JP2019218916A - Control system of engine - Google Patents

Abstract

To suitably determine whether condensate water generated in an EGR cooler flows into an intake passage or not in an engine in which the EGR cooler is provided in EGR piping.SOLUTION: An ECU controls an engine in which an EGR pre-cooler and an EGR main cooler are provided in EGR piping. The ECU calculates "pre-cooler inlet humidity Ha" showing an amount of steam contained in exhaust gas in the vicinity of an inlet (pre-cooler inlet) to the EGR pre-cooler in the EGR piping, and acquires "EGR gas outlet humidity Hb" showing the amount of the steam contained in the exhaust gas in the vicinity of an outlet (EGR gas outlet) to an intake passage in the EGR piping from a humidity sensor provided in the EGR gas outlet. The ECU determines that condensate water generated in the EGR pre-cooler flows into the intake passage when the pre-cooler inlet humidity Ha is larger than the EGR gas outlet humidity Hb.SELECTED DRAWING: Figure 6

Description

  The present disclosure relates to an engine control system including an EGR (Exhaust Gas Recirculation) device.

  Japanese Patent Application Laid-Open No. 2015-1970078 (Patent Document 1) discloses an engine control system including an EGR pipe for recirculating a part of exhaust gas in an exhaust passage to an intake passage, and an EGR cooler provided in the EGR pipe. Is disclosed. This control system calculates the gas temperature and the dew point temperature in the EGR cooler, determines that condensed water is generated in the EGR cooler when the gas temperature is lower than the dew point temperature, and stops the EGR. Thereby, since the generation of condensed water in the EGR cooler is suppressed, it is possible to prevent a problem that the condensed water generated in the EGR cooler flows into the intake passage and corrodes the inside of the cylinder.

Japanese Patent Application Laid-Open No. 2015-1970078

  In order to prevent in-cylinder corrosion due to condensed water generated in the EGR device, it is desirable to appropriately determine whether or not condensed water generated in the EGR cooler flows into the intake passage.

  However, the control system disclosed in Patent Literature 1 merely determines whether or not condensed water is generated in the EGR cooler. Therefore, it is determined whether or not the condensed water generated in the EGR cooler flows into the intake passage. It cannot be determined properly.

  For example, when condensed water is generated in the EGR cooler and the condensed water remains in the EGR pipe without evaporating before reaching the intake passage, it is assumed that the condensed water flows into the intake passage. When the condensed water evaporates before reaching the intake passage, it is assumed that the condensed water does not flow into the intake passage. However, the control system disclosed in Patent Literature 1 merely determines whether or not condensed water is generated in the EGR cooler, and determines whether or not condensed water evaporates before reaching the intake passage. Therefore, it cannot be properly determined whether or not the condensed water flows into the intake passage.

  The present disclosure has been made to solve the above-described problem, and an object of the present disclosure is to determine whether condensed water generated in an EGR cooler flows into an intake passage in an engine in which an EGR cooler is provided in an EGR pipe. Is determined appropriately.

  (1) The control system according to the present disclosure is an engine control system. The engine includes an EGR pipe for recirculating a part of the exhaust gas in the exhaust passage to the intake passage, and an EGR cooler provided in the EGR pipe. The control system includes a control device configured to determine whether or not the condensed water generated in the EGR cooler flows into the intake passage. The control device compares the first steam amount included in the exhaust gas at the inlet to the EGR cooler in the EGR pipe with the second steam amount included in the exhaust gas at the outlet to the intake passage in the EGR pipe. The control device determines that the condensed water generated in the EGR cooler flows into the intake passage when the first steam amount is larger than the second steam amount.

  According to the above system, the first steam amount included in the exhaust gas at the inlet to the EGR cooler in the EGR pipe is compared with the second steam amount included in the exhaust gas at the outlet to the intake passage in the EGR pipe. It is determined whether condensed water flows into the intake passage. Therefore, it is possible to appropriately determine whether the condensed water generated in the EGR cooler remains without evaporating before reaching the intake passage, or whether the condensed water has evaporated and disappeared. As a result, it is possible to appropriately determine whether or not the condensed water generated in the EGR cooler flows into the intake passage.

