JP4331972B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an internal combustion engine to which a reducing agent is supplied when performing an S poison recovery process of a NOx purification catalyst.
[0002]
[Prior art]
In recent years, NOx purification catalysts that purify NOx (nitrogen oxides) in exhaust gas have been provided in the exhaust passages of some internal combustion engines.
[0003]
When the air-fuel ratio of the exhaust gas is lean, this NOx purification catalyst occludes (absorbs) NOx in the exhaust gas and reduces the NOx concentration in the exhaust gas. Further, when the air-fuel ratio of the exhaust gas becomes rich, that is, when placed in a reducing atmosphere, the stored NOx is reduced and released.
[0004]
On the other hand, this NOx purification catalyst absorbs not only NOx but also sulfur and its compounds contained in fuel and the like (hereinafter referred to as “S poisoning”). Therefore, the NOx purification catalyst by so-called S poisoning in which the amount of storable NOx decreases and the NOx purification function decreases when the amount of accumulation (hereinafter referred to as “S accumulation amount”) increases in the NOx purification catalyst. The functional deterioration phenomenon occurs.
[0005]
Here, in a reducing atmosphere in which the NOx purification catalyst is at a temperature close to 600 ° C. and the oxygen concentration around the catalyst is low, sulfur accumulated in the NOx purification catalyst is released in a reduced state from the NOx purification catalyst. It is known that
[0006]
In order to perform such so-called S poison recovery, the apparatus described in Patent Document 1 supplies a reducing agent to the NOx purification catalyst via the exhaust passage. When the reducing agent is thus supplied to the NOx purification catalyst, the reducing agent contributes to the reduction reaction of the sulfur content. The reducing agent is burned in the NOx purification catalyst, and the temperature of the catalyst is increased by the heat. Moreover, since the oxygen around the NOx purification catalyst is consumed by the combustion of the reducing agent and the oxygen concentration around the catalyst is also reduced, conditions such as a high temperature and a reducing atmosphere are satisfied, and S poisoning recovery is performed.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-13456
[0008]
[Problems to be solved by the invention]
By the way, in the reducing agent supply described above, the reducing agent is supplied to the NOx purification catalyst via the exhaust passage. For this reason, among the supplied reducing agents, reducing agents that have not evaporated or are not atomized may adhere to the wall surface of the exhaust passage before reaching the NOx purification catalyst.
[0009]
When the reducing agent adheres to the wall surface of the exhaust passage in this way, the attached reducing agent is atomized by the flow of the exhaust gas when the exhaust flow rate or the exhaust flow rate increases, for example, sudden start or acceleration of the vehicle, and the unburned state There is a risk that such white smoke may be discharged into the atmosphere.
[0010]
Incidentally, the temperature of the NOx purification catalyst is low when the engine is started from a cold engine state. If the reducing agent adheres to the wall of the exhaust passage in such a state, even if the reducing agent reaches the catalyst by exhaust, consumption (oxidation) of the reducing agent is not performed on the catalyst. Is more likely to occur.
[0011]
The present invention has been made in view of such circumstances, and an object of the present invention is an internal combustion engine that supplies a reducing agent for recovery of S poisoning, and suppresses the attachment of the reducing agent to the wall surface of the exhaust passage. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can perform the above-described operation.
[0012]
[Means for Solving the Problems]
  The means for achieving the above object and the effects thereof will be described below.
  An invention according to claim 1 is an internal combustion engine exhaust gas purification apparatus comprising a NOx purification catalyst disposed in an exhaust passage and a reducing agent supply means for supplying a reducing agent for S poison recovery to the NOx purification catalyst. And a restricting means for restricting supply of the reducing agent by the reducing agent supply means when the wall temperature of the exhaust passage is equal to or lower than a predetermined temperature T1.In addition, the internal combustion engine is provided with a supercharger driven by exhaust pressure in its exhaust passage, and the limiting means is a temperature of a member defining the exhaust passage in the supercharger as a wall temperature of the exhaust passage. referThis is the gist.
[0013]
  When the temperature of the wall surface of the exhaust passage is a temperature that promotes vaporization of the reducing agent, even if the reducing agent is supplied by the reducing agent supply means, the reducing agent does not easily adhere to the wall surface. In other words, when the temperature of the wall surface of the exhaust passage is equal to or lower than a certain temperature, the supply of the reducing agent can be restricted to prevent the reducing agent from attaching to the wall surface. Therefore, in the above configuration, when the wall temperature of the exhaust passage is equal to or lower than the predetermined temperature T1, the supply of the reducing agent by the reducing agent supply means is limited. For this reason, when the reducing agent is supplied, it is possible to suppress the attachment of the reducing agent to the wall surface, and thus the generation of the white smoke can also be suitably suppressed.
The exhaust gas that passes through the supercharger consumes thermal energy by driving the supercharger, and the temperature of the exhaust gas is deprived by the components of the supercharger. Therefore, in some cases, the temperature of the wall surface of the supercharger that constitutes a part of the exhaust passage may be lower than the wall temperature of the exhaust pipe that constitutes the exhaust passage. In this case, the wall surface in the supercharger It is easy for the reducing agent and combustion fuel to adhere to the surface. Further, reducing agents and combustion fuel tend to adhere to the wall surface that greatly changes the flow direction of the exhaust gas in the supercharger. In the turbocharger to which the reducing agent and the combustion fuel are likely to adhere as described above, the temperature of the member defining the exhaust passage is referred to as the wall temperature of the exhaust passage. It is possible to more suitably suppress the adhesion of the reducing agent and the combustion fuel to the wall surface of the passage.
[0014]
According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, prior to the supply of the reducing agent by the reducing agent supply means, combustion fuel is supplied to the NOx purification catalyst. The gist is to further include a temperature raising means for raising the temperature.
[0015]
Although the temperature of the NOx purification catalyst is raised by the supply of the reducing agent for S poison recovery, it takes some time until the temperature of the NOx purification catalyst is actually raised after the supply of the reducing agent. Therefore, S poison recovery may not be performed immediately after supplying the reducing agent. In this regard, in the above configuration, the temperature increasing combustion fuel is supplied to the NOx purification catalyst prior to the supply of the reducing agent for S poison recovery. Therefore, the S poison recovery process can be performed in a state where the temperature of the NOx purification catalyst is sufficiently increased, and the S poison recovery can be surely performed immediately after the execution of the S poison recovery process. . In addition, since the S poison recovery starts from the state in which the NOx purification catalyst has been preliminarily raised in this way, when the S poison recovery process is executed, the amount of reducing agent supplied necessary for raising the temperature of the NOx purification catalyst is reduced. This makes it possible to reduce the amount of reducing agent adhering to the wall surface of the exhaust passage.
[0016]
According to a third aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the second aspect, the restricting means supplies the combustion fuel by the temperature raising means when the wall temperature of the exhaust passage is equal to or lower than a predetermined temperature T2. The gist of the present invention is to include processing for limiting supply as the limiting processing.
[0017]
According to this configuration, as the restriction process, the supply of combustion fuel by the temperature raising means is restricted when the wall temperature of the exhaust passage is equal to or lower than the predetermined temperature T2. Therefore, it becomes possible to suppress the adhesion of the combustion fuel to the wall surface due to the supply of the combustion fuel by the temperature raising means.
[0018]
According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the second or third aspect, the temperature raising means maintains the temperature of the NOx purification catalyst at a predetermined temperature T3 or higher continuously for a predetermined period. The gist is to execute the temperature raising process.
[0019]
According to this configuration, the temperature of the entire NOx purification catalyst can be reliably raised. Therefore, it becomes possible to reliably recover S poisoning, and as a result, the amount of reducing agent supplied during recovery from S poisoning can be reliably reduced, and the effect according to claim 2 can be achieved. You will be able to get it reliably.
[0020]
  The invention according to claim 5 is the claim.25. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the limiting means prohibits execution of at least one of a reducing agent supply by the reducing agent supply means and a combustion fuel supply by the temperature raising means. The gist is to execute the process as the restriction process.
[0021]
According to this configuration, since at least one of the supply of the reducing agent and the supply of the combustion fuel is not performed as the restriction process, the attachment of the reducing agent or the combustion fuel to the wall surface can be reliably suppressed. Become.
[0022]
  The invention according to claim 6 is the26. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the limiting means includes a reducing agent supply of the reducing agent supply means and a combustion fuel for the temperature raising means when the wall temperature is equal to or higher than a predetermined temperature T4. While permitting the start of at least one of the treatments of the supply, when the wall temperature falls below a predetermined temperature T5,Authorized to startThe gist of this is to interrupt one process.
[0023]
When the wall temperature is a temperature that promotes vaporization of the reducing agent and the combustion fuel, adhesion of the reducing agent and the combustion fuel to the wall surface is suppressed. Therefore, in the above configuration, when the wall temperature is equal to or higher than the predetermined temperature T4, the start of at least one of the reducing agent supply and the combustion fuel supply is permitted. Therefore, it is possible to suppress the attachment of the reducing agent and the combustion fuel to the wall surface of the exhaust passage. In addition, the supply process that is permitted to start is interrupted when the wall temperature falls below a predetermined temperature T5. Therefore, even when the wall temperature decreases during the execution of the supply process, it is possible to reliably prevent the reducing agent and the combustion fuel from adhering to the wall surface of the exhaust passage.
[0024]
Here, when the reducing agent supply process by the reducing agent supply means is interrupted, the sulfur content remains in the NOx purification catalyst. Therefore, according to the invention as set forth in claim 7, the reducing agent supply means estimates the S accumulation amount of the NOx purification catalyst based on the engine operation state, and the estimated S accumulation amount is not less than a predetermined amount. When the reducing agent supply process by the reducing agent supply means is interrupted as the one process, the S is performed based on the execution time of the supply process. The remaining amount of the accumulated amount is calculated, and this is added to the estimated accumulated amount of S deposited on the NOx purification catalyst after interruption of the supply process, thereby adopting the S deposition of the NOx purification catalyst. The amount can be calculated accurately. Therefore, when determining whether or not to execute the S poison recovery process based on the S accumulation amount, it is possible to improve the determination accuracy.
[0025]
The gist of an eighth aspect of the invention is the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to seventh aspects, wherein the wall temperature is estimated based on an engine operating state.
[0026]
Although the wall temperature can be detected by providing a temperature sensor or the like in the exhaust passage, generally such a sensor is not provided in the exhaust passage of the internal combustion engine. Therefore, it is necessary to provide a new sensor, which causes an increase in the mounting process and an increase in component costs. Here, the wall temperature of the exhaust passage has a correlation with the exhaust temperature, and this exhaust temperature can be estimated based on the engine operating state. Therefore, according to the above configuration, the wall temperature can be grasped without providing a new sensor or the like in the exhaust passage of the internal combustion engine.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is embodied in a common rail type four-cylinder diesel engine mounted on an automobile will be described in detail with reference to FIGS.
[0030]
FIG. 1 is a schematic configuration diagram showing an exhaust purification device for an internal combustion engine according to the present embodiment, an engine 1 to which the exhaust purification device is applied, and the peripheral configuration thereof.
The engine 1 is provided with a plurality of cylinders # 1 to # 4. Fuel injection valves 4 a to 4 d are attached to the cylinder head 2 for each cylinder. These fuel injection valves 4a to 4d inject fuel into the cylinders of the cylinders # 1 to # 4. Further, the cylinder head 2 is provided with intake ports for introducing outside air into the cylinders and exhaust ports 6a to 6d for discharging combustion gas outside the cylinders corresponding to the respective cylinders # 1 to # 4. ing.
[0031]
The fuel injection valves 4a to 4d are connected to a common rail 9 that accumulates high-pressure fuel. The common rail 9 is connected to the supply pump 10. The supply pump 10 sucks fuel in a fuel tank (not shown) and supplies high-pressure fuel to the common rail 9. The high-pressure fuel supplied to the common rail 9 is injected into the cylinder from the fuel injection valves 4a to 4d when the fuel injection valves 4a to 4d are opened.
