Patent Publication Number: US-9903260-B2

Title: Apparatus and method for determining pore clogging in engine cooling system

Description:
PRIORITY INFORMATION 
     This application claims priority to Japanese Patent Application No. 2014-243387 filed on Dec. 1, 2014, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a structure of an apparatus and a method for determining pore clogging in an engine cooling system. 
     BACKGROUND ART 
     An engine has a cooling apparatus for maintaining an engine temperature at an appropriate operating temperature. Commonly used cooling apparatuses include the apparatus that, by using a radiator, cools a coolant having a temperature that has increased inside the engine, and circulates the coolant through the engine, thereby cooling the engine. Such a cooling apparatus uses a method that does not circulate the coolant at the time of a cold start where the engine temperature is low, and circulates the coolant, when the engine temperature increases to a predetermined temperature. However, when no coolant flows inside the engine immediately after the cold start of the engine, a temperature distribution may occur inside the engine, leading to a stress or the like. Therefore, even when the engine temperature is low and the engine is not cooled by circulating the coolant, a very small amount of coolant is often allowed to flow inside the engine to avoid large unevenness in the temperature at various parts in the engine. For this purpose, a very small pore or a notch that allows the coolant to flow is often provided in a valve body in the cooling system. 
     In a cooling system with such a configuration, when the coolant does not flow due to foreign matter clogged in the pore or the notch, temperature unevenness may occur in the engine, leading to an increased stress and a reduced lifetime. Therefore, there has been proposed a method for estimating and determining clogging of the pore or the notch based on a difference in the coolant temperatures detected at different positions. In this case, one coolant temperature sensor is provided at an engine outlet and another one is provided in a bypass passage that bypasses the engine (for example, refer to WO 2013-150619). 
     Meanwhile, when no coolant has been injected in a cooling passage, or air remains in the cooling passage immediately after injection of the coolant, the cooling passage is not filled with the coolant. This may cause a failure in circulating the coolant by a coolant pump, and then the degree of increase in the coolant temperature at an engine outlet may be similar to a case when, there is clogging of a pore or a notch, leading to an erroneous determination of clogging of the pore or the notch. 
     Therefore, an object of the present invention is to suppress an erroneous determination of clogging of a pore that allows the coolant to flow in an engine cooling system. 
     SUMMARY 
     A pore clogging determination apparatus according to an embodiment of the present invention is used in an engine cooling system. The engine cooling system includes: a first cooling passage passing through the inside of an engine; a second cooling passage branching from the first cooling passage and bypassing the engine; a coolant pump controlled by a command from an ECU and configured to circulate a coolant in the first and second cooling passages; a connection passage connecting an engine outlet of the first cooling passage to the second cooling passage; a switching valve disposed in the connection passage, configured to open and close the connection passage, and including a pore that allows the coolant to flow through the connection passage; and a first temperature sensor configured to detect a coolant temperature at the engine outlet. The pore clogging determination apparatus includes a CPU and is connected to the ECU. The CPU tentatively determines clogging of the pore based on the degree of increase in the coolant temperature at the engine outlet, the coolant temperature being detected by the first temperature sensor at a cold start of the engine. Upon tentatively determining the pore clogging, the CPU outputs, to the ECU, a command for increasing a rotation speed of the coolant pump to increase the rotation speed of the coolant pump. With the above state, the CPU determines the presence or absence of idling in the coolant pump. Upon determining that no idling is present in the coolant pump, the CPU executes a process of finalizing the determination of the pore clogging. 
     In the pore clogging determination apparatus according to an embodiment of the present invention, the CPU preