DE112014001523T5 - Control device for internal combustion engine - Google Patents

Abstract

A control device for an internal combustion engine is a control device for an internal combustion engine having a filter on a downstream side of a catalyst having an oxidation function, and a control unit for maintaining an exhaust gas temperature at a sulfur sorption temperature for a certain period of time and then adjusting the Exhaust gas temperature to be at least equal to a PM oxidation start temperature, wherein the sulfur sorption temperature in the case where a PM regeneration requirement of the filter is lower than the PM oxidation start temperature and higher than the highest achievable temperature of the exhaust gas temperature or a catalyst bed temperature from the time the earlier PM regeneration is completed to the time the current PM regeneration is required. In this way, rapid desorption of sulfur is avoided and the generation of white smoke can be suppressed.

Description

TECHNICAL AREA

The invention relates to a control device for an internal combustion engine or an internal combustion engine.

STATE OF THE ART

Conventionally, it has been known to carry out filter bed temperature processing in the case where a deposited amount of particulate matter (PM) is large when sulfur release processing is performed by an oxidation catalyst. For example, Patent Literature 1 is available as related literature. Incidentally, it has been known that sulfur dioxide (SO ₂ ) contained in the exhaust gas of an internal combustion engine is converted to sulfur trioxide (SO ₃ ) in the oxidation catalyst and further by reaction with water (H ₂ O) in H ₂ SO _{4 is} converted. There is a case where H ₂ SO _{4 is converted} into white smoke (white sulfate smoke) and released into the atmosphere. However, such a chemical reaction is not disclosed in Patent Document 1.

LITERATURE FROM THE PRIOR ART

Patent Literature

• Patent Document 1: Japanese Patent Application Publication No. 2009-299572 ( JP 2009-299572 A )

BRIEF EXPLANATION OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

As described above, SO ₃ reacts with H ₂ O and is converted to H ₂ SO ₄ . The oxidation catalyst also has a property of adsorbing SOx. Accordingly, a large amount of white smoke may be generated when a filter that is installed together with the oxidation catalyst to trap the PM (for example, a diesel particulate filter; DPF) is regenerated. In other words, a sulfur component (an S component) contained in the fuel burned in the internal combustion engine and adsorbed SOx adsorbed on the oxidation catalyst and therefrom due to an increase in the exhaust gas temperature associated with a PM Regeneration requirement is desorbed, possibly converted to the white smoke.

In view of this, a control apparatus for an internal combustion engine disclosed in this document deals with the problem of suppressing the generation of white smoke caused by the desorption of sulfur during PM production.

DEVICE FOR SOLVING THE PROBLEM

To solve such a problem, a control apparatus for an internal combustion engine disclosed in this specification is a control apparatus for an internal combustion engine including a filter on a downstream side of a catalyst having an oxidation function, and comprises A control unit for maintaining an exhaust gas temperature at a sulfur sorption temperature for a certain period of time and then adjusting the exhaust gas temperature to be equal to a PM oxidation start temperature at least in the case where there is a PM regeneration request of the filter, the sulfur sorption temperature from a time, at which the previous PM regeneration is completed until a time when the current PM regeneration is required lower than the PM oxidation start temperature and higher than the highest achievable temperature of the exhaust gas temperature or a Katalysatorbetttemperatu r is. In the case where the highest achievable temperature is at least equal to a permissible transformation temperature at which a conversion rate of SO ₂ in SO ₃ in the catalyst is at least equal to an allowable value, the control unit may set the sulfur sorption temperature to any temperature higher than the highest achievable temperature and at least equal to the temperature that allows the conversion.

As a property, sulfur that is deposited and adsorbed on the catalyst begins to be desorbed when the temperature rises to a temperature higher than a temperature during deposition and adsorption. Accordingly, sulfur can not be desorbed until the exhaust gas temperature becomes at least equal to the highest achievable temperature in the exhaust gas temperature history from the time the earlier PM regeneration is completed to the time when the current filter regeneration is required , Thus, sulfur can be desorbed in the case where the exhaust gas temperature is controlled to become the PM oxidation start temperature at the beginning of the request of filter regeneration. Meanwhile, however, sulfur desorbs rapidly as the temperature rises and a sulfur release rate increases. As a result, the generation of white smoke may be caused.

In view of the above, the exhaust gas temperature is maintained at a minimum temperature at which sulfur S adsorbed on the catalyst can be desorbed and released, that is, the sulfur sorption temperature for a certain period of time, and then sulfur is desorbed and released. Thereafter, the exhaust gas temperature is raised to become at least equal to the PM oxidation start temperature. In this way, it is possible to suppress the generation of the white smoke during the sulfur sorption and the generation of the white smoke during the PM regeneration.

