JP2009013847A - Exhaust fuel addition control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily suppress blocking of an exhaust fuel addition valve even when the concentration of a biofuel is high. <P>SOLUTION: The exhaust fuel addition control device for an engine 1 is equipped with a NOx catalyst such as an NSR catalyst converter 41a and a DPNR catalyst converter 41b, and the exhaust fuel addition valve 17 for injecting and adding a portion of used fuel in the exhaust gas flowing into the catalyst converters 41a, 41b as a reducing agent. The exhaust fuel addition control device performs blockage suppressing control for suppressing blockage in the exhaust fuel addition valve 17. The device is further equipped with a bio concentration sensor for detecting the concentration of the biofuel. When the biofuel concentration is a predetermined value or more, a period without addition until blockage suppressing control is set short. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust fuel addition control device for an internal combustion engine equipped with an exhaust fuel addition valve and capable of using biofuel, and more particularly, easily suppresses clogging of the exhaust fuel addition valve even when the biofuel concentration is high. The present invention relates to an exhaust fuel addition control device for an internal combustion engine.

  In recent years, internal combustion engines mounted on automobiles and the like have been required to improve exhaust emission. That is, before releasing exhaust gas from the internal combustion engine to the atmosphere, gas components such as carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) contained in the exhaust gas are purified or removed. It is requested that.

  In a diesel engine or a gasoline engine capable of lean combustion, an operation region in which an engine operation is performed by using a high air-fuel ratio (lean atmosphere) mixture for combustion occupies most of the entire operation region. In this type of engine, the exhaust system is generally provided with a NOx catalyst that can absorb NOx in a lean atmosphere.

  The NOx catalyst has a characteristic of absorbing NOx when the reducing component concentration in the exhaust gas is low and releasing NOx when the reducing component concentration in the exhaust gas is high. The NOx released into the exhaust reacts quickly with the reducing components such as HC and CO in the exhaust and is reduced to nitrogen.

  Further, there is a limit amount (saturation amount) in the amount of NOx that can be stored by the NOx catalyst, and when the catalyst stores NOx exceeding the saturation amount, the concentration of the reducing component in the exhaust gas becomes low. Even if it exists, it no longer absorbs NOx.

  Therefore, a conventional exhaust gas purification device for an internal combustion engine includes an exhaust fuel addition valve for supplying a reducing agent (a part of the fuel of the internal combustion engine) to the exhaust system of the internal combustion engine, and stores the NOx in the NOx catalyst. Before the amount reaches a predetermined amount, exhaust fuel addition control is performed in which fuel as a reducing agent is repeatedly added to the exhaust gas flowing into the NOx catalyst at predetermined intervals.

  Thus, when the reducing agent is supplied to the exhaust system at a predetermined timing through the exhaust fuel addition valve, the reducing agent increases the concentration of reducing components in the exhaust, and releases and reduces and purifies NOx stored in the NOx catalyst. The NOx absorption capacity of the NOx catalyst is recovered. Therefore, the amount of reducing components in the exhaust gas flowing into the NOx catalyst can be increased at a desired time, and the exhaust gas purification efficiency of the NOx catalyst can always be kept high.

  In particular, in a compression ignition type diesel engine using light oil as fuel, in addition to the above-mentioned CO, HC, NOx, etc., soot contained in exhaust gas, particulate matter such as SOF (Sol bule Organic Fraction) (PM: Particulate) Matter) is required to be purified or removed.

  Therefore, clogging of the nozzle holes of the exhaust fuel addition valve due to deposits causes a serious hindrance to these exhaust purification actions, and therefore various technologies for suppressing clogging of the exhaust fuel addition valve are provided. Has been.

  For example, the injector includes a metal ion removing unit that separates and removes metal and metal ions contained in the fuel from the fuel tank and the injector in the path from the fuel tank to the internal combustion engine. There has been proposed a technique for preventing deposition and deposition of metal in the interior and driving the injector stably for a long period of time (see, for example, Patent Document 1).