  (2) In one embodiment, when it is determined that the condensed water flows into the intake passage, the control device executes a warm-up process of warming up the EGR cooler.

  In the above embodiment, when it is determined that the condensed water flows into the intake passage, a warm-up process for warming up the EGR cooler is executed. This makes it difficult for the EGR cooler to generate condensed water.

  (3) In one embodiment, the control system further includes an EGR valve configured to adjust a flow rate of the EGR gas returned from the EGR pipe to the intake passage. The warm-up process includes a process of increasing the opening of the EGR valve.

  In the above embodiment, a process of increasing the opening of the EGR valve is performed as the warm-up process. Thereby, the flow rate of the EGR gas increases, and the EGR cooler is warmed up by the heat of the increased EGR gas. As a result, it is possible to make it difficult to generate condensed water in the EGR cooler while continuing the EGR.

  (4) In one embodiment, the warm-up process includes a process of increasing the temperature of the exhaust gas of the engine.

  When the opening degree of the EGR valve is increased as the warming-up process, there is a concern that condensed water in the EGR pipe easily flows into the intake passage due to an increase in the EGR gas flow rate.

  Thus, in the above embodiment, a process of increasing the temperature of the exhaust gas of the engine (increase the load on the engine) is performed as the warm-up process. Thereby, the temperature of the EGR gas flowing in the EGR cooler increases, so that the EGR cooler is warmed up. As a result, it is possible to make it difficult to generate condensed water in the EGR cooler while continuing the EGR and without increasing the EGR gas flow rate.

  (5) In one mode, the EGR cooler cools the EGR gas in the EGR pipe with the coolant. The warm-up process includes a process of increasing the temperature of the coolant.

  When the opening degree of the EGR valve is increased as the warming-up process, there is a concern that condensed water in the EGR pipe easily flows into the intake passage due to an increase in the EGR gas flow rate. Further, when the temperature of the exhaust gas of the engine is increased as the warming-up process, the load on the engine is increased, so that there is a concern that a trade-off such as deterioration of fuel efficiency may occur.

  Therefore, in the above-described embodiment, a process of increasing the temperature of the coolant of the EGR cooler (for example, a process of decreasing the flow rate of the coolant) is performed as the warm-up process. Thus, it is possible to make it difficult to generate condensed water in the EGR cooler while continuing the EGR, without increasing the flow rate of the EGR gas, and without increasing the load on the engine.

  (6) In one embodiment, the control system includes an air flow meter that detects an intake air flow rate in the intake passage, and a humidity sensor provided at an outlet portion. The control device calculates the first water vapor amount using the detection result of the air flow meter. The control device acquires the detection result of the humidity sensor as the second water vapor amount.

  Since the EGR gas before being cooled by the EGR cooler flows through the inlet to the EGR cooler, the temperature becomes high. For this reason, it is difficult to attach a sensor at the entrance to the EGR cooler. Therefore, in the above embodiment, the first water vapor amount is calculated using the detection result of the air flow meter provided in the intake passage.

  On the other hand, the outlet portion of the EGR pipe to the intake passage does not become so hot because the EGR gas cooled by the EGR cooler flows. Therefore, in the above embodiment, a humidity sensor is provided at an exit portion of the EGR pipe to the intake passage. Therefore, the detection value of the humidity sensor can be used as the second water vapor amount.

  According to the present disclosure, in an engine in which an EGR cooler is provided in an EGR pipe, it is possible to appropriately determine whether or not condensed water generated in the EGR cooler flows into the intake passage.

FIG. 1 is a diagram schematically illustrating an entire configuration of an engine system. It is a figure which shows typically the principle which the condensed water generated in the EGR precooler flows into an intake pipe. It is a figure which shows typically the state in which the condensed water does not exist in the EGR pipe from the precooler inlet part A to the EGR gas outlet part B. FIG. 4 is a view schematically showing a state in which condensed water generated in an EGR precooler evaporates and returns to steam before reaching an EGR gas outlet B. FIG. 4 is a diagram schematically illustrating a state in which condensed water generated in an EGR precooler is flowing into an EGR gas outlet B. 4 is a flowchart illustrating an example of a processing procedure of an ECU.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. Their names and functions are the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a diagram schematically illustrating an overall configuration of an engine system 1 according to the present embodiment. The engine system 1 is mounted on a vehicle and is used to generate a driving force for running the vehicle.

