JP2015108341A - Water supply controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently reduce NOx and soot in exhaust.SOLUTION: A water supply controller for internal combustion engine includes: water supply means (250) for supplying water (410, 420) to a combustion chamber (201) of an internal combustion engine (200); operation condition determination means (151) for determining whether an operation condition of the internal combustion engine is a first operation condition in which NOx as a component of exhaust produced in the combustion chamber of the internal combustion engine is requested to be reduced more than soot as a component thereof or a secondo condition in which the soot is requested to be reduced more than the NOx; and nitric acid concentration control means (154) for making the nitric acid concentration of the water supplied by the water supply means higher when it is determined that the operation condition of the internal combustion engine is the second operation condition than when it is determined that the operation condition is the first operation condition.

Description

  The present invention relates to a technical field of a water supply control device for an internal combustion engine that supplies water to a combustion chamber of the internal combustion engine in order to reduce NOx, for example.

  In an internal combustion engine, NOx is generated with combustion in the combustion chamber. As a technique for reducing this NOx emission, a technique for supplying water to a combustion chamber of an internal combustion engine has been proposed. For example, Patent Document 1 discloses a technique in which condensed water generated in a cooling unit that cools exhaust gas recirculated from an exhaust side to an intake side is injected into an intake passage of an internal combustion engine.

  In addition, there is Patent Document 2 as a prior art document related to the present invention.

Japanese Patent Laid-Open No. 10-318049 Japanese Patent Laid-Open No. 2004-060539

  The amount of NOx emission can be reduced by supplying water to the internal combustion engine as in the technique described in Patent Document 1. However, as with NOx, soot contained in exhaust gas cannot be effectively reduced by simply supplying water to the internal combustion engine. That is, the prior art including Patent Document 1 has a technical problem that even if NOx in exhaust gas can be reduced, soot cannot be reduced.

  Examples of problems to be solved by the present invention include the above. An object of the present invention is to provide a water supply control device for an internal combustion engine capable of efficiently reducing NOx and soot in exhaust gas.

<1>
The water supply control device for an internal combustion engine of the present invention includes a water supply means for supplying water to a combustion chamber of the internal combustion engine, and an operating condition of the internal combustion engine is a component of combustion gas generated in the combustion chamber of the internal combustion engine. An operating condition determining means for determining whether the first operating condition is required to reduce NOx rather than soot, or the second operating condition required to reduce soot than NOx; and the operation of the internal combustion engine Nitric acid concentration control for increasing the nitric acid concentration of water supplied by the water supply means when it is determined that the condition is the second operating condition as compared to the case where the condition is determined to be the first operating condition Means.

  According to the water supply control device for an internal combustion engine of the present invention, water can be supplied to the combustion chamber of the internal combustion engine by the water supply means. Thereby, reduction of NOx, soot, etc. contained in the exhaust gas of the internal combustion engine is realized. Specifically, by supplying water to the combustion chamber of the internal combustion engine, the combustion temperature is lowered by the heat of vaporization, and the amount of NOx generated due to combustion is suppressed. Or the nitric acid in a water | moisture content couple | bonds with a hydrocarbon and generates a carbon dioxide, The generation amount of soot is suppressed.

  Incidentally, the water supply means according to the present invention is not limited to the one that supplies water directly to the combustion chamber of the internal combustion engine, but indirectly supplies water to the combustion chamber, for example, by injecting water into the intake passage of the internal combustion engine. It may be supplied.

  During operation of the water supply control device for an internal combustion engine of the present invention, it is first determined by the operating condition determination means whether the operating condition of the internal combustion engine is the first operating condition or the second operating condition. Here, the “first operating condition” is an operating condition that requires a reduction in NOx rather than soot for the component of the combustion gas generated in the combustion chamber of the internal combustion engine. On the other hand, the “second operating condition” is an operating condition that requires a reduction in soot compared to NOx. The operating condition determination means makes a determination by estimating the amount of each component contained in the exhaust gas from the rotational speed and torque of the internal combustion engine, for example. Specifically, when it is estimated that the load on the internal combustion engine is high and a relatively large amount of NOx is discharged, it is determined that the internal combustion engine is in the first operating condition, and the load on the internal combustion engine is low and the NOx is relatively low. If the operating conditions are estimated to be low (in other words, relatively high soot emissions), the internal combustion engine may be determined to be the second operating condition.

  When the operating condition is determined, the nitric acid concentration of the water (that is, water supplied to the combustion chamber of the internal combustion engine by the water supply unit) by the nitric acid concentration control unit is adjusted based on the determination result. Specifically, the nitric acid concentration control means is supplied by the water supply means when the operating condition of the internal combustion engine is determined to be the second operating condition, compared to the case where it is determined to be the first operating condition. Increase the concentration of nitric acid in the water. Conversely, when the operating condition of the internal combustion engine is determined to be the first operating condition, the nitric acid concentration control means uses the water supply means to compare with the case where it is determined that the operating condition is the second operating condition. Reduce the concentration of nitric acid in the supplied water.