  In addition, the following has been proposed as a technique for suppressing clogging of the exhaust fuel addition valve as described above (see, for example, Patent Document 2). That is, a NOx catalyst that is provided in an exhaust passage of an internal combustion engine and reduces nitrogen oxides in the presence of a reducing agent, a reducing agent supply device that supplies the NOx catalyst with a reducing agent, and a timing when an injection hole of the reducing agent supply device is clogged A clogging estimating means for estimating the clogging time estimated by the clogging estimating means, and a clogging suppressing means for injecting a small amount of a reducing agent for suppressing clogging of the injection hole before the clogging timing estimated by the clogging estimating means. The reducing agent is injected before the time when the reducing agent is supplied to suppress clogging of the reducing agent supply device.

  In recent years, alcohol and oxygen-containing fuels such as so-called biofuels have attracted attention as alternative fuels to standard fuels such as gasoline and light oil from the viewpoint of energy and environmental measures, and these fuels can be used. Development of an internal combustion engine is also required.

JP 2006-105092 A Japanese Patent Laid-Open No. 2003-222019

  However, biodiesel (for example, RME, waste cooking oil, etc.), which is such a biofuel, has a feature that evaporability is very poor compared to standard diesel oil. For example, as shown in FIG. 11, the bio diesel oil evaporates only 10 volume% or less even at a temperature (about 330 ° C.) at which the standard diesel oil evaporates by 90 volume%. Here, FIG. 11 is explanatory drawing which shows the distillation characteristic of standard light oil and bio light oil.

  In the related art according to Patent Document 1, since the bio diesel oil concentration is not taken into consideration, the bio fuel concentration is used when a mixed fuel of bio fuel and diesel oil is used for the internal combustion engine (for example, diesel engine). The higher the value, the more easily the fuel residue which has not evaporated yet remains in the exhaust fuel addition valve, and this residue becomes a nucleus and develops into a deposit. For this reason, there is a problem that the exhaust fuel addition valve is more easily clogged as the biofuel concentration is higher.

  In addition, during the suspension period of the exhaust fuel addition, the temperature in the vicinity of the exhaust fuel addition valve becomes high, and deposit cleaning due to fuel addition cannot be performed, so the deposit of the exhaust fuel addition valve is most easily formed during the suspension period. Deposits were the main cause of clogging of the exhaust fuel addition valve.

  Furthermore, when the exhaust fuel addition valve is clogged, NOx reduction, PM regeneration, and sulfur poisoning regeneration cannot be performed, which may cause a problem in vehicle travel.

  The present invention has been made in view of the above, and provides an exhaust fuel addition control device for an internal combustion engine that can easily suppress clogging of an exhaust fuel addition valve even when the biofuel concentration is high. For the purpose.

  In order to solve the above-described problems and achieve the object, an exhaust fuel addition control device for an internal combustion engine according to claim 1 of the present invention is provided in an exhaust system of the internal combustion engine and has a high concentration of reducing components in the exhaust gas. Then, a NOx catalyst having a characteristic for promoting a reduction reaction of NOx, an exhaust fuel addition valve for injecting and adding a part of the used fuel as a reducing agent into the exhaust gas flowing into the NOx catalyst through the exhaust system, and the exhaust In addition to the addition valve clogging suppression means for performing control for suppressing clogging of the fuel addition valve, an exhaust fuel addition control device for an internal combustion engine further comprising a biofuel concentration detection for detecting or estimating the concentration of biofuel as the fuel used Means, and when the biofuel concentration detected or estimated by the biofuel concentration detection means is a predetermined value or more, at least according to the biofuel concentration, Increasing the frequency of execution of clogging suppression control by serial addition valve clogging suppression means, characterized in that to increase the capacity of the clogging suppression control by the adding valve clogging suppression means.

  According to a second aspect of the present invention, there is provided the exhaust fuel addition control device for an internal combustion engine according to the first aspect, wherein the clogging suppression control increases the frequency of fuel addition from the exhaust fuel addition valve. It is what.

  According to a third aspect of the present invention, the exhaust fuel addition control device for an internal combustion engine according to the first or second aspect further comprises addition pressure adjusting means for adjusting the fuel addition pressure from the exhaust fuel addition valve. The clogging suppression control is characterized in that the fuel addition pressure from the exhaust fuel addition valve is increased by the addition pressure adjusting means.

  According to a fourth aspect of the present invention, the exhaust fuel addition control device for an internal combustion engine according to the first or second aspect further comprises an addition valve cooling means for lowering the temperature of the exhaust fuel addition valve, The clogging suppression control is characterized in that the temperature of the exhaust fuel addition valve is lowered by the addition valve cooling means.

  According to the exhaust fuel addition control device for an internal combustion engine according to the present invention (Claim 1), even if the biofuel is at a predetermined high concentration, the execution frequency of the clogging suppression control is increased or the capability of the clogging suppression control is increased. As a result, the temperature in the vicinity of the exhaust fuel addition valve can be lowered, and unevaporated fuel residue can be easily washed with the added fuel, so that it is difficult for deposits to be formed in the nozzle holes of the exhaust fuel addition valve. Clogging of the addition valve can be suppressed. Further, by suppressing this clogging, NOx reduction, PM regeneration, and sulfur poisoning regeneration can be performed without any trouble.

  Further, according to the exhaust fuel addition control device for an internal combustion engine according to the present invention (Claim 2), even if the biofuel has a predetermined high concentration, by setting a short period of no addition until the clogging suppression control. Since it becomes difficult to form deposits in the nozzle holes of the exhaust fuel addition valve, clogging of the exhaust fuel addition valve can be suppressed.

  Further, according to the exhaust fuel addition control device for an internal combustion engine according to the present invention (Claim 3), even when the biofuel has a predetermined high concentration, the fuel addition pressure is increased by the addition pressure adjusting means during the clogging suppression control. By doing so, it is difficult to form deposits in the nozzle holes of the exhaust fuel addition valve, and clogging of the exhaust fuel addition valve can be suppressed.

  According to the exhaust fuel addition control device for an internal combustion engine according to the present invention (Claim 4), the exhaust fuel addition valve is configured to be cooled by the addition valve cooling means such as a cooling medium. The temperature in the vicinity of the nozzle hole can be lowered to suppress the development of non-evaporated fuel residues into deposits, and clogging of the exhaust fuel addition valve can be suppressed.

  Hereinafter, an embodiment of an exhaust fuel addition control device for an internal combustion engine according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  1 is a schematic configuration diagram showing a diesel engine system to which an exhaust fuel addition control device for an internal combustion engine according to Embodiment 1 of the present invention is applied. As shown in FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 includes a fuel supply system 10, a combustion chamber 20, and an intake system that forms a passage (intake passage) of intake air supplied into the combustion chamber 20. 30, an in-line four-cylinder diesel engine system having an exhaust system 40 and the like forming a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20 as a main part.

  The fuel supply system 10 includes a fuel tank 18 for storing biofuel, a main fuel passage P0, a fuel filter 18a, a supply pump 11, a common rail 12, a fuel injection valve 13, a shutoff valve 14, an exhaust fuel addition valve 17, and an engine fuel passage P1. And an additional fuel passage P2 and the like.

  The fuel tank 18 is provided with a bio-concentration sensor (bio-fuel concentration detection means) 19 that detects the bio-concentration of the fuel. The bio-concentration sensor 19 may be configured so as to be able to detect or estimate the biofuel concentration from, for example, measured values such as fuel viscosity and temperature, and the detection / estimation principle is not limited.

  The supply pump 11 increases the pressure of the fuel pumped from the fuel tank 18 via the main fuel passage P0 and supplies it to the common rail 12 via the engine fuel passage P1. The common rail 12 accumulates the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure and distributes it to each fuel injection valve 13. A fuel injection valve 13 that is an electromagnetic valve injects fuel into the combustion chamber 20 at a predetermined time.

  Further, the supply pump 11 supplies a part of the fuel pumped from the fuel tank 18 to the exhaust fuel addition valve 17 via the addition fuel passage P2. The shut-off valve 14 shuts off the fuel supply P2 when necessary and stops the fuel supply.

