JP4276910B2 - Management method of NOx catalyst - Google Patents

Description

  The present invention relates to a method for managing a NOx catalyst that is provided in an exhaust passage of a diesel engine and reduces NOx in exhaust gas, and more particularly to a method for regenerating the function of the NOx catalyst.

  Conventionally, a NOx catalyst that is provided in an exhaust passage of a diesel engine or the like and efficiently stores nitrogen oxides (NOx) in the exhaust under a condition in which a lean air-fuel mixture is used for combustion and engine operation is performed. It has been known.

  The NOx catalyst has a characteristic of storing NOx in exhaust in an oxidizing atmosphere and releasing NOx in exhaust in a reducing atmosphere. Incidentally, the NOx released into the exhaust gas reacts with these reducing components quickly and is reduced to nitrogen (N2) if there are reducing components such as hydrocarbons (HC) in the exhaust gas.

  Therefore, in an internal combustion engine provided with such a NOx catalyst in the exhaust passage, NOx in the exhaust is efficiently reduced (purified) by appropriately switching the exhaust flowing into the NOx catalyst between an oxidizing atmosphere and a reducing atmosphere.

  By the way, the fuel of an internal combustion engine usually contains a sulfur component, and in addition to NOx, the exhaust also contains a sulfur component originating from the sulfur component in such fuel. Sulfur components present in the exhaust combine with the NOx catalyst at a higher efficiency than NOx, and under sufficient conditions (the concentration of the reducing component in the exhaust is sufficient to release NOx stored in the catalyst). Even under conditions exceeding the predetermined value, it is not easily released from the catalyst. For this reason, as the engine operation continues, so-called sulfur poisoning occurs in which the sulfur component in the exhaust gas is gradually accumulated in the NOx catalyst. As sulfur poisoning progresses, the limit value of the NOx occlusion amount by the NOx catalyst and the NOx occlusion efficiency decrease, resulting in a decrease in NOx purification efficiency.

  The sulfur component accumulated in the NOx catalyst is released from the catalyst by satisfying the conditions for further increasing the concentration of the reducing component in the exhaust gas and the temperature of the NOx catalyst than the conditions achieved by the normal reducing agent supply control. It is known. For this reason, in an engine equipped with an exhaust passage, such as a NOx catalyst, in which the sulfur component gradually accumulates as engine operation continues, the concentration of reducing components in the exhaust upstream of the NOx catalyst is increased, and In general, the sulfur component accumulated in the NOx catalyst is released by executing control (hereinafter referred to as sulfur treatment (S treatment) control) of bringing the NOx catalyst into a high temperature state (for example, about 690 ° C.).

In Patent Document 1, spraying is performed upstream of the NOx catalyst in the exhaust passage while performing pretreatment for lowering the air-fuel ratio of the air-fuel mixture used for engine combustion within a range (operation region) that does not affect the combustion state of the engine. A method for releasing sulfur by directly adding a reducing agent in the state is described. Thus, if the adjustment (pretreatment) of the air-fuel ratio and the addition of the reducing agent are used in combination, efficient S processing control with reduced consumption of the reducing agent can be performed.
Japanese Patent No. 3104692

  By the way, the combustion state of the engine, and hence the exhaust characteristics, tend to vary with the execution of pre-processing accompanied by a reduction (riching) of the air-fuel ratio. For this reason, when the S process control is executed, it is difficult to control the air-fuel ratio of the exhaust gas to the optimum value for releasing the sulfur component accumulated in the NOx catalyst at the initial stage. As a result, there is a concern that the exhaust characteristics may be temporarily deteriorated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a diesel engine having a NOx catalyst in an exhaust passage, and to treat the sulfur component accumulated in the NOx catalyst with an exhaust characteristic. An object of the present invention is to provide a method capable of efficiently performing processing without causing deterioration.

In order to achieve the above object, according to the invention described in each claim, there is provided a method for managing a NOx catalyst provided in an exhaust passage of a diesel engine for reducing NOx in exhaust gas, which is used for combustion of the engine. By performing a first process for reducing the air-fuel ratio of the air-fuel mixture and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage, the sulfur component accumulated in the NOx catalyst is released. It includes the step, and, in the step, after the start of the first treatment, on condition that the air-fuel ratio of the exhaust gas of the NOx catalyst upstream of the exhaust passage stable, you start the second processing.

According to this configuration, the controllability of the air-fuel ratio of the exhaust by the second process is enhanced. Therefore, after the start of the second process, the air-fuel ratio of the exhaust gas can be quickly converged to the target value (a value suitable for releasing the sulfur component accumulated in the NOx catalyst). For example, the air-fuel ratio of the exhaust does not decrease excessively (become rich) with the start of the second process.
In the first to third aspects of the present invention, a predetermined period required to stabilize the air-fuel ratio of the exhaust gas upstream of the NOx catalyst in the exhaust passage has elapsed after the start of the first process. the you and the conditions.

According to this configuration, the controllability of the air-fuel ratio of the exhaust gas by the second process can be improved based on a simple control structure. For example, a complicated control structure for confirming the stability of the air-fuel ratio of the exhaust is not required.
In the inventions according to claims 4 to 6, after the start of the first processing, the counter decremented for each fuel injection of fuel supplied to the combustion of the diesel engine becomes a predetermined value or less. This is the above condition.
In the course of the first process, when the fuel injection amount of the fuel provided for the combustion of the diesel engine is gradually increased, this increase is performed for each fuel injection of the engine. Such an increase in the fuel injection amount for each fuel injection affects the air-fuel ratio of the exhaust during the execution of the first process. Therefore, the counter decremented for each fuel injection of the diesel engine after the start of the first process becomes a value related to the influence on the air-fuel ratio of the exhaust gas accompanying the increase in the fuel injection amount for each fuel injection. According to the above configuration, since the second process is started based on the counter being less than the predetermined value, the fuel injection amount is increased in the course of the first process. The second process can be started at an appropriate timing.
Particularly, in the invention according to claims 1 and 4, when the parameter relating to intake air amount of the engine is less than a predetermined value, it cancels the condition.

For example, even if the air-fuel ratio of the exhaust gas is too low and an excessive reducing component flows into the NOx catalyst, if the intake air amount of the engine is low to a certain extent, the excessive reducing component becomes oxygen (O2) of the NOx catalyst. Purified by storage action. According to this configuration, when the NOx catalyst has a high O2 storage action, the time required for the step of releasing the sulfur component accumulated in the NOx catalyst can be shortened as a whole by releasing the condition. Thereby, the consumption of the reducing agent required for the same process can be reduced.
Particularly, in the invention according to claims 2 and 5, when the parameter relating to the degree of deterioration of the NOx catalyst is lower than the predetermined value, it cancels the condition.

For example, even if the exhaust air-fuel ratio is too low and excess reducing components flow into the NOx catalyst, if the NOx catalyst purification function is sufficiently high, the excess reducing components are purified by the NOx catalyst's O2 storage function. Is done. That is, even with this configuration, when the O2 storage action of the NOx catalyst is high, the time required for the step of releasing the sulfur component accumulated in the NOx catalyst can be shortened as a whole by releasing the condition. Thereby, the consumption of the reducing agent required for the same process can be reduced.
In particular, the invention according to claim 3 and claim 6 includes a step of detecting the amount of change in the air-fuel ratio upstream of the NOx catalyst in the exhaust passage based on the first processing and learning the amount of change, after learning is completed, it releases the conditions.

A change amount of the air-fuel ratio upstream of the NOx catalyst in the exhaust passage based on the first process is detected, and the change amount is once learned. For this reason, the amount of the reducing agent added through the second process can be adjusted by taking into account the amount of change in the air-fuel ratio of the exhaust gas based on the first process. As a result, even if the condition is canceled, the exhaust characteristics are not deteriorated with the start of the second process. As a result, the sulfur component accumulated in the NOx catalyst can be efficiently released without deteriorating the exhaust characteristics accompanying the start of the second treatment .

In the invention according to claim 7, the diesel engine can be switched to a low-temperature combustion mode in which a large amount of EGR gas is introduced into the combustion chamber, and is decremented for each fuel injection of the engine after the start of the low-temperature combustion mode. The fuel injection amount is gradually increased to a predetermined value until the counter reaches “0” from the initial value, and the first process is realized by switching to the low temperature combustion mode. in some cases, after the start of the low temperature combustion mode, the counter you with the proviso that less than the predetermined value.

  In the low-temperature combustion mode, the amount of air sucked into the combustion chamber decreases with the introduction of a large amount of EGR gas into the combustion chamber, so that the air-fuel ratio of the air-fuel mixture supplied to the combustion of the diesel engine decreases. Become. The first process is realized by executing the low temperature combustion mode. During the execution of the first process associated with the execution of the low-temperature combustion mode, the fuel injection amount of the engine is predetermined until the counter decremented for each fuel injection of the diesel engine becomes “0” from the initial value. The amount is gradually increased to the value. This increase in the fuel injection amount is performed for each fuel injection. The increase in the fuel injection amount for each fuel injection affects the air-fuel ratio of the exhaust gas during the execution of the first process (low temperature combustion mode). Since the counter is decremented for each fuel injection, the counter has a value related to the influence on the air-fuel ratio of the exhaust gas as the fuel injection amount increases for each fuel injection. According to the above configuration, since the second process is started when the counter becomes less than the predetermined value, the diesel engine in which the fuel injection amount is increased in accordance with the execution of the low-temperature combustion mode is provided. The process 2 can be started at an appropriate timing.

When the start timing of the second process is not appropriate, for example, when the start timing is too early, the second process is performed in a state where the exhaust air-fuel ratio is not decreasing in the first process. Thus, the addition of the reducing agent (fuel) to the upstream side of the NOx catalyst is started. For this reason, a large amount of the above reducing agent is required to reduce the air-fuel ratio of the exhaust gas to a value at which the sulfur component accumulated in the NOx catalyst can be released. Problems arise in terms of controllability of the air-fuel ratio. That is, the catalyst bed temperature rises and the controllability of the exhaust air / fuel ratio deteriorates due to the large amount of reducing agent added. According to the said structure, it can suppress that such a malfunction arises.

  As described above, according to the method of the present invention, sulfur accumulated in the NOx catalyst can be efficiently treated without deteriorating exhaust characteristics.

[First Embodiment]
Hereinafter, a first embodiment in which the present invention is embodied as an exhaust emission control device for a diesel engine will be described.

[Engine structure and function]
In FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 is an in-line four-cylinder diesel engine having a fuel supply system 10, a combustion chamber 20, an intake passage 30 and an exhaust passage 40 as main parts.

  First, the fuel supply system 10 includes a supply pump 11, a common rail 12, a fuel injection valve 13, a fuel addition valve 14, an engine fuel passage P1, an addition fuel passage P2, and the like. The supply pump 11 makes the fuel pumped up from a fuel tank (not shown) into a high pressure and supplies it to the common rail 12 via the engine fuel passage P1. The common rail 12 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 13. The fuel injection valve 13 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and is appropriately opened to inject and supply fuel into the combustion chamber 20. On the other hand, the supply pump 11 supplies a part of the fuel pumped from the fuel tank to the fuel addition valve 14 via the addition fuel passage P2. The fuel addition valve 14 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and adds fuel that functions as a reducing agent to the upstream of the catalyst casing 41 in the exhaust passage 40 in an appropriate amount at an appropriate timing. To do.

  The throttle valve 31 provided in the intake passage 30 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner, and the intake air passage area is changed under a predetermined condition. It has a function of adjusting the supply amount (flow rate) of air.

  A catalyst casing 41 is provided downstream of the fuel addition valve 14 in the exhaust passage 40. Inside the catalyst casing 41, a known wall flow type particulate filter mainly composed of a porous material is accommodated. A well-known storage reduction type NOx catalyst (hereinafter referred to as NOx catalyst) is supported on the surface of the particulate filter. The NOx catalyst is composed of a NOx storage agent and a noble metal catalyst.

  In addition, various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of the part and the operating state of the engine 1 are output. For example, the oxygen concentration sensor 60 provided upstream of the catalyst casing 41 in the exhaust passage 40 outputs a detection signal that continuously changes according to the oxygen concentration in the exhaust. The detection signal of the oxygen concentration sensor 60 reflects the amount of the reducing component supplied into the exhaust gas through the fuel addition valve 14 in addition to the air-fuel ratio of the air-fuel mixture used for engine combustion, and the oxidation component ( Oxygen (O2 etc.) and reducing components (hydrocarbon (HC) etc.) are directly indicative of the amount. Thus, the component ratio of the oxidation component and the reduction component in the exhaust gas calculated based on the detection signal of the oxygen concentration sensor 60 is referred to as the air-fuel ratio (A / FEHT) of the exhaust gas for convenience. Incidentally, as the reducing agent increases through the fuel addition valve 14, the air-fuel ratio of the exhaust gas becomes relatively lower (richer) than the air-fuel ratio A / F of the air-fuel mixture used for engine combustion. On the other hand, when the amount of the reducing agent supplied through the fuel addition valve 14 is “0”, the air-fuel ratio of the air-fuel mixture used for engine combustion and the air-fuel ratio of the exhaust gas are substantially equal. The oxygen concentration sensor 60 is electrically connected to an electronic control unit (ECU) 50.

  The ECU 50 includes a logical operation circuit including a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM) and a backup RAM, a timer counter 95, and the like. The ECU 50 configured in this way executes various controls relating to the operating state of the engine 1. For example, under predetermined conditions, the ECU 50 controls the fuel injection valve 13 so that the air-fuel ratio A / FEHT of the exhaust gas grasped based on the detection signal of the oxygen concentration sensor 60 converges to a target value ( Feedback control). Further, the ECU 50 performs control (feed forward control) for operating the fuel injection valve 13 with reference to a preset map (not shown) based on the operating state of the engine 1 under predetermined conditions.

[Function of NOx catalyst]
As described above, the NOx catalyst is composed of the NOx storage agent and the noble metal catalyst.
The NOx storage agent has a characteristic of storing and holding NOx in a state where the oxygen concentration in the exhaust gas is high, and releasing NOx in a state where the oxygen concentration in the exhaust gas is low (a state where the concentration of the reducing component is high). In addition, when NOx is released into the exhaust, if no HC or CO exists in the exhaust, the noble metal catalyst promotes the oxidation reaction of these HC and CO, so that NOx is converted into the oxidizing component and HC and CO into the exhaust. A redox reaction as a reducing component occurs between the two. That is, HC and CO are oxidized to CO2 and H2O, and NOx is reduced to N2.

  On the other hand, if the NOx storage agent stores a predetermined limit amount of NOx even when the oxygen concentration in the exhaust gas is high, the NOx storage agent no longer stores NOx. In the engine 1, the reducing component is intermittently supplied upstream of the catalyst casing 41 in the exhaust passage 40 through the addition of fuel, and the concentration of the reducing component in the exhaust increases. Before the NOx occlusion amount of the NOx catalyst (NOx occlusion agent) reaches the limit amount, this reducing component periodically releases and reduces and purifies the NOx occluded in the NOx catalyst, and the NOx occlusion capacity of the NOx occlusion agent Will be restored.

[S processing control overview]
As the engine operation continues, sulfur components originating from sulfur components contained in the fuel accumulate in the NOx catalyst (so-called sulfur poisoning occurs). As a process for removing the sulfur component accumulated in the NOx catalyst, the ECU 50 executes a sulfur process (S process) control. The S process control establishes a specific condition defined by the air-fuel ratio A / FEHT of the exhaust to which the NOx catalyst is exposed through the drive control of the fuel addition valve 14 and the control of the combustion state of the engine 1.

FIG. 2 is an example of a time chart showing the transition of the exhaust air-fuel ratio A / FEHT observed during the execution of the S process control.
When there is a request to execute the S process control (time t1), the ECU 50 determines the air-fuel ratio A / FEHT of the exhaust gas so that the fuel in the spray state supplied through the fuel addition acts efficiently on the NOx catalyst. Pre-processing is performed to reduce (enrich) the target value (for example, about 25: hereinafter referred to as air-fuel ratio pre-processing value) α. As the pretreatment, for example, the throttle valve 31 may be throttled to control to reduce the air introduced into the combustion chamber 20. In addition, the timing and amount of fuel injection through the fuel injection valve 13 can be controlled as preprocessing. For example, in order to obtain engine output, the main fuel injection is performed in the vicinity of the compression top dead center, and the auxiliary fuel injection is performed at a different timing to reduce (enrich) the air-fuel ratio A / FEHT of the exhaust. Can do.

  After the air-fuel ratio A / FEHT of the exhaust gas reaches the air-fuel ratio pretreatment value α by the pretreatment, a treatment for actually releasing sulfur (S release treatment) is started (time t2). As the S release process starts, intermittent fuel addition is executed through the fuel addition valve 14. As a result, the fluctuation of the air-fuel ratio A / FEHT of the exhaust gas is repeated between the rich (A / FEHT = β (for example, about 14)) and the intake (A / FEHT = α). Further, the reaction temperature generated when the added fuel is oxidized in the catalyst casing 41 raises the bed temperature of the NOx catalyst to a predetermined value (for example, about 700 ° C.), and thereafter maintains a substantially constant value.

  The ease with which the sulfur component accumulated in the NOx catalyst is released is related to the air-fuel ratio A / FEHT of the exhaust to which the NOx catalyst is exposed. Generally, as the air-fuel ratio A / F of the exhaust gas becomes lower (richer), the sulfur component is released more efficiently.

[Setting of waiting time TS]
Here, the combustion state of the engine, and hence the exhaust characteristics, tend to fluctuate with the execution of pre-processing that involves a reduction (riching) of the air-fuel ratio. This is because when the target value of the air-fuel ratio A / FEHT of the exhaust gas is changed significantly with the start of the pretreatment, it is difficult to quickly converge the exhaust air-fuel ratio A / FEHT to the target value. As a result, if the S release process is started simultaneously with the execution of the preprocess or immediately after the start of the preprocess, the air-fuel ratio A / FEHT of the exhaust easily deviates from the target value in the initial stage.

  When the control for converging the air-fuel ratio A / FEHT of the exhaust gas to the target value is performed as feedback control based on the detection signal of the oxygen concentration sensor 60, the air-fuel ratio A / FEHT of the exhaust gas caused by the significant change of the target value Variations are particularly noticeable.

  In contrast, in the present embodiment, the time required for the air-fuel ratio A / FEHT of the exhaust gas to stabilize in the vicinity of the air-fuel ratio pretreatment value α after the start of the pretreatment is preset as the standby time TS. Then, the S release process is started after the standby time TS has elapsed. Thereby, in the S release process, controllability (convergence to the target value of the air-fuel ratio A / FEHT of the exhaust gas) particularly in the initial stage is enhanced.

On the other hand, when the predetermined condition is satisfied, the setting of the waiting time TS is canceled, and the S release process is started simultaneously with the start of the preprocess or immediately after the start of the preprocess.
For example, if the intake air amount of the engine 1 is low to some extent, the O2 storage action (capacity) of the NOx catalyst is large, so even if excessive reducing components flow into the NOx catalyst due to the air-fuel ratio A / FEHT of the exhaust, The NOx catalyst purifies excess reducing components with higher efficiency than usual. For this reason, in the present embodiment, when the intake air amount GA is less than a predetermined value, the setting of the standby time TS is canceled.

  Further, the NOx catalyst has a reduced O2 storage capacity with time as it is used. In other words, when the degree of deterioration of the NOx catalyst is small, the NOx catalyst purifies the excessive reducing component with sufficiently high efficiency even if excessive reducing component flows into the NOx catalyst due to the air-fuel ratio A / FEHT of the exhaust gas. To do. For this reason, in the present embodiment, for example, an index (hereinafter referred to as a catalyst deterioration index) CATDG that represents the degree of deterioration of the NOx catalyst as a numerical value, such as the usage period of the NOx catalyst, the total flow rate of exhaust gas that has passed through the NOx catalyst, and the like is calculated. If the catalyst deterioration index CATDG is equal to or greater than a predetermined value, the setting of the standby time TS is cancelled.

  In the present embodiment, when the pre-processing and the S processing are executed, feedback control based on the detection signal of the oxygen concentration sensor 60 is performed to converge the exhaust air-fuel ratio A / FEHT to the target value. Then, when the pre-processing or S-processing is executed, the measured value (oxygen concentration sensor) of the air-fuel ratio of the exhaust corresponding to the operating state of various elements of the engine 1 (fuel injection valve 13, fuel addition valve 14, throttle valve 31, etc.) 60) Value based on 60 signal) Deviation between A / FEHT and target value is monitored, and the deviation is stored as learning value FAFG. Then, when preprocessing or S processing is executed after the next time, the operation of the fuel injection valve 13, the fuel addition valve 14, the throttle valve 31, and the like is corrected using the learning value FAFG. Thereby, the convergence speed and accuracy to the target value of the air-fuel ratio A / FEHT of the exhaust in the pretreatment and the S treatment are increased. For this reason, in the present embodiment, when the learning value FAFG has already been set (when the learning value FAFG has already been stored), the setting of the waiting time TS is cancelled. Note that the learning value FAFG is preferably set as a different numerical value for each operation region of the engine 1 (operation region defined by the load, the rotational speed, etc.).

[Specific procedure for S release treatment]
FIG. 3 is a flowchart showing a specific procedure (routine) of the S release process according to the present embodiment. This routine is repeatedly executed every predetermined time through the ECU 50 after the engine 1 is started.

In this routine, the ECU 50 first acquires various information (for example, the fuel injection amount Q, the engine speed NE, etc.) reflecting the operating state of the engine 1 in step S101.
In the following step S102, the ECU 50 determines whether or not there is currently a request for S release processing, in other words, whether or not a sulfur component exceeding a predetermined amount is accumulated in the NOx catalyst. If the determination in step S102 is affirmative, the processing by the ECU 50 proceeds to step S103. If the determination in step S102 is negative, the process by the ECU 50 temporarily exits this routine. It should be noted that the S release process is not performed at the present time and the necessity thereof is not recognized, but the S release process has been performed up to the present time, and a sufficient amount of sulfur component has already been released from the NOx catalyst. Even in such a situation, a negative determination is made in step S102. Further, if the preprocessing or the S process is being executed when a negative determination is made in step S102, the ECU 50 interrupts (or terminates) the preprocessing and the S process that are being executed.

  In step S103, the ECU 50 starts preprocessing (or continues execution of preprocessing). Note that the ECU 50 sets a standby time TS commensurate with the operating state of the engine 1 simultaneously with the start of preprocessing, and starts time measurement.

  In a series of subsequent steps S104, S105, and S106, the ECU 50 determines whether or not the intake air amount GA is equal to or greater than a predetermined value γ (S104), whether the catalyst deterioration index CATDG is equal to or greater than a predetermined value δ (S105), It is determined whether air-fuel ratio learning is incomplete (S106). If an affirmative determination is made in all of steps S104, S105, and S106, the processing by the ECU 50 proceeds to step S107. On the other hand, when a negative determination is made in any of steps S104, S105, and S106, the processing by the ECU 50 jumps to step S108. In step S108, the ECU starts the S process (or continues the execution of the S process).

  In step S107, the ECU 50 determines whether or not the preprocessing duration tx is equal to or longer than the standby time TS (set when starting the current preprocessing), and the determination is affirmative. In step S108, the S process is started (or the execution of the S process is continued). On the other hand, if the determination in step S107 is negative, the process by the ECU 50 temporarily exits this routine.

  According to the NOx catalyst management method in which the S treatment control is performed according to such a procedure, after the start of the S treatment, the air-fuel ratio A / FEHT of the exhaust gas is quickly set to the target value (in order to release the sulfur component accumulated in the NOx catalyst). Can be converged to a suitable value). For example, the air-fuel ratio A / FEHT of the exhaust does not decrease excessively (become rich) with the start of the S process. Therefore, generation | occurrence | production of the white smoke and sulfur smell in the initial stage after the start of S process is suppressed effectively.

  Further, the controllability of the air-fuel ratio of the exhaust by the second process can be improved based on a simple control structure in which the standby time TS is set based on the operating state of the engine 1. For example, a complicated control structure for confirming the stability of the exhaust air-fuel ratio A / FEHT is not required.

  Also, under certain conditions (“GA <γ”, “CATDG <δ”, or “learning value FAFG is set”), the sulfur component accumulated in the NOx catalyst is released by releasing the waiting time TS. The time required for the process to be performed can be shortened as a whole. Thereby, the consumption of the fuel or reducing agent required for the same process can be reduced.

  In the present embodiment, the standby time TS is determined based on the operating state of the engine 1 at the start of the preprocessing. On the other hand, even if a predetermined numerical value is adopted, an effect equivalent to this embodiment can be obtained. Further, the standby time TS may be expanded and contracted sequentially in response to a change in the operating state of the engine 1 after the start of preprocessing (during execution).

  Further, instead of the control structure for setting the standby time TS, after the start of the preprocessing, for example, the fluctuation range of the output of the oxygen concentration sensor 60 is monitored, and the air-fuel ratio of the exhaust gas is sufficiently stabilized (the air-fuel ratio of the exhaust gas is sufficient S processing may be started when it is determined that the target value has been converged. In this case, although the control structure is complicated, the control precision is further improved.

  Further, for example, an oxygen concentration sensor or the like is installed downstream of the NOx catalyst in the exhaust passage 40, and the catalyst deterioration index CATDG is calculated by referring to the transition history of the detection signal of the oxygen concentration sensor corresponding to the operating state of the engine 1. May be.

  In step S104 of the S process control routine, the condition that “the amount of intake air is greater than or equal to a predetermined value” is employed. Instead of this, any parameter relating to the intake air amount is greater than or equal to a predetermined value, such as “the accelerator pedal depression amount is greater than or equal to a predetermined value” or “the fuel injection amount through the fuel injection valve 13 is greater than or equal to a predetermined value”. Other conditions of “Yes” may be set.

  Further, the learning value FAFG adopted for the condition setting in step S106 of the S process control routine is a parameter that is set when the feedback control based on the detection signal of the oxygen concentration sensor 60 is executed. However, the present invention is not limited to this, and other parameters may be adopted as having the same significance as the learning value FAFG as long as it relates to the amount of change in the air-fuel ratio of the exhaust caused by the execution of preprocessing.

Further, as the NOx catalyst, various materials having a function of reducing NOx in the exhaust are used, and an effect equivalent to or equivalent to the present embodiment can be achieved.
[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS.

  FIG. 4 shows a schematic configuration of the engine 1 in this embodiment. The engine 1 is obtained by adding an EGR mechanism 71 to the engine 1 of the first embodiment, and the parts other than the parts related to the EGR mechanism 71 are the same as the engine 1. The EGR mechanism 71 opens and closes the EGR passage 72 that connects the upstream portion of the exhaust passage 40 with respect to the catalyst casing 41 to the downstream portion of the intake passage 30 with respect to the throttle valve 31 and the flow area of the EGR passage 72 is variable. And an EGR valve 73 for adjusting the flow rate of the EGR gas.

  The ECU 50 performs the opening degree control of the throttle valve 31 and the opening degree control of the EGR valve 73 based on the operating state of the engine 1. For example, the EGR valve 73 is opened so that the intake air amount becomes a target intake air amount (target value per one rotation of the engine 1) set based on the engine load (or fuel injection amount) and the engine speed NE. Intake air amount feedback control in which the degree is adjusted is performed. Further, EGR for adjusting the opening of the throttle valve 31 and the opening of the EGR valve 73 so that the EGR rate becomes a target EGR rate set based on the engine load (or fuel injection amount) and the engine speed NE. Control is performed.

  In the engine 1, the combustion mode associated with EGR control can be switched between two types of combustion modes, a normal combustion mode and a low-temperature combustion mode. Here, the low temperature combustion mode is a combustion mode in which NOx and smoke are simultaneously reduced by slowing the increase in combustion temperature by introducing a large amount of EGR gas into the combustion chamber 20. The combustion mode other than this is a normal combustion mode in which normal EGR control (including the case where EGR is not performed) is executed. In the low-temperature combustion mode, the amount of air sucked into the combustion chamber 20 decreases with the introduction of a large amount of EGR gas into the combustion chamber 20, so the air-fuel ratio A / F of the air-fuel mixture provided for combustion of the engine 1 As a result, the air-fuel ratio A / FEHT of the exhaust gas also decreases accordingly. In this embodiment, the pretreatment for reducing the air-fuel ratio A / FEHT of the exhaust gas to the air-fuel ratio pretreatment value α is realized by executing the low temperature combustion mode.

  By the way, in the low temperature combustion mode and the normal combustion mode, the optimum values of parameters of the fuel injection system in the engine 1, for example, parameters such as fuel injection timing, fuel injection pressure, and fuel injection amount are different. When switching between the two is performed, the parameter of the fuel injection system is also changed to an optimum value corresponding to the combustion mode after switching. For example, when switching from the normal combustion mode to the low temperature combustion mode, the fuel injection timing is changed to the advance side, the fuel injection pressure is changed to the increase side, and the fuel injection amount is changed to the increase side. As described above, the fuel injection timing is changed to the advance side and the fuel injection pressure is changed to the increase side in the low temperature combustion mode because a large amount of EGR gas exists in the combustion chamber 20 and the ignitability to the fuel is increased. This tends to decrease and is intended to improve the ignitability. The reason for changing the fuel injection amount to the increase side is that the output torque of the diesel engine 1 tends to decrease with the introduction of a large amount of EGR gas into the combustion chamber 20 in the low temperature combustion mode. It is for suppressing.

  Next, a specific procedure (routine) of the S release process according to the present embodiment will be described with reference to the flowchart of FIG. This routine is executed for each fuel injection in the engine 1 through the ECU 50. In this routine, processes (S203, S207, S210) other than the processes (S201, S203 to S206, S208, S210) corresponding to steps S101, S103 to S106, S108, and S110 in the flowchart of FIG. 3 in the first embodiment. S211) is different from the first embodiment.

  In FIG. 5, in step S201, various information reflecting the operating state of the engine 1 is acquired, and in step S202, it is determined whether there is a request for S release processing. If an affirmative determination is made here, the low temperature combustion mode for executing the S process is started (or the execution of the low temperature combustion mode is continued) as the process of step S203. By executing such a low temperature combustion mode, pre-processing is realized, and the air-fuel ratio A / FEHT of the exhaust gas decreases toward the air-fuel ratio pre-processing value α. Further, in the process of step S203, after the start of the low temperature combustion mode (pre-process), the permission flag F for determining whether or not to execute the S process is “1 (permitted)” under a predetermined condition. Set to When a negative determination is made in step S202, if the low temperature combustion mode (pre-processing) or the S processing is being executed, they are interrupted or terminated. Further, the permission flag F is set to “0 (prohibited)” (S211).

  In a series of steps S204, S205, and S206 following step S203, whether or not the intake air amount GA is equal to or greater than a predetermined value γ (S204), whether or not the catalyst deterioration index CATDG is equal to or greater than a predetermined value δ (S205), It is determined whether or not air-fuel ratio learning is incomplete (S206). If all of them are positive, the process proceeds to step S207. In the process of step S207, it is determined whether or not the permission flag F for determining whether or not to execute the S process is “1 (permitted)”. For this reason, after execution of the low-temperature combustion mode, if the permission flag F becomes “1 (permitted)” under a predetermined condition, an affirmative determination is made in step S207. If the determination in step S207 is affirmative, the process proceeds to step S208 where the S process is executed (or the S process is continued), and intermittent fuel addition through the fuel addition valve 14 is performed.

  On the other hand, if a negative determination is made in any of steps S204, S205, and S206, the process jumps to step S208 to perform the S process regardless of whether or not the permission flag F is “1 (permitted)”. Executed.

Here, an outline of a procedure for setting the permission flag F to “1 (permission)” will be described with reference to the time chart of FIG. 6.
The permission flag F is set to “1 (permitted)” under a predetermined condition after the start of the low-temperature combustion mode for executing the S process. In this low temperature combustion mode, in order to introduce a large amount of EGR gas into the combustion chamber 20, the throttle valve 31 is controlled to the closed side and the EGR valve 73 is controlled to the open side as compared with the execution of the normal combustion mode. Further, the parameters of the fuel injection system such as the fuel injection timing, the fuel injection pressure, and the fuel injection amount are also controlled to values suitable for the low temperature combustion mode.

  As shown in FIG. 6A, if the low temperature combustion mode for executing the S process is started at timing t3, the target opening of the throttle valve 31 changes to the closing side at that timing (FIG. 6). (Solid line in (c)), the target opening degree of the EGR valve 73 changes to the open side (solid line in FIG. 6 (d)). Thereafter, the actual opening of the throttle valve 31 gradually changes to the closed side with a predetermined response delay with respect to the change of the target opening (dashed line in FIG. 6C), and the actual opening of the EGR valve 73 also changes to the target opening. It gradually changes to the closing side with a predetermined response delay with respect to the change in the degree (broken line in FIG. 6 (d)). Furthermore, a response delay occurs even when the flow rate of the EGR gas changes to the increase side with respect to the change in the actual opening of the throttle valve 31 and the EGR valve 73.

  As described above, a response delay occurs in the increase in the flow rate of the EGR gas accompanying the start of the low temperature combustion mode. On the other hand, the parameters of the fuel injection system can be changed to values suitable for the low temperature combustion mode with almost no response delay. Is possible. Therefore, when the change of each parameter is started simultaneously with the start of the low temperature combustion mode (t3), the change of each parameter is completed in a state where the flow rate of EGR gas has not been changed, and the change of the flow rate of EGR gas is changed. Until the completion, there is a problem that each of the parameters becomes a value not corresponding to the flow rate of the EGR gas.

  For this reason, the change of each parameter is started with a predetermined delay from the start (t3) of the low temperature combustion mode, that is, with a delay corresponding to the response delay of the EGR gas flow rate. Specifically, a delay counter C1 that is decremented for each fuel injection of the engine 1 is set to an initial value greater than “0” as shown in FIG. 6B at timing t3, and the delay counter C1 When the value reaches “0” (timing t4), the change of each parameter is started. Thus, by delaying the start of changing each parameter, it is possible to suppress the occurrence of the above-described problems.

  Moreover, the predetermined period after the start of the change of each parameter is a gradual change period for gradually changing these parameters. The reason for setting such a gradual change period is to avoid a sudden change of each parameter and to suppress a shock or the like accompanying the sudden change. The gradual change counter C2 in FIG. 6 (e) is for setting the gradual change period. The gradual change counter C2 is set to an initial value larger than “0” when the delay counter C1 reaches “0” (timing t4), and is decremented for each fuel injection of the engine 1. A period (t4 to t5) in which the gradual change counter C2 is larger than “0” is the gradual change period, and the initial change of the gradual change counter C2 is completed so that the change of each parameter is completed during the gradual change period. Value is set. FIG. 6F shows the transition of the fuel injection amount, which is one of these parameters, during the gradual change period.

  In the present embodiment, when the gradual change counter C2 decreases to a predetermined value, for example, when it decreases to “0” (timing t5), the permission flag F is set to “1 (permission) as shown in FIG. To "". Then, as the permission flag F is set to “1”, when an affirmative determination is made in step S207 of FIG. 5, the S process of step S208 is started. In this case, the S process is performed after the permission flag F becomes “1” after the start of the low temperature combustion mode (pre-processing). Accordingly, after the low temperature combustion mode is started and until the permission flag F becomes “1”, in other words, while the gradual change counter C2 is larger than “0”, the S process is not performed, and the exhaust air is empty during that time. The fuel ratio A / FEHT tends to stabilize. Therefore, the S process starts after the air-fuel ratio A / FEHT of the exhaust gas is stabilized, and the convergence of the air-fuel ratio A / FEHT to the target value after the start of the S process is quickly performed. Can be.

  By the way, during the above-described gradual change period, that is, during the period when the gradual change counter C2 is larger than “0”, the gradual change of the fuel injection amount to the increase side is performed every fuel injection. The increase in the fuel injection amount for each fuel injection affects the air / fuel ratio A / FEHT of the exhaust gas during execution of the low temperature combustion mode (pretreatment). Here, since the gradual change counter C2 is decremented for each fuel injection, the gradual change counter C2 has a value related to the influence on the air-fuel ratio A / FEHT of the exhaust gas accompanying the increase of the fuel injection amount for each fuel injection. In the present embodiment, the S process is started in accordance with the gradual change counter C2, that is, based on the gradual change counter C2 becoming “0”. In the engine 1 in which the injection amount is increased, the S process can be started at an appropriate timing related to the exhaust air-fuel ratio A / FEHT.

  Next, details of the procedure for setting the permission flag F to “1 (permission)” will be described based on the flowchart showing the low-temperature combustion execution routine of FIGS. 7 and 8. This low temperature combustion execution routine is executed every time the process proceeds to step S203 in the flowchart of FIG.

  In the low temperature combustion execution routine, it is first determined whether or not it is the start time of the low temperature combustion mode (S301 in FIG. 7). If the determination here is affirmative, an opening change of the throttle valve 31 and the EGR valve 73 for increasing the EGR rate is instructed (S302), thereby introducing a large amount of EGR gas into the combustion chamber 20 in the low temperature combustion mode. Is started. Subsequently, as an initial setting of the delay counter C1, the counter C1 is set to an initial value (S303). The delay counter C1 set to the initial value in this way is decremented in the process of step S105 when it is determined in step S304 that “C1 = 0” is not satisfied (S305). Accordingly, the delay counter C1 after being set to the initial value is decremented for each fuel injection and approaches “0”.

  When the delay counter C1 reaches “0” (S304: YES), it is determined whether or not it is immediately after the counter C1 becomes “0” (S306). If the determination here is affirmative, an instruction is given to change the parameters of the fuel injection system such as fuel injection timing, fuel injection pressure, and fuel injection amount to values corresponding to the low-temperature combustion mode (S307), and then the gradual change counter C2 As an initial setting, the counter C2 is set to an initial value (S308). When the gradual change counter C2 is set to the initial value, it is determined in step S309 in FIG. 8 that “C2 = 0” is not satisfied, and the gradual change toward the values corresponding to the low-temperature combustion mode of the respective parameters is executed. At the same time (S310), the gradual change counter C2 is decremented (S311). Accordingly, when the fuel injection amount, which is one of the above parameters, is gradually increased for each fuel injection as a gradual change toward the value corresponding to the low temperature combustion mode, the gradual change counter C2 is also added for each fuel injection. Is decremented to approach “0”.

  When the gradual change counter C2 reaches “0” (S309: YES), it is determined whether or not it is immediately after the counter C2 becomes “0” (S312). If the determination here is affirmative, the permission flag F is set to “1 (permitted)”. As the permission flag F is set to “1” in this way, when an affirmative determination is made in step S207 of FIG. 5, the S process of step S208 is executed.

According to the present embodiment described in detail above, the following effects can be obtained in addition to the effects of the first embodiment.
After the start of the low-temperature combustion mode (pre-processing) for executing the S process, the fuel injection amount is increased for each fuel injection toward the value corresponding to the low-temperature combustion mode, and the fuel injection for each fuel injection at that time The increase in the amount affects the air-fuel ratio A / FEHT of the exhaust. However, in response to the increase in the fuel injection amount, the S process is started in accordance with the gradual change counter C2 that is decremented for each fuel injection, that is, based on the counter C2 becoming “0”. Even in the engine 1 in which the fuel injection amount is increased in accordance with the execution of the combustion mode, the S process can be started at an appropriate timing.

  When the start timing of the S process is not appropriate, for example, when the start timing is too early, the air-fuel ratio A / FEHT of the exhaust gas in the low-temperature combustion mode (pre-processing) is set to the air-fuel ratio pre-processing value α. In a state where the reduction of the fuel is not progressing, the reducing agent (fuel) is added from the fuel addition valve 14 to the upstream of the NOx catalyst by the S treatment. For this reason, a large amount of the reducing agent is required to reduce the exhaust air-fuel ratio A / FEHT to a value at which the sulfur component accumulated in the NOx catalyst can be released, and accordingly, the catalyst bed temperature increases and the exhaust air-fuel ratio A / Failure such as deterioration of controllability of FEHT occurs. According to the present embodiment, it is possible to suppress the occurrence of such a problem.

1 is a schematic configuration diagram showing a Diese engine according to a first embodiment of the present invention. The time chart which shows transition of the air fuel ratio of exhaust gas observed during S process control. The flowchart which shows the specific procedure of S process control concerning 1st Embodiment. The schematic block diagram which shows the Diese engine concerning the 2nd Embodiment of this invention. The flowchart which shows the specific procedure of S process control concerning 2nd Embodiment. (A)-(g) is a time chart which shows the change mode of the combustion mode at the time of execution of S process, the opening degree of a delay counter, a throttle valve, and an EGR valve, a gradual change counter, a fuel injection amount, and the permission flag F. The flowchart which shows the execution procedure of low temperature combustion mode, and the setting procedure of the permission flag F. FIG. The flowchart which shows the execution procedure of low temperature combustion mode, and the setting procedure of the permission flag F. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 10 ... Fuel supply system, 11 ... Supply pump, 12 ... Common rail, 13 ... Fuel injection valve, 14 ... Fuel addition valve, 20 ... Combustion chamber, 30 ... Intake passage, 31 ... Throttle valve, 40 ... Exhaust 1. Passage, 41 ... Catalyst casing, 50 ... Electronic control unit (ECU), 60 ... Oxygen concentration sensor, P1 ... Engine fuel passage, P2 ... Addition fuel passage, 71 ... EGR mechanism, 72 ... EGR passage, 73 ... EGR valve.

Claims (7)

A method for managing a NOx catalyst provided in an exhaust passage of a diesel engine to reduce NOx in exhaust gas,
The NOx catalyst is executed by executing a first process for reducing the air-fuel ratio of the air-fuel mixture provided for combustion of the engine and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage. A step of releasing the sulfur component accumulated in the
In the step, after the start of the first processing, the second processing is started on the condition that a predetermined period required for stabilizing the air-fuel ratio of the exhaust gas upstream of the NOx catalyst in the exhaust passage has elapsed. And
The NOx catalyst management method , wherein the condition is canceled when a parameter relating to an intake air amount of the engine is less than a predetermined value . A method for managing a NOx catalyst provided in an exhaust passage of a diesel engine to reduce NOx in exhaust gas,
The NOx catalyst is executed by executing a first process for reducing the air-fuel ratio of the air-fuel mixture provided for combustion of the engine and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage. A step of releasing the sulfur component accumulated in the
In the step, after the start of the first processing, the second processing is started on the condition that a predetermined period required for stabilizing the air-fuel ratio of the exhaust gas upstream of the NOx catalyst in the exhaust passage has elapsed. And
Wherein when the parameter relating to the degree of deterioration of the NOx catalyst is lower than the predetermined value, the management method of N Ox catalyst you and cancels the condition. A method for managing a NOx catalyst provided in an exhaust passage of a diesel engine to reduce NOx in exhaust gas,
The NOx catalyst is executed by executing a first process for reducing the air-fuel ratio of the air-fuel mixture provided for combustion of the engine and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage. A step of releasing the sulfur component accumulated in the
In the step, after the start of the first processing, the second processing is started on the condition that a predetermined period required for stabilizing the air-fuel ratio of the exhaust gas upstream of the NOx catalyst in the exhaust passage has elapsed. And
Detecting a change amount of the air-fuel ratio upstream of the NOx catalyst in the exhaust passage based on the first process, and learning the change amount;
Wherein after completion of the learning, the management method of N Ox catalyst you and cancels the condition. A method for managing a NOx catalyst provided in an exhaust passage of a diesel engine to reduce NOx in exhaust gas,
The NOx catalyst is executed by executing a first process for reducing the air-fuel ratio of the air-fuel mixture provided for combustion of the engine and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage. A step of releasing the sulfur component accumulated in the
In the step, after the start of the first process, the second process is performed on the condition that a counter decremented for each fuel injection of fuel supplied to the combustion of the diesel engine becomes a predetermined value or less. Start,
If the parameter relating to intake air amount of the engine is less than a predetermined value, N Ox managing a catalyst you and cancels the condition. A method for managing a NOx catalyst provided in an exhaust passage of a diesel engine to reduce NOx in exhaust gas,
The NOx catalyst is executed by executing a first process for reducing the air-fuel ratio of the air-fuel mixture provided for combustion of the engine and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage. A step of releasing the sulfur component accumulated in the
In the step, after the start of the first process, the second process is performed on the condition that a counter decremented for each fuel injection of fuel supplied to the combustion of the diesel engine becomes a predetermined value or less. Start,
Wherein when the parameter relating to the degree of deterioration of the NOx catalyst is lower than the predetermined value, the management method of N Ox catalyst you and cancels the condition. A method for managing a NOx catalyst provided in an exhaust passage of a diesel engine to reduce NOx in exhaust gas,
The NOx catalyst is executed by executing a first process for reducing the air-fuel ratio of the air-fuel mixture provided for combustion of the engine and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage. A step of releasing the sulfur component accumulated in the
In the step, after the start of the first process, the second process is performed on the condition that a counter decremented for each fuel injection of fuel supplied to the combustion of the diesel engine becomes a predetermined value or less. Start,
Detecting a change amount of the air-fuel ratio upstream of the NOx catalyst in the exhaust passage based on the first process, and learning the change amount;
Wherein after completion of the learning, the management method of N Ox catalyst you and cancels the condition. A method for managing a NOx catalyst provided in an exhaust passage of a diesel engine to reduce NOx in exhaust gas,
The NOx catalyst is executed by executing a first process for reducing the air-fuel ratio of the air-fuel mixture provided for combustion of the engine and a second process for adding a reducing agent upstream of the NOx catalyst in the exhaust passage. A step of releasing the sulfur component accumulated in the
In the step, after the start of the first process, the second process is started on the condition that the air-fuel ratio of the exhaust upstream of the NOx catalyst in the exhaust passage is stabilized,
The diesel engine can be switched to a low-temperature combustion mode in which a large amount of EGR gas is introduced into the combustion chamber, and a counter that is decremented each time fuel is injected into the engine after the start of the low-temperature combustion mode. Between the initial value and “0”, the fuel injection amount of the engine is gradually increased to a predetermined value,
The first process is realized by switching to the low temperature combustion mode,
Wherein after the start of the low temperature combustion mode, management of N Ox catalyst you characterized in that said counter is to the condition that falls below a predetermined value.

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