If the nitric acid concentration is adjusted as described above, water with a relatively high nitric acid concentration is supplied to the combustion chamber of the internal combustion engine when soot reduction is required rather than NOx (that is, in the second operating condition). Is done. When water is supplied to the combustion chamber of the internal combustion engine, the amount of NOx generated can be reduced by lowering the combustion temperature. In addition, since water having a high nitric acid concentration has a strong ability to oxidize soot, the amount of soot generated due to combustion can be effectively reduced. However, nitric acid generates NO ₂ (that is, NOx) when oxidizing soot. Therefore, water with a high concentration of nitric acid is not necessarily effective from the viewpoint of reducing the amount of NOx generated while greatly reducing the amount of soot generated.

However, in the present invention, when NOx reduction is required rather than soot (that is, in the first operating condition), water having a relatively low nitric acid concentration is supplied to the combustion chamber of the internal combustion engine. In this case, the effect of reducing the amount of soot is reduced, but the generation of NO ₂ due to the oxidation of soot is also suppressed. Therefore, the NOx reduction effect by supplying water to the combustion chamber of the internal combustion engine is remarkably exhibited.

  As described above, according to the water supply control device for an internal combustion engine of the present invention, water having different nitric acid concentrations is supplied to the combustion chamber of the internal combustion engine according to which of NOx and soot should be reduced with priority. The Therefore, components to be reduced from the exhaust can be effectively reduced by supplying water.

  The nitric acid concentration of water supplied to the combustion chamber of the internal combustion engine is limited to one that selectively determines two values (that is, a low value or a high value) according to the first operating condition or the second operating condition. For example, it may be varied in multiple stages or linearly depending on the amount of NOx or soot generated. Specifically, even when the first operating condition is determined, when it is estimated that the amount of NOx generated is extremely large, water having a lower nitric acid concentration may be supplied. Similarly, even when it is determined as the second operating condition, when it is estimated that the amount of generated soot is extremely large, water having a higher nitric acid concentration may be supplied. In other words, NOx and soot in the exhaust can be efficiently reduced by increasing the concentration of nitric acid in the water supplied to the internal combustion engine as the soot reduction requirement increases.

<2>
In another aspect of the water supply control device for an internal combustion engine according to the present invention, the water supply means generates condensed water generated in a recirculation exhaust cooling means for cooling the exhaust gas recirculated from the exhaust side to the intake side. To the combustion chamber.

  According to this aspect, it is possible to reduce NOx and soot in the exhaust using the condensed water generated in the reflux exhaust cooling means. Therefore, it is not necessary to separately prepare dedicated water to be supplied to the combustion chamber of the internal combustion engine, and it is possible to prevent the device configuration from becoming complicated, large, or costly.

<3>
As described above, in the aspect in which the condensed water generated in the recirculation exhaust cooling means is supplied to the combustion chamber of the internal combustion engine, the nitric acid concentration control means may estimate that the nitric acid concentration is higher as the pH of the condensed water is lower. .

The condensed water generated in the reflux exhaust cooling means changes its pH depending on the concentration of nitric acid derived from NO ₂ contained in the refluxing exhaust gas, due to its characteristics. Therefore, when the condensed water generated in the recirculation exhaust cooling means is supplied to the combustion chamber of the internal combustion engine, it is possible to estimate the nitric acid concentration according to the pH that is relatively easy to detect without detecting the nitric acid concentration of the condensed water. It becomes.

<4>
Alternatively, in the aspect in which the condensed water generated in the recirculation exhaust cooling means is supplied to the combustion chamber of the internal combustion engine, the condensed water nitric acid generated in the recirculation exhaust cooling means is based on the amount of NOx discharged from the internal combustion engine. Concentration estimation means for estimating the concentration or pH, and condensate storage means for storing the condensate in a plurality of storage tanks according to the nitric acid concentration or pH estimated by the concentration estimation means, The nitric acid concentration control means may adjust the nitric acid concentration or pH of the water supplied by the water supply means by changing the ratio of the condensed water taken out from each of the plurality of storage tanks.

  In this case, when collecting condensed water, first, the concentration estimating means estimates the nitric acid concentration or pH of the condensed water generated in the recirculation exhaust cooling means based on the amount of NOx discharged from the internal combustion engine. . Specifically, when a large amount of NOx is discharged from the internal combustion engine, it is considered that the amount of NOx in the recirculated exhaust gas also increases. Therefore, the concentration of nitric acid in the condensed water generated in the recirculation exhaust cooling means is estimated to be high. . Similarly, when the amount of NOx emitted from the internal combustion engine is small, it is considered that the NOx in the recirculated exhaust gas is also small, so the concentration of nitric acid in the condensed water generated in the recirculation exhaust cooling means is estimated to be low.

  When the concentration or pH of the condensed water is estimated, the condensed water generated in the reflux exhaust cooling means is divided and stored in a plurality of storage tanks according to the estimated nitric acid concentration or pH by the condensed water storage means. . That is, the condensed water having a high nitric acid concentration and the condensed water having a low nitric acid concentration are stored in different storage tanks.

  In particular, when adjusting the nitric acid concentration or pH by the nitric acid concentration control means, the ratio of condensed water taken out from each of the plurality of storage tanks is changed to adjust the nitric acid concentration or pH of the water supplied by the water supply means. . Specifically, when water with a high concentration of nitric acid is to be supplied to the internal combustion engine, a large amount of water is taken out from a storage tank that stores condensed water with a high concentration of nitric acid, and condensed water with a low concentration of nitric acid is stored. A small amount of water can be taken from the existing storage tank. Similarly, if you want to supply water with low nitric acid concentration to the internal combustion engine, take out a small amount of water from the storage tank that stores condensed water with high nitric acid concentration, and store with condensed water with low nitric acid concentration. A lot of water can be removed from the tank.

  According to the configuration described above, it is possible to accurately adjust the concentration of nitric acid or pH of condensed water only by changing the ratio of water taken out from the storage tank. Therefore, an appropriate concentration of condensed water can be suitably supplied to the combustion chamber of the internal combustion engine.

<5>
As described above, in the aspect in which the concentration of nitric acid is higher as the pH of the condensed water is lower, the pH detecting means is provided at the position where the condensed water is generated in the reflux exhaust cooling means, and detects the pH of the condensed water. And condensate storage means for storing the condensate in a plurality of storage tanks according to the pH detected by the pH detection means, and the nitric acid concentration control means The concentration of nitric acid or pH of the water supplied by the water supply means may be adjusted by changing the ratio of the condensed water taken out from each.

  In this case, when collecting condensed water, the pH of the condensed water (that is, a value corresponding to the nitric acid concentration) is first detected by the pH detecting means provided at the position where the condensed water is generated in the reflux exhaust cooling means. The The pH detection means is configured as a pH sensor, for example.

  When the pH of the condensed water is detected, the condensed water generated in the recirculation exhaust cooling means is divided and stored in a plurality of storage tanks according to the detected pH. That is, the condensed water having a high pH and the condensed water having a low pH are stored in different storage tanks.

  In particular, when adjusting the nitric acid concentration or pH by the nitric acid concentration control means, the ratio of condensed water taken out from each of the plurality of storage tanks is changed to adjust the nitric acid concentration or pH of the water supplied by the water supply means. . Specifically, when water with a high concentration of nitric acid is to be supplied to the internal combustion engine, a large amount of water is taken out from a storage tank that stores condensed water having a low pH, and a storage that stores condensed water having a high pH is stored. A small amount of water can be removed from the tank. Similarly, when water with low nitric acid concentration is to be supplied to the internal combustion engine, a small amount of water is taken out from the storage tank storing condensate with low pH, and from the storage tank storing condensate with high pH. Just need to drain a lot of water.

  According to the configuration described above, it is possible to accurately adjust the concentration of nitric acid or pH of condensed water only by changing the ratio of water taken out from the storage tank. Therefore, an appropriate concentration of condensed water can be suitably supplied to the combustion chamber of the internal combustion engine.

  The effect | action and other gain of this invention are clarified from the form for implementing demonstrated below.

It is a schematic structure figure showing the whole engine system composition concerning an embodiment. It is a schematic block diagram which shows the structure of the water supply control apparatus of the internal combustion engine which concerns on embodiment. It is a flowchart which shows the operation | movement at the time of the condensate collection by the water supply control apparatus of the internal combustion engine which concerns on embodiment. It is a map which shows the relationship between the driving | running condition of an engine, and the area | region which collects the condensed water in an EGR cooler. It is a flowchart which shows the operation | movement at the time of the condensed water supply by the water supply control apparatus of the internal combustion engine which concerns on embodiment. It is a map which shows the relationship between the driving | running condition of an engine, and the pH of the condensed water supplied. It is a characteristic view which shows the relationship between the bed temperature of a catalyst, and the purification rate of NOx. It is a map which shows the relationship between the operating condition of the engine at the time of cold, and the pH of the condensed water supplied. It is a map which shows the relationship between the driving | running condition of an engine at the time of half warm-up, and pH of the condensed water supplied.

  Hereinafter, an embodiment of a water supply control device for an internal combustion engine will be described.

(1) Vehicle Engine System Configuration First, a vehicle engine system configuration in which the water supply control device for an internal combustion engine according to the present embodiment is mounted will be described with reference to FIG. FIG. 1 is a schematic configuration diagram showing the overall configuration of the engine system according to the embodiment.

  In FIG. 1, an engine 200 according to the present embodiment is configured as a supercharged engine including a compressor 110 and a turbine 120.

  The compressor 110 compresses the air that has flowed in and supplies the compressed air downstream. Turbine 120 rotates using exhaust gas supplied from engine 200 via exhaust pipe 115 as power. The turbine 120 is connected to the compressor 110 via a shaft, and is configured to be able to rotate integrally with each other. That is, the turbine 120 and the compressor 110 constitute a turbocharger.

  The engine 200 is, for example, an in-line four-cylinder engine in which four cylinders 201 are arranged in series in a cylinder block. Although detailed illustration is omitted here, the engine 200 performs the reciprocating motion of the piston that occurs when the air-fuel mixture burns inside each cylinder 201 via the connecting rod. It can be converted into a rotational motion.

  An air flow meter 102 is provided in the intake pipe 101 on the inlet side (that is, upstream side of the compressor 110) of the compressor 110. The air flow meter 102 is configured to be able to detect the amount of air sucked from the outside. Further, an intake throttle valve 103 is provided downstream of the air flow meter 102. The intake throttle valve 103 is an electronically controlled valve, for example, and is configured such that its opening / closing operation is controlled by a throttle valve motor (not shown). The amount of air flowing into the intake pipe 101 is adjusted by opening and closing the intake throttle valve 103.