  A metering valve (not shown) is also provided in the added fuel passage P2. This metering valve controls the pressure (fuel pressure) of the fuel supplied to the exhaust fuel addition valve 17. Further, the exhaust fuel addition valve 17 that is an electromagnetic valve adds and supplies the fuel functioning as a reducing agent in an appropriate amount at an appropriate timing to the upstream of the catalytic converters 41a and 41b described later.

  Further, the engine 1 includes a turbocharger 50 that supercharges intake air by the exhaust gas. The intercooler 31 provided in the turbocharger 50 forcibly cools the intake air whose temperature has been increased by supercharging. The throttle valve 32 provided downstream of the intercooler 31 is a so-called electronic throttle, and adjusts the amount of intake air supplied.

  Further, the engine 1 is provided with an EGR passage 60 that bypasses the intake system 30 and the exhaust system 40 and returns a part of the exhaust to the intake system 30. The EGR passage 60 is provided with an EGR valve 61 that adjusts the exhaust gas flow rate and an EGR cooler 62 that cools the exhaust gas. A catalyst (not shown) is provided on the upstream side of the EGR cooler 62.

  The exhaust system 40 includes an NSR (NOx Storage Reduction) catalytic converter 41a in which a NOx storage reduction catalyst is supported on a carrier, and a DPNR (Diesel Particulate NOx Reduction) in which a NOx storage reduction catalyst is supported on a porous ceramic structure. ) A catalytic converter 41b and an oxidation catalytic converter 42 provided downstream thereof are provided.

  These catalytic converters 41a and 41b are for storing NOx when the air-fuel ratio of the exhaust gas is lean, and for releasing and reducing the NOx stored in the reducing atmosphere while reducing the oxygen concentration in the exhaust gas. .

  In particular, the DPNR catalytic converter 41b is configured such that the NOx storage reduction catalyst is supported on a porous ceramic structure that functions as a filter that supplements PM, and therefore, during lean combustion, the PM has a porous structure. It is temporarily collected in the ceramic structure and oxidized by oxygen in the exhaust gas.

  Further, NOx is temporarily stored in the catalyst during lean combustion, and then reduced and purified when rich combustion is instantaneously performed. During rich combustion, PM is oxidized and purified by oxygen generated when the stored NOx is reduced.

  When the temperature of the catalytic converters 41a and 41b is relatively low, the added fuel from the exhaust fuel addition valve 17 may slip through the catalytic converters 41a and 41b. Can be oxidized to.

  Further, each part of the engine 1 includes an air flow meter 72 that detects an intake air amount, an air-fuel ratio sensor 73 that detects an oxygen concentration in exhaust gas, and an exhaust gas temperature that detects exhaust gas temperatures upstream and downstream of the DPNR catalytic converter 41b. A pressure sensor 75 for detecting a pressure difference between the upstream side and the downstream side of the sensors 74a and 74b, the NSR catalytic converter 41a and the DPNR catalytic converter 41b is provided.

  Although not shown, each part of the engine 1 includes a temperature sensor and a pressure sensor for detecting the temperature and pressure of the fuel in the common rail 12, a crank position sensor for detecting the crankshaft rotation of the engine 1, and an intake air temperature. Intake temperature sensor for detecting, intake pressure sensor for detecting intake pressure, accelerator position sensor for detecting accelerator pedal depression amount (accelerator position), throttle position sensor for detecting position of throttle valve 32, and cooling of engine 1 A water temperature sensor or the like for detecting the water temperature is provided.

  An ECU (not shown) receives detection signals from the various sensors via an external input circuit, and controls the operation of the engine 1 such as opening / closing control of the fuel injection valve 13 and the exhaust fuel addition valve 17 based on these signals. Various controls related to the state are performed, and the addition valve clogging suppression means and the exhaust fuel addition control device function.