In the case where the highest achievable temperature is at least equal to the allowable transformation temperature at which the conversion rate of SO ₂ to SO ₃ in the catalyst is at least equal to the allowable value, the controller may set the sulfur sorption temperature to the value allowed for the conversion.

In the case where the highest achievable temperature is at least equal to the allowable transformation temperature, the sulfur sorption temperature may be set at a temperature falling within a range at least equal to the allowable transformation temperature. SO ₃ as a cause of generation of the white smoke is generated by oxidation of SO ₂ . The conversion rate of SO ₂ in SO ₃ is influenced by the exhaust gas temperature. Accordingly, the white smoke can be suppressed within a permissible range when the sulfur sorption temperature is set to the temperature falling within the range at most equal to the allowable transformation temperature. Note that the sulfur sorption temperature must be a higher temperature than the highest achievable temperature. In addition, the efficiency of sulfur sorption is increased when the sulfur sorption temperature is high. In view of this, if the highest achievable temperature is at most equal to the allowable transformation temperature, the sulfur sorption temperature is set to the temperature allowable for the conversion. In this way, the white smoke can be suppressed within the allowable range, and efficient sulfur sorption can be carried out. By setting the sulfur sorption temperature at the temperature permissible for the conversion, it is possible to effectively suppress the generation of the white smoke and to accelerate the sulfur sorption.

The control unit may increase the exhaust gas temperature or the catalyst bed temperature in stages until the exhaust gas temperature or the catalyst bed temperature reaches the sulfur sorption temperature. In this way, it is possible to desorb several kinds of sulfur having different deposited temperatures while suppressing generation of the white smoke.

In the case where the PM regeneration request of the filter is present and an exhaust gas temperature increase request is performed on the downstream side of the catalyst, the control unit may reduce the oxygen concentration in the exhaust gas flowing into the catalyst to be at most equal to an upper threshold value of the exhaust gas Oxygen concentration corresponding to an S concentration value in the fuel burned in the internal combustion engine.

Oxygen is needed to regenerate the filter provided in the exhaust passage and located on the downstream side of the oxidation function catalyst. Meanwhile, when the oxygen concentration is too large, SO ₂ oxidized due to combustion of the fuel containing the S component is oxidized, and thereby SO _{3 is} generated. Similarly, the sulfur-S component deposited on the catalyst or filter is also converted to SO ₃ by desorption and oxidation. The SO ₃ thus produced is associated with the H ₂ O and forms H ₂ SO ₄ , and turns into mist, that is, the white smoke. Accordingly, for the purpose of regenerating a substance deposited on the filter, mainly particulate matter (PM), the control for reducing the oxygen concentration is carried out when the exhaust gas temperature increase request is recognized. In this way, the generation of the white smoke can be suppressed.

EFFECT OF THE INVENTION

According to the control apparatus for the internal combustion engine disclosed in this specification, it is possible to suppress generation of the white smoke caused by the desorption of sulfur during the PM regeneration.

BRIEF EXPLANATION OF THE FIGURES

1 FIG. 11 is an explanatory view of a schematic structure of an internal combustion engine according to an embodiment. FIG.

2 FIG. 10 is a flowchart of an example of a control executed by a control apparatus for the internal combustion engine according to the embodiment. FIG.

3 FIG. 12 is a graph of a relationship between an exhaust gas temperature and a SO ₃ conversion rate.

4 Fig. 12 is a graph of a relationship between an S-deposition temperature and an S-desorption temperature.

5 FIG. 10 is a flowchart of a control example that executes the internal combustion engine controller of the embodiment. FIG.

6 FIG. 10 is an example of a PM regeneration time chart that executes the internal combustion engine controller of the embodiment. FIG.

7 FIG. 16 is an illustration of the view of a relationship between an amount of deposited S and a concentration of S in the fuel.

8th FIG. 12 is a graph of a relationship between an S concentration value in the fuel and a white smoke suppression target A / Ftrg. FIG.

9 is a diagram of situations of production of white smoke.

10 FIG. 12 is a graph showing a relationship between the concentration value of S in the fuel and a period of time τtrg for executing the white smoke suppression control.

11 is a graph of A / F influence during PM regeneration on white smoke.

12 (A) FIG. 12 is a schematic explanatory view of a situation in which a preselected candidate candidate is stored for each job site; and FIG 12 (B) Fig. 12 is a schematic illustration of the view of a situation in which a set value is set according to the place of use.

13 FIG. 12 is a diagram of an example of a temperature change during a PM generation interval. FIG.

MODES FOR IMPLEMENTING THE INVENTION

Hereinafter, a description will be given of an embodiment of the invention with reference to the accompanying drawings. Note that each component in the figures need not be shown in such a manner that dimensions, ratios and the like fully correspond to those of the actual components. In addition, it may be dependent on the figures that details are not shown.