  An intercooler 113 is provided on the intake pipe 111 on the outlet side of the compressor 110 (that is, on the downstream side of the compressor 110) and on the intake side (that is, on the upstream side of the cylinder 201) of the engine 200. The intercooler 113 is configured to be able to cool intake air and increase the supercharging efficiency of the air. Further, a condensed water injection valve 250 for supplying condensed water (condensed water generated in an EGR cooler 127 described later) to the engine 200 is provided at the subsequent stage of the intercooler. The condensed water injection valve is an example of the “water supply means” in the present invention.

  In the combustion chamber in the cylinder 201 of the engine 200, an air-fuel mixture obtained by mixing the air supplied through the intake pipe 111 and the fuel injected and supplied from the injector 210 is sucked. The air-fuel mixture introduced into the cylinder 201 from the intake side is ignited by, for example, a spark plug (not shown) or compression ignition, and an explosion process is performed in the cylinder 201. When the explosion process is performed, the burned air-fuel mixture (including a partially unburned air-fuel mixture) is discharged to an exhaust port (not shown) in the exhaust process following the explosion process. The exhaust discharged to the exhaust port is guided to the exhaust pipe 115.

  The exhaust pipe 121 on the outlet side of the turbine 120 (that is, the downstream side of the turbine 120) includes an EGR pipe 125, an EGR valve 126, and an EGR cooler 127 in addition to the start converter 123 and the aftertreatment device 124. A system is provided.

  The start converter 123 includes, for example, an oxidation catalyst, and purifies substances contained in the exhaust gas that has passed through the turbine 120.

  The post-processing device 124 is provided downstream of the start converter 123 in the exhaust pipe 122 and collects and reduces particulate matter contained in the exhaust.

  The EGR pipe 125 is configured so that the exhaust downstream of the start converter 123 can be returned to the intake pipe 101 on the inlet side of the compressor 110. An EGR valve 126 is provided on the EGR pipe 125 so that the amount of the recirculated EGR gas can be adjusted. An EGR cooler 127 that cools the recirculated EGR gas is provided on the EGR pipe 125. The EGR cooler 127 here is an example of the “reflux exhaust cooling means” of the present invention, and collects condensed water generated during cooling of the exhaust, and collects the condensed water through the condensed water injection valve 250. Via the engine 200.

(2) Configuration of Water Supply Control Device for Internal Combustion Engine Next, the configuration of the water supply control device for the internal combustion engine according to the present embodiment will be described with reference to FIG. FIG. 2 is a schematic configuration diagram showing the configuration of the water supply control device for the internal combustion engine according to the embodiment.

  In FIG. 2, the internal-combustion-engine water supply control device according to the present embodiment includes a condensed water collection device provided around the EGR cooler 127, and a condensed water supply device that supplies the collected condensed water to the engine 200. And ECU100 which controls them is comprised.

  The condensed water collecting device includes refrigerant passages 311, 312, 313 and 315, a three-way valve 315, a first storage tank 321, a second storage tank 322, and pH sensors 331 and 332. Yes.

  The refrigerant passage 311 is a passage for supplying refrigerant to the forefront of the EGR cooler 127 (the right side in the figure is the front and the left side is the rear). On the other hand, each of the refrigerant passages 312, 313, and 315 is a passage for discharging the refrigerant circulated through the EGR cooler 127. The refrigerant passage 312 is provided on the front side of the EGR cooler 127, and the refrigerant passage 313 is provided on the rear side of the EGR cooler 127. The refrigerant that has passed through each of the refrigerant passages 312 and 313 is discharged through a refrigerant passage 314 that extends from the connecting portion of the refrigerant passages 312 and 313.

  In addition, a three-way valve 315 for controlling the flow of the refrigerant is provided at a connection portion between the refrigerant passages 312 and 313. The three-way valve 315 has a first state in which the refrigerant passage 312 and the refrigerant passage 314 are connected and the refrigerant passage 313 and the refrigerant passage 314 are closed by adjusting the angle thereof, and the refrigerant passage 312 and the refrigerant passage. 314 and the second state in which both the refrigerant passage 313 and the refrigerant passage 314 are connected can be realized. Therefore, when the three-way valve is in the first state, the refrigerant circulates only through the front portion of the EGR cooler 127 and is discharged. On the other hand, when the three-way valve is in the second state, the refrigerant circulates throughout the EGR cooler 127 and is discharged.

  The first storage tank 321 is configured to be able to store condensed water generated at the front portion of the EGR cooler. Low pH condensed water 410 having a low pH is stored in the first storage tank 321 by control at the time of collecting condensed water, which will be described later. On the other hand, the second storage tank 322 is configured to be able to store condensed water generated in the rear portion of the EGR cooler. In the second storage tank 322, high pH condensed water 420 having a high pH is stored by control at the time of collecting condensed water described later. Each of the first storage tank 321 and the second storage tank 322 is provided with pH sensors 331 and 332 for detecting the pH of the stored condensed water.

  The condensed water supply apparatus includes condensed water passages 341, 342 and 343 and a three-way valve 344.

