JP2010127251A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine exhaust gas purifier capable of restoring sulfur poisoning in a short time period. <P>SOLUTION: The internal combustion engine exhaust gas purifier in which an NO<SB>x</SB>storage catalyst is disposed in the path for an engine exhaust gas, an air-fuel ratio sensor for controlling a feedback is disposed on the downstream side of the NO<SB>x</SB>storage catalyst, and a fuel addition valve is disposed on the upstream side of the NO<SB>x</SB>storage catalyst, performs the restoration from sulfur poisoning by alternately repeating a temperature rise control for raising the temperature of the NO<SB>x</SB>storage catalyst by supplying a fuel through the fuel addition valve and a SO<SB>x</SB>discharge control for discharging an SO<SB>x</SB>from the NO<SB>x</SB>storage catalyst by carrying out after-injection in the combustion chamber to make rich the air-fuel ratio of the exhaust gas, and learning the output value of the air-fuel ratio sensor is performed, while the air-fuel ratio of the exhaust gas is decreased, immediately after the temperature rise control has been completed by reducing the time period of the temperature rise control and increasing the supply of the fuel through the fuel addition valve for learning the output value of the air-fuel ratio sensor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

In addition to carbon monoxide (CO), unburned hydrocarbons (HC), and particulates (PM), exhaust gases from internal combustion engines such as diesel engines and gasoline engines contain nitrogen oxides (NO _x ). One method of removing nitrogen oxides, NO _X storage catalyst has been proposed to be located in the engine exhaust passage.

_The NO _X storage catalyst, the air-fuel ratio of the exhaust gas is occluded NO _X when the lean. When the stored amount of NO _X reaches an allowable amount, the stored NO _X is released by making the air-fuel ratio of the exhaust gas rich or the stoichiometric air-fuel ratio. When the exhaust gas has a rich air-fuel ratio or a stoichiometric air-fuel ratio, the exhaust gas contains a large amount of reducing agent such as unburned hydrocarbons, so that the released NO _X is reduced and converted to N _2. Can do.

The exhaust gas of the internal combustion engine may contain sulfur oxide (SO _x ). In this case, the NO _X storage catalyst stores SO _X simultaneously with NO _X storage. When SO _X is occluded, the amount of NO _X that can be occluded decreases. Thus, so-called sulfur poisoning occurs in the NO _X storage catalyst. In order to eliminate sulfur poisoning, a sulfur poisoning recovery process that releases SO _X is performed. SO _X is occluded in the NO _X storage catalyst in a stable state as compared to the NO _X. For this reason, in the sulfur poisoning recovery process, SO _X is released by making the air-fuel ratio of the exhaust gas rich or the stoichiometric air-fuel ratio while the temperature of the NO _X storage catalyst is raised.

  When the air-fuel ratio of the exhaust gas is made rich or stoichiometric in the sulfur poisoning recovery process, an air-fuel ratio sensor is arranged in the engine exhaust passage to bring the air-fuel ratio of the exhaust gas closer to the target air-fuel ratio. It is known to perform feedback control for adjusting the air-fuel ratio of exhaust gas by detecting the air-fuel ratio of gas.

In JP 2006-307806 discloses, comprising a plurality of cylinders, by merging a plurality of cylinders connected to a common one exhaust pipe, an exhaust purification device arranged _the NO _X storage catalyst is disclosed in the exhaust pipe ing. In the exhaust gas purifying apparatus, the linear air-fuel ratio sensor upstream of the NO _X storage catalyst, is disposed an oxygen sensor downstream of the NO _X storage catalyst. When performing sulfur poisoning recovery control, the output value from the linear air-fuel ratio sensor is used so that the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst becomes a predetermined air-fuel ratio, and the air-fuel ratio in each cylinder Is disclosed.

JP 2006-307806 A

In an internal combustion engine that can change the injection pattern of fuel injected into the combustion chamber, the air-fuel ratio of the exhaust gas can be controlled to be rich or stoichiometric by increasing the amount of fuel injected into the combustion chamber. In the sulfur poisoning recovery process, when reducing the air-fuel ratio of exhaust gas to rich or stoichiometric air-fuel ratio, heavy reduction in the combustion chamber is performed by injecting the increased amount of fuel injected into the combustion chamber at a combustible time The agent can be converted to a light reducing agent. A suitable reducing agent can be supplied to the NO _X storage catalyst.

  In this internal combustion engine, by arranging an air-fuel ratio sensor in the engine exhaust passage, the air-fuel ratio of the exhaust gas flowing through the engine exhaust passage can be detected, and the detected air-fuel ratio becomes the target air-fuel ratio. As described above, the amount of fuel injected into the combustion chamber can be controlled. That is, feedback control for adjusting the fuel injection amount by actually measuring the air-fuel ratio of the exhaust gas can be performed.

  By the way, the air-fuel ratio sensor has a phenomenon that the output value shifts to the rich side when the air-fuel ratio of the exhaust gas becomes less than the stoichiometric air-fuel ratio in a high temperature atmosphere. For this reason, during the sulfur poisoning recovery process, the air-fuel ratio sensor is calibrated before the air-fuel ratio of the exhaust gas is made rich or stoichiometric, and learning to update the correction coefficient of the output value of the air-fuel ratio sensor is performed. Is doing. The learning of the output value of the air-fuel ratio sensor is performed in a period selected with a predetermined interval among a plurality of periods in which the air-fuel ratio of the exhaust gas is rich or stoichiometric.

Learning of the output value of the air-fuel ratio sensor is performed by lowering the air-fuel ratio of the exhaust gas in order to ensure calibration accuracy. In the prior art, the output value of the air-fuel ratio sensor is learned within a period when the air-fuel ratio of the exhaust gas is rich or stoichiometric. That is, the output value of the air-fuel ratio sensor is learned using a part of the period during which the air-fuel ratio of the exhaust gas is rich or the stoichiometric air-fuel ratio. For this reason, there is a problem that a part of the period for releasing SO _X is eroded and the time for the sulfur poisoning recovery process becomes longer.

  An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can perform sulfur poisoning recovery processing in a short time.

The exhaust gas purification apparatus for an internal combustion engine of the present invention occludes NO _x contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean in the engine exhaust passage, and the air-fuel ratio of the inflowing exhaust gas is rich or It becomes the stoichiometric air-fuel ratio and placing the NO _X storing catalyst to release the occluded NO _{X, the} NO _X storage air-fuel ratio sensor disposed in the engine exhaust passage downstream of the catalyst, SO _X amount stored in the NO _X storage catalyst Increases the temperature of the NO _X storage catalyst to a temperature at which SO _X can be released, and the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is made rich or stoichiometric. By doing so, the sulfur poisoning recovery process is performed. The exhaust purification device includes fuel supply means for supplying fuel into the engine exhaust passage on the upstream side of the NO _X storage catalyst. When SO _X is to be released, the fuel is supplied from the fuel supply means to supply exhaust gas. a Atsushi Nobori control the air-fuel ratio causes the temperature of the _the NO _X storage catalyst in a lean state, by injecting additional fuel in timing that can be combusted in the combustion chamber, the air-fuel ratio of the exhaust gas based on the output signal of the air-fuel ratio sensor By performing feedback control to a rich or stoichiometric air-fuel ratio, SO _X release control for releasing SO _X from the NO _X storage catalyst is repeatedly performed alternately. When learning the output value of the air-fuel ratio sensor, the exhaust purification device shortens the temperature raising control period, increases the fuel supply flow rate from the fuel supply means, and can combust immediately after completion of the temperature raising control. By injecting additional fuel into the combustion chamber at an appropriate time, the air-fuel ratio of the exhaust gas is lowered in a lean state, and the output value of the air-fuel ratio sensor is learned. With this configuration, the sulfur poisoning recovery process can be performed in a short time.

