JP2004211649A - EGR cooler system - Google Patents

Abstract

An object of the present invention is to suppress a decrease in heat exchange efficiency and an increase in flow resistance of an EGR cooler due to adhesion of PM and the like, and to suppress an operation of a variable capacity turbocharger from being limited by thermal distortion.
An EGR passage (25) branched from an exhaust passage (7) of an internal combustion engine (1) and connected to an intake passage (3), an EGR cooler (27) for cooling EGR gas in the middle of the EGR passage (25), and a branch from a downstream of the EGR cooler (27). And a branch passage 28 not connected to the intake passage 3. The high-temperature exhaust gas can be circulated through the EGR cooler 27 to remove PM and the like, and the high-temperature exhaust gas can be prevented from flowing into the downstream turbocharger 15.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an EGR cooler system.
[0002]
[Prior art]
When the exhaust gas flows through the EGR cooler when the temperature of the exhaust gas is low, particulate matter (hereinafter, referred to as PM) contained in the EGR gas may adhere to the inside of the cooler. The PM thus adhered is difficult to remove and causes clogging of the EGR cooler.
[0003]
In contrast, in a turbocharged diesel engine, an EGR cooler and an EGR valve are provided in an EGR pipe having one end connected to an exhaust pipe and the other end connected to an intake pipe on the upstream side of a compressor of the supercharger. At the same time, an intake branch pipe having a first throttle valve, one end of which is connected to an intake pipe on the downstream side of the compressor of the supercharger, is connected to the upstream side of the EGR cooler, and the EGR gas diluted with the intake air is cooled by the EGR cooler. To prevent dew condensation in the EGR cooler (for example, see Patent Document 1), and an EGR passage having an EGR valve that connects an intake passage and an exhaust passage on the downstream side of a compressor of a supercharged engine. The EGR passage is connected to the upstream side of the intake passage where the EGR passage merges with a branch passage for dilution having a flow rate regulating valve, and the branch passage for dilution of the EGR passage is connected to the branch passage for dilution. The EGR valve upstream to continue the EGR cooler respectively provided to constitute the downstream side, techniques to keep the combustion state of the engine good (e.g., see Patent Document 2) is known.
[0004]
[Patent Document 1]
JP-A-10-141151 (pages 2, 3; FIG. 1)
[Patent Document 2]
JP-A-10-213020 (pages 3, 4; FIG. 1)
[0005]
[Problems to be solved by the invention]
However, once PM or the like has adhered to the EGR cooler, it is difficult to remove the PM or the like that has adhered.
[0006]
In addition, it is difficult to prevent the nozzle vanes from sticking due to thermal distortion without significantly deteriorating the performance of a general variable capacity turbocharger.
[0007]
The present invention has been made in view of the various problems as described above, and suppresses a decrease in heat exchange efficiency and an increase in flow resistance of an EGR cooler due to adhesion of PM and the like. An object is to suppress the operation from being limited by thermal strain.
[0008]
[Means for Solving the Problems]
The EGR cooler system according to the present invention for achieving the above object employs the following means. That is,
An EGR passage branched from an exhaust passage of the internal combustion engine and connected to an intake passage;
An EGR cooler for cooling EGR gas in the middle of the EGR passage;
A branch passage that branches off from the downstream of the EGR cooler and is not connected to the intake passage;
It is characterized by having.
[0009]
The greatest feature of the present invention resides in that PM adhering in the EGR cooler is oxidized and removed by returning exhaust gas that has passed through the EGR cooler to the exhaust passage again.
[0010]
In the EGR cooler system configured as described above, the exhaust gas flowing through the EGR passage is cooled by the EGR cooler. When the temperature of the exhaust gas is high, PM attached to the EGR cooler wall surface is oxidized and removed by the heat of the exhaust gas. Then, the temperature decreases, and the exhaust gas from which PM has been oxidized and removed flows into the branch passage. This makes it possible to introduce high-temperature exhaust gas into the EGR cooler even when the engine does not need the EGR gas, for example, at a high load. Further, when the exhaust gas is returned to the exhaust passage, the temperature of the exhaust gas flowing through the exhaust passage can be reduced, and the rise of the temperature of the exhaust passage constituent member provided downstream can be suppressed.
[0011]
In the present invention, the branch passage may be connected to an exhaust passage, and a variable capacity turbocharger may be provided downstream of a junction of the branch passage and the exhaust passage. In the EGR cooler system configured as described above, the exhaust gas cooled by the EGR cooler can be supplied to the variable displacement turbocharger. Therefore, it is possible to suppress the operation of the variable displacement turbocharger from being limited due to the occurrence of thermal distortion.
[0012]
In the present invention, the air conditioner further includes an adjustment valve for adjusting a flow rate of the exhaust gas flowing through the branch passage, and the flow rate of the exhaust gas flowing through the branch passage can be increased as the temperature of the exhaust gas increases. In the EGR cooler system configured as described above, the amount of exhaust flowing through the EGR cooler and the amount of exhaust flowing from the branch passage into the exhaust passage can be changed by the flow control valve. By increasing the amount of exhaust gas flowing into the EGR cooler as the temperature of exhaust gas discharged from the engine increases, PM attached to the EGR cooler wall surface can be effectively oxidized and removed. The temperature of the exhaust gas can be reduced to a temperature at which the operation of the charger is not limited, and on the other hand, it is possible to suppress an excessive decrease in the exhaust gas temperature due to the EGR cooler.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
<First embodiment>
Hereinafter, specific embodiments of the EGR cooler system according to the present invention will be described with reference to the drawings. Here, an example in which the EGR cooler system according to the present invention is applied to a diesel engine for driving a vehicle will be described.
[0014]
FIG. 1 is a diagram showing a schematic configuration of an engine 1 to which an exhaust purification device according to the present invention is applied and an intake / exhaust system thereof.
[0015]
The engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0016]
Next, an intake branch pipe 3 is connected to the engine 1, and each branch pipe of the intake branch pipe 3 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown).
[0017]
The intake branch pipe 3 is connected to an intake pipe 4. An intake throttle valve 5 that adjusts a flow rate of intake air flowing through the intake pipe 4 is provided at a position of the intake pipe 4 immediately upstream of the intake branch pipe 3. The intake throttle valve 5 is provided with an intake throttle actuator 6 configured by a step motor or the like and driving the intake throttle valve 5 to open and close.
[0018]
A compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using exhaust energy as a driving source is provided in the intake pipe 4 located upstream of the intake throttle valve 5.
[0019]
In the intake system configured as described above, the intake air flows into the compressor housing 15a via the intake pipe 4.
[0020]
The intake air flowing into the compressor housing 15a is compressed by rotation of a compressor wheel provided inside the compressor housing 15a. The intake air compressed in the compressor housing 15a flows into the intake branch pipe 3 with the flow rate adjusted by the intake throttle valve 5 as necessary. The intake air flowing into the intake branch pipe 3 is distributed to the combustion chamber of each cylinder 2 through each branch pipe, and is burned using the fuel injected in each cylinder 2 as an ignition source.
[0021]
On the other hand, an exhaust branch pipe 7 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 7 communicates with a combustion chamber of each cylinder 2 via an exhaust port (not shown).
[0022]
The exhaust branch pipe 7 is connected to a turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 8, and the exhaust pipe 8 communicates downstream with the atmosphere.
[0023]
An NOx storage reduction catalyst 9 (hereinafter simply referred to as NOx catalyst) is provided in the exhaust pipe 8.
[0024]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) burned in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 7 through the exhaust port, and then centrifugally supercharged from the exhaust branch pipe 7. Machine 15 into the turbine housing 15b. The exhaust gas flowing into the turbine housing 15b rotates a turbine wheel rotatably supported in the turbine housing 15b by using energy of the exhaust gas. At this time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.
[0025]
The exhaust gas discharged from the turbine housing 15b flows into the NOx catalyst 9 via the exhaust pipe 8, and the NOx in the exhaust gas is stored. Thereafter, the exhaust gas flows through the exhaust pipe 8 and is discharged into the atmosphere.
[0026]
In the present embodiment, a variable displacement turbocharger is used as the turbocharger 15.
[0027]
Next, a specific configuration of the variable capacity turbocharger 15 will be described with reference to FIGS.
[0028]
FIG. 2 is a cross-sectional view showing a configuration of the variable displacement turbocharger.
[0029]
FIG. 3 is a view showing a variable nozzle mechanism of the variable displacement turbocharger.
[0030]
As shown in FIG. 2, the variable capacity turbocharger (hereinafter simply referred to as a turbocharger) 15 is configured by connecting a compressor housing 15a and a turbine housing 15b via a center housing 15c.
[0031]
In the center housing 15c, one end of the rotor shaft 48 protrudes into the compressor housing 15a, and the protruding portion is attached to a compressor wheel 46 having a plurality of compressor impellers 46a.
[0032]
The other end of the rotor shaft 48 protrudes into the turbine housing 15b, and the protruding portion is attached to a turbine wheel 47 having a plurality of turbine impellers 47a.