  The condensed water passage 341 is connected to the first storage tank 321 and is configured to be able to take out the low pH condensed water 410 stored in the first storage tank 321. The condensed water passage 342 is connected to the second storage tank 322, and is configured to be able to take out the high pH condensed water 420 stored in the second storage tank 322. The condensed water that has passed through each of the condensed water passage 341 and the condensed water passage 342 passes through a condensed water passage 343 that extends from a connecting portion of the condensed water passage 341 and the condensed water passage 342, and the condensed water injection valve 250 (see FIG. 1). To be supplied.

  Further, a three-way valve 344 for adjusting the amount of condensed water taken out from each of the first storage tank 321 and the second storage tank 322 is provided at a connection portion between the condensed water passage 341 and the condensed water passage 342. . The three-way valve 315 changes the ratio of the condensed water taken out from each of the first storage tank 321 and the second storage tank 322 (that is, passed to the condensed water passage 343 side) by adjusting the angle thereof. Is possible. Thereby, the pH of the condensed water supplied from the cooling passage 343 to the condensed water injection valve 250 can be adjusted.

  Specifically, if a relatively large amount of the low pH condensed water 410 is taken out from the first storage tank 321 and a relatively small amount of the high pH condensed water 420 is taken out from the second storage tank 322, the condensed water having a low pH is obtained. The condensed water injection valve 250 can be supplied. Similarly, if a relatively small amount of low pH condensed water 410 is taken out from the first storage tank 321 and a relatively large amount of high pH condensed water 420 is taken out from the second storage tank 322, the condensed water having a high pH is condensed into condensed water. The fuel can be supplied to the injection valve 250. Further, if the same amount of the low pH condensed water 410 and the high pH condensed water 420 is taken out from each of the first storage tank 321 and the second storage tank 322, the condensed water injection valve extracts the condensed water having a medium pH. 250 can be supplied.

  The ECU 150 is an electronic control unit that includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and is configured to be able to control the operation of each part of the water supply control device of the internal combustion engine. . ECU 150 may be configured to control the operation of the entire vehicle on which the water supply control device for the internal combustion engine is mounted.

  In particular, the ECU 150 according to the present embodiment includes an operating condition determination unit 151, a pH estimation unit 152, a condensed water collection control unit 153, and a condensed water supply control unit 154.

  The operation condition determination unit 151 is an example of the “operation condition determination unit” of the present invention, and determines the operation condition of the engine 200 based on, for example, the torque Tq and the rotation speed Ne of the engine 200 detected by various sensors. Specifically, the operating condition determination unit 151 determines how much NOx is discharged by the engine 200 during the condensate collection control. In addition, the operating condition determination unit 151 is an operating condition in which the engine 200 is required to reduce NOx rather than the soot in the exhaust during the condensate supply control, or the soot is required to be reduced more than the NOx. It is determined whether the operating condition is such that

  The pH estimating unit 152 estimates the pH of the condensed water to be collected based on the operating conditions of the engine 200 determined by the operating condition determining unit 151 during the condensate collecting control. For example, the pH estimation unit 152 estimates the amount of NOx in the exhaust from the operating conditions of the engine 200, and estimates the collected pH based on the estimated amount of NOx. More specifically, the pH estimation unit estimates that the pH of the condensed water is low because the amount of NOx in the recirculated exhaust gas also increases when the operating conditions are such that the amount of NOx in the exhaust gas is relatively large. . On the other hand, when the operating condition is such that the amount of NOx in the exhaust gas is relatively low, the pH estimating unit estimates that the pH of the condensed water is high because NOx in the exhaust gas being refluxed is also reduced. The pH estimation unit 152 in this case is an example of the “concentration estimation unit” in the present invention.

  If a pH sensor is provided at the position where the condensed water is generated in the EGR cooler 127 so that the pH of the generated condensed water can be directly detected, the detected pH value is used as the pH of the condensed water collected as it is. It can also be used. The pH sensor in this case is an example of the “pH detection means” in the present invention.

  The pH estimating unit 152 further controls the pH of the condensed water to be supplied to the engine 200 based on the operating conditions of the engine 200 determined by the operating condition determining unit 151 (hereinafter referred to as “target pH” as appropriate) during the supply control of the condensed water. Is called). Specifically, when the operating condition is such that engine 200 generates a large amount of NOx, pH estimating unit 152 sets the target pH as a relatively high value. On the other hand, the pH estimation unit 152 compares the target pH when the engine 200 has an operation condition that reduces the NOx generation amount (in other words, an operation condition that increases the relative generation amount of soot). Set as a low value.

  Note that the pH of the condensed water generated in the EGR cooler 127 greatly depends on NOx contained in the exhaust gas. Specifically, when the amount of NOx contained in the exhaust gas is large and the concentration of nitric acid in condensed water is high, the pH is lowered. Conversely, when the amount of NOx contained in the exhaust gas is small and the concentration of nitric acid in the condensed water is low, the pH becomes high. Therefore, the high pH of the condensed water can be rephrased as the low concentration of nitric acid. Therefore, the ECU 100 may include a nitric acid concentration determination unit that estimates the nitric acid concentration instead of the pH estimation unit 152 described above.

  The condensed water collection control unit 153 adjusts the angle of the three-way valve 315 of the condensed water collection device based on the pH estimated by the pH estimation unit 152. The specific control by the condensed water collection control unit 153 will be described in detail in the subsequent operation description.

  The condensed water supply control unit 154 adjusts the angle of the three-way valve 344 of the condensed water supply device based on the target pH estimated by the pH estimation unit 152. The specific control by the condensed water supply control unit 154 will be described in detail later in the description of the operation.

(3) Operation at the time of collecting condensed water Next, the operation at the time of collecting condensed water by the water supply control device for an internal combustion engine according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing the operation at the time of collecting condensed water by the water supply control device for the internal combustion engine according to the embodiment.

  In FIG. 3, when condensate water is collected by the water supply control device for an internal combustion engine according to the present embodiment, first, the operating condition of the engine 200 is determined by the operating condition determination unit 151 (step S101). That is, based on the torque Tq of the engine 200 and the rotational speed Ne, it is determined how much NOx the operating condition causes the engine 200 to generate.

  When the operating condition of engine 200 is determined, pH estimation unit 152 estimates the pH of the condensed water collected by EGR cooler 127 (step S102). Specifically, the pH estimating unit 152 estimates the pH based on the amount of NOx generated by the engine 200.

  When the pH of the condensed water is estimated, the condensed water collection control unit 153 determines whether or not the estimated pH is 6 or more (step S103). Here, “pH 6” is an example of a threshold value for determining the level of collected pH, and a different pH can be set as the threshold value as appropriate.

  When the estimated pH is less than 6 (step S103: NO), cooling of the EGR gas and collection of condensed water are performed only in front of the EGR cooler 127 (step S105). Therefore, condensed water having a pH of less than 6 is generated only in the front portion of the EGR cooler 127 and stored in the first storage tank 321.

  On the other hand, when the estimated pH is 6 or more (step S103: YES), cooling of the EGR gas and collection of condensed water are performed in the entire area of the EGR cooler 127 (step S104). Therefore, condensed water having a pH of 6 or higher is also generated at the rear portion of the EGR cooler 127 and stored in the second storage tank 322.

  Here, the change of the collection method based on the pH of the condensed water mentioned above is demonstrated concretely, referring FIG. FIG. 4 is a map showing the relationship between the operating conditions of the engine and the region for collecting condensed water in the EGR cooler.

  As shown in FIG. 4, when both the torque Tq and the rotational speed Ne of the engine 200 are high, the engine 200 is in a high load state, and it is considered that a relatively large amount of NOx is generated with combustion. Therefore, in this case, the amount of NOx in the recirculated exhaust gas is increased, and as a result, the pH of the condensed water generated in the EGR cooler 127 is estimated to be low.

  When it is estimated that the pH of the condensed water is low, the three-way valve 315 is in the first state (that is, the refrigerant passage 312 and the refrigerant passage 314 are connected and the refrigerant passage 313 and the refrigerant passage 314 are closed). Thus, the EGR gas is cooled only on the front side of the EGR cooler 127. Therefore, the condensed water having a low pH is generated only in the front portion of the EGR cooler 127, and as a result, the condensed water stored in the first storage tank 321 on the front side becomes the low pH condensed water 410.

  On the other hand, when the torque Tq and the rotational speed Ne of the engine 200 are relatively low, it is considered that the engine 200 is in a low load state and the amount of NOx generated due to combustion is small. Therefore, in this case, it is estimated that the amount of NOx in the recirculated exhaust gas is also reduced, and as a result, the pH of the condensed water generated in the EGR cooler 127 is increased.

  When it is estimated that the pH of the condensed water is high, the three-way valve 315 is in the second state (that is, a state where both the refrigerant passage 312 and the refrigerant passage 314 and between the refrigerant passage 313 and the refrigerant passage 314 are connected). Thus, the EGR gas is also cooled on the rear side of the EGR cooler 127. Therefore, condensed water having a high pH is generated also in the rear portion of the EGR cooler 127, and as a result, the condensed water stored in the second storage tank 322 on the rear side becomes the high pH condensed water 420.

  In the present embodiment, the example in which the condensed water is divided and stored in two storage tanks according to the pH has been described, but may be stored in more storage tanks. For example, in addition to the 1st storage tank 321 which stores condensed water with low pH, and the 2nd storage tank 322 which stores condensed water with high pH, the 3rd storage tank which stores condensed water with medium pH is provided. You may comprise as follows.

  Moreover, when the pH of the stored condensed water is extremely low (for example, about pH 1-2), the path | route which supplies condensed water with a strong oxidizing power may corrode. Therefore, condensed water having an extremely low pH may not be collected or discarded after collection. Incidentally, the collected condensed water may be discarded on the exhaust side of the engine 200.

(4) Operation at the time of supplying condensed water Next, the operation at the time of supplying condensed water by the water supply control device for an internal combustion engine according to the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing an operation at the time of supplying condensed water by the water supply control device for the internal combustion engine according to the embodiment.

