JP2005083354A - Purification capacity recovery method for exhaust gas purifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a purification capacity recovery method for an exhaust gas purifier for suppressing worsening of fuel economy by performing each removal treatment according to a plan. <P>SOLUTION: This purification capacity recovery method comprises an HC/SOF removal process in which air-fuel ratio of exhaust gas flowing into a filter 23 is maintained in a lean condition and temperature of the filter is maintained within a scope of predetermined temperature, a Soot removal process in which air-fuel ratio is maintained in a lean condition and temperature of the filter is maintained at temperature above the scope of predetermined temperature, a sulfur removal process in which air-fuel ratio of exhaust gas is maintained in a rich condition and temperature of the filter is maintained at temperature above the scope of predetermined temperature, and an oxygen removal process in which air-fuel ratio of exhaust gas is maintained in a rich condition and temperature of the filter is maintained within the scope of predetermined temperature. When it is determined that any of the removal processes must be carried out, these removal processes are carried out in this order. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a filter regeneration method for an internal combustion engine.

Conventionally, a particulate filter (hereinafter referred to as “filter”) carrying a NO _x retention agent such as potassium (K) is known. In such a filter, particulate matter such as soot contained in the exhaust gas can be collected, and NO in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the filter is lean. _x is held, and the NO _x held when the air-fuel ratio of the exhaust gas flowing into the filter is rich can be released, and the released NO _x is reduced by the reducing agent (HC or CO) in the exhaust gas.・ Can be purified.

In such a filter, in order to keep the pressure loss due to the filter low, the particulate matter deposited on the filter must be periodically oxidized and removed. Soluble organic substance adhering on the filter surface (hereinafter, "SOF" and referred) is to prevent oxidation capacity reduction and NO _x holding capacity decreases due to the covering supported precious metal and NO _x holding agent such as filter Furthermore, it is necessary to oxidize and remove the SOF adhering to the filter surface.
In addition, the NO _x retention agent retains not only NO _x in the exhaust gas but also sulfur components such as SO _x , and this reduces the NO _x retention capacity of the NO _x retention agent. It is necessary to release the sulfur component held in the NO _x holding agent supported on the catalyst. In addition, a carrier layer that supports a noble metal is generally provided on the filter surface. However, if the amount of oxygen retained in the carrier layer increases, the ability to oxidize noble metals (catalytic metals) such as platinum (Pt) decreases. Resulting in. For this reason, it is also necessary to release oxygen held in the carrier layer on the filter surface.

As a device that satisfies such a need, devices described in Patent Documents 1 to 4 can be cited. The devices described in Patent Literature 1 to Patent Literature 4 include a sulfur removal treatment for removing sulfur components from the NO _x retention agent, a PM removal treatment for oxidizing and removing particulate matter deposited on the filter surface, and a filter surface. Purification performance of an exhaust purifier carrying a filter or NO _x retention agent by executing oxygen removal treatment (hereinafter collectively referred to as “removal treatment”) to release oxygen retained in the carrier layer Like to maintain. In particular, in these apparatuses, the above-described processing is performed when the operation of the internal combustion engine is stopped (that is, after an engine stop command to the internal combustion engine is detected), thereby performing these processing during operation of the vehicle. Deterioration of vehicle driving performance (drivability, etc.) is prevented.

Japanese Patent Laid-Open No. 10-231720 Japanese Patent Laid-Open No. 05-240027 JP 2000-8837 A JP-A-10-252527 Japanese Patent Laid-Open No. 06-275441

By the way, in the apparatuses described in Patent Documents 1 to 4, the execution conditions are determined for each removal process. For example, the sulfur removal process is performed when the sulfur component retention amount of the NO _x retention agent is equal to or greater than the predetermined retention amount. The PM removal process is executed when the amount of particulate matter deposited on the filter exceeds a predetermined amount.

However, _if each removal process is performed under different execution conditions in a filter carrying a NO _x retention agent, for example, a PM removal process is performed when the operation of a certain internal combustion engine is stopped, and sulfur is detected when the operation of the next internal combustion engine is stopped. The number of executions of the removal process increases, for example, the removal process is executed.
On the other hand, in each of the above-described removal processes, it is necessary to control the air-fuel ratio of the exhaust gas, raise the temperature of the filter, etc. Therefore, fuel is consumed to execute these removal processes.

  Therefore, as a method for recovering the purification capacity of the filter (hereinafter referred to as “purification capacity recovery method”), a condition for executing the removal process is determined independently for each removal process, and a method for executing each removal process independently. If it is adopted, wasteful exhaust gas air-fuel ratio control and filter temperature rise control are performed, and the number of times of removal processing increases, resulting in deterioration of fuel consumption.

  Therefore, an object of the present invention is to provide a method for recovering the purification capacity of an exhaust gas purifier that executes each removal process in a planned manner and suppresses deterioration of fuel consumption.

In order to solve the above problems, the first aspect of the invention, there is provided a purification capacity recovery method of the exhaust gas purifier carrying the NO _x holding agent and a noble metal which is provided on an exhaust passage of an internal combustion engine, in the exhaust purifier An SOF removal step of maintaining the air-fuel ratio of the inflowing exhaust gas lean, maintaining the temperature of the exhaust purifier within a predetermined temperature range, and removing SOF deposited on the surface of the exhaust purifier; The air-fuel ratio of the exhaust gas flowing into the purifier is maintained lean, the temperature of the exhaust purifier is maintained at a temperature equal to or higher than the predetermined temperature range, and the soot accumulated on the surface of the exhaust purifier is removed. The soot removal step and the air-fuel ratio of the exhaust gas flowing into the exhaust purifier are maintained rich, the temperature of the exhaust purifier is maintained at a temperature equal to or higher than the predetermined temperature range, and is held by the NO _x holding agent. To remove sulfur components Leaving the air-fuel ratio of the exhaust gas flowing into the exhaust gas purifier and the exhaust step, maintaining the temperature of the exhaust gas purifier within the predetermined temperature range, and releasing the oxygen held in the exhaust gas purifier In the method for recovering the purification capacity of an exhaust gas purifier comprising an oxygen removal step, when it is determined that any one of the removal steps should be performed, an HC / SOF removal step, a soot removal step The sulfur removal step and the oxygen removal step are performed in this order.
According to the first invention, the removal steps of the HC / SOF removal step, the Soot removal step, the sulfur removal step, and the oxygen removal step are not executed separately, but executed at a time. For this reason, another removal step is executed as it is without lowering the temperature of the exhaust gas purifier that has been heated by executing a certain removal step to the temperature during normal operation. The fuel required for temperature increase control is reduced.
The “exhaust gas purifier” means a carrier and a substance (for example, a noble metal) having a catalytic action supported on the carrier. And a particulate filter that collects SOF).

In the second invention, in the first invention, the maintenance time of the HC / SOF removal step, the soot removal step, the sulfur removal step, and the oxygen removal step, and the maintenance temperature of the exhaust purifier during the execution of each removal step are: They are changed according to the HC / SOF accumulation amount, the soot accumulation amount, the sulfur retention amount, and the oxygen retention amount, respectively, in the exhaust purifier.
According to the second aspect of the present invention, each removal is performed at the minimum necessary maintenance temperature for the minimum necessary maintenance time with respect to the HC / SOF accumulation amount, the Soot accumulation amount, the sulfur retention amount, and the oxygen retention amount to the exhaust gas purifier. If the process is performed, it is possible to reliably remove HC, SOF, soot, sulfur components, and oxygen while minimizing fuel consumption.

In the third invention, in the first or second invention, when it is determined that any one of the removal steps should be executed, the soot removal step or the sulfur removal step is executed. This is when it should be.
In the soot removal step and the sulfur removal step, the temperature of the exhaust purifier is raised to a temperature that is equal to or higher than a predetermined temperature range, so that the fuel consumption is large. On the other hand, the HC / SOF removal step and the oxygen removal step can be executed with a relatively small amount of fuel consumption. Therefore, in the third invention, the entire series of removal steps is executed only when the soot removal step or the sulfur removal step is to be executed. Thus, in any case, the entire removal process is executed only when the temperature of the exhaust purifier must be raised to a temperature equal to or higher than the predetermined temperature range, so that the fuel consumption can be reduced.

In the fourth invention, in the first or second invention, when it is determined that any one of the above-described removal steps should be executed is when a stop command for the internal combustion engine is detected And when the amount of soot deposited on the surface of the exhaust purifier is greater than or equal to a predetermined amount, or when the sulfur component retention amount of the NO _x retention agent is greater than or equal to a predetermined retention amount. .
In general, even if each of the removal steps is executed while a vehicle equipped with the internal combustion engine is running, the operating condition of the internal combustion engine changes variously. It is difficult to keep the air-fuel ratio rich). For this reason, uselessly long time is required for execution of each removal process. According to the fourth aspect of the invention, it is performed when a stop command for the internal combustion engine is detected, that is, when the operating state of the internal combustion engine can be freely changed without running the vehicle. Thus, the air-fuel ratio of the exhaust gas and the temperature of the exhaust purifier can be maintained so that each removal step can be completed in the minimum necessary time.

According to a fifth aspect, in the third aspect, when a stop command for the internal combustion engine is detected, and the amount of soot deposited on the surface of the exhaust purifier is equal to or greater than a predetermined amount, or Even when the sulfur component retention amount of the NO _x retention agent is equal to or greater than the predetermined retention amount, the air-fuel ratio of the exhaust gas flowing into the exhaust purifier when the stop command is detected is lean. When the temperature of the exhaust purifier is equal to or higher than the predetermined temperature range, the HC / SOF removal step is not executed, and the soot removal step, sulfur removal step, and oxygen removal step are executed in this order.
In the fifth invention, when the soot removal process is executed at the start of execution of the purification capacity recovery method of the present invention, only the removal process after the soot removal process is executed. Thereby, it is not necessary to perform useless control of executing the removal process in order from the HC / SOF removal process and executing the soot removal process again even though the execution condition of the soot removal process is satisfied. , Fuel consumption can be reduced.

According to a sixth aspect, in the third aspect, when a stop command for the internal combustion engine is detected and the amount of soot deposited on the surface of the exhaust purifier is equal to or greater than a predetermined amount, or Even when the sulfur component retention amount of the NO _x retention agent is equal to or greater than the predetermined retention amount, the exhaust gas air-fuel ratio is rich and the temperature of the exhaust purifier is equal to or greater than the predetermined temperature range. In this case, the sulfur removal step and the oxygen removal step are performed in this order without performing the HC / SOF removal step and the soot removal step.
In 6th invention, when the sulfur removal process is performed at the time of the start of execution of the purification capacity recovery method of this invention, only the removal process after a sulfur removal process is performed. This eliminates the need for wasteful control in which the removal step is executed in order from the HC / SOF removal step and the sulfur removal step is executed again, even though the execution condition of the sulfur removal step is satisfied. , Fuel consumption can be reduced.

According to a seventh aspect, in the fourth aspect, when a vehicle equipped with the internal combustion engine is selectively or simultaneously driven by the internal combustion engine and an electric motor and a stop command for the internal combustion engine is detected This is when the vehicle is driven only by an electric motor.
According to the seventh aspect, when the vehicle is driven only by the electric motor, that is, a series of removal steps are executed while the vehicle is running, even if the sulfur component is discharged by the sulfur removal step, it is discharged. It is suppressed that a sulfur component accumulates only in the specific area | region in air | atmosphere.

  According to the present invention, since the various removal processes are not performed independently, but are performed at one time, the number of times of temperature increase control for performing the removal process is reduced, and thus fuel consumption is deteriorated. It is suppressed.

  Hereinafter, the purification capacity recovery method of the present invention will be described with reference to the drawings. FIG. 1 shows a diesel-type compression self-ignition internal combustion engine in which the purification capacity recovery method of the present invention is used. The present invention is also applicable to a spark ignition type internal combustion engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13.

  A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 13, and a cooling device 18 for cooling intake air flowing in the intake duct 13 is arranged around the intake duct 13. In the internal combustion engine shown in FIG. 1, engine cooling water is guided into the cooling device 18 and the intake air is cooled by the engine cooling water. On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to a casing 24 containing an exhaust purifier 23 via an exhaust pipe 22. Connected.

  The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 25, and an electrically controlled EGR control valve 26 is disposed in the EGR passage 25. Around the EGR passage 25, an EGR cooling device 27 for cooling the EGR gas flowing in the EGR passage 25 is disposed. In the internal combustion engine shown in FIG. 1, engine cooling water is guided into the EGR cooling device 27, and the EGR gas is cooled by the engine cooling water.

  On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 28, through a fuel supply pipe 6a. Fuel is supplied into the common rail 28 from an electrically controlled fuel pump 29 with variable discharge amount, and the fuel supplied into the common rail 28 is supplied to the fuel injection valve 6 through each fuel supply pipe 6a. A fuel pressure sensor 30 for detecting the fuel pressure in the common rail 28 is attached to the common rail 28, and a fuel pump 29 is used so that the fuel pressure in the common rail 28 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 30. The discharge amount is controlled.

  The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 are connected. It comprises. The output signal of the fuel pressure sensor 33 is input to the input port 45 via the corresponding AD converter 47.

  A load sensor 50 that generates an output voltage proportional to the amount of depression of the accelerator pedal 49 is connected to the accelerator pedal 49, and the output voltage of the load sensor 50 is input to the input port 45 via the corresponding AD converter 47. Further, the input port 45 is connected to a crank angle sensor 51 that generates an output pulse every time the crankshaft rotates, for example, 30 °. Further, a differential pressure sensor 52 for detecting a differential pressure between the exhaust upstream of the filter 23 and the exhaust downstream is provided on the exhaust upstream side and the exhaust downstream side of the filter 23, and the filter 23 includes the filter 23. A temperature sensor 53 is provided for detecting the temperature. The differential pressure sensor 52 and the temperature sensor 53 are connected to the input port 45 via a corresponding AD converter 47. The output port 46 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 26, and the fuel pump 29 via a corresponding drive circuit 48.

  Next, the exhaust gas purifier 23 used in this embodiment will be described. In the present embodiment, a particulate filter (hereinafter referred to as “filter”) 23 carrying a noble metal such as platinum (Pt) is used as the exhaust purifier 23. The filter 23 is made of a porous ceramic, and thus has a collection capability (hereinafter referred to as “Soot collection capability”) for collecting the soot content in the exhaust gas flowing into the filter 23. Further, since the filter 23 carries a noble metal such as platinum (Pt), it has an oxidizing ability to oxidize components in the exhaust gas flowing into the filter 23.

Further, the filter 23 carries a NO _x holding agent having a NO _x holding capability for holding NO _x in the exhaust gas by a mechanism described later. NO _x holding agent, when the air-fuel ratio of NO to _x holding agent (in other words the filter 23) flowing to the exhaust gas is lean holds the NO _x in the exhaust gas, the air-fuel ratio of the exhaust gas flowing into the NO _x holding agent When NO becomes rich, the held NO _x is released. The separated NO _x is reduced and purified by a reducing agent such as hydrocarbon (HC) or carbon monoxide (CO) present in the exhaust gas.

As described above, the filter 23 carrying the NO _x holding agent has the soot collection ability, the oxidation ability, and the NO _x holding ability, but the oxidation ability and the NO _x holding ability are mainly lowered by the following factors. In addition, the pressure loss due to the filter 23 (hereinafter referred to as “pressure loss”), which is one of the performance indexes of the filter 23, is also increased due to the following factors. Hereinafter, these factors and a method for eliminating each factor will be described with reference to FIG.

(1) Accumulation of soot The exhaust gas flowing into the filter 23 contains soot, and this soot is on the surface of the partition wall constituting the filter 23 or on the surface of the pore formed in the partition wall. It is collected by adhering to. Since the collected soot is gradually deposited on the surface of the filter 23, the pores of the filter 23 are blocked when the amount of deposition increases. On the other hand, the exhaust gas flowing into the filter 23 is discharged from the filter 23 through the pores. For this reason, when the number of closed pores increases, the flow resistance against the exhaust gas by the filter 23 increases, and the pressure loss due to the filter 23 increases.

  In order to avoid such a situation, in many filters 23, when the amount of soot deposited on the filter 23 increases, the deposited soot is oxidized and removed (hereinafter referred to as “Soot”). "Removal processing"). The soot will not burn unless it is in a high temperature above a certain temperature (for example, 600 ° C.) and in an atmosphere where oxygen is present. Therefore, the soot removal process is performed by maintaining the air-fuel ratio of the exhaust gas flowing into the filter 23 lean while maintaining the temperature of the filter 23 at or above the temperature at which the apportionment burns. That is, in the soot removal process, the air-fuel ratio of the exhaust gas and the temperature of the filter 23 are set to B in FIG. 2, that is, the temperature of the filter 23 is equal to or higher than the second temperature and the air-fuel ratio of the exhaust gas flowing into the filter 23 is lean. Done by keeping it on.

  The amount of soot deposited on the filter 23 is estimated based on the output of the differential pressure sensor 52 and the like.

(2) HC poisoning (SOF poisoning)
The exhaust gas contains unburned hydrocarbons that are not burned in the combustion chamber 5. This unburned hydrocarbon is adsorbed on the surface of the filter 23, that is, on the surface of the pores formed in the partition wall surface or in the partition wall constituting the filter 23. In addition, in the exhaust gas, fuel evaporated at a high temperature during combustion and hydrocarbons (HC) in the engine oil are deposited in a low temperature during the expansion stroke and become particles (soluble organic substances. "SOF"). This SOF is a hydrocarbon with a high boiling point, and is sticky. For this reason, SOF adheres on the surface of the filter 23.

On the other hand, the surface of the filter 23 is provided with a carrier layer carrying a NO _x holding agent and a noble metal. Since HC and SOF are adsorbed or adhered to cover these NO _x holding agents and precious metals, the amount of HC and SOF adhering to the surface of the filter 23 (hereinafter referred to as “HC / SOF adhesion amount”) increases. As a result, the NO _x retention capacity of the NO _x retention agent, the oxidation capacity of noble metals, and the like are reduced (HC / SOF poisoning).

  In order to avoid such a situation, when the amount of HC / SOF attached to the surface of the filter 23 increases, a process for oxidizing and removing the attached HC and SOF (hereinafter referred to as “HC / SOF”). "Removal processing"). The temperature at which HC or SOF is oxidized and burned is lower than the temperature at which the soot is oxidized and burned (about 300 ° C. or higher for HC and about 400 ° C. or higher for SOF). Therefore, in the HC / SOF removal process, the air-fuel ratio of the exhaust gas flowing into the filter 23 is made lean while maintaining the temperature of the filter 23 at or above the temperature at which HC or SOF burns and below the temperature at which the apportionment burns. Done by maintaining. That is, in the HC / SOF removal process, the air-fuel ratio of the exhaust gas and the temperature of the filter 23 are set to A in FIG. 2, that is, the exhaust gas flowing into the filter 23 when the temperature of the filter 23 is between the first temperature and the second temperature. This is done by maintaining the gas air-fuel ratio in a lean state.

  HC and SOF are oxidized and burned even when the temperature of the filter 23 is equal to or higher than the temperature at which the apportionment burns. However, as will be described later, the temperature rise of the filter 23 causes a deterioration in fuel consumption. The temperature of the filter 23 is kept low by maintaining the following.

  Further, the HC / SOF adhesion amount on the surface of the filter 23 is estimated based on the output of the differential pressure sensor 52 and the like.

(3) Sulfur poisoning In the case of a NO _x holding agent, when the NO _x holding amount increases and the NO _x holding capacity decreases, the air-fuel ratio of the exhaust gas flowing into the NO _x holding agent is almost equal to the stoichiometric air-fuel ratio. or so that to recover the NO _x holding capacity disengaged and reduced the NO _x held by the rich. On the other hand, the exhaust gas flowing into the filter 23 includes a SO _x, this SO _x is held in NO _x holding agent. Without departing from the NO _x holding agent even when the SO _x held in the NO _x holding agent leaves and reduced the NO _x as described above. For this reason, when the amount of SO _x retained by the NO _x retention agent (hereinafter referred to as “SO _x retention amount”) increases, the NO _x retention ability of the NO _x retention agent decreases (sulfur poisoning). ).

To avoid such a situation, when the increasing number stored SO _x amount of the NO _x holding agent, the process of separating the SO _x held in the NO _x holding agent (hereinafter, "sulfur removal process" It is supposed to be executed. NO SO _x held in the _x holding agent is stoichiometric or even during rich atmosphere of the NO _x holding agent temperature is a constant temperature (e.g., 600 ° C.) without departing if not higher than the temperature. Therefore, the sulfur removal process is performed by making the air-fuel ratio of the exhaust gas flowing into the filter 23 rich while maintaining the temperature of the filter 23 at or above the temperature at which the SO _x held in the NO _x holding agent is released. . That is, in the sulfur removal process, the air-fuel ratio of the exhaust gas and the temperature of the filter 23 are set to C in FIG. 2, that is, the temperature of the filter 23 is equal to or higher than the second temperature and the air-fuel ratio of the exhaust gas flowing into the filter 23 is rich. Done by keeping it on.

Note that the sulfur retention amount of the NO _x retention agent is estimated based on the total fuel injection amount from the fuel injection valve 6 and the like and the sulfur content in the fuel.

(4) Oxygen poisoning When the air-fuel ratio of the exhaust gas flowing into the filter 23 is lean, the exhaust gas contains a large amount of oxygen. These oxygens adsorb on the surface of the filter 23, that is, adsorb so as to cover the NO _x holding agent and the noble metal. Further, noble metals such as platinum (Pt) are combined with each other at a high temperature to become large particles, and this bonding reaction is promoted by oxygen held in the carrier layer on the surface of the filter 23. For this reason, when the amount of oxygen retained on the surface of the filter 23 (hereinafter referred to as “oxygen retention amount”) increases, the NO _x retention capacity of the NO _x retention agent, the oxidation capacity of the noble metal, and the like are reduced. (Oxygen poisoning).

  In order to avoid such a situation, when the amount of oxygen retained in the filter 23 increases, a process for releasing the retained oxygen (hereinafter referred to as “oxygen removal process”) is performed. Yes. If it is only for releasing oxygen, the surroundings of the filter 23 may be maintained in a theoretical air-fuel ratio or a rich atmosphere, and the temperature of the filter 23 may be set to a relatively low constant temperature (for example, 300 ° C.) or higher. However, if oxygen is desorbed while the temperature of the filter 23 is high and the surroundings of the filter 23 are in a lean atmosphere while the temperature of the filter 23 is decreasing, oxygen is retained again. Therefore, the oxygen removing process is performed by making the air-fuel ratio of the exhaust gas flowing into the filter 23 lean and setting the temperature of the filter 23 to a low temperature while being equal to or higher than the predetermined temperature. That is, in the oxygen removal process, the air-fuel ratio of the exhaust gas and the temperature of the filter 23 are set to D in FIG. 2, that is, the temperature of the filter 23 is between the first temperature and the second temperature, This is done by making the air-fuel ratio rich.

  The amount of oxygen retained on the surface of the filter 23 is estimated based on the time during which the temperature of the filter 23 detected by the temperature sensor 53 is within a specific range and the air-fuel ratio of the exhaust gas flowing into the filter 23 is lean. Is done. Here, the specified range is a temperature range in which oxygen is retained on the surface of the filter 23 when the ambient atmosphere of the filter 23 is lean.

  In a compression self-ignition internal combustion engine, the temperature of the filter 23 is relatively low when the engine is in a normal engine operation state. Therefore, in each of the removal processes, the temperature of the filter 23 is often increased. In this case, a temperature increasing process for increasing the temperature of the filter 23 is performed. As the temperature raising process, for example, the timing of injecting fuel into the combustion chamber of the internal combustion engine is delayed, a small amount of fuel is injected after injecting engine driving fuel into the combustion chamber of the internal combustion engine, or upstream of the filter 23 For example, a fuel addition device (not shown) for adding fuel to the exhaust gas may be provided, and the fuel may be added to the exhaust gas from the fuel addition device.

  Further, in the compression self-ignition internal combustion engine, when the engine is in a normal engine operating state, the air-fuel ratio of the exhaust gas discharged from the combustion chamber 5 of the internal combustion engine is lean. Accordingly, the air-fuel ratio of the exhaust gas is controlled by injecting or adding an appropriate amount of fuel between the intake passage and the exhaust passage upstream of the filter 23. Such air-fuel ratio control includes, for example, injecting a small amount of fuel after injecting engine driving fuel into a combustion chamber of an internal combustion engine, or adding fuel to exhaust gas from a fuel addition device. It is done.

  In each of the above removal processes, the temperature increase process and air-fuel ratio control as described above are executed. However, if these temperature increase process and air-fuel ratio control are executed during normal engine operation, the engine speed may fluctuate. In many cases, the engine is operated in a state different from the optimum engine operating state, and thus the drivability of a vehicle equipped with the internal combustion engine is deteriorated. Conversely, if the above-described temperature increase process or air-fuel ratio control is performed so as to minimize such deterioration in drivability, very complicated control is required to execute the temperature increase process or air-fuel ratio control. In addition, the specific temperature and the specific air-fuel ratio cannot be maintained, and the execution period of the temperature raising process and the air-fuel ratio control becomes long.

  Therefore, it has been proposed to execute each removal process when a stop command for the internal combustion engine is detected, for example, when an ignition switch is turned off. Thus, when the stop command for the internal combustion engine is detected, it is not necessary to consider drivability, and therefore it is possible to perform the temperature increase process and the air-fuel ratio control that accompany the fluctuations in the engine speed. Further, complicated control is not required to execute the temperature raising process or the air-fuel ratio control, and the temperature of the filter 23 is maintained at a specific temperature, or the air-fuel ratio of the exhaust gas flowing into the filter 23 is set to the specific air-fuel ratio. It can be easily maintained.

  By the way, as described above, when the execution condition is determined for each removal process and each removal process is executed every time the execution condition is satisfied, various removal processes may be executed at short time intervals. To do. In this case, temperature increase processing and air-fuel ratio control are performed each time, and the fuel consumption increases, resulting in deterioration of fuel consumption. This example is shown in FIG. FIG. 3A is a time chart of the filter temperature, and shows a case where four removal processes are performed in a short period of time.

Therefore, in the present invention, when a stop command for the internal combustion engine is detected, the amount of soot deposited on the surface of the filter 23 and the SO _x retention amount of the NO _x retention agent are estimated by the method described later. Then, when the estimated accumulation amount of the soot is greater than or equal to the predetermined accumulation amount, or when the estimated SO _x retention amount is greater than or equal to the predetermined retention amount, the HC / SOF removal process and the soot removal process Then, the sulfur removal process and the oxygen removal process are successively performed in this order. Therefore, the air-fuel ratio of the exhaust gas flowing into the filter 23 and the temperature of the filter 23 are changed in the order of ABCD in FIG. That is, the temperature of the filter 23 is raised while maintaining the air-fuel ratio of the inflowing exhaust gas lean, and the temperature of the filter 23 is lowered while maintaining the air-fuel ratio of the inflowing exhaust gas rich.

Here, the predetermined volume quantity, the soot content is deposited more filter 23, an amount that would have a significant adverse effect on the engine operating condition, the predetermined holding amount, SO the more NO _x holding agent _{If x} is maintained, it is an amount that will have a significant adverse effect on engine operating conditions.

  By executing the four removal processes at once as described above, the temperature of the filter 23 does not decrease once between the removal processes as shown in FIG. Therefore, in the removal process executed second to fourth, the amount of heat given to the filter 23 in the removal process executed before that can be used as it is, so that the fuel required for the temperature increase control is reduced.

In addition, the maintenance time of each removal process and the maintenance temperature of the filter 23 at the time of each removal process are the HC / SOF adhesion amount, the soot accumulation amount, the sulfur retention amount, and the oxygen retention amount estimated by the methods described later, respectively. Will be changed accordingly. Thus, HC · SOF, soot content, because each removal process is executed in the minimum required maintenance time only minimum maintenance temperature to remove SO _x, while suppressing the fuel consumption to a minimum these Can be reliably removed.

In the present embodiment, when the deposition amount of the soot content as described above is equal to or larger than a predetermined deposit amount, or stored SO _x amount four removal processing only the case of equal to or more than the predetermined retention amount is performed. That is, in the soot removal process and the sulfur removal process corresponding to the accumulation amount and the retention amount, the temperature of the filter 23 must be set to a high temperature that is equal to or higher than the predetermined temperature. Since the entire removal process is executed only when it has to be heated, the amount of fuel consumption can be reduced.

  In the present embodiment, the HC / SOF removal process is executed before the soot removal process. If HC and SOF are held on the surface of the filter 23 during execution of the soot removal process, HC and SOF are also burned and removed in the soot removal process, but HC and SOF are burned and removed in the soot removal process. Then, the execution time of the soot removal process becomes long. In the soot removal process, the temperature of the filter 23 is maintained above the predetermined temperature, so that the fuel consumption is large. By executing the HC / SOF removal process before the soot removal process, the execution time of the soot removal process can be minimized and the fuel consumption can be reduced.

  Furthermore, in the present embodiment, the soot removal process is executed before the sulfur removal process. When the soot is burned, a large amount of heat is generated. Therefore, if the soot is burned indefinitely, the filter 23 becomes very hot and may be thermally deteriorated. Therefore, in the soot removal process, control is normally performed so that the soot is burned so as not to reach such a high temperature. However, such control is usually not performed in the sulfur removal process. For this reason, if the sulfur removal process is executed when a large amount of soot is accumulated, the filter 23 may become very hot. Here, since the soot removal process is executed before the sulfur removal process, soot is not deposited on the surface of the filter 23 when the sulfur removal process is executed, and the filter 23 becomes very hot. It is suppressed.

  In addition, when a removal process (for example, HC / SOF removal process or soot removal process) in which the air-fuel ratio of the exhaust gas is lean after execution of the oxygen removal process is performed, the oxygen retained in the exhaust purifier by the oxygen removal process is reduced. Despite being separated, oxygen is again retained in the exhaust purifier. According to the first invention, since the oxygen removing process is performed at the end of the series of removing processes, at the end of the series of removing processes, the exhaust purifier can be in a state in which almost no oxygen is retained.

  In the present embodiment, each removal process may be executed independently in a normal engine operation state before a stop command for the internal combustion engine is detected. If the soot removal process is already being executed when the stop command for the internal combustion engine is detected, the HC / SOF removal process is not executed, and only the soot removal process, the sulfur removal process and the oxygen removal process are performed in this order. Execute. If the sulfur removal process is already being executed when the stop command for the internal combustion engine is detected, only the sulfur removal process and the oxygen removal process are performed without performing the HC / SOF removal process and the soot removal process. Run in order.

  Thereby, although the soot removal process or the sulfur removal process is being executed, the temperature of the filter 23 is once lowered to perform the HC / SOF removal process, and then the temperature of the filter 23 is raised and the soot removal process is performed again. Or it is prevented that the useless control of performing a sulfur removal process is performed.

  Next, the purification ability recovery operation in the present invention will be described with reference to the flowchart shown in FIG. First, in steps 101 to 103, it is determined whether it is time to execute a series of removal controls. In step 101, it is determined whether or not the ignition switch is turned off. If it is determined that the ignition switch is not turned off, the subsequent steps are not executed. On the other hand, if it is determined that the ignition switch has been turned off, the routine proceeds to step 102.

In step 102, it is determined whether or not the apportioned accumulation amount Vsoot is equal to or greater than the predetermined accumulation amount Vsoota. On the other hand, if it is determined that the apportioning amount Vsoot is less than the predetermined amount Vsoota, the routine proceeds to step 103. In step 103, it is determined whether or not the sulfur retention amount Vs of the NO _x retention agent is equal to or greater than the predetermined retention amount Vsa, and if it is determined that it is greater than or equal to the predetermined retention amount Vsa, the process proceeds to step 104. . On the other hand, when it is determined in step 103 that the sulfur retention amount Vs is smaller than the predetermined retention amount Vsa, the routine proceeds to step 113 where the internal combustion engine is stopped.

  In steps 104 to 112, a series of removal processing is executed. In step 104, times Thc, Tsoot, Ts, and To at which the HC / SOF removal process, the soot removal process, the sulfur removal process, and the oxygen removal process are to be executed are calculated. The time Thc for executing the HC / SOF removal process and the time Tsoot for executing the soot removal process are calculated based on the output of the differential pressure sensor 52, etc., and the time Ts for executing the sulfur removal process is an integrated fuel injection amount, etc. The time To for performing the oxygen removal process is calculated based on the output of the temperature sensor 53 and the like. Next, in step 105, the temperature raising process is performed so that the air-fuel ratio of the exhaust gas is lean and the temperature of the filter 23 is 350 ° C. In step 106, it is determined whether or not the time Thc for executing the HC / SOF removal process has elapsed since the start of step 105. If it is determined that the time Thc has not elapsed, step 105 is repeated. On the other hand, if it is determined that the time Thc has elapsed, the routine proceeds to step 107.

  In step 107, the temperature raising process is performed so that the temperature of the filter 23 becomes 650 ° C. while maintaining the air-fuel ratio of the exhaust gas lean. Next, in step 108, it is determined whether or not the time Tsoot for executing the soot removal process has elapsed since the start of step 107. If it is determined that the time Tsoot has not elapsed, step 107 is repeated. On the other hand, if it is determined that the time Tsoot has elapsed, the routine proceeds to step 109.

  In step 109, the air-fuel ratio of the exhaust gas is made rich while maintaining the temperature of the filter 23 at 650 ° C. Next, in step 110, it is determined whether or not the time Ts at which the sulfur removal process should be performed has elapsed since the start of step 109. If it is determined that the time Ts has not elapsed, step 109 is repeated. On the other hand, if it is determined that the time Ts has elapsed, the process proceeds to step 111.

  In step 111, the temperature of the filter 23 is lowered to 350 ° C. while maintaining the air-fuel ratio of the exhaust gas rich. Next, in step 112, it is determined whether or not the time To at which the oxygen removal process should be performed has elapsed since the start of step 111. If it is determined that the time To has not elapsed, step 111 is repeated. On the other hand, if it is determined that the time To has elapsed, the routine proceeds to step 113. In step 113, the operation of the internal combustion engine is stopped, and the filter purification capacity recovery operation is completed.

  In the present embodiment, since the temperature raising process and the air-fuel ratio control are performed after the ignition switch is turned off, the engine speed may be changed by executing the temperature raising process and the air-fuel ratio control. Therefore, in this embodiment, in addition to the above-described temperature raising method, the temperature raising process is also performed by adjusting the engine speed. Further, the temperature lowering process for lowering the temperature of the filter 23 in a state where the air-fuel ratio of the exhaust gas is rich can be performed by lowering the engine speed. Further, the temperature raising process and the air-fuel ratio control may be executed by using both the EGR for allowing the exhaust gas to flow again into the combustion chamber and the engine speed control.

  Further, in the above-described embodiment, the time when the stop command for the internal combustion engine is detected is when the ignition switch is turned off, but another timing may be used. For example, when a vehicle equipped with an internal combustion engine is selectively or simultaneously driven by an internal combustion engine and an electric motor (not shown), that is, when the vehicle is a hybrid vehicle, in this hybrid vehicle, The vehicle may be driven only by the electric motor, and the operation of the internal combustion engine may be stopped. Therefore, the time when the stop command for the internal combustion engine is detected may be the time when the vehicle is driven only by the electric motor.

The filter may also be capable of continuous oxidation. Even in a filter that can be continuously oxidized, if so much of the soot exceeds the ability of continuous oxidation flows into the filter, soot may accumulate on the surface of the filter, and soot removal processing needs to be performed. Further, instead of a filter, a NO _x catalyst carrying a NO _x holding agent may be used. Even in this NO _x catalyst, soot may accumulate on the surface of the NO _x catalyst and the pressure loss may increase, so that even in this case, it is necessary to perform the soot removal process.

Finally, the exhaust gas purification mechanism using the NO _x retention agent, particularly the NO _x retention / release and the reduction purification action in the exhaust gas will be described with reference to FIG. The NO _x retention agent 23 was selected from, for example, alkali metals such as potassium K, sodium Na, lithium Li 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.

Next, the mechanism of retention and extraction and reduction purification action of the NO _x of platinum (Pt) as the noble metal, also NO _x holding agent as barium (Ba) will be described in but other as an example of the exhaust purifier which was supported The same mechanism can be obtained by using noble metals, alkali metals, alkaline earths and rare earths. 5A and 5B schematically show enlarged views of the surface of the carrier layer formed on the surface of the partition wall of the exhaust gas purifier and the pore surface of the partition wall. FIGS. 5 (a) and 60 in (b) shows the platinum particles, 61 denotes a carrier layer comprising a NO _x holding agent such as barium.

When the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the exhaust gas greatly increases. As shown in FIG. 5 (a), these oxygens are in the form of O ₂ ⁻ or O ²⁻ of platinum 60. Adhere to the surface. On the other hand, NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum 60 and becomes NO ₂ (2NO + O ₂ → 2NO ₂ ). Next, a part of the generated NO ₂ is further oxidized on the platinum 60 while being absorbed in the NO _x retention agent 61 and combined with barium oxide (BaO), as shown in FIG. It diffuses into the NO _x retention agent 61 in the form of (NO ₃ ⁻ ). In this way, NO _x is held in the NO _x holding agent 61.

NO ₂ is produced on the oxygen concentration is as high as the surface of the platinum 60 in the exhaust gas flowing, NO unless NO ₂ to NO _x holding capacity is not saturated in the _x holding agent 61 is held in the NO _x holding agent 61 nitrate ions (NO ₃ ⁻ ) is generated. On the other hand, when the oxygen concentration in the exhaust gas decreases and the amount of NO ₂ produced decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ions (NO ₃ in the NO _x holding agent 61 ( NO ₃ ⁻ ) is released from the NO _x retention agent in the form of NO ₂ . That is, the oxygen concentration in the exhaust gas flowing so that the NO _x is made to leave from the NO _x holding agent 61 when lowered. Becomes lower lean degree of the inflowing exhaust gas the oxygen concentration in exhaust gas decreases, NO _x will be induced to leave therefore from the NO _x holding agent 61 when lowering the lean degree of the exhaust gas flowing .

On the other hand, when the air-fuel ratio of the exhaust gas flowing in at this time is reduced, HC and CO react with O ₂ ⁻ or O ²⁻ on the platinum 60 and are oxidized. Further, if the air-fuel ratio of the inflowing exhaust gas is reduced, the oxygen concentration in the exhaust gas extremely decreases, so that NO ₂ is released from the NO _x holding agent 61, and this NO ₂ is as shown in FIG. 5 (b). It can be reduced and purified by reacting with unburned HC and CO. Such is NO ₂ on the surface of the platinum 60 in the NO ₂ is detached from comes to NO _x holding agent 61 does not exist to the next from the next. Therefore to reduce the air-fuel ratio of the exhaust gas flowing into, and NO _x from the NO _x holding agent 61 in a short time when a state in which the reducing agent is present is to be reduced and purified is disengaged.

Furthermore, the mechanism of sulfur poisoning of the NO _x absorbent 61 will be described. When the SO _x component is contained in the exhaust gas, the NO _x holding agent 61 holds SO _x in the exhaust gas by the same mechanism as in the case of holding the above-mentioned NO _x . That is, when the air-fuel ratio of the exhaust gas is lean, SO _x (eg, SO ₂ ) in the exhaust gas is oxidized on the platinum 60 to become SO ₃ ⁻ , SO ₄ ⁻ , and combines with barium oxide (BaO) and sulfuric acid. Barium (BaSO ₄ ) is formed. BaSO ₄ is relatively stable, and since crystals are likely to be coarse, once they are produced, they are not easily decomposed and released. For this reason, when the amount of BaSO ₄ produced in the NO _x retention agent 61 increases, the amount of BaO that can participate in retention of NO _x decreases, and the ability to retain NO _x decreases.

In order to eliminate this sulfur poisoning, BaSO ₄ produced in the NO _x retention agent 61 is decomposed at a high temperature, and SO ₃ ⁻ and SO ₄ ⁻ sulfate ions produced thereby contain slite lean. It is necessary to perform reduction under a substantially stoichiometric air-fuel ratio or a rich atmosphere (hereinafter simply referred to as “rich atmosphere”), convert it into gaseous SO _2, and release it from the NO _x holding agent 61. Therefore, in order to perform the sulfur removal process, it is necessary to make the NO _x retention agent 61 in a high temperature and rich atmosphere state.

In the present specification, it has been described that the air-fuel ratio of the exhaust gas flowing in is substantially the stoichiometric air-fuel ratio or rich when the NO _x or sulfur component is released from the NO _x holding agent. When the oxygen concentration of the gas is lower than the predetermined oxygen concentration, NO _x or sulfur components are easily released. Therefore, the description “making the air-fuel ratio of the exhaust gas substantially the stoichiometric air-fuel ratio or rich” in the above-described embodiment also means “making the oxygen concentration of the inflowing exhaust gas equal to or lower than a predetermined oxygen concentration”.

In this specification, the term “retaining” is used to include both “absorption” and “adsorption”. Accordingly, the “NO _x retention agent” includes both “NO _x absorbent” and “NO _x adsorbent”, the former accumulates NO _x in the form of nitrate and the like, and the latter adsorbs in the form of NO _{2 and the} like. . The term “desorption” from the NO _x retention agent is also used to include the meaning of “desorption” corresponding to “adsorption” in addition to “release” corresponding to “absorption”.

It is a figure which shows the whole internal combustion engine in which the purification capacity recovery method of the exhaust gas purification device of this invention is used. It is a figure which shows the execution conditions of each removal process. It is a time chart of the temperature of a filter. It is a flowchart which shows the control in the purification capacity recovery method of the exhaust gas purification device of this invention. It is a figure for demonstrating the NOx holding | maintenance / detachment | _desorption of the NOx holding _| maintenance agent used in this invention, and a reduction | purification purification action.

Explanation of symbols

5 ... Combustion chamber 6 ... Fuel injection valve 23 ... Particulate filter (filter)
24 ... Casing 40 ... Electronic control unit (ECU)
52 ... Differential pressure sensor 53 ... Temperature sensor

Claims (7)

A method for recovering the purification capacity of an exhaust purifier carrying a NO _x holding agent and a noble metal provided on an exhaust passage of an internal combustion engine,
The air-fuel ratio of the exhaust gas flowing into the exhaust purifier is maintained lean, the temperature of the exhaust purifier is maintained within a predetermined temperature range, and HC and SOF deposited on the surface of the exhaust purifier are removed. HC / SOF removal process,
The air-fuel ratio of the exhaust gas flowing into the exhaust purifier is maintained lean, the temperature of the exhaust purifier is maintained at a temperature equal to or higher than the predetermined temperature range, and the apportionment deposited on the surface of the exhaust purifier is reduced. A soot removal step to be removed;
The air-fuel ratio of the exhaust gas flowing into the exhaust purifier is kept rich, the temperature of the exhaust purifier is maintained at a temperature equal to or higher than the predetermined temperature range, and the sulfur component held in the NO _x retention agent is released. A sulfur removal step,
An oxygen removal step of maintaining the air-fuel ratio of the exhaust gas flowing into the exhaust purifier rich, maintaining the temperature of the exhaust purifier within the predetermined temperature range, and releasing oxygen held in the exhaust purifier In the exhaust gas purifier recovery method recovery method comprising:
When it is determined that any one of the above removal steps should be performed, the exhaust purifier that performs the HC / SOF removal step, the soot removal step, the sulfur removal step, and the oxygen removal step in this order. Purification capacity recovery method.   The maintenance time of the HC / SOF removal step, the soot removal step, the sulfur removal step, and the oxygen removal step, and the maintenance temperature of the exhaust purifier during the execution of each removal step are the amount of HC / SOF deposited on the exhaust purifier, respectively. The method for recovering the purification ability of an exhaust gas purifier according to claim 1, wherein the method is changed according to the soot accumulation amount, the sulfur retention amount, and the oxygen retention amount.   The exhaust according to claim 1 or 2, wherein the time when it is determined that any one of the removal steps should be executed is when the soot removal step or the sulfur removal step should be executed. How to recover the purification capacity of the purifier. The time when it is determined that any one of the removal steps should be executed is when a stop command for the internal combustion engine is detected and apportioning on the surface of the exhaust gas purifier. deposit amount exhaust purifier purification capacity recovery according to claim 1 or 2 in which when the sulfur component holding amount or the NO _x holding agent when is equal to or greater than the predetermined deposit amount is equal to or greater than the predetermined retention amount Method. When a stop command for the internal combustion engine is detected, and when the amount of soot deposited on the surface of the exhaust purifier is greater than or equal to a predetermined amount, or the sulfur component retention amount of the NO _x retention agent is predetermined Even when the amount is larger than the holding amount, the air-fuel ratio of the exhaust gas flowing into the exhaust gas purifier when the stop command is detected is lean, and the temperature of the exhaust gas purifier is the predetermined temperature. The exhaust purification device recovery capability recovery according to claim 3, wherein when the amount is above the range, the soot removal step, the sulfur removal step and the oxygen removal step are executed in this order without executing the HC / SOF removal step. Method. When a stop command for the internal combustion engine is detected, and when the amount of soot deposited on the surface of the exhaust purifier is greater than or equal to a predetermined amount, or the sulfur component retention amount of the NO _x retention agent is predetermined Even when the amount is higher than the holding amount, if the air-fuel ratio of the exhaust gas is rich and the temperature of the exhaust purifier is equal to or higher than the predetermined temperature range, the HC / SOF removal step and the soot removal are performed. The method for recovering the purification capacity of an exhaust gas purifier according to claim 3, wherein the sulfur removal step and the oxygen removal step are executed in this order without executing the steps.   The vehicle equipped with the internal combustion engine is selectively or simultaneously driven by the internal combustion engine and the electric motor, and when the stop command for the internal combustion engine is detected, the vehicle is driven only by the electric motor. The method for recovering the purification ability of an exhaust gas purifier according to claim 4.

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