[0033]
An intake port 62a for taking in intake air into the compressor housing 15a is formed in a portion of the compressor housing 15a opposite to the center housing 15c. A spiral compressor passage 64 surrounding the outer periphery of the compressor wheel 46 is formed in the compressor housing 15a, and an annular delivery passage 65 communicating the interior portion of the compressor wheel 46 and the compressor passage 64 is formed. I have. At the end of the compressor passage 64, an intake outlet (not shown) for discharging the intake air compressed in the compressor housing 15a is formed.
[0034]
On the other hand, a spiral scroll passage 66 surrounding the outer periphery of the turbine wheel 47 is formed in the turbine housing 15b, and an annular nozzle passage 67 communicating the interior portion of the turbine wheel 47 and the scroll passage 66 is formed. Have been. An exhaust inlet (not shown) for taking exhaust gas into the turbine housing 15b is formed at the base end of the scroll passage 66. An exhaust outlet 63a for exhausting exhaust gas from the turbine housing 15b is provided at a portion of the turbine housing 15b opposite to the center housing 15c.
[0035]
Further, a variable nozzle mechanism 71 is provided on the center housing 15c side of the turbine housing 15b. The variable nozzle mechanism 71 includes a nozzle back plate 72 formed in a ring shape as shown in FIGS. The nozzle back plate 72 is fixed to the turbine housing 15b by bolts (not shown). Subsequently, a plurality of shafts 73 are provided on the nozzle back plate 72 at equal angles around the center of the plate 72.
[0036]
Each shaft 73 is rotatably supported by penetrating the nozzle back plate 72 in the thickness direction. A nozzle vane 74 is fixed to one end of each shaft 73 (the left end in FIG. 3A). On the other hand, an opening / closing lever 75 which is perpendicular to the shaft 73 and extends to the outer edge of the nozzle back plate 72 is fixed to the other end of the shaft 73 (the right end in FIG. 3A). And are integrally rotatable. At the tip of the opening / closing lever 75, a pair of forked portions 75a is provided.
[0037]
An annular ring plate 76 is provided between each opening / closing lever 75 and the nozzle back plate 72 so as to overlap the nozzle back plate 72. This ring plate 76 is rotatable in the circumferential direction about the center of the circle. A plurality of pins 77 are provided on the ring plate 76 at equal angles around the center of the circle, and the pins 77 are rotatably held between the holding portions 75 a of the opening / closing levers 75. I have.
[0038]
In the variable nozzle mechanism 71 configured as described above, when the above-described ring plate 76 is rotated around the center of the circle, each pin 77 causes the holding portion 75 a of each open / close lever 75 to move in the same direction as the rotation direction of the ring plate 76. Push in the direction. As a result, the opening / closing lever 75 rotates the shaft 73, and the nozzle vanes 74 rotate about the shaft 73 in synchronization with the rotation of the shaft 73.
[0039]
For example, when the ring plate 76 is rotated to rotate an end of the nozzle vane 74 located on the side of the center of the ring plate 76 away from the center of the circle, the gap between the adjacent nozzle vanes 74 is reduced, and the nozzle vane 74 is closed. The flow path between them will be closed.
[0040]
On the other hand, when the ring plate 76 is rotated in such a manner that the end of the nozzle vane 74 located on the side of the center of the ring plate 76 approaches the center of the circle, the gap between the adjacent nozzle vanes 74 increases, and The flow path between 74 will be opened.
[0041]
Next, a mechanism for driving the variable nozzle mechanism 71, that is, a mechanism for rotating the ring plate 76 will be described. As shown in FIGS. 2 and 3, a pin 86 extending in the same direction as the axis L is attached to a part of the outer edge of the ring plate 76, and a driving mechanism 82 is connected to the pin 86.
[0042]
The drive mechanism 82 includes a support shaft 83 that is rotatably supported by the center housing 15c so as to extend toward the compressor housing 15a in parallel with the pin 86. A drive lever 84 rotatably connected to a pin 86 is fixed to an end (left end in FIG. 2) of the support shaft 83 on the turbine housing 15b side. An operation piece 85 that is rotatable about the support shaft 83 is attached to an end (the right end in FIG. 2) of the support shaft 83 on the compressor housing 15a side. The operation piece 85 is connected to a negative pressure type VNT actuator 87.
[0043]
FIG. 4 is a schematic configuration diagram of the VNT actuator 87.