  The engine system 1 includes an engine (engine body) 10, an intake passage including an intake pipe 20 and an intake manifold 25, an exhaust passage including an exhaust manifold 35 and an exhaust pipe 30, an EGR device 40, an air flow meter 81, and the like. , An engine speed sensor 82, a humidity sensor 83, and an ECU (Electronic Control Unit) 100.

  The engine 10 is a diesel engine having a plurality of (three in the example shown in FIG. 1) cylinders. The number of cylinders is not limited to a plurality, and may be a single cylinder. The engine to which the present disclosure can be applied is not limited to a diesel engine, but can be applied to, for example, a gasoline engine.

  An intake port of each cylinder of the engine 10 is connected to an intake pipe 20 via an intake manifold 25. Air (fresh air) required for combustion in each cylinder is collected from an intake pipe 20 to an intake manifold 25 and then distributed to each cylinder.

  An exhaust port of each cylinder of the engine 10 communicates with an exhaust pipe 30 via an exhaust manifold 35. The exhaust gas generated in each cylinder is collected in an exhaust manifold 35 and then discharged to an exhaust pipe 30. The exhaust pipe 30 is provided with an exhaust purification catalyst (not shown) for purifying exhaust gas. The exhaust gas flowing through the exhaust pipe 30 is discharged outside the vehicle after being purified by the exhaust purification catalyst.

  The EGR device 40 is configured to take in and cool a part of the exhaust gas flowing through the exhaust pipe 30 and to return the cooled exhaust gas to the intake pipe 20. Thereby, reduction of nitrogen oxides (NOx) in the exhaust gas is achieved.

  The EGR device 40 includes EGR pipes G1, G2, G3, a bypass pipe G4, an EGR precooler 41, an EGR main cooler 42, a switching valve 43, and an EGR valve 44.

  The EGR pipes G1, G2, and G3 are connected in series in this order in a direction from the exhaust pipe 30 to the intake pipe 20, and communicate the exhaust pipe 30 and the intake pipe 20. The EGR pipes G1, G2, and G3 may be those that communicate the exhaust passage and the intake passage, and may be, for example, those that communicate the exhaust manifold 35 and the intake manifold 25.

  An EGR main cooler 42 is provided between the EGR pipes G2 and G3. Since a part of the exhaust gas is cooled by the EGR main cooler 42 and then returned to the intake pipe 20, an increase in the combustion temperature in each cylinder of the engine 10 is suppressed, so that nitrogen oxides (NOx) in the exhaust gas Is reduced.

  Further, in the present embodiment, in order to further reduce nitrogen oxides in the exhaust gas, in addition to the EGR main cooler 42, an EGR precooler 41 is provided between the EGR pipes G1 and G2 upstream of the EGR main cooler 42. Is provided. Therefore, the exhaust gas (hereinafter, also referred to as “EGR gas”) recirculated from the exhaust pipe 30 to the intake pipe 20 through the EGR device 40 is cooled by both the EGR precooler 41 and the EGR main cooler 42. As a result, as compared with the case where the EGR precooler 41 is not provided, the increase in the combustion temperature in each cylinder is further suppressed, so that the nitrogen oxides in the exhaust gas are further reduced.

  Both the EGR precooler (hereinafter, also simply referred to as “precooler”) 41 and the EGR main cooler (hereinafter, simply referred to as “main cooler”) 42 exchange heat between the EGR gas flowing through the inside and the cooling water. Is a water-cooled cooling device. In the present embodiment, the cooling water for the precooler 41 and the main cooler 42 is shared with the cooling water for the engine 10. Specifically, the operation of the water pump 45 causes the cooling water in the water jacket of the engine 10 to pass through the cooling water pipe W1, the pre-cooler 41, the cooling water pipe W2, the main cooler 42, and the cooling water pipe W3, and the radiator. (Not shown). The cooling water that has been radiated to the outside air by the radiator is returned to the water jacket of the engine 10 again through the cooling water pipe W4. The cooling water circulation path is not limited to the above-described path.

  The bypass pipe G4 connects the EGR pipe G2 on the inlet side of the main cooler 42 and the EGR pipe G3 on the outlet side of the main cooler 42 without passing through the main cooler 42. The switching valve 43 is provided at a branch portion between the EGR pipe G2 and the bypass pipe G4. The switching valve 43 is switched to one of a first state in which the EGR gas flows through the main cooler 42 and a second state in which the EGR gas flows through the bypass pipe G4 without flowing through the main cooler 42 according to a control signal from the ECU 100. Can be switched. Therefore, for example, under specific operating conditions, the cooling function of the main cooler 42 can be disabled by switching the switching valve 43 to the second state.

  In the present embodiment, a bypass pipe G4 for bypassing the main cooler 42 is provided, but a bypass pipe for bypassing the precooler 41 is not provided due to a limitation of a mounting space or the like.

  The EGR valve 44 is provided downstream of a portion where the EGR pipe G3 joins the bypass pipe G4. The EGR valve 44 is configured to adjust the flow rate of the EGR gas returned to the intake pipe 20 according to a control signal from the ECU 100.

  The air flow meter 81 detects a flow rate (intake air flow rate) Gin of the intake air flowing through the intake pipe 20 and transmits the detection result to the ECU 100. The unit of the intake air flow rate Gin is “g / s”. The engine rotation speed sensor 82 detects the rotation speed NE of the crankshaft of the engine 10 (engine rotation speed) NE and transmits the detection result to the ECU 100. The unit of the engine rotation speed NE is "rotation speed / minute". The humidity sensor 83 will be described later.

  The ECU 100 includes a CPU (Central Processing Unit) and a memory (not shown). The ECU 100 executes a predetermined calculation process using the information stored in the memory and information from each sensor (such as the air flow meter 81), and outputs the output of the engine 10 (specifically, fuel injection, The ignition timing, etc.), the state of the switching valve 43, the opening of the EGR valve 44, the rotation speed of the water pump 45 (the flow rate of cooling water), and the like are controlled.

<Prevention of inflow of condensed water from the EGR device into the intake passage>
As described above, in EGR device 40 according to the present embodiment, in order to further reduce nitrogen oxides in exhaust gas, precooler 41 is provided in addition to main cooler 42. Therefore, the EGR gas is returned to the intake pipe 20 after being cooled by the precooler 41 and the main cooler 42.

  Here, the EGR gas contains steam generated by combustion. Therefore, when the EGR gas is cooled by the pre-cooler 41 and the main cooler 42, water vapor is condensed in each cooler and condensed water may be generated. In the main cooler 42, a bypass pipe G4 is provided as a countermeasure against condensed water generation. By setting the second state, the EGR gas can be prevented from passing through the main cooler 42.

  However, as described above, the precooler 41 is not provided with a bypass pipe due to a limitation of a mounting space or the like. Therefore, even in an environment where condensed water can be generated (for example, when the temperature of the cooling water in the precooler 41 is excessively low), the EGR gas is cooled by the precooler 41. As a result, there is a concern that condensed water is generated in the precooler 41 and the condensed water flows into the intake pipe 20.

  FIG. 2 is a diagram schematically illustrating the principle that condensed water is generated in the precooler 41 and the condensed water flows into the intake pipe 20. The inside of the precooler 41 is provided with an EGR gas passage Gp through which EGR gas flows, and a cooling water passage Wp through which cooling water flows. The inner wall of the EGR gas passage Gp is formed by the cooling water passage Wp. When water vapor contained in the EGR gas flowing through the EGR gas flow path Gp is cooled by contacting the inner wall (the cooling water passage Wp) of the EGR gas flow path Gp, the water is condensed (liquefied) to generate condensed water. When this condensed water moves along the flow of the EGR gas, it flows into the intake pipe 20 soon.

  The EGR gas contains sulfur oxides (SOx) or nitrogen oxides (NOx) generated by the fuel in addition to water vapor. When sulfur oxides (SOx) or nitrogen oxides (NOx) dissolve in the condensed water, the condensed water becomes acidic. When such acidic condensed water flows into the intake pipe 20, the acidic condensed water reaches each cylinder and may cause corrosion in the cylinder.

  Therefore, ECU 100 according to the present embodiment determines the humidity of the portion of EGR pipe G1 near the inlet of precooler 41 (hereinafter also referred to as “precooler inlet A”) and the portion of EGR pipe G3 near the outlet to intake pipe 20 ( It is determined whether or not the condensed water generated in the precooler 41 flows into the intake pipe 20 by comparing with the humidity of the “EGR gas outlet B”. When it is determined that the condensed water flows into the intake pipe 20, the ECU 100 executes a process for suppressing the generation of the condensed water in the precooler 41. Hereinafter, these processing contents will be described in detail.

In the following, the humidity at the precooler inlet A is also described as “precooler inlet humidity Ha”, and the humidity at the EGR gas outlet B is also described as “EGR gas outlet humidity Hb”. Both the pre-cooler inlet humidity Ha and the EGR gas outlet humidity Hb are absolute humidity, and the unit is “g / m ³ ”.

<< Comprehension (calculation) of pre-cooler inlet humidity Ha >>
Since the temperature of the precooler inlet A becomes extremely high due to exhaust gas after combustion, it is difficult to attach a sensor to the precooler inlet A. Therefore, ECU 100 according to the present embodiment does not detect pre-cooler inlet humidity Ha with a sensor, but calculates pre-cooler inlet humidity Ha using intake air flow rate Gin detected by air flow meter 81 or the like.

The unit of the precooler inlet humidity Ha is “g / m ³ ” as described above. Therefore, the precooler inlet humidity Ha is a value indicating the amount of water vapor (first water vapor amount) contained per unit volume of the EGR gas flowing through the precooler inlet portion A.

  Hereinafter, an example of a method of calculating the precooler inlet humidity Ha will be described. When the fuel and the intake air completely react in the cylinder, the reaction equation is represented by the following equation (1).

CHx + (1 + x / 4 + y) O ₂ + zH ₂ O = CO ₂ + (x / 2 + z) H ₂ O + yO ₂ (1)
On the left side of equation (1), “CHx” is a component in fuel, and “O ₂ ” and “H ₂ O” are components in intake air. The mass (g / s) of “CHx” in the fuel injected per second (unit time) can be calculated from the amount of fuel injected into each cylinder per unit time. Further, the mass (unit: g / s) of “H ₂ O” in the air taken in per _second is a predetermined ratio (for example, included in the air) to the intake air flow rate Gin detected by the air flow meter 81. (Average value of the ratio of the amount of water vapor). Therefore, the number of moles of “H ₂ O” in the EGR gas, that is, the amount of water vapor can be calculated from the above equation (1).

For example, assume that x = 4, the mass of CH _{4 in} the fuel is 1.6 (g / s), and the amount of H ₂ O in the intake air is 14.4 (g / s). In this case, since the mass per mole of CH ₄ is 16 g and the mass per mole of H ₂ O is 18 g, 0.1 mol of CH _{4 in} the fuel and 0.1 mol of H ₂ O in the intake air are used. Since 8 moles have reacted, it is derived that z = 8 in the formula (1). Thus, the ratio of the number of moles of CH _{4 in} the fuel to the number of moles of H ₂ O in the exhaust gas becomes 1: (x / 2 + z) = 1: (4/2 + 8) = 1: 10. You. Therefore, when 0.1 mol of CH ₄ in the fuel reacts, 1.0 mol (= 18 g) of H ₂ O is contained in the exhaust gas. Then, assuming that, for example, 10% of the H ₂ O in the exhaust gas is recirculated as EGR gas, the mass Mt of water vapor contained in the recirculated EGR gas per unit time is 18 × 0.1 = 1. 8 (g / s).

The ECU 100 calculates the mass Mt of water vapor contained in the EGR gas recirculated per unit time by the above-described calculation method. The ECU 100 converts the calculated water vapor mass Mt (g / s) into the water vapor mass contained in the EGR gas per unit volume (1 m ³ ), thereby obtaining the precooler inlet humidity Ha (g / m ³ ). Is calculated.

  For example, assuming that the mass of the inflow gas per one revolution of the engine is “α” (unit: g / revolution), the mass of the inflow gas per second can be calculated as “α · NE / 60 "(unit: g / s). Note that “α” may be a value measured during engine operation, or a value calculated using, for example, the engine speed NE as a parameter.

Further, when the density of the inflow gas amount is “β” (unit: g / m ³ ), the inflow gas volume per second is “α · NE / 60 / β” (unit: m ³ / s). Note that “β” can be a predetermined fixed value.

Therefore, as shown in the following equation (2), the ECU 100 calculates the water vapor mass Mt (g / s) per second by the inflow gas volume “α · NE / 60 / β” (m ³ / The value divided by s) is calculated as pre-cooler inlet humidity Ha (g / m ³ ).

Ha = Mt / (αNE / 60 / β) (2)
By calculating the precooler inlet humidity Ha in this way, the precooler inlet humidity Ha can be grasped without attaching a sensor to the precooler inlet portion A.

  The above-described method of calculating the pre-cooler inlet humidity Ha is merely an example, and the present invention is not limited to this. For example, a correspondence relationship between the intake air flow rate Gin, the engine rotation speed NE, and the pre-cooler inlet humidity Ha is obtained in advance through experiments or the like and mapped, and the pre-cooler corresponding to the actually detected intake air flow rate Gin and the engine rotation speed NE is obtained. The inlet humidity Ha may be calculated with reference to this map.

<< Grasp (detection) of EGR gas outlet humidity Hb >>
The EGR gas outlet B does not become very hot because the EGR gas cooled by the precooler 41 and the main cooler 42 flows. Therefore, in the present embodiment, a humidity sensor 83 is provided at the EGR gas outlet B. The humidity sensor 83 detects an EGR gas outlet humidity Hb (humidity of the EGR gas outlet B). The unit of the EGR gas outlet humidity Hb is “g / m ³ ” as described above. Therefore, the EGR gas outlet humidity Hb is a value indicating the amount of water vapor (the second amount of water vapor) contained per unit volume of the EGR gas flowing through the EGR gas outlet B.

  Therefore, the ECU 100 can obtain the EGR gas outlet humidity Hb by acquiring the detection result of the humidity sensor 83 from the humidity sensor 83.

<< Determining whether condensed water flows into the intake pipe >>
The ECU 100 determines whether the condensed water generated in the precooler 41 flows into the intake pipe 20 by comparing the precooler inlet humidity Ha and the EGR gas outlet humidity Hb obtained as described above.

  FIG. 3 is a diagram schematically showing a state in which condensed water does not exist in the EGR pipe from the precooler inlet portion A to the EGR gas outlet portion B. In such a state, since the steam passing through the precooler inlet A also passes through the EGR gas outlet B as it is, the precooler inlet humidity Ha and the EGR gas outlet humidity Hb have substantially the same value.

  FIG. 4 is a diagram schematically illustrating a state in which condensed water is generated in the precooler 41, but the condensed water evaporates and returns to steam before reaching the EGR gas outlet B. Even in such a state, almost the same amount of steam as the steam passing through the precooler inlet A passes through the EGR gas outlet B, so that the precooler inlet humidity Ha and the EGR gas outlet humidity Hb are different from each other. The values are almost the same.

  In the state shown in FIGS. 3 and 4, that is, when the pre-cooler inlet humidity Ha and the EGR gas outlet humidity Hb have substantially the same value, the ECU 100 causes the condensed water generated in the pre-cooler 41 to flow into the intake pipe 20. It is determined not to be performed.

  FIG. 5 is a diagram schematically illustrating a state in which condensed water is generated in the precooler 41 and flows into the EGR gas outlet B without evaporating. In such a state, the amount of steam passing through the EGR gas outlet B becomes smaller by the amount of condensed water than the amount of steam passing through the precooler inlet A. As a result, the pre-cooler inlet humidity Ha becomes a value larger than the EGR gas outlet humidity Hb.

  In the state shown in FIG. 5, that is, when the pre-cooler inlet humidity Ha is higher than the EGR gas outlet humidity Hb, the ECU 100 determines that the condensed water generated in the pre-cooler 41 flows into the intake pipe 20.

<< Reduction of condensed water generation >>
When it is determined that the condensed water generated in the precooler 41 flows into the intake pipe 20, the ECU 100 performs a process for suppressing the generation of the condensed water in the precooler 41.

  As described with reference to FIG. 2 described above, the steam is brought into contact with the inner wall of the EGR gas flow path Gp (hereinafter, also referred to as “precooler wall surface”) in the precooler 41 to be cooled, and condensed water is formed in the precooler 41. Occurs. In view of this point, ECU 100 suppresses the generation of condensed water in precooler 41 by performing a process of promoting a rise in the temperature of the precooler wall surface (hereinafter, also referred to as a “precooler warm-up process”).

  In the present embodiment, ECU 100 performs a process of increasing the opening of EGR valve 44 from the current opening as precooler warm-up processing. Thereby, the flow rate of the EGR gas passing through the precooler 41 increases, and the precooler wall surface is warmed up by the heat of the increased EGR gas. As a result, it is possible to suppress the generation of condensed water in the precooler 41 while continuing the EGR.

<< processing flow >>
FIG. 6 is a flowchart illustrating an example of a processing procedure performed by ECU 100. This flowchart is repeatedly executed at a predetermined cycle, for example.

  The ECU 100 calculates the pre-cooler inlet humidity Ha using the intake air flow rate Gin detected by the air flow meter 81 (step S10). The method of calculating the pre-cooler inlet humidity Ha has already been described in detail, and the detailed description will not be repeated here.

  Next, the ECU 100 acquires the detection result of the humidity sensor 83 as the EGR gas outlet humidity Hb (Step S20).

  Next, the ECU 100 determines whether or not the precooler inlet humidity Ha calculated in step S10 is higher than the EGR gas outlet humidity Hb obtained in step S20 (step S30).

  If it is determined that the pre-cooler inlet humidity Ha is higher than the EGR gas outlet humidity Hb (YES in step S30), it is assumed that the state shown in FIG. It is determined that water flows into the intake pipe 20 (step S40). In this case, the ECU 100 suppresses the generation of condensed water in the precooler 41 by performing the precooler warm-up process described above (step S50). Specifically, the ECU 100 performs a process of increasing the opening of the EGR valve 44 from the current opening as the pre-cooler warm-up process.

  On the other hand, when it is not determined that the pre-cooler inlet humidity Ha is higher than the EGR gas outlet humidity Hb (NO in step S30), it is assumed that the state shown in FIG. 3 or FIG. It is determined that the condensed water generated in step does not flow into the intake pipe 20 (step S60). Thereafter, ECU 100 shifts the processing to return.

  As described above, the ECU 100 according to the present embodiment provides the “precooler inlet humidity Ha” indicating the amount of water vapor included in the exhaust gas at the precooler inlet A, and the “EGR” indicating the amount of water vapor included in the exhaust gas from the EGR gas outlet B. When the pre-cooler inlet humidity Ha is higher than the EGR gas outlet humidity Hb, it is determined that the condensed water generated in the pre-cooler 41 flows into the intake pipe 20. Therefore, it is possible to appropriately determine whether or not the condensed water generated in the precooler 41 flows into the intake pipe 20.

  Further, when it is determined that the condensed water flows into the intake pipe 20, the ECU 100 executes a "precooler warm-up process" for promoting a rise in the temperature of the precooler wall surface. Thereby, it is possible to make it difficult for the precooler 41 to generate condensed water.

  In particular, the ECU 100 according to the present embodiment performs a process of increasing the opening of the EGR valve 44 from the current opening as the pre-cooler warm-up process. Thereby, the flow rate of the EGR gas passing through the precooler 41 increases, and the precooler wall surface is warmed up by the heat of the increased EGR gas. As a result, it is possible to make it difficult for the precooler 41 to generate condensed water while continuing EGR.

<Modification 1>
In the above-described embodiment, an example has been described in which the process of increasing the opening of the EGR valve 44 is performed as the pre-cooler warm-up process. In this case, there is a concern that the condensed water in the EGR pipe tends to flow into the intake pipe 20 due to an increase in the EGR gas flow rate.

