KR20150119366A - Controlling device for internal combustion engines - Google Patents

Abstract

A control device for an internal combustion engine is a control device for an internal combustion engine provided with a filter downstream of a catalyst having an oxidizing function, characterized in that when the PM regeneration request of the filter is satisfied, the exhaust temperature is lower than the PM oxidation start temperature, And a control unit for maintaining the temperature at or above the PM oxidation start temperature after the exhaust gas at the time of completion of the PM regeneration to the current time of the PM regeneration request or at the sulfur elimination temperature higher than the maximum attainable temperature of the catalyst for a predetermined period. By doing so, abrupt desorption of sulfur can be avoided, and the occurrence of white smoke can be suppressed.

Description

[0001] CONTROLLING DEVICE FOR INTERNAL COMBUSTION ENGINES [0002]

The present invention relates to a control apparatus for an internal combustion engine.

Conventionally, it has been known that when the particulate matter (PM) accumulation amount is large when performing the sulfur release treatment of the oxidation catalyst, the filter is subjected to a room temperature treatment. As a document related to this, for example, there is Patent Document 1. It is known that SO ₂ (sulfur dioxide) contained in the exhaust gas of the internal combustion engine becomes SO ₃ (sulfur trioxide) in the oxidation catalyst and reacts with H ₂ O (water) to become H ₂ SO ₄ . H ₂ SO ₄ may become white smoke (sulfate white smoke) and be discharged to the atmosphere in some cases. Patent Document 1 does not disclose such a chemical reaction.

Japanese Patent Application Laid-Open No. 2009-299572

As described above, SO ₃ becomes H ₂ SO ₄ by reacting with H ₂ O. The oxidation catalyst also has a property of adsorbing SOx. Therefore, there is a possibility that a large amount of white smoke is generated when a filter (for example, DPF; Diesel Particulate Filter) provided together with the oxidation catalyst and satisfying the PM is regenerated. That is, there is a possibility that the sulfur component (S component) included in the fuel burned in the internal combustion engine and the adsorbed SOx adsorbed on the oxidation catalyst and desorbed due to the increase of the exhaust temperature accompanied by the PM regeneration request become white smoke.

Therefore, the internal combustion engine control device disclosed in this specification is intended to suppress the occurrence of white smoke due to sulfur elimination during PM regeneration.

In order to solve such a problem, the control apparatus for an internal combustion engine disclosed in this specification is a control apparatus for an internal combustion engine having a filter provided downstream of a catalyst having an oxidizing function. When a PM regeneration request of the filter is established, Temperature is lower than the PM oxidation start temperature and is maintained at a sulfur removal temperature higher than the maximum temperature of the exhaust gas at the time of the completion of the PM regeneration from the time of the completion of the PM regeneration to the time of the present regeneration of the PM regeneration, And a control unit for controlling the temperature to be higher than the temperature. Wherein the control unit is configured to set the sulfur removal temperature higher than the maximum reachable temperature when the maximum attained temperature is lower than or equal to a permissible switching temperature at which the conversion rate of SO ₂ to SO ₃ in the catalyst becomes lower than a permissible value, The temperature can be set to any temperature below the allowable temperature.

Sulfur deposited and adsorbed on the catalyst is heated to a temperature higher than the temperature at the time of its deposition and adsorption, thereby initiating desorption. Therefore, the sulfur can be desorbed only when the temperature reaches the maximum attained temperature in the exhaust temperature history from the completion of the previous PM reproduction to the request for generation of the current filter. Therefore, when the filter is regenerated to be at the PM oxidation start temperature from the beginning when there is a request to regenerate the sulfur, the sulfur can be desorbed. However, the higher the temperature, the faster the desorption of sulfur and the faster the release rate of sulfur. As a result, there is a possibility of causing the occurrence of white smoke.

Therefore, sulfur (S) adsorbed to the catalyst is desorbed and maintained at a lowest temperature at which the exhaust gas can be released, that is, at a desulfurization temperature for a certain period of time. After the sulfur is desorbed and released, the exhaust temperature . This makes it possible to suppress the occurrence of white smoke at the time of sulfur elimination and the occurrence of white smoke at the time of PM regeneration.

Wherein, when the the maximum attained temperature, the less switching allowable temperature from the SO ₂ conversion rate of the SO ₃ which is below the allowable value in the catalyst, it is possible to set the sulfur desorption temperature to the switching allowable temperature.