[0044]
The VNT actuator 87 is divided into a negative pressure chamber 87a and an atmosphere chamber 87b by a diaphragm 88 as shown in FIG. In the negative pressure chamber 87a, a coil spring 88a that expands and contracts in a direction perpendicular to the diaphragm 88 is provided. Further, a negative pressure passage 89 is connected to the negative pressure chamber 87a, and the negative pressure passage 89 is connected to a vacuum pump 91 which is drivingly connected to a crankshaft of the engine 1. An electric vacuum regulating valve (EVRV) 90 is provided in the middle of the negative pressure passage 89.
[0045]
The EVRV 90 is provided with an air inlet (not shown) opened to the atmosphere. The EVRV 90 is connected between the negative pressure passage 89a located on the VNT actuator 87 side from the EVRV 90 and the air inlet, and is located on the vacuum pump 91 side from the EVRV 90. Between the negative pressure passage 89b and the negative pressure passage 89a on the VNT actuator 87 side.
[0046]
The EVRV 90 is provided with an electromagnetic solenoid. When the electromagnetic solenoid is in a non-excited state, the negative pressure passage 89a and the air introduction port are kept in a conductive state. When the electromagnetic solenoid is in an excited state, the negative pressure is maintained. The passage 89a and the negative pressure passage 89b are kept in the conducting normal state. On the other hand, the atmosphere chamber 87b of the VNT actuator 87 communicates with the outside (in the atmosphere) of the VNT actuator 87 so that the pressure in the atmosphere chamber 87b is always at the atmospheric pressure.
[0047]
On the atmosphere chamber 87b side of the diaphragm 88, a rod 88b extending in the direction in which the coil spring 88a extends is protrudingly provided. The rod 88b penetrates through the atmosphere chamber 87b and protrudes to the outside of the VNT actuator 87, and its tip is connected to the operation piece 85.
[0048]
In the VNT actuator 87 configured as described above, when the electromagnetic solenoid of the EVRV 90 is in a non-excited state, the negative pressure passage 89a and the air inlet are in a conductive state, and the inside of the negative pressure chamber 87a is at atmospheric pressure. In this case, the rod 88b of the VNT actuator 87 is held in the most advanced state by the urging force of the coil spring 88a.
[0049]
When the electromagnetic solenoid of the EVRV 90 is in the excited state, the negative pressure passage 89a and the negative pressure passage 89b are in a conductive state, and the inside of the negative pressure chamber 87a of the VNT actuator 87 has a negative pressure. In this case, the diaphragm 88 is displaced against the urging force of the coil spring 88a, and accordingly, the rod 88b is held in the most retracted state.
[0050]
Further, by controlling the duty of the excitation and non-excitation of the electromagnetic solenoid of the EVRV 90, it is possible to adjust the amount of movement of the rod 88b.
[0051]
The operation piece 85 is rotated by the advance / retreat operation of the rod 88b of the VNT actuator 87 as described above. When the operation piece 85 is rotated, the support shaft 83 rotates in synchronization with the operation piece 85, and the drive lever 84 rotates about the support shaft 83 with the rotation of the support shaft 83. As a result, the drive lever 84 pushes the ring plate 76 in the circumferential direction via the pin 86, and rotates the ring plate 76 about the axis L.
[0052]
In the variable displacement turbocharger 15 described above, the direction of the flow path between the nozzle vanes 74 and the gap between the nozzle vanes 74 are changed by adjusting the rotation direction and the rotation amount of the nozzle vanes 74 by the driving mechanism 82. Becomes possible. That is, by controlling the rotation direction and the rotation amount of the nozzle vane 74, the direction and the flow velocity of the exhaust gas blown from the scroll passage 66 to the turbine wheel 47 are adjusted.
[0053]
For example, when the amount of exhaust from the engine 1 is small, by operating the drive mechanism 82 to close the nozzle vanes 74 of the variable nozzle mechanism 71, the flow velocity of the exhaust blown to the turbine wheel 47 increases, and the exhaust and turbine impeller Since the collision angle with 47a becomes closer to vertical, it is possible to increase the rotation speed and the rotation force of the turbine wheel 47 even with a small displacement.
[0054]
On the other hand, when the amount of exhaust gas from the engine 1 is sufficiently large, the drive mechanism 82 is operated to open the nozzle vanes 74 of the variable nozzle mechanism 71, so that the flow velocity of exhaust gas blown to the turbine wheel 47 is excessively increased. As a result, it is possible to suppress an excessive increase in the rotation speed and the rotation force of the turbine wheel 47.
[0055]
In the present embodiment, when the electromagnetic solenoid of the EVRV90 is in the non-excited state and the rod 88b of the VNT actuator 87 is in the most advanced state, the nozzle vane 74 is held in the most open state, and the electromagnetic solenoid of the EVRV90 is Is in the excited state, and when the rod 88b of the VNT actuator 87 is in the most retracted state, the nozzle vane 74 is held in the most closed state.
