JP2014020345A - Egr system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR system that can suppress a reduction in the heat exchange efficiency and an increase in flow resistance of an EGR cooler due to deposition of PM.SOLUTION: An EGR system includes an EGR cooler 3 for cooling exhaust by causing heat exchange between the exhaust of an engine 1 and cooling water. The EGR cooler 3 has a cooling water channel 36 in which cooling water flows, a cooling water inlet 37 for allowing the cooling water to flow into the cooling water channel 36, and a first cooling water outlet 38 and a second cooling water outlet 39 for allowing the cooling water to flow out from the cooling water channel 36. The first cooling water outlet 38 is positioned downstream of the second cooling water outlet 39 in an exhaust flow direction. The EGR system further includes a three-way valve 51 for switching between a first cooling water circuit for allowing the cooling water flowing in from the cooling water inlet 37 to flow out from the first cooling water outlet 38, and a second cooling water circuit for allowing the cooling water flowing in from the cooling water inlet 37 to flow out from the second cooling water outlet 39.

Description

  The present invention relates to an EGR system that recirculates a part of exhaust discharged from an internal combustion engine to an intake system.

Recently, in order to reduce of the NO _X in the improvement and the exhaust of the vehicle fuel economy, even vehicles using gasoline as fuel, the engine intake passage a part of the exhaust as EGR (Exhaust Gas Recirculation) gas of an engine (internal combustion engine) The adoption of an EGR system (exhaust gas recirculation system for an internal combustion engine) that recirculates downstream of a throttle valve and burns a mixture of intake air and EGR gas in a combustion chamber is increasing (for example, see Patent Document 1). .

  In such an EGR system, an EGR cooler for cooling the exhaust and an EGR valve for adjusting the passage opening degree of the EGR passage are provided in the EGR passage that communicates the exhaust passage and the intake passage of the engine.

JP 2004-2111649 A

  However, in the EGR system described in Patent Document 1, PM (Particulate Matter) contained in exhaust gas accumulates on the EGR cooler and the EGR valve, so that the function is deteriorated. In particular, components derived from engine oil and unburned fuel, which are called SOF (Soluble Organic Fraction), have high viscosity at low temperatures and are likely to accumulate. For this reason, when exhaust gas is cooled in the EGR cooler, if SOF adheres and accumulates on the inner wall surface of the EGR cooler, there is a problem in that the heat exchange efficiency is lowered and the ventilation resistance is increased.

  In particular, the EGR cooler is designed so that high-temperature exhaust is cooled by engine cooling water so that the exhaust temperature becomes a predetermined temperature or less. That is, the EGR cooler is exhausted by cooling water at around 90 ° C. even under the most severe engine load conditions (exhaust temperature is the highest temperature and exhaust flow rate is the maximum flow rate) such that the EGR valve opens. The exhaust gas temperature at the outlet of the EGR cooler is designed to be equal to or lower than a predetermined temperature.

  However, under an actual use environment, the exhaust flow rate is small or the exhaust temperature flowing into the EGR cooler is often low, and the cooling water temperature is also low. For this reason, since the exhaust temperature when passing through the EGR valve from the outlet of the EGR cooler is approximately the same as the cooling water temperature (70 ° C. to 90 ° C.), there is a problem that PM is easily deposited.

  An object of this invention is to provide the EGR system which can suppress the fall of the heat exchange efficiency of the EGR cooler by adhesion of PM, and the increase in ventilation resistance in view of the said point.

  In order to achieve the above object, according to the first aspect of the present invention, an EGR passage (2) connecting the exhaust passage (11) and the intake passage (13) of the internal combustion engine (1) is provided. 1) In the EGR system including the EGR cooler (3) that cools the exhaust gas by exchanging heat between the exhaust gas and the heat medium, the EGR cooler (3) includes a heat medium flow path (36 ), A heat medium inlet (37) through which the heat medium flows into the heat medium flow path (36), a first heat medium outlet (38) and a second heat medium through which the heat medium flows out from the heat medium flow path (36). The first heat medium outlet (38) is disposed downstream of the second heat medium outlet (39) in the flow direction of the exhaust gas, and further the heat medium inlet (37). ) Flow out of the first heat medium outlet (38). A heat medium circuit switching means (51) for switching between the first heat medium circuit and the second heat medium circuit for allowing the heat medium flowing in from the heat medium inlet (37) to flow out from the second heat medium outlet (39); Features.

  According to this, the first heat medium outlet (38) is arranged downstream of the second heat medium outlet (39) in the flow direction of the exhaust gas, and the heat medium flowing in from the heat medium inlet (37) is transferred to the first heat medium. Heat medium circuit switching for switching between a first heat medium circuit that flows out from the medium outlet (38) and a second heat medium circuit that flows out the heat medium flowing in from the heat medium inlet (37) from the second heat medium outlet (39) By providing the means (51), the heat medium circuit switching means (51) switches the heat medium flowing from the heat medium inlet (37) to the second heat medium circuit that flows out from the second heat medium outlet (39). In this case, the heat medium circulates between the second heat medium outlet (39) and the second heat medium outlet (39) and the first heat medium outlet (38) downstream of the second heat medium outlet (39) in the EGR cooler (3). No longer. For this reason, on the downstream side of the exhaust flow of the second heat medium outlet (39) in the EGR cooler (3), heat exchange is hardly performed between the exhaust gas and the heat medium, and the exhaust gas is not cooled. Therefore, since it can suppress that the exhaust gas which passes the exhaust flow downstream of the 2nd heat-medium exit (39) in EGR cooler (3) becomes low temperature, it can suppress that PM accumulates on EGR cooler (3). . Thereby, the fall of the heat exchange efficiency of EGR cooler by adhesion of PM and the increase in ventilation resistance can be controlled.

  In the invention according to claim 2, the EGR passage (2) connecting the exhaust passage (11) and the intake passage (13) of the internal combustion engine (1) and the exhaust of the internal combustion engine (1) In an EGR system including an EGR cooler (3) that cools exhaust gas by exchanging heat with a heat medium, and an EGR valve (4) that adjusts the passage opening degree of the EGR passage (2), an EGR cooler ( 3), a first EGR cooler (3A) and a second EGR cooler (3B) disposed downstream of the first EGR cooler (3A) in the exhaust flow direction are provided, and the EGR valve (4) The first EGR cooler (3A) and the second EGR cooler (3B) are provided.

  According to this, as the EGR cooler (3), the first EGR cooler (3A) and the second EGR cooler (3B) disposed downstream of the first EGR cooler (3A) in the exhaust flow direction are provided. If the heat medium is allowed to flow only through the first EGR cooler (3A) of the first EGR cooler (3A) and the second EGR cooler (3B), the heat medium does not circulate through the second EGR cooler (3B). For this reason, in the second EGR cooler (3B), heat exchange between the exhaust and the heat medium is hardly performed, and the exhaust is not cooled. Therefore, since it can suppress that 2nd EGR cooler (3B) becomes low temperature, it can suppress that PM accumulates on 2nd EGR cooler (3B). Thereby, the fall of the heat exchange efficiency of EGR cooler (3) by adhesion of PM and the increase in ventilation resistance can be suppressed.

  Furthermore, by providing the EGR valve (4) between the first EGR cooler (3A) and the second EGR cooler (3B), the exhaust before being cooled by the second EGR cooler (3B) is supplied to the EGR valve (4). Can flow in. Therefore, since it can suppress that the exhaust gas which passes an EGR valve (4) becomes low temperature too much, it can suppress that PM accumulates on an EGR valve (4).

  Further, in the invention described in claim 7, the EGR passage (2) connecting the exhaust passage (11) and the intake passage (13) of the internal combustion engine (1) is provided, and the exhaust of the internal combustion engine (1) In an EGR system including an EGR cooler (3) that cools exhaust gas by exchanging heat with a heat medium, the EGR cooler (3) has a heat medium flow path (36) through which the heat medium flows. And a flow rate adjusting means (53) for adjusting the flow rate of the heat medium flowing through the heat medium flow path (36). The flow rate adjusting means (53) increases the temperature of the heat medium as the temperature of the heat medium increases. The flow rate of the heat medium which circulates through (36) is increased.

  According to this, by providing the flow rate adjusting means (53) that increases the flow rate of the heat medium flowing through the heat medium flow path (36) as the temperature of the heat medium increases, when the heat medium temperature is low, Since the flow rate of the heat medium flowing through the heat medium flow path (36) is reduced, heat exchange between the exhaust gas and the heat medium is difficult to be performed in the EGR cooler (3). Therefore, when the heat medium temperature is low, it is possible to suppress the exhaust gas passing through the EGR cooler (3) from becoming too low, and therefore it is possible to suppress PM from being deposited on the EGR cooler (3). For this reason, the fall of the heat exchange efficiency of an EGR cooler by adhesion of PM and the increase in ventilation resistance can be controlled.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is the schematic which shows the whole structure of the EGR system which concerns on 1st Embodiment. It is the schematic which shows the EGR cooler in 1st Embodiment. It is III-III sectional drawing of FIG. It is a characteristic view which shows the relationship between the core dimension of the EGR cooler in 1st Embodiment, and exhaust temperature. It is the schematic which shows the EGR cooler in 2nd Embodiment. It is a characteristic view which shows the relationship between the core dimension of the EGR cooler in 2nd Embodiment, and exhaust temperature. It is the schematic which shows the EGR cooler in 3rd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, an EGR system includes an exhaust pipe (exhaust passage) 11 through which exhaust gas from a gasoline engine 1 as an internal combustion engine flows, and an intake pipe (intake passage) 13 through which intake air filtered by an air cleaner 12 flows. And an EGR passage 2 connected to each other. The EGR passage 2 is for recirculating a part of the exhaust gas flowing through the exhaust pipe 11 to the intake pipe 13.

