next period of temporarily rich operation. The permissible range of the NOx cleaning rate is determined, for example, on the basis of laws and regulations.

[0034] In this case, it is possible to reduce the amount of fuel injected by fuel injection valve 7 per cycle by limiting the output of internal combustion engine 1. This makes it possible to lower the combustion temperature in the cylinder. Consequently, it is possible to inhibit NOx production. Therefore, it is possible to reduce the amount of NOx emitted by internal combustion engine 1. It should be noted that limiting the output of internal combustion engine 1 may involve reducing the maximum torque of internal combustion engine 1 and decreasing the vehicle's maximum speed. For example, the output of internal combustion engine 1 can be limited to a predetermined value by setting an upper limit for the amount of fuel injected by fuel injection valve 7 per cycle.

[0035] In this way, the emissions from engine 1 with internal combustion are limited so that the amount of NOx emitted by engine 1 with internal combustion is sufficient to be adequately cleaned by the SCR catalyst 4. It is therefore possible to inhibit the release of NOx into the atmosphere even when the residual amount of aqueous urea solution is small and the ammonia in the SCR catalyst 6 is insufficient. The vehicle can therefore be driven while the release of NOx into the atmosphere is inhibited during the period until tank 51 is refilled with aqueous urea solution.

[0036] The Fig. Figure 3 shows a flowchart illustrating the flow of the output limitation control according to this embodiment. This flowchart is executed by the ECU 10 each time a pre-determined time elapses.

[0037] In step S101, the ECU 10 assesses whether the residual amount of aqueous urea solution is less than a first threshold. The residual amount of aqueous urea solution is the amount of aqueous urea solution remaining in tank 51, as detected by the residual amount sensor 55. The first threshold is the residual amount of aqueous urea solution set to facilitate refilling by the user. This threshold represents the amount of aqueous urea solution at which refilling becomes necessary. However, it is confirmed that the first threshold is the residual amount of aqueous urea solution that has not been reduced to such an extent that the dispensing limit control needs to be activated.It is therefore confirmed that step S101 assesses whether refilling tank 51 with aqueous urea solution is necessary. If the assessment in step S101 is positive, the routine proceeds to step S102. Conversely, if the assessment is negative, the routine proceeds to step S106.

[0038] In step S102, the ECU 10 executes the residual quantity warning. During step S102, the fact that it is necessary to refill with aqueous urea solution because the remaining quantity of aqueous urea solution is low is indicated on display 20. If the processing of step S102 is complete, the routine continues with step S103.

[0039] In step S103, the ECU 10 assessed whether the residual amount of aqueous urea solution was less than a second threshold. The second threshold is the value lower than the first threshold. This second threshold represents the lower limit of the aqueous urea solution quantity at which the NOx can be adequately removed by the SCR catalyst 6, or the lower limit of the aqueous urea solution quantity at which the removal rate of the SCR catalyst 6 remains within an acceptable range. If the residual amount of aqueous urea solution is less than the second threshold, it is virtually zero, making it impossible to adequately remove the NOx by the SCR catalyst 6. In other words, step S103 assesses whether a condition exists in which the NOx cannot be removed by the SCR catalyst 6.If a positive assessment is made in step S103, the routine continues with step S104. If, on the other hand, a negative assessment is made, the routine continues with step S105.

[0040] In step S104, the ECU 10 limits the output of engine 1 with internal combustion to ensure it does not exceed the pre-determined output. This means that in step S104, the output limitation control is executed so that the amount of NOx emitted by engine 1 with internal combustion is the amount that can be adequately cleaned by the NSR catalyst 4. The limitation of engine 1's output continues even after step S104 is complete. In this case, the upper limit for the amount of fuel injected by fuel injection valve 7 is set, and the fuel injection is carried out so that the amount of fuel injected does not exceed the upper limit.The upper limit of the fuel injection quantity is set so that the NOx cleaning rate achieved by the NSR catalyst 4 is within the permissible range. It is then confirmed that the pre-determined output is the output of engine 1 with internal combustion, as intended when the fuel injection quantity is set to the upper limit. The upper limit of the fuel injection quantity is determined in advance, for example, by means of an experiment or a simulation, and is stored beforehand in the ECU 10. Furthermore, during this procedure, the fact that the output limiting control is being executed is indicated on display 20. Once the processing of step S104 is complete, this flowchart is finished.It should be noted that in this embodiment, the ECU 10 performs the processing of step S104, and therefore the ECU 10 functions as the control device according to the present invention. Furthermore, in this embodiment, the second threshold corresponds to the pre-determined storage quantity according to the present invention.