  In FIG. 5, when the condensed water is supplied by the water supply control device for an internal combustion engine according to the present embodiment, first, the operating condition of the engine 200 is determined by the operating condition determination unit 151 (step S201). That is, based on the torque Tq and the rotational speed Ne of the engine 200, the engine 200 is in an operating condition that requires a reduction in NOx rather than the soot in the exhaust, or a reduction in soot is required rather than NOx. It is determined whether the operating conditions are such. In other words, the operation condition determination unit 151 determines the NOx reduction priority for soot corresponding to the operation condition of the engine 200 or the soot reduction priority for NOx.

  When the operating condition of engine 200 is determined, target pH of condensed water supplied to engine 200 is estimated in pH estimating unit 152 (step S202). Specifically, the pH estimation unit 152 estimates the target pH according to which of NOx and soot in the exhaust gas should be preferentially reduced.

  Here, a method for estimating the target pH of the condensed water from the operating conditions of the engine 200 will be specifically described with reference to FIG. FIG. 6 is a map showing the relationship between the engine operating conditions and the pH of the condensed water to be supplied.

  As shown in FIG. 6, the target pH is estimated as a lower value as the torque Tq and the rotational speed Ne of the engine 200 are higher (that is, the load of the engine 200 is higher). This is because as the torque Tq and the rotational speed Ne of the engine 200 are higher, the amount of NOx generated with combustion increases, and as a result, the NOx reduction priority becomes relatively higher. Conversely, the target pH is estimated as a higher value as the torque Tq and the rotational speed Ne of the engine 200 are lower (that is, the load of the engine 200 is lower). This is because as the torque Tq and the rotational speed Ne of the engine 200 are lower, the amount of NOx generated with combustion is reduced, and as a result, the priority for reducing soot is relatively increased.

  Here, the nitric acid contained in the condensed water has an effect of oxidizing the soot and suppressing the generation amount (see the following formula).

C + 4HNO ₃ → CO ₂ + 4NO ₂ + 2H ₂ O
Therefore, the higher the concentration of nitric acid (that is, the lower the pH), the higher the effect of reducing soot. Therefore, when the soot reduction priority is high, soot can be effectively reduced by supplying condensed water having a low pH to the engine 200.

However, nitric acid generates NO ₂ (ie, NOx) when oxidizing soot, as can be seen from the above equation. Therefore, condensed water having a high concentration of nitric acid (that is, condensed water having a low pH) is not necessarily effective from the viewpoint of reducing the amount of NOx generated while greatly reducing the amount of soot generated.

  On the other hand, in this embodiment, when the NOx reduction priority is high, condensed water having a high pH is supplied to the engine 200. Thereby, the NOx reduction effect by a combustion temperature fall can be exhibited, suppressing generation | occurrence | production of NOx by an upper type.

  Note that the NOx reduction priority can also change depending on the state of the catalyst that purifies NOx (that is, the start converter 123). Specifically, if the catalyst is completely warmed up and can perform its original NOx purification function, the demand for NOx reduction is unlikely to increase. However, in a state where the NOx purification function of the catalyst is low, such as during cold start, the demand for NOx reduction tends to increase.

  Hereinafter, the change of the pH estimation method based on the warm-up state of the catalyst will be described with reference to FIGS. FIG. 7 is a characteristic diagram showing the relationship between the bed temperature of the catalyst and the NOx purification rate. FIG. 8 is a map showing the relationship between the operating conditions of the engine during cold and the pH of the condensed water to be supplied, and FIG. It is a map which shows the relationship.

  As shown in FIG. 7, the NOx purification rate of start converter 123 (hereinafter sometimes simply referred to as “catalyst”) varies depending on the catalyst bed temperature. Specifically, if the catalyst is completely warmed up, the NOx purification rate is high and it is considered that NOx can be sufficiently purified. However, the NOx purification rate is lower in the cold or semi-warm-up state than in the complete warm-up state, and there is a possibility that NOx cannot be sufficiently purified. Therefore, the map for estimating the target pH as shown in FIG. 6 should be different depending on the warm-up state of the catalyst. Incidentally, the map shown in FIG. 6 is a map when the catalyst is completely warmed up.

  As shown in FIG. 8, when the NOx purification rate of the start converter 123 is very low during cold weather, it is preferable not to supply condensed water having a low pH that may increase NOx to the engine 200. More specifically, when the torque Tq and the rotational speed Ne of the engine 200 are low (that is, at a low speed and a low load), the condensed water is not supplied to the engine 200, and the torque Tq and the rotational speed Ne of the engine 200 are not supplied. Is high (that is, at high speed and high load), the condensed water may be supplied to the engine 200 only from the second storage tank 322 (that is, the tank storing the high pH condensed water 420). If it does in this way, generation of NOx resulting from supplying condensed water to engine 200 can be controlled effectively. Therefore, even when the NOx purification rate of the catalyst is low, the generation of excessive NOx can be prevented.

  As shown in FIG. 9, when the start converter 123 is in a semi-warm-up state and the NOx purification rate is not sufficient, the map at the time of complete warm-up shown in FIG. 6 and the map at the time of cold shown in FIG. You can use an intermediate map. Specifically, the condensed water is not supplied to the engine 200 only when the torque Tq and the rotational speed Ne of the engine 200 are extremely low, and in other cases, the higher the torque Tq and the rotational speed Ne of the engine 200, the higher the pH It is sufficient to supply low-condensed water to the engine 200. In this way, even when the NOx purification rate is not sufficiently increased, the generation of excessive NOx can be prevented, and soot can be effectively reduced.

