JP2011179353A - Exhaust recirculation device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust recirculation device for an internal combustion engine condensing steam contained in EGR gas as much as possible, in an EGR cooler. <P>SOLUTION: The exhaust recirculation device for an internal combustion engine includes: one or a plurality of first EGR passage(s); one or a plurality of second EGR passage(s); a first EGR cooler disposed to each first EGR passage; a second EGR cooler disposed to each second EGR passage; a means for adjusting a ratio of a flow rate, adjusting a ratio of a flow rate of EGR gas recirculated by the first EGR passage, in a total EGR gas flow rate recirculated by the first EGR passage and second EGR passage; and a control means controlling the means for adjusting a ratio of a flow rate so that the ratio of the EGR gas recirculated by the first EGR passage in a total EGR gas flow rate when the total EGR gas flow rate is not less than a predetermined value gets smaller as the total EGR gas flow rate gets higher, and thereby controlling a temperature of EGR gas flowing out of a first EGR cooler to be not higher than a predetermined target temperature that is not higher than a dew-point temperature of the steam in the EGR gas. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine.

  In an engine with a supercharger, an EGR cooler is provided in the EGR passage, and the EGR cooler is provided with a condensed water removing means to suppress an increase in intake air temperature due to the introduction of EGR gas and to condense and remove moisture in the EGR gas. There is known an exhaust gas recirculation system that improves engine durability (see Patent Document 1).

JP-A-10-068358 JP 2009-270476 A JP 2007-092715 A JP 2009-270513 A JP 2004-156585 A

  When the EGR gas is introduced into the intake air, the specific heat ratio of the intake air decreases, so the thermal efficiency decreases. However, the EGR cooler condenses water vapor in the EGR gas and dehumidifies the EGR gas, thereby suppressing the decrease in the specific heat ratio of the intake air. It is possible to suppress a decrease in thermal efficiency. However, when the outside air temperature is high or the EGR gas flow rate is high, the temperature of the EGR gas flowing out from the EGR cooler increases, the temperature difference from the dew point temperature of the water vapor decreases, and the amount of water vapor condensation in the EGR cooler decreases. Condensation does not occur when the temperature of the EGR gas flowing out of the EGR cooler exceeds the dew point temperature. In such a case, the water vapor in the EGR gas cannot be sufficiently condensed in the EGR cooler.

  The present invention has been made in view of this point, and an object of the present invention is to provide an exhaust gas recirculation device for an internal combustion engine that can condense more water vapor in EGR gas in an EGR cooler.

In order to achieve this object, an exhaust gas recirculation device for an internal combustion engine according to the present invention includes:
One or a plurality of first EGR passages for recirculating a part of the exhaust from the exhaust system of the internal combustion engine to the intake system of the internal combustion engine as EGR gas;
One or a plurality of second EGR passages for recirculating part of the exhaust gas from the exhaust system of the internal combustion engine to the intake system of the internal combustion engine as EGR gas;
A first EGR cooler that is provided in each of the first EGR passages and cools EGR gas flowing through the first EGR passage;
A second EGR cooler for cooling EGR gas provided in each of the second EGR passages and flowing through the second EGR passage;
A flow rate ratio adjusting means for adjusting a ratio of the flow rate of the EGR gas recirculated through the first EGR passage in the flow rate of the total EGR gas recirculated through the first EGR passage and the second EGR passage;
The flow rate ratio adjustment so that the ratio of the EGR gas recirculated through the first EGR passage in the flow rate of the total EGR gas when the flow rate of the total EGR gas is equal to or greater than a predetermined value decreases as the flow rate of the total EGR gas increases. Control means for controlling the temperature of the EGR gas flowing out of the first EGR cooler to be equal to or lower than a predetermined target temperature lower than or equal to a dew point temperature of water vapor in the EGR gas by controlling the means;
It is characterized by providing.

  According to the above configuration, when the total EGR gas flow rate is equal to or higher than the predetermined value, an increase in the flow rate of EGR gas passing through the first EGR cooler is suppressed even if the total EGR gas flow rate increases. Specifically, the flow rate of the EGR gas passing through the first EGR cooler is suppressed to such a flow rate that the temperature of the EGR gas flowing out from the first EGR cooler is equal to or lower than a predetermined temperature. In this case, since the flow rate of the EGR gas recirculated through the second EGR passage increases by the amount of the EGR gas recirculated through the first EGR passage, the amount of condensation in the second EGR cooler decreases. Condensation may not occur, but even in such a case, since condensation occurs at least in the first EGR cooler, EGR is performed as in the case where the flow rate of all EGR gases is high or the outside air temperature is high. It is possible to reliably condense water vapor in the EGR gas in the first EGR cooler even under conditions where condensation is unlikely to occur in the cooler.

  Here, the predetermined value flows out from the first EGR cooler when the ratio of the EGR gas recirculating through the first EGR passage in the flow rate of the total EGR gas is not decreased with the increase in the flow rate of the total EGR gas. At least one of the temperature of the EGR gas and the temperature of the EGR gas flowing out from the second EGR cooler can be set to a value determined based on the upper limit value of the total EGR gas flow rate that can be made equal to or lower than the target temperature. That is, when the flow rate of all EGR gases is equal to or greater than a predetermined value, if the ratio of EGR gas recirculated through the first EGR passage is not decreased when the flow rate of all EGR gases is increased, the first EGR cooler Both the temperature of the EGR gas flowing out and the temperature of the EGR gas flowing out of the second EGR cooler exceed the target temperature. The target temperature is a temperature equal to or lower than the dew point temperature of the water vapor in the EGR gas, and is determined according to the demand for the amount of condensation in the first EGR cooler. If the target temperature is set to a low value, a larger amount of condensation can be obtained.