  Next, the control method according to the first embodiment will be described with reference to FIGS. 1, 3, and 4 based on FIG. Here, FIG. 2 is a flowchart showing a control method, FIG. 3 is an explanatory diagram showing a period TA without addition of fuel when the biofuel is at a low concentration and when the fuel is only light oil, and FIG. 4 is at a high concentration of the biofuel. It is explanatory drawing which shows the period TB without fuel addition in. The period TA and the period TB without addition shown in FIGS. 3 and 4 have a relationship of TA> TB.

  This control is executed by the ECU (not shown). As shown in FIG. 2, first, the biofuel concentration is detected by the bioconcentration sensor 19 (step S10). Next, it is determined whether or not the detected biofuel concentration exceeds a predetermined value WL (step S20).

  This predetermined value WL is a “non-addition period TA” as a limit value set when the fuel used is only ordinary light oil or a predetermined low concentration during the clogging suppression control of the exhaust fuel addition valve 17. This is a judgment threshold when setting the “no-addition period TB” shorter than this so as to maintain the effect of suppressing clogging, and is obtained in advance by experiments or the like.

  As shown in FIG. 3, when the fuel used is only ordinary light oil or a predetermined low concentration (less than a predetermined value WL), fuel as a reducing agent is supplied from the exhaust fuel addition valve 17 to reduce NOx, regenerate PM, It is added at a predetermined timing for sulfur poisoning regeneration, and further, after a “period TA without addition”, for clogging suppression (in FIGS. 3 and 4, “clogging prevention” is described). The fuel will be added again. These addition controls are repeatedly executed at a constant timing when necessary.

  On the other hand, when the fuel used is biofuel and has a predetermined high concentration (predetermined value WL or more), the “non-addition period TB” shown in FIG. 4 is selected and the exhaust fuel addition control is executed. Become.

  That is, in the case of light oil mixed with biofuel and the biofuel concentration exceeds the predetermined value WL (Yes at Step S20), the period without fuel addition is set to TB (<TA) (Step S30). Then, the conventional exhaust fuel addition control is performed (step S50), and the control is terminated. The period TB without this addition is shown in FIG. Note that the exhaust fuel addition control has the same control content as the conventional one, and thus the description thereof is omitted.

  Even when the biofuel has a predetermined high concentration, the temperature in the vicinity of the exhaust fuel addition valve 17 can be lowered by addition of fuel at shorter intervals than in the case of only light oil or the like, and unvaporized fuel residue is also added. Since it becomes easy to wash with fuel, it becomes difficult to form deposits in the nozzle holes of the exhaust fuel addition valve 17, and clogging of the exhaust fuel addition valve 17 is suppressed. Further, by suppressing this clogging, NOx reduction, PM regeneration, and sulfur poisoning regeneration can be performed without any trouble.

  On the other hand, if the biofuel concentration does not exceed the predetermined value WL (No in step S20), the clogging suppression effect is considered to be maintained in the same manner as in the case of light oil alone, so In the case of only TA (step S40), exhaust fuel addition control is performed (step S50), and the control is terminated.

  As described above, according to the exhaust fuel addition control device for an internal combustion engine according to the first embodiment, even if the biofuel has a predetermined high concentration, by setting a short period without addition until the clogging suppression control. Since it becomes difficult to form deposits in the nozzle holes of the exhaust fuel addition valve 17, clogging of the exhaust fuel addition valve 17 can be suppressed. Further, by suppressing this clogging, NOx reduction, PM regeneration, and sulfur poisoning regeneration can be performed without any trouble.

  FIG. 5 is a flowchart showing a control method according to Embodiment 2 of the present invention, and FIG. 6 is a map showing an example of a period without addition set according to the biofuel concentration. In the following description, the same or corresponding parts as those already described or the step numbers are denoted by the same reference numerals, and redundant description is omitted or simplified.

  The system configuration of the second embodiment is the same as the configuration shown in FIG. In the first embodiment, the determination threshold value of the detected biofuel concentration is determined by one WL, and the period without addition is set to two types (TA and TB) (see steps S20 to S40 in FIG. 2). ). On the other hand, in the present Example 2, as shown in the map of FIG. 6, the period without addition is set for every 10% of biofuel concentration, for example.

  That is, in the second embodiment, as shown in FIG. 5, from the biofuel concentration detected in step S10 and the map of FIG. 6 read in step S15, a more detailed response according to the biofuel concentration is obtained. A period without addition is set (step S25), and exhaust fuel addition control is performed (step S50).

  Therefore, according to the exhaust fuel addition control device for an internal combustion engine according to the second embodiment, the exhaust fuel addition control can be performed based on the period without fine addition according to the biofuel concentration. 17 can be more effectively suppressed.

  FIG. 7 is a schematic configuration diagram showing a diesel engine system to which an exhaust fuel addition control device for an internal combustion engine according to Embodiment 3 of the present invention is applied, and FIG. 8 is a flowchart showing a control method.

  In the third embodiment, when the biofuel concentration is increased to a predetermined value, the fuel addition pressure is set at the time of exhaust fuel addition (at the time of addition for preventing or suppressing clogging) after the non-addition period continues. By setting it high, it is difficult to form deposits in the nozzle holes of the exhaust fuel addition valve 17, and clogging of the exhaust fuel addition valve 17 can be suppressed.

  As shown in FIG. 7, the system configuration of the third embodiment is different from the configuration shown in FIG. That is, the supply pump (addition pressure adjusting means) 11 is variable in pressure, and the pressure sensor (addition pressure adjusting means) 81 is provided in the added fuel passage P2, so that the target added pressure of the exhaust fuel addition valve 17 is set in the ECU. It can be changed by a command.

  Further, in order to reduce the pressure when the added fuel passage P2 becomes a predetermined high pressure, a fuel return passage (addition pressure adjusting means) P3 communicating with the added fuel passage P2 and the fuel tank 18, an added fuel passage P2, An electromagnetic relief valve (additional pressure adjusting means) 80 provided at a connection portion of the fuel return passage P3 and opening the valve to return a predetermined amount of fuel to the fuel tank 18 through the fuel return passage P3 to reduce the pressure. And.

  Next, a control method according to the third embodiment will be described with reference to FIG. 7 based on FIG. The following control is also executed by the ECU. As shown in FIG. 8, first, the biofuel concentration is detected by the bioconcentration sensor 19 (step S10), and it is determined whether or not the detected biofuel concentration exceeds a predetermined value WL (step S20).

  The predetermined value WL is a threshold value for determining whether or not the fuel addition pressure needs to be changed from the normal pressure target value PA to the high pressure target value PB (> PA), and is obtained in advance through experiments or the like. is there.

  If the biofuel concentration exceeds the predetermined value WL (Yes at Step S20), the addition pressure is set to the high pressure target value PB (Step S35), and the output value of the pressure sensor 81 is set so as to be the high pressure target value PB. The supply pump 11 is operated while referring to the exhaust fuel addition control (step S50).

  The feature of the third embodiment is that the target value of the addition pressure is variably set according to the biofuel concentration, and the exhaust fuel addition control method based on the target value is the same as the conventional method. Is omitted.

  On the other hand, if the biofuel concentration does not exceed the predetermined value WL (No in step S20), the addition pressure is set to the target value PA of the normal pressure (step S45), and the pressure sensor 81 is set to the high pressure target value PA. The supply pump 11 is operated while referring to the output value, and exhaust fuel addition control is performed (step S50).

  As described above, in the third embodiment, when the biofuel concentration is increased to a predetermined value, the exhaust fuel is added after the non-addition period continues (at the time of addition for preventing or suppressing clogging). The fuel addition pressure is set high to prevent clogging of the exhaust fuel addition valve 17. During control other than this clogging suppression control, that is, fuel addition control for NOx reduction, PM regeneration, and sulfur poisoning regeneration, the addition pressure is left at the basic setting (set to the target value PA of the normal pressure) It is necessary to suppress adverse effects on overheating and emission of the catalytic converters 41a and 41b. Therefore, following step S50, the following control is performed.

