EXHAUST GAS RECIRCULATION DEVICE

An exhaust gas recirculation (EGR) device includes an EGR passage, a cooling medium circuit, an EGR cooler, and an intercooler. A part of exhaust gas flowing through an exhaust passage of an internal combustion engine is recirculated as EGR gas into an intake passage of the engine through the EGR passage. A cooling medium flows through the cooling medium circuit. The EGR cooler performs a heat exchange between EGR gas flowing through the EGR passage and the cooling medium flowing through the cooling medium circuit so as to cool EGR gas. The intercooler is disposed at the intake passage on a downstream side of a merging part between the intake passage and the EGR passage in a flow direction of intake air, and performs a heat exchange between intake air including EGR gas and flowing through the intake passage, and the cooling medium flowing through the cooling medium circuit so as to cool intake air. The cooling medium circuit is configured independently from a coolant circuit through which coolant for cooling the engine flows. The cooling medium circuit is configured such that at least at time of low-load operation of the engine, the cooling medium which has passed through the EGR cooler flows into the intercooler.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2012-112389 filed on May 16, 2012, and Japanese Patent Application No. 2013-47930 filed on Mar. 11, 2013, the disclosures of which are incorporated herein by reference.

1. Technical Field

The present disclosure relates to an exhaust gas recirculation device that recirculates a part of exhaust gas from an internal combustion engine to an intake system.

2. Background Art

Conventionally, there exists an internal combustion engine including a configuration that compresses air drawn into a combustion chamber through a supercharger (turbocharger) and cools the air with an intercooler to improve output by enhancing volumetric efficiency in the combustion chamber (in a cylinder).

In this kind of the internal combustion engine, generally, there is introduced an exhaust gas recirculation (EGR) system (exhaust gas recirculation device) that recirculates a part of exhaust gas into an intake passage to reduce harmful substances (e.g., NOx) contained in exhaust gas.

For such an exhaust gas recirculation device, there are used a high-pressure EGR (HPL-EGR) that recirculates a part of exhaust gas as EGR gas from an upstream side of a filter provided in an exhaust system in a flow direction of gas to an intake system; and a low-pressure EGR (LPL-EGR) that recirculates a part of exhaust gas from a downstream side of the filter provided in the exhaust system in the gas flow direction to the intake system.

Water is contained in large quantity as watery vapor in the EGR gas recirculated from the exhaust system to the intake system of the internal combustion engine. When the low-pressure EGR is used as an exhaust gas recirculation device, the water (watery vapor) in the EGR gas may be condensed at the time of cooling the EGR gas by the intercooler.

Accordingly, there is proposed an exhaust gas recirculation device whereby the EGR gas is cooled by an EGR cooler disposed in an EGR passage of the low-pressure EGR through which the EGR gas flows to condense the water contained in the EGR gas, and cooling capacity of the intercooler is controlled such that the temperature of air after passing through the intercooler is higher than the dew point temperature of air flowing into the intercooler (see, e.g., Patent Document 1).

PRIOR ART DOCUMENT

Patent Document

However, the EGR cooler described in Patent Document 1 is configured such that heat is exchanged between high-temperature engine coolant (around 90° C.) whose temperature is elevated in the engine and the EGR gas, and the water contained in the EGR gas can hardly be condensed by the EGR cooler. For this reason, in the exhaust gas recirculation device described in Patent Document 1, the water contained in the EGR gas still may condense at the intercooler, and a defect such as liquid compression in the internal combustion engine, or corrosion of each member may be caused.

As a result of the research study by the present inventors, at the time of low-load operation of the internal combustion engine with a small flow rate of intake air, the condensed water is easily accumulated in the intercooler. The accumulated condensed water enters into the internal combustion engine at once, so that the above defect tends to be more easily caused than at the time of high-load operation.

SUMMARY OF INVENTION

The present disclosure addresses the above-described issues. Thus, it is an objective of the present disclosure to provide an exhaust gas recirculation device that can restrain an occurrence of a defect caused by condensation of water contained in EGR gas at least at the time of low-load operation of an internal combustion engine.

To achieve the above objective, there is provided an exhaust gas recirculation (EGR) device for an internal combustion engine in one aspect of the present disclosure, including an EGR passage, a cooling medium circuit, an EGR cooler, and an intercooler. A part of exhaust gas flowing through an exhaust passage of the engine is recirculated as EGR gas into an intake passage of the engine through the EGR passage. A cooling medium flows through the cooling medium circuit. The EGR cooler performs a heat exchange between EGR gas flowing through the EGR passage and the cooling medium flowing through the cooling medium circuit so as to cool EGR gas. The intercooler is disposed at the intake passage on a downstream side of a merging part between the intake passage and the EGR passage in a flow direction of intake air, and performs a heat exchange between intake air including EGR gas and flowing through the intake passage, and the cooling medium flowing through the cooling medium circuit so as to cool intake air. The cooling medium circuit is configured independently from a coolant circuit through which coolant for cooling the engine flows. The cooling medium circuit is configured such that at least at time of low-load operation of the engine, the cooling medium which has passed through the EGR cooler flows into the intercooler.

Accordingly, at the EGR cooler, the heat exchange is made between the EGR gas and the low-temperature cooling medium instead of the high-temperature coolant whose temperature is elevated in the internal combustion engine. As a result, the water contained in the EGR gas can be condensed at the EGR cooler.

In addition, at least at the time of low-load operation of the internal combustion engine, at the intercooler, a heat exchange is made between the cooling medium whose temperature is elevated as a result of the absorption of heat from the EGR gas at the EGR cooler, and the intake air including the EGR gas dehumidified at the EGR cooler. Accordingly, the production of condensed water at the intercooler can be limited.

Accordingly, in the present disclosure, the entry of condensed water into the internal combustion engine, which leads to a problem at the time of low-load operation of the internal combustion engine, can be avoided, and an occurrence of a defect caused by the condensation of water contained in the EGR gas can thereby be curbed.

At the time of high-load operation of the internal combustion engine, a flow rate of intake air into the internal combustion engine increases in comparison with at the time of low-load operation, and a flow rate of the EGR gas is accordingly increased. Thus, at the time of high-load operation of the internal combustion engine, if the water contained in the EGR gas is condensed at the EGR cooler, the condensed water existing in the EGR cooler enters easily into the intake passage together with the EGR gas. If the condensed water enters into the intake passage, there is an issue that a liquid compression of the compressor of the supercharger, for example, is caused.

For this reason, the EGR device in another aspect of the present disclosure further includes a cooling capacity adjusting means for adjusting a capacity for cooling EGR gas by the EGR cooler. At time of high-load operation of the engine, the cooling capacity adjusting means reduces the capacity for cooling EGR gas by the EGR cooler as compared to at the time of low-load operation.

In this manner, as a result of the configuration for decreasing the cooling capacity at the EGR cooler at the time of high-load operation of the internal combustion engine, the production of condensed water in the EGR cooler can be limited at the time of high-load operation. Consequently, the entry of the condensed water into the intake passage can be avoided. Thus, the entry of condensed water into the internal combustion engine which leads to concerns at the time of low-load operation of the internal combustion engine can be averted, and the liquid compression of the compressor of the supercharger which becomes problematic at the time of high-load operation of the internal combustion engine, for example, can be prevented.

Therefore, an occurrence of a defect caused by the condensation of water contained in the EGR gas can be restricted even more appropriately.

In addition, The EGR device in yet another aspect of the present disclosure further includes an EGR valve that changes a cross-sectional area of the EGR passage. The EGR cooler is provided on a downstream side of the EGR valve at the EGR passage in a flow direction of EGR gas.

Accordingly, when the EGR passage is closed by the EGR valve, a flow of the EGR gas flowing from the exhaust passage side into the EGR cooler can be prevented. Thus, there can be prevented an unnecessary heat exchange between the EGR gas and the cooling medium at the EGR cooler. As a result, the cooling performance at the intercooler can be ensured.

EMBODIMENTS FOR CARRYING OUT INVENTION

Embodiments will be described below in reference to the drawings. For the same or equivalent component in the following embodiments, its corresponding reference numeral is used in the drawings.

First Embodiment

An exhaust gas recirculation device in the present embodiment is applied to an engine1disposed in a vehicle. This engine1is an internal combustion engine of a water-cooled type gasoline engine that constitutes a driving source for vehicle traveling.

As illustrated in a general configuration diagram inFIG. 1, the engine1of the present embodiment is connected to an engine coolant circuit10through which engine coolant flows, and is configured to release the heat of the engine1to the engine coolant. At the engine coolant circuit10, there are provided a circulating pump11that circulates the engine coolant, and a radiator12that makes the engine coolant, whose temperature is elevated in the engine1, release heat.

An intake passage2through which intake air taken in from the outside of the vehicle is guided into a cylinder, and an exhaust passage3through which exhaust gas produced in the cylinder (in a combustion chamber) is discharged to the outside of the vehicle are connected to the engine1.

At the intake passage2, there are provided a compressor4aof a supercharger (turbocharger)4that operates with the energy of discharged air as its driving source, an intercooler21that cools the air having high temperature and high pressure compressed by the compressor4ain this order from an upstream side in an air flow direction, and so forth.

The supercharger4includes the compressor4aprovided at the intake passage2, and a turbine4bprovided at the exhaust passage3, and flows the compressed air with high temperature and high pressure to the intercooler21on the downstream side.

The intercooler21is a heat exchanger through which heat is exchanged between the air with high temperature and high pressure compressed by the compressor4a,and a cooling medium (e.g., antifreezing fluid) flowing through a cooling medium circuit6so as to cool the intake air. The cooling medium circuit6will be described later.

On the other hand, the turbine4bof the supercharger4, a filter31and so forth are provided at the exhaust passage3in this order from an upstream side in an gas flow direction. The filter31includes a collection part that collects particulate matter, and a three-way catalyst that purifies NOx and the like, and collects particulate matter contained in exhaust gas and purifies NOx and the like.

An EGR device that recirculates a part of exhaust gas as EGR gas from an exhaust system to an intake system of the engine1is provided for the engine1of the present embodiment. The EGR device of the present embodiment is configured by a low-pressure EGR (LPL-EGR), and includes a low-pressure EGR passage5, an EGR valve51, and an EGR cooler52.

The low-pressure EGR passage5is an EGR passage connecting together a branched part B that is located on a downstream side of the turbine4bof the supercharger4and the filter31at the exhaust passage3in the gas flow direction, and a merging part A that is located on an upstream side of the compressor4aof the supercharger4at the intake passage2in the gas flow direction.

The EGR valve51changes a passage sectional area of the low-pressure EGR passage5. By changing the passage sectional area of the low-pressure EGR passage5, a flow rate of EGR gas recirculated from the exhaust system to the intake system through the low-pressure EGR passage5can be adjusted. At the time of idling at which operation of the engine1is unstable, or at the time of maximum output of engine output, the EGR valve51can close the low-pressure EGR passage5to stop the recirculation of EGR gas to the intake system.

The EGR cooler52is a heat exchanger through which heat is exchanged between the EGR gas flowing through the low-pressure EGR passage5, and the cooling medium flowing through the cooling medium circuit6which will be described later so as to cool the EGR gas. The EGR cooler52of the present embodiment is provided on a downstream side of the EGR valve51at the low-pressure EGR passage5in the gas flow direction.

The cooling medium circuit6will be described. The cooling medium circuit6is configured independently of the engine coolant circuit10through which the engine coolant for cooling the engine1flows. The cooling medium circuit6is a circulation circuit through which the cooling medium having temperature that is lower than the temperature of the engine coolant circulates.

In addition to the EGR cooler52and the intercooler21, a cooling medium pump61for pressure-feeding the cooling medium, and a radiator62for releasing the heat of the cooling medium are connected to the cooling medium circuit6.

The cooling medium pump61, the EGR cooler52, and the intercooler21are connected to the cooling medium circuit6of the present embodiment such that the cooling medium cooled by the radiator62flows through the cooling medium pump61->the EGR cooler52->the intercooler21. Thus, the EGR cooler52is connected to a downstream side of the radiator62in a flow direction of the cooling medium such that the cooling medium which has flowed through the radiator62flows into the EGR cooler52through the cooling medium circuit6. The intercooler21is connected to a downstream side of the EGR cooler52in the cooling medium flow direction such that the cooling medium which has flowed through the EGR cooler52flows into the intercooler21through the cooling medium circuit6.

The operation of the exhaust gas recirculation device of the present embodiment will be explained. The air drawn into the intake passage2as a result of the actuation of the engine1is compressed by the compressor4aof the supercharger4to be turned into the air with high temperature and high pressure. Then, the air exchanges heat with the cooling medium at the intercooler21to be cooled and supplied to the engine1. On the other hand, the exhaust gas discharged from the engine1through the exhaust passage3flows through the turbine4bof the supercharger4and is then discharged to the outside with foreign substances removed at the filter31.

If the low-pressure EGR passage5is opened by the EGR valve51, a part of exhaust gas is recirculated as the EGR gas into the intake passage2through the low-pressure EGR passage5. When flowing through the low-pressure EGR passage5, the EGR gas exchanges heat with the low-temperature cooling medium to be cooled at the EGR cooler52, and the water contained in the EGR gas condenses at the EGR cooler52. Accordingly, the EGR gas which has been dehumidified at the EGR cooler52is recirculated into the intake passage2.

In the above-described present embodiment, the cooling medium circuit6which is connected to the EGR cooler52and the intercooler21is configured independently of the engine coolant circuit10, and the intercooler21is connected to the downstream side of the EGR cooler52in the cooling medium flow direction.

Accordingly, at the EGR cooler52, the heat exchange can be made between the EGR gas and the low-temperature cooling medium instead of the high-temperature engine coolant whose temperature is elevated in the engine1, so that the water contained in the EGR gas can be condensed at the EGR cooler52.

Additionally, at the intercooler21, the heat exchange is made between the cooling medium whose temperature is elevated as a result of the absorption of heat from the EGR gas at the EGR cooler52, and the air including the EGR gas dehumidified at the EGR cooler52. Accordingly, the production of condensed water at the intercooler21can be limited.

Thus, as a result of the configuration of the present embodiment, the entry of condensed water into the engine1, which leads to a problem at the time of low-load operation of the engine1, can be avoided, and an occurrence of a defect caused by the condensation of water contained in the EGR gas can thereby be curbed. The low-load operation means an operating condition in which a large output is not required for the engine1, such as in a case of traveling on a flat road or in a case of a constant speed or deceleration. A high-load operation means an operating condition in which a large output is required for the engine1, such as in a case of traveling on a climbing lane or in a case of acceleration.

If the EGR valve51is provided on a downstream side of the EGR cooler52in the low-pressure EGR passage5in the gas flow direction, the EGR gas passes through the inside of the EGR cooler52to reach an inlet side of the EGR valve51due to pulsation of the engine1, for example. Even if the low-pressure EGR passage5is closed by the EGR valve51, a heat exchange may be carried out between the EGR gas and the cooling medium at the EGR cooler52.

Particularly, when the EGR cooler52and the intercooler21are arranged in the same cooling medium circuit6as in the present embodiment, even though the low-pressure EGR passage5is closed by the EGR valve51, the cooling medium absorbs heat from the EGR gas so that the temperature of the cooling medium rises at the EGR cooler52, and this cooling medium whose temperature has risen flows into the intercooler21. Accordingly, there is an issue of a deterioration in performance of cooling the air at the intercooler21is caused.

As a measure against this issue, in the present embodiment, there is employed a configuration in which the EGR valve51is provided at the low-pressure EGR passage5on an upstream side of the EGR cooler52in the gas flow direction. Accordingly, when the low-pressure EGR passage5is closed by the EGR valve51, a flow of the EGR gas from the exhaust passage 3-side into the EGR cooler52can be prevented, and there can be prevented an unnecessary heat exchange between the EGR gas and the cooling medium at the EGR cooler52. As a result, the deterioration in cooling performance of the intercooler21, which is caused when the low-pressure EGR passage5is closed by the EGR valve51, can be avoided.

Second Embodiment

A second embodiment will be described. In the present embodiment, a mode of arrangement of an EGR valve51is different from the first embodiment. In the present embodiment, explanation will be given with the description of a part similar or equivalent to the first embodiment omitted or simplified.

As illustrated in a general configuration diagram inFIG. 2, in the present embodiment, there is employed a configuration in which the EGR valve51is provided at a low-pressure EGR passage5on a downstream side of an EGR cooler52in the gas flow direction. The other configurations are similar to the first embodiment.

In the present embodiment, similar to the first embodiment, the water contained in the EGR gas can be condensed at the EGR cooler52. Furthermore, at an intercooler21, a heat exchange is made between the cooling medium whose temperature is elevated as a result of the absorption of heat from the EGR gas at the EGR cooler52, and the air including the EGR gas dehumidified at the EGR cooler52. Accordingly, the production of condensed water at the intercooler21can be limited.

Additionally, the present embodiment employs the configuration in which the EGR valve51is provided at the low-pressure EGR passage5on a downstream side of the EGR cooler52in the gas flow direction. As a consequence, the low-temperature EGR gas cooled by the EGR cooler52flows into near the EGR valve51. Thus, the EGR valve51can be configured by a valve having low heat resistance, thereby ensuring design flexibility.

Third Embodiment

A third embodiment will be described. In the present embodiment, explanation will be given with the description of a part similar or equivalent to the above-described embodiments omitted or simplified.

As a result of research studies by the inventors, it is found that when the water contained in the EGR gas is condensed at an EGR cooler52at the time of high-load operation of an engine1at which a flow rate of intake air is large, a defect such as liquid compression is caused at a compressor4aof a supercharger4.

As a factor in this defect, it can be pointed out that at the time of high-load operation of the engine1, a flow rate of EGR gas flowing through a low-pressure EGR passage5increases in accordance with an increased flow rate of intake air and that the condensed water accumulated in the EGR cooler52thereby enters easily into an intake passage together with the EGR gas. In addition, at the time of low-load operation of the engine1, because of a low flow rate of intake air, the entry of the condensed water accumulated in the EGR cooler52into the intake passage is not easily caused compared to at the time of high-load operation.

Thus, in the present embodiment, an occurrence of a defect caused at the time of high-load operation of the engine1is curbed by adjusting the capacity for cooling the EGR gas at the EGR cooler52according to a loaded condition of the engine1.

In the present embodiment, as illustrated inFIG. 3, a cooling medium pump61is configured by a pump (e.g., axial flow pump) that can change a flow direction of the cooling medium. Specifically, the cooling medium pump61is configured to be capable of changing the flow direction of the cooling medium between a flow direction in which the cooling medium flows in order of the EGR cooler52->an intercooler21->a radiator62, and a flow direction in which the cooling medium flows in order of the radiator62->the intercooler21->the EGR cooler52. In addition, the cooling medium pump61of the present embodiment is configured to change the flow direction of the cooling medium in accordance with a control signal from a control device100.

The control device100includes a microcomputer having a CPU, a memory configured as a storage means, and its peripheral circuit. The control device100is a control means for performing various kinds of arithmetic processings based on a control program stored in the memory to control operations of various devices connected to an output side.

Various kinds of sensors such as an intake flow rate sensor (not shown) for detecting a flow rate of intake air are connected to an input side of the control device100, and detection signals from the various kinds of sensors are inputted to the input side of the control device100. In addition, various devices such as the cooling medium pump61are connected to the output side of the control device100, and based on, for example, the detection signals from the various kinds of sensors, the output side of the control device100outputs the control signal to the various devices.

The control device100of the present embodiment is configured to be capable of determining whether the loaded condition of the engine1is high-load operation or low-load operation. For example, the control device100determines that the loaded condition of the engine1is high-load operation if a detection value by the intake flow rate sensor (flow rate of intake air) is a preset determination threshold value or higher, and determines that the loaded condition is low-load operation if the detection value is smaller than the determination threshold value. The determination threshold value may be set in a flow rate range of intake air assumed at the time of high-load operation.

The control device100of the present embodiment is configured to control the operation of the cooling medium pump61according to the loaded condition of the engine1. In the present embodiment, the configuration of the control device100for controlling the operation of the cooling medium pump61constitutes a pump control means100a.

Specifically, at the time of low-load operation of the engine1, the control device100outputs to the cooling medium pump61a control signal for directing the cooling medium pump61to change the flow direction of the cooling medium such that the cooling medium which has flowed through the EGR cooler52flows into the intercooler21.

Accordingly, as indicated by an alternate long and short dash line with an arrow around the cooling medium circuit6inFIG. 3, the cooling medium discharged from the cooling medium pump61flows through the EGR cooler52->the intercooler21->the radiator62in this order. In addition, at the time of low-load operation, at the EGR cooler52, a heat exchange is made between the low-temperature cooling medium whose heat has already been released at the radiator62, and the EGR gas.

On the other hand, at the time of high-load operation of the engine1, the control device100outputs to the cooling medium pump61a control signal for directing the cooling medium pump61to change the flow direction of the cooling medium such that the cooling medium which has flowed through the intercooler21flows into the EGR cooler52.

Accordingly, as indicated by an alternate long and two short dashes line with an arrow around the cooling medium circuit6inFIG. 3, the cooling medium discharged from the cooling medium pump61flows through the radiator62->the intercooler21->the EGR cooler52in this order.

In this case, at the EGR cooler52, a heat exchange is made between the cooling medium whose temperature has risen as a result of the absorption of heat from the intake air at the intercooler21, and the EGR gas. Accordingly, at the time of high-load operation, the capacity for cooling the EGR gas at the EGR cooler52is reduced compared with at the time of low-load operation.

In the present embodiment, the cooling medium pump61, and the configuration100aof the control device100for performing the control processing on the cooling medium pump61constitute a changing means (cooling capacity adjusting means) for changing the flow direction of the cooling medium in the cooling medium circuit6.

The other configurations and operations are similar to the above-described first embodiment. The present embodiment employs a configuration to change the flow direction of the cooling medium by the cooling medium pump61such that the cooling medium which has flowed through the EGR cooler52flows into the intercooler21at the time of low-load operation of the engine1.

Accordingly, at the intercooler21, a heat exchange is made between the cooling medium whose temperature is elevated as a result of the absorption of heat from the EGR gas at the EGR cooler52, and the intake air including the EGR gas dehumidified at the EGR cooler52. As a result, the production of condensed water at the intercooler21can be limited. Thus, by the configuration of the present embodiment, similar to the first embodiment, the entry of condensed water into the engine1which leads to concerns at the time of low-load operation of the engine1can be averted.

Moreover, the present embodiment employs a configuration to change the flow direction of the cooling medium by the cooling medium pump61such that the cooling medium which has flowed through the intercooler21flows into the EGR cooler52at the time of high-load operation of the engine1.

Accordingly, at the EGR cooler52, a heat exchange is made between the cooling medium whose temperature has risen as a result of the absorption of heat from the intake air at the intercooler21, and the EGR gas. As a result, the production of condensed water at the intercooler21can be limited.

Therefore, by the configuration of the present embodiment, the entry of condensed water into the engine1which leads to concerns at the time of low-load operation of the engine1can be averted, and the entry of condensed water into the compressor4aof the supercharger4which becomes problematic at the time of high-load operation of the engine1can be avoided.

In this manner, as a result of the configuration of the present embodiment, an occurrence of a defect caused by the condensation of water contained in the EGR gas both at the time of low-load operation and at the time of high-load operation of the engine1can be curbed.

Additionally, in the present embodiment, there has been described an example of the change of the flow direction of the cooling medium in the cooling medium circuit6by the cooling medium pump61. However, this is not the only mode of the present disclosure. For example, the cooling medium circuit6may be configured by a circuit connecting a discharge side of the cooling medium pump61to an inlet side of the EGR cooler52, and a circuit connecting the discharge side of the cooling medium pump61to an inlet side of the radiator62; and the cooling medium circuit6may be switched between the circuits according to the loaded condition of the engine1.

Fourth Embodiment

A fourth embodiment will be described. In the present embodiment, there will be explained an example of a modification to the third embodiment, in configuration for adjusting the capacity for cooling the EGR gas at an EGR cooler52at the time of high-load operation. In the present embodiment, explanation will be given with the description of a part similar or equivalent to the above-described embodiments omitted or simplified.

As illustrated inFIG. 4, a cooling medium circuit6of the present embodiment is configured to include a cooling passage6ain which the cooling medium flows through the EGR cooler52, and a bypass passage6bwhich bypasses the EGR cooler52and through which the cooling medium flows.

A flow regulating valve63is provided at a branched part of the cooling medium circuit6between the cooling passage6aand the bypass passage6b. This flow regulating valve63is configured to be capable of regulating a flow rate ratio between a flow rate of the cooling medium flowing into the EGR cooler52through the cooling passage6a,and a flow rate of the cooling medium flowing through the bypass passage6b.The flow regulating valve63of the present embodiment is configured as an electrical three-way valve that can regulate the flow rate ratio between the cooling media through the passages6a,6bin response to a control signal from a control device100.

The control device100of the present embodiment is configured to control the operation of the flow regulating valve63according to the loaded condition of an engine1. In the present embodiment, the configuration of the control device100for controlling the operation of the flow regulating valve63serves as a flow control means100b.

Specifically, the control device100outputs to the flow regulating valve63the control signal to command the regulation of the flow rate ratio between the cooling media through the passages6a,6b,such that the flow rate of the cooling medium flowing into the EGR cooler52at the time of high-load operation is lower than at the time of low-load operation.

For example, the control device100outputs to the flow regulating valve63the control signal to command the regulation of the flow rate ratio between the cooling media through the passages6a,6b,such that the entire cooling medium discharged from a cooling medium pump61at the time of low-load operation flows through the cooling passage6a.

Accordingly, as indicated by an alternate long and short dash line with an arrow around the cooling medium circuit6inFIG. 4, the entire cooling medium discharged from a cooling medium pump61flows through the EGR cooler52->an intercooler21->a radiator62in this order.

On the other hand, the control device100outputs to the flow regulating valve63the control signal to command the regulation of the flow rate ratio between the cooling media through the passages6a,6b,such that the cooling medium discharged from the cooling medium pump61flows through the passages6a,6bat the time of high-load operation of the engine1.

Accordingly, as indicated by an alternate long and two short dashes line with an arrow around the cooling medium circuit6inFIG. 4, the cooling medium discharged from the cooling medium pump61flows through the EGR cooler52->the intercooler21->the radiator62in this order, and bypasses the EGR cooler52to flow through the intercooler21.

In this case, the flow rate of the cooling medium flowing into the EGR cooler52is reduced, so that the amount of heat exchanged with the EGR gas becomes small. Accordingly, at the time of high-load operation, the capacity for cooling the EGR gas at the EGR cooler52is reduced compared with at the time of low-load operation.

In addition, the flow rate ratio between the cooling media through the passages6a,6bmay be regulated by the flow regulating valve63, such that the temperature of the cooling medium at an outlet part of the EGR cooler52does not decrease to equal to or lower than the dew-point temperature of the cooling medium.

In the present embodiment, the flow regulating valve63, and the configuration100bof the control device100for performing the control processing on the flow regulating valve63serve as a flow regulating means (cooling capacity adjusting means) for regulating the flow rate of the cooling medium flowing into the EGR cooler52through the cooling passage6a.

The other configurations and operations are similar to the above-described first embodiment. The present embodiment employs the configuration for regulating the flow rate ratio between the cooling media through the passages6a,6bby the flow regulating valve63such that the entire cooling medium discharged from a cooling medium pump61flows through the EGR cooler52at the time of low-load operation of the engine1.

Accordingly, at the intercooler21, a heat exchange is made between the cooling medium whose temperature is elevated as a result of the absorption of heat from the EGR gas at the EGR cooler52, and the intake air including the EGR gas dehumidified at the EGR cooler52. As a result, the production of condensed water at the intercooler21can be limited. Thus, by the configuration of the present embodiment, similar to the first embodiment, the entry of condensed water into the engine1which leads to concerns at the time of low-load operation of the engine1can be averted.

Furthermore, the present embodiment employs the configuration for regulating the flow rate ratio between the cooling media through the passages6a,6bby the flow regulating valve63such that the flow rate of the cooling medium flowing into the EGR cooler52at the time of high-load operation of the engine1is lower than at the time of low-load operation.

Accordingly, at the time of high-load operation of the engine1, the amount of heat exchanged between the EGR gas and the cooling medium at the EGR cooler52is reduced in comparison with at the time of low-load operation, so that the capacity for cooling the EGR gas is lowered. As a result, the production of condensed water at the intercooler21can be restrained.

Thus, as a result of the configuration of the present embodiment, similar to the third embodiment, the entry of condensed water into the engine1which leads to concerns at the time of low-load operation of the engine1can be averted, and the entry of condensed water into the compressor4aof the supercharger4which becomes problematic at the time of high-load operation of the engine1can be avoided.

As illustrated inFIG. 5, a subcooler14for making a heat exchange between the high-temperature engine coolant and the EGR gas may be added at the low-pressure EGR passage5on an upstream side of the EGR cooler52in a flow direction of the EGR gas.

Accordingly, the EGR gas can be cooled by both the EGR cooler52and the subcooler14, and the water contained in the EGR gas can thereby be condensed appropriately at the EGR cooler52at the time of low-load operation. Additionally, at the time of high-load operation, the amount of heat exchanged between the EGR gas and the cooling medium at the EGR cooler52is reduced in comparison with at the time of low-load operation, so that the entry of condensed water into an intake passage2can be inhibited.

In the present embodiment, there has been described an example of the regulation of the flow rate ratio between the cooling media through the passages6a,6bby the flow regulating valve63such that the entire cooling medium flows through the cooling passage6aat the time of low-load operation. However, this is not the only example of the present disclosure. As long as the flow rate of the cooling medium flowing into the EGR cooler52at the time of high-load operation is lower than at the time of low-load operation, the flow rate ratio between the cooling media through the passages6a,6bby the flow regulating valve63may be regulated, for example, such that a part of the cooling medium flows through the bypass passage6bat the time of low-load operation.

In the present embodiment, there has been described an example of the flow regulating valve63being provided at the branched part of the cooling medium circuit6between the cooling passage6aand the bypass passage6b. However, this is not the only example of the present disclosure. For example, the flow regulating valve63may be provided at a merging part in the cooling medium circuit6between the cooling passage6aand the bypass passage6b.

Fifth Embodiment

A fifth embodiment will be described. In the present embodiment, there will be explained an example of a modification to the third and fourth embodiments, in configuration for adjusting the capacity for cooling the EGR gas at an EGR cooler52at the time of high-load operation. In the present embodiment, explanation will be given with the description of a part similar or equivalent to the above-described embodiments omitted or simplified.

As illustrated inFIG. 6, a low-pressure EGR passage5of the present embodiment is configured to include a gas passage5athrough which the EGR gas flows into the EGR cooler52, and a bypass passage5bthrough which the EGR gas bypasses the EGR cooler52.

A gas flow regulating valve53is provided at a branched part of the low-pressure EGR passage5between the gas passage5aand the bypass passage5b.This gas flow regulating valve53is configured to be capable of regulating a flow rate ratio between a flow rate of the EGR gas flowing into the EGR cooler52through the gas passage5a,and a flow rate of the EGR gas flowing through the bypass passage5b.The gas flow regulating valve53of the present embodiment is configured as an electrical three-way valve that can regulate the flow rate ratio between the EGR gas through the passages5a,5bin response to a control signal from a control device100.

The control device100of the present embodiment is configured to control the operation of the gas flow regulating valve53according to the loaded condition of an engine1. In the present embodiment, the configuration of the control device100for controlling the operation of the gas flow regulating valve53serves as a gas flow control means100c.

Specifically, the control device100outputs to the gas flow regulating valve53the control signal to command the regulation of the flow rate ratio between the EGR gas through the passages5a,5b,such that the flow rate of the EGR gas flowing into the EGR cooler52at the time of high-load operation is lower than at the time of low-load operation.

For example, the control device100outputs to the gas flow regulating valve53the control signal to command the regulation of the flow rate ratio between the EGR gas through the passages5a,5b,such that the entire EGR gas flowing into the low-pressure EGR passage5flows through the gas passage5aat the time of low-load operation.

Accordingly, as indicated by an arrow of a continuous line around the low-pressure EGR passage5inFIG. 6, the entire EGR gas flowing into the low-pressure EGR passage5flows into the EGR cooler52through the gas passage5a.

On the other hand, the control device100outputs to the gas flow regulating valve53the control signal to command the regulation of the flow rate ratio between the EGR gas through the passages5a,5bsuch that the EGR gas flowing into the low-pressure EGR passage5flows through the passages5a,5bat the time of high-load operation of the engine1.

Accordingly, as indicated by an arrow of a short dashes line around the low-pressure EGR passage5inFIG. 6, the EGR gas flowing into the low-pressure EGR passage5flows into the EGR cooler52through the gas passage5a,and flows through the bypass passage5bto bypass the EGR cooler52.

