Patent Publication Number: US-2023133765-A1

Title: Engine controller and engine controlling method

Description:
BACKGROUND 
     1. Field 
     The present disclosure relates to an engine controller and an engine controlling method that control an engine equipped with a turbocharger. 
     2. Description of Related Art 
     In an engine equipped with a turbocharger and a blow-by gas reducing device, blow-by gas flows into the compressor of the turbocharger together with intake air. Oil mist in the blow-by gas may be carbonized and accumulated on the compressor. Japanese Laid-Open Patent Publication No. 2020-128724 discloses a technique that supplies cooling water to a turbocharger when the temperature of intake air flowing out of a compressor is higher than or equal to a certain value of the temperature, thereby reducing carbonization and accumulation of oil mist. 
     A turbocharger contains oil used, for example, to lubricate journals. When the engine is operating, exhaust gas heats the turbocharger so that its internal temperature increases. This carbonizes oil in the turbocharger and the carbonized oil is accumulated, for example, on the wall surfaces of the oil passage and components such as the journals. An increased accumulation of carbonized oil, which is referred to as oil coke, can hinder flow of oil or rotation of the turbine shaft. Accordingly, there is a demand for reduction in accumulation of oil coke in turbochargers. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     In one general aspect, an engine controller configured to control an engine is provided. The engine includes a turbocharger and an electric pump that supplies a cooling water to the turbocharger. The engine controller includes circuitry. The circuitry is configured to vary a flow rate of the cooling water supplied to the turbocharger by the electric pump during operation of the engine, based on a housing temperature, which is a temperature of a turbine housing of the turbocharger, and a generation site temperature, which is a temperature of a generation site of oil coke inside the turbocharger. 
     In the above-described engine controller, the processing device sets the flow rate of the cooling water supplied to the turbocharger by the electric pump during operation of the engine based on the temperature of the turbine housing and the temperature of the generation site of oil coke. This allows the flow rate of the cooling water to be set appropriately taking into consideration a future temperature increase of the generation site due to heat transfer from the turbine housing. Accordingly, the formation and accumulation of oil coke are reduced effectively. 
     In the above-described engine controller, the circuitry is configured to: execute a post-stoppage cooling control by driving the electric pump after the engine is stopped, the post-stoppage cooling control supplying the cooling water to the turbocharger; and vary driving time of the electric pump in the post-stoppage cooling control, based on an engine-stoppage housing temperature, which is the housing temperature when the engine is stopped, and an engine-stoppage generation site temperature, which is the generation site temperature when the engine is stopped. This configuration allows the driving time of the electric pump after stoppage of the engine to be set appropriately taking into consideration heat transfer from the turbine housing after the stoppage of the engine to the generation site. The circuitry may be configured to vary the flow rate of the cooling water supplied to the turbocharger in the post-stoppage cooling control, based on the engine-stoppage housing temperature and the engine-stoppage generation site temperature. 
     In another general aspect, an engine controlling method of controlling an engine is provided. The engine includes a turbocharger and an electric pump that supplies a cooling water to the turbocharger. The engine controlling method includes varying a flow rate of the cooling water supplied to the turbocharger by the electric pump during operation of the engine, based on a housing temperature, which is a temperature of a turbine housing of the turbocharger, and a generation site temperature, which is a temperature of a generation site of oil coke inside the turbocharger. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram showing an engine controller according to one embodiment. 
         FIG.  2    is a flowchart of a mid-operation cooling control routine executed by the engine controller. 
         FIG.  3    is a flowchart of a post-stoppage cooling control routine executed by the engine controller. 
       Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
     
    
    
     DETAILED DESCRIPTION 
     This description provides a comprehensive understanding of the methods, apparatuses, and/or systems described. Modifications and equivalents of the methods, apparatuses, and/or systems described are apparent to one of ordinary skill in the art. Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted. 
     Exemplary embodiments may have different forms, and are not limited to the examples described. However, the examples described are thorough and complete, and convey the full scope of the disclosure to one of ordinary skill in the art. 
     In this specification, “at least one of A and B” should be understood to mean “only A, only B, or both A and B.” 
     An engine controller according to one embodiment will be described with reference to  FIGS.  1  to  3   . The engine controller according to the present embodiment is employed in an engine  10  mounted on a vehicle. 
     Configuration of Engine Controller 
     First, the configuration of the engine controller according to the present embodiment will be described with reference to  FIG.  1   . As shown in  FIG.  1   , the engine  10  is provided with an intake passage  11  and an exhaust passage  12 . The engine  10  is also provided with an oil pump  13 , which is driven by rotation of the engine  10 . 
     The engine  10  is provided with a turbocharger  20 . The turbocharger  20  includes a turbine housing  21 , which is provided on the exhaust passage  12  of the engine  10 , and a compressor housing  22 , which is provided on the intake passage  11  of the engine  10 . The turbine housing  21  and the compressor housing  22  are coupled to each other by a journal housing  23 . The turbine housing  21  incorporates a turbine wheel  24 , which is rotated by receiving flow of exhaust gas flowing through the exhaust passage  12 . The compressor housing  22  incorporates a compressor wheel  25 , which rotates to compress intake air flowing through the intake passage  11 . The journal housing  23  receives a turbine shaft  26 , which couples the turbine wheel  24  and the compressor wheel  25  to each other. The turbine shaft  26  is supported by a floating bearing  27  so as to be rotatable with respect to the journal housing  23 . A seal ring  28  is attached to a section of the turbine shaft  26  that is close to the section coupled to the turbine wheel  24  to restrict inflow of exhaust gas from the turbine housing  21  into the journal housing  23 . 
     An oil passage  29  is formed in the journal housing  23  to cause oil to flow through the floating bearing  27 . The oil passage  29  is supplied with some of the oil discharged by the oil pump  13 . Also, a water jacket  30  is formed in the journal housing  23 . The water jacket  30  is a passage through which cooling water flows. The water jacket  30  is supplied with cooling water by an electric pump  31 , which is located outside the turbocharger  20 . 
     The vehicle in which the engine  10  is mounted is equipped with an engine control module (ECM)  40 . The ECM  40  includes a processing device  41 , which executes various types of processes to control the engine, and a storage  42 , which stores programs and data for controlling the engine. The ECM  40  receives detection signals of state quantities indicating the traveling state of the vehicle, such as a vehicle speed V, an engine rotation speed NE, an accelerator pedal depression amount ACC, a boost pressure PB, an intake air flow rate GA, an intake air temperature THA, and an outside air temperature THO. The ECM  40  also receives an IG signal, which indicates an operating state of an ignition switch  43 . Based on the received signals, the ECM  40  controls, for example, a throttle opening degree TA, a fuel injection amount QINJ, an ignition timing AOP of the engine  10 . 
     During the operation of the engine  10 , the ECM  40  estimates a housing temperature TH1, which is the temperature of the turbine housing  21 , and temperatures of generation sites P 1  to P 3  of oil coke. The generation site P 1  is a section in the oil passage  29  that is close to the seal ring  28 . The generation site P 2  is a section in the oil passage  29  that is close to the floating bearing  27 . The generation site P 3  is an oil drain portion, which is a section of the oil passage  29  that is on the downstream side of the floating bearing  27 . In the following description, the temperature of the generation site P 1  will be referred to as a seal ring temperature TH2, the temperature of the generation site P 2  will be referred to as a bearing temperature TH3, and the temperature of the generation site P 3  will be referred to as an oil drain temperature TH4. 
     The ECM  40  estimates the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4 based on various state quantities that represent the traveling condition of the vehicle. The state quantities used to estimate the temperatures include the vehicle speed V, the engine rotation speed NE, the accelerator pedal depression amount ACC, the fuel injection amount QINJ, the boost pressure PB, the intake air flow rate GA, the intake air temperature THA, and the outside air temperature THO. The temperatures are estimated, for example, by a neural network that has been trained through machine learning. 
     Mid-Operation Cooling Control 
     The ECM  40  performs a mid-operation cooling control to cool the turbocharger  20  during the operation of the engine  10 . The mid-operation cooling control is performed to cool the turbocharger  20  by driving the electric pump  31  when the temperature of the turbocharger  20  is relatively high. The mid-operation cooling control determines whether to drive the electric pump  31  based on the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4. Also, the mid-operation cooling control determines the flow rate of cooling water supplied to the turbocharger  20  by the electric pump  31  based on the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4. 
       FIG.  2    shows a flowchart of a mid-operation cooling control routine. The ECM  40  performs the routine to implement the mid-operation cooling control. The ECM  40  repeatedly executes the routine at each predefined control cycle during the operation of the engine  10 . 
     When starting this routine, the ECM  40  obtains, in step S 100 , values of the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4 that have been estimated in advance. Next, the ECM  40  determines whether a cooling request flag is set in step S 110 . The cooling request flag indicates whether a request to drive the electric pump  31  was made in the previous execution of this routine. If the cooling request flag is set (YES), the ECM  40  advances the process to step S 120 . If the cooling request flag is not set (NO), the ECM  40  advances the process to step S 170 . 
     A process that is executed when the cooling request flag is not set (S 110 : NO) will now be described. In this case, the ECM  40  determines, in step S 120 , whether the electric pump  31  needs to be driven based on the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4. Specifically, the ECM  40  determines whether the electric pump  31  needs to be driven depending on whether at least one of conditions (A) to (D) is met. Condition (A) is that the housing temperature TH1 is higher than or equal to a first high-temperature determination value TX1. Condition (B) is that the seal ring temperature TH2 is higher than or equal to a second high-temperature determination value TX2. Condition (C) is that the bearing temperature TH3 is higher than or equal to the third high-temperature determination value TX3. Condition (D) is that the oil drain temperature TH4 is higher than or equal to the fourth high-temperature determination value TX4. When determining that the electric pump  31  does not need to be driven (NO), the ECM  40  ends the current process of this routine. In contrast, when determining that the electric pump  31  needs to be driven, the ECM  40  advances the process to step S 130 . Then, the ECM  40  sets the cooling request flag in step S 130 . 
     Subsequently, the ECM  40  calculates first to fourth request flow rates Q1 to Q4 in step S 140 . The first request flow rate Q1 is calculated based on the housing temperature TH1 using a first calculation map MAP1. The first request flow rate Q1 represents a flow rate of the cooling water required to lower the housing temperature TH1 to an appropriate temperature. The first calculation map MAP1 is designed to increase the value of the first request flow rate Q1 as the housing temperature TH1 increases after exceeding a first low-temperature determination value TY1, which will be discussed below. 
     The second request flow rate Q2 is calculated based on the seal ring temperature TH2 using a second calculation map MAP2. The second request flow rate Q2 represents a flow rate of the cooling water required to lower the seal ring temperature TH2 to an appropriate temperature that reduces the formation of oil coke in the vicinity of the seal ring  28 . The second calculation map MAP2 is designed to increase the value of the second request flow rate Q2 as the seal ring temperature TH2 increases after exceeding a second low-temperature determination value TY2, which will be discussed below. The third request flow rate Q3 is calculated based on the bearing temperature TH3 using a third calculation map MAP3. The third request flow rate Q3 represents a flow rate of the cooling water required to lower the bearing temperature TH3 to an appropriate temperature that reduces the formation of oil coke in the vicinity of the floating bearing  27 . The third calculation map MAP3 is designed to increase the value of the third request flow rate Q3 as the bearing temperature TH3 increases after exceeding a third low-temperature determination value TY3, which will be discussed below. The fourth request flow rate Q4 is calculated based on the oil drain temperature TH4 using a fourth calculation map MAP4. The fourth request flow rate Q4 represents a flow rate of the cooling water required to lower the temperature of the oil drain portion of the oil passage  29  to an appropriate temperature that reduces the formation of oil coke. The fourth calculation map MAP4 is designed to increase the value of the fourth request flow rate Q4 as the oil drain temperature TH4 increases after exceeding a fourth low-temperature determination value TY4, which will be discussed below. 
     Then, in step S 150 , the ECM  40  sets the value of a request flow rate QR to the greatest value of the first to fourth request flow rates Q1 to Q4. Next, in step S 160 , the ECM  40  drives the electric pump  31  to discharge the cooling water at the request flow rate QR. Then, the ECM  40  ends the process of the current routine. 