[0032]
An intake manifold 7 is connected to the intake port. The intake manifold 7 is connected to the intake passage 3. A throttle valve 16 for adjusting the intake air amount is provided in the intake passage 3.
[0033]
An exhaust manifold 8 is connected to the exhaust ports 6a to 6d. A turbocharger 11 to be described later is connected to an exhaust downstream side of the exhaust manifold 8, and an exhaust pipe 26 is connected to the exhaust downstream side of the turbocharger 11. A NOx purification catalyst 12 for purifying NOx in the exhaust is installed in the middle of the exhaust pipe 26. The NOx purification catalyst 12 is a carrier on which a NOx occlusion reduction type catalyst is supported. When the air-fuel ratio of the exhaust is lean, the NOx purification catalyst 12 occludes NOx in the exhaust, and when the air-fuel ratio is rich, the occluded NOx. Is reduced and released.
[0034]
In addition, the engine 1 is provided with an EGR device 28. The EGR device 28 is a device that reduces the amount of NOx generated by lowering the combustion temperature in the cylinder by introducing part of the exhaust gas into the intake air. The EGR device 28 includes an EGR passage 13 that connects the intake passage 3 and the exhaust manifold 8, an EGR valve 15 that is provided in the EGR passage 13, and an EGR cooler 14. The opening degree of the EGR valve 15 is adjusted by the control device 25. As a result, the amount of exhaust gas (EGR amount) introduced from the exhaust manifold 8 into the intake passage 3 is adjusted. The EGR cooler 14 reduces the temperature of the exhaust gas flowing in the EGR passage 13.
[0035]
Further, the engine 1 is provided with a turbocharger (supercharger) 11 that supercharges intake air introduced into the cylinder using exhaust pressure. The turbocharger 11 includes a center housing 40, a turbine housing 42, and a compressor housing 41. The exhaust manifold 8 is connected to the opening provided in the outer peripheral portion of the turbine housing 42, and the exhaust pipe 26 is connected to the opening provided in the central portion of the turbine housing 42. An air cleaner-side intake passage 3 is connected to an opening provided in the center of the compressor housing 41, and a combustion chamber-side intake passage 3 is connected to an opening provided in the outer peripheral portion of the compressor housing 41. Has been.
[0036]
In the turbine housing 42, a turbine wheel that rotates by exhaust gas fed from the exhaust manifold 8 is provided. The compressor housing 41 is provided with a compressor wheel that forcibly sends the air in the intake passage 3 to the combustion chamber. The turbine wheel and the compressor wheel are connected via a rotor shaft so as to be integrally rotatable. Then, when exhaust is blown onto the turbine wheel and the turbine wheel rotates, the compressor wheel also rotates, and the air in the intake passage 3 is forcibly sent into the combustion chamber.
[0037]
Further, an intercooler 18 is provided in the intake passage 3 between the compressor housing 41 and the throttle valve 16 in order to reduce the temperature of the intake air whose temperature rises due to supercharging of the turbocharger 11.
[0038]
Various sensors for detecting the engine operation state are attached to the engine 1. For example, the air flow meter 19 detects the intake air amount GA in the intake passage 3. The throttle opening sensor 20 detects the opening of the throttle valve 16, that is, the throttle opening TA. The air-fuel ratio sensor 21 detects the air-fuel ratio λ of the exhaust. The engine rotational speed sensor 22 detects the rotational speed of the crankshaft, that is, the engine rotational speed NE. The accelerator opening sensor 24 detects an accelerator pedal depression amount, that is, an accelerator opening ACCP. An exhaust temperature sensor 29 provided on the exhaust downstream side of the NOx purification catalyst 12 detects an exhaust temperature ET on the exhaust downstream side of the NOx purification catalyst 12.
[0039]
The outputs of these various sensors are input to the control device 25. The control device 25 includes a central processing control device (CPU), a read only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, an input interface, and an output. It is mainly composed of a microcomputer equipped with an interface. The control device 25 controls, for example, the fuel injection amount control and fuel injection timing control of the fuel injection valves 4a to 4d, the discharge pressure control of the supply pump 10, the drive amount control of the actuator 17 that opens and closes the throttle valve 16, and the EGR valve. Various controls of the engine 1 such as opening degree control of 15 are performed.
[0040]
On the other hand, an injection nozzle 5 for supplying fuel to the NOx purification catalyst 12 is attached to the exhaust manifold 8. The injection nozzle 5 and the supply pump 10 are connected by a fuel supply pipe 27 so that light oil as fuel is supplied. The injection nozzle 5 has the same structure as the fuel injection valves 4a to 4d, and the injection amount and injection timing are controlled by the control device 25. The injection nozzle 5 is provided upstream of the turbocharger 11 so that fuel can be added to high-temperature exhaust. For this reason, the temperature of the fuel supplied from the injection nozzle 5 to the exhaust system can be sufficiently raised, and as a result, the temperature of the NOx purification catalyst 12 can be sufficiently raised in the S poison recovery control described later. It is like that.
[0041]
Now, it is known that the NOx purification catalyst 12 absorbs not only NOx but also sulfur and its compounds contained in fuel and the like. Therefore, when the S accumulation amount of the NOx purification catalyst increases, the NOx purification catalyst function deterioration phenomenon due to so-called S poisoning occurs in which the storable NOx amount decreases and the NOx purification function deteriorates.
[0042]
Here, in a reducing atmosphere in which the NOx purification catalyst 12 is at a temperature close to 600 ° C. and the oxygen concentration around the catalyst is low, the sulfur content deposited on the NOx purification catalyst is released in a reduced state. That is, under the above conditions, the S accumulation amount of the NOx purification catalyst 12 can be reduced.
[0043]
Therefore, in this embodiment, in order to perform such so-called S poison recovery, a reducing agent, that is, fuel for the engine 1 is supplied to the NOx purification catalyst 12. This fuel supply is performed by supplying fuel from the injection nozzle 5 described above. When fuel is thus supplied to the NOx purification catalyst 12, this fuel contributes to the reduction reaction of the sulfur content. The fuel is combusted in the NOx purification catalyst, and the temperature of the NOx purification catalyst 12 is increased by the heat. In addition, the oxygen around the NOx purification catalyst 12 is consumed by the combustion of the fuel, and the oxygen concentration around the NOx purification catalyst 12 is also lowered, so that conditions such as high temperature and a reducing atmosphere are satisfied, and S poisoning recovery is performed.