  It is determined whether or not fuel addition for suppressing clogging of the exhaust fuel addition valve 17 has been completed (step S60). If the fuel addition is not completed, the process waits until the process ends (No at Step S60). If the process ends (Yes at Step S60), the fuel supply pressure (addition pressure) to the exhaust fuel addition valve 17 is the normal pressure target value PA. It is judged whether or not (step S70).

  If the fuel supply pressure exceeds the target value PA of the normal pressure (Yes at Step S70), the predetermined amount of fuel is returned to the fuel tank 18 via the fuel return passage P3 by adjusting the opening of the electromagnetic relief valve 80. Then, the fuel supply pressure is lowered to the normal pressure target value PA (basic set value) (step S80).

  Then, based on the normal pressure target value PA, normal catalyst control (fuel addition control) such as NOx reduction, PM regeneration, sulfur poisoning regeneration, and the like is performed (step S90). Thus, by returning the fuel supply pressure to the basic setting value except when necessary, the catalyst converters 41a, 41b and the like are prevented from being adversely affected by overheating and emission.

  On the other hand, if the fuel supply pressure does not exceed the target value PA of the normal pressure (No at Step S70), the normal catalyst control (fuel addition control) may be performed while maintaining the basic set pressure (Step S90). In addition, since the said normal catalyst control method is the same as that of the past, description is abbreviate | omitted.

  As described above, according to the exhaust fuel addition control device for an internal combustion engine according to the third embodiment, when the biofuel concentration increases to a predetermined value, the fuel addition pressure is set high during the clogging suppression control. Therefore, it is difficult to form deposits in the nozzle holes of the exhaust fuel addition valve 17 and clogging of the exhaust fuel addition valve 17 can be suppressed.

  In addition to the clogging suppression control, that is, the fuel addition control for NOx reduction, PM regeneration, and sulfur poisoning regeneration, the addition pressure can be kept at the basic setting (normal pressure). The adverse effects on overheating and emission of the converters 41a and 41b can be suppressed.

  FIG. 9 is a flowchart showing a control method according to Embodiment 4 of the present invention, and FIG. 10 is a map showing an example of the addition pressure set according to the biofuel concentration.

  The system configuration of the fourth embodiment is the same as the configuration shown in FIG. In Example 3 described above, the determination threshold of the detected biofuel concentration is determined by one WL, and two types of addition pressures (PA and PB) are set (Steps S20, S35, and S45 in FIG. 8). See). On the other hand, in the present Example 4, as shown in the map of FIG. 10, for example, the addition pressure is set for every 10% of the biofuel concentration.

  That is, in the fourth embodiment, as shown in FIG. 9, from the biofuel concentration detected in step S10 and the map of FIG. 10 read in step S16, a finer detail according to the biofuel concentration is obtained. An addition pressure is set (step S26), and exhaust fuel addition control is performed (step S50). The other control methods (steps S60 to S90) are the same as in the case of the third embodiment, and a duplicate description is omitted.

  Therefore, according to the exhaust fuel addition control device for an internal combustion engine according to the fourth embodiment, the exhaust fuel addition control can be performed based on the fine addition pressure corresponding to the biofuel concentration. Clogging can be further effectively suppressed.

  In the first to fourth embodiments, an in-line four-cylinder diesel engine system has been described as an example. However, the present invention is not limited to this and may be applied to other engine systems, and the same effect can be expected.

  Further, the exhaust fuel addition control may be performed by appropriately combining any of the above-described Examples 1 to 4, that is, according to the biofuel concentration, by changing the set value of the non-addition period and the addition pressure. .

  Moreover, in the said Example 3 and 4, although demonstrated as what raises the capability of clogging suppression control by increasing addition pressure when biofuel concentration is more than predetermined value, it is not limited to this, Clogging suppression control The clogging suppression control may be any means as long as it is a means for improving the ability. Also in this case, it may be carried out in combination with the above embodiments.

  That is, for example, a means for lowering the temperature of the exhaust fuel addition valve 17 may be used. By configuring the exhaust fuel addition valve 17 so that it can be cooled by a cooling medium or the like, the temperature in the vicinity of the injection hole of the exhaust fuel addition valve 17 can be achieved. , And it is possible to suppress the unevaporated fuel residue from developing into a deposit, and to suppress clogging of the exhaust fuel addition valve 17.