     Next, a process that is executed when the cooling request flag is set (S 110 : YES) will be described. In this case, the electric pump  31  was being driven during the previous execution of this routine. In step S 170 , the ECM  40  determines whether the electric pump  31  needs to continue to be driven based on the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4. Specifically, the ECM  40  determines to stop the electric pump  31  when all of the following conditions (E) to (H) are met. If at least one of the conditions (E) to (H) is not met, the ECM  40  determines to continue to drive the electric pump  31 . Condition (E) is that the housing temperature TH1 is lower than the first low-temperature determination value TY1. The first low-temperature determination value TY1 is set to a temperature that is lower than the first high-temperature determination value TX1. Condition (F) is that the seal ring temperature TH2 is lower than the second low-temperature determination value TY2. The second low-temperature determination value TY2 is set to a temperature that is lower than the second high-temperature determination value TX2. Condition (G) is that the bearing temperature TH3 is lower than the third low-temperature determination value TY3. The third low-temperature determination value TY3 is set to a temperature that is lower than the third high-temperature determination value TX3. Condition (H) is that the oil drain temperature TH4 is lower than the fourth low-temperature determination value TY4. The fourth low-temperature determination value TY4 is set to a temperature that is lower than the fourth high-temperature determination value TX4. 
     When determining to continue to drive the electric pump  31  (S 170 : NO), the ECM  40  advances the process to step S 140 . When determining to stop the electric pump  31  (S 170 : YES), the ECM  40  clears the cooling request flag in step S 180 . After stopping the electric pump  31  in step S 190 , the ECM  40  ends the current process of this routine. 
     Post-Stoppage Cooling Control Routine 
     Further, if the temperature of the turbocharger  20  is relatively high when the engine  10  stops, the ECM  40  drives the electric pump  31  after the engine  10  stops, thereby cooling the turbocharger  20 . A post-stoppage cooling control will now be described, which is related to driving of the electric pump  31  after the engine  10  stops. 
       FIG.  3    shows a procedure performed by the ECM  40  in accordance with the post-stoppage cooling control. The ECM  40  starts the process shown in  FIG.  3    in response to stoppage of the engine  10 . 
     When the engine  10  stops, the ECM  40  first obtains, in step S 200 , the current values of the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, at the oil drain temperature TH4. The obtained value of the housing temperature TH1 corresponds to an engine-stoppage housing temperature. Also, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4 that are obtained at this time correspond to engine-stoppage generation site temperatures. 
     Next, the ECM  40  calculates fifth to eighth request flow rates Q5 to Q8 in step S 210 . The fifth request flow rate Q5 is calculated based on the housing temperature TH1, which has been obtained in step S 200 , using a fifth calculation map MAP5. The fifth request flow rate Q5 represents a flow rate of the cooling water required to lower the housing temperature TH1 to an appropriate temperature. The sixth request flow rate Q6 is calculated based on the seal ring temperature TH2, which has been obtained in step S 200 , using a sixth calculation map MAP6. The sixth request flow rate Q6 represents a flow rate of the cooling water required to lower the seal ring temperature TH2 to an appropriate temperature that reduces the formation of oil coke. The seventh request flow rate Q7 is calculated based on the bearing temperature TH3, which has been obtained in step S 200 , using a seventh calculation map MAP7. The seventh request flow rate Q7 represents a flow rate of the cooling water required to lower the bearing temperature TH3 to an appropriate temperature that reduces the formation of oil coke. The eighth request flow rate Q8 is calculated based on the oil drain temperature TH4, which has been obtained in step S 200 , using an eighth calculation map MAP8. The eighth request flow rate Q8 represents a flow rate of the cooling water required to lower the oil drain temperature TH4 to an appropriate temperature that reduces the formation of oil coke. The fifth to eighth calculation maps MAP5 to MAP8 are each designed to set the value of the request flow rate to 0 when the temperature of the corresponding site is lower than a certain value of the temperature. Also, the fifth to eighth calculation maps MAP5 to MAP8 are each designed to increase the value of the request flow rate as the temperature at the corresponding site increases, when the temperature at the corresponding site is higher than or equal to the certain value of the temperature. The certain value is different for each of the fifth to eighth calculation maps MAP5 to MAP8. 
     Subsequently, the ECM  40  calculates a first request driving time TM1, a second request driving time TM2, a third request driving time TM3, and a fourth request driving time TM4 in step S 220 . The first request driving time TM1 is calculated based on the housing temperature TH1, which has been obtained in step S 200 , using a ninth calculation map MAP9. The first request driving time TM1 represents driving time of the electric pump  31  required to lower the housing temperature TH1 to an appropriate temperature. The ninth calculation map MAP9 is designed to set the value of the first request driving time TM1 to 0 when the housing temperature TH1 is lower than a certain value of the temperature. The ninth calculation map MAP9 is designed to increase the value of the first request driving time TM1 as the housing temperature TH1 increases when the housing temperature TH1 is higher than or equal to the certain value. The second request driving time TM2 is calculated based on the seal ring temperature TH2, which has been obtained in step S 200 , using a tenth calculation map MAP10. The second request driving time TM2 represents driving time of the electric pump  31  required to lower the seal ring temperature TH2 to an appropriate temperature that reduces the formation of oil coke. The third request driving time TM3 is calculated based on the bearing temperature TH3, which has been obtained in step S 200 , using an eleventh calculation map MAP11. The third request driving time TM3 represents driving time of the electric pump  31  required to lower the bearing temperature TH3 to an appropriate temperature that reduces the formation of oil coke. The fourth request driving time TM4 is calculated based on the oil drain temperature TH4, which has been obtained in step S 200 , using a twelfth calculation map MAP12. The fourth request driving time TM4 represents driving time of the electric pump  31  required to lower the oil drain temperature TH4 to an appropriate temperature that reduces the formation of oil coke. The ninth to twelfth calculation maps MAP9 to MAP12 are each designed to set the value of the request driving time to 0 when the temperature of the corresponding site is lower than a certain value of the temperature. Also, the ninth to twelfth calculation maps MAP9 to MAP12 are each designed to increase the value of the request driving time as the temperature of the site increases, when the temperature of the corresponding site is higher than or equal to the certain value of the temperature. The certain value is different for each of the ninth to twelfth calculation maps MAP9 to MAP12. 
     Next, in step S 230 , the ECM  40  sets the value of the request flow rate QR to the greatest value of the fifth to eighth request flow rates Q5 to Q8. Also, in step S 230 , the ECM  40  sets the value of a request driving time TMR to the greatest value of the first to fourth request driving times TM1 to TM4. 
     Then, in step S 240 , the ECM  40  starts driving the electric pump  31  while setting the discharge flow rate to the request flow rate QR. Thereafter, in step S 250 , the ECM  40  waits until a time period corresponding to the value of the request driving time TMR has elapsed. When the time period corresponding to the value of the request driving time TMR has elapsed (S 250 : YES), the ECM  40  advances the process to step S 260 . In a case in which the value of the request driving time TMR has been set to 0, the ECM  40  advances the process to step S 260  without driving the electric pump  31 . In step S 260 , the ECM  40  stops the electric pump  31 . The ECM  40  thus ends the post-stoppage cooling control. 
     Operation and Advantages of Embodiment 
     Operation and advantages of the present embodiment will now be described. 
     High-temperature exhaust gas flows into the turbine housing  21  during the operation of the engine  10 . The heat of the exhaust gas is transferred to the turbine housing  21 . The heat transfer from the turbine housing  21  increases the temperatures of the generation sites P 1  to P 3  of oil coke inside the turbocharger  20 . If the temperatures of the generation sites P 1  to P 3  continue to be higher than a certain value of the temperature, oil coke will be generated and accumulated. 
     The mid-operation cooling control drives the electric pump  31  when the temperature of the turbocharger  20  is relatively high. Accordingly, the cooling water is supplied to the water jacket  30  of the turbocharger  20  to cool the generation sites P 1  to P 3 . This reduces the formation and accumulation of oil coke at the generation sites P 1  to P 3 . 
     Even in a case in which the temperatures of the generation sites P 1  to P 3  are not significantly high, if the housing temperature TH1 is relatively high, heat transfer from the turbine housing  21  can eventually increase the temperatures of the generation sites P 1  to P 3 . In the present embodiment, the flow rate of the cooling water supplied to the turbocharger  20  is varied depending on the temperatures of the generation sites P 1  to P 3  and the temperature of the turbine housing  21 . This allows the flow rate of the cooling water to be set appropriately taking into consideration a future temperature increase of the generation sites P 1  to P 3  due to heat transfer from the turbine housing  21 . 
     Also, in the present embodiment, if the temperature of the turbocharger  20  is relatively high when the engine  10  is stopped, the post-stoppage cooling control is performed to drive the electric pump  31  after the engine  10  is stopped. In a case in which the engine  10  is stopped and the temperatures of the generation sites P 1  to P 3  are not significantly high, heat transfer from the turbine housing  21  can subsequently increase the temperatures of the generation sites P 1  to P 3  if the housing temperature TH1 is relatively high. In the post-stoppage cooling control according to the present embodiment, the flow rate of the cooling water supplied to the turbocharger  20  and the driving time of the electric pump  31  are varied depending on the temperatures of the generation sites P 1  to P 3  and the temperature of the turbine housing  21 . This allows the flow rate of the cooling water and the driving time to be set appropriately taking into consideration a future temperature increase of the generation sites P 1  to P 3  due to the heat transfer from the turbine housing  21 . 