  In view of this point, in the first modification, as a precooler warm-up process, a process of increasing the exhaust temperature of the engine 10 by increasing the load on the engine 10 (for example, increasing the fuel injection amount) is performed. I do. Accordingly, the temperature of the EGR gas flowing in the precooler 41 increases, and the precooler 41 is warmed up. As a result, it is possible to make it difficult for the precooler 41 to generate condensed water while continuing EGR and without increasing the EGR gas flow rate.

<Modification 2>
In the above-described embodiment, an example has been described in which the process of increasing the opening of the EGR valve 44 is performed as the pre-cooler warm-up process. In this case, there is a concern that the condensed water in the EGR pipe tends to flow into the intake pipe 20 due to an increase in the EGR gas flow rate.

  Further, in the above-described first modification, an example in which the process of increasing the exhaust temperature of the engine 10 is performed as the precooler warm-up process has been described. In this case, the load on the engine 10 is increased (the fuel injection amount is increased), and contradiction such as deterioration of fuel efficiency or an increase in the amount of water vapor due to an increase in hydrocarbons (CHx) in the fuel may occur. Is done.

  In view of these points, in the second modification, as the pre-cooler warm-up process, the rotation speed of the water pump 45 is reduced to reduce the flow rate of the cooling water, thereby increasing the temperature of the cooling water in the pre-cooler 41. Perform processing. Thereby, it is possible to make it difficult to generate condensed water in the precooler 41 without continuing the EGR, without increasing the flow rate of the EGR gas, and without increasing the load on the engine 10.

  As the pre-cooler warm-up process, a process of increasing the opening degree of the EGR valve 44, a process of increasing the exhaust gas temperature of the engine 10, and a process of increasing the temperature of the cooling water in the pre-cooler 41 are appropriately combined and executed. Is also good.

<Modification 3>
In the above-described embodiment, an example in which two EGR coolers (the precooler 41 and the main cooler 42) are provided in the EGR pipe has been described, but the number of EGR coolers provided in the EGR pipe is not limited to two. , Or three or more.

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Reference Signs List 1 engine system, 10 engine, 20 intake pipe, 25 intake manifold, 30 exhaust pipe, 35 exhaust manifold, 40 EGR device, 41 EGR precooler, 42 EGR main cooler, 43 switching valve, 44 EGR valve, 45 water pump, 81 air flow Meter, 82 engine speed sensor, 83 humidity sensor, 100 ECU, A precooler inlet, B gas outlet, G1, G2, G3 EGR pipe, G4 bypass pipe, Gp gas flow path, W1, W2, W3, W4 cooling Water piping, Wp cooling water channel.

Claims (6)

An engine control system,
The engine is
An EGR pipe for recirculating a part of the exhaust gas in the exhaust passage to the intake passage,
An EGR cooler provided in the EGR pipe,
The control system includes a control device configured to determine whether condensed water generated in the EGR cooler flows into the intake passage,
The control device includes:
Comparing the first steam amount contained in the exhaust gas at the inlet to the EGR cooler in the EGR pipe with the second steam amount contained in the exhaust gas at the outlet to the intake passage in the EGR pipe;
An engine control system that determines that the condensed water flows into the intake passage when the first steam amount is larger than the second steam amount.   The engine control system according to claim 1, wherein the control device executes a warm-up process of warming up the EGR cooler when it is determined that the condensed water flows into the intake passage. The control system further includes an EGR valve configured to adjust an EGR gas flow rate recirculated from the EGR pipe to the intake passage,
The engine control system according to claim 2, wherein the warming-up process includes a process of increasing an opening degree of the EGR valve.   The engine control system according to claim 2, wherein the warm-up process includes a process of increasing an exhaust gas temperature of the engine. The EGR cooler cools EGR gas in the EGR pipe with a coolant,
The engine control system according to claim 2, wherein the warm-up process includes a process of increasing a temperature of the coolant. The control system includes:
An air flow meter for detecting an intake flow rate in the intake passage;
A humidity sensor provided at the outlet portion,
The control device includes:
Calculating the first water vapor amount using the detection result of the air flow meter,
The engine control system according to claim 1, wherein the detection result of the humidity sensor is acquired as the second water vapor amount.

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