  As described above, the exhaust fuel addition control device for an internal combustion engine according to the present invention is useful for an internal combustion engine that is equipped with an exhaust fuel addition valve and can use biofuel, even when the biofuel concentration is high. It is suitable for an internal combustion engine aiming at easily suppressing clogging of an exhaust fuel addition valve.

1 is a schematic configuration diagram showing a diesel engine system to which an exhaust fuel addition control device for an internal combustion engine according to Embodiment 1 of the present invention is applied. FIG. It is a flowchart which shows a control method. It is explanatory drawing which shows the period TA without a fuel addition at the time of a biofuel low concentration and when a fuel is only light oil. It is explanatory drawing which shows period TB without fuel addition at the time of biofuel high concentration. It is a flowchart which shows the control method which concerns on Example 2 of this invention. It is a map which shows an example of the period without addition set according to biofuel concentration. It is a schematic block diagram which shows the diesel engine system to which the exhaust fuel addition control apparatus of the internal combustion engine which concerns on Example 3 of this invention is applied. It is a flowchart which shows a control method. It is a flowchart which shows the control method which concerns on Example 4 of this invention. It is a map which shows an example of the addition pressure set according to biofuel concentration. It is explanatory drawing which shows the distillation characteristic of standard light oil and bio light oil.

Explanation of symbols

1 engine (internal combustion engine)
10 Fuel supply system 11 Supply pump (addition pressure adjusting means)
17 Exhaust fuel addition valve 18 Fuel tank 18a Fuel filter 19 Bio concentration sensor (bio fuel concentration detection means)
20 Combustion chamber 30 Intake system 40 Exhaust system 41a NSR catalytic converter (NOx catalyst)
41b DPNR catalytic converter (NOx catalyst)
42 Oxidation catalytic converter 73 Air-fuel ratio sensor 74a, 74b Exhaust temperature sensor 80 Electromagnetic relief valve (addition pressure adjusting means)
81 Pressure sensor (addition pressure adjusting means)
P0 Main fuel passage P1 Engine fuel passage P2 Addition fuel passage P3 Fuel return passage (addition pressure adjusting means)

Claims (4)

A NOx catalyst that is provided in an exhaust system of an internal combustion engine and has a characteristic that promotes a reduction reaction of NOx when the concentration of a reducing component in the exhaust gas increases;
An exhaust fuel addition valve for injecting and adding a part of the used fuel as a reducing agent into the exhaust gas flowing into the NOx catalyst through the exhaust system;
Addition valve clogging suppression means for performing control to suppress clogging of the exhaust fuel addition valve;
An exhaust fuel addition control device for an internal combustion engine comprising:
Furthermore, a biofuel concentration detection means for detecting or estimating the concentration of biofuel as the fuel used is provided,
When the biofuel concentration detected or estimated by the biofuel concentration detection means is a predetermined value or more, according to the biofuel concentration, at least increase the execution frequency of the clogging suppression control by the addition valve clogging suppression means, An exhaust fuel addition control device for an internal combustion engine characterized by enhancing the ability of clogging suppression control by the addition valve clogging suppression means.   The exhaust fuel addition control apparatus for an internal combustion engine according to claim 1, wherein the clogging suppression control increases a frequency of fuel addition from the exhaust fuel addition valve.   And further comprising an addition pressure adjusting means for adjusting a fuel addition pressure from the exhaust fuel addition valve, wherein the clogging suppression control increases a fuel addition pressure from the exhaust fuel addition valve by the addition pressure adjustment means. The exhaust fuel addition control device for an internal combustion engine according to claim 1 or 2.   The addition valve cooling means for lowering the temperature of the exhaust fuel addition valve is further provided, and the clogging suppression control lowers the temperature of the exhaust fuel addition valve by the addition valve cooling means. 2. An exhaust fuel addition control device for an internal combustion engine according to 1.

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