  Returning to FIG. 5, when the target pH is estimated by the above-described method, the target pH and the preparation pH that can be actually supplied (more specifically, the ratio of the low pH condensed water 410 and the high pH condensed water 420 are adjusted. Are compared with each other, and it is determined whether or not the preparation pH is higher than the target pH (step S203).

  Here, if it is determined that the preparation pH is not higher than the target pH (step S203: NO), it is further determined whether or not the difference between the target pH and the preparation pH is less than 2 (step S204). . When it is determined that the difference between the target pH and the created pH is not less than 2 (that is, 2 or more) (step S204: NO), a series of processing ends without supplying condensed water to the engine 200. If it does in this way, it can prevent that the inside of the channel | path which supplies condensed water is corroded by the strong oxidizing power of condensed water with low pH. Or it can prevent that NOx which should be reduced increases conversely because the pH of the condensed water supplied to the engine 200 is too low.

  On the other hand, if it is determined that the difference between the target pH and the created pH is less than 2 (step S204: YES), the three-way valve 344 is controlled and condensed water having the created pH is supplied to the engine 200 (step S205). . If it is determined that the preparation pH is higher than the target pH (step S203: YES), there is no concern about corrosion even if the difference between the target pH and the preparation pH is 2 or more. 344 is controlled and condensed water having a created pH is supplied to engine 200 (step S205).

  As described above, according to the water supply control device for an internal combustion engine according to the present embodiment, the condensed water separately collected according to the pH in the EGR cooler 127 is preferably used according to the operating conditions of the engine 200. Supplied. Accordingly, it is possible to efficiently reduce NOx and soot in the exhaust gas.

  In the present embodiment, the example in which only the condensed water collected by the EGR cooler 127 is supplied to the engine 200 has been described, but the same effect can be obtained even when other water is supplied to the engine 200. Needless to say. Therefore, without including the condensed water collecting device according to the present embodiment, for example, it may be configured such that water stored in advance and adjusted in pH is appropriately mixed and supplied to the engine 200. Alternatively, the pH-adjusted water stored in advance may be mixed with the condensed water collected by the EGR cooler 127 and supplied to the engine 200.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. A water supply control device is also included in the technical scope of the present invention.

101, 111 Intake pipe 102 Air flow meter 103 Intake throttle valve 110 Compressor 113 Intercooler 120 Turbine 115, 121 Exhaust pipe 123 Start converter 124 Aftertreatment device 125 EGR pipe 126 EGR valve 127 EGR cooler 150 ECU
151 Operation condition determination unit 152 pH estimation unit 153 Condensed water collection control unit 154 Condensed water supply control unit 200 Engine 201 Cylinder 210 Injector 250 Condensed water injection valve 311, 312, 313, 314 Refrigerant passage 315 Three-way valve 321 First storage Tank 322 Second storage tank 331,332 pH sensor 341,342,343 Condensate passage 344 Three-way valve 410 Low pH condensed water 420 High pH condensed water

Claims (5)

Water supply means for supplying water to the combustion chamber of the internal combustion engine;
The operating condition of the internal combustion engine is the first operating condition in which the reduction of NOx is required rather than soot for the component of the combustion gas generated in the combustion chamber of the internal combustion engine, or the reduction of soot is required rather than NOx Operating condition determining means for determining whether the second operating condition is satisfied,
When it is determined that the operating condition of the internal combustion engine is the second operating condition, the concentration of nitric acid in the water supplied by the water supply means is smaller than when it is determined that the operating condition is the first operating condition. A water supply control device for an internal combustion engine, comprising: a nitric acid concentration control means for increasing the temperature.   The said water supply means supplies the condensed water which generate | occur | produces in the recirculation exhaust cooling means which cools the exhaust_gas | exhaustion recirculated from an exhaust side to an intake side to the combustion chamber of the said internal combustion engine. Water supply control device for internal combustion engine.   The water supply control device for an internal combustion engine according to claim 2, wherein the nitric acid concentration control unit estimates that the nitric acid concentration is higher as the pH of the condensed water is lower. Concentration estimation means for estimating the concentration or pH of the condensed water generated in the recirculation exhaust cooling means based on the amount of NOx discharged from the internal combustion engine;
According to the nitric acid concentration or pH estimated by the concentration estimating means, further comprising condensed water storage means for storing the condensed water in a plurality of storage tanks,
The nitric acid concentration control means adjusts the nitric acid concentration or pH of water supplied by the water supply means by changing a ratio of the condensed water taken out from each of the plurality of storage tanks. The water supply control device for an internal combustion engine according to 2 or 3. A pH detecting means provided at a position where the condensed water is generated in the reflux exhaust cooling means, and detecting a pH of the condensed water;
According to the pH detected by the pH detection means, further comprising a condensed water storage means for storing the condensed water divided into a plurality of storage tanks,
The nitric acid concentration control means adjusts the nitric acid concentration or pH of water supplied by the water supply means by changing a ratio of the condensed water taken out from each of the plurality of storage tanks. The water supply control device for an internal combustion engine according to claim 3.

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