  In the above invention, the fuel supply means can include a fuel addition valve for supplying fuel into the engine exhaust passage.

In the above invention, the fuel supply means, by supplying the fuel from the fuel addition valve in a pulsed manner during the temperature increase control, temporarily rich air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst It is preferable. With this configuration, SO _X can be released from the NO _X storage catalyst even during the temperature increase control period.

In the above invention, when the fuel is supplied from the fuel supply means during the temperature raising control period, if the air-fuel ratio of the exhaust gas is continuously rich or stoichiometric, the air-fuel ratio is increased after the temperature raising control. It is preferable to perform SO _X release control without learning the sensor output value, and to learn the output value of the air-fuel ratio sensor immediately after the subsequent other temperature increase control. With this configuration, it is possible to eliminate learning of the output value of the air-fuel ratio sensor when the state of the internal combustion engine is not suitable for learning of the output value of the air-fuel ratio sensor.

Another internal combustion engine exhaust gas purification apparatus of the present invention occludes NO _X contained in exhaust gas when the air-fuel ratio of the exhaust gas flowing into the engine exhaust passage is lean, and the air-fuel ratio of the exhaust gas flowing in is becomes rich or the stoichiometric air-fuel ratio and placing the NO _X storing catalyst to release the occluded NO _X, the air-fuel ratio sensor disposed downstream of the engine exhaust passage of the NO _X storage catalyst, were stored in the NO _X storage catalyst SO _{When the X} amount exceeds a predetermined allowable amount, the temperature of the NO _X storage catalyst is raised to a temperature at which SO _X can be released, and the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is made rich or stoichiometric. The sulfur poisoning recovery process is performed by setting the fuel ratio. When the exhaust gas purification apparatus should release SO _X , it raises the temperature of the NO _X storage catalyst by injecting additional fuel into the combustion chamber at a time when combustion is impossible, while the air-fuel ratio of the exhaust gas is lean. control and, by injecting additional fuel in timing that can be combusted in the combustion chamber, by feedback control the air-fuel ratio rich or stoichiometric air-fuel ratio of the exhaust gas based on the output signal of the air-fuel ratio sensor from the NO _X storing catalyst The SO _X release control for releasing SO _X is repeated alternately. The exhaust emission control device shortens the temperature raising control period when learning the output value of the air-fuel ratio sensor, and immediately after completion of the temperature raising control, in addition to fuel injection at a time when combustion is impossible, combustion is possible. By injecting additional fuel into the combustion chamber at an appropriate time, the air-fuel ratio of the exhaust gas is lowered in a lean state, and the output value of the air-fuel ratio sensor is learned. With this configuration, the sulfur poisoning recovery process can be performed in a short time.

In the above invention, the oxidation catalyst is arranged upstream of the NO _X storage catalyst, and unburned hydrocarbons are supplied to the oxidation catalyst. By this configuration, it is possible to raise the temperature of the exhaust gas by the oxidation reaction in the oxidation catalyst, it is possible to raise the temperature of the NO _X storage catalyst in a short time.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification apparatus of the internal combustion engine which performs a sulfur poisoning recovery process in a short time can be provided.

(Embodiment 1)
With reference to FIG. 1 to FIG. 10, an exhaust gas purification apparatus for an internal combustion engine in the first embodiment will be described.

  FIG. 1 shows an overall view of an internal combustion engine in the present embodiment. In the present embodiment, a compression ignition type diesel engine will be described as an example. The internal combustion engine includes an engine body 1. The engine body 1 includes a combustion chamber 2 for each cylinder, an electronically controlled fuel injection valve 3 for injecting fuel into each combustion chamber 2, an intake manifold 4, and an exhaust manifold 5.

  The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6. Further, a cooling device 11 for cooling the intake air flowing through the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.

On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7 b is connected to the oxidation catalyst 13 through the exhaust pipe 12. A particulate filter 16 for collecting particulates in the exhaust gas is disposed in the engine exhaust passage downstream of the oxidation catalyst 13. Further, a NO _X storage catalyst (NSR) 17 is disposed in the engine exhaust passage downstream of the particulate filter 16.

  An EGR passage 18 is arranged between the exhaust manifold 5 and the intake manifold 4 for exhaust gas recirculation (EGR). An electronically controlled EGR control valve 19 is disposed in the EGR passage 18. A cooling device 20 for cooling the EGR gas flowing in the EGR passage 18 is disposed around the EGR passage 18. In the embodiment shown in FIG. 1, the engine cooling water is guided to the cooling device 20, and the EGR gas is cooled by the engine cooling water.

  Each fuel injection valve 3 is connected to a common rail 22 via a fuel supply pipe 21. The common rail 22 is connected to a fuel tank 24 via an electronically controlled fuel pump 23 having a variable discharge amount. The fuel stored in the fuel tank 24 is supplied into the common rail 22 by the fuel pump 23. The fuel supplied to the common rail 22 is supplied to the fuel injection valve 3 through each fuel supply pipe 21.

  The electronic control unit 30 is composed of a digital computer. The control device for the internal combustion engine in the present embodiment includes an electronic control unit 30. The electronic control unit 30 includes a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, and an output port 36 connected to each other by a bidirectional bus 31. The ROM 32 is a read-only storage device and stores information such as a map necessary for control in advance. The CPU 34 can perform arbitrary calculations and determinations. The RAM 33 is a readable / writable storage device, and can store information such as an operation history or temporarily store a calculation result.

In the engine exhaust passage, a temperature sensor 29 for detecting the temperature of the exhaust gas flowing into the oxidation catalyst 13 is disposed upstream of the oxidation catalyst 13. A temperature sensor 27 for detecting the temperature of the oxidation catalyst 13 is disposed downstream of the oxidation catalyst 13. Downstream of the NO _X storage catalyst 17, a temperature sensor 26 for detecting the temperature of the NO _X storage catalyst 17 or particulate filter 16 is arranged. Further, an air-fuel ratio sensor 60 for detecting the air-fuel ratio of the exhaust gas is disposed downstream of the NO _X storage catalyst 17. Output signals from the temperature sensors 26, 27, 29 and the air-fuel ratio sensor 60 are input to the input port 35 via the corresponding AD converters 37.

  A differential pressure sensor 28 for detecting the differential pressure across the particulate filter 16 is attached to the particulate filter 16. Output signals of the differential pressure sensor 28 and the intake air amount detector 8 are input to the input port 35 via the corresponding AD converters 37.

  A fuel addition valve 15 is disposed in the engine exhaust passage upstream of the oxidation catalyst 13 as fuel supply means for supplying a reducing agent into the engine exhaust passage. The fuel addition valve 15 in the present embodiment is formed so as to inject fuel toward the inside of the exhaust pipe 12. In the present embodiment, the same fuel as that of the engine body 1 is injected. However, the present embodiment is not limited to this, and a fuel different from that of the engine body 1 may be used.

  Connected to the accelerator pedal 40 is a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40. The output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the EGR control valve 19, and the fuel pump 23 through corresponding drive circuits 38. Further, the output port 36 is connected to the fuel addition valve 15 via a corresponding drive circuit 38. The fuel addition valve 15 in the present embodiment is controlled by the electronic control unit 30.

  The oxidation catalyst 13 is a catalyst having oxidation ability for purifying exhaust gas. The oxidation catalyst 13 includes, for example, a base body having a partition wall extending in the exhaust gas flow direction inside a cylindrical case body. The substrate is formed in a honeycomb structure, for example. A coating layer made of, for example, porous oxide powder is formed on the surface of the substrate, and a noble metal catalyst such as platinum Pt is supported on the coating layer. CO or HC contained in the exhaust gas is oxidized by the oxidation catalyst 13 and converted into a substance such as water or carbon dioxide.

  The particulate filter 16 is a filter that removes particulate matter (particulates) such as carbon particulates and ionic particulates such as sulfate contained in the exhaust gas. The particulate filter has, for example, a honeycomb structure and has a plurality of flow paths extending in the gas flow direction. In the plurality of channels, the channels whose downstream ends are sealed and the channels whose upstream ends are sealed are alternately formed. The partition walls of the flow path are formed of a porous material such as cordierite. Particulates are captured when the exhaust gas passes through the partition walls.

  Particulate matter is collected on the particulate filter 16 and oxidized. The particulate matter gradually deposited on the particulate filter 16 is oxidized and removed by raising the temperature to, for example, about 600 ° C. in an atmosphere containing excess air. In the apparatus example shown in FIG. 1, when the differential pressure across the particulate filter 16 detected by the differential pressure sensor 28 exceeds an allowable value, the amount of particulate matter deposited on the particulate filter 16 indicates the allowable amount. It is judged that it exceeded. When the amount of particulate matter exceeds the allowable amount, the temperature of the particulate filter 16 is raised while the air-fuel ratio of the exhaust gas is lean, and the deposited particulate matter is oxidized and removed.

FIG. 2 is a schematic sectional view of the NO _X storage catalyst. The NO _X storage catalyst 17 has a catalyst carrier 45 made of alumina, for example, supported on a substrate. A noble metal catalyst 46 is dispersed and supported on the surface of the catalyst carrier 45. A layer of NO _X absorbent 47 is formed on the surface of the catalyst carrier 45. As the noble metal catalyst 46, for example, platinum Pt is used. The components constituting the NO _X absorbent 47 are selected from, for example, alkali metals such as potassium K, sodium Na and cesium Cs, alkaline earth such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. At least one of these is used.

When the ratio of air and fuel (hydrocarbon) supplied to the engine intake passage, combustion chamber, or engine exhaust passage is referred to as the air-fuel ratio (A / F) of the exhaust gas, the air-fuel ratio of the exhaust gas is lean (theoretical). When the air-fuel ratio is larger), NO contained in the exhaust gas is oxidized on the noble metal catalyst 46 to become NO ₂ . NO ₂ is nitrate ions NO ₃ ^- are occluded in the NO _X absorbent 47 in the form of.

On the other hand, when the air-fuel ratio of the exhaust gas is rich (smaller than the stoichiometric air-fuel ratio) or becomes the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas decreases and the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO Go to ₂ ). _The NO _X absorbent in the 47 nitrate ions NO ₃ ^- are released from _the NO _X absorbent 47 in the form of NO _2. The released NO _X is reduced to N ₂ by unburned hydrocarbons and carbon monoxide contained in the exhaust gas.

In the operating example of the present embodiment, to detect the _the NO _X storage amount stored in _the NO _X storage catalyst. For example, a map of the accumulated amount of NO _X per unit time that has the engine speed N and the required torque TQ as functions is built in the ROM 32 of the electronic control unit 30. By integrating the storage amount of the NO _X per unit is calculated time in accordance with the operating conditions, it is possible to detect _the NO _X storage amount stored in the NO _X storage catalyst. Before the absorption capacity of the NO _X absorbent 47 is saturated, fuel is added from the fuel addition valve 15 to enrich the air-fuel ratio of the exhaust gas. By temporarily make the air can be reduced along with the release of NO _X from _the NO _X absorbent 47.

FIG. 3 shows another schematic cross-sectional view of the NO _X storage catalyst. The exhaust gas contains SO _X , that is, SO ₂ . When this SO ₂ flows into the NO _X storage catalyst 17, it is oxidized in the noble metal catalyst 46 to become SO ₃ . The SO ₃ is absorbed in _the NO _X absorbent 47, for example, while bonding with the barium carbonate BaCO _3, and diffuses in the NO _X absorbent 47 in sulfate ions _SO ^{4 2-form,} generating the sulfate BaSO ₄ To do. Since the NO _X absorbent 47 has a strong basicity, the sulfate BaSO ₄ is stable and difficult to decompose. Simply by making the air-fuel ratio of the exhaust gas rich, the sulfate BaSO ₄ remains as it is without being decomposed. . For this reason, if the use of the NO _X storage catalyst is continued, the sulfate BaSO ₄ in the NO _X absorbent 47 increases, and the amount of NO _X that can be absorbed by the NO _X storage catalyst decreases.

In this way, so-called sulfur poisoning occurs in the NO _X storage catalyst 17. In order to eliminate the sulfur poisoning, a sulfur poisoning recovery process for releasing SO _X from the NO _X storage catalyst is performed. In the sulfur poisoning recovery process, the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst 17 the temperature of the NO _X storage catalyst 17 in a state of being raised to a temperature capable of SO _X release the rich or the stoichiometric air-fuel ratio Thus, SO _X is released from the NO _X storage catalyst.

  FIG. 4 shows a graph for explaining the relationship between the output current of the air-fuel ratio sensor and the air-fuel ratio in the present embodiment. The air-fuel ratio sensor in the present embodiment is an all-region type air-fuel ratio sensor that indicates an output value corresponding to each point of the air-fuel ratio of the exhaust gas. The smaller the air-fuel ratio (the richer the air-fuel ratio), the smaller the output current of the air-fuel ratio sensor. Further, when the air-fuel ratio is 14.7, the output current of the air-fuel ratio sensor becomes 0A. The air-fuel ratio sensor in the present embodiment is a linear air-fuel ratio sensor in which the air-fuel ratio and the output value have a substantially proportional relationship, and can detect the air-fuel ratio in each state of the exhaust gas.

FIG. 5 is a time chart when the sulfur poisoning recovery process is performed in the internal combustion engine of the present embodiment. Until time t ₀ is a normal operation, at a time t ₀ to start the sulfur poisoning recovery process. From time _{t 0} to time _{t 1,} the temperature of the NO _X storage catalyst is raised to the temperature of the NO _X storage catalyst to be equal to or greater than the SO _X release temperature. That is, the bed temperature of the NO _X storage catalyst is raised. From time t ₁ to time t _2, the while maintaining the temperature of the NO _X storage catalyst than SO _X release temperature, the air-fuel ratio of intermittently exhaust gas by the rich or the stoichiometric air-fuel ratio, releases SO _X I am letting. In the time t ₂ or later, it has carried out a normal operation to end the sulfur poisoning recovery process.

The control device for an internal combustion engine in the present embodiment detects the SO _X storage amount accumulated in the NO _X storage catalyst. For example, should an internal map of the accumulated amount of SO _X per unit time to the the required torque TQ engine speed N to the function ROM32 of the electronic control unit 30. By integrating the SO _X storage amount per unit is calculated time in accordance with the operating conditions, it is possible to detect the SO _X storage amount stored in the NO _X storage catalyst. When the SO _X storage amount of the NO _X storage catalyst reaches a predetermined amount, a sulfur poisoning recovery process is performed.

  The control apparatus for an internal combustion engine in the present embodiment is formed so that the injection pattern of fuel injected into the combustion chamber can be changed. That is, the fuel injection amount and the fuel injection timing can be controlled by electronic control of the fuel injection valve 3.

  FIG. 6 shows a fuel injection pattern during normal operation of the internal combustion engine in the present embodiment. The injection pattern A is a fuel injection pattern during normal operation. During normal operation, the main injection FM is performed at a compression top dead center TDC. Main injection FM is performed at a crank angle of approximately 0 °. Further, in order to stabilize the combustion of the main injection FM, the pilot injection FP is performed before the main injection FM. The pilot injection FP is performed, for example, in a range where the crank angle is approximately 10 ° to approximately 40 ° before the compression top dead center TDC. During normal operation, as shown in the injection pattern B, the pilot injection FP may not be performed and only the main injection FM may be performed. In this embodiment, an injection pattern in which pilot injection FP is performed will be described as an example.

Referring to FIG. 5, when the engine is operated with the injection pattern A in the normal operation, the air-fuel ratio of the exhaust gas is lean. The operation of the internal combustion engine is continued and it is detected that SO _X has accumulated to a predetermined allowable amount, and the temperature increase of the NO _X storage catalyst is started at time t ₀ . At time _{t 1} from time _{t 0,} performs control to raise the temperature of the NO _X storage catalyst.

FIG. 7 shows an injection pattern for raising the temperature of the NO _X storage catalyst. The injection pattern C is an injection pattern in which the temperature of the exhaust gas rises. In the injection pattern C, the injection timing of the main injection FM is delayed from the compression top dead center TDC. That is, the injection timing of the main injection FM is retarded. As the injection timing of the main injection FM is retarded, the injection timing of the pilot injection FP is also retarded. By delaying the injection timing of the main injection FM, the temperature of the exhaust gas can be raised.

  Further, after the main injection FM, after injection FA as auxiliary injection is performed. The after injection FA is performed at a combustible time after the main injection. The after injection FA is performed, for example, in a range where the crank angle after compression top dead center is approximately 40 °, for example, in the range where the crank angle after compression top dead center is approximately 20 ° to approximately 30 °. By performing after-injection FA, the afterburning period becomes longer and the temperature of the exhaust gas can be raised. Further, the amount of combustion in the combustion chamber can be increased and the temperature of the exhaust gas can be raised.

Referring to FIG. 5, during the period from time t ₀ to time t ₁ , the temperature of the exhaust gas rises by performing injection pattern C in the combustion chamber. When operating with the injection pattern C, the air-fuel ratio of the exhaust gas is lean. By the temperature of the exhaust gas increases, the temperature of the NO _X storage catalyst is increased. The temperature of the NO _X storage catalyst is raised to a predetermined target temperature that is equal to or higher than the SO _X release temperature. As the target temperature at this time, for example, 600 ° C. can be adopted. Note that the temperature increase of the NO _X storage catalyst, but the invention is not limited to this, it is possible to employ any method.

When the temperature of the NO _X storage catalyst reaches the target temperature, temperature increase control is performed in order to maintain the temperature of the NO _X storage catalyst at or above the SO _X release temperature. Further, in order to release SO _X , SO _X release control is performed to make the air-fuel ratio of the exhaust gas rich or the stoichiometric air-fuel ratio.

In the temperature rise control of the present embodiment, fuel is supplied into the exhaust pipe 12 by the fuel addition valve 15 as fuel supply means. In the combustion chamber 2, fuel is injected by an injection pattern A performed during normal operation. The air-fuel ratio of the exhaust gas is in a lean state. In the temperature rise control, fuel is supplied by the fuel addition valve 15. The fuel supplied by the fuel addition valve 15 reaches the oxidation catalyst 13. An oxidation reaction occurs in the oxidation catalyst 13. The temperature of the exhaust gas can be raised by the oxidation reaction heat generated at this time. When the temperature of the exhaust gas rises, the NO _X storage catalyst 17 disposed downstream of the oxidation catalyst 13 can be raised in temperature. Since the temperature of the NO _X storage catalyst decreases at the time of the SO _X release control, the temperature of the NO _X storage catalyst is increased by the temperature increase control.

FIG. 8 shows an injection pattern for making the air-fuel ratio of the exhaust gas rich or stoichiometric in the present embodiment. In the SO _X release control in the present embodiment, fuel is injected into the combustion chamber by the injection pattern D. The supply of fuel from the fuel addition valve is stopped. Injection pattern D are performed intermittently during the period from time t ₁ to time t _2. When the injection pattern D is compared with the combustion pattern C, the injection amount of the after injection FA is increased. By increasing the injection amount of the after injection FA, the air-fuel ratio of the exhaust gas can be made rich or the stoichiometric air-fuel ratio.

In the SO _X release control, the amount of combustion in the combustion chamber increases by increasing the injection amount of the after injection FA. By burning at least part of the increased fuel, light unburned hydrocarbons (HC), CO, etc. contained in the exhaust gas increase. For this reason, light unburned hydrocarbon (HC) or CO can be supplied to the engine exhaust passage as a reducing agent. Light unburned hydrocarbons, CO, and the like are excellent as reducing agents and are preferable as reducing agents. In the NO _X storage catalyst, SO _X is released by supplying the reducing agent. In the present embodiment, the SO _X release control is performed by increasing the injection amount of the after injection FA. However, the present embodiment is not limited to this, and the injection amount of the main injection FM may be increased, for example.

Referring to FIG. 5, during the period from time t ₁ to time t ₂ , the temperature increase control and the SO _X release control are alternately performed. That is, the fuel supply by the injection pattern A and the fuel addition valve and the injection pattern D are repeated.

The exhaust gas purification apparatus for an internal combustion engine in the present embodiment performs feedback control based on the output signal of the air-fuel ratio sensor 60 during SO _X release control. That is, when the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor 60 deviates from a predetermined target air-fuel ratio, control is performed so that the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio. .

  Referring to FIG. 1, the amount of fuel injected into combustion chamber 2 and the amount of intake air sent to combustion chamber 2 are adjusted. The amount of fuel injected into the combustion chamber 2 can be adjusted by increasing or decreasing the fuel injected from the electronically controlled fuel injection valve 3. Further, the intake air amount can be adjusted by adjusting the opening of the throttle valve 10. For example, when the output value of the air-fuel ratio sensor 60 deviates from the target air-fuel ratio to the lean side (when the air-fuel ratio of the exhaust gas is larger than the target air-fuel ratio), the throttle valve 10 is adjusted in the closing direction. The rich side can be adjusted by increasing the amount of fuel injected from the fuel injection valve 3.

Here, the air-fuel ratio sensor in the present embodiment has a characteristic that, when the exhaust gas temperature is high, the CO shift reaction occurs and the output value shifts to the rich side when the exhaust gas temperature becomes lower than the stoichiometric air-fuel ratio. In an atmosphere where the temperature of the exhaust gas is, for example, 500 ° C. or more and 700 ° C. or less, when the air-fuel ratio of the exhaust gas becomes less than the stoichiometric air-fuel ratio, a so-called rich shift appears. The CO shift reaction is a reaction in which CO (carbon monoxide) reacts with H ₂ O (water) to generate H ₂ (hydrogen) and CO ₂ (carbon dioxide). When the hydrogen generated at this time enters the air-fuel ratio sensor, the hydrogen acts as a reducing agent equivalent to the fuel. Therefore, the air-fuel ratio sensor is a signal that is apparently shifted to the rich side from the true air-fuel ratio. Is output. This CO shift reaction is also called a water gas shift reaction. The conditions under which the CO shift reaction occurs depend on the catalyst.

  When the sulfur poisoning recovery process is performed, the air-fuel ratio sensor learns the output value of the air-fuel ratio sensor because a rich shift occurs. In the present embodiment, the output value of the air-fuel ratio sensor is learned a plurality of times at predetermined intervals. In the learning in the present embodiment, a learning correction coefficient for correcting the output value of the air-fuel ratio sensor is calculated, and the learning correction coefficient is replaced with the previous learning correction coefficient and stored. The learning correction coefficient is stored in the RAM 33 of the electronic control unit 30, for example. Thus, learning to calculate a correction coefficient for correcting the output value of the air-fuel ratio sensor and update the stored correction coefficient is called learning.

  In the present embodiment, the learning period during which the output value of the air-fuel ratio sensor is learned is set when the air-fuel ratio of the exhaust gas is reduced and the air-fuel ratio of the exhaust gas is reduced within the lean range. The learning period is a region where the air-fuel ratio of the exhaust gas is lean and the air-fuel ratio sensor is not richly shifted. During the learning period, the output value of the air-fuel ratio sensor is detected. The air-fuel ratio of the exhaust gas is obtained by calculation based on the amount of fuel injected into the combustion chamber 2 and the amount of intake air supplied to the combustion chamber 2.

  Next, a correction coefficient for the output value of the air-fuel ratio sensor is calculated based on the air-fuel ratio of the exhaust gas obtained by calculation. That is, the learning correction coefficient for the output value of the air-fuel ratio sensor is calculated so that the output value of the air-fuel ratio sensor becomes the same value as the air-fuel ratio of the exhaust gas obtained by calculation. The learning correction coefficient may be a coefficient that is multiplied by the output value of the air-fuel ratio sensor, or may be a coefficient that is added to or subtracted from the output value of the air-fuel ratio sensor. When the learning correction coefficient for the output value of the air-fuel ratio sensor is calculated, the learning correction coefficient is replaced with the previous learning correction coefficient and stored. By performing this learning, the deviation of the air-fuel ratio sensor when performing feedback control can be reduced.

Further, after the air-fuel ratio of the exhaust gas is reduced to a rich or stoichiometric air-fuel ratio, the output value of the air-fuel ratio sensor may be learned again. The amount of fuel injected and the amount of intake air injected into the combustion chamber when the air-fuel ratio of the exhaust gas is lowered to the air-fuel ratio at which SO _X is released are obtained by calculation. When the air-fuel ratio of the exhaust gas is rich or stoichiometric, the air-fuel ratio sensor may be richly shifted. The output value from the air-fuel ratio sensor is detected, and the learning correction coefficient is calculated again so that the output value of the air-fuel ratio sensor becomes the target air-fuel ratio. The calculated learning correction coefficient is replaced with the stored learning correction coefficient and stored.

In the SO _X release control, the learning correction coefficient is used to detect the air-fuel ratio of the exhaust gas from the air-fuel ratio sensor. Based on the detected air-fuel ratio of the exhaust gas, feedback control is performed to adjust at least one of the fuel injection amount and the intake air amount in the combustion chamber. By performing feedback control, SO _X can be released in a state close to the target air-fuel ratio. Referring to FIG. 5, in the present embodiment, during the period from time t ₁ to the time t _2, the is performed learning output values for a plurality of times the air-fuel ratio sensor.

In FIG. 9, the enlarged view of the time chart when performing the sulfur poisoning recovery process in this Embodiment is shown. FIG. 9 is a time chart when learning the output value of the air-fuel ratio sensor when the temperature raising control and the SO _X release control are alternately performed. When learning of the output value of the air-fuel ratio sensor is not performed, the temperature rise control is performed for a certain time, and then the SO _X release control is performed for a certain time (see FIG. 5).

In the exhaust gas purification apparatus for an internal combustion engine in the present embodiment, the learning period for learning the output value of the air-fuel ratio sensor is set during the temperature increase control period. That is, of the repeated performing Atsushi Nobori control, the timing of the end of one period of the temperature increase control, learning period T ₁ is set. When performing the learning period L ₁ of the temperature rise control of the learning period immediately before is shorter compared to the period L _sta other Atsushi Nobori control.

In learning period T _1, the air-fuel ratio of the exhaust gas performs the air-fuel ratio lowering control closer to the stoichiometric air-fuel ratio within the lean. In the present embodiment, the air-fuel ratio of the exhaust gas is slightly leaner than the stoichiometric air-fuel ratio. While maintaining this state, the output value of the air-fuel ratio sensor is learned. When learning the output value of the air-fuel ratio sensor, it is possible to perform highly accurate learning by bringing the air-fuel ratio of the exhaust gas closer to the air-fuel ratio when feedback control is performed.

In the air-fuel ratio reduction control of the present embodiment, the air-fuel ratio is reduced by adjusting the amount of after-injection FA that is performed after the main injection. When after-injection FA is performed, at least a part of the combustion chamber burns, so that a light reducing agent can be supplied to the oxidation catalyst 13 disposed in the engine exhaust passage. Many reducing agents supplied to the oxidation catalyst 13 are consumed by the oxidation catalyst 13. For this reason, unburned hydrocarbons that pass through the oxidation catalyst 13 and the NO _X storage catalyst 17 can be reduced, and release of unburned hydrocarbons into the atmosphere can be suppressed. Alternatively, adverse effects on the air-fuel ratio sensor 60 can be suppressed.

In FIG. 10, the enlarged view of the time chart when performing the sulfur poisoning recovery process of the comparative example in this Embodiment is shown. In the sulfur poisoning recovery process of the comparative example, when the temperature increase control and the SO _X release control are alternately performed, the learning period T _com for learning the output value of the air-fuel ratio sensor is equal to the SO _X release control. It is set during the period. In other words, the learning period T _com is set at the beginning of one SO _X release control period among the repeated SO _X release controls. For this reason, the time for performing SO _X release control is shortened. The fuel supply flow rate from the fuel addition valve during the temperature increase control period is a constant supply flow rate Q _sta regardless of whether or not learning of the output value of the air-fuel ratio sensor is performed. Also in the case of performing learning, the temperature increase control period _Lcom immediately before the learning period is the same length as the other temperature _increase control periods _Lsta .

Referring to FIG. 9, in the present embodiment, the learning period T ₁ is set to a period of warm-up control. During the learning period of the output value of the air-fuel ratio sensor, the supply of fuel from the fuel addition valve is stopped. If fuel is supplied from the fuel addition valve during the learning period, heavy unburned hydrocarbons may reach the air-fuel ratio sensor, causing a lean shift in which the output value shifts to the lean side. Therefore, during the learning period, it is preferable not to supply fuel from the fuel addition valve in order to avoid adverse effects on the air-fuel ratio sensor. However, when the influence on the air-fuel ratio sensor is small, fuel may be supplied from the fuel addition valve during the learning period.

In learning period T _1, although after injection FA is performed in the combustion chamber, the supply of fuel by the fuel addition valve in order to have stopped, the temperature of the exhaust gas is lowered. In the present embodiment, the temperature of the NO _X storage catalyst is prevented from excessively decreasing during the SO _X release period by increasing the supply flow rate of the fuel addition valve in the temperature increase control period immediately before the learning period. . In the temperature increase control immediately before the learning period, the fuel is supplied at a supply flow rate Q _h that is higher than the supply flow rate Q _{sta of the} temperature increase control when learning is not performed. Thus, in the present embodiment, the period of temperature increase control is shortened and the fuel supply flow rate from the fuel addition valve is increased.

Learning of the output value of the air-fuel ratio sensor in the present embodiment is performed a plurality of times during a period in which the temperature increase control and the SO _X release control are repeated (see FIG. 5). By performing learning a plurality of times, highly accurate feedback control can be performed. On the other hand, if the supply flow rate is not increased at the time of temperature increase control immediately before the learning period, the temperature increase control period is shortened each time learning is performed, and the temperature of the NO _X storage catalyst finally becomes the SO _X release temperature. May be: However, in the present embodiment, it is possible to prevent the temperature of the NO _X storage catalyst from becoming lower than the SO _X release temperature by increasing the supply flow rate of the fuel addition valve in the temperature increase control immediately before the learning period. it can. Alternatively, it is possible to prevent the average temperature of the NO _X storage catalyst from becoming lower than the target temperature.

  The exhaust emission control device in the present embodiment calculates the required amount of fuel supplied from the fuel addition valve when performing the sulfur poisoning recovery process. The required amount of fuel per unit time supplied from the fuel addition valve is as follows.

(Required amount of fuel per unit time supplied from the fuel addition valve) = k [(target temperature of NO _X storage catalyst) − (temperature of exhaust gas flowing into the catalyst)] × (exhaust gas flow rate)... (1)
Here, k is a constant, and the target temperature of the NO _X storage catalyst is predetermined. The target temperature of the NO _X storage catalyst in the present embodiment is a constant value. In the present embodiment, since the temperature of the exhaust gas is mainly raised by the oxidation catalyst, the gas temperature flowing into the catalyst is the gas temperature at the inlet of the oxidation catalyst 13.

As shown in FIG. 9, the temperature of the exhaust gas at the inlet of the oxidation catalyst 13 is lower than the target temperature of the NO _X storage catalyst. The temperature of the exhaust gas at the inlet of the oxidation catalyst 13 is substantially constant during the temperature increase control period. In the period of the SO _X release control, the amount of fuel combusted in the combustion chamber 2 increases, so that it rises. The temperature of the exhaust gas at the inlet of the oxidation catalyst 13 rises because the amount of fuel combusted in the combustion chamber 2 increases even during the air-fuel ratio lowering control period.

The required amount of fuel supplied from the fuel addition valve 15 is an integrated value of the required amount per unit time at each time point. The required amount of the fuel addition valve 15 is integrated and gradually increased when performing SO _X release control. By supplying fuel from the fuel addition valve 15 in the temperature rise control, the required amount of the fuel addition valve 15 gradually decreases.

In the present embodiment, the amount of fuel supplied from the fuel addition valve in the immediately preceding temperature increase control so that the required amount of the fuel addition valve becomes zero at the start of SO _X release control (at the end of the learning period). Is calculated. The calculated supply amount to be supplied within a period of warm-up control, the supply flow rate Q _h of the fuel addition valve is calculated. The calculated feed flow rate Q _h, is performed the supply of fuel during the temperature increase control. At the end of the temperature increase control (at the start of the air-fuel ratio reduction control), the required amount of the fuel addition valve becomes a value exceeding zero. By this control, the average value of the temperature of the NO _X storage catalyst can be made higher than the target temperature. On the other hand, in the sulfur poisoning recovery process of the comparative example, control is performed so that the required amount of the fuel addition valve becomes zero at the end of the temperature increase control (at the start of the learning period) ( (See FIG. 10).

In the present embodiment, in order to increase the fuel supply flow rate of the fuel addition valve in the temperature increase control period immediately before the learning period, the maximum temperature of the NO _X storage catalyst is higher than that in other temperature increase control periods. Get higher. During the learning period, the temperature of the NO _X storage catalyst decreases, and further, in the SO _X release control, the temperature of the NO _X storage catalyst also decreases. At this time, the temperature of the NO _X storage catalyst at the end of the SO _X release control is preferably the same as the temperature when learning is not performed. That is, the temperature is preferably the same as the temperature at the end of the SO _X release control in the comparative example shown in FIG. Thus, the temperature of the NO _X storage catalyst can be prevented from excessively decreasing, and the average temperature of the NO _X storage catalyst can be kept above the target temperature.

In this embodiment, it is possible to incorporate a learning period within the period of warm-up control, when performing the learning of the output value of the air-fuel ratio sensor, it can be avoided that the time of the SO _X release control is shortened. Referring to FIG. 9 and FIG. 10, when the control in the present embodiment and the control in the comparative example are compared, one heating control period, one learning period, and one SO _X release control period are totaled. The time for one cycle is the same. However, by incorporating the learning period into the temperature increase control period, it is possible to avoid shortening the SO _X release control period. As a result, the sulfur poisoning recovery process can be performed in a short time.

In the present embodiment, the supply flow rate of the fuel supplied from the fuel addition valve during the temperature rise control is made constant. By performing this control, it is possible to reduce the maximum value of the supply flow rate supplied from the fuel supply valve, unburned hydrocarbons can be prevented from slipping through the oxidation catalyst and _the NO _X storage catalyst.

Exhaust purification system of this embodiment, the oxidation catalyst is disposed between the fuel addition valve and _the NO _X storage catalyst. With this configuration, it is possible to accelerate the oxidation reaction, it is possible to perform heating of the NO _X storage catalyst in a short time. The exhaust purification device is not limited to this form, and the oxidation catalyst may not be disposed. The NO _X storage catalyst carries a noble metal that causes an oxidation reaction. For this reason, an oxidation reaction also occurs in the NO _X storage catalyst. In the case where the upstream oxidation catalyst of the NO _X storage catalyst is not disposed may, by supplying a reducing agent to the NO _X storage catalyst, it is possible to raise the temperature of the _the NO _X storage catalyst.

  The fuel supply means in the present embodiment includes a fuel addition valve for supplying fuel into the engine exhaust passage. However, the fuel supply means is not limited to this form, and the fuel supply means includes any means for supplying fuel into the engine exhaust passage. Can be adopted.

(Embodiment 2)
With reference to FIGS. 11 to 13, an exhaust emission control device for an internal combustion engine in the second embodiment will be described.

FIG. 11 is a time chart of a first operation example in which the sulfur poisoning recovery process is performed in the exhaust purification apparatus of the present embodiment. The first operation example is different from the first embodiment in the temperature rise control immediately before the learning period. In the first operation example, it performs a control to increase the learning period T ₂ for performing learning of the output value of the air-fuel ratio sensor. In the first operational example, the temperature increase control of the immediately preceding learning period T _2, while maintaining the air-fuel ratio is lean state of the exhaust gas, and supplies a large amount of fuel from the fuel supply valve. The supply flow rate _Qhh is calculated so that the air-fuel ratio of the exhaust gas is slightly larger than the stoichiometric air-fuel ratio. The supply flow rate Q _hh is greater than the supply flow rate Q _h in the first embodiment shown in FIG. When performing the learning period L ₂ of the heating control of the learning period immediately before is shorter compared to the period L _sta other Atsushi Nobori control.

Next, as in the first embodiment, the amount of fuel supplied from the fuel addition valve during the temperature rise control period is set so that the required amount of fuel supplied from the fuel addition valve becomes zero at the start of the SO _X release control. Find the supply. Based on the calculated supply flow rate _Qhh , the time for supplying the fuel from the fuel addition valve in the temperature raising control can be calculated. By subtracting the time for supplying the fuel from the time of Atsushi Nobori control when not performing learning, it is possible to calculate the learning period T _2.

In the first operation example, it is possible to increase the learning period T _2. It is possible to ensure a longer learning period T ₂ than learning period T ₁ of the first embodiment shown in FIG. As described above, in the temperature increase control immediately before the learning period, the learning period is lengthened by supplying the fuel from the fuel addition valve so that the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio within the lean range. can do.

FIG. 12 shows a time chart of a second operation example in which the sulfur poisoning recovery process is performed in the exhaust gas purification apparatus of the present embodiment. The second operation example is different from the first embodiment in the temperature rise control immediately before the learning period. In the second operational example, during the temperature increase control of the immediately preceding learning period T _3, by supplying the fuel from the fuel addition valve in a pulse form, the air-fuel ratio of the exhaust gas rich. During the temperature increase control of the immediately preceding learning period T _3, performs so-called rich spike control. By performing the rich spike control, SO _X is released. When performing the learning period L ₃ of the temperature increase control is shortened as compared with the period L _sta other Atsushi Nobori control.

Also in the second operation example, the supply amount of fuel supplied during the temperature increase control immediately before the learning period so that the required amount of fuel supplied from the fuel addition valve becomes zero at the start of the SO _X release control. Is calculated. In the temperature rise control immediately before the learning period, the calculated amount of fuel is supplied in pulses.

  In rich spike control, the supply flow rate of the fuel addition valve is adjusted so that the air-fuel ratio of the exhaust gas does not become excessively rich, or the unburned hydrocarbons released into the atmosphere do not exceed the allowable amount. In addition, it is preferable to leave a pulse interval. If a sufficient pulse interval cannot be provided, it is preferable to stop the rich spike control and perform other controls.

In the second operation example, SO _X can be released during the temperature increase control period, and the sulfur poisoning recovery processing time can be shortened. That is, in addition to SO _X release control, it also can be released SO _X in some periods of the temperature increase control can be performed in a short time sulfur poisoning recovery.

  Next, a third operation example in the present embodiment will be described. In the third operation example, when the operation state of the internal combustion engine is in an unsuitable state for learning the output value of the air-fuel ratio sensor, control for stopping the learning is performed.

In the sulfur poisoning recovery process of the exhaust purification apparatus according to the present embodiment, in the SO _X release control, the amount of fuel combusted in the combustion chamber is increased so that the air-fuel ratio of the exhaust gas becomes rich or stoichiometric. ing. For this reason, the temperature of the exhaust gas discharged from the combustion chamber rises, and the temperature of the exhaust manifold 5 rises. On the other hand, during the temperature raising control period, the temperature of the exhaust manifold 5 can be lowered because the temperature of the exhaust gas discharged from the combustion chamber is low. For this reason, the time required for reducing the temperature of the exhaust manifold is determined during the temperature raising control period. Also, for learning of the output value of the air-fuel ratio sensor, the minimum time required for learning is determined.

  Here, the time during which the temperature increase control can be performed is expressed by the following equation. Further, the supply flow rate of the fuel addition valve is expressed by the following equation using the temperature increase control time when the supply flow rate is constant.

(Time of temperature rise control) = (Time of temperature rise control when learning is not performed) − (Time required for learning) (2)
(Supply flow rate of fuel addition valve) = (Supply amount of fuel supplied from fuel addition valve) / (Time of temperature rise control) (3)
The air-fuel ratio of the exhaust gas is expressed by the following equation based on the flow rate of the exhaust gas and the supply flow rate of the fuel addition valve calculated by the equation (3). The flow rate of the exhaust gas can be calculated from the intake air amount of the engine body, for example.

(Air-fuel ratio of exhaust gas) = (Flow rate of exhaust gas) / (Supply flow rate of fuel addition valve) (4)
The flow rate of the exhaust gas varies depending on the operating state of the internal combustion engine. When the flow rate of the exhaust gas is small, the air-fuel ratio becomes small, and the air-fuel ratio of the exhaust gas may become less than the stoichiometric air-fuel ratio in the temperature increase control immediately before the learning period. For this reason, in the third operation example, the air-fuel ratio of the exhaust gas is calculated, and if the air-fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air-fuel ratio, control is performed to stop learning the output value of the air-fuel ratio sensor. .

  FIG. 13 shows a flowchart of the third operation example of the present embodiment. Each time the learning of the output value of the air-fuel ratio sensor is performed, the determination based on this control flow is performed. In step 101, the amount of fuel supplied from the fuel addition valve is calculated. Next, in step 102, the temperature increase control time during which fuel can be supplied from the fuel addition valve is calculated by the above equation (2). In the present embodiment, the temperature raising control time and the time required for learning when learning according to the above equation (2) is not performed are determined in advance. For this reason, the temperature raising control time is predetermined.

  Next, in step 103, using the calculated temperature increase control time, the amount of fuel supplied from the fuel addition valve is calculated according to the above equation (3) and equation (4). The air-fuel ratio of exhaust gas when supplied over time is calculated.

  Next, in step 104, it is determined whether or not the calculated air-fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air-fuel ratio. If the air-fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air-fuel ratio at step 104, the routine proceeds to step 105 and learning of the output value of the air-fuel ratio sensor is stopped. If the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio at step 104, the routine proceeds to step 106 where the output value of the air-fuel ratio sensor is learned.

  When learning of the output value of the air-fuel ratio sensor is stopped, for example, the learning can be performed during any one of the plurality of subsequent temperature increase controls. For example, the output value of the air-fuel ratio sensor can be learned when the operating state of the internal combustion engine changes and the air-fuel ratio of the exhaust gas becomes small.

  As described above, in the third operation example, it is possible to eliminate learning when the output value of the air-fuel ratio sensor is unsuitable for learning.

  Other configurations, operations, and effects are the same as those in the first embodiment, and thus description thereof will not be repeated here.

(Embodiment 3)
With reference to FIGS. 14 to 16, an exhaust gas purification apparatus for an internal combustion engine in the third embodiment will be described. The exhaust gas purification apparatus for an internal combustion engine in the present embodiment does not include a fuel addition valve that supplies fuel to the engine exhaust passage. The exhaust purification device controls the sulfur poisoning recovery process by changing the fuel injection pattern in the combustion chamber.

In FIG. 14, the enlarged view of the time chart when performing the sulfur poisoning recovery process in this Embodiment is shown. Control of normal operation, control for raising the NO _X storage catalyst to be higher than the SO _X release temperature, and SO _X release control are the same as in the first embodiment.

FIG. 15 shows an injection pattern when performing the temperature rise control in the present embodiment. In the injection pattern E, post injection FPO is performed after the main injection FM. The post injection FPO is an injection in which fuel does not burn in the combustion chamber. The post-injection FPO is an auxiliary injection similar to the after-injection, but the post-injection affects the engine output, while the post-injection has a feature that does not contribute to the engine output. The post injection FPO is performed, for example, when the crank angle after compression top dead center is in the range of approximately 90 ° to approximately 120 °. When operating with the injection pattern E, the air-fuel ratio of the exhaust gas is lean. By injecting the post-injection FPO, unburned hydrocarbons can be supplied to the oxidation catalyst, and the temperature of the oxidation catalyst rises. The temperature of the exhaust gas rises, the _the NO _X storage catalyst can be heated.

  FIG. 16 shows an injection pattern when air-fuel ratio lowering control is performed in the present embodiment. The injection pattern F performs after injection FA in addition to the injection pattern E. By performing after injection FA, the air-fuel ratio of the exhaust gas can be brought close to the stoichiometric air-fuel ratio. The air-fuel ratio can be lowered while maintaining the exhaust gas in a lean state.

In the present embodiment, by performing an injection containing the post injection FPO as the temperature rise control is performed raising the temperature of the NO _X storage catalyst. Further, the post-injection FPO is also performed during the air-fuel ratio lowering control during the learning period. Since the post injection FPO is injected in the combustion chamber, the temperature rises. For this reason, the unburned hydrocarbons supplied by the post-injection FPO have high reactivity in the oxidation catalyst 13. The unburned hydrocarbons supplied by the post injection FPO are almost entirely oxidized in the oxidation catalyst 13. For this reason, the amount of unburned hydrocarbons that pass through the oxidation catalyst 13 and are released into the atmosphere can be reduced. Alternatively, adverse effects on the output of the air-fuel ratio sensor 60 can be avoided. For this reason, post-injection can also be performed during the learning period during which the air-fuel ratio output value is learned.