(Embodiment]

1 Fig. 10 is an explanatory view of a schematic structure of a machine 1 with internal combustion or an internal combustion engine 1 according to the embodiment. The machine 1 with internal combustion includes an engine block 2 and a control device 3 (hereinafter referred to as control device) for an internal combustion engine. An intake passage 4 and an exhaust passage 5 are with the engine block 2 connected. The end of an exhaust gas recirculation (EGR) passage 6 is with the engine block 2 connected. The other end of the EGR passage 6 is connected to the suction passage. An EGR cooler 7 and an EGR valve 8th are in the passage 6 arranged. A throttle 9 is in the intake passage 4 arranged. A diesel oxidation catalyst (DOC) 10 is in the exhaust passage 5 arranged. The DOC 10 is a catalyst with an oxidation function and is in the machine 1 with internal combustion included. A diesel particulate filter (DPF) 11 is on a downstream side of the DOC 10 arranged in the exhaust passage. The DPF 11 is a filter for collecting PM and is in the machine 1 with internal combustion included.

An SOx sensor 12 , an exhaust fuel injection valve 13 and a first temperature sensor 14 are consecutively from the upstream side in the exhaust passage 5 between the engine block 2 and the DOC 10 arranged. Together with an A / F sensor (air / fuel or air-fuel ratio sensor) described below 17 is the SOx sensor 12 in the machine 1 more specifically, in a device for obtaining an S-concentration value in the engine block 2 burnt fuel (hereinafter referred to as S-fuel concentration). The exhaust fuel injection valve 13 puts the exhaust gas with fuel by putting the fuel into the exhaust passage 5 is injected. The offset with the fuel exhaust gas is in the DOC 10 burned and becomes high-temperature exhaust gas. The first temperature sensor 14 measures a temperature of the DOC 10 introduced exhaust gas (a DOC temperature, a catalyst input gas temperature).

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

On a downstream side of the DPF 11 in the exhaust passage 5 are a third temperature sensor 16 and the A / F sensor 17 arranged sequentially from the upstream side. The third temperature sensor 16 measures a temperature of the DPF 11 discharged exhaust gas. The DPF temperature, that is, a catalyst bed temperature Tm, is obtained from a reading of this third one temperature sensor 16 and a measured value of the aforementioned second temperature sensor 15 , Note that the catalyst temperature Tm may be set as the DOC temperature, or the catalyst bed temperature Tm may be obtained by using a value correlated therewith.

Note that the control device 3 of this embodiment, as described later, performs a control to maintain the exhaust gas temperature or the catalyst bed temperature at a sulfur sorption temperature higher than the highest attainable temperature of the exhaust gas or the catalyst bed temperature for a certain period of time, the highest achievable temperature from a time point at which the previous PM regeneration is completed until a time when the current PM regeneration is requested. Here, one of the exhaust gas temperature Tex and the catalyst bed temperature Tm may be taken into consideration when the highest achievable temperature is defined. A sulfur (S) component as a subject of desorption is deposited on the catalyst and adsorbed. Thus, the catalyst bed temperature has a direct correlation. However, because the exhaust temperature and the catalyst bed temperature are correlated, any of the temperatures may be considered. In the explanation below, the exhaust gas temperature Tex is used throughout the specification.

The A / F sensor 17 measures the exhaust gas A / F ratio. As described above, the A / F sensor 17 together with the SOx sensor 12 in the device for obtaining an S-fuel concentration value. The S-fuel concentration value and the SOx concentration in the exhaust gas are correlated with each other. Thus, the S-fuel concentration may be from a SOx concentration value in the SOx sensor 12 detected exhaust gas and the exhaust gas A / F ratio are calculated. Note that from the engine block 2 discharged SOx is mainly SO ₂ . Thus, an SO ₂ sensor can be used as a SOx sensor.

The machine 1 with internal combustion includes an electronic control unit (ECU) 18 , The ECU 18 carries different types of controls in the machine 1 with internal combustion through. In addition, the ECU 18 in the control device 3 contains and works as a control unit of the control device 3 , The ECU 18 is electric with the EGR valve 8th , the throttle 9 , the SOx sensor 12 , the exhaust fuel injection valve 13 , the first temperature sensor 14 , the second temperature sensor 15 , the third temperature sensor 16 and the A / F sensor 17 connected and forms the control device 3 , The ECU 18 receives a deposited PM amount. The ECU calculates even more precisely 18 the amount of PM deposited in the DPF 11 from an operating pattern of the machine 1 with internal combustion (a vehicle driving pattern). Then the ECU determines 18 whether the PM regeneration request is present. In addition, the ECU records 18 Tex exhaust gas temperature is continuously maintained and reaches a maximum achievable temperature TexMAX of the exhaust gas temperature from the time when the earlier PM regeneration is completed to the time when the current PM regeneration is required.

The ECU 18 acting as the control unit regenerates the PM based on an exhaust temperature increase request on the downstream side of the DOC 10 , more specifically, the PM regeneration request in the DPF 11 , In the case where a regeneration request for the DPF 11 the ECU holds 18 first for a certain period of time from the time when the earlier PM regeneration is completed to the time the current PM regeneration is requested, the exhaust gas temperature Tex at the sulfur sorption temperature, the sulfur sorption temperature being lower than a PM oxidation start temperature and higher than the highest attainable temperature TexMAX is. Then the ECU increases 18 Thereafter, the exhaust gas temperature Tex to such an extent that it is at least equal to the PM oxidation start temperature. At that time, the ECU is leading 18 Also, an oxygen concentration reduction control to reduce the concentration of oxygen in the DOC 10 flows.

Next, a description will be given of an example by the control device 3 performed control with respect to a in 2 given flowchart given. The in 2 The flow chart shown illustrates the overall control of the filter, that is, the PM regeneration of the DPF 11 ,

First, a numerical value of the deposited PM amount stored in the ECU 18 is stored, cleared and reset when the previous PM regeneration is completed, and the control for the current PM regeneration is triggered. In step S1, the exhaust gas temperature Tex is continuously obtained during a trip and in the ECU 18 saved. Then, in step S2, each time the exhaust gas temperature Tex is obtained, it is determined whether the currently-obtained exhaust gas temperature Tex is higher than the exhaust gas temperature Tex stored at that time (the Tex previously obtained). If "Yes" is determined in step S2, the processing proceeds to step S3, and the currently obtained Tex is stored as the highest attainable temperature TexMAX at the time. Note that when the exhaust gas temperature Tex is first obtained, it does not Value that is available for comparison. Accordingly, the exhaust gas temperature Tex is stored as it is as the highest attainable temperature TexMAX.

In step S4, which is executed after step S3, it is determined whether there is a PM regeneration request. In addition, the processing in step S4 is executed if "NO" is determined in step S2. If "No" is determined in step S4, the processing from step S1 is repeated. If "Yes" is determined in step S4, it is assumed that the current PM regeneration request is present and the processing proceeds to step S5.

In step S5, it is determined whether the highest achievable temperature TexMAX of the exhaust gas temperature at the time is higher than an allowable transformation temperature TSO ₃ at which a conversion rate of SO ₂ in SO ₃ in the DOC 10 or the DPF 11 at most equal to a permissible value. In other words, it is determined in step S5 whether the highest achievable temperature TexMAX is higher than the allowable transformation temperature from the time when the earlier PM regeneration is completed to the time when the current PM regeneration is required TSO _third Here is a description of the permissible transformation temperature TSO ₃ with reference to FIG 3 carried out. In relation to 3 For example, the permissible transition temperature TSO _{3 is} linked to a ratio in which SO _{2 is converted} to SO ₃ when SO _{2 is} oxidized. Accordingly, the highest temperature within an "allowable range" in 3 For example, in the case where the SO ₃ conversion rate of up to 40% is allowed, the allowable transformation temperature TSO ₃ . In addition, the lowest temperature within the "allowable range" in 3 to the permissible transformation temperature TSO ₃ when, for example, the SO ₃ conversion rate becomes 0%. Note that this allowable transition temperature TSO ₃ varies depending on a specification of the catalyst and is adjusted by adjustment.

If "Yes" is determined in step S5, the processing proceeds to step S6. In step S6, TexMAX is adopted as it is as the value of the TexMAX. On the other hand, if "No" is determined in step S5, the processing proceeds to step S7. In step S7, the allowable transformation temperature TSO _{3 is} assumed to be the value of the TexMAX. Here is the value that can be assumed as the TexMAX, for example, in the case where the allowable SO ₃ conversion rate is in a wide range as in 3 is shown as follows. That is, the value that can be assumed as the TexMAX is any temperature set within a range between a temperature higher than the highest attainable temperature TexMAX set in step S3 and a temperature which is at least equal to the temperature TSO ₃ at which the conversion is allowed. Here, a requirement for the desorption of sulfur is made that the value is higher than the highest achievable temperature TexMAX is required. In addition, a request that the value is at most equal to the temperature TSO ₃ at which the conversion is allowed is made so that the SO ₃ conversion rate falls within the allowable range. Here, a temperature which can satisfy the above-explained conditions can be adopted because the value is set as the arbitrary temperature. However, in order to effectively desorb sulfur, it is desired to assume the permissible temperature for conversion TSO ₃ . For example, if the highest achievable temperature TexMAX is much lower than the temperature TSO ₃ at which the conversion is allowed, there is a considerable range for the temperature TSO ₃ at which the conversion is allowed. If the highest achievable temperature TexMAX is set as a reference despite the fact explained above, there is room for improvement in terms of efficiency. In other words, the conversion of SO ₂ into SO _{3 is} allowed if the value is at least equal to the temperature TSO ₃ at which the conversion is allowed. Therefore, it is intended to desorb sulfur within the range as efficiently as possible.

In step S8-1, which is executed after step S6, TexMAX + α is set as the sulfur sorption temperature. Here, + α means to set a higher temperature than TexMAX. Regarding 4 It should be understood that a temperature at which sulfur is desorbed is at least equal to a temperature at which sulfur is separated. More specifically, at the exhaust gas temperature A ° C, SO ₂ deposited on the catalyst is desorbed when the catalyst temperature becomes A + α ° C. In addition, at the exhaust gas temperature B ° C, SO ₂ deposited on the catalyst is desorbed when the catalyst temperature becomes B + α ° C. As described above, it is necessary to exceed a deposition temperature to desorb sulfur S deposited and adsorbed on the catalyst. Therefore, in this embodiment, TexMAX + α is set as the sulfur sorption temperature. Note that a specific value of + α can be suitably determined by adaptation. At this time, a release rate of sulfur S becomes high when the temperature becomes much higher than TexMAX, and white smoke is likely to be generated. Therefore, the value of α is determined in view of this viewpoint. That is, the sulfur sorption temperature is set on the basis of such an intention that a minimum temperature is adopted, can be desorbed and released at the sulfur.

Meanwhile, in step S8-2, which is executed after step S7, the TexMAX is set as the sulfur sorption temperature. That is, there is no need to perform a measure to adjust + α. In view of this, sulfur sulfur S is desorbed because the temperature TSO ₃ at which the conversion is allowed is substituted by the value TexMAX in step S7, and the replaced temperature TexMAX is higher than the actual TexMAX.

In step S9 executed after step S8-1 or step S8-2, sulfur sorption processing is carried out. This step S9 is a subroutine and its contents will be described in detail below. In step S10, which is executed after step S9, the value of the TexMAX is cleared. Then, in step S11, a PM regeneration control is executed. More specifically, the exhaust gas temperature Tex is increased to become at least equal to the PM oxidation start temperature. In this way, PM regeneration is performed. Here, the PM oxidation start temperature is a higher temperature than the sulfur sorbent temperature. However, before the PM regeneration control, the exhaust gas temperature Tex is kept at the sulfur sorption temperature for a certain period of time, and thereby sulfur S is desorbed. In this way, the generation of white smoke during the PM regeneration is suppressed.

When the processing in step S11 is completed, a flow of processing for the current PM regeneration is completed. Then, the processing from step S1 is repeated again for the next PM regeneration request.

Next will be the one from the controller 3 1 is executed, that is, a detailed example of the control in step S9 in FIG 2 shown flowchart with reference to a flowchart, which in 5 is shown. Note that the processing returns to the normal PM regeneration control (step S11) after sulfur is desorbed by, for a certain period of time, TexMAX + α in the case where the program has passed through step S8-1 and TexMAX in FIG is maintained in the case where the program has passed through step S8-2.

First, in step S91, it is determined whether an exhaust fuel injection condition is satisfied. More specifically, it is determined whether one of the first temperature sensor 14 measured catalyst input gas temperature exceeds a threshold T1. This threshold value T1 is set with respect to whether the injected fuel can be brought into a combustible state. If "Yes" is determined in step S91, the processing proceeds to step S92. If "No" is determined in step S91, the processing in step S91 is repeated until "yes" is determined in step S91.

In step S92, the S fuel concentration value is obtained. In other words, as described above, the S-fuel concentration value is obtained on the basis of the measured values of the SOx sensor 12 and the A / F sensor 17 , Note that a fuel property sensor instead of the SOx sensor 12 and the S fuel concentration value can be obtained from a reading of this fuel property sensor.

In step S93, which is executed after step S92, a white smoke suppression target A / F ratio and an oxygen concentration reduction control execution period are read. Regarding 6 For example, the oxygen concentration reduction control execution period is a period in which the sulfur absorption processing is performed. Regarding 6 For example, an example of a PM regeneration chart of this embodiment is shown, and the A / F is controlled in the sulfur sorption processing performed before the PM regeneration so as to shift to a rich condition side. In other words, the A / F in the sulfur absorption processing is controlled in a direction to decrease the oxygen concentration. Here, as the control in the direction for reducing the oxygen concentration, control for decreasing only the oxygen concentration has to be performed. More specifically, the control for reducing the oxygen concentration includes not only a case in which the A / F exceeds a stoichiometry and is shifted to the rich state, but also a case in which the A / F approaches a stoichiometric state. Regarding 6 For example, in this embodiment, a white smoke suppression A / F is set in a range before and after the stoichiometry as a reference.

When the control for reducing the oxygen concentration is carried out as described, an amount of oxygen remaining in the exhaust gas is reduced. Thus, the generation of SO _{3 can be} suppressed, resulting in the production of H ₂ SO ₄ , which is recognized as white smoke. The oxygen concentration reduction control includes the following measures. An intension of the respective measure is as follows.

The ECU 18 sets the oxygen concentration based on the S-fuel concentration value. This is done in consideration of a fact that the S concentration in the exhaust gas increases depending on the S fuel concentration value. In addition, the ECU lays down 18 an upper threshold of the oxygen concentration matching the S-fuel concentration value. In other words, an upper limit of the oxygen concentration is an upper lean limit. The situation in which the A / F becomes lean means that a quantity of air becomes relatively higher. Therefore, it is intended not to increase the air amount too much by setting the upper limit of the oxygen concentration. SO ₃ is generated when from the engine block 2 discharged SO ₂ or on the DOC 10 or the DPF 11 deposited SO _{2 is} oxidized. The S concentration in the exhaust gas is increased to match the S fuel concentration value. Thus, it is possible to effectively suppress the generation of SO ₃ by adjusting the upper limit of the oxygen concentration to match the S fuel concentration value.

Here, a relationship between a deposited S amount in the DOC 10 or in the DPF 11 and the S fuel concentration value or concentration value of S in the fuel is described in detail. Regarding 7 For example, a relationship between a travel of a vehicle and the deposited S amount is shown for three types of fuel. There are three types of S-fuel concentration value, namely 2000 ppm, 500 ppm and 50 ppm. The deposited S amount increases as the S fuel concentration value becomes higher. An S-release amount during the PM regeneration increases when the amount of S deposited is large. Accordingly, a state occurs in which the generation of SO _{3 is} facilitated as the S-fuel concentration value increases. As described, a large amount of SO _{3 may be} generated when the S-fuel concentration value is high. Thus, as in 8th shown an upper threshold of the white smoke suppression target A / Ftrg set. More specifically, a range within ± β of the reference A / F corresponding to the S fuel concentration value is set as an allowable range of the white smoke suppression target A / Ftrg. The fact that it is difficult to precisely control the A / F to a target value is here a reason to set the range ± β. By providing the upper limit of the oxygen concentration that matches the S-fuel concentration value, it is possible to suppress the generation of the white smoke during the DPF 11 Oxygen is supplied to a lean or near a lean state. Therefore, the deterioration of the fuel economy can be suppressed.

Next, referring to 9 describes a difference in the white smoke generation situation caused by a difference in the S fuel concentration value. When the concentration of SO ₃ exceeds a predetermined threshold (a white smoke generation threshold), the white smoke is detected. Regarding 9 For example, it is to be understood that a period in which the concentration of SO ₃ exceeds this white smoke threshold becomes a longer period when the S fuel concentration value is increased. So it's like in 10 2, it is necessary to set a time period τtrg for executing the oxygen concentration reduction control to be a longer period as the S fuel concentration value increases.

In step S94, which is executed after step S93, it is determined whether A / Fm, that of the A / F sensor 17 is at most equal to the white smoke suppression target A / Ftrg + β. If "No" is determined in step S94, the processing proceeds to step S95. In step S95, an EGR addition amount is increased by ΔEGR. If "No" is determined in step S94, the A / Fn exceeds the allowable range of the white smoke suppression target value A / Ftrg, that is, the upper limit of the oxygen concentration. Accordingly, it is intended to take a measure to increase an EGR amount and decrease the amount of air so as to reduce the oxygen concentration. After the processing in step S35 is completed, the processing from step S94 is repeated.

On the other hand, if "Yes" is determined in step S94, the processing proceeds to step S96. In step S96, it is determined whether this is from the A / F sensor 17 measured A / Fn is at least equal to the white smoke suppression target value A / Ftrg-β. If "No" is determined in step S96, the processing proceeds to step S97. In step S97, an EGR amount is decreased by ΔEGR. If "No" is determined in step S96, the A / Fm exceeds the allowable range of the white smoke suppression target value A / Ftrg. Accordingly, it is intended to reduce the EGR amount to maintain the air concentration. After the processing in step S97 is finished, the processing of step S94 is repeated.

Note that in this embodiment, the EGR amount is adjusted to control the A / Fm to be within a suitable range. However, another device capable of controlling the A / Fm may also be used. For example, the A / Fm may be controlled to be within the appropriate range by adjusting the amount of fuel injected into the exhaust gas.

Note that the provision of a lower limit of the oxygen concentration is not necessary in view of the process of producing the white smoke. However, if the oxygen concentration is reduced too much, CO, HC, H2S or PM may be increased. Therefore, the A / Fm is desirably maintained within the appropriate range.

The white smoke suppression target value A / Ftrg is controlled to be within the allowable range by execution of the processing from step S94 to step S97. Then, the exhaust gas temperature and the catalyst temperature are set to be substantially equal to the sulfur sorption temperature when the white smoke suppression target value A / Ftrg is controlled as described above. The sulfur sorption temperature is the temperature set in step S8-1 or step S8-2. The sulfur sorption temperature is set in consideration of the deposition temperature of sulfur so that no rapid desorption occurs. Thus, it is possible to suppress the generation of the white smoke.

If "Yes" is determined in step S96, the processing proceeds to step S98. In step S98, it is determined whether the measured catalyst bed temperature Tm is at least equal to the sulfur sorption temperature. Normally, the exhaust gas temperature may be considered to be substantially equal to the catalyst bed temperature. Therefore, sulfur is desorbed when the exhaust gas temperature is at least equal to the sulfur sorption temperature. Here, the value referred to as the sulfur sorption temperature differs depending on whether the processing includes the step S8-1 or the step S8-2 in the 2 goes through the flowchart shown. More specifically, the value of TexMAX + α set in step S8-1 is used as the heavy field sorption temperature when processing passes through step S8-1. On the other hand, the TexMAX set in step S8-2 is set as the sulfur sorption temperature when processing passes through step S8-2.

If "No" is determined in step S98, the processing proceeds to step S99. In step S99, the amount of fuel added to the exhaust gas is increased. In this way, the bed temperature Tm is increased. After the processing in step S99, the processing in step S98 is repeated again. If "Yes" is determined in step S98, that is, if it is determined that the bed temperature Tm becomes at least equal to the sulfur sorption temperature and sulfur can be desorbed, the processing proceeds to step S100. In step S100, it is determined whether the control execution period τtrg for the desorption of sulfur has elapsed. If "NO" is determined in step S100, the processing of step S94ff. repeated. If "Yes" is determined in step S100, the subroutine is ended. Then, the processing proceeds to step S10 which is in 2 is shown and thereafter goes to PM regeneration control in step S11. The step S11 includes a subroutine, and the processing is terminated (end) when the subroutine is finished.

What has been described thus far is the one example of the control device 3 executed control. Here is with respect to 11 describe an influence of the A / F on the white smoke during the sulfur sorption processing performed before the PM regeneration. 11 is a graph of the influence of A / F during PM regeneration on the white smoke. Regarding 11 It should be understood that a quantity of white smoke increases as SO ₃ increases. In addition, it should be understood that the generation of the white smoke is suppressed when the A / F is controlled to be on the rich side during the PM regeneration, more specifically when the A / F is from a point a in FIG a direction of a point b moves. It is also understood that a peak of SO _{3 is} reduced when the A / F is driven to the rich side. From the above, suppression of white smoke and PM regeneration can be realized in a well-balanced manner by controlling the A / F to fall within the allowable range of the white smoke suppression target value A / Ftrg as described above with reference to FIGS 5 described control falls.

(Modified example)

In the case where the S concentration value of the fuel used in the internal combustion engine has already been known, or in the case where the S concentration value of the fuel used in the internal combustion engine is estimated, the oxygen concentration and the execution period of the oxygen concentration reduction control may be so set in advance be fit by adjusting to the S concentration value. In this case, the actions in step S92 and step S93 are omitted. The approximate S-concentration value of the fuel used in the internal combustion engine is often known on the job site. Thus, the adjustment is made in consideration of the S concentration value estimated in advance for each destination. In this way, the oxygen concentration in the exhaust gas, so the white smoke suppression target value A / Ftrg have a fixed value. This set value may be set as a value set to become the S concentration value of the in-machine 1 with internal combustion of burned fuel fits. In addition, the execution time period of the oxygen concentration reduction control may be set as a period set to become the S concentration value of the in-machine 1 with internal combustion of burned fuel fits. As already described, when the oxygen concentration is adjusted by adjustment, the oxygen concentration is set lower as the estimated S concentration value increases. In addition, the time period is set as a longer period if the estimated S concentration value increases when the execution time period of the oxygen concentration reduction control is adjusted by the adjustment. This execution period may be a period of time set to the S concentration value of the in-machine 1 with internal combustion of burned fuel fits.

Regarding 12 (A) is the oxygen concentration for the respective place of use, more particularly the white smoke suppression target value A / Ftrg-n in the ECU 18 saved. In addition, the oxygen concentration reduction control execution period τtrg-n is similarly stored. In other words, the ECU 18 prepared in a state where it is versatile, and once a place of use is determined, it selects the white smoke suppression target A / Ftrg-n and the execution period τtrg-n which match the job site. In this way, a state is set in which the oxygen concentration reduction control is executed on the basis of a set value that matches the place of use. In addition, in a setting method of the set value as in 12 (B) the white smoke suppression target value A / Ftrg-n and the execution period τtrg-n are not provided in the ECU from the beginning. Then, the white smoke suppression target value A / Ftrg-n and the execution time period τtrg-n that match the job site are written in the ECU after the job site is determined. In this way, it is possible to set the state in which the oxygen concentration reduction control is executed on the basis of the set value appropriate to the job site.

Regarding 13 For example, there is a case in which TexMAX1 and TexMAX2 (TexMAX1> TexMAX2) are recorded between the PM regeneration intervals as an example of a history of the exhaust gas temperature Tex. It is assumed that sulfur sorption processing is carried out at a higher temperature than TexMAX1, which is the highest achievable temperature in the case where the plurality of shutdown temperatures exist, as just described. In this case, sulfur deposited on TexMAX1 is desorbed at a moderate rate. Thus, generation of the white smoke can be suppressed. Meanwhile, sulfur deposited at TexMAX2 is desorbed at a significantly higher temperature than the temperature at the time of shutdown, and is released at a high rate. As a result, the probability of producing the white smoke is high. In view of this, the exhaust gas temperature is gradually increased until TexMAX is reached. Accordingly, the sulfur sorption processing can be performed in accordance with the deposition temperature, and the generation of the white smoke can be suppressed. In this case, the highest achievable temperature can be extracted by appropriately dividing time periods, such as in 13 such as the highest achievable temperature before the start of PM regeneration and the highest achievable temperature before the time when 80% of the deposited amount is recognized as a trigger of the start of PM regeneration.

The embodiment explained above is merely an example of the practice of the invention. The invention is not limited thereto and various modifications of these examples are within the scope of the invention. In addition, it is apparent from the present description that various other examples are possible within the scope of the invention.

LIST OF REFERENCE NUMBERS

1

MACHINE WITH INTERNAL COMBUSTION or INTERNAL COMBUSTION ENGINE

2

 ENGINE BLOCK

3

 CONTROL DEVICE

4

 intake passage

5

 EXHAUST PASSAGE

10

 DOC or diesel oxidation catalyst

11

 DPF or diesel particulate filter

12

 SOx SENSOR

13

 EXHAUST FUEL INJECTION VALVE

17

 A / F SENSOR or air-fuel ratio sensor

Claims (4)

A control apparatus for an internal combustion engine having a filter on a downstream side of a catalyst having an oxidation function, comprising: a control unit for maintaining an exhaust gas temperature at a sulfur sorption temperature for a certain period of time, and then setting the exhaust gas temperature at least equal to one PM Oxidation start temperature, wherein the sulfur sorption temperature is lower than the PM oxidation start temperature and higher than the highest achievable temperature of the exhaust gas temperature or a catalyst bed temperature from a time when the previous PM regeneration was completed to a time when the current PM regeneration is required if a PM regeneration request of the filter is present, and if the highest achievable temperature is at most equal to an allowable transformation temperature at which a conversion rate of SO ₂ to SO ₃ in the catalyst becomes at most equal to an allowable value, the controller sets the sulfur sorption temperature to an arbitrary temperature which is higher than the highest achievable temperature and at most equal to the permissible transformation temperature. A control device for an internal combustion engine according to claim 1, wherein in the case where the highest achievable temperature is at most equal to the allowable transformation temperature at which the conversion rate of SO ₂ in SO ₃ in the catalyst becomes at most equal to the allowable value Control unit sets the sulfur sorption temperature to the permissible conversion temperature.  The control apparatus for an internal combustion engine according to claim 1 or 2, wherein the control unit gradually increases the exhaust gas temperature or the catalyst bed temperature until the exhaust gas temperature or the catalyst bed temperature reaches the sulfur sorption temperature.  The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein in the case where the PM regeneration request of the filter is present and an exhaust gas temperature increase request is generated on the downstream side of the catalyst, the control unit determines an oxygen concentration in the exhaust gas that is in the catalyst flows so as to be at most equal to an upper limit of the oxygen concentration that matches an S concentration value of the fuel burned in the internal combustion engine.

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