  The EGR passage 2 is provided with an EGR cooler 3 that cools the exhaust gas by exchanging heat between the engine coolant as a heat medium and the exhaust gas of the engine 1. An EGR valve 4 is provided on the exhaust gas downstream side (intake pipe 13 side) of the EGR cooler 3 in the EGR passage 2 to adjust the passage opening of the EGR passage 2 to control the exhaust circulation amount. The operation of the EGR valve 4 is controlled by a control signal output from a control device 6 described later.

  As shown in FIGS. 2 and 3, the EGR cooler 3 according to the present embodiment is arranged on both ends in the longitudinal direction of the plurality of tubes 31 and the core portion 32 having the plurality of tubes 31 through which the exhaust flows. And a pair of distribution and collection tanks 33 for collecting and distributing the exhaust gas. Inner fins 34 that increase the heat transfer area between the cooling water and the tubes 31 to promote heat exchange between the cooling water and the exhaust are provided inside the plurality of tubes 31.

  The inner fin 34 is formed in a wave shape in which a cross-sectional shape perpendicular to the flow direction of the exhaust gas, that is, the longitudinal direction of the tube 31 is bent with the convex portions positioned alternately on one side and the other side. Specifically, the inner fin 34 is a straight fin in which a cross-sectional shape orthogonal to the longitudinal direction of the tube 31 is formed in a rectangular wave shape.

  The plurality of tubes 31 are covered with a cylindrical housing 35 that forms the outer shell of the EGR cooler 3. That is, the plurality of tubes 31 are disposed inside the housing 35. Both ends in the longitudinal direction of the housing 35 are joined to the distribution and collection tank 33, respectively. As a result, a space is formed by the surface of the distribution assembly tank 33 on the core portion 32 side and the housing 35. By circulating the cooling water in this space, heat exchange can be performed between the cooling water and the exhaust in the tube 31 to cool the exhaust. Hereinafter, a space formed by the surface on the core portion 32 side in the distribution and collection tank 33 and the housing 35 is referred to as a cooling water flow path 36.

  Connected to the housing 35 are a cooling water inlet 37 through which cooling water flows into the cooling water flow path 36, and a first cooling water outlet 38 and a second cooling water outlet 39 through which cooling water flows out from the cooling water flow path 36. . The cooling water inlet 37 is connected to the most upstream part of the exhaust flow of the housing 35. The second cooling water outlet 39 is disposed on the upstream side of the exhaust flow from the first cooling water outlet 38. In the present embodiment, the first cooling water outlet 38 is connected to the most downstream portion of the exhaust flow of the housing 35. As a result, the cooling water flowing into the cooling water flow path 36 from the cooling water inlet 37 exchanges heat with the exhaust flowing through the tube 31 and flows out from the first cooling water outlet 38 or the second cooling water outlet 39.

  Here, by connecting the cooling water inlet 37 to the most upstream part of the exhaust flow of the housing 35, the high-temperature exhaust just flowing into the core part 32 and the low-temperature cooling water can be heat-exchanged. It can suppress that water boils.

  An electric three-way valve 51 is connected to the downstream side of the cooling water flow of the first cooling water outlet 38 and the second cooling water outlet 39. The three-way valve 51 includes a first cooling water circuit that causes the cooling water flowing from the cooling water inlet 37 to the cooling water flow path 36 to flow out from the first cooling water outlet 38, and the cooling water that flows from the cooling water 37 to the cooling water flow path 36. It is a cooling water circuit switching means for switching between the second cooling water circuit flowing out from the second cooling water outlet 39. The operation of the three-way valve 51 is controlled by a control signal output from the control device 6 described later.

  Further, the EGR system of this embodiment is provided with a control device (ECU) 6 as a control means for performing various controls. The control device 6 controls the operation of various control devices constituting the EGR system based on various input signals. The control device 6 includes a well-known microcomputer having a CPU, a ROM, a RAM, an I / O, and the like. In accordance with a control program stored in the storage unit, etc., processes such as various calculations are executed.

  In the present embodiment, a detection signal or the like from a cooling water temperature sensor (not shown) that detects the temperature of the cooling water is input to the input side of the control device 6. On the other hand, an EGR valve 4, a three-way valve 51, and the like are connected to the output side of the control device 6 and output control signals to various control devices.

  Specifically, the three-way valve 51 switches to the first cooling water circuit when the cooling water temperature exceeds a predetermined reference cooling water temperature, and when the cooling water temperature becomes equal to or lower than the reference cooling water temperature. Switch to the second coolant circuit. As a result, when the cooling water temperature exceeds the reference cooling water temperature, the cooling water flowing in from the cooling water inlet 37 circulates throughout the cooling water flow path 36 and flows out from the first cooling water outlet 38. For this reason, as shown by the solid line a in FIG. 4, heat exchange is performed between the cooling water and the exhaust gas in the entire area of the core portion 32 to cool the exhaust gas.

  In addition, when the cooling water temperature becomes equal to or lower than the reference cooling water temperature, the cooling water that has flowed from the cooling water inlet 37 flows out from the second cooling water outlet 39. That is, the cooling water circulates from the cooling water inlet 37 to the second cooling water outlet 39 in the cooling water flow path 36. For this reason, as shown by a broken line b1 in FIG. 4, heat is exchanged between the cooling water and the exhaust between the cooling water inlet 37 and the second cooling water outlet 39 in the core portion 32, and the exhaust Is cooled.

  On the other hand, the cooling water stays in the portion between the second cooling water outlet 39 and the first cooling water outlet 38 in the cooling water flow path 36, and stagnation occurs in the cooling water flow. Therefore, as indicated by a broken line b2 in FIG. 4, the cooling water temperature is close to the exhaust temperature between the second cooling water outlet 39 and the first cooling water outlet 38 in the core portion 32, and the cooling water and the exhaust gas are exhausted. Most of the heat exchange between the two is performed. Therefore, the exhaust temperature is maintained up to the exhaust outlet of the core portion 32 without substantially decreasing from the temperature at the second cooling water outlet 39 portion.

  According to the present embodiment, the first cooling water outlet 38 is arranged on the downstream side of the second cooling water outlet 39 and the cooling water flowing in from the cooling water inlet 37 flows out from the first cooling water outlet 38. By providing the three-way valve 51 for switching between the first cooling water circuit and the second cooling water circuit for allowing the cooling water flowing in from the cooling water inlet 37 to flow out from the second cooling water outlet 39, the three-way valve 51 allows the cooling water inlet When switching to the second cooling water circuit that causes the cooling water flowing in from 37 to flow out from the second cooling water outlet 39, the exhaust gas flow downstream of the second cooling water outlet 39 in the EGR cooler 3, that is, the second cooling water outlet 39. And the first cooling water outlet 38 no longer circulates the cooling water.

  For this reason, on the downstream side of the exhaust flow of the second cooling water outlet 39 in the EGR cooler 3, heat exchange is hardly performed between the exhaust gas and the cooling water, and the exhaust gas is not cooled. Therefore, it is possible to suppress the exhaust gas passing through the exhaust gas downstream side of the second cooling water outlet 39 in the EGR cooler 3 from becoming too low in temperature, and therefore it is possible to suppress PM from accumulating in the EGR cooler 3.

  On the other hand, even if the three-way valve 51 is switched to any one of the first cooling water circuit and the second cooling water circuit, the exhaust gas flow upstream of the second cooling water outlet 39 in the EGR cooler 3 Cooling water circulates. For this reason, on the upstream side of the second cooling water outlet 39 in the EGR cooler 3, the exhaust gas is cooled by exchanging heat between the exhaust gas and the cooling water regardless of the operation of the three-way valve 51. Therefore, while ensuring the cooling performance of the EGR cooler 3, it is possible to suppress the decrease in the heat exchange efficiency of the EGR cooler and the increase in the ventilation resistance due to the adhesion of PM.

  In the present embodiment, the three-way valve 51 is switched to the first cooling water circuit when the cooling water temperature exceeds the reference cooling water temperature, and the three-way valve 51 is switched to the first cooling water temperature when the cooling water temperature falls below the reference cooling water temperature. It is configured to switch to a 2-cooling water circuit. For this reason, when the temperature of the cooling water is low, the cooling water does not circulate downstream of the second cooling water outlet 39 in the EGR cooler 3, and the downstream of the second cooling water outlet 39 in the EGR cooler 3. Then, almost no heat exchange is performed between the exhaust gas and the cooling water. Therefore, when the cooling water temperature is low, it is possible to suppress the exhaust gas passing through the downstream side of the exhaust flow of the second cooling water outlet 39 in the EGR cooler 3 from becoming too low, so that PM is deposited on the EGR cooler 3. It can suppress more reliably.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. The second embodiment is different from the first embodiment in the structure of the EGR cooler 3.

  As shown in FIG. 5, as the EGR cooler 3 of the present embodiment, a first EGR cooler 3A and a second EGR cooler 3B are provided. The first EGR cooler 3A is disposed upstream of the second EGR cooler 3B in the exhaust flow. An EGR valve 4 is disposed between the first EGR cooler 3A and the second EGR cooler 3B.

  Similar to the first embodiment, the first EGR cooler 3A includes a first core portion 321 having a plurality of first tubes 311 through which exhaust flows. Moreover, the 2nd EGR cooler 3B is provided with the 2nd core part 322 which has the several 2nd tube 312 through which exhaust_gas | exhaustion distribute | circulates similarly to 1st Embodiment. Inside the first tube 311 and the second tube 312, inner fins (not shown) having the same shape as in the first embodiment are arranged.

  The upstream end portion of the first tube 311 on the exhaust flow side is connected to a distribution tank 331 that distributes the exhaust gas to the first tube 311. Further, the downstream end portion of the second tube 312 in the exhaust flow is communicated with a collecting tank 332 that collects the exhaust gas flowing out from the second tube 312. Further, the exhaust flow downstream end of the first tube 311 and the exhaust flow upstream end of the second tube 312 are each connected to the EGR valve 4.

  Therefore, when the EGR valve 4 is opened, the exhaust gas flowing into the distribution tank 331 flows into the tube 31 of the first EGR cooler 3A. The exhaust gas that has flowed into the tube 31 of the first EGR cooler 3A flows through the tube 31 and flows out to the EGR valve 4 side. Then, the exhaust gas that has passed through the EGR valve 4 flows into the tube 31 of the second EGR cooler 3B. The exhaust gas flowing into the tube 31 of the second EGR cooler 3B flows through the tube 31 and flows out to the collecting tank 332.

  Incidentally, the plurality of first tubes 311 are covered with a cylindrical first housing 351 that forms an outer shell of the first EGR cooler 3A. Similarly, the plurality of second tubes 312 are covered with a cylindrical second housing 352 that forms the outer shell of the second EGR cooler 3B.

  One end side in the longitudinal direction of the first housing 351 is joined to the distribution tank 331. The other end side in the longitudinal direction of the first housing 351 is joined to the EGR valve 4. Thus, a space is formed by the surface on the first core portion 321 side of the distribution tank 331, the surface on the first core portion 321 side of the EGR valve 4, and the first housing 351. By circulating the cooling water in this space, heat exchange can be performed between the cooling water and the exhaust in the first tube 311 to cool the exhaust. Hereinafter, the space formed by the surface on the first core portion 321 side in the distribution tank 331, the surface on the first core portion 321 side in the EGR valve 4 and the first housing 351 is referred to as a first cooling water flow path 361.

  Connected to the first housing 351 are a first cooling water inlet 371 that allows cooling water to flow into the first cooling water flow path 361 and a first cooling water outlet 381 that allows cooling water to flow out of the first cooling water flow path 361. Yes. The first cooling water inlet 371 is connected to the most upstream part of the exhaust flow of the first housing 351. The first coolant outlet 381 is connected to the most downstream side of the exhaust flow of the first housing 351. As a result, the cooling water that has flowed into the first cooling water channel 361 from the first cooling water inlet 371 exchanges heat with the exhaust gas flowing through the first tube 311 and flows out from the first cooling water outlet 381.

  One end side in the longitudinal direction of the second housing 352 is joined to the collecting tank 332. The other end side in the longitudinal direction of the second housing 352 is joined to the EGR valve 4. Thus, a space is formed by the surface on the second core portion 322 side in the collecting tank 332, the surface on the second core portion 322 side in the EGR valve 4, and the second housing 352. By circulating the cooling water in this space, heat exchange can be performed between the cooling water and the exhaust in the second tube 312 to cool the exhaust. Hereinafter, the space formed by the second core portion 322 side surface of the collecting tank 332, the second core portion 322 side surface of the EGR valve 4, and the second housing 352 is referred to as a second cooling water flow path 362.

  The second housing 352 is connected to a second cooling water inlet 372 that allows cooling water to flow into the second cooling water flow path 362 and a second cooling water outlet 382 that allows cooling water to flow out of the second cooling water flow path 362. Yes. The second cooling water inlet 372 is connected to the most downstream part of the exhaust flow of the second housing 352. The second cooling water outlet 382 is connected to the most upstream side of the exhaust flow of the second housing 352. As a result, the cooling water that has flowed into the second cooling water flow path 362 from the second cooling water inlet 372 exchanges heat with the exhaust flowing through the second tube 312 and flows out from the second cooling water outlet 382.

  Here, the second cooling water inlet 372 is connected to the most downstream portion of the exhaust flow of the second housing 352, and the second cooling water outlet 382 is connected to the most upstream portion of the exhaust flow of the second housing 352, so that the second Since the exhaust flow and the cooling water flow in the core portion 322 can be made to be opposite flows, the heat exchange efficiency between the exhaust and the cooling water can be improved.

  A first outlet passage 391 through which the cooling water flowing out from the first cooling water outlet 381 flows is connected to the first cooling water outlet 381. A second outlet passage 392 through which the cooling water flowing out from the second cooling water outlet 382 flows is connected to the second cooling water outlet 382. The second outlet passage 392 is configured to merge with the first outlet passage 391.

  The second outlet passage 392 is provided with a thermostat 52 as a cooling water temperature responsive valve that opens and closes the second outlet passage 392 by displacing the valve body by a thermowax (temperature-sensitive member) whose volume changes with temperature.

  The thermostat 52 is a known technique. When the cooling water temperature is higher than a predetermined temperature (90 ° C. in this example), the second outlet passage 392 is opened and the cooling water is supplied to the second cooling water flow path 362 of the second EGR cooler 3B. When the cooling water temperature is lower than the predetermined temperature, the second outlet passage 392 is closed and control is performed so that the cooling water does not circulate in the second cooling water flow path 362 of the second EGR cooler 3B. Temperature control is performed. At this time, the cooling water circulates in the first cooling water flow path 361 of the first EGR cooler 3A regardless of the temperature of the cooling water.

  That is, the thermostat 52 is a cooling water circuit that switches between a first cooling water circuit for flowing cooling water to both the first EGR cooler 3A and the second EGR cooler 3B and a second cooling water circuit for flowing cooling water only to the first EGR cooler 3A. It functions as a switching means. Specifically, the thermostat 52 switches to the first cooling water circuit when the cooling water temperature is higher than the reference temperature, and switches to the second cooling water circuit when the cooling water temperature is equal to or lower than the reference temperature.

  Thereby, when the cooling water temperature exceeds the reference cooling water temperature, the second outlet passage 392 is opened, so that the cooling water flowing in from the first cooling water inlet 371 passes through the first cooling water flow path 361 of the first EGR cooler 3A. It circulates and flows out from the first cooling water outlet 381. Further, the cooling water flowing in from the second cooling water inlet 372 circulates through the second cooling water flow path 362 of the second EGR cooler 3B and flows out from the second cooling water outlet 382. For this reason, as shown by the solid line a in FIG. 6, the exhaust gas cooled in the first EGR cooler 3A is further cooled in the second EGR cooler 3B.

  When the cooling water temperature becomes equal to or lower than the reference cooling water temperature, the second outlet passage 392 is closed, so that the cooling water flowing in from the first cooling water inlet 371 passes through the first cooling water channel 361 of the first EGR cooler 3A. Although it circulates and flows out from the 1st cooling water exit 381, cooling water does not circulate through the 2nd cooling water channel 362 of the 2nd EGR cooler 3B. Therefore, as indicated by a broken line b1 in FIG. 6, the exhaust gas is cooled in the first EGR cooler 3B, but in the second cooling water flow path 362 of the second EGR cooler 3B, the cooling water temperature becomes close to the exhaust gas temperature. As shown by a broken line b2 in FIG. 6, heat exchange is almost performed between the cooling water and the exhaust. Therefore, the exhaust temperature is maintained up to the exhaust outlet of the second core part 322 of the second EGR cooler 3B without substantially decreasing from the temperature at the outlet part of the first core part 321 of the first EGR cooler 3A.

  According to the present embodiment, as the EGR cooler 3, the first EGR cooler 3A and the second EGR cooler 3B disposed downstream of the first EGR cooler 3A in the exhaust flow direction are provided. If the cooling water is supplied only to the first EGR cooler 3A in the second EGR cooler 3B, the heat medium does not circulate in the second EGR cooler 3B. For this reason, in the second EGR cooler 3B, heat exchange between the exhaust gas and the heat medium is hardly performed, and the exhaust gas is not cooled. Therefore, since it can suppress that the exhaust gas which passes 2nd EGR cooler 3B becomes low temperature, it can suppress that PM accumulates on 2nd EGR cooler 3B.

  At this time, since the heat medium circulates in the first EGR cooler 3A, heat exchange is performed between the exhaust gas and the heat medium to cool the exhaust gas. Therefore, it is possible to suppress a decrease in heat exchange efficiency and an increase in ventilation resistance of the second EGR cooler 3B due to adhesion of PM while ensuring the cooling performance of the exhaust by the first EGR cooler 3A.

  Furthermore, in this embodiment, when the temperature of the cooling water exceeds the reference cooling water temperature, the first cooling water circuit is switched to, and when the cooling water temperature becomes equal to or lower than the reference cooling water temperature, the second cooling water circuit is set. A thermostat 52 for switching is provided. For this reason, when the temperature of the cooling water is low, the cooling water does not circulate in the second EGR cooler 3B, and the second EGR cooler 3B hardly exchanges heat between the exhaust gas and the cooling water. Therefore, when the cooling water temperature is low, it is possible to suppress the exhaust gas passing through the second EGR cooler 3B from becoming too low, and thus it is possible to more reliably suppress PM from being deposited on the second EGR cooler 3B.

  By the way, when the exhaust temperature falls below a predetermined value (54 ° C. in this example), condensed water is generated. In order to prevent corrosion due to the condensed water, the EGR cooler 3 needs to be made of a material having high corrosion resistance such as stainless steel.

  On the other hand, in this embodiment, when the cooling water temperature is low, it is possible to suppress the exhaust gas passing through the second EGR cooler 3B from becoming too low temperature, so that the second EGR cooler 3B does not generate condensed water. Accordingly, the second EGR cooler 3B can be made of a material having lower corrosion resistance than the material constituting the first EGR cooler 3A.

  In this example, the first EGR cooler 3A is made of stainless steel, and the second EGR cooler 3B is made of aluminum. Since aluminum has better thermal conductivity than stainless steel, the cooling performance of the second EGR cooler 3B can be improved. Moreover, since aluminum is cheaper than stainless steel, the cost of the EGR cooler 3 can be reduced.

  Furthermore, in this embodiment, the EGR valve 4 is disposed between the first EGR cooler 3A and the second EGR cooler 3B. Thereby, since the exhaust before being cooled by the second EGR cooler 3B can be caused to flow into the EGR valve 4, it is possible to suppress the exhaust passing through the EGR valve 4 from becoming too low. Therefore, PM can be suppressed from being deposited on the EGR valve 4.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is different from the first embodiment in the structure of the EGR cooler 3.

  As shown in FIG. 7, in the housing 35 of the EGR cooler 3 of the present embodiment, a cooling water inlet 37 that allows cooling water to flow into the cooling water flow path 36, and a cooling water outlet 38 that allows cooling water to flow out from the cooling water flow path 36. Is connected. The cooling water inlet 37 is connected to the most upstream part of the exhaust flow of the housing 35. The cooling water outlet 38 is connected to the most downstream part of the exhaust flow of the housing 35. As a result, the cooling water flowing into the cooling water flow path 36 from the cooling water inlet 37 exchanges heat with the exhaust gas flowing through the tube 31 and flows out from the cooling water outlet 38.

  The cooling water outlet 38 is connected to the suction side of a cooling water circulation pump 53 that pumps the cooling water. The cooling water circulation pump 53 is mechanically connected to the pump motor 54. By rotating the pump motor 54, the cooling water circulation pump 53 can be rotated to circulate the cooling water in the cooling water flow path 36.

  By adjusting the rotation speed of the cooling water circulation pump 53, the cooling water flow rate of the cooling water flow path 36 can be adjusted. For this reason, the cooling water circulation pump 53 corresponds to a flow rate adjusting means for adjusting the flow rate of the cooling water flowing through the cooling water flow path 36. The operation of the pump motor 54 is controlled by a control signal output from the control device 6. Specifically, the cooling water circulation pump 53 increases the flow rate of the cooling water flowing through the cooling water flow path as the temperature of the cooling water is higher.

  According to the present embodiment, by providing the cooling water circulation pump 53 that increases the flow rate of the cooling water flowing through the cooling water flow path 36 as the temperature of the cooling water increases, the cooling water flow path is provided when the cooling water temperature is low. Since the flow rate of the cooling water flowing through 36 is reduced, heat exchange between the exhaust gas and the cooling water is difficult to be performed in the EGR cooler 3. Therefore, when the cooling water temperature is low, it is possible to suppress the exhaust gas passing through the EGR cooler 3 from becoming too low temperature, and therefore it is possible to suppress PM from being deposited on the EGR cooler 3.

  On the other hand, when the cooling water temperature is high, the flow rate of the cooling water flowing through the cooling water flow path 36 increases, so that heat exchange is reliably performed between the exhaust gas and the cooling water in the EGR cooler 3, and the exhaust gas is cooled. Is done. Therefore, while ensuring the cooling performance of the EGR cooler 3, it is possible to suppress the decrease in the heat exchange efficiency of the EGR cooler and the increase in the ventilation resistance due to the adhesion of PM.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and can be variously modified as follows without departing from the spirit of the present invention.

  (1) In the first embodiment, the example in which the three-way valve 51 is configured to switch the cooling water circuit based on the temperature of the cooling water has been described. You may comprise so that a cooling water circuit may be switched based on the load (specifically engine speed, gear position, etc.) of the engine 1.

  Specifically, the three-way valve 51 is switched to the first cooling water circuit when the exhaust temperature exceeds a predetermined reference exhaust temperature, and is switched to the second cooling water circuit when the exhaust temperature falls below the reference exhaust temperature. You may comprise so that it may switch. Further, the three-way valve 51 is switched to the first cooling water circuit when the load of the engine 1 exceeds a predetermined reference load, and is switched to the second cooling water circuit when the load of the engine 1 becomes equal to or lower than the reference load. You may comprise as follows.

  (2) In the first embodiment, the coolant flow downstream of the first coolant outlet 38 and the second coolant outlet 39 as the coolant circuit switching means for switching between the first coolant circuit and the second coolant circuit. Although the example which employ | adopted the electric three-way valve 51 connected to was demonstrated, a cooling water circuit switching means is not limited to this.

  For example, an on-off valve is connected to each of the first cooling water outlet 38 and the second cooling water outlet 39, and the opening and closing of these on-off valves is controlled to switch between the first cooling water circuit and the second cooling water circuit. May be. In this case, it is possible to switch to the first cooling water circuit by opening the opening / closing valve connected to the first cooling water outlet 38 and closing the opening / closing valve connected to the second cooling water outlet 39. . On the other hand, it is possible to switch to the second cooling water circuit by closing the on-off valve connected to the first cooling water outlet 38 and opening the on-off valve connected to the second cooling water outlet 39.

  (3) In the second embodiment, the example in which the thermostat 52 as the cooling water temperature responsive valve is employed as the cooling water circuit switching means for switching between the first cooling water circuit and the second cooling water circuit has been described. Not limited to this, an electromagnetic on-off valve whose opening / closing operation is controlled by a control signal output from the control device 6 may be adopted.