The supply flow rate of the post injection during the Atsushi Nobori control and the learning period of the learning period immediately before the demand of fuel by post injection at the start of the SO _X release control is calculated to be zero.

Thus, even in an internal combustion engine that does not have a fuel addition valve, the learning period can be incorporated into the period of temperature rise control by shortening the period of temperature rise control and injecting post injection. It can be avoided that the period of SO _X release control is shortened. As a result, the sulfur poisoning recovery process can be performed in a short time.

  Other configurations, operations, and effects are the same as those in the first or second embodiment, and thus description thereof will not be repeated here.

  The above embodiments can be combined as appropriate. For example, in the exhaust gas purification apparatus for an internal combustion engine having the fuel supply means in the first embodiment, the air-fuel ratio of the exhaust gas is lowered by injecting post-injection in the combustion chamber during the air-fuel ratio reduction control during the learning period. It doesn't matter.

  In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. Further, in the embodiment, changes included in the scope of claims are intended.

1 is a schematic diagram of an internal combustion engine in a first embodiment. The NO _X is an enlarged schematic sectional view of the NO _X storage catalyst when occluding. It is an enlarged schematic sectional view of the NO _X storage catalyst when occluding SO _X. 5 is a graph for explaining the characteristics of the air-fuel ratio sensor in the first embodiment. 3 is a time chart when performing sulfur poisoning recovery processing in the first embodiment. It is explanatory drawing of the injection pattern at the time of normal driving | operation. It is an explanatory view of the injection pattern when raising the temperature of the NO _X storage catalyst. It is a figure explaining the injection pattern when making the air fuel ratio of exhaust gas rich or a stoichiometric air fuel ratio. It is an enlarged view of a time chart when performing the sulfur poisoning recovery process in the first embodiment. It is an enlarged view of a time chart when the sulfur poisoning recovery process of the comparative example in Embodiment 1 is performed. 6 is an enlarged view of a time chart of a first operation example of sulfur poisoning recovery processing in Embodiment 2. FIG. FIG. 11 is an enlarged view of a time chart of a second operation example of sulfur poisoning recovery processing in the second embodiment. 12 is a flowchart of a third operation example of the sulfur poisoning recovery process in the second embodiment. FIG. 11 is an enlarged view of a time chart when performing sulfur poisoning recovery processing in the third embodiment. FIG. 10 is an explanatory diagram of an injection pattern when performing temperature rise control in a third embodiment. FIG. 10 is an explanatory diagram of an injection pattern when air-fuel ratio lowering control is performed in a third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 2 Combustion chamber 3 Fuel injection valve 5 Exhaust manifold 8 Intake air amount detector 10 Throttle valve 12 Exhaust pipe 13 Oxidation catalyst 15 Fuel addition valve 16 Particulate filter 17 NO _X storage catalyst 26 Temperature sensor 27 Temperature sensor 28 Differential pressure Sensor 29 Temperature sensor 30 Electronic control unit 45 Catalyst carrier 46 Precious metal catalyst 47 NO _X absorbent 60 Air-fuel ratio sensor

Claims (6)

The engine exhaust passage, occludes NO _X air-fuel ratio when the lean contained in the exhaust gas in the exhaust gas flowing, the air-fuel ratio of the inflowing exhaust gas becomes rich or the stoichiometric air-fuel ratio release the occluded NO _X the NO _X storing catalyst was placed to the air-fuel ratio sensor disposed downstream of the engine exhaust passage of the NO _X storage catalyst, when the SO _X amount stored in the NO _X storage catalyst exceeds an allowable amount predetermined In addition, the temperature of the NO _X storage catalyst is raised to a temperature at which SO _X can be released, and the sulfur poisoning recovery process is performed by making the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst rich or stoichiometric. In the exhaust gas purification apparatus for an internal combustion engine,
Fuel supply means for supplying fuel into the engine exhaust passage upstream of the NO _X storage catalyst;
When SO _X is to be released, temperature increase control is performed to raise the temperature of the NO _X storage catalyst while supplying the fuel from the fuel supply means while the air-fuel ratio of the exhaust gas is lean. The fuel is injected and the air-fuel ratio of the exhaust gas is feedback-controlled to rich or stoichiometric air-fuel ratio based on the output signal of the air-fuel ratio sensor, so that SO _X release control for releasing SO _X from the NO _X storage catalyst is alternated Repeat to
When learning the output value of the air-fuel ratio sensor, the temperature increase control period is shortened, the fuel supply flow rate from the fuel supply means is increased, and the combustion chamber is combusted immediately after completion of the temperature increase control. An exhaust gas purification apparatus for an internal combustion engine, wherein the output value of the air-fuel ratio sensor is learned by lowering the air-fuel ratio of the exhaust gas in a lean state by injecting additional fuel into the engine.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the fuel supply means includes a fuel addition valve for supplying fuel into the engine exhaust passage. Fuel supply means, by supplying the fuel from the fuel addition valve in a pulsed manner during the temperature increase control, characterized by temporarily rich air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst An exhaust purification device for an internal combustion engine according to claim 2. If the air-fuel ratio of the exhaust gas is continuously rich or stoichiometric when the fuel is supplied from the fuel supply means during the temperature increase control period, the output value of the air-fuel ratio sensor is increased after the temperature increase control. 3. The internal combustion engine according to claim 1, wherein the SO _X release control is performed without learning, and the output value of the air-fuel ratio sensor is learned immediately after another subsequent temperature increase control. 4. Exhaust purification device. The engine exhaust passage, occludes NO _X air-fuel ratio when the lean contained in the exhaust gas in the exhaust gas flowing, the air-fuel ratio of the inflowing exhaust gas becomes rich or the stoichiometric air-fuel ratio release the occluded NO _X the NO _X storing catalyst was placed to the air-fuel ratio sensor disposed downstream of the engine exhaust passage of the NO _X storage catalyst, when the SO _X amount stored in the NO _X storage catalyst exceeds an allowable amount predetermined In addition, the temperature of the NO _X storage catalyst is raised to a temperature at which SO _X can be released, and the sulfur poisoning recovery process is performed by making the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst rich or stoichiometric. In the exhaust gas purification apparatus for an internal combustion engine,
When SO _X is to be released, temperature increase control for raising the temperature of the NO _X storage catalyst while the air-fuel ratio of the exhaust gas is lean by injecting additional fuel into the combustion chamber at a time when combustion is impossible, The additional fuel is injected at a combustible time, and the air-fuel ratio of the exhaust gas is feedback-controlled to rich or stoichiometric air-fuel ratio based on the output signal of the air-fuel ratio sensor, so that SO _X is released from the NO _X storage catalyst. Alternating with SO _X release control,
When learning the output value of the air-fuel ratio sensor, the temperature raising control period is shortened, and immediately after completion of the temperature raising control, in addition to the fuel injection at the non-combustible time, an additional time is added at the combustible time. An exhaust emission control device for an internal combustion engine, wherein the output value of the air-fuel ratio sensor is learned by injecting fuel into the combustion chamber to reduce the air-fuel ratio of the exhaust gas in a lean state. 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein an oxidation catalyst is disposed upstream of the NO _X storage catalyst, and unburned hydrocarbons are supplied to the oxidation catalyst.

Images