[0056]
Further, the engine 1 is provided with a crank position sensor 10 that outputs an electric signal corresponding to the rotational position of the crankshaft.
[0057]
The engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 11 for controlling the engine 1. The ECU 11 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's requirements.
[0058]
Various sensors are connected to the ECU 11 via electric wiring.
[0059]
On the other hand, the intake throttle actuator 6 and the like are connected to the ECU 11 via electrical wiring, so that the ECU 11 can control the above-described components.
[0060]
Further, the exhaust branch pipe 7 and the intake branch pipe 3 are communicated via an exhaust gas recirculation passage (EGR passage) 25 for recirculating a part of the exhaust flowing through the exhaust branch pipe 7 to the intake branch pipe 3. I have. A flow regulating valve (e.g., an EGR gas) that changes the flow rate of the exhaust gas (hereinafter, referred to as EGR gas) flowing through the EGR passage 25 in accordance with the magnitude of the applied power is provided in the middle of the EGR passage 25. An EGR valve 26 is provided.
[0061]
An EGR cooler 27 that cools EGR gas flowing through the EGR passage 25 is provided in the EGR passage 25 and upstream of the EGR valve 26. A cooling water passage (not shown) is provided in the EGR cooler 27, and a part of cooling water for cooling the engine 1 circulates.
[0062]
On the other hand, between the EGR valve 26 and the EGR cooler 27, one end of a return passage 28 that guides the EGR gas to the exhaust branch pipe 7 is connected, and the other end of the return passage 28 is in the middle of the exhaust branch pipe 7. Thus, it is connected between the branch point of the EGR passage 25 and the turbine housing 15b. In the middle of the return passage 28, there is provided a flow regulating valve 29 which is constituted by a step motor or the like and is driven to open and close when changing the flow rate of the exhaust EGR gas flowing through the return passage 28.
[0063]
Here, the EGR gas includes water (H ₂ O) and carbon dioxide (CO ₂ ), Etc., because it does not burn itself and contains an endothermic inert gas component, when the EGR gas is contained in the mixture, the combustion temperature of the mixture decreases. Thus, the generation amount of nitrogen oxides (NOx) is suppressed.
[0064]
In the EGR system configured as described above, when the EGR valve 26 is opened and the flow control valve 29 is closed, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing through the exhaust branch pipe 7 becomes EGR. The gas flows into the EGR passage 25 and is introduced into the EGR cooler 27. In the EGR cooler 27, the EGR gas exchanges heat with the cooling water to lower the temperature of the EGR gas. The EGR gas that has passed through the EGR cooler 27 and returned to the intake branch pipe 3 is guided to the combustion chamber of each cylinder 2 while being mixed with fresh air flowing from the upstream of the intake branch pipe 3.
[0065]
On the other hand, when the EGR valve 26 is closed and the flow control valve 29 is opened, the return passage 28 becomes conductive, and a part of the exhaust flowing through the exhaust branch pipe 7 becomes EGR gas to the EGR passage 25. And flows into the EGR cooler 27. In the EGR cooler 27, the EGR gas exchanges heat with the cooling water to lower the temperature of the EGR gas. Then, the EGR gas returned to the exhaust branch pipe 7 through the EGR cooler 27 is guided to the turbine housing 15b while being mixed with the exhaust gas flowing from the upstream of the exhaust branch pipe 7.
[0066]
In the present embodiment, when the EGR gas is recirculated to the intake system, the flow control valve 29 is fully closed in order to secure the EGR gas amount. Therefore, the flow regulating valve 29 is opened only when the EGR valve 26 is fully closed. When the temperature of the exhaust gas is low, it is not necessary to return the cooled EGR gas to the exhaust branch pipe 7 via the return passage 28, so the flow control valve 29 is fully closed.
[0067]
By the way, when the EGR cooler 27 is cold, dew condensation occurs in the EGR cooler 27, and PM contained in the EGR gas tends to adhere to the wall surface of the EGR cooler 27.
[0068]
When the engine 1 is operating in the lean burn mode, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is reduced and the concentration of the reducing agent is increased before the NOx storage capacity of the NOx catalyst is saturated, so that the NOx catalyst stores the NOx. It is necessary to reduce the generated NOx.
[0069]
As a method of reducing the oxygen concentration in this way, the amount of EGR gas is further increased after adding the fuel in the exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of generated soot to a maximum. Low-temperature combustion (Japanese Patent No. 3116876) and a method of sub-injection of re-injecting fuel during an expansion stroke after main injection for injecting fuel for engine output can be considered. For example, when fuel is added to exhaust gas, a reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to exhaust gas flowing through the exhaust pipe 8 upstream of the NOx catalyst 9 is provided. By adding the fuel, the oxygen concentration of the exhaust gas flowing into the NOx catalyst 9 can be reduced and the concentration of the reducing agent can be increased.
[0070]
However, when the exhaust gas at this time passes through the EGR cooler 27, a large amount of hydrocarbons (HC) contained in the exhaust gas may adhere to the EGR cooler 27.
[0071]
The PM and hydrocarbons (HC) thus deposited gradually accumulate and lower the cooler efficiency and cause resistance when the EGR gas passes. Therefore, conventionally, control has been performed so that PM and hydrocarbon (HC) do not adhere to the EGR cooler 27.
[0072]
However, once PM has adhered to the EGR cooler 27, it has been difficult to remove the PM.
[0073]
Thus, in the present embodiment, high-temperature exhaust gas is passed through the EGR cooler 27 to oxidize and remove PM.
[0074]
On the other hand, in the variable displacement turbocharger, an exhaust leak flowing from the scroll passage 66 to the exhaust outlet 63 a through a space other than the gap between the nozzle vanes 74 deteriorates the performance of the variable displacement turbocharger 15. As a result, the gap between each nozzle vane 74 and the adjacent housing surface in the height direction is very small, and such exhaust leakage is minimized.
[0075]
By the way, if the variable nozzle mechanism 71 is frequently exposed to extremely high-temperature exhaust gas, thermal distortion occurs in the height direction and the length direction. There is no particular problem if the nozzle vanes 74 extend in the length direction due to thermal strain, but if they extend in the height direction, there is a possibility that the nozzle vanes 74 come into contact with and adhere to the adjacent housing surface. Since all the nozzle vanes 74 are rotated by the rotation of the ring plate 76, if one nozzle vane 74 is fixed, the rotation of all the variable nozzles becomes impossible. In order to prevent this, it is conceivable to increase the gap between the nozzle vane 74 and the adjacent housing surface. However, the performance of the variable displacement turbocharger is greatly deteriorated, so that difficulty is involved.
[0076]
Therefore, in the present embodiment, when the temperature of the exhaust gas is so high that the nozzle vane 74 sticks, the flow control valve 29 is opened to flow the exhaust gas through the return passage 28. Since the exhaust gas passes through the EGR cooler 27, the temperature of the exhaust gas is reduced by the EGR cooler 27. By returning the exhaust gas whose temperature has decreased to the exhaust branch pipe 7, the temperature of the exhaust gas flowing into the turbine housing 15b can be decreased, and the nozzle vanes 74 can be prevented from sticking.
[0077]
When the flow control valve 29 is stopped at an arbitrary valve opening position, the amount of EGR gas flowing through the EGR cooler 27 can be reduced. As a result, the amount of EGR gas cooled by the EGR cooler 27 and returned to the exhaust branch pipe 7 decreases, while the amount of exhaust gas directly flowing into the turbine housing 15b without passing through the EGR cooler 27 increases. The temperature of the exhaust gas flowing into the housing 15b rises. Therefore, by adjusting the opening angle of the flow control valve 29, it is possible to adjust the temperature of the exhaust gas flowing into the turbine housing 15b. By adjusting the opening of the flow control valve 29 based on the temperature of the exhaust gas, it is possible to suppress a decrease in output due to a decrease in energy of the exhaust gas and a decrease in the temperature of the NOx storage reduction catalyst. Become.
[0078]
Next, a control flow of the flow control valve according to the present embodiment will be described.
[0079]
FIG. 5 is a flowchart showing a control flow of the flow control valve according to the present embodiment.
[0080]
In step S101, it is determined whether or not the EGR valve 26 is fully closed. When the EGR valve 26 is opened, it is necessary to supply EGR gas to the intake system, so that the EGR gas is not allowed to flow through the return passage 28.
[0081]
If an affirmative determination is made in step S101, the process proceeds to step S102, while if a negative determination is made, this routine ends.
[0082]
In step S102, the target opening of the flow control valve 29 is determined. Here, the temperature of the exhaust gas has a correlation with the engine speed and the fuel injection amount. Therefore, in the present embodiment, the relationship between the engine speed and the fuel injection amount and the target opening of the flow control valve 29 is obtained in advance through experiments or the like, and is stored in the ECU 11. Then, the engine speed is determined from the output signal of the crank position sensor 10, and the ECU 11 calculates the fuel injection amount, and substitutes these values into a map to determine the target opening of the flow control valve 29.
[0083]
In step S103, the ECU 11 opens the flow control valve 29 to the target opening.
[0084]
In this way, the flow control valve 29 can be set to an opening degree suitable for the engine operating conditions.
[0085]
As described above, the sticking of the nozzle vanes 74 due to the thermal strain can be suppressed. Further, even if high-temperature exhaust gas is discharged from the engine 1, the temperature can be lowered downstream, so that it is not necessary to lower the combustion temperature of the engine 1, and therefore, the output can be improved. . Further, by causing the high-temperature exhaust gas to flow through the EGR cooler 27, it becomes possible to oxidize and remove PM adhering to the EGR cooler 27.
<Second embodiment>
This embodiment differs from the first embodiment in the installation position of the flow control valve. The basic configuration of the other hardware is the same as that of the first embodiment, and the description is omitted.
[0086]
FIG. 6 is a diagram showing an installation position of the flow control valve 29a according to the present embodiment.
[0087]
In the present embodiment, a flow control valve 29a including a step motor or the like is provided in the middle of the exhaust branch pipe 7 and between the branch point of the EGR passage 25 and the junction of the return passage 28.
[0088]
In the present embodiment, when the EGR gas is recirculated to the intake system, the flow control valve 29a is fully opened in order to make the EGR gas amount appropriate. Therefore, the flow regulating valve 29a is closed only when the EGR valve 26 is fully closed. When the temperature of the exhaust gas is low, it is not necessary to return the cooled EGR gas to the exhaust branch pipe 7 via the return passage 28, so the flow control valve 29a is fully opened.
[0089]
In the same manner as in the first embodiment, the ECU 11 stores the relationship between the engine speed, the fuel injection amount, and the target opening of the flow control valve 29 obtained in advance through experiments or the like and mapped. Then, the engine speed is obtained from the output signal of the crank position sensor 10, and the ECU 11 calculates the fuel injection amount, and substitutes these values into a map to obtain the opening of the flow control valve 29. Based on this value, the ECU 11 opens the flow control valve 29 to the target opening.
[0090]
In this way, the nozzle vanes 74 can be prevented from sticking due to thermal distortion. Further, even if high-temperature exhaust gas is discharged from the engine 1, the temperature can be lowered downstream, so that it is not necessary to lower the combustion temperature of the engine 1, and therefore, the output can be improved. . Further, by causing the high-temperature exhaust gas to flow through the EGR cooler 27, it becomes possible to oxidize and remove PM adhering to the EGR cooler 27.
[0091]
Further, by fully closing the flow control valve 29a, it becomes possible to introduce a large amount of exhaust gas into the EGR cooler 27.
<Third embodiment>
The present embodiment is different from the first embodiment in that a three-way valve is provided at the junction of the return passages instead of the flow control valve. The basic configuration of the other hardware is the same as that of the first embodiment, and the description is omitted.
[0092]
In the present embodiment, a three-way valve 29 b is provided in the middle of the exhaust branch pipe 7 and at the junction of the return passage 28.
[0093]
FIG. 7 is a diagram showing an installation position of the three-way valve 29b according to the present embodiment. FIG. 7A shows a valve position when exhaust gas is circulated without passing through the EGR cooler 27, and FIG. 7B shows a valve position when exhaust gas is circulated through the EGR cooler 27. .
[0094]
In the present embodiment, when the EGR gas is recirculated to the intake system, the three-way valve 29b is set to the valve position shown in FIG. 7A in order to make the EGR gas amount appropriate. When the temperature of the exhaust gas is low, it is not necessary to return the cooled EGR gas to the exhaust branch pipe 7 via the return passage 28, so that the three-way valve 29b is set to the valve position shown in FIG.
[0095]
On the other hand, when the EGR valve 26 is closed and the three-way valve 29b is set to the valve position shown in FIG. 7B, the entire amount of exhaust gas can be introduced into the turbine housing 15b via the EGR cooler 27.
[0096]
Next, a control flow of the three-way valve according to the present embodiment will be described.
[0097]
FIG. 8 is a flowchart illustrating a control flow of the three-way valve according to the present embodiment.
[0098]
In step S201, it is determined whether or not the EGR valve 26 is fully closed. When the EGR valve 26 is open, it is necessary to supply EGR gas to the intake system, so that the EGR gas is not circulated through the return passage 28.
[0099]
If an affirmative determination is made in step S201, the process proceeds to step S202, while if a negative determination is made, this routine ends.
[0100]
In step S202, it is determined whether the exhaust gas temperature is high. Here, the temperature of the exhaust gas has a correlation with the engine speed and the fuel injection amount. Therefore, in the present embodiment, the relationship between the engine speed and the fuel injection amount and the valve position of the three-way valve 29b is obtained in advance through experiments or the like, and is stored in the ECU 11 as a map. Then, the engine speed is obtained from the output signal of the crank position sensor 10, the ECU 11 calculates the fuel injection amount, and substitutes these values into a map to obtain the valve position of the three-way valve 29b.
[0101]
In the present embodiment, a sensor for detecting the temperature of the exhaust gas may be provided upstream of the turbine housing, and the determination may be made based on whether or not the detected value is higher than a predetermined temperature.
[0102]
If an affirmative determination is made in step S202, the process proceeds to step S203, while if a negative determination is made, the process proceeds to step S204.
[0103]
In step S203, the ECU 11 sets the valve position of the three-way valve 29b to the position shown in FIG.
[0104]
In step S204, the ECU 11 sets the valve position of the three-way valve 29b to the position shown in FIG.
[0105]
Thus, the three-way valve 29b can be set to a valve position suitable for the engine operating conditions.
[0106]
As described above, by using the three-way valve 29b in place of the flow control valve, the conventional EGR system can be changed through the EGR cooler 27 by making a simple change in comparison with the first and second embodiments. Exhaust gas can be introduced into the turbine housing 15b. Thereby, the sticking of the nozzle vanes 74 due to the thermal strain can be suppressed. Further, even if high-temperature exhaust gas is discharged from the engine 1, the temperature can be lowered downstream, so that it is not necessary to lower the combustion temperature of the engine 1, and therefore, the output can be improved. . Further, by causing the high-temperature exhaust gas to flow through the EGR cooler 27, it is possible to oxidize and remove PM attached to the EGR cooler 27.
[0107]
In addition, the three-way valve facilitates control.
[0108]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, sticking by the thermal distortion of a nozzle vane can be suppressed. Further, the output of the engine can be improved. Furthermore, PM adhering to the EGR cooler is oxidized and removed, and a decrease in cooler efficiency of the EGR cooler can be suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an engine 1 to which an exhaust purification device is applied and an intake / exhaust system thereof.
FIG. 2 is a diagram showing a configuration of a variable capacity turbocharger.
FIG. 3A is a diagram showing a side view of a variable nozzle mechanism of a variable displacement turbocharger. FIG. 3B is a front view of the variable nozzle mechanism of the variable displacement turbocharger.
FIG. 4 is a diagram showing a configuration of a VNT actuator of a variable displacement turbocharger.
FIG. 5 is a flowchart illustrating a control flow of the flow control valve according to the first embodiment.
FIG. 6 is a diagram showing an installation position of a flow control valve according to a second embodiment.
FIG. 7 is a diagram showing an installation position of a three-way valve according to a third embodiment. FIG. 7A shows a valve position when exhaust gas is circulated without passing through the EGR cooler, and FIG. 7B shows a valve position when exhaust gas is circulated through the EGR cooler.
FIG. 8 is a flowchart illustrating a control flow of a three-way valve according to a third embodiment.
[Explanation of symbols]
1 engine
2 cylinders
3 Intake branch pipe
4 Intake pipe
5 Intake throttle valve
6. Intake throttle actuator
7 Exhaust branch pipe
8 Exhaust pipe
9 NOx storage reduction catalyst
10 Crank position sensor
11 ECU
15 Variable capacity turbocharger
15a Compressor housing
15b Turbine housing
15c center housing
25 EGR passage
26 EGR valve
27 EGR cooler
28 EGR return passage
29 Flow control valve
29a Flow control valve
29b Three-way valve
71 Variable nozzle mechanism
74 nozzle vane

Claims (3)

An EGR passage branched from an exhaust passage of the internal combustion engine and connected to an intake passage;
An EGR cooler for cooling EGR gas in the middle of the EGR passage;
A branch passage that branches off from the downstream of the EGR cooler and is not connected to the intake passage;
An EGR cooler system comprising: The EGR cooler system according to claim 1, wherein the branch passage is connected to an exhaust passage, and a variable displacement turbocharger is provided downstream of a junction of the branch passage and the exhaust passage. 3. The EGR according to claim 1, further comprising an adjustment valve that adjusts a flow rate of the exhaust gas flowing through the branch passage, wherein the flow rate of the exhaust gas flowing through the branch passage increases as the temperature of the exhaust gas increases. Cooler system.

Images