In this case, at the EGR cooler52, the flow rate of the EGR gas flowing into the EGR cooler52is lowered, and the amount of heat exchanged with the cooling medium thereby becomes small. Accordingly, at the time of high-load operation, the capacity for cooling the EGR gas at the EGR cooler52is reduced compared with at the time of low-load operation.

In addition, the flow rate ratio between the cooling media through the passages5a,5bmay be regulated by the gas flow regulating valve53, such that the temperature of the cooling medium at an outlet part of the EGR cooler52does not decrease to equal to or lower than the dew-point temperature of the cooling medium.

In the present embodiment, the gas flow regulating valve53, and the configuration100cof the control device100for performing control processing on the gas flow regulating valve53serve as a gas flow regulating means (cooling capacity adjusting means) for regulating the flow rate of the EGR gas flowing into the EGR cooler52through the gas passage5a.

The other configurations and operations are similar to the above-described first embodiment. The present embodiment employs the configuration for regulating the flow rate ratio between the EGR gas through the passages5a,5bby the gas flow regulating valve53, such that the entire EGR gas flowing into the low-pressure EGR passage5flows through the EGR cooler52at the time of low-load operation of the engine1.

Accordingly, at an intercooler21, a heat exchange is made between the cooling medium whose temperature is elevated as a result of the absorption of heat from the EGR gas at the EGR cooler52, and the intake air including the EGR gas dehumidified at the EGR cooler52. As a result, the production of condensed water at the intercooler21can be limited. Thus, by the configuration of the present embodiment, similar to the first embodiment, the entry of condensed water into the engine1which leads to concerns at the time of low-load operation of the engine1can be averted.

Moreover, the present embodiment employs the configuration for regulating the flow rate ratio between the EGR gas through the passages5a,5bby the gas flow regulating valve53, such that the flow rate of the EGR gas flowing into the EGR cooler52at the time of high-load operation of the engine1is lower than at the time of low-load operation.

Accordingly, at the time of high-load operation of the engine1, the amount of heat exchanged between the EGR gas and the cooling medium at the EGR cooler52is reduced in comparison with at the time of low-load operation, and the capacity for cooling the EGR gas is thereby reduced. As a result, the production of condensed water at the intercooler21can be restrained.

Thus, as a result of the configuration of the present embodiment, similar to the third and fourth embodiments, the entry of condensed water into the engine1which leads to concerns at the time of low-load operation of the engine1can be averted, and the entry of condensed water into a compressor4aof a supercharger4which becomes problematic at the time of high-load operation of the engine1can be avoided.

In the present embodiment, there has been described an example of the regulation of the flow rate ratio between the EGR gas through the passages5a,5bby the gas flow regulating valve53such that the entire EGR gas flows through the gas passage5aat the time of low-load operation. However, this is not the only example of the present disclosure. As long as the flow rate of the EGR gas flowing into the EGR cooler52at the time of high-load operation is lower than at the time of low-load operation, the flow rate ratio between the EGR gas through the passages5a,5bby the gas flow regulating valve53may be regulated, for example, such that a part of the EGR gas flows through the bypass passage5bat the time of low-load operation.

In the present embodiment, there has been described an example of the gas flow regulating valve53being provided at the branched part of the low-pressure EGR passage5between the gas passage5aand the bypass passage5b.However, this is not the only example of the present disclosure. For example, the gas flow regulating valve53may be provided at a merging part in the low-pressure EGR passage5between the gas passage5aand the bypass passage5b.

Modifications to the above embodiments will be described below.

The embodiments have been described above. However, the present disclosure is not limited to these, and can be modified in a variety of modes without departing from the scope of the disclosure. For example, the disclosure can be modified as follows.

(1) In the above-described embodiments, there has been explained an example of only the low-pressure EGR provided as the EGR device. However, this is not the only example. For example, the present disclosure may be applied to a device including both a low-pressure EGR and a high-pressure EGR (HPL-EGR) as the EGR device.

(2) In the above-described embodiments, there has been explained an example of the engine1configured as a gasoline engine. However, this is not the only example. A diesel engine can also be employed.

(3) The above-described embodiments can be appropriately combined together unless they are independent of one another or the combination is clearly impossible.

(4) In the above-described embodiments, it goes without saying that the elements that constitute the embodiment are not necessarily essential, for example, unless it is clearly specified that they are particularly essential or it is believed that they are obviously essential in principle.

(5) In the above-described embodiments, when the numerical value for the number of components, the numerical value, the amount, or the range of the embodiment, for example, is mentioned, unless it is clearly specified that they are particularly essential or it is obviously limited to a specified number in principle, for example, the numerical value is not limited to this specified number.

(6) In the above-described embodiments, when the shape or positional relationship of the component or the like is mentioned, unless it is particularly specified clearly or it is limited to a specified shape or positional relationship in principle, for example, the component is not limited to that shape or positional relationship.