[0041] If, on the other hand, a negative assessment is made in step S103, the routine then proceeds to step S105, and the ECU 10 displays the remaining distance traveled until the discharge limit control is executed (the remaining distance traveled until the discharge limit) on display 20. The remaining distance traveled until the discharge limit is the estimated distance traveled until the remaining amount of aqueous urea solution falls below the second threshold. The relationship between the remaining amount of aqueous urea solution and the remaining distance traveled until the discharge limit is determined beforehand, for example, by means of an experiment or a simulation, and this relationship is stored in the ECU 10 beforehand. Furthermore, the NOx can be cleaned by the SCR catalyst 6 at the time step S105 is processed.Therefore, the dispensing limit control is not executed in step S105. Furthermore, if the dispensing limit control is already executed (for example, if refilling with a small amount of aqueous urea solution is performed when the dispensing limit control is executed), the dispensing limit control is terminated. Once the processing of step S105 is complete, this flowchart ends.

[0042] Furthermore, if a negative assessment is made in step S101, and the routine proceeds to step S106, does ECU 10 terminate the discharge limit control if it is executed, and does ECU 10 remove the warning or similar message if it is displayed on display 20? The remaining quantity of aqueous urea solution is not less than the first threshold, and a sufficient quantity of ammonia can be supplied to the SCR catalyst 6 at the time step 106 is processed. Therefore, the discharge limit control is not executed in step S106. Additionally, it is not necessary to display the remaining quantity warning in step S102, the discharge limit control in step S104, and the remaining distance to the discharge limit in step S105 on display 20.If these are displayed, the display will be cleared. This flowchart ends once the processing of step S106 is complete.

[0043] Next, the Fig. 4 A time diagram resulting when the discharge limit control is implemented according to this embodiment. The “residual amount of aqueous urea solution”, which is in the Fig. Figure 4 shows the remaining quantity of aqueous urea solution in tank 51. The first and second thresholds, which are relevant for the remaining quantity of aqueous urea solution, are the same values ​​as the first and second thresholds described above. Furthermore, the SCR operating state indicates the NOx purification status of the SCR catalyst 6, where A1 indicates a state in which the NOx can be purified by the SCR catalyst 6, and A2 indicates a state in which the NOx cannot be purified by the SCR catalyst 6. The "warning state," which is shown in the Fig. Figure 4 shows the status of the warning displayed on display 20, where B1 indicates a state in which the warning is not issued, B2 indicates a state (step S102) in which a warning is issued that the remaining quantity is small, and B3 indicates a state (step S104) in which a warning is issued that the dispensing limit control is being executed. The "operating state" shown in the Fig. Figure 4 shows the operating state of engine 1 with internal combustion, where C1 indicates a normal operating state in which the emission limit is not applied, C2 indicates an operating state in which the emission limit for engine 1 with internal combustion is applied, and C3 indicates a state in which restarting engine 1 with internal combustion is prevented. Furthermore, in relation to the "NOx emission quantity" shown in the Fig. Figure 4 shows a solid line representing the amount of NOx emitted per unit time by the internal combustion engine 1, and an alternating long and short dashed line representing the amount of NOx exiting the SCR catalyst 6 per unit time. Furthermore, the "NOx quantity capable of being treated or processed by the NSR catalyst" relative to the "NOx emission quantity" indicates the lower limit of the NOx quantity capable of being treated or processed by the NSR catalyst 4. In this case, the NOx quantity capable of being processed by the NSR catalyst 4 can change depending on the NOx occlusion quantity of the NSR catalyst 4. However, if the output of engine 1 with internal combustion is changed depending on the amount of NOx that is able to be processed by the NSR catalyst 4, the control becomes complicated.For this reason, in this embodiment, the lower limit of the NOx quantity capable of being processed by the NSR catalyst 4 is set as the NOx quantity capable of being processed by the NSR catalyst, so that the NOx can also be processed by the NSR catalyst 4 in a state in which the NOx quantity capable of being processed by the NSR catalyst 4 is maximally reduced. The NOx quantity capable of being processed by the NSR catalyst can be determined beforehand, for example, by means of an experiment or a simulation.

[0044] The remaining quantity of aqueous urea solution is less than the first threshold at T1 (JA in step S101). This means that at T1, a condition is created in which it is necessary to refill tank 51 with aqueous urea solution. Accordingly, the warning state changes from B1 to B2, and display 20 indicates that refilling with aqueous urea solution is necessary because the remaining quantity of aqueous urea solution is small (step S102). In this situation, the aqueous urea solution is still present, and it is possible to clean the NOx by the SCR catalyst 6 in this state. Therefore, the SCR operating state remains A1, and the operating state of engine 1 with internal combustion also remains the normal state, i.e., it remains C1.

[0045] The remaining quantity of aqueous urea solution is less than the second threshold at T2 (JA in step S103). It should be noted that the remaining range until the discharge limit is displayed on indicator 20, in addition to the fact that it is necessary to refill with aqueous urea solution during the period from T1 to T2 (step S105). If the remaining quantity of aqueous urea solution is less than the second threshold at T2, it becomes impossible to clean the NOx using the SCR catalyst 6. The SCR operating state is therefore changed from A1 to A2. Simultaneously, the output of engine 1 with internal combustion is limited to clean the NOx using the NSR catalyst 4, and therefore the operating state is changed from C1 to C2 (step S104). Then, indicator 20 shows that the discharge limit control is being executed.Therefore, the warning state is changed from B2 to B3 (step S104).

[0046] In this respect, conventional technology, for example, creates a condition that prevents the restart of internal combustion engine 1 at T2 (the condition C3 indicated by the broken line in the operating state). Therefore, in conventional technology, if internal combustion engine 1 has stopped at or after T2, it is impossible to restart it unless the aqueous urea solution is added during the period from T1 to T2. It should be noted that it is impossible to clean NOx using the SCR catalyst 6 at or after T2. Furthermore, if the vehicle is immobilized, adding the aqueous urea solution is also difficult.It is therefore also permissible for the evacuation movement to be carried out during the period until a pre-determined movement distance is reached.

[0047] In this embodiment, the NOx emission from engine 1 with internal combustion is inhibited so that, even during the period T2 or thereafter, it does not exceed the "NOx quantity capable of being processed by the NSR catalyst." This means that the emission limit for engine 1 with internal combustion is implemented, allowing the NOx to be processed by the NSR catalyst 4 at or after T2. Therefore, it is not necessary to prevent the restart of engine 1 with internal combustion. Then, at T3, the refilling with the aqueous urea solution is carried out (NO in step S101), and thus it is possible to clean the NOx using the SCR catalyst 6. The emission limit control is therefore terminated (step S106).In this way, even though the restart of engine 1 with internal combustion during the period extending from T2 to T3 is prevented in the case of conventional technology, the restart of engine 1 with internal combustion is not prevented in the case of this embodiment.

[0048] It should be noted that in this embodiment, the output of the internal combustion engine 1 is limited in order to reduce the amount of NOx emitted by the internal combustion engine 1. However, it is also possible to use one or more other means to reduce the amount of NOx emitted by the internal combustion engine 1 in combination. For example, if an EGR device is provided, it is possible to reduce the amount of NOx emitted by the internal combustion engine 1 by increasing the amount of EGR gas. In addition, the combustion temperature is lowered by retarding the timing of the fuel injection by the fuel injection valve 7. It is therefore possible to reduce the amount of NOx emitted by the internal combustion engine 1.Therefore, the EGR gas quantity can be increased, or the fuel injection timing can be retarded, in combination with limiting the output of engine 1 with internal combustion.

[0049] As explained above, according to this embodiment, the emission limiting control is implemented so that the NOx can be cleaned by the NSR catalyst 4 even in the event that it is impossible to supply a sufficient amount of ammonia to the SCR catalyst 6. It is therefore possible to inhibit the release of NOx into the atmosphere while the engine 1 is operating with internal combustion. <Zweite Ausführungsform>

[0050] The Fig. Figure 5 shows a relationship between the amount of NOx occlusion and the NOx occlusion rate of the NSR catalyst 4. The NOx occlusion rate is the ratio of the amount of NOx occluded by the NSR catalyst 4 to the amount of NOx flowing into the NSR catalyst 4. As shown in the Fig. As shown in Figure 5, the NOx occlusion rate is reduced more as the amount of NOx occlusion increases. Therefore, the NOx occlusion rate tends to increase in states where the amount of NOx occlusion is small. As shown in the Fig. As shown in Figure 5, the NOx occlusion rate in the NSR catalyst 4 is low in some cases. Therefore, even when the discharge limitation control described in the first embodiment is implemented, some of the NOx will not be occluded by the NSR catalyst 4 in some cases.

[0051] In this process, the NOx that is not occluded by the NSR catalyst 4 flows into the SCR catalyst 6. However, if a sufficient amount of ammonia cannot be supplied to the SCR catalyst 6, it is impossible to clean the NOx by the SCR catalyst 6. For this reason, the NOx that flows into the SCR catalyst 6 flows out of the SCR catalyst 6 as is. It is therefore preferable to reduce the NOx flowing out of the NSR catalyst 4 if it is impossible to supply a sufficient amount of ammonia to the SCR catalyst 6. That is, it is preferable to create a condition in which the NOx occlusion rate of the NSR catalyst 4 is high.

[0052] As it is in the Fig. As shown in Figure 5, to maintain a high NOx occlusion rate, it is appropriate to create a state in which the NOx occlusion quantity is small. This procedure creates a state in which the NOx occlusion quantity is relatively small by increasing the frequency of the transiently rich operation. As explained in the first embodiment, the transiently rich operation is usually carried out such that the NOx in the first occlusion quantity is reduced when the NOx occlusion quantity of the NOx catalyst 4 is the first occlusion quantity. In this embodiment, on the other hand, the transiently rich operation is carried out at the NOx occlusion quantity which is smaller than the first occlusion quantity when the discharge limiting control is carried out according to the first embodiment.This means that the temporarily rich operation is normally executed when the NOx occlusion quantity reaches or arrives at the first occlusion quantity. However, when the discharge limit control is executed, the temporarily rich operation is executed when the NOx occlusion quantity reaches the second occlusion quantity, which is smaller than the first. In this case, the temporarily rich operation is executed so that the NOx in the second occlusion quantity can be reduced. As described above, in this embodiment, the NOx occlusion quantity of the NSR catalyst 4, which is the threshold for executing the temporarily rich operation, is changed between when the discharge limit control is executed and when the discharge limit control is not executed.

[0053] In this way, the temporarily rich operating mode is executed each time the NOx occlusion quantity of the NSR catalyst 4 reaches the second occlusion quantity. This creates a state in which the NOx occlusion quantity is relatively small. It is therefore possible to increase the NOx occlusion rate. The amount of NOx that flows out of the NSR catalyst 4 without being occluded by it is thus reduced. For this reason, it is possible to further and more reliably reduce the amount of NOx that flows through the NSR catalyst 4 and the SCR catalyst 6 and is released into the atmosphere when the emission limiting control is executed.

[0054] The Fig. Figure 6 shows a relationship between the distance at exhaust pipe 2 from the internal combustion engine 1 and the NOx quantity per unit volume of exhaust gas. Fig. Figure 6 shows such a situation, in which the NOx quantity per unit volume of gas emitted or released by the internal combustion engine 1 is set such that the NOx quantity per unit volume of exhaust gas flowing out of the SCR catalyst 6 (the NOx quantity per unit volume of exhaust gas at the downstream end of the SCR catalyst 6) is identical. The area indicated by "NSR" shows the range extending from the upstream end to the downstream end of the NSR catalyst 4, and the area indicated by "SCR" shows the range extending from the upstream end to the downstream end of the SCR catalyst 6. "NORMAL" indicates a situation in which the NOx can be cleaned by both the NSR catalyst 4 and the SCR catalyst 6. In this case, the NOx can be cleaned by both the NSR catalyst 4 and the SCR catalyst 6.Even though the amount of NOx per unit volume of gas emitted by the internal combustion engine 1 is relatively large, the amount of NOx is therefore sufficiently reduced during the period until the downstream end of the SCR catalyst 6 is reached.

[0055] In the Fig. Figure 6, “CASE 1,” represents a situation in which only the output limitation control is implemented according to the first embodiment. “CASE 2” represents a situation in which the frequency of the transient rich operation is increased in addition to the implementation of the output limitation control according to the first embodiment. When “CASE 1” and “CASE 2” are compared, there is no difference in the amount of NOx flowing out of the NSR catalyst 4. However, in “CASE 2,” it is possible to inhibit the NOx flow from the NSR catalyst 4 to such an extent that the frequency of the transient rich operation is increased, even though the amount of NOx per unit volume of gas emitted from the internal combustion engine 1 is greater.Even when the emission limiting control is executed, it is therefore possible to inhibit the deterioration of drivability because the emission in the second embodiment can be further increased compared to the first embodiment. In light of the above, in this embodiment the NOx occlusion quantity, which is the threshold for initiating transient rich operation, is reduced, so that the interval of transient rich operation is shortened (i.e., the frequency of transient rich operation is increased) when the emission of engine 1 with internal combustion is limited, compared to when the emission of engine 1 with internal combustion is not limited.

[0056] The Fig. Figure 7 shows a flowchart illustrating a control flow for the temporarily rich operation according to this embodiment. This flowchart is executed by the ECU 10 each time a pre-determined period of time elapses. It should be noted that the flowchart shown in the Fig. 3 is shown, which is explained in the first embodiment, separately from the flowchart shown in the Fig. 7 is shown, is executed.

[0057] In step S201, the ECU 10 calculates the NOx occlusion quantity of the NSR catalyst 4. The ECU 10 calculates the estimated NOx occlusion quantity at all times, as explained in the first embodiment, and from then on, the calculated value is read. If the processing of step S201 is complete, the routine continues with step S202.

[0058] In step S202, the ECU 10 assessed whether or not the delivery limit control should be executed. Step S202 also determined whether it was necessary to shorten the interval of the temporarily rich operating mixture. If the assessment in step S202 was positive, the routine proceeded to step S203. Conversely, if the assessment was negative, the routine proceeded to step S206.

[0059] In step S203, the ECU 10 assesses whether the estimated NOx occlusion quantity, read in step S201, is at least as high as the second occlusion quantity. When the emission limit control is executed, it is difficult to clean the NOx using the SCR catalyst 6. The interval of the temporarily rich operation is therefore shortened, thus increasing the NOx occlusion rate of the NSR catalyst 4. If the estimated NOx occlusion quantity is not as high as the second occlusion quantity, the routine then proceeds to step S204, and the temporarily rich operation is executed. That is, if the assessment in step S203 is positive, the routine proceeds to step S204, and the ECU 10 executes the temporarily rich operation.If, on the other hand, the negative assessment is made in step S203, no opportunity is given to execute the temporarily rich operation. Therefore, this flowchart is terminated.

[0060] If, on the other hand, a negative assessment is made in step S202, the routine proceeds to step S205. In step S205, the ECU 10 assesses whether the estimated NOx occlusion quantity is not less than the initial occlusion quantity. If the NSR catalyst 4 is functioning normally and the discharge limit control is not executed, a condition is created in which the residual amount of aqueous urea solution is sufficiently large, and therefore it is possible to adequately clean the NOx using the SCR catalyst 6. Similarly, if the interval of temporarily rich operation is extended and the NOx occlusion rate of the NSR catalyst 4 is reduced due to the estimated NOx occlusion quantity being not less than the initial occlusion quantity, it is also possible to clean the NOx using the SCR catalyst 6 for this reason.If the estimated NOx occlusion quantity is not less than the first occlusion quantity, the routine proceeds to step S206, and the temporarily rich operation is executed. That is, if a positive assessment is made in step S205, the routine proceeds to step S206, and ECU 10 executes the temporarily rich operation. Conversely, if a negative assessment is made in step S205, no opportunity is given to execute the temporarily rich operation. Therefore, this flowchart ends.

[0061] As explained above, according to this embodiment, if the reducing agent cannot be supplied to the SCR catalyst 6, the output of the engine 1 with internal combustion is limited. Furthermore, the interval of temporarily rich operation is shortened, and therefore the NOx flowing out of the NSR catalyst 4 is reduced. Consequently, the NOx flowing into the SCR catalyst 6 is also reduced. Even in the event that it is impossible to supply the reducing agent to the SCR catalyst 6, it is therefore possible to drive the vehicle while the release of NOx into the atmosphere is even more reliably inhibited. Moreover, the outflow of NOx from the NSR catalyst 4 is inhibited by shortening the interval of temporarily rich operation.It is therefore possible to set a larger value for the pre-determined charge, which is the maximum value of the charge that is intended when the charge limitation control is executed.

[0062] It should be noted that in this embodiment, the interval of the temporarily rich operating mode is shortened by reducing the threshold of the estimated NOx occlusion quantity. However, if the temporarily rich operating mode is executed every time a pre-determined period of time elapses, or every time a pre-determined travel distance is reached, then the interval of the temporarily rich operating mode can be shortened by reducing the pre-determined period of time or the pre-determined refueling distance. [Description of reference symbols] 1 internal combustion engine 2 Exhaust pipe 3 Fuel addition valve 4 Storage Reduction NOx Catalyst (NOx Storage Reduction Catalyst) (NSR Catalyst) 5 Reducing agent supply device 6 NOx catalyst for selective catalytic reduction (SCR catalyst) 7 Fuel injection valve 8 Intake pipe 9 throttle 10 ECU (control unit) 11 Temperature sensor 12 first NOx sensor 13 second NOx sensor 15 airflow meters 16 Accelerator pedal 17 Accelerator opening degree sensor 18 Crank position sensor 20 ads 51 Tank (storage unit) 52 Valve for adding aqueous urea solution 53 Line for aqueous urea solution 54 Pump 55 Residual quantity sensor

[0063] An exhaust gas purification device for an internal combustion engine comprises an ammonia supply device which includes a storage unit configured to store a precursor of ammonia or ammonia (a reducing agent or the like), and a control device configured to perform a discharge limiting control such that the discharge of the internal combustion engine is limited to not exceeding a predetermined discharge, so that a NOx cleaning rate effected by the storage-reducing NOx catalyst is within an acceptable range if the quantity of the reducing agent or the like stored in the storage unit is less than a predetermined storage quantity.

Claims

[1] An exhaust gas purification device for an internal combustion engine (1), comprising: a storage-reduction NOx catalyst (4) which is provided for an exhaust line (2) of the engine (1) with internal combustion, a NOx catalyst (6) for selective catalytic reduction, which is provided for the exhaust line (2) and which is configured to selectively reduce NOx by using ammonia as a reducing agent, a reducing agent supply device (5) which includes a storage unit (51) configured to store a precursor of ammonia or the ammonia, and wherein the reducing agent supply device (5) is configured to supply the ammonia to the NOx catalyst (6) for selective catalytic reduction, characterized by a control device (10) configured to perform a discharge limiting control such that the discharge of the internal combustion engine (1) is limited to not exceeding a predetermined discharge, so that the NOx cleaning rate effected by the storage reduction NOx catalyst (4) remains within an acceptable range if the amount of ammonia precursor or ammonia stored in the storage unit (51) is less than a predetermined storage amount, and further comprising: an estimation unit configured to estimate an amount of NOx occluded by the storage-reduction NOx catalyst (4), wherein: the control device (10) is configured to allow the air-fuel ratio of an exhaust gas flowing into the storage-reduction NOx catalyst (4) to not exceed a stoichiometric air-fuel ratio in order to perform a temporarily rich operation for reducing the NOx occluded by the storage-reduction NOx catalyst (4) each time the amount of NOx estimated by the estimating unit is not less than a first occlusion quantity, provided that the amount of ammonia precursor or ammonia stored in the storage unit (51) is not less than the pre-determined storage quantity, and the control device (10) is configured to perform the discharge limiting control, and it is configured to perform the temporarily rich operation each time the amount of NOx estimated by the estimating unit is not less than a second occlusion quantity, which is a quantity smaller than the first occlusion quantity, if the quantity of the ammonia precursor or of ammonia stored in the storage unit (51) is less than the pre-determined storage quantity. [2] The exhaust gas purification device for the internal combustion engine (1) according to claim 1, wherein: a total amount of NOx that can be occluded per unit time by the storage-reduction NOx catalyst (4) and of NOx that can be reduced per unit time by the NOx catalyst (6) for selective catalytic reduction, is a pre-determined NOx amount if the amount of the ammonia precursor or of ammonia stored in the storage unit (51) is not less than the pre-determined storage amount in the exhaust gas purification device for the internal combustion engine (1), a maximum NOx quantity that can be occluded per unit time by the storage-reduction-NOx catalyst (4) is smaller than the previously determined NOx quantity, and The pre-determined emission is an emission from the engine (1) with internal combustion, in which the amount of NOx emitted per unit time by the engine (1) with internal combustion does not exceed the maximum amount of NOx.

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