  In this case, the electromagnetic on-off valve may be controlled so that the cooling water circuit is switched based on the cooling water temperature, the exhaust temperature, the load on the engine 1 (specifically, the engine speed, gear position, etc.), and the like. Specifically, when the cooling water temperature exceeds the reference cooling water temperature, the first cooling water circuit is switched, and when the cooling water temperature becomes the reference cooling water temperature or lower, the second cooling water circuit is switched. The electromagnetic on-off valve may be controlled. The electromagnetic on-off valve is switched so that the first cooling water circuit is switched when the exhaust temperature exceeds a predetermined reference exhaust temperature, and the second cooling water circuit is switched when the exhaust temperature becomes lower than the reference exhaust temperature. You may control. Further, the electromagnetic switching is performed so that the first cooling water circuit is switched to when the load of the engine 1 exceeds a predetermined reference load, and the second cooling water circuit is switched when the load of the engine 1 falls below the reference load. The valve may be controlled.

1 engine (internal combustion engine)
2 EGR passage 3 EGR cooler 4 EGR valve 36 Cooling water flow path (heat medium flow path)
37 Cooling water inlet (heat medium inlet)
38 1st cooling water exit (1st heat-medium exit)
39 Second cooling water outlet (second heat medium outlet)
51 Three-way valve (heat medium circuit switching means)
52 Thermostat (heat medium circuit switching means)

Claims (7)

Provided in the EGR passage (2) connecting the exhaust passage (11) and the intake passage (13) of the internal combustion engine (1), and performs heat exchange between the exhaust of the internal combustion engine (1) and the heat medium. An EGR system comprising an EGR cooler (3) for cooling the exhaust gas,
The EGR cooler (3)
A heat medium flow path (36) through which the heat medium flows;
A heat medium inlet (37) through which the heat medium flows into the heat medium flow path (36);
A first heat medium outlet (38) and a second heat medium outlet (39) for allowing the heat medium to flow out from the heat medium flow path (36);
The first heat medium outlet (38) is disposed downstream of the second heat medium outlet (39) in the exhaust flow direction,
Furthermore, the first heat medium circuit for flowing out the heat medium flowing in from the heat medium inlet (37) from the first heat medium outlet (38), and the heat medium flowing in from the heat medium inlet (37) An EGR system comprising a heat medium circuit switching means (51) for switching between a second heat medium circuit that flows out from the second heat medium outlet (39). Provided in the EGR passage (2) connecting the exhaust passage (11) and the intake passage (13) of the internal combustion engine (1), and performs heat exchange between the exhaust of the internal combustion engine (1) and the heat medium. An EGR cooler (3) for cooling the exhaust gas,
An EGR system comprising an EGR valve (4) for adjusting a passage opening degree of the EGR passage (2),
As the EGR cooler (3), a first EGR cooler (3A) and a second EGR cooler (3B) disposed downstream of the first EGR cooler (3A) in the exhaust flow direction are provided.
The EGR valve (4) is provided between the first EGR cooler (3A) and the second EGR cooler (3B).   Furthermore, among the first EGR cooler (3A) and the second EGR cooler (3B), the first heat medium circuit for flowing the heat medium through both the first EGR cooler (3A) and the second EGR cooler (3B), and the first EGR cooler (3A) and the second EGR cooler (3B) The EGR system according to claim 2, further comprising a heat medium circuit switching means (52) for switching between the second heat medium circuit for flowing the heat medium only in the first EGR cooler (3A).   The heat medium circuit switching means (51, 52) switches to the first heat medium circuit when the temperature of the heat medium exceeds a predetermined reference heat medium temperature, and the temperature of the heat medium is changed to the reference heat medium. 4. The EGR system according to claim 1, wherein the EGR system is switched to the second heat medium circuit when the temperature becomes lower than the temperature. 5.   The heat medium circuit switching means (51, 52) switches to the first heat medium circuit when the temperature of the exhaust gas exceeds a predetermined reference exhaust gas temperature, and the temperature of the exhaust gas becomes equal to or lower than the reference exhaust gas temperature. 4. The EGR system according to claim 1, wherein the EGR system is switched to the second heat medium circuit.   The heat medium circuit switching means (51, 52) switches to the first heat medium circuit when the load of the internal combustion engine (1) exceeds a predetermined reference load, and the load of the internal combustion engine (1) 4. The EGR system according to claim 1, wherein the EGR system is switched to the second heat medium circuit when the reference load becomes lower than the reference load. 5. Provided in the EGR passage (2) connecting the exhaust passage (11) and the intake passage (13) of the internal combustion engine (1), and performs heat exchange between the exhaust of the internal combustion engine (1) and the heat medium. An EGR system comprising an EGR cooler (3) for cooling the exhaust gas,
The EGR cooler (3) has a heat medium flow path (36) through which the heat medium flows,
And a flow rate adjusting means (53) for adjusting the flow rate of the heat medium flowing through the heat medium flow path (36).
The EGR system, wherein the flow rate adjusting means (53) increases the flow rate of the heat medium flowing through the heat medium flow path (36) as the temperature of the heat medium is higher.

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