When the maximum reachable temperature is equal to or lower than the switching permitting temperature, the sulfur elimination temperature can be set within a range below the permissible switching temperature. SO ₃ , which is a cause of white smoke, is generated by oxidation of SO ₂ . The conversion rate from SO ₂ to SO ₃ is influenced by the exhaust temperature. Therefore, if the sulfur elimination temperature is set within the range of the allowable transition temperature or lower, the white smoke can be suppressed within the allowable range. The desulfurization temperature is required to be higher than the maximum attained temperature, and the higher the temperature is, the higher the efficiency of desulfurization is. Taking these into consideration, when the maximum attained temperature is lower than the switching permitting temperature, by setting the sulfur elimination temperature to the switching permitting temperature, it is possible to perform efficient sulfur elimination while suppressing the white smoke to an allowable range. By setting the desulfurization temperature to the above-mentioned transition permitting temperature, the desulfurization can be accelerated while effectively suppressing the occurrence of white smoke.

The control unit may raise the temperature of the exhaust gas or the temperature of the catalyst step by step until the sulfur removal temperature is reached. As a result, sulfur having a different deposition temperature can be desorbed while suppressing the occurrence of white smoke.

Wherein when the PM regeneration request of the filter is satisfied and there is a request for increasing the exhaust temperature on the downstream side of the catalyst, the control unit sets the oxygen concentration in the exhaust gas flowing into the catalyst to the fuel It is possible to lower the oxygen concentration to the upper limit threshold value of the oxygen concentration according to the S concentration value.

Oxygen is required when regenerating a filter disposed in the exhaust passage and disposed downstream of the catalyst having an oxidizing function. On the other hand, if the oxygen concentration is excessively high, the SO ₂ produced due to the combustion of the fuel containing the S component is oxidized to produce SO ₃ . Likewise, the sulfur (S) component deposited on the catalyst or filter is also removed and oxidized to SO ₃ . In this way, the generated SO ₃ is, in conjunction with H ₂ O is in H ₂ SO ₄ is a fine mist, i.e., white smoke. Therefore, when the exhaust temperature rise request is recognized in order to regenerate the substance deposited on the filter, mainly PM (Particulate Matter), control for lowering the oxygen concentration is performed. Thus, the occurrence of white smoke can be suppressed.

According to the control apparatus for an internal combustion engine disclosed in this specification, it is possible to suppress the occurrence of white smoke attributable to sulfur elimination during PM regeneration.

1 is an explanatory view showing a schematic structure of an internal combustion engine according to an embodiment.
2 is a flowchart showing an example of the control performed by the control apparatus of the internal combustion engine in the embodiment.
3 is a graph showing the relationship between the exhaust temperature and the SO ₃ conversion rate.
4 is a graph showing the relationship between the S accumulation temperature and the S-elimination temperature.
5 is a flowchart showing an example of the control performed by the control apparatus of the internal combustion engine in the embodiment.
6 is an example of a time chart of PM regeneration performed by the control apparatus of the internal combustion engine in the embodiment.
7 is an explanatory diagram showing the relationship between the amount of S deposited and the concentration of fuel S;
Fig. 8 is a graph showing the relationship between the fuel S concentration value and the white smoke suppression target A / Ftrg.
9 is a graph showing occurrence of white smoke.
10 is a graph showing the relationship between the fuel S concentration value and the white smoke suppression control execution period τ trg.
11 is a graph showing the influence of A / F on white smoke during PM regeneration.
FIG. 12A is an explanatory view schematically showing a state in which a fixed value candidate for each destination is stored in advance. FIG. 12B is a diagram schematically showing a state in which a fixed value is set in accordance with a destination, Fig.
13 is a graph showing an example of change in exhaust temperature between PM regeneration intervals.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, and the like of the respective parts may not be shown so as to be completely matched with actual ones. Further, there are cases in which details are omitted according to the drawings.

(Embodiments)

1 is an explanatory view showing a schematic structure of an internal combustion engine 1 of an embodiment. The internal combustion engine 1 includes an engine main body 2 and a control device (hereinafter referred to as a control device) 3 for an internal combustion engine. An intake passage 4 and an exhaust passage 5 are connected to the engine main body 2. One end of an exhaust gas recirculation (EGR) passage 6 is connected to the engine main body 2. The other end of the EGR passage 6 is connected to the intake passage. In the EGR passage 6, an EGR cooler 7 and an EGR valve 8 are disposed. In the intake passage 4, a throttle 9 is disposed. In the exhaust passage 5, a DOC (Diesel Oxidation Catalyst) 10 is disposed. The DOC 10 is a catalyst having an oxidizing function and is included in the internal combustion engine 1. A DPF (Diesel Particulate Filter) 11 is disposed downstream of the DOC 10 in the exhaust passage. The DPF 11 is a filter that replenishes the PM and is included in the internal combustion engine 1.

An SOx sensor 12, an exhaust adding fuel valve 13 and a first temperature sensor 14 are arranged in this order from the upstream side in the exhaust passage 5 between the engine main body 2 and the DOC 10. The SOx sensor 12 together with the A / F sensor 17 described later calculates the S concentration value (hereinafter referred to as the fuel S concentration) in the fuel combusted in the internal combustion engine 1, more specifically the engine body 2 ). The exhaust adding fuel valve 13 injects fuel into the exhaust passage 5, thereby adding fuel to the exhaust gas. The exhaust gas to which the fuel is added is burnt in the DOC 10, and becomes a high temperature exhaust gas. The first temperature sensor 14 measures the temperature of the exhaust gas (DOC temperature, catalyst-containing gas temperature) introduced into the DOC 10.

A second temperature sensor (15) is disposed in the exhaust passage (5) between the DOC (10) and the DPF (11). The second temperature sensor 15 measures the temperature (DPF temperature) Tex of the exhaust gas introduced into the DPF 11. In the following description, the temperature of the exhaust gas will be described as the exhaust temperature Tex.

A third temperature sensor 16 and an A / F sensor 17 are arranged in this order from the upstream side in the exhaust passage 5 on the downstream side of the DPF 11. [ The third temperature sensor 16 measures the temperature of the exhaust gas discharged from the DPF 11. From the measured value of the third temperature sensor 16 and the measured value of the second temperature sensor 15, the DPF temperature, that is, the room temperature Tm of the catalyst is grasped. Alternatively, the catalyst temperature Tm may be set to the DOC temperature, or a value having a correlation with these values may be used to obtain the room temperature Tm of the catalyst.

In the control device 3 of the present embodiment, as described later in detail, the exhaust gas temperature at the time from the completion of the previous PM-regeneration to the current-time PM regeneration request or the sulfur elimination temperature For a certain period of time. Here, when defining the maximum attained temperature, either the exhaust temperature Tex or the room temperature Tm of the catalyst may be taken into consideration. Since the sulfur component to be desorbed is deposited and adsorbed on the catalyst, the room temperature of the catalyst is directly involved. However, since the exhaust temperature and the room temperature of the catalyst are correlated, any one of the temperatures may be taken into account . In the following description, the exhaust temperature Tex is unified.

The A / F sensor 17 measures the exhaust A / F. The A / F sensor 17 is included in the means for acquiring the fuel S concentration value together with the SOx sensor 12, as described above. The fuel S concentration value and the SOx concentration in exhaust gas have a correlation. Therefore, the fuel S concentration can be calculated from the SOx concentration value in the exhaust gas detected by the SOx sensor 12 and the exhaust A / F. Because addition, SOx discharged from the engine body 2 is almost the SO _2, SOx sensor, you can use the SO ₂ Sensor.

The internal combustion engine 1 is provided with an ECU (Electronic Control Unit) The ECU 18 performs various controls in the internal combustion engine 1. The ECU 18 is also included in the control device 3 and functions as a control section of the control device 3. [ The ECU 18 controls the EGR valve 8, the throttle 9, the SOx sensor 12, the exhaust adding fuel valve 13, the first temperature sensor 14, the second temperature sensor 15, And is electrically connected to the sensor 16 and the A / F sensor 17 to form the control device 3. [ The ECU 18 acquires the PM accumulation amount. Specifically, the ECU 18 calculates the PM accumulation amount in the DPF 11 from the operating pattern of the internal combustion engine 1 (running pattern of the vehicle). Then, it is judged whether or not the PM regeneration request is established. Further, the ECU 18 continuously records the exhaust temperature Tex, and obtains the maximum reached temperature TexMAX of the exhaust temperature from the completion of the previous PM reproduction to the current PM regeneration request.

The ECU 18 functioning as the control unit performs the PM regeneration based on the exhaust temperature rise request on the downstream side of the DOC 10, more specifically, the PM regeneration request in the DPF 11. When the regeneration request of the DPF 11 is established, the ECU 18 first sets the exhaust temperature Tex to be lower than the PM oxidation start temperature, and the maximum reached temperature TexMAX It is maintained at a higher sulfur removal temperature for a certain period. Then, the ECU 18 thereafter sets the exhaust temperature Tex to the PM oxidation start temperature or higher. At this time, oxygen concentration lowering control for lowering the oxygen concentration flowing into the DOC 10 is performed.

Next, an example of control performed by the control device 3 will be described with reference to the flowchart shown in Fig. The flow chart shown in Fig. 2 shows the filter, that is, the entire control for PM regeneration of the DPF 11.

First, when the previous PM regeneration is completed, the numerical value of the PM accumulation amount stored in the ECU 18 is cleared and reset, and the control for regeneration of PM is started this time. In step S1, the exhaust temperature Tex during traveling is continuously acquired and stored in the ECU 18. [ In step S2, it is determined whether or not the exhaust temperature Tex is higher than the stored exhaust temperature Tex (last acquisition Tex) at that time. When it is determined to be YES in step S2, the process proceeds to step S3, and the current time acquisition Tex is stored as the maximum arrival temperature TexMAX at that time. Further, when the exhaust temperature Tex is obtained for the first time, since there is no comparison value, the exhaust temperature Tex is stored as the maximum arrival temperature TexMAX as it is.

In step S4, which is performed subsequent to step S3, it is determined whether there is a PM regeneration request. When the result of the determination in step S2 is "NO ", the processing in step S4 is also performed. When it is judged "NO" in the step S4, the processing from the step S1 is repeated. When it is determined as "YES " in the step S4, it is determined that the current PM regeneration request has been established, and the process proceeds to the step S5.

In step S5, the maximum reached temperature TexMAX of the exhaust temperature at that point is higher than the transition permissive temperature TSO ₃ at which the conversion rate from the SO ₂ to the SO ₃ in the DOC 10 or the DPF 11 becomes the allowable value or less . That is, in step S5, it is determined whether the temperature is higher than the maximum attained TexMAX switch allows temperature TSO ₃ at the last time to the current time o'clock PM recovery completion PM regeneration request. Here, for the switch allows temperature TSO _3, a description will be given, with reference to FIG. Referring to FIG. 3, the conversion allowable temperature TSO ₃ is related to the rate at which SO ₂ is oxidized and converted from SO ₂ to SO ₃ . Therefore, for example, when the SO ₃ conversion rate is allowed up to 40%, the highest temperature in the "allowable range" in FIG. ₃ is the switching allowable temperature TSO ₃ . In addition, for example, when the SO ₃ conversion rate is 0%, the lowest temperature of the "allowable range" in FIG. ₃ is the switching allowable temperature TSO ₃ . In addition, the switching allowable temperature TSO ₃ differs depending on the catalyst specification, and is set by suitability.

In the step S5, when the result is YES, the process proceeds to the step S6. In step S6, TexMAX is directly adopted as the value of TexMAX. On the other hand, when it is determined in step S5 that the answer is "no", the process proceeds to step S7. In step S7, the switching allowable temperature TSO ₃ is employed as the value of TexMAX. Here, as shown in Fig. 3, for example, when the allowable SO ₃ conversion rate is wide, values that can be adopted as TexMAX are as follows. That is, the value that can be employed as TexMAX, is set to any temperature in the range of the switching allowable temperature TSO ₃ or less higher than the maximum attained temperature TexMAX set in step S3. Here, the requirement that the maximum reaching temperature TexMAX is higher is required for desorbing sulfur. Also, the requirement that the conversion allowable temperature is within the range of TSO ₃ or less is required in order to keep the SO ₃ conversion rate within the allowable range. Here, since the temperature is set to an arbitrary temperature, a temperature satisfying the above conditions can be adopted, but in order to efficiently remove sulfur, it is preferable to employ the transition permissive temperature TSO ₃ . For example, if the ultimate temperature TexMAX switches allow temperature TSO ₃ than the very low temperatures, and although there is room for the switching allowable temperature TSO _3, relative to the temperature TexMAX maximum attained, the improvement in the efficiency of There is room. That is, since the conversion from SO ₂ to SO ₃ is allowed when the conversion allowable temperature is lower than TSO ₃ , sulfur removal is most efficiently performed within the range.

In step S8-1 performed after step S6, TexMAX + alpha is set as the sulfur elimination temperature. Here, + alpha means to set the temperature higher than TexMAX. Referring to FIG. 4, it can be seen that the temperature at which the sulfur is removed is equal to or higher than the temperature at which the sulfur is deposited. Specifically, the SO ₂ deposited on the catalyst when the exhaust temperature is A 캜 is desorbed when the catalyst temperature becomes A +? 占 폚. In addition, SO ₂ has been deposited on the catalyst when the exhaust temperature is ℃ B, when the catalyst temperature is in B + α ℃, is desorbed. As described above, in order to desorb the sulfur S deposited and adsorbed on the catalyst, it is necessary to exceed the deposition temperature. Therefore, in this embodiment, TexMAX + alpha is set as the sulfur elimination temperature. Further, the concrete value of + alpha can be appropriately determined by suitability. At this time, if the temperature is excessively higher than TexMAX, the release rate of sulfur (S) is accelerated and it tends to become white smoke, so the value of alpha is determined in consideration of this point. Namely, the desulfurization temperature is set to adopt the lowest temperature at which sulfur can be desorbed and released.

On the other hand, in step S8-2, which is performed after step S7, TexMAX is set as the sulfur elimination temperature. That is, an action of + α is unnecessary. This is considered because the transition permissive temperature TSO ₃ is replaced with TexMAX in step S7 and the substituted TexMAX is higher in temperature than the actual TexMAX so that the sulfur S is desorbed.

In step S9 to be followed by step S8-1 or step S8-2, sulfur elimination processing is performed. This step S9 is a subroutine, and its contents will be described in detail later. In step S10, which is performed after step S9, the value of TexMAX is cleared. Then, in step S11, PM regeneration control is performed. Specifically, the exhaust temperature Tex becomes equal to or higher than the PM oxidation start temperature. Thereby, the PM regeneration is performed. Here, the PM oxidation starting temperature is higher than the sulfur elimination temperature, but before the PM regeneration control, the exhaust temperature Tex is maintained at the sulfur elimination temperature for a certain period of time and the sulfur S is desorbed. As a result, the occurrence of white smoke at the time of PM regeneration is suppressed.

When the processing of the step S11 is completed, the series of processing for the PM reproduction at this time is completed, and the processing from the step S1 is repeated again toward the next PM reproduction request.

Next, with reference to a flowchart shown in Fig. 5, an example of sulfur process execution control performed by the control device 3, that is, detailed control of step S9 in the flowchart shown in Fig. 2 will be described. Further, in the case of passing through the step S8-1, when TexMAX + alpha and the step S8-2 are passed, the TexMAX is maintained for a predetermined time, and after the sulfur is desorbed, the routine proceeds to the normal PM regeneration control (step S11).

First, in step S91, it is determined whether or not the exhaust added fuel condition is satisfied. Specifically, it is determined whether or not the temperature of the catalyst-containing gas measured by the first temperature sensor 14 exceeds the threshold value T1. The threshold value T1 is set in view of whether or not the added fuel can be brought into a combustible state. When the result of the determination in step S91 is "YES ", the process proceeds to step S92. When the result of the determination in step S91 is "NO ", the processing in step S91 is repeated until it is determined in step S91 that" YES ".

In step S92, the fuel S concentration value is acquired. That is, the fuel S concentration value is acquired based on the measured values of the SOx sensor 12 and the A / F sensor 17 as described above. Alternatively, a fuel property sensor may be provided instead of the SOx sensor 12, and the fuel S concentration value may be obtained from the measured value of the fuel property sensor.

In step S93, which is performed subsequent to step S92, the white smoke suppression target A / F and the oxygen concentration reduction control execution period are read. Referring to FIG. 6, the oxygen concentration lowering control execution period is a period during which sulfur elimination processing is performed. Referring to Fig. 6, an example of the PM regeneration chart of the present embodiment is shown, and the A / F is controlled toward the rich state in the sulfur elimination process performed prior to the PM regeneration. In other words, the oxygen concentration is controlled to decrease in the sulfur elimination treatment. Here, the control in the direction of lowering the oxygen concentration may be performed by controlling the oxygen concentration to be lowered. That is, the oxygen concentration lowering control includes not only the case where the rich air-fuel ratio exceeds the stoichiometric air-fuel ratio but also the case where the stoichiometric air-fuel ratio is close to the stoichiometric air-fuel ratio. Referring to Fig. 6, in the present embodiment, the white smoke suppression A / F is set based on the range before and after the stoichiometric air-fuel ratio.

By controlling the oxygen concentration lowering control in this manner, the amount of oxygen remaining in the exhaust gas is reduced, so that generation of SO ₃ , which is a cause of generation of H ₂ SO ₄ recognized as white smoke, can be suppressed. The oxygen concentration lowering control includes the following measures. The intent of each measure is as follows.

The ECU 18 sets the oxygen concentration based on the fuel S concentration value. This considers that the S concentration in the exhaust gas increases corresponding to the fuel S concentration value. Further, the ECU 18 sets the upper limit threshold value of the oxygen concentration in accordance with the fuel S concentration value. The upper limit value of the oxygen concentration is, in other words, the upper limit value of lean. To be lean means that the air amount is relatively increased, and therefore, when the upper limit value of the oxygen concentration is set, it is intended that the air amount is not excessively increased. When the SO ₂ is oxidized to SO _2, or accumulation, DOC (10), and DPF (11) discharged from the engine body 2, the SO ₃ is produced. Since the S concentration in the exhaust gas increases with the fuel S concentration value, if the upper limit value of the oxygen concentration is set in accordance with the fuel S concentration value, the generation of SO ₃ can be effectively suppressed.

Here, the relationship between the accumulated S amount and the fuel S concentration value in the DOC 10 and the DFP 11 will be described in detail. Referring to Fig. 7, the relationship between the running distance of the vehicle and the amount of deposited S is shown for three types of fuel. The fuel S concentration values are in the range of 2000 ppm, 500 ppm and 50 ppm. The amount of sediment S increases as the fuel S concentration value increases. If the amount of accumulated S is large, the amount of S emission increases at the time of PM regeneration. Therefore, the higher the fuel S concentration value is, the more easily the SO ₃ is generated. Thus, if the fuel S concentration value is high, there is a possibility that a large amount of SO ₃ is generated. Therefore, as shown in Fig. 8, the upper limit threshold value of the white smoke suppression target A / Ftrg is set. Specifically, the range of ± β of the reference A / F according to the fuel S concentration value is set as the allowable range of the anti-whitening target A / Ftrg. In addition, the reason why the range is set to ± β is that it is difficult to control the A / F accurately. By setting the upper limit value of the oxygen concentration according to the fuel S concentration value, the occurrence of white smoke can be suppressed while oxygen is supplied to the DFP 11 in a state close to lean or lean, and deterioration of fuel efficiency can be suppressed.

Next, with reference to Fig. 9, the difference in the occurrence status of white smoke due to the difference in the fuel S concentration value will be described. If the concentration of SO ₃ exceeds a predetermined threshold (white smoke generation threshold value), white smoke is recognized. Referring to FIG. 9, it can be seen that the period over which the white smoke threshold value is exceeded is longer as the fuel S concentration value is higher. Therefore, in order to effectively suppress the white smoke, as shown in Fig. 10, it is necessary to set the oxygen concentration decrease control execution period τ trg to the long term as the fuel S concentration value becomes higher.

In step S94, which is performed after step S93, it is determined whether or not A / Fm measured by the A / F sensor 17 is equal to or less than the anti-whitening target A / Ftrg + ?. When it is determined as NO in step S94, the flow proceeds to step S95. In step S95, EGR additional increase by ΔEGR is performed. When it is determined as NO in the step S94, since the allowable range of the white smoke suppression target A / Ftrg, that is, the upper limit value of the oxygen concentration, is exceeded, the EGR amount is increased to reduce the air amount and to reduce the oxygen concentration . After the processing of step S95 is completed, the processing from step S94 is repeated.

On the other hand, when it is determined as "YES " in the step S94, the process proceeds to the step S96. In step S96, it is determined whether or not the A / Fm measured by the A / F sensor 17 is equal to or higher than the anti-whitening target A / Ftrg-beta. When the result of the determination in step S96 is "NO ", the process proceeds to step S97. In step S97, EGR reduction by ΔEGR is performed. When it is determined as NO in the step S96, it exceeds the allowable range of the anti-whitening target A / Ftrg, so that the EGR amount is decreased to maintain the air concentration. After the processing of step S97 is completed, the processing from step S94 is repeated.

In the present embodiment, the EGR amount is adjusted to control the A / Fm to an appropriate range, but other means capable of controlling the A / Fm may also be used. For example, the A / Fm may be controlled to an appropriate range by adjusting the amount of exhaust added fuel.

Further, from the viewpoint of suppressing the generation of white smoke, it is important not to set the lower limit of the oxygen concentration, but there is a possibility of an increase in the surface oxygen concentration is too low, CO, HC, H ₂ S or PM, A / F Is preferably maintained in an appropriate range.

By performing the processing from the step S94 to the step S97, the white smoke suppression target A / Ftrg is controlled within the allowable range. When the target of white smoke inhibition A / Ftrg is controlled in this manner, the exhaust temperature and the catalyst temperature are set so as to be substantially the sulfur elimination temperatures. The sulfur elimination temperature is the temperature set in step S8-1 or step S8-2. Since the desulfurization temperature is set so that abrupt desorption is not performed in consideration of the deposition temperature of sulfur, the occurrence of white smoke can be suppressed.

When the result of the determination in step S96 is "YES ", the process proceeds to step S98. In step S98, it is determined whether the measured room temperature Tm is equal to or higher than the sulfur elimination temperature. Normally, since the exhaust temperature and the normal temperature of the catalyst can be considered to be almost the same, the sulfur is desorbed by setting the exhaust temperature to the sulfur elimination temperature or higher. Here, the sulfur elimination temperature differs in the flow chart shown in Fig. 2 from the value referred to by whether or not the process goes through step S8-1 or step S8-2. In other words, when passing through the step S8-1, the value of TexMAX + alpha set in the step S8-1 is employed as the sulfur elimination temperature. On the other hand, in the case of passing through the step S8-2, the TexMAX set in the step S8-2 is adopted as the sulfur elimination temperature.

When the result of the determination in step S98 is "NO ", the process proceeds to step S99. In step S99, the exhaust added fuel is increased. Thereby, the room temperature Tm is raised. After the processing of step S99, the processing of step S98 is repeated again. When it is determined to be YES in step S98, that is, when it is determined that the room temperature Tm is equal to or higher than the sulfur elimination temperature and the sulfur can be desorbed, the process proceeds to step S100. In step S100, it is determined whether or not the control execution period τ trg for desorbing sulfur has elapsed. When the result of the determination in step S100 is "NO ", the processing in step S94 is repeated. When it is determined as "YES " in the step S100, the subroutine is ended. Thereafter, the process proceeds to step S10 shown in Fig. 2, and thereafter, the process proceeds to the PM regeneration control in step S11. Step S11 is a subroutine, but when the subroutine ends, the process ends (ends).

The above is an example of the control performed by the control device 3. Here, the influence of A / F on the whiteness in the sulfur elimination process performed prior to the PM regeneration will be described with reference to Fig. 11 is a graph showing the influence of A / F on white smoke during PM regeneration. Referring to FIG. 11, it can be seen that the larger the amount of SO ₃ , the larger the amount of white smoke. Further, it can be seen that as the A / F is controlled to the rich side during PM regeneration, the closer to the point a from the point a, the more the white smoke is generated. It can also be seen that the more the A / F is controlled to the rich side, the lower the SO ₃ peak value. From the above, by controlling the A / F to the allowable range of the white smoke suppression target A / Ftrg as in the above-described control described with reference to Fig. 5, it is possible to realize balanced suppression of white smoke and regeneration of PM.

(Modified example)

In the case where the S concentration value of the fuel used in the internal combustion engine is known or assumed, the oxygen concentration and the oxygen concentration lowering control period corresponding to the S concentration value may be appropriately set in advance. In this case, the steps S92 and S93 are omitted. The S concentration value of the fuel used in the internal combustion engine is often grasped by the destination. Therefore, it is possible to set the oxygen concentration in the exhaust gas, that is, the white smoke suppression target A / Ftrg, to a fixed value by performing adaptation in consideration of the previously assumed S concentration value for each destination. This fixed value may be a value set corresponding to the S concentration value of the fuel burned in the internal combustion engine 1. [ Likewise, the execution period of the oxygen concentration reduction control may be set to a period set in correspondence with the S concentration value of the fuel burned in the internal combustion engine 1. Thus, when the oxygen concentration is set by suitability, the higher the S concentration value assumed, the lower the oxygen concentration is set. Further, when the execution period of the oxygen concentration reduction control is set by suitability, the higher the S concentration value assumed, the longer the duration is set. This period may be set in correspondence with the S concentration value of the fuel combusted in the internal combustion engine 1.

Referring to Fig. 12 (A), the oxygen concentration for each destination in the ECU 18, specifically, the white smoke suppression target A / Ftrg-n is stored. Likewise, the execution period? Tgg-n of the oxygen concentration reduction control is stored. That is, the ECU 18 is prepared in a state having general versatility, and when the destination is determined, the white smoke suppression target A / Ftrg-n and the implementation period? Ttrg-n corresponding to the destination are selected. In this way, the oxygen concentration reduction control is performed based on the fixed value corresponding to the destination. As a method for setting the fixed value, as shown in Fig. 12 (B), the white smoke suppression target A / Ftrg-n and the execution period tau trg-n in the ECU are initially set as blanks. Then, when the destination is determined, the white smoke suppression target A / Ftrg-n and the execution period? Ttrg-n in the ECU corresponding to the destination are written. In this way, the oxygen concentration reduction control may be performed based on the fixed value corresponding to the destination.

Referring to Fig. 13, there are cases where TexMAX1 and TexMAX2 (TexMAX1 > TexMAX2) are recorded as an example of the history of the exhaust temperature Tex between the PM regeneration interval. Thus, in the case where a plurality of deposition temperatures exist, for example, the desulfurization treatment is performed at a temperature higher than the maximum reaching temperature TexMAX1. Then, since the sulfur deposited in TexMAX1 is desorbed at a gentle speed, the occurrence of white smoke can be suppressed. However, the sulfur deposited in TexMAX 2 is desorbed at a temperature considerably higher than the temperature at the time of deposition, and is released at a high speed. As a result, white smoke is likely to occur. Therefore, by raising the exhaust temperature stepwise until reaching TexMAX, it is possible to carry out the sulfur elimination treatment according to the accumulation temperature, and the occurrence of white smoke can be suppressed. In this case, as shown in Fig. 13, for example, after 80% accumulation amount for starting the PM regeneration is recognized, a period of time The maximum reachable temperature may be extracted.

It is to be understood that the foregoing embodiments are merely examples for carrying out the present invention and that the present invention is not limited to these embodiments and various modifications of these embodiments are within the scope of the present invention, It is apparent from the above description that various embodiments are possible.

1: Internal combustion engine
2: engine body
3: Control device
4: Intake passage
5: Exhaust passage
10: DOC
11: DPF
12: SOx sensor
13: Exhaust additive fuel valve
17: A / F sensor

Claims (4)

A control device for an internal combustion engine provided with a filter downstream of a catalyst having an oxidation function,
When the PM regeneration request of the filter is established,
The exhaust temperature is maintained lower than the PM oxidation start temperature and maintained at a sulfur removal temperature higher than the maximum temperature of the exhaust gas at the time of the completion of the PM regeneration from the completion of the previous PM regeneration to the regeneration of the PM regeneration, And a control section for controlling the temperature to be equal to or higher than the start temperature,
Wherein the control unit is configured to set the sulfur removal temperature higher than the maximum reachable temperature when the maximum attained temperature is lower than or equal to a permissible switching temperature at which the conversion rate of SO ₂ to SO ₃ in the catalyst becomes lower than a permissible value, Is set to an arbitrary temperature which is lower than or equal to an allowable temperature. The method according to claim 1,
Wherein the control unit, wherein the the ultimate temperature, if from the SO ₂ in said catalyst less than or equal to switch allows temperature the conversion of the SO ₃ which is below the acceptable value, setting the sulfur desorption temperature to the switching allowable temperature, the internal combustion Control device of the engine. 3. The method according to claim 1 or 2,
Wherein the control unit gradually increases the temperature of the exhaust gas or the temperature of the catalyst until the sulfur removal temperature is reached. 4. The method according to any one of claims 1 to 3,
Wherein when the PM regeneration request of the filter is satisfied and there is a request for increasing the exhaust temperature on the downstream side of the catalyst, the control unit sets the oxygen concentration in the exhaust gas flowing into the catalyst to the fuel To the upper limit threshold value of the oxygen concentration according to the S concentration value in the internal combustion engine.

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