  The control means is the first when the total EGR gas flow rate is smaller than a predetermined value, and the total EGR gas is recirculated using only one of the first EGR passage and the second EGR passage. When the temperature of the EGR gas flowing out from the EGR cooler or the second EGR cooler is equal to or higher than a second predetermined value determined according to the upper limit value of the total EGR gas flow rate that can be set to a target temperature or lower, the above flow rate You may control a ratio adjustment means.

In the present invention, it comprises first temperature detection means for detecting the temperature of the EGR gas flowing out from the first EGR cooler,
The control means may include means for feedback-controlling the flow rate ratio adjusting means so that the temperature detected by the first temperature detecting means is equal to or lower than the target temperature.

  If such feedback control is performed, it is less susceptible to transient fluctuations and disturbances, and the water vapor in the EGR gas can be condensed more stably in the first EGR cooler.

  In the present invention, the control means includes at least the temperature of the EGR gas flowing out from the first EGR cooler and the second temperature within a range in which the temperature of the EGR gas flowing out from the first EGR cooler does not exceed the target temperature. The flow rate ratio adjusting means may be controlled so that the difference from the temperature of the EGR gas flowing out from the EGR cooler becomes small.

By this control, when the total EGR gas flow rate is smaller than a predetermined value, it is possible to control the total amount of condensation in the first EGR cooler and the amount of condensation in the second EGR cooler as much as possible. Become.

In the present invention, it comprises a second temperature detecting means for detecting the temperature of the EGR gas flowing out from the second EGR cooler,
The control means includes at least a temperature detected by the first temperature detection means and a second temperature detection means within a range in which the temperature of the EGR gas flowing out from the first EGR cooler does not exceed the target temperature. The flow rate ratio adjusting means may be feedback-controlled so that the difference from the detected temperature is small.

  By performing such feedback control, it becomes less susceptible to transient fluctuations and disturbances, and the total amount of condensation in the first EGR cooler and the amount of condensation in the second EGR cooler is increased as much as possible. Can be.

In the present invention, comprising a concentration detection means for detecting the water vapor concentration of the EGR gas,
The control means controls the flow rate ratio adjusting means so that the proportion of the EGR gas recirculated through the first EGR passage in the flow rate of the total EGR gas decreases as the water vapor concentration detected by the concentration detection means decreases. You may make it do.

  Since the dew point temperature decreases as the water vapor concentration of the EGR gas decreases, it is necessary to further reduce the temperature of the EGR gas flowing out of the EGR cooler in order to condense the water vapor in the EGR gas. According to the above configuration, as the water vapor concentration in the EGR gas decreases, the flow rate of the EGR gas flowing through the first EGR passage decreases, so the flow rate of the EGR gas passing through the first EGR cooler decreases. The temperature of the EGR gas flowing out from the first EGR cooler can be lowered. Therefore, the required amount of condensation can be obtained regardless of fluctuations in the water vapor concentration in the EGR gas.

  In the present invention, the flow rate ratio adjusting means is a flow rate ratio adjusting valve that is provided closer to the intake system than the first EGR cooler in the first EGR passage and adjusts the flow area of the first EGR passage. There may be.

  By providing a flow rate ratio adjusting valve on the intake system side of the first EGR cooler, when the flow rate ratio adjusting valve is throttled to reduce the flow rate of the EGR gas flowing through the first EGR passage, the EGR in the first EGR cooler As the gas pressure increases, the dew point temperature increases. Thereby, the amount of condensation in the first EGR cooler can be increased.

  According to the exhaust gas recirculation apparatus for an internal combustion engine according to the present invention, it becomes possible to condense more water vapor in the EGR gas in the EGR cooler.

1 is a diagram illustrating a schematic configuration of an exhaust gas recirculation device for an internal combustion engine according to a first embodiment. In the exhaust gas recirculation apparatus for an internal combustion engine according to the first embodiment and the prior art, the relationship between the flow rate of all EGR gas and the temperature of EGR gas flowing out from EGR cooler A under the condition of constant temperature of EGR gas flowing into EGR cooler The relationship between the flow rate of all EGR gas and the temperature of EGR gas flowing out from EGR cooler B, the flow rate of all EGR gas and the flow rate of EGR gas passing through EGR cooler A of all EGR gas, and passing through EGR cooler B It is a conceptual diagram which shows typically the relationship with the ratio of the flow volume of EGR gas. It is a figure which shows an example of the relationship between the EGR gas temperature which flows in into the EGR cooler A, and the correction value by which the flow rate ratio adjustment valve basic opening is multiplied. It is a figure which shows an example of the relationship between the correction value which multiplies the temperature of the refrigerant | coolant of EGR cooler A, and a flow rate ratio adjustment valve basic opening. It is a figure which shows an example of the relationship between the water vapor | steam density | concentration in EGR gas, and the correction value which multiplies the flow rate ratio adjustment valve basic opening. 3 is a flowchart illustrating opening degree control of a flow rate ratio adjusting valve in the first embodiment. FIG. 3 is a diagram showing a schematic configuration of an exhaust gas recirculation device for an internal combustion engine according to a modified example of Embodiment 1. FIG. 6 is a diagram illustrating a schematic configuration of an exhaust gas recirculation device for an internal combustion engine according to another modified example of the first embodiment. FIG. 6 is a diagram illustrating a schematic configuration of an exhaust gas recirculation device for an internal combustion engine according to another modified example of the first embodiment. FIG. 6 is a diagram illustrating a schematic configuration of an exhaust gas recirculation device for an internal combustion engine according to another modified example of the first embodiment. 7 is a flowchart illustrating opening degree control of a flow rate ratio adjusting valve in the second embodiment. FIG. 6 is a diagram illustrating a schematic configuration of an exhaust gas recirculation device for an internal combustion engine according to a third embodiment. In the exhaust gas recirculation apparatus for an internal combustion engine according to the third embodiment and the prior art, the relationship between the flow rate of all EGR gas and the temperature of EGR gas flowing out from EGR cooler A under the condition of constant temperature of EGR gas flowing into EGR cooler The relationship between the flow rate of all EGR gas and the temperature of EGR gas flowing out from EGR cooler B, the flow rate of all EGR gas and the flow rate of EGR gas passing through EGR cooler A of all EGR gas, and passing through EGR cooler B It is a conceptual diagram which shows typically the relationship with the ratio of the flow volume of EGR gas. 10 is a flowchart illustrating opening degree control of a flow rate ratio adjusting valve in the third embodiment.

Example 1
Hereinafter, embodiments of the present invention will be described in detail. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and an intake system and an exhaust system thereof according to an embodiment of an exhaust gas recirculation apparatus for an internal combustion engine of the present invention. In FIG. 1, an internal combustion engine 1 includes four cylinders 2 and a fuel injection valve 13 that injects fuel into each cylinder 2. Each cylinder 2 communicates with an intake manifold 5 via an intake port (not shown) and also communicates with an exhaust manifold 6 via an exhaust port (not shown). The intake port and the exhaust port are opened and closed by an unillustrated intake valve and exhaust valve, respectively. An intake passage 3 is connected to the intake manifold 5, and a throttle valve 15 that adjusts the flow passage area of the intake passage 3 in order from the side close to the intake manifold 5 to the upstream side of the intake passage 3, intake air flowing through the intake passage 3 Are provided with an intercooler 11 for cooling the air, a compressor 7 for the turbocharger 12, and an air flow meter 14 for detecting the intake air amount. An exhaust passage 4 is connected to the exhaust manifold 6, and the turbine 8 of the turbocharger 12 and a filter that removes particulate matter (PM) in the exhaust in order from the side close to the exhaust manifold 6 to the downstream side. And an exhaust purification device 24 having a catalyst for reducing NOx and the like. The internal combustion engine 1 is provided with a sensor 16 for detecting the rotational speed and a sensor 17 for detecting a load.

The exhaust manifold 6 and the intake manifold 5 communicate with each other through an EGR passage 10. A part of the exhaust discharged from the internal combustion engine 1 through the EGR passage 10 returns to the intake manifold 5 as EGR gas. The EGR passage 10 is branched into two branch passages 22 and 20 on the way, and the two branch passages merge on the side close to the intake manifold 5. A flow rate ratio adjusting valve 9 is provided at the junction, and all the EGs flowing through the EGR passage 10 are adjusted by adjusting the opening degree of the flow rate adjusting valve 9.
The ratio of the flow rate of EGR gas flowing through the branch passage 22 and the flow rate of EGR gas flowing through the branch passage 20 in the R gas can be adjusted. In the present embodiment, the flow rate of the EGR gas flowing through the branch passage 22 among all the EGR gases can be increased as the flow rate adjustment valve 9 is opened more (opened). And

  The branch passage 22 is provided with an EGR cooler 21 (hereinafter referred to as “EGR cooler A”) for cooling the EGR gas, and the temperature of the EGR gas flowing out from the EGR cooler A in the branch passage 22 on the intake manifold 5 side from the EGR cooler A is provided. Is provided. The branch passage 20 is provided with an EGR cooler 19 (hereinafter referred to as “EGR cooler B”) for cooling the EGR gas. The EGR passage 10 closer to the intake manifold 5 than the junction of the branch passages 22 and 20 is provided with an EGR valve 25 that adjusts the flow area of the EGR passage 10. By adjusting the opening of the EGR valve 25, The flow rate of total EGR gas can be adjusted.

  In the present embodiment, the EGR gas passage that joins the EGR passage 10 from the EGR passage 10 through the branch passage 22 and flows into the intake manifold 5 functions as the first EGR passage in the present invention. The EGR gas passage that joins the EGR passage 10 from the EGR passage 10 via the branch passage 20 and flows into the intake manifold 5 functions as the second EGR passage in the present invention. In the present embodiment, the EGR cooler A functions as a first EGR cooler, and the EGR cooler B functions as a second EGR cooler. That is, in the present embodiment, each of the first EGR passage, the second EGR passage, the first EGR cooler, and the second EGR cooler is one, but there may be a plurality of them. The flow rate adjusting valve 9 functions as a flow rate adjusting means in the present invention.

  The internal combustion engine 1 is provided with an ECU 18 that is a microcomputer for controlling the operating state. The ECU 18 is connected to the air flow meter 14, the temperature sensor 23, the sensor 16 for detecting the rotational speed, and various sensors in addition to the sensor 17 for detecting the load. Values detected by the various sensors are input to the ECU 18. The ECU 18 detects the operating state of the internal combustion engine 1 and the request of the driver based on the input detection value, and based on the detected value, the throttle valve 15, the fuel injection valve 13, the flow rate ratio adjusting valve 9, the EGR valve 25, and other various types. Control the equipment.

  EGR gas recirculation provides effects such as a reduction in pump loss and a reduction in the amount of NOx produced. On the other hand, the specific heat ratio of the gas sucked into the cylinder 2 is reduced, leading to a reduction in thermal efficiency. The EGR gas contains a large amount of water vapor, and by removing the water vapor and dehumidifying the EGR gas, it is possible to suppress a decrease in the specific heat ratio of the cylinder intake gas when the EGR gas is recirculated, thereby reducing the thermal efficiency. Can be suppressed. In the internal combustion engine 1 of the present embodiment, the EGR gas is cooled in the EGR coolers A and B provided in the EGR passage 10, the water vapor in the EGR gas is condensed, and the EGR gas can be dehumidified. . However, when the temperature of the heat medium (refrigerant) supplied to the EGR coolers A and B is high under operating conditions where the outside air temperature is high such as in summer, or when the flow rate of EGR gas passing through the EGR coolers A and B is large. In such a case, the cooling in the EGR coolers A and B cannot catch up, and the water vapor may not be sufficiently condensed in the EGR coolers A and B. When the temperature of the refrigerant in the EGR coolers A and B exceeds the dew point temperature of the water vapor in the EGR gas, the water vapor does not condense. In this case, it becomes difficult to dehumidify the EGR gas, which may cause a decrease in thermal efficiency for the reason described above.

FIG. 2 shows the flow rate of the total EGR gas in the exhaust gas recirculation apparatus for the internal combustion engine according to the present embodiment and the prior art under the condition that the temperature of the EGR gas flowing into the EGR coolers A and B (EGR cooler inlet gas temperature) is constant. Between EGR gas flowing out from EGR cooler A (EGR cooler A outlet gas temperature), relationship between the flow rate of all EGR gases and the temperature of EGR gas flowing out from EGR cooler B (EGR cooler B outlet gas temperature) The ratio of the flow rate of all EGR gas and the flow rate of EGR gas (EGR cooler A flow rate) passing through EGR cooler A and the flow rate of EGR gas (EGR cooler B flow rate) passing through EGR cooler B of all EGR gases. It is a conceptual diagram which shows a relationship typically.

  As indicated by the broken line in FIG. 2, when the flow rate of EGR gas passing through the EGR cooler A and the ratio of the flow rate of EGR gas passing through the EGR cooler B are equal, the total EGR gas flow rate increases. Both the gas temperature and the EGR cooler B exit gas temperature rise, and both the total EGR gas flow rates reach the dew point temperature at Ge3. The amount of water vapor condensed in the EGR cooler depends on the difference between the EGR cooler outlet gas temperature and the dew point temperature and the flow rate of the EGR gas passing through the EGR cooler. After the EGR cooler exit gas temperature reaches the dew point temperature, the amount of water vapor condensed in the EGR cooler becomes 0, and the water vapor in the EGR gas cannot be condensed.

  Therefore, in the internal combustion engine 1 of the present embodiment, as shown by the solid line in FIG. 2, when the total EGR gas flow rate is equal to or higher than the predetermined value Ge1, the EGR cooler A outlet gas temperature is below a predetermined target temperature lower than the dew point temperature. Thus, the ratio of the flow rate of the EGR gas passing through the EGR cooler A out of the total EGR gas is decreased as the total EGR gas flow rate is increased. As a result, even when the total EGR gas flow rate increases, the increase in the flow rate of EGR gas passing through the EGR cooler A can be suppressed, and the EGR cooler A outlet gas temperature is maintained below the target temperature as shown in FIG. can do. In this case, although the flow rate of the EGR gas passing through the EGR cooler B is increased by the amount of suppression of the flow rate of the EGR gas passing through the EGR cooler A, the condensation always occurs at least in the EGR cooler A. If so, it is possible to dehumidify the EGR gas recirculated to the intake manifold 5 even under the operating condition of the total EGR gas flow rate Ge3 or more in which both the EGR coolers A and B no longer condense. Here, the total EGR gas flow rate Ge1 is an upper limit value of the total EGR gas flow rate that allows the EGR cooler A outlet gas temperature to be equal to or lower than the target temperature when all the EGR gas is recirculated using the branch passage 22. .

  FIG. 2 shows an example in which the ratio of EGR gas passing through the EGR cooler A is adjusted so that the EGR cooler A outlet gas temperature matches the target temperature, but the ratio of EGR gas passing through the EGR cooler A is shown. May be adjusted to any ratio that satisfies the condition that the EGR cooler A outlet gas temperature is equal to or lower than the target temperature. This ratio may be a constant value as shown in FIG. 2, or may be a variable value within a range that satisfies the above conditions. Since the amount of condensation depends on various conditions, the optimum ratio of EGR gas passing through the EGR cooler A that maximizes the amount of condensation in the EGR coolers A and B is experimentally determined for each operating condition, and the optimum ratio is realized. The opening degree of the flow rate ratio adjusting valve 9 for this purpose is obtained as a target opening degree (flow rate ratio adjusting valve basic opening degree) for each operating condition and stored in the ECU 18. Then, the flow rate ratio adjusting valve basic opening is read from the ECU 18 in accordance with the operating conditions of the internal combustion engine 1, and the flow rate adjusting valve 9 is controlled to be the basic opening (open control). As a result, as shown in FIG. 2, even when the EGR gas flow rate is increased, the EGR cooler A can condense the water vapor in the EGR gas.

  Here, the amount of water vapor condensed in the EGR cooler A also depends on the temperature of the EGR gas flowing into the EGR cooler A, the temperature of the refrigerant in the EGR cooler A, and the water vapor concentration in the EGR gas. Specifically, the amount of water vapor condensed in the EGR cooler A tends to decrease as the temperature of the EGR gas flowing into the EGR cooler A increases. Further, the amount of water vapor condensed in the EGR cooler A tends to decrease as the temperature of the refrigerant in the EGR cooler A increases. Further, the amount of water vapor condensed in the EGR cooler A tends to decrease as the water vapor concentration in the EGR gas decreases.

  In view of these properties, the flow rate adjusting valve basic opening calculated as described above is used as the EGR that flows into the EGR cooler A so that the required amount of water vapor condensation can be ensured more reliably. You may make it correct | amend based on the temperature of gas, the temperature of the refrigerant | coolant of EGR cooler A, and the water vapor | steam density | concentration in EGR gas.

  Specifically, it is preferable to multiply the flow rate ratio adjusting valve basic opening by a correction value that decreases as the temperature of the EGR gas flowing into the EGR cooler A increases. FIG. 3 is a diagram showing an example of the relationship between the EGR gas temperature (ethegin) flowing into the EGR cooler A and the correction value (emthegin) multiplied by the basic flow rate adjustment valve opening. By multiplying this correction value, the higher the EGR gas temperature flowing into the EGR cooler A, the closer the opening of the flow rate adjusting valve 9 becomes, so the flow rate of EGR gas passing through the EGR cooler A decreases. The temperature of the EGR gas flowing out from the EGR cooler A decreases, and the amount of condensation in the EGR cooler A increases. As a result, it is possible to correct a decrease in the amount of condensation due to an increase in the temperature of the EGR gas flowing into the EGR cooler A.

  Moreover, it is good to multiply the correction value which becomes small, so that the temperature of the refrigerant | coolant of EGR cooler A becomes high to the flow rate ratio adjustment valve basic opening. FIG. 4 is a diagram showing an example of the relationship between the refrigerant temperature (ethegcm) of the EGR cooler A and the correction value (emthegcm) multiplied by the flow rate ratio adjustment valve basic opening. By multiplying this correction value, the higher the temperature of the refrigerant in the EGR cooler A, the closer the opening of the flow rate adjusting valve 9 becomes, so the flow rate of EGR gas passing through the EGR cooler A decreases, and the EGR cooler The temperature of the EGR gas flowing out from A decreases, and the amount of condensation in the EGR cooler A increases. Thereby, the reduction | decrease in the amount of condensation by the raise of the temperature of the refrigerant | coolant of EGR cooler A can be correct | amended.

  Further, the flow rate ratio adjusting valve basic opening may be multiplied by a correction value that decreases as the water vapor concentration in the EGR gas decreases. FIG. 5 is a diagram showing an example of the relationship between the water vapor concentration (erstream) in the EGR gas and the correction value (emrteam) multiplied by the flow rate ratio adjustment valve basic opening. By multiplying this correction value, the lower the water vapor concentration in the EGR gas, the closer the opening of the flow rate adjusting valve 9 is to the close side, and thus the flow rate of the EGR gas passing through the EGR cooler A is reduced, and the EGR cooler A The temperature of the EGR gas flowing out from the refrigerant decreases, and the amount of condensation in the EGR cooler A increases. Thereby, the reduction | decrease in the amount of condensation by the fall of the water vapor | steam density | concentration in EGR gas can be correct | amended.

  FIG. 6 is a flowchart showing the open control of the flow rate ratio adjusting valve 9 for condensing more water vapor in the EGR gas in the EGR cooler A described above. The process represented by the flowchart of FIG. 6 is repeatedly executed by the ECU 18 at predetermined intervals.

  In step S101, the ECU 18 first calculates the rotational speed (ene) and the load (eqfin) as parameters representing the operating state of the internal combustion engine 1. The ECU 18 calculates the rotational speed ene and the load eqfin based on the detection values of the sensor 16 that detects the rotational speed and the sensor 17 that detects the load. Based on the rotational speed ene and the load eqfin, a flow rate ratio adjusting valve basic opening (epegrb) is calculated in step S102. As for the flow rate ratio adjusting valve basic opening degree epegrb, the optimum value obtained in advance as described above is stored in a map using the rotation speed ene and the load eqfin as parameters.

  In step S103, the temperature of the EGR gas flowing into the EGR cooler A is calculated. The EGR cooler inlet gas temperature etegin is calculated based on a detection value by a temperature sensor (not shown) (for example, provided in the EGR passage 10 closer to the exhaust manifold 6 than the EGR cooler A) and the operating state of the internal combustion engine 1. On the basis of the EGR cooler input gas temperature ethegin, a correction value emthegin is calculated in the subsequent step S104. The calculation of the correction value emthegin uses the relationship between the EGR cooler inlet gas temperature and the correction value as shown in FIG.

In step S105, the refrigerant temperature (ethegcm) of the EGR cooler A is calculated.
The refrigerant temperature ethegcm of the EGR cooler A is calculated based on a detection value by a temperature sensor (not shown) (for example, provided in the refrigerant flow path of the EGR cooler A) or the operating state of the internal combustion engine 1. Based on the EGR cooler refrigerant temperature ethegcm, a correction value embegcm is calculated in the subsequent step S106. For the calculation of the correction value emthegcm, the relationship between the EGR cooler refrigerant temperature and the correction value as shown in FIG.

  In step S107, the water vapor concentration (erstream) in the EGR gas is calculated. The water vapor concentration erstream in the EGR gas is calculated based on a detection value by a sensor (not shown) (for example, provided in the branch passage 22 closer to the exhaust manifold 6 than the EGR cooler A) and the operating state of the internal combustion engine 1. On the basis of the EGR gas water vapor concentration erstream, a correction value emrstream is calculated in the subsequent step S108. For the calculation of the correction value emrteam, the relationship between the EGR gas water vapor concentration and the correction value as shown in FIG. In this embodiment, the ECU 18 that calculates the water vapor concentration erstream functions as the concentration detection means in the present invention.

  In step S109, the flow rate ratio adjusting valve basic opening degree epegrb obtained in step S102 is corrected by multiplying the correction values emthegin, emthegcm, and emrsteam calculated in steps S104, 106, and 108, and the flow rate ratio adjusting valve opening command value ( epegrfin) is calculated. Next, based on the flow rate ratio adjusting valve opening command value epegrfin, the flow rate ratio adjusting valve 9 is controlled in step S110.

  By performing the open control described above, even when the total amount of EGR gas increases, the EGR cooler A can condense the water vapor in the EGR gas, so that a large amount of EGR gas is introduced. A decrease in thermal efficiency can be suppressed even in the operating state. ECU18 which performs control mentioned above functions as a control means in the present invention.

(Modification)
Any means other than the above-described flow rate ratio adjusting valve 9 can be used as long as it is a means capable of adjusting the ratio between the flow rate of EGR gas flowing through the branch passage 22 and the flow rate of EGR gas flowing through the branch passage 20 out of all EGR gas. Forms are also possible. For example, as shown in FIG. 7, a flow rate adjusting valve 28 for adjusting the flow area is provided in the branch passage 22, and a flow rate adjusting valve 29 for adjusting the flow area is provided in the branch passage 20. The ratio of the flow rate of EGR gas flowing through the branch passage 22 and the flow rate of EGR gas flowing through the branch passage 20 out of all EGR gases can also be adjusted by adjusting the opening degree. In this case, the flow rate adjusting valves 28 and 29 are controlled by the ECU 18. In this configuration, the flow rate adjusting valves 28 and 29 function as flow rate ratio adjusting means in the present invention.

  Further, in the present embodiment, the configuration in which one EGR passage 10 branches into the branch passages 22 and 20 on the way and merges on the downstream side has been described. However, as shown in FIG. 8, the EGR gas is supplied from the exhaust manifold 6 to the intake manifold 5. It is also possible to employ a configuration in which two EGR passages for refluxing are independently provided (EGR passages 32 and 33). In this case, each EGR passage is provided with an EGR cooler and flow rate adjusting valves (flow rate adjusting valves 34 and 35). In this case, the flow rate adjusting valves 34 and 35 function as an EGR valve that adjusts the flow rate of all EGR gases, and as flow rate rate adjusting means that adjusts the rate of the flow rate of EGR gas that passes through the EGR cooler A in the total EGR gas. Will also work. In this configuration, the EGR passage 32 functions as a first EGR passage in the present invention, and the EGR passage 33 functions as a second EGR passage in the present invention. Further, the flow rate adjusting valves 34 and 35 function as flow rate adjusting means in the present invention.

In short, the EGR gas that recirculates from the exhaust manifold 6 to the intake manifold 5 passes through the E
There are two types of GR coolers, and any configuration may be used as long as the ratio of the flow rate of the EGR gas passing through one EGR cooler can be adjusted.

  Further, as shown in FIG. 9, the flow rate adjusting valve 31 similar to the flow rate adjusting valve 9 is provided at the branch portion on the upstream side (the side closer to the exhaust manifold 6) of the branch passage 22 and the EGR coolers A and B of the branch passage 20. May be provided. In this configuration, the flow rate adjustment valve 31 functions as the flow rate adjustment means in the present invention. However, as shown in FIG. 1, by providing the flow rate ratio adjusting valve 9 at the junction on the downstream side (the side closer to the intake manifold 5) than the EGR coolers A and B, the pressure in the EGR cooler A increases and the dew point temperature increases. Therefore, there is an advantage that the amount of condensation can be increased. Accordingly, the position where the flow rate ratio adjusting valve is provided is preferably the position of the flow rate ratio adjusting valve 9 in FIG. 1 from the viewpoint of the amount of condensation.

(Modification)
Also, under operating conditions where the cylinder intake gas is preferably at a high temperature, such as during cold start, it is better to recirculate the EGR gas without cooling. Accordingly, as shown in FIG. 10, a bypass passage 30 is provided to bypass the EGR coolers A and B, and the ratio of the flow rate of EGR gas flowing through the EGR coolers A and B and the flow rate of EGR gas flowing through the bypass passage 30 can be adjusted. A flow rate adjusting valve 26 is provided in the EGR passage 10 on the downstream side of the flow rate adjusting valve 9 so that the ratio of EGR gas passing through the bypass passage 30 is increased under operating conditions where it is preferable to recirculate hot EGR gas. The opening degree of the flow rate ratio adjusting valve 26 may be adjusted. As a result, it is possible to improve combustion under operating conditions where it is preferable to recirculate high-temperature EGR gas.

  The opening degree control of the flow rate adjusting valve 9 of this embodiment is an open control based on the operating state of the internal combustion engine 1, and the temperature of the EGR gas flowing out from the EGR cooler A is controlled as in the control of the embodiment 2 described later. Since it is not used for control, in this embodiment, the temperature sensor 23 for detecting the temperature of the EGR gas flowing out from the EGR cooler A may not be provided.

(Example 2)
In the open control described in the first embodiment, the flow rate ratio adjusting valve 9 is controlled to an opening previously determined so that the temperature of the EGR gas flowing out from the EGR cooler A (EGR cooler A outgas temperature) becomes the target temperature. However, since the amount of condensation is affected by various disturbances such as outside air temperature and transient fluctuations, a sufficient amount of condensation may not be obtained even if correction as described in the first embodiment is performed. It is done. Therefore, in this embodiment, feedback control is performed so that the EGR cooler A outgas temperature, which is one of the most essential parameters for the amount of condensation in the EGR cooler A, follows the target temperature.

  FIG. 11 is a flowchart showing the feedback control of the flow rate ratio adjusting valve according to the present embodiment for causing the EGR cooler A outlet gas temperature to follow the target temperature. The processing represented by this flowchart is repeatedly executed by the ECU 18 at predetermined intervals.

  In step S201, the ECU 18 calculates an EGR cooler A outgas temperature (ethega). The ECU 18 calculates the EGR cooler A outgas temperature ethega based on the value detected by the temperature sensor 23. Next, in step S202, the ECU 18 calculates a target temperature (ethegtrg) of the EGR cooler A outlet gas temperature. The target temperature ethegtrg may be a constant value stored in the ECU 18 in advance, or a variable value corresponding to an operating condition or the like may be calculated.

In step S203, the ECU 18 compares the EGR cooler A outlet gas temperature ethega calculated in step S201 with the target temperature ethegrg calculated in step S202. If the EGR cooler A outlet gas temperature ethega is higher than the target temperature ethegtrg, the process proceeds to step S204. Thus, control is performed to reduce the flow rate of the EGR gas passing through the EGR cooler A. On the other hand, if the EGR cooler A outlet gas temperature ethega is equal to or lower than the target temperature ethegtrg, the process proceeds to step S205, and control is performed to increase the flow rate of EGR gas passing through the EGR cooler A.

  In step S204, the control for reducing the flow rate of the EGR gas passing through the EGR cooler A is control for changing the opening of the flow rate adjusting valve 9 to the closed side in the configuration of FIG. 1, and the flow rate in the configuration of FIG. This is control for changing the opening degree of the regulating valve 28 to the closed side and / or control for changing the opening degree of the flow regulating valve 29 to the open side. In step S205, the control for reducing the flow rate of the EGR gas passing through the EGR cooler A is control for changing the opening of the flow rate adjusting valve 9 to the open side in the configuration of FIG. 1, and the flow rate in the configuration of FIG. This is control for changing the opening degree of the adjustment valve 28 to the open side and / or control for changing the opening degree of the flow rate adjustment valve 29 to the closing side.

  By executing the feedback control described above, it becomes possible to condense the water vapor in the EGR gas in the EGR cooler A while suppressing the influence due to the disturbance and the transient fluctuation, and thus more reliably in various operating conditions. A decrease in thermal efficiency can be suppressed. In this embodiment, the temperature sensor 23 functions as the first temperature detecting means in the present invention. Moreover, ECU18 which performs the said control functions as a control means in this invention.

(Example 3)
In the first and second embodiments, the example in which the flow rate ratio adjusting valve 9 is controlled so that the flow rate of the EGR gas passing through the EGR cooler A is maximized in a range where the EGR cooler A outlet gas temperature is equal to or lower than the target temperature has been described. However, the flow rate ratio adjusting valve 9 may be controlled in a range that satisfies the condition that the EGR cooler A outgas temperature is equal to or lower than the target temperature. For example, the difference between the EGR cooler A outlet gas temperature and the EGR cooler B outlet gas temperature may be controlled within a range where the EGR cooler A outlet gas temperature falls below the target temperature.

  FIG. 13 shows the flow rate of all EGR gases and the EGR cooler A outlet gas temperature under the condition that the temperature of EGR gas flowing into the EGR coolers A and B (EGR cooler inlet gas temperature) is constant when such control is performed. , The relationship between the flow rate of all EGR gas and the EGR cooler B outlet gas temperature, the flow rate of all EGR gas and the flow rate of EGR gas that passes through EGR cooler A (EGR cooler A flow rate) and EGR cooler 5 is a diagram schematically showing a relationship with a ratio of a flow rate of EGR gas passing through B (EGR cooler B flow rate). FIG.

  As shown by the solid line in FIG. 13, in the control of this embodiment, the EGR that passes through the EGR cooler A until the EGR cooler A outgas temperature reaches the target temperature (until the total EGR gas flow rate becomes Ge4 in FIG. 13). The flow rate of the gas and the flow rate of the EGR gas passing through the EGR cooler B are equal. When the ratio of the flow rate of the EGR gas passing through the EGR cooler A in the total EGR gas is not decreased with the increase in the total EGR gas flow rate, the total EGR gas flow rate Ge4 is the EGR cooler A outlet gas temperature and the EGR cooler B. This is the upper limit value of the total EGR gas flow rate at which at least one of the outgas temperatures can be made equal to or lower than the target temperature. In the range until the total EGR gas flow rate reaches Ge4, the EGR cooler A outlet gas temperature and the EGR cooler B outlet gas temperature are controlled to be equal to or lower than the target temperature and as small as possible. That is, the EGR cooler A outlet gas temperature and the EGR cooler B outlet gas temperature are controlled to be equal. Thereby, it is possible to obtain as much condensation as possible in both the EGR coolers A and B until the total EGR gas flow rate becomes Ge4.

FIG. 14 is a flowchart when the control of this embodiment is performed by feedback control based on the temperature of the EGR gas flowing out from the EGR cooler A and the temperature of the EGR gas flowing out from the EGR cooler B. The control represented by this flowchart is periodically and repeatedly executed by the ECU 18. In order to perform this feedback control, in this embodiment, as shown in FIG. 12, a temperature sensor 27 for detecting the temperature of the EGR gas flowing out from the EGR cooler B is provided in the branch passage 20 on the downstream side of the EGR cooler B. The detected value by the temperature sensor 27 is input to the ECU 18. In this embodiment, the temperature sensor 27 functions as the second temperature detecting means in the present invention.

  In step S301, the ECU 18 calculates an EGR cooler A outgas temperature (ethega). The ECU 18 calculates the EGR cooler A outgas temperature ethega based on the value detected by the temperature sensor 23. Next, in step S302, the ECU 18 calculates an EGR cooler B outlet gas temperature (ethegb). The ECU 18 calculates the EGR cooler B outgas temperature ethegb based on the detected value by the temperature sensor 27.

  In step S303, the ECU 18 compares the EGR cooler A outlet gas temperature ethega calculated in step S301 with the EGR cooler B outlet gas temperature ethegb calculated in step S302, and the EGR cooler A outlet gas temperature ethega is the EGR cooler B outlet gas temperature. If it is higher than ethegb, the process proceeds to step S304, and control is performed to decrease the flow rate of the EGR gas passing through the EGR cooler A. On the other hand, if the EGR cooler A outlet gas temperature ethega is equal to or lower than the EGR cooler B outlet gas temperature ethegb, the process proceeds to step S305 to calculate the target temperature (ethegtrg) of the EGR cooler A outlet gas temperature. The target temperature ethegtrg may be a constant value stored in the ECU 18 in advance, or a variable value corresponding to an operating condition or the like may be calculated.

  In step S306, the ECU 18 compares the EGR cooler A outlet gas temperature ethega calculated in step S301 with the target temperature ethegrg calculated in step S305. Thus, control is performed to reduce the flow rate of the EGR gas passing through the EGR cooler A. On the other hand, if the EGR cooler A outlet gas temperature ethega is equal to or lower than the target temperature ethegtrg, the process proceeds to step S307 and control is performed to increase the flow rate of EGR gas passing through the EGR cooler A.

  The control for decreasing the flow rate of the EGR gas passing through the EGR cooler A in step S304 and the control for increasing the flow rate of the EGR gas passing through the EGR cooler A in step S307 are equivalent to the control in the first or second embodiment.

  By executing the feedback control described above, the EGR cooler A outlet gas temperature and the EGR cooler B outlet gas temperature are set under the operating conditions in which both the EGR cooler A outlet gas temperature and the EGR cooler B outlet gas temperature are equal to or lower than the target temperature. The difference is controlled to be small. Further, under an operating condition where either the EGR cooler A outlet gas temperature or the EGR cooler B outlet gas temperature exceeds the target temperature, the total EGR gas flow rate increases so that the EGR cooler A outlet gas temperature becomes equal to or lower than the target temperature. The ratio of EGR gas passing through the EGR cooler A in all EGR gas is controlled to be small. As a result, it is possible to enhance the condensing effect by exerting the condensing capacity of the EGR coolers A and B as much as possible. In the present embodiment, the ECU 18 that executes the above control functions as the control means in the present invention.

  In this embodiment, an example of performing control to equalize the flow rates of the EGR coolers A and B until the total EGR gas flow rate becomes Ge4 by feedback control based on the detected values of the EGR cooler A outgoing gas temperature and the EGR cooler B outgoing gas temperature. However, the same control may be performed by open loop control as in the first embodiment. In that case, it is also preferable to perform correction using parameters related to the amount of condensation as in the first embodiment.

  Each embodiment described above is an example for explaining the present invention, and the above-described embodiments can be changed or combined as much as possible within the scope of the present invention. For example, in the above-described embodiment, a configuration including two branch passages and an EGR cooler is illustrated, but the number of branch passages and EGR coolers may be larger than two. In that case, the plurality of EGR coolers are divided into a group of EGR coolers in which the flow rate of EGR gas passing through the EGR cooler is controlled so that the outgas temperature is equal to or lower than the target temperature, and other groups, and at least for each group. A mechanism capable of adjusting the ratio of the passing EGR gas flow rate to the total EGR gas flow rate may be provided.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Intake manifold 6 Exhaust manifold 7 Compressor 8 Turbine 9 Flow rate adjustment valve 10 EGR passage 11 Intercooler 12 Turbocharger 13 Fuel injection valve 14 Air flow meter 15 Throttle valve 16 Rotation speed detection sensor 17 Load detection sensor 18 ECU
19 EGR cooler B
20 Branch passage 21 EGR cooler A
22 Branch passage 23 Temperature sensor 24 Exhaust gas purification device 25 EGR valve 26 Flow rate adjustment valve 27 Temperature sensor 28 Flow adjustment valve 29 Flow adjustment valve 30 Bypass passage 31 Flow rate adjustment valve

Claims (6)

One or a plurality of first EGR passages for recirculating a part of the exhaust from the exhaust system of the internal combustion engine to the intake system of the internal combustion engine as EGR gas;
One or a plurality of second EGR passages for recirculating part of the exhaust gas from the exhaust system of the internal combustion engine to the intake system of the internal combustion engine as EGR gas;
A first EGR cooler that is provided in each of the first EGR passages and cools EGR gas flowing through the first EGR passage;
A second EGR cooler for cooling EGR gas provided in each of the second EGR passages and flowing through the second EGR passage;
A flow rate ratio adjusting means for adjusting a ratio of the flow rate of the EGR gas recirculated through the first EGR passage in the flow rate of the total EGR gas recirculated through the first EGR passage and the second EGR passage;
The flow rate ratio is such that the ratio of the EGR gas recirculated through the first EGR passage in the flow rate of the total EGR gas when the flow rate of the total EGR gas is equal to or greater than a predetermined value decreases as the flow rate of the total EGR gas increases. Control means for controlling the temperature of the EGR gas flowing out of the first EGR cooler to be equal to or lower than a predetermined target temperature not higher than a dew point temperature of water vapor in the EGR gas by controlling the adjusting means;
An exhaust gas recirculation device for an internal combustion engine, comprising: In claim 1,
First temperature detecting means for detecting the temperature of the EGR gas flowing out of the first EGR cooler;
The exhaust gas recirculation apparatus for an internal combustion engine, wherein the control means includes means for feedback-controlling the flow rate ratio adjusting means so that the temperature detected by the first temperature detecting means is equal to or lower than the target temperature. . In claim 1 or 2,
The control means includes at least the temperature of the EGR gas flowing out from the first EGR cooler and the second EGR cooler within a range in which the temperature of the EGR gas flowing out from the first EGR cooler does not exceed the target temperature. An exhaust gas recirculation apparatus for an internal combustion engine, wherein the flow rate ratio adjusting means is controlled so that a difference from the temperature of the EGR gas flowing out becomes small. In claim 3,
A second temperature detecting means for detecting the temperature of the EGR gas flowing out of the second EGR cooler;
The control means includes at least a temperature detected by the first temperature detection means and a second temperature detection means within a range in which the temperature of the EGR gas flowing out from the first EGR cooler does not exceed the target temperature. An exhaust gas recirculation device for an internal combustion engine, wherein the flow rate ratio adjusting means is feedback-controlled so that a difference from the detected temperature is small. In any one of Claims 1-4,
A concentration detecting means for detecting a water vapor concentration of the EGR gas;
The control means controls the flow rate ratio adjusting means so that the proportion of the EGR gas recirculated through the first EGR passage in the flow rate of the total EGR gas decreases as the water vapor concentration detected by the concentration detection means decreases. An exhaust gas recirculation device for an internal combustion engine. In any one of Claim 1 to 5,
The flow rate ratio adjusting means is a flow rate ratio adjusting valve that is provided closer to the intake system than the first EGR cooler in the first EGR passage and adjusts the flow area of the first EGR passage. An exhaust gas recirculation device for an internal combustion engine.

Images