     The housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4 are estimated during the operation of the engine  10 . This allows the flow rate of the cooling water to be adjusted constantly in accordance with changes in the temperatures in the mid-operation cooling control. In contrast, after the engine  10  is stopped, the temperatures are not estimated, and the flow rate of the cooling water must be determined based only on the temperatures at the time of stoppage of the engine  10 . Also, after the engine  10  is stopped, the turbine housing  21  stops being heated by the exhaust gas. Further, after the engine  10  is stopped, the oil pump  13  is stopped, so that the flow of oil through the oil passage  29  stagnates. In this manner, the conditions after the stoppage of the engine  10  are significantly different from those during the operation of the engine  10 . Therefore, the post-stoppage cooling control uses calculation maps different from those used in the mid-operation cooling control in order to calculate the request flow rates. 
     The engine controller of the present embodiment has the following advantages. 
     (1) The flow rate of the cooling water supplied to the turbocharger  20  by the electric pump  31  during the operation of the engine  10  is varied based on the respective temperatures of the turbine housing  21  and the generation sites P 1  to P 3  of oil coke. Accordingly, the cooling water of an appropriate flow rate is supplied to the turbocharger  20 , so as to reduce the formation and accumulation of oil coke effectively.   (2) The electric pump  31  is driven to supply an appropriate amount of the cooling water. This reduces the power consumption and the operating noise of the electric pump  31 .   (3) The driving time of the electric pump  31  after the engine  10  is stopped is varied based on the housing temperature TH1 and the temperatures of the generation sites P 1  to P 3   at the time of stoppage of the engine  10 . This sets the driving time of the electric pump  31  after the stoppage of the engine  10  to time appropriate for reducing oil coke.   (4) The flow rate of the cooling water supplied to the turbocharger  20  by the electric pump  31  after the engine  10  is stopped is varied based on the housing temperature TH1 and the respective temperatures of the generation sites P 1  to P 3  at the time of stoppage of the engine  10 . This sets the flow rate of the cooling water supplied by the electric pump  31  after the engine  10  is stopped to time appropriate for reducing oil coke.   

     The above-described embodiment may be modified as follows. The above-described embodiment and the following modifications can be combined as long as the combined modifications remain technically consistent with each other. 
     In the above-described embodiment, the request flow rate QR in the post-stoppage cooling control is varied in accordance with the temperatures (TH1 to TH4). However, the request flow rate QR may be a fixed value. The request driving time TMR for the electric pump  31  and the request flow rate QR in the post-stoppage cooling control may be fixed values irrespective of the temperatures (TH1 to TH4). 
     Only the mid-operation cooling control, of the mid-operation cooling control and post-stoppage cooling control, may be performed. 
     In the above-described embodiment, the housing temperature TH1, the seal ring temperature TH2, the bearing temperature TH3, and the oil drain temperature TH4 are estimated based on the traveling condition of the vehicle. One or all of these temperatures may be measured by temperature sensors. 
     The positions of sites where oil coke is generated and the number of such sites vary depending on the structure of the turbocharger. Therefore, the positions and number of sites the temperatures of which are used to calculate the request flow rate QR and the request driving time TMR may be changed in accordance with the structure of the turbocharger. 
     The ECM  40  or the processing device  41  may include one or more processors that perform various processes according to computer programs (software). The ECM  40  or the processing device  41  may be circuitry including one or more dedicated hardware circuits such as application specific integrated circuits (ASICs) that execute at least part of various processes, or a combination thereof. The processor includes a CPU and a memory such as a RAM and a ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. The memory, which is a computer-readable medium, includes any type of media that are accessible by general-purpose computers and dedicated computers. 
     Various changes in form and details may be made to the examples above without departing from the spirit and scope of the claims and their equivalents. The examples are for the sake of description only, and not for purposes of limitation. Descriptions of features in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if sequences are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined differently, and/or replaced or supplemented by other components or their equivalents. The scope of the disclosure is not defined by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure.