Abstract:
An engine system includes a turbocharger ( 16 ), an exhaust gas control apparatus ( 81 ), a fuel addition device ( 82 ), a heating unit, and an ECU. The turbocharger includes a variable nozzle mechanism ( 34 ). The exhaust gas control apparatus is disposed on an exhaust downstream side of the exhaust turbine in an exhaust passage. The fuel addition device is configured to add a fuel to the exhaust gas of the engine to recover the function of the exhaust gas control apparatus on a further exhaust upstream side than the exhaust turbine. The heating unit is configured to heat the link chamber ( 52 ). The ECU is configured to execute heating control for controlling the initiation and the stopping of heating by the heating unit and execute the heating control in a period overlapping with at least part of a period when the addition of the fuel by the fuel addition device is executed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an engine system that has a turbocharger which is provided with a variable nozzle mechanism and a fuel addition device which performs fuel addition to exhaust gas and a control apparatus and a control method for an engine system. 
         [0003]    2. Description of Related Art 
         [0004]    Japanese Patent Application Publication No. 2006-152948 (JP 2006-152948 A) discloses a turbocharger that is provided with a variable nozzle mechanism. The variable nozzle mechanism is provided with a plurality of nozzle vanes around a turbine wheel in a flow path (exhaust flow path) through which exhaust gas passes in an exhaust turbine. The plurality of nozzle vanes are arranged at predetermined intervals around the axis of rotation of the turbine wheel. The nozzle vanes are connected to each other by a link mechanism in a link chamber adjacent to the exhaust flow path and are subjected to opening and closing operations in a state of being synchronized with each other. In the turbocharger, the nozzle vanes are driven to be opened and closed at the same time through operation control for the variable nozzle mechanism so that the gaps between the adjacent nozzle vanes are changed. In this manner, the flow speed of the exhaust gas that is sprayed to the turbine wheel through the spaces between the nozzle vanes is changed, and the pressure-feeding amount of intake air is adjusted. 
         [0005]    JP 2006-152948 A discloses a fuel addition device that regularly executes fuel addition to the exhaust gas for functional recovery of an exhaust gas control apparatus (exhaust gas purifying catalyst, filter, or the like) that is disposed in an exhaust passage of an internal combustion engine. A fuel addition valve that adds a fuel to a further exhaust upstream side than a turbine in the exhaust passage is disposed in a fuel ignition device described above. The fuel is added to the exhaust gas through the fuel injection from the fuel addition valve. 
       SUMMARY OF THE INVENTION 
       [0006]    The turbocharger that is provided with the variable nozzle mechanism has a structure in which the nozzle vane that is arranged in the exhaust flow path and the link mechanism that is disposed outside the exhaust flow path (specifically, in the link chamber) are connected to each other. Accordingly, a gap may be formed in a partition wall between the exhaust flow path and the link chamber. In the turbocharger, part of the exhaust gas that passes through the exhaust flow path may flow into the link chamber via the gap when the pressure in the exhaust flow path is high. 
         [0007]    If the fuel addition to the exhaust gas is performed on a further exhaust upstream side than the exhaust turbine in the turbocharger, the exhaust gas that contains the fuel passes through the exhaust turbine. Accordingly, part of the exhaust gas may permeate into the link chamber via the gap along with the fuel. In this case, the fuel that permeates into the link chamber may be altered to become a deposit, which is a factor causing malfunctioning of the link mechanism and the variable nozzle mechanism. 
         [0008]    The invention provides an engine system that is capable of suppressing the accumulation of a deposit in a link chamber of a turbocharger and a control apparatus and a control method for an engine system. 
         [0009]    According to a first aspect of the invention, there is provided an engine system including a turbocharger, an exhaust gas control apparatus, a fuel addition device, a heating unit, and an electronic control unit. The turbocharger includes a variable nozzle mechanism. The variable nozzle mechanism includes a plurality of nozzle vanes, a link chamber, and a link mechanism. The plurality of nozzle vanes is disposed in an exhaust flow path of an exhaust turbine. The link chamber is adjacent to the exhaust flow path. The link mechanism is disposed in the link chamber and is configured to connect the plurality of nozzle vanes. The exhaust gas control apparatus is disposed on an exhaust downstream side of the exhaust turbine in an exhaust passage of an internal combustion engine, and the exhaust gas control apparatus is configured to purify exhaust gas. The fuel addition device is disposed on an exhaust upstream side of the exhaust turbine, and the fuel addition device is configured to add fuel to the exhaust gas of the internal combustion engine to recover a function of the exhaust gas control apparatus. The heating unit is configured to heat the link chamber. The electronic control unit is configured to execute a heating control. In the heating control, the electronic control unit is configured to initiate and stop heating of the link chamber by the heating unit, and the electronic control unit is configured to execute the heating control in a period overlapping with at least part of a period when an addition of fuel by the fuel addition device is executed. 
         [0010]    If a state where a liquid fuel adheres into the link chamber of the turbocharger continues, the adhering fuel may be gradually altered to give rise to a deposit. Even if the fuel permeates into the link chamber, the liquefaction of the permeating fuel is suppressed if the temperature in the link chamber is sufficiently high. Then, the adhesion of the fuel in the link chamber is suppressed, and thus the accumulation of the deposit is suppressed. Still, maintaining a high-temperature state of the turbocharger by heating the turbocharger without stopping the heating may result in overheating deteriorating the reliability of the turbocharger. 
         [0011]    According to the control apparatus described above, the link chamber can have a high temperature therein through the heating by the heating unit when the fuel addition by the fuel addition device is executed for functional recovery of the exhaust gas control apparatus. Accordingly, even in a case where the fuel has permeated into the link chamber, the permeating fuel can be vaporized and the link chamber can have a dry state therein. Since the exhaust gas of the internal combustion engine flows at a high speed in the exhaust flow path, the exhaust gas in the link chamber is discharged out of the link chamber through a gap by the flow of the exhaust gas. Accordingly, the fuel vaporized in the link chamber is also discharged out of the link chamber into the exhaust flow path along with the flow of the exhaust gas. Accordingly, a state where the liquid fuel adheres into the link chamber can be suppressed, and the alteration of the permeating fuel to the deposit can be suppressed. The heating of the link chamber can be stopped when the possibility of the permeation of the fuel into the link chamber is low with the fuel addition by the fuel addition device not executed. In this case, the temperature of the turbocharger can be lowered. Compared to heating the turbocharger without stopping the heating, an increase in the temperature of the turbocharger can be suppressed according to the control apparatus described above. In this manner, deterioration in the reliability of the turbocharger attributable to overheating can be suppressed. 
         [0012]    In the engine system described above, the electronic control unit may be configured to set a timing of the initiation of the heating of the link chamber to precede a timing of the initiation of the addition of fuel by the fuel addition device. 
         [0013]    According to the engine system described above, the temperature in the link chamber can be increased in advance when the fuel addition to the exhaust gas by the fuel addition device is initiated. Accordingly, it is possible to suppress the liquefaction of the fuel permeating into the link chamber, and the adhesion of the deposit to the link mechanism can be suppressed. 
         [0014]    In the engine system described above, the electronic control unit may be configured to set a timing of the stopping of the addition of fuel by the fuel addition device to precede a timing of the stopping of the heating of the link chamber. 
         [0015]    According to the engine system described above, the temperature in the link chamber can be maintained at a high temperature until the termination of the fuel addition by the fuel addition device. Accordingly, it is possible to appropriately suppress the liquefaction of the fuel permeating, into the link chamber, and the adhesion of the deposit to the link mechanism can be appropriately suppressed. 
         [0016]    In the engine system described above, the turbocharger may include a compressor, the exhaust turbine and a center housing. The compressor may be disposed in an intake passage of the internal combustion engine. The center housing may be configured to connect the compressor and the exhaust turbine to each other. The link chamber may be disposed between the exhaust turbine and the center housing. The center housing may include a housing coolant passage through which a coolant circulates. The heating unit may be configured to heat the link chamber by introducing a high-temperature coolant into the housing coolant passage. 
         [0017]    According to the engine system described above, the link chamber arranged between the center housing and the exhaust turbine can be heated by introducing high-temperature water into the housing coolant passage and heating the center housing. In a case where the engine system is provided with the turbocharger that is provided in advance with the housing coolant passage, the heating unit can be disposed, without changing the structure of the turbocharger, by using the housing coolant passage. 
         [0018]    The engine system may further include a communication passage and a flow path switching valve. The communication passage may be configured to connect an outlet of a turbine coolant passage and an inlet of the housing coolant passage. The exhaust turbine may include the turbine coolant passage through which the coolant circulates. The flow path switching valve may be disposed in the communication passage. The electronic control unit may be configured to execute operation control of the flow path switching valve to allow the flow of the coolant from the outlet of the turbine coolant passage into the inlet of the housing coolant passage via the communication passage during the execution of the heating of the link chamber by the heating unit. The electronic control unit may be configured to prohibit the flow of the coolant from the outlet of the turbine coolant passage into the inlet of the housing coolant passage via the communication passage during the stopping of the heating of the link chamber by the heating unit. 
         [0019]    According to the engine system described above, the water that is increased in temperature through the turbine coolant passage in the exhaust turbine can be introduced into the housing coolant passage in the center housing via the communication passage through the operation control for the flow path switching valve. Accordingly, the link chamber can be heated. Through the operation control for the flow path switching valve, the flow of the high-temperature water into the housing coolant passage can be prevented and it is possible to allow only the water that has a relatively low temperature in an introduction path to flow into the housing coolant passage. Accordingly, the heating of the link chamber can be stopped. 
         [0020]    The engine system may further include the introduction path and a discharge path. The introduction path may be configured to connect an inlet of the turbine coolant passage and the inlet of the housing coolant passage to each other in parallel. The discharge path may be configured to connect the outlet of the turbine coolant passage and an outlet of the housing coolant passage to each other in parallel. The electronic control unit may be configured to connect the housing coolant passage and the turbine coolant passage to each other in series during execution of the heating of the link chamber by the heating unit. The electronic control unit may be configured to connect the housing coolant passage and the turbine coolant passage to each other in parallel during the stopping of the heating of the link chamber by the heating unit. 
         [0021]    According to the engine system described above, only the water that is increased in temperature through the turbine coolant passage flows into the housing coolant passage via the communication passage during the execution of the heating by the heating unit. Accordingly, the link chamber can be efficiently heated by using the high-temperature water. When the heating by the heating unit is stopped, the water that is increased in temperature through the turbine coolant passage does not flow into the housing coolant passage and it is possible to allow only the water that has a relatively low temperature in the introduction path without passing through the turbine coolant passage to flow into the housing coolant passage. Accordingly, the temperature of the center housing can be lowered. 
         [0022]    In the engine system described above, the electronic control unit may be configured to prohibit the heating of the link chamber when a temperature of the exhaust gas of the internal combustion engine is at least a predetermined temperature during the execution of the fuel addition by the fuel addition device. 
         [0023]    When the temperature of the exhaust gas of the internal combustion engine is high, both the temperature of the turbocharger and the temperature in the link chamber are likely to be increased. The fuel that has permeated into the link chamber is vaporized and the link chamber can have a dry state therein, even if the heating by the heating unit is not performed, if the temperature in the link chamber is sufficiently increased by heat received from the exhaust gas of the internal combustion engine. Accordingly, the alteration of the fuel to the deposit is suppressed. 
         [0024]    According to the engine system described above, unnecessary execution of the heating by the heating unit can be suppressed when the accumulation of the deposit in the link chamber is suppressed with the temperature in the link chamber being sufficiently increased. Accordingly, deterioration in the reliability of the turbocharger attributable to overheating can be suppressed. 
         [0025]    According to a second aspect of the invention, there is provided a control apparatus for an engine system, the engine system including a turbocharger, an exhaust gas control apparatus, a fuel addition device, and a heating unit. The turbocharger includes a variable nozzle mechanism. The variable nozzle mechanism includes a plurality of nozzle vanes, a link chamber, and a link mechanism. The plurality of nozzle vanes is disposed in an exhaust flow path of an exhaust turbine. The link chamber is adjacent to the exhaust flow path. The link mechanism is disposed in the link chamber and is configured to connect the plurality of nozzle vanes. The exhaust gas control apparatus is disposed on an exhaust downstream side of the exhaust turbine in an exhaust passage of an internal combustion engine, and the exhaust gas control apparatus is configured to purify exhaust gas. The fuel addition device is disposed on an exhaust upstream side of the exhaust turbine, and the fuel addition device is configured to add fuel to the exhaust gas of the internal combustion engine to recover a function of the exhaust gas control apparatus. The heating unit is configured to heat the link chamber. The control apparatus includes an electronic control unit configured to execute a heating control. In the heating control, the electronic unit is configured to initiate and stop heating of the link chamber by the heating unit, and the electronic control unit is configure d to execute the heating control in a period overlapping with at least part of a period when an addition of fuel by the fuel addition device is executed. 
         [0026]    According to a third aspect of the invention, there is provided a control method for an engine system. The engine system includes a turbocharger, an exhaust gas control apparatus, a fuel addition device and a heating unit. The turbocharger includes a variable nozzle mechanism. The variable nozzle mechanism includes a plurality of nozzle vanes, a link chamber, and a link mechanism. The plurality of nozzle vanes is disposed in an exhaust flow path of an exhaust turbine. The link chamber is adjacent to the exhaust flow path. The link mechanism is disposed in the link chamber and is configured to connect the plurality of nozzle vanes. The exhaust gas control apparatus is disposed on an exhaust downstream side of the exhaust turbine in an exhaust passage of an internal combustion engine, and the exhaust gas control apparatus is configured to purify exhaust gas. The fuel addition device is disposed on an exhaust upstream side of the exhaust turbine, and the fuel addition device is configured to add fuel to the exhaust gas of the internal combustion engine to recover a function of the exhaust gas control apparatus. The heating unit is configured to heat the link chamber. The control method includes executing heating control for controlling the initiation and the stopping of heating of the link chamber by the heating unit, and executing the heating control in a period overlapping with at least part of a period when an addition of the fuel by fuel addition device is executed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
           [0028]      FIG. 1  is a schematic diagram illustrating a schematic configuration of a control apparatus for an engine system according to an embodiment; 
           [0029]      FIG. 2  is a cross-sectional view of a turbocharger according to the embodiment; 
           [0030]      FIG. 3A  is a cross-sectional view of a variable nozzle mechanism according to the embodiment; 
           [0031]      FIG. 3B  is a side view of the variable nozzle mechanism according to the embodiment; 
           [0032]      FIG. 4  is an enlarged cross-sectional view of the variable nozzle mechanism of the turbocharger according to the embodiment and a part in the vicinity thereof; 
           [0033]      FIG. 5  is a schematic diagram illustrating an engine cooling system and a coolant circuit of a turbo cooling system according to the embodiment; 
           [0034]      FIG. 6  is a schematic diagram illustrating a flow passage of a coolant in a first flow aspect in a turbo cooling system according to the embodiment; 
           [0035]      FIG. 7  is a schematic diagram illustrating the flow passage of the coolant in a second flow aspect in the turbo cooling system according to the embodiment; 
           [0036]      FIG. 8  is a flowchart illustrating an execution procedure of heating control processing according to the embodiment; 
           [0037]      FIG. 9  is a timing chart illustrating a first example of an execution aspect of the heating control processing; 
           [0038]      FIG. 10  is a timing chart illustrating a second example of the execution aspect of the heating control processing; 
           [0039]      FIG. 11  is a timing chart illustrating a third example of the execution aspect of the heating control processing; 
           [0040]      FIG. 12  is a timing chart illustrating a fourth example of the execution aspect of the heating control processing; 
           [0041]      FIG. 13  is a timing chart illustrating a fifth example of the execution aspect of the heating control processing; and 
           [0042]      FIG. 14  is a schematic diagram illustrating a coolant circuit of a turbo cooling system according to a modification example. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0043]    Hereinafter, an embodiment of a control apparatus for an engine system will be described. As illustrated in  FIG. 1 , an internal combustion engine  11  is provided with an intake passage  12 , combustion chambers  13 , and an exhaust passage  14 . An air cleaner  15  is disposed in the most upstream portion of the intake passage  12 . The air cleaner  15  purifies air suctioned into the intake passage  12 . In the intake passage  12 , a compressor  17  of a turbocharger  16 , an intercooler  18 , and an intake throttle valve  19  are arranged in order from the air cleaner  15  toward the intake downstream side. The intake passage  12  branches at an intake manifold  21  that is disposed on the intake downstream side of the intake throttle valve  19 . The intake passage  12  is connected to the combustion chambers  13  for respective cylinders of the internal combustion engine  11  through branch parts in the intake manifold  21 . 
         [0044]    In the internal combustion engine  11 , fuel injection valves  22  are disposed for the respective cylinders. The fuel injection valves  22  inject fuels that are used for combustion in the respective combustion chambers  13 . A common rail  23  that accumulates a high-pressure fuel is connected to the respective fuel injection valves  22 . The high-pressure fuel that is discharged from a fuel pump  24  is supplied to the common rail  23 . 
         [0045]    Parts of the exhaust passage  14  that are connected to the respective combustion chambers  13  are exhaust ports  25 . An exhaust manifold  26  and an exhaust turbine  27  of the turbocharger  16  are disposed in the exhaust passage  14 . Exhaust gases discharged through the exhaust ports  25  from the respective combustion chambers  13  are collected in the exhaust manifold  26 . 
         [0046]    In the internal combustion engine  11 , the air that is suctioned into the intake passage  12  is purified by the air cleaner  15  and then is introduced into the compressor  17  of the turbocharger  16 . The compressor  17  has a compressor wheel  17 A that rotates in the compressor  17 . The air that is introduced into the compressor  17  is compressed by the rotation of the compressor wheel  17 A and is discharged to the intercooler  18 . The air, the temperature of which is increased by the compression, is cooled by the intercooler  18  and then is distributed and supplied to the combustion chambers  13  for the respective cylinders via the intake throttle valve  19  and the intake manifold  21 . The flow rate of the air in the intake passage  12  is adjusted through opening control for the intake throttle valve  19 . 
         [0047]    In the combustion chambers  13  into which the air is introduced, the fuels are injected from the fuel injection valves  22  during the compression strokes of the respective cylinders. The air-fuel mixture of the air introduced through the intake passage  12  and the fuels injected from the fuel injection valves  22  is combusted in the combustion chambers  13 . A piston (not illustrated) reciprocates by using a high-temperature and high-pressure combustion gas that is generated in this case. A crankshaft  20 , which is an output shaft, rotates and a driving force (output torque) of the internal combustion engine  11  is obtained as a result of the reciprocation of the piston. 
         [0048]    The exhaust gases that are generated by the combustion in the respective combustion chambers  13  are introduced into the exhaust turbine  27  of the turbocharger  16  through the exhaust manifold  26 . A turbine wheel  27 A in the exhaust turbine  27  is driven to rotate by the flow force of the introduced exhaust gases. The compressor wheel  17 A of the compressor  17  is disposed in the intake passage  12 . The compressor wheel  17 A is driven to rotate in conjunction with the rotation of the turbine wheel  27 A, and the compression of the air described above is performed. 
         [0049]    The turbocharger  16  is provided with a variable nozzle mechanism  34  for adjusting the flow speed of the exhaust gas that is sprayed to the turbine wheel  27 A. Hereinafter, a specific configuration of the turbocharger  16  will be described. 
         [0050]    As illustrated in  FIG. 2 , a rotor shaft  36  is supported, to be rotatable about an axis  37  of the rotor shaft  36 , in a center housing  35  of the turbocharger  16 . The compressor wheel  17 A is attached to an end portion of the rotor shaft  36 . The turbine wheel  27 A is attached to the end portion of the rotor shaft  36  that is on the side opposite to the end portion to which the compressor wheel  17 A is attached. A compressor housing  38  of the compressor  17  is attached to one end portion of the center housing  35  in a direction along the axis  37  of the rotor shaft  36  (axial direction) and a turbine housing  39  of the exhaust turbine  27  is attached to the other end portion. In this manner, the compressor  17  and the exhaust turbine  27  are connected by the center housing  35  in the turbocharger  16 . 
         [0051]    An intake inlet  41  is open on the axis  37  in the compressor housing  38 . A compressor vortex chamber  42  is disposed around the compressor wheel  17 A in the compressor housing  38 . The compressor vortex chamber  42  spirally extends and communicates with the intake passage  12  (refer to  FIG. 1 ). Accordingly, in the compressor housing  38 , air is forced to be sent out to the intake passage  12  through the intake inlet  41  and then the compressor vortex chamber  42  when the compressor wheel  17 A rotates about the axis  37  based on the rotation of the rotor shaft  36 . 
         [0052]    In the turbine housing  39 , a spirally-extending turbine vortex chamber  44  is disposed around the turbine wheel  27 A. The turbine vortex chamber  44  communicates with the exhaust passage  14  (refer to  FIG. 1 ) of the internal combustion engine  11 , and the exhaust gas of the internal combustion engine  11  is fed into the turbine vortex chamber  44  through the exhaust passage  14 . This exhaust gas is sprayed to the turbine wheel  27 A from an inner circumferential portion  44 A, which is an outlet of the turbine vortex chamber  44 . This spraying causes the turbine wheel  27 A to rotate about the axis  37 . An exhaust gas outlet  46  is open on the axis  37  in the turbine housing  39 . The exhaust gas sprayed to the turbine wheel  27 A is sent out to the exhaust downstream side of the exhaust passage  14  through the exhaust gas outlet  46 . 
         [0053]    Next, the variable nozzle mechanism  34  will be described in detail. As illustrated in any one of  FIGS. 3A, 3B, and 4 , the variable nozzle mechanism  34  is provided with a nozzle ring  47 , which is fixed in a state of facing the inner circumferential portion  44 A of the turbine vortex chamber  44  between the center housing  35  and the turbine housing  39 . In the nozzle ring  47 , a plurality of shafts  48  are equiangularly disposed about the center of the circle of the nozzle ring  47 . Each of the shafts  48  is pivotably supported while penetrating the nozzle ring  47  in the thickness direction of the nozzle ring  47 . Nozzle vanes  49  are fixed as variable nozzles in end portions of the respective shafts  48  on the turbine vortex chamber  44  side. 
         [0054]    The variable nozzle mechanism  34  is provided with a link mechanism  51  for synchronized pivoting of the plurality of nozzle vanes  49 . A link chamber  52  is formed on the side (left side in  FIG. 4 ) opposite to the inner circumferential portion  44 A of the turbine vortex chamber  44  across the nozzle ring  47 . The link mechanism  51  is incorporated into the link chamber  52 . 
         [0055]    The link mechanism  51  will be described in detail. A nozzle arm  53  is orthogonal to the shaft  48  and extends toward an outer edge portion of the nozzle ring  47 . The nozzle arm  53  is fixed to the end portion (left end portion in  FIG. 4 ) of each of the shafts  48  on the side opposite to the turbine vortex chamber  44 . A bifurcating pair of pinching portions  53 A is formed at a tip of the nozzle arm  53 . 
         [0056]    A unison ring  54  is pivotably disposed coaxially with the nozzle ring  47  between the nozzle arm  53  and the nozzle ring  47 . In the unison ring  54 , a plurality of pins  55  are equiangularly disposed about the center of the circle of the unison ring  54 . The pin  55  is pinched by both of the pinching portions  53 A of each of the nozzle arms  53 . In this manner, the plurality of nozzle vanes  49  and the unison ring  54  are connected to each other by the shafts  48  of the respective nozzle vanes  49 , the nozzle arms  53 , and the like. 
         [0057]    When the unison ring  54  pivots about the center of the circle of the unison ring  54 , the pins  55  push the pinching portions  53 A of the respective nozzle arms  53  in the pivoting direction of the unison ring  54 . As a result, the nozzle arms  53  cause the shafts  48  to pivot. As a result of the pivoting of the shafts  48 , the nozzle vanes  49  are subjected to opening and closing operations in a state of being synchronized about the respective shafts  48 . 
         [0058]    In the turbocharger  16 , a drive mechanism for the pivoting of the unison ring  54  is disposed so as to operate the link mechanism  51 . Specifically, a pin  56  is disposed in an outer edge portion of the unison ring  54  (lower end portion of the unison ring  54  in  FIG. 4 ) and a support shaft  57  is pivotably inserted into the center housing  35 . A connecting member  58  is fixed to an end portion of the support shaft  57  on the link chamber  52  side (right side in  FIG. 4 ) and a lever  59  is fixed to the end portion on the opposite side. The connecting member  58  is pivotably connected to the pin  56 . An actuator  61  such as an electric motor is connected to the lever  59 . 
         [0059]    When the actuator  61  is driven, the lever  59  is operated, and the support shaft  57  pivots, the connecting member  58  pivots about the support shaft  57  as a result of the pivoting of the support shaft  57 . As a result, the unison ring  54  is pushed in a circumferential direction via the pin  56  by the connecting member  58  and pivots about the axis  37 . As the unison ring  54  pivots, the gaps between the adjacent nozzle vanes  49  have a size corresponding to the pivot angle (nozzle opening) of each of the nozzle vanes  49 . In this manner, the flow speed of the exhaust gas that is sprayed to the turbine wheel  27 A is adjusted through the gap. 
         [0060]    Since the flow speed of the exhaust gas is regulated as described above, the rotation speeds of the turbine wheel  27 A, the rotor shaft  36 , and the compressor wheel  17 A are appropriately regulated and a supercharging pressure is adjusted. When the adjustment of the supercharging pressure is performed, the output of the internal combustion engine  11  can be improved and an overpressure in the combustion chambers  13  can be prevented at the same time. 
         [0061]    As illustrated in  FIG. 2 , the turbocharger  16  is provided with a turbine coolant passage  39 A and a housing coolant passage  35 A. The turbine coolant passage  39 A is formed in the turbine housing  39  as a coolant passage through which a coolant for the internal combustion engine  11  circulates. The housing coolant passage  35 A is formed in the center housing  35 . The turbocharger  16  has a structure in which the turbine housing  39  and the center housing  35  are cooled as the coolant for the internal combustion engine  11  is supplied to the turbine coolant passage  39 A and the housing coolant passage  35 A. 
         [0062]    As illustrated in  FIG. 5 , an engine cooling system for cooling the internal combustion engine  11  is provided with a water jacket  63  that is formed in the internal combustion engine  11  and a radiator  64  that is a heat exchanger. The engine cooling system is provided with an engine coolant conduit  65  that guides the coolant flowing out of the water jacket  63  to the radiator  64  and an engine coolant conduit  66  that returns the coolant flowing out of the radiator  64  to the water jacket  63 . In addition, a water pump  67  that pumps the coolant in the engine cooling system is disposed in the engine cooling system. 
         [0063]    A turbo cooling system for cooling the turbocharger  16  is provided with a turbo supply coolant passage  68 . The turbo supply coolant passage  68  is a coolant passage that guides the coolant to the turbocharger  16 . The turbo supply coolant passage  68  is branched and extends from the water jacket  63 . In addition, a first supply coolant passage  69  and a second supply coolant passage  71  are disposed in the turbo cooling system. The first supply coolant passage  69  guides the coolant in the turbo supply coolant passage  68  to the turbine coolant passage  39 A. The second supply coolant passage  71  guides the coolant in the turbo supply coolant passage  68  to the housing coolant passage  35 A. In this embodiment, the turbo supply coolant passage  68 , the first supply coolant passage  69 , and the second supply coolant passage  71  correspond to introduction paths that connect an inlet of the turbine coolant passage  39 A and an inlet of the housing coolant passage  35 A to each other in parallel. 
         [0064]    The turbo cooling system is provided with a turbo discharge coolant passage  72 . The turbo discharge coolant passage  72  is a coolant passage that guides the coolant discharged from the turbocharger  16  to the radiator  64  and merges with the engine coolant conduit  65 . In addition, the turbo cooling system is provided with a first discharge coolant passage  73  and a second discharge coolant passage  74 . The first discharge coolant passage  73  guides the coolant that is discharged from the turbine coolant passage  39 A to the turbo discharge coolant passage  72 . The second discharge coolant passage  74  guides the coolant that is discharged from the housing coolant passage  35 A to the turbo discharge coolant passage  72 . In this embodiment, the turbo discharge coolant passage  72 , the first discharge coolant passage  73 , and the second discharge coolant passage  74  correspond to discharge paths that connect an outlet of the turbine coolant passage  39 A and an outlet of the housing coolant passage  35 A to each other in parallel. 
         [0065]    The turbo cooling system is provided with a communication passage  75  that allows the outlet of the turbine coolant passage  39 A (specifically, the first discharge coolant passage  73 ) and the inlet of the housing coolant passage  35 A (specifically, the second supply coolant passage  71 ) to communicate with each other. A first flow path switching valve  76  is disposed at a branch part of the communication passage  75  and the first discharge coolant passage  73 . A second flow path switching valve  77  is disposed in the middle of the second supply coolant passage  71 . In the turbo cooling system, the flow aspect of the coolant can be switched into any one of two flow aspects (first flow aspect and second flow aspect) through operation control for the first flow path switching valve  76  and the second flow path switching valve  77 . 
         [0066]    As illustrated in  FIG. 6 , the housing coolant passage  35 A and the turbine coolant passage  39 A are connected in parallel in the first flow aspect. The arrows in  FIG. 6  illustrate the flow of the coolant. In the state of the first flow aspect, the operation of the first flow path switching valve  76  is controlled, the turbine coolant passage  39 A and the turbo discharge coolant passage  72  communicate with each other through the first discharge coolant passage  73 , and communication between the turbine coolant passage  39 A and the housing coolant passage  35 A by the communication passage  75  is blocked. In addition, in the state of the first flow aspect, the operation of the second flow path switching valve  77  is controlled and the turbo supply coolant passage  68  and the housing coolant passage  35 A communicate with each other through the second supply coolant passage  71 . 
         [0067]    As illustrated in  FIG. 7 , the housing coolant passage  35 A and the turbine coolant passage  39 A are connected in series in the second flow aspect. The arrows in  FIG. 7  illustrate the flow of the coolant. In the state of the second flow aspect, the operation of the first flow path switching valve  76  is controlled, communication between the turbine coolant passage  39 A and the turbo discharge coolant passage  72  through the first discharge coolant passage  73  is blocked, and the turbine coolant passage  39 A and the housing coolant passage  35 A communicate with each other through the communication passage  75 . In addition, in the state of the second flow aspect, the operation of the second flow path switching valve  77  is controlled and communication between the turbo supply coolant passage  68  and the housing coolant passage  35 A through the second supply coolant passage  71  is blocked. 
         [0068]    As illustrated in  FIG. 1 , an exhaust gas control apparatus  81  for purifying exhaust gas is disposed in the exhaust passage  14  of the internal combustion engine  11 . The exhaust gas control apparatus  81  is provided with a fuel addition valve  82  for adding a fuel to the exhaust gas. The exhaust gas control apparatus  81  is provided with an oxidation catalyst  83  that oxidizes hydrocarbon (HC) in the exhaust gas and a filter  84  that collects particulate matter (PM) in the exhaust gas. 
         [0069]    The oxidation catalyst  83  is disposed on the exhaust downstream side of the exhaust turbine  27  in the exhaust passage  14 . The oxidation catalyst  83  is a catalyst that purifies the exhaust gas through the oxidation of the HC and carbon monoxide (CO) in the exhaust gas. The filter  84  is disposed on a further exhaust downstream side than the oxidation catalyst  83  in the exhaust passage  14 . A porous material that allows the passage of a gas component in the exhaust gas and prevents the passage of the PM in the exhaust gas constitutes the filter  84 . In the filter  84 , a catalyst for promoting the oxidation of the PM is supported. The fuel addition valve  82  is disposed on a further exhaust upstream side (specifically, the exhaust manifold  26 ) than the exhaust turbine  27  in the exhaust passage  14 . The fuel addition valve  82  is connected to the fuel pump  24  through a fuel passage  82 A. The fuel addition valve  82  injects (adds) a fuel provided from the fuel pump  24  into the exhaust gas. 
         [0070]    Various sensors for detecting operating conditions of the internal combustion engine  11  are disposed in the engine system, the main component of which is the internal combustion engine  11 . Examples of the various sensors include a crank sensor  91 , a water temperature sensor  92 , and a differential pressure sensor  93 . The crank sensor  91  detects the rotation speed (engine rotation speed NE) of the crankshaft  20 . The water temperature sensor  92  detects the temperature of the coolant (coolant temperature THW) for the internal combustion engine  11 . The differential pressure sensor  93  detects the exhaust gas pressure difference (pressure difference ΔP) between the exhaust upstream side and the exhaust downstream side of the filter  84  in the exhaust passage  14 . 
         [0071]    The engine system is provided with an electronic control unit  90 , the main component of which is, for example, a microcomputer. Output signals from the various sensors are incorporated into the electronic control unit  90 . The electronic control unit  90  performs various types of computation based on the output signals from the various sensors, and executes various types of control regarding the operation of the internal combustion engine  11  based on the results of the computation. Examples of the various types of control include operation control for the fuel injection valves  22 , operation control for the intake throttle valve  19 , operation control for the fuel pump  24 , and operation control for the variable nozzle mechanism  34  (specifically, the actuator  61 ). 
         [0072]    The electronic control unit  90  executes operation control for the fuel addition valve  82  (PM regeneration control) for functional recovery of the filter  84  as one of the various types of control. During the PM regeneration control, the electronic control unit  90  drives the fuel addition valve  82  to be intermittently opened. In this manner, the fuel is added to the exhaust gas of the internal combustion engine  11 . As the PM regeneration control is executed, the added fuel is oxidized in the exhaust gas and the filter  84 . Then, the temperature of the filter  84  increases. During the PM regeneration control, the intermittent valve-opening driving for the fuel addition valve  82  is repeatedly executed so that the filter  84  is in a predetermined temperature state (for example, at least 600° C.). In this manner, the PM accumulated in the filter  84  is oxidized, turned into carbon dioxide (CO 2 ) and water (H 2 O), and is discharged. In this manner, the PM is oxidized and regenerated in the filter  84 . 
         [0073]    In this embodiment, the execution of the PM regeneration control is controlled in accordance with the execution flag that is described below. In a case where the execution flag is ON, the execution of PM regeneration processing is allowed. In a case where the execution flag is OFF, the execution of PM regeneration control is prohibited. 
         [0074]    The execution flag is turned ON when the following [Condition A] and [Condition B] are satisfied at the same time during the non-execution of the PM regeneration control. 
         [0075]    [Condition A] PM accumulation amount PMsm reaching at least a pre-defined accumulation amount determination value A 
         [0076]    [Condition B] Coolant temperature THW reaching at least a water temperature determination value B 
         [0077]    The PM accumulation amount PMsm is an estimated value of the amount of the PM that is collected by the filter  84  and accumulated. The PM accumulation amount PMsm is sequentially calculated by using a known method based on the operating conditions of the internal combustion engine  11  such as the pressure difference ΔP. 
         [0078]    When the [Condition A] and the [Condition B] are satisfied at the same time, it is determined that the PM accumulation amount PMsm has reached an amount requiring the execution of the PM regeneration control and the temperature of the internal combustion engine  11  is high enough to sufficiently increase the temperature of the exhaust gas through the execution of the PM regeneration control. In this case, the execution flag for the PM regeneration control is turned ON and the execution of the PM regeneration processing is allowed. When the [Condition A] is not satisfied, the PM accumulation amount PMsm is below the amount requiring the regeneration processing. In this case, the execution flag is not turned ON and the execution of the PM regeneration control is not allowed. When the [Condition B] is not satisfied, the temperature of the internal combustion engine  11  is low and the temperature of the exhaust gas cannot be sufficiently increased even if the PM regeneration processing is performed. In this case, the execution flag is not turned ON and the execution of the PM regeneration processing is not allowed. 
         [0079]    In this embodiment, the amount of the PM collected by the filter  84  and accumulated is considered to be sufficiently decreased when the following [Condition C] is satisfied during the execution of the PM regeneration control. In this case, the execution flag is turned OFF. As the execution flag is turned OFF, the execution of the PM regeneration control is stopped. 
         [0080]    [Condition C] PM accumulation amount PMsm becoming equal to or less than a predetermined regeneration termination value PMe 
         [0081]    In the turbocharger  16 , a gap  62  ( FIG. 4 ) is present in a partition wall between the inner circumferential portion  44 A of the turbine vortex chamber  44  as an exhaust flow path and the link chamber  52  (specifically, between the turbine housing  39  and the nozzle ring  47 ). Accordingly, if the pressure of the exhaust gas in the turbine vortex chamber  44  is high, part of the exhaust gas may permeate into the link chamber  52  through the gap  62  while moving from the turbine vortex chamber  44  toward the turbine wheel  27 A. The fuel that is added from the fuel addition valve  82  is insufficiently vaporized if the temperature of the exhaust gas is low or causes aggregation on the surface of the turbine housing  39  if the temperature of the turbine housing  39  is low. If the insufficiently-vaporized fuel and the aggregated fuel (hereinafter, these fuels will be referred to as a liquid fuel) move along with the exhaust gas into the link chamber  52  through the gap  62  from the turbine vortex chamber  44 , the liquid fuel may adhere to the wall surface of the link chamber  52  and each portion of the link mechanism  51 . In a case where the temperature in the link chamber  52  is low, the fuel that adheres to the link mechanism  51  may remain in a liquid state as it is instead of being vaporized immediately. If the state where the liquid fuel adheres to the link mechanism  51  continues, soot in the exhaust gas may adhere to the adhering fuel or the fuel may be gradually altered to give rise to a deposit. 
         [0082]    In this embodiment, the link chamber  52  is heated when the PM regeneration control is executed. Hereinafter, processing regarding the control for heating the link chamber  52  (heating control processing) will be described. 
         [0083]      FIG. 8  illustrates an execution procedure of the heating control processing. A series of processing that is illustrated in the flowchart in this drawing is executed by the electronic control unit  90  as interruption processing for each predetermined cycle. In this processing, as illustrated in  FIG. 8 , it is determined first whether or not the execution flag for the PM regeneration control is ON state (Step S 11 ). 
         [0084]    In a case where the execution flag is ON state (Step S 11 : YES), the operations of the first flow path switching valve  76  and the second flow path switching valve  77  are controlled and the flow aspect of the coolant becomes the second flow aspect (Step S 12 ). Since the turbine coolant passage  39 A (refer to  FIG. 7 ) and the housing coolant passage  35 A are connected in series in the second flow aspect, the coolant that is increased in temperature through the turbine coolant passage  39 A in the exhaust turbine  27  flows into the housing coolant passage  35 A in the center housing  35 . The center housing  35  and the link chamber  52 , which is arranged at a position adjacent to the center housing  35 , are heated by the high-temperature coolant introduced into the housing coolant passage  35 A in this manner. 
         [0085]    In a case where the execution flag is OFF state (Step S 11 : NO), the operations of the first flow path switching valve  76  and the second flow path switching valve  77  are controlled and the flow aspect of the coolant becomes the first flow aspect (Step S 13 ). Since the turbine coolant passage  39 A (refer to  FIG. 6 ) and the housing coolant passage  35 A are connected in parallel in the first flow aspect, the coolant that has a relatively low temperature in the turbo supply coolant passage  68  flows into each of the turbine coolant passage  39 A and the housing coolant passage  35 A. In this case, the flow of the high-temperature coolant, which passed through the turbine coolant passage  39 A, into the housing coolant passage  35 A is stopped, and thus the heating of the center housing  35  and the link chamber  52  by the coolant is also stopped. 
         [0086]    Hereinafter, an effect of the execution of the heating control processing will be described. In the turbocharger  16 , the liquid fuel adheres into the link chamber  52 , and the adhering fuel may be gradually altered to give rise to the deposit if the state where the fuel adheres continues. Accordingly, the liquefaction of the fuel permeating into the link chamber  52  can be suppressed by sufficiently increasing the temperature in the link chamber  52 . In this manner, the adhesion of the fuel into the link chamber  52  is suppressed, and thus the accumulation of the deposit can also be suppressed. As a result of various experiments by the inventor, it has been found that the adhesion of the liquid fuel in the link chamber  52  rarely occurs and the accumulation of the deposit is appropriately suppressed, even in a case where the fuel has permeated into the link chamber  52 , once the fuel in the link chamber  52  is vaporized by sufficiently increasing the temperature in the link chamber  52 . Still, maintaining a high-temperature state of the turbocharger  16  by heating the turbocharger  16  without stopping the heating may result in overheating deteriorating the reliability of the turbocharger  16 . 
         [0087]    In this embodiment, the link chamber  52  can be heated therein for a high temperature, by the high-temperature coolant that passed through the turbine coolant passage  39 A, during the execution of the PM regeneration control. Accordingly, even in a case where the fuel has permeated into the link chamber  52 , the fuel can be vaporized and the link chamber  52  can have a dry state therein. Since the exhaust gas of the internal combustion engine  11  flows at a high speed in the turbine vortex chamber  44 , the exhaust gas in the link chamber  52  is discharged out of the link chamber  52  through the gap  62  ( FIG. 4 ) in the partition wall between the inner circumferential portion  44 A of the turbine vortex chamber  44  and the link chamber  52 . Accordingly, the fuel vaporized in the link chamber  52  is also discharged out of the link chamber  52  into the turbine vortex chamber  44  along with the flow of the exhaust gas. In this manner, the fuel that has permeated into the link chamber  52  is discharged to the turbine vortex chamber  44  and treated and a state where the liquid fuel adheres into the link chamber  52  is suppressed, and thus the alteration of the fuel to the deposit can be suppressed. Accordingly, malfunctioning of the variable nozzle mechanism  34  attributable to the accumulation of the deposit can be suppressed. 
         [0088]    In addition, the heating of the link chamber  52  can be stopped when the possibility of the permeation of the fuel into the link chamber  52  is low with the PM regeneration control not executed. In this case, the temperature of the turbocharger  16  can be lowered. Compared to heating the turbocharger  16  without stopping the heating, an increase in the temperature of the turbocharger  16  can be suppressed. In this manner, deterioration in the reliability of the turbocharger  16  attributable to overheating can be suppressed. 
         [0089]    In this embodiment, the center housing  35  and the link chamber  52  are heated by using the housing coolant passage  35 A, which is disposed so as to cool the center housing  35 . Accordingly, a structure for heating the center housing  35  and the link chamber  52  can be realized without adding complexity to the structure of the turbocharger  16 . 
         [0090]    In this embodiment, the housing coolant passage  35 A and the turbine coolant passage  39 A are connected in series (refer to  FIG. 7 ) when the flow aspect of the coolant becomes the second flow aspect through the operation control for the first flow path switching valve  76  and the second flow path switching valve  77  during the execution of the heating of the link chamber  52 . Then, it is possible to allow only the coolant that is increased in temperature through the turbine coolant passage  39 A to flow into the housing coolant passage  35 A, and thus the link chamber  52  can be efficiently heated by using the coolant. When the heating of the link chamber  52  is stopped, the flow aspect of the coolant becomes the first flow aspect through the operation control for the first flow path switching valve  76  and the second flow path switching valve  77 , and the housing coolant passage  35 A and the turbine coolant passage  39 A are connected in parallel (refer to  FIG. 6 ). Accordingly, it is possible to allow only the coolant that has a relatively low temperature without passing through the turbine coolant passage  39 A to flow into the housing coolant passage  35 A instead of allowing the coolant that is increased in temperature through the turbine coolant passage  39 A to flow into the housing coolant passage  35 A. Then, the center housing  35  can be appropriately cooled by using the coolant. 
         [0091]    According to the embodiment described above, the following effects can be achieved. Even in a case where the fuel has permeated into the link chamber  52  with the PM regeneration control executed, the alteration of the fuel into the deposit can be suppressed. The turbocharger  16  is temporarily heated so that the accumulation of the deposit in the link chamber  52  is suppressed. Compared to heating the turbocharger  16  without stopping the heating, an increase in the temperature of the turbocharger  16  can be suppressed, and deterioration in the reliability of the turbocharger  16  attributable to overheating can be suppressed. 
         [0092]    According to this embodiment, the center housing  35  and the link chamber  52  can be heated by using the housing coolant passage  35 A, which is disposed so as to cool the center housing  35 . Accordingly, a structure for heating the center housing  35  and the link chamber  52  can be realized without adding complexity to the structure of the turbocharger  16 . 
         [0093]    This embodiment is provided with the communication passage  75  that allows the outlet of the turbine coolant passage  39 A and the inlet of the housing coolant passage  35 A to communicate with each other and the first flow path switching valve  76  that is disposed in the communication passage  75 . In addition, according to this embodiment, the heating of the link chamber  52  is executed by allowing the flow of water from the outlet of the turbine coolant passage  39 A into the inlet of the housing coolant passage  35 A via the communication passage  75  through the operation control for the first flow path switching valve  76 . Accordingly, it is possible to allow the coolant that is increased in temperature through the turbine coolant passage  39 A to be introduced into the housing coolant passage  35 A in the center housing  35  via the communication passage  75 . In this manner, the link chamber  52 , which is arranged at a position adjacent to the center housing  35 , can be heated. 
         [0094]    According to this embodiment, the heating of the link chamber  52  is stopped by prohibiting the flow of the coolant from the outlet of the turbine coolant passage  39 A into the inlet of the housing coolant passage  35 A via the communication passage  75  through the operation control for the first flow path switching valve  76 . Accordingly, it is possible to prohibit the flow of the coolant that is increased in temperature through the turbine coolant passage  39 A into the housing coolant passage  35 A while allowing only the coolant that has a relatively low temperature in the second supply coolant passage  71  to flow into the housing coolant passage  35 A. Accordingly, a state where the heating of the link chamber  52  is stopped can be achieved. 
         [0095]    According to this embodiment, the housing coolant passage  35 A and the turbine coolant passage  39 A are connected in series during the execution of the heating of the link chamber  52 . Accordingly, the link chamber  52  can be efficiently heated by using the coolant that is increased in temperature through the turbine coolant passage  39 A. In addition, when the heating of the link chamber  52  is stopped, the housing coolant passage  35 A and the turbine coolant passage  39 A are connected in parallel, and thus the center housing  35  can be appropriately cooled by using the coolant that has a relatively low temperature without passing through the turbine coolant passage  39 A. 
         [0096]    The embodiment described above may be modified as follows. A period when the flow aspect of the coolant is switched into the second flow aspect (refer to  FIG. 7 ) so as to heat the link chamber  52  may overlap with at least part of a period when the PM regeneration control is executed. The timing of the initiation of the execution of the PM regeneration control and the timing of the switching into the second flow aspect may be the same as the timing of the ON operation of the execution flag. The timing of the initiation of the execution of the PM regeneration control and the timing of the switching into the second flow aspect may be a short period of time after the ON operation of the execution flag. The timing of the stopping of the execution of the PM regeneration control and the timing of the switching into the first flow aspect may be the same as the timing of the OFF operation of the execution flag. The timing of the stopping of the execution of the PM regeneration control and the timing of the switching into the first flow aspect may be a short period of time after the OFF operation of the execution flag. Hereinafter, examples of the setting of the respective periods (Examples 1 to 5) will be described. 
       Example 1 
       [0097]    As illustrated in  FIG. 9 , the execution of the PM regeneration control is initiated and the switching into the second flow aspect is executed at the same time at time t 11 . Then, at time t 12 , the execution of the PM regeneration control is stopped and the switching into the first flow aspect is executed at the same time. 
       Example 2 
       [0098]    The switching into the second flow aspect is executed prior to the initiation of the execution of the PM regeneration control. For example, as illustrated in  FIG. 10 , the switching into the second flow aspect is executed at time t 21 , and the execution of the PM regeneration control is initiated at time t 22 , which is a short period of time after time t 21 . 
         [0099]    If the timing of the initiation of the heating of the link chamber  52  precedes the timing of the initiation of the fuel addition by the PM regeneration control as in this example, the temperature in the link chamber  52  can be increased in advance when the fuel addition to the exhaust gas by the PM regeneration control is initiated. Accordingly, it is possible to suppress the liquefaction of the fuel permeating into the link chamber  52 , and the adhesion of the deposit to the link mechanism  51  can be suppressed. 
       Example 3 
       [0100]    The switching into the first flow aspect is executed a short period of time after the stopping of the execution of the PM regeneration control. For example, as illustrated in  FIG. 11 , the execution of the PM regeneration control is stopped at time t 31 , and the switching into the first flow aspect is executed at time t 32 , which is a short period of time after time t 31 . 
         [0101]    If the timing of the stopping of the fuel addition by the PM regeneration control precedes the timing of the stopping of the heating of the link chamber  52  as in this example, the temperature in the link chamber  52  can be maintained at a high temperature until the termination of the fuel addition by the PM regeneration control. Accordingly, it is possible to suppress the liquefaction of the fuel permeating into the link chamber  52 , and the adhesion of the deposit to the link mechanism  51  can be suppressed. 
       Example 4 
       [0102]    As illustrated in  FIG. 12 , the execution of the PM regeneration control is initiated at time t 41 , and the switching into the second flow aspect is executed at time t 42 , which is a short period of time after time t 41 . (Example 5) As illustrated in  FIG. 13 , the switching into the first flow aspect is executed at time t 51 , and the execution of the PM regeneration control is stopped at time t 52 , which is a short period of time after time t 51 . 
         [0103]    The arrangement of the flow path switching valves in the turbo cooling system can be changed to any arrangement if the flow aspect of the coolant can be switched into any one of the two flow aspects (first flow aspect and second flow aspect). 
         [0104]    For example, as illustrated in  FIG. 14 , a third flow path switching valve  106  can be disposed at a branch part of the second supply coolant passage  71  and the communication passage  75  and the third flow path switching valve  106  can be disposed in the middle of the first discharge coolant passage  73 . In the state of the first flow aspect of this example, the third flow path switching valve  106  may allow the turbo supply coolant passage  68  and the housing coolant passage  35 A to communicate with each other through the second supply coolant passage  71  and communication between the turbine coolant passage  39 A and the housing coolant passage  35 A by the communication passage  75  may be blocked. In addition, in the state of the first flow aspect, a fourth flow path switching valve  107  may allow the turbine coolant passage  39 A and the turbo discharge coolant passage  72  to communicate with each other through the first discharge coolant passage  73 . In the state of the second flow aspect, the third flow path switching valve  106  may block communication between the housing coolant passage  35 A and the turbo supply coolant passage  68  through the second supply coolant passage  71  and allow the turbine coolant passage  39 A and the housing coolant passage  35 A to communicate with each other through the communication passage  75 . In addition, in the state of the second flow aspect, the fourth flow path switching valve  107  may block communication between the turbine coolant passage  39 A and the turbo discharge coolant passage  72  through the first discharge coolant passage  73 . 
         [0105]    During the execution of the PM regeneration control, the housing coolant passage  35 A and the turbine coolant passage  39 A may not be connected in series if the coolant that is heated in the turbine coolant passage  39 A can be introduced into the housing coolant passage  35 A. For example, a communication passage that connects the middle of the housing coolant passage  35 A to the inlet of the turbine coolant passage  39 A can be disposed and a communication passage that connects the outlet of the housing coolant passage  35 A to the middle of the turbine coolant passage  39 A can be disposed instead of the communication passage  75 . In addition, the second flow path switching valve  77  can be omitted. 
         [0106]    The link chamber  52  may be heated by introducing the coolant at a high-temperature part of the engine cooling system (for example, part extending around the combustion chambers  13 ) into the housing coolant passage  35 A instead of heating the link chamber  52  by introducing the coolant that is heated in the turbine coolant passage  39 A into the housing coolant passage  35 A. Also, the link chamber  52  can be heated by, for example, energizing an electric heater attached to the center housing  35 . 
         [0107]    When the temperature of the exhaust gas of the internal combustion engine  11  is high, both the temperature of the turbocharger  16  and the temperature in the link chamber  52  are likely to be increased. The fuel that has permeated into the link chamber  52  is vaporized and the link chamber  52  can have a dry state therein, even if the link chamber  52  is not heated by using a high-temperature coolant, a heater, or the like, if the temperature in the link chamber  52  is sufficiently increased by heat received from the exhaust gas of the internal combustion engine  11 . Accordingly, the alteration of the fuel to the deposit is suppressed. 
         [0108]    In the engine system, the heating of the link chamber  52  by a high-temperature coolant, a heater, or the like may be prohibited, even when the PM regeneration control is executed, if the temperature of the link chamber  52  is high enough to appropriately suppress the accumulation of the deposit. According to this apparatus, unnecessary execution of heating by a high-temperature coolant, a heater, or the like can be suppressed when the accumulation of the deposit in the link chamber  52  is suppressed so that the temperature in the link chamber  52  is sufficiently increased. Accordingly, deterioration in the reliability of the turbocharger  16  attributable to overheating can be suppressed. Whether the temperature of the link chamber  52  is high enough to appropriately suppress the accumulation of the deposit can be determined based on, for example, “the temperature of the exhaust gas of the internal combustion engine  11  being at least a predetermined temperature”, “the operating condition of the internal combustion engine  11  being in a predetermined high-load operation area”, or “the temperature in the link chamber  52  that is estimated from the operating condition of the internal combustion engine  11  being at least a predetermined temperature”. 
         [0109]    In the embodiment described above, the fuel addition to the exhaust gas is executed so as to oxidize the PM collected by the filter  84 . However, the invention is not limited thereto. The engine system may execute the fuel addition to the exhaust gas for functional recovery of an exhaust gas control apparatus (for example, an exhaust gas purifying catalyst). Examples of the engine system include a system in which fuel addition to exhaust gas is executed so as to emit sulfur dioxide (SOx) from a nitrogen oxide (NOx) storage-reduction catalyst in a case where the NOx storage-reduction catalyst is poisoned by SOx and the storage capacity of NOx is reduced. 
         [0110]    The embodiment described above is not limited to the engine system in which the fuel addition is performed through the fuel injection from the fuel addition valve  82 . The embodiment described above can also be applied to an engine system in which fuel addition to exhaust gas is performed through fuel injection from the fuel injection valves  22  performed during an expansion stroke and an exhaust stroke after fuel injection for combustion in the combustion chambers  13  (so-called after-injection or post-injection).