[0044]
By the way, when the above-described fuel supply process for S poison recovery is executed, the fuel is supplied to the NOx purification catalyst 12 through the exhaust passages such as the exhaust manifold 8, the turbocharger 11, and the exhaust pipe 26. Therefore, of the supplied fuel, fuel that has not evaporated and fuel that has not been atomized may adhere to the wall surface of the exhaust passage before reaching the NOx purification catalyst 12.
[0045]
In particular, fuel tends to adhere to the wall surface of the turbine housing 42 of the turbocharger 11. This is due to the following reason.
That is, the exhaust gas passing through the turbocharger 11 consumes heat energy by driving the turbocharger 11, and the temperature of the exhaust gas is deprived by the constituent members of the turbocharger 11. Therefore, the fuel is likely to adhere to the wall surface of the turbine housing 42 and the like. Further, since the flow direction of the exhaust gas is greatly changed inside the turbocharger 11, for example, in the turbine housing 42, fuel tends to adhere to the wall surface of the turbine housing 42.
[0046]
When fuel adheres to the wall surface of the exhaust system in this way, the adhering fuel is atomized by the flow of exhaust gas when the exhaust flow rate or exhaust flow rate increases, for example, sudden start or acceleration of the vehicle, and the unburned white There is a risk of inconveniences such as being discharged into the atmosphere as smoke. Incidentally, the temperature of the NOx purification catalyst 12 is low when the engine is started from a cold engine state. If fuel adheres to the wall surface of the exhaust system in such a state, fuel consumption (oxidation) is not performed on the NOx purification catalyst 12 even if the fuel reaches the NOx purification catalyst 12 by exhaust. The white smoke is more likely to be generated.
[0047]
Therefore, in the present embodiment, when executing the S poisoning recovery process, a limiting means for limiting the fuel supply to the NOx purification catalyst 12 based on the wall temperature of the exhaust passage is provided. More specifically, the temperature (hereinafter referred to as the turbo wall temperature) of the inner wall (hereinafter referred to as the turbo wall surface) of the turbine housing 42, which is a part of the exhaust passage, in particular a part of the exhaust passage and is a member defining the exhaust passage, is defined. When the temperature is lower than the predetermined temperature, the fuel supply to the NOx purification catalyst 12 is prohibited.
[0048]
Here, although the turbo wall temperature can be detected by providing a temperature sensor or the like in the turbine housing 42, such a sensor is generally not provided in the turbocharger 11 of the internal combustion engine. Therefore, in this embodiment, the turbo wall temperature is estimated from the engine operating state.
[0049]
Hereinafter, the S poison recovery control executed by the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment will be described with reference to FIGS.
2 and 3 show a processing procedure of S poison recovery control executed by the control device 25. FIG.
[0050]
When this processing is started, first, the S accumulation amount S accumulated on the NOx purification catalyst 12 is calculated based on the following equation (1) (S100).
S deposition amount S = S absorption amount NS + S residual amount RS (1)
Note that the S absorption amount NS is the exhaust flow rate obtained from the intake air amount GA, the engine rotational speed NE, etc., the elapsed time since the last S poisoning recovery, the travel distance of the vehicle, or the operating time of the engine 1 It is a value estimated based on the above. That is, this is the amount of sulfur absorbed in the NOx purification catalyst 12 since the previous S poison recovery. The S residual amount RS is a value calculated in the processing of S230 described later, and is the amount of sulfur remaining in the NOx purification catalyst 12 when the previous S poisoning recovery processing is completed. .
[0051]
Next, it is determined whether or not the estimation of the turbo wall temperature T is started (S110). Here, an affirmative determination is made when the S accumulation amount S is equal to or greater than the limit accumulation amount Smax obtained by a prior experiment or the like. If the S accumulation amount S is smaller than the limit accumulation amount Smax and NOx can still be sufficiently stored (NO in S110), the estimation of the turbo wall temperature T is not started and the S accumulation amount S is calculated again. Is done.
[0052]
On the other hand, when the S accumulation amount S is equal to or greater than the limit accumulation amount Smax (YES in S110), the NOx purification catalyst 12 may not be able to store NOx sufficiently due to S poisoning, and the S poisoning recovery process is executed. There is a need. Therefore, prior to the execution of the S poison recovery process, first, estimation of the turbo wall temperature T for determining whether or not to prohibit the fuel supply to the NOx purification catalyst 12 is started (S120). The estimation of the turbo wall temperature T is performed by a process different from the present process, and details thereof will be described later.
[0053]
Next, the turbo wall temperature T estimated in the separately executed turbo wall temperature T estimation process is read (S130), and whether or not the S poison recovery process is executed, that is, whether or not the fuel supply is prohibited. Is made (S140). Here, it is determined that the fuel supply is prohibited when the S accumulation amount S is less than the limit accumulation amount Smax or the estimated turbo wall temperature T is equal to or lower than the predetermined temperature T2.
[0054]
Here, in the engine 1 according to the present embodiment, FIG. 4 shows the minimum value of the turbo wall temperature and the generation state of white smoke during the period when the fuel addition from the injection nozzle 5 is executed. Here, the turbo inlet gas temperature (exhaust temperature flowing into the turbocharger 11), the engine rotational speed, the engine load, and the fuel addition time when fuel addition from the injection nozzle 5 is started are variously changed. From the state of generation of white smoke shown in FIG. 4, the present inventor confirmed that in the case of the engine 1 in this embodiment, white smoke is not generated if the turbo wall temperature is 120 ° C. or higher. That is, it has been found that if the turbo wall temperature is 120 ° C. or higher, the vaporization of fuel is promoted, and the fuel adhesion to the wall surface is suppressed. Therefore, in the present embodiment, the predetermined temperature T2 for determining whether or not to limit the fuel supply process is set to 120 ° C. The predetermined temperature T2 is not limited to this value (120 ° C.) as long as the temperature can suppress the fuel adhesion to the turbo wall.
[0055]
If the turbo wall temperature T is equal to or lower than the predetermined temperature T2 (NO in S140), fuel may adhere to the wall surface due to fuel supply. Therefore, the processes of S100 to S140 are repeated and the S coverage is increased. Execution of poison recovery processing is put on hold. That is, a restriction process for restricting the supply of combustion fuel is substantially performed.
[0056]
On the other hand, if the turbo wall temperature T is higher than the predetermined temperature T2 (YES in S140), the fuel poisoning hardly occurs even if the fuel is supplied, so that the execution of the S poisoning recovery process is permitted.
[0057]
Here, although the temperature of the NOx purification catalyst 12 is raised by the fuel supply in the S poison recovery process, a certain amount of time is required from when the fuel is supplied until the temperature of the NOx purification catalyst 12 is actually raised. Take it. Therefore, S poison recovery may not be performed immediately after the fuel supply. Therefore, in this embodiment, prior to supplying fuel for S poison recovery, combustion fuel for raising the temperature of the NOx purification catalyst 12 is supplied to the NOx purification catalyst 12. With this combustion fuel supply process, the temperature of the NOx purification catalyst 12 is raised prior to the recovery of the S poison, and the S poison recovery is performed immediately after the execution of the S poison recovery process. In addition, since the S poison recovery is started from the state where the NOx purification catalyst has been heated in advance as described above, the fuel necessary for raising the temperature of the NOx purification catalyst 12 when executing the S poison recovery process, That is, the supply amount of the reducing agent can be reduced, whereby the amount of the reducing agent adhering to the turbo wall surface can be reduced.
[0058]
Therefore, if an affirmative determination is made in S140, that is, if the turbo wall temperature T is higher than the predetermined temperature T2 (YES in S140), this temperature increase process is executed (S150). In this temperature raising process, fuel is injected from the injection nozzle 5 and the injected fuel is burned on the NOx purification catalyst 12, whereby the NOx purification catalyst 12 is heated. The combustion fuel supply process in the temperature increasing process constitutes the temperature increasing means.
[0059]
In this temperature raising process, the temperature of the NOx purification catalyst 12 is raised by supplying combustion fuel. However, when this process is performed, the turbo wall temperature T is set to the predetermined temperature T2 according to the determination in S140. Higher than that. Therefore, the fuel adhesion to the wall surface due to the fuel supply for combustion in the temperature raising process is suppressed.
[0060]
Next, it is determined whether or not the temperature raising process has been completed (S160). This determination is made based on whether or not the temperature of the NOx purification catalyst 12 is continuously maintained at a predetermined temperature T3 or higher for a predetermined period. The temperature of the NOx purification catalyst 12 is estimated from the exhaust temperature ET. Further, as the predetermined temperature T3, a temperature at which the S poisoning recovery performed thereafter can be quickly performed is set, and the temperature of the entire NOx purification catalyst 12 can be set to the predetermined temperature T3 as the predetermined period. The time is set.
[0061]
If the temperature raising process has not ended yet (NO in S160), the processes of S150 and S160 are repeatedly executed until it is determined that the temperature raising process has ended.
[0062]
On the other hand, when the temperature raising process is completed (YES in S160), the NOx purification catalyst 12 is sufficiently heated, and the S poisoning recovery process can be performed quickly. (S170 in FIG. 3). When this S poisoning recovery process is executed, fuel is injected from the injection nozzle 5 and fuel that is a reducing agent is supplied to the NOx purification catalyst 12. When the reducing agent is thus supplied to the NOx purification catalyst 12, the sulfur component deposited on the NOx purification catalyst 12 is released in a reduced state as described above. Further, when the S poisoning recovery process is executed, the throttle valve 16 is controlled to the closed side. As a result, the oxygen concentration in the exhaust gas is lowered, and the reduction / release of the sulfur content is further promoted. Note that the reducing agent supply process in the S poisoning recovery process constitutes the reducing agent supply means.
[0063]
Next, the turbo wall temperature T is read (S180 in FIG. 3), and it is determined whether the turbo wall temperature T is equal to or lower than a predetermined temperature T1 (S190 in FIG. 3). The predetermined temperature T1 is set to the same value as the predetermined temperature T2. If it is determined that the turbo wall temperature T is equal to or lower than the predetermined temperature T1 (YES in S190 of FIG. 3), fuel may adhere to the turbo wall surface, and therefore fuel supply from the injection nozzle 5 is prohibited. Is done. In other words, the S poisoning recovery process is interrupted (S200 in FIG. 3), and a limiting process for limiting the supply of the reducing agent is performed.
[0064]
Here, when the fuel supply process for S poison recovery is interrupted, the fuel supply is prohibited before the sulfur content accumulated on the NOx purification catalyst 12 is sufficiently reduced and released. Therefore, the S residual amount RS, which is the amount of sulfur remaining in the NOx purification catalyst 12, is calculated (S210 in FIG. 3), and the calculation result is stored in the RAM in the control device 25. Since the S residual amount RS decreases as the execution time of the S poisoning recovery process (the execution time of supplying the reducing agent by the injection nozzle 5) becomes longer, it can be estimated based on the execution time. And the estimation process of the turbo wall temperature T currently performed separately is complete | finished (S240 of FIG. 3), and this process is complete | finished.
[0065]
On the other hand, when it is determined in the previous S190 that the turbo wall temperature T is higher than the predetermined temperature T1 (NO in S190), it is determined whether or not the S poison recovery process is completed (FIG. 5). 3 S220). Here, an affirmative determination is made when the fuel injection from the injection nozzle 5 has been executed for a time that can be estimated that the S poison recovery has been sufficiently performed and the fuel injection from the injection nozzle 5 has been completed. If the S poison recovery process has not been completed (NO in S220), the processes of S170 to S190 and S220 are repeatedly executed until the end of the S poison recovery process is determined.
[0066]
On the other hand, when the S poisoning recovery process has been completed (YES in S220), the S remaining amount RS is reset to “0” (S230 in FIG. 3), and the turbo wall temperature T that is separately executed is estimated. The process is terminated (S240 in FIG. 3), and the present process is terminated.
[0067]
Next, estimation of the turbo wall temperature T will be described with reference to FIGS. In the present embodiment, the turbo wall temperature T is estimated based on the engine operating state, more specifically, based on the fuel injection amount and the engine speed. This is because the exhaust temperature tends to rise and the turbo wall temperature tends to increase as the fuel injection amount increases. Further, when the engine rotation speed increases, the exhaust flow rate increases, and the amount of heat that moves from the exhaust to the turbo wall surface also increases, so the turbo wall temperature tends to increase. For these reasons, if the steady state of the engine operation continues for a certain period of time, heat transfer from the exhaust to the turbo wall surface is sufficiently performed, so the turbo wall temperature T is set based on the engine operation state at that time. Can be estimated.
[0068]
Here, as shown in FIG. 5, when the engine operating state changes from the steady state A to another steady state B (time tα), the turbo wall temperature estimated based on the engine operating state in the steady state A a is immediately changed to the turbo wall temperature b (one-dot chain line) estimated based on the engine operating state in the steady state B. On the other hand, heat transfer from the exhaust to the turbo wall requires a certain amount of time. Therefore, the actual turbo wall temperature T gradually changes from the turbo wall temperature a toward the turbo wall temperature b as indicated by the solid line. That is, the change in the turbo wall temperature is delayed with respect to the change in the engine operating state. For this reason, even if the turbo wall temperature is estimated based on the fuel injection amount and the engine rotation speed for a while after the engine operating state changes, the estimation accuracy is lowered. Therefore, in the present embodiment, in order to accurately estimate the turbo wall temperature when the engine operating state changes, the turbo wall temperature T is calculated using a first-order lag model equation described later.
[0069]
FIG. 6 shows a processing procedure for estimating the turbo wall temperature T. When an affirmative determination is made in S110 in FIG. 2, the control device 25 repeatedly executes the processing every predetermined time.
[0070]
When this process is started, first, the fuel injection amount Q and the engine speed NE are read (S300). The fuel injection amount Q is separately calculated based on the accelerator opening ACCP, the engine speed NE, and the like.
[0071]
Next, the turbo wall temperature TM during steady operation is estimated with reference to the turbo wall temperature estimation map shown in FIG. 7 based on the fuel injection amount Q and the engine speed NE (S310). This turbo wall temperature estimation map is set so that the calculated turbo wall temperature TM increases as the fuel injection amount Q increases or as the engine speed NE increases.
[0072]
Next, the turbo wall temperature T is calculated based on the following equation (2) (S320).
T = (TM_n-1−TM) × e ^ (− t / τ) + TM (2)
Turbo wall temperature TM_n-1Is the turbo wall temperature estimated last time based on the turbo wall temperature estimation map, and the turbo wall temperature TM is the turbo wall temperature estimated this time based on the map. The elapsed time t indicates the elapsed time from when the engine operating state changes to the present, and in FIG. 5 indicates the elapsed time t from time tα. The time constant τ is a value reflecting a response delay until the turbo wall temperature changes after the exhaust temperature or the exhaust flow rate changes due to a change in the engine operating state. Is set. “E” is the base of the natural logarithm, and its value is an irrational number such that “e = 2.182. That is, this equation (2) is a first-order lag model equation for estimating the transition of the turbo wall temperature when the engine operating state changes from one steady state to another steady state. As can be seen from this equation (2), the longer the elapsed time t, the more “(TM_n-1The value of “−TM) × e ^ (− t / τ)” becomes smaller. That is, as shown in FIG. 5, the turbo wall temperature T becomes the turbo wall temperature TM estimated last time as the elapsed time t after the engine operating state changes at time tα becomes longer._n-1To approach the estimated turbo wall temperature TM.
[0073]
When the turbo wall temperature T is calculated in this way, this process is terminated. Then, the above-described series of estimation processes is performed every predetermined time, and the turbo wall temperature T is updated. By this turbo wall temperature estimation process, a value approximating the actual turbo wall temperature (solid line) shown in FIG. 5 is calculated, and the turbo wall temperature T after the engine operating state changes can be accurately estimated. it can.
[0074]
As described above, according to the present embodiment, the following effects can be obtained.
(1) When supplying the reducing agent for S poison recovery, the temperature (turbo wall temperature T) of the wall of the turbine housing 42, which is a member that divides the exhaust passage and is particularly susceptible to fuel adhesion, is equal to or lower than a predetermined temperature T1. In this case, the supply of the reducing agent is restricted. For this reason, when the reducing agent is supplied, it becomes possible to suppress the attachment of the reducing agent to the turbo wall surface, and thus it is possible to suitably suppress the generation of the white smoke.
[0075]
(2) When the turbo wall temperature T becomes equal to or lower than the predetermined temperature T1 during the execution of the S poisoning recovery process, the supply of the reducing agent is interrupted. That is, since the turbo wall temperature T is monitored during the execution of the S poisoning recovery process, the turbo wall temperature T decreases during the execution of the reducing agent supply process so that fuel adheres to the turbo wall surface. Even in such a situation, it is possible to reliably suppress fuel adhesion to the turbo wall surface.
[0076]
(3) When the execution of the reducing agent supply process is interrupted in this way, the sulfur content remains in the NOx purification catalyst 12. Therefore, in the above embodiment, when the supply of the reducing agent for S poison recovery is interrupted, the amount of sulfur remaining in the NOx purification catalyst 12 is calculated, and this calculated S residual amount is used as the NOx purification catalyst. 12 is added to the calculation of the amount of S accumulated on the surface. For this reason, even when the S poisoning recovery process is interrupted, the S accumulation amount S can be calculated accurately, and the determination accuracy related to the execution request for the S poisoning recovery process can be improved.
[0077]
(4) Prior to the supply of the reducing agent for S poison recovery, the combustion fuel for raising the temperature is supplied to the NOx purification catalyst 12. Therefore, the S poison recovery process can be performed in a state in which the temperature of the NOx purification catalyst 12 is sufficiently increased, and the S poison recovery can be surely performed immediately after the execution of the S poison recovery process. Become. Further, since the S poison recovery starts from the state in which the NOx purification catalyst 12 has been heated in advance in this way, the amount of the reducing agent supply during the S poison recovery can also be reduced. The amount of reducing agent adhering to the turbo wall surface can be reduced.
[0078]
(5) Further, the temperature raising process is executed until the temperature of the NOx purification catalyst 12 is maintained at a predetermined temperature T3 or higher continuously for a predetermined period. Therefore, the temperature of the entire NOx purification catalyst 12 can be reliably raised. Therefore, it becomes possible to reliably perform S poison recovery, and as a result, the amount of reducing agent supplied during S poison recovery can be reliably reduced, and the effect described in (3) above can be achieved. You will be able to get it reliably.
[0079]
(6) Further, when the temperature raising process is executed, the supply of combustion fuel is restricted when the turbo wall temperature is equal to or lower than a predetermined temperature T2. Therefore, it is possible to suppress the adhesion of the combustion fuel to the turbo wall surface due to the supply of the combustion fuel.
[0080]
(7) As a restriction mode by the restriction process, supply of combustion fuel and supply of reducing agent are prohibited. Therefore, it is possible to reliably suppress the attachment of the reducing agent and the combustion fuel to the turbo wall surface.
[0081]
(8) The turbo wall temperature T is estimated based on the engine operating state such as the fuel injection amount Q and the engine rotational speed NE. Further, the turbo wall temperature T after the engine operating state is changed is accurately estimated using the first-order lag model formula. Therefore, the turbo wall temperature T can be grasped without providing a new sensor or the like on the turbo wall surface.
[0082]
In addition, the said embodiment can also be changed and implemented as follows.
The predetermined temperature T2 in the temperature raising process and the predetermined temperature T1 in the S poisoning recovery process may be different from each other. For example, the predetermined temperatures T1 and T2 may be set to different and appropriate values by experiments or the like.
[0083]
In the above embodiment, the limiting process for limiting the supply of the reducing agent is performed during the S poison recovery process, that is, when the reducing agent is being supplied. It may be executed any time after the determination that the accumulation amount is Smax or more is made. For example, the processes of S400 and S410 shown in FIG. 8 may be added prior to the process of S170 in FIG. That is, prior to the execution of the S poison recovery process, the turbo wall temperature T is read (S400), and it is determined whether the turbo wall temperature T is equal to or lower than the predetermined temperature T1 (S410). If the turbo wall temperature T is equal to or lower than the predetermined temperature T1 (YES in S410), the processes after S200 shown in FIG. 3 are executed. On the other hand, when the turbo wall temperature T is higher than the predetermined temperature T1 (NO in S410), the processes after S170 shown in FIG. 3 are executed. In this case, the same effect as that of the above embodiment can be obtained. In this case, the restriction process performed during the execution of the S poison recovery process may be omitted.
[0084]
In addition, when the turbo wall temperature T is equal to or higher than the predetermined temperature T4, the start of the reducing agent supply process is permitted, while the reducing agent supply process is interrupted when the turbo wall temperature T falls below the predetermined temperature T5. You may make it do. Note that the predetermined temperature T4 and the predetermined temperature T5 at this time may be the same values as the predetermined temperature T1, and the predetermined temperatures T4 and T5 may be set to different and appropriate values by experiments, for example. Also in this case, since the start of the reducing agent supply process is permitted when the turbo wall temperature T is equal to or higher than the predetermined temperature T4, it is possible to suppress the attachment of the reducing agent to the turbo wall surface. In addition, for the reducing agent supply process that is permitted to start, the process is interrupted when the turbo wall temperature T falls below a predetermined temperature T5. Therefore, when the turbo wall temperature T falls during the execution of the supply process. However, it is possible to reliably suppress the reducing agent from adhering to the turbo wall surface.
[0085]
In the above embodiment, the restriction process for restricting the supply of the combustion fuel is performed before the temperature raising process, but during the temperature raising process, that is, when the combustion fuel is being supplied. The restriction process may be executed. In this case, even when the temperature increase process is being performed and the turbo wall temperature T is lowered, the adhesion of the combustion fuel to the turbo wall surface can be suppressed. In this case, the limiting process performed before the temperature raising process may be omitted.
[0086]
In addition, when the turbo wall temperature T is equal to or higher than the predetermined temperature T4, the start of the combustion fuel supply process is permitted, while when the turbo wall temperature T falls below the predetermined temperature T5, the combustion fuel supply process is started. May be interrupted. Note that the predetermined temperature T4 and the predetermined temperature T5 at this time may be the same values as the predetermined temperature T2, and the predetermined temperatures T4 and T5 may be set to different and appropriate values by experiments, for example. Also in this case, since the start of the combustion fuel supply process is permitted when the turbo wall temperature T is equal to or higher than the predetermined temperature T4, the adhesion of the combustion fuel to the turbo wall surface can be suppressed. Become. In addition, for the combustion fuel supply process that is permitted to start, the process is interrupted when the turbo wall temperature T falls below a predetermined temperature T5, so the turbo wall temperature T decreases during execution of the supply process. Even in this case, it is possible to reliably suppress the combustion fuel from adhering to the turbo wall surface.
[0087]
-Although the supply of the fuel for combustion and the supply of the reducing agent are prohibited as the limiting process, the execution of at least one of the supply may be prohibited. Also in this case, it is possible to obtain an operational effect similar to the above embodiment.
[0088]
-As a restriction | limiting aspect in the said restriction | limiting process, you may make it reduce the supply amount of a fuel for combustion, and the supply amount of a reducing agent. Also in this case, it is possible to obtain an operational effect similar to the above embodiment.
[0089]
When the NOx purification catalyst 12 can be quickly heated by supply of the reducing agent executed in the S poison recovery process, the above temperature increase process (the processes of S150 and S160) may be omitted.
[0090]
In the above embodiment, the turbo wall temperature T is estimated, but a temperature detection element such as a temperature sensor may be attached to the turbo wall surface to detect the actual turbo wall temperature. Further, since the temperature of the inner wall of the turbine housing 42 and the temperature of the outer wall thereof are correlated, the temperature of the outer wall of the turbine housing 42 is estimated or detected, and these values are referred to as the wall temperature of the exhaust passage. It may be.
[0091]
In the above embodiment, the temperature of the turbo wall surface is estimated. However, the portion in the exhaust passage where the wall temperature is estimated can be arbitrarily selected. Note that the generation of the white smoke can be suitably suppressed by estimating the wall temperature of the portion where the fuel adhesion is likely to occur.
[0092]
In the above embodiment, the turbo wall temperature T is estimated based on the fuel injection amount Q and the engine rotational speed NE. Here, since the exhaust temperature tends to increase as the engine load increases, the turbo wall temperature T may be estimated using another parameter correlated with the engine load, such as the accelerator opening ACCP. .
[0093]
-The NOx purification catalyst in the said embodiment was a NOx storage reduction type catalyst. In addition, the present invention can be similarly applied to a NOx purification catalyst to which a reducing agent is supplied, for example, a NOx purification catalyst such as a NOx selective reduction catalyst.
[0094]
In the above embodiment, the reducing agent injected from the injection nozzle 5 is a fuel for an internal combustion engine, but any reducing agent that contributes to S poison recovery can be used. In this case, the same effect as that of the above embodiment can be obtained.
[0095]
-The internal combustion engine in the said embodiment was a diesel engine. However, the above embodiment can be applied to any engine that includes a carrier carrying a NOx purification catalyst and supplies a reducing agent such as fuel to the carrier. In this case as well, the same effect as the above embodiment can be applied. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an internal combustion engine to which an exhaust emission control device according to an embodiment is applied, and a peripheral configuration thereof.
FIG. 2 is a flowchart showing a processing procedure for S poison recovery control according to the embodiment;
FIG. 3 is a flowchart showing a processing procedure of S poison recovery control according to the embodiment;
FIG. 4 is an explanatory diagram showing the minimum value of the turbo wall temperature and the generation state of white smoke under various conditions.
FIG. 5 is a timing chart illustrating the transition of turbo wall temperature when the engine operating state changes.
FIG. 6 is a flowchart showing a procedure of turbo wall temperature estimation processing according to the embodiment.
FIG. 7 is a view showing a map structure for calculating a turbo wall temperature in the embodiment.
FIG. 8 is a flowchart showing a processing procedure of S poison recovery control in a modification of the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 5 ... Injection nozzle, 6a-6d ... Exhaust port, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Common rail, 10 ... Supply pump, 11 ... turbocharger, 12 ... NOx purification catalyst, 13 ... EGR passage, 14 ... EGR cooler, 15 ... EGR valve, 16 ... throttle valve, 17 ... actuator, 18 ... intercooler, 19 ... air flow meter, 20 ... Throttle opening sensor, 21 ... Air-fuel ratio sensor, 22 ... Engine speed sensor, 24 ... Accelerator opening sensor, 25 ... Control device, 26 ... Exhaust pipe, 27 ... Fuel supply pipe, 28 ... EGR device, 29 ... Exhaust temperature Sensor, 40 ... center housing, 41 ... compressor housing, 42 ... turbine housing, # ... first cylinder, # 2 ... second cylinder, # 3 ... third cylinder, # 4 ... fourth cylinder.

Claims (8)

In an exhaust gas purification apparatus for an internal combustion engine, comprising: a NOx purification catalyst disposed in an exhaust passage; and a reducing agent supply means for supplying a reducing agent for S poison recovery to the NOx purification catalyst.
A limiting unit that executes a limiting process of limiting the supply of the reducing agent by the reducing agent supply unit when the wall temperature of the exhaust passage is equal to or lower than a predetermined temperature T1 ,
The internal combustion engine includes a supercharger driven by exhaust pressure in its exhaust passage,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the limiting means refers to a temperature of a member defining the exhaust passage in the supercharger as a wall temperature of the exhaust passage . The exhaust emission control device for an internal combustion engine according to claim 1, further comprising a temperature raising means for supplying combustion fuel to the NOx purification catalyst and raising the temperature thereof prior to the supply of the reducing agent by the reducing agent supply means. The exhaust purification device for an internal combustion engine according to claim 2, wherein the restriction means includes, as the restriction process, a process of restricting the supply of combustion fuel by the temperature raising means when the wall temperature of the exhaust passage is equal to or lower than a predetermined temperature T2. . The exhaust gas purification device for an internal combustion engine according to claim 2 or 3, wherein the temperature raising means performs the temperature raising process until the temperature of the NOx purification catalyst is continuously maintained for a predetermined period of time at a predetermined temperature T3 or higher. Any said limiting means according to claim 2-4 which executes processing for prohibiting the execution for at least one of the supply of combustion fuel by the supply and the Atsushi Nobori means of the reducing agent by the reducing agent supplying means as said restriction processing 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. The limiting means permits the start of at least one of the reducing agent supply of the reducing agent supply means and the combustion fuel supply of the temperature raising means when the wall temperature is equal to or higher than a predetermined temperature T4, while the wall The exhaust emission control device for an internal combustion engine according to any one of claims 2 to 5, wherein when the temperature falls below a predetermined temperature T5 , one of the processes permitted to start is interrupted. The reducing agent supply means estimates the S accumulation amount of the NOx purification catalyst based on the engine operating state, and executes the supply of the reducing agent on the condition that the estimated S accumulation amount is a predetermined amount or more. In addition, when the reducing agent supply process by the reducing agent supply means is interrupted as the one process, the remaining amount is calculated for the S accumulation amount based on the execution time of the supply process. The exhaust purification device for an internal combustion engine according to claim 6, wherein is added to an S accumulation amount estimated to have accumulated on the NOx purification catalyst after interruption of the supply process. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 7, wherein the wall temperature is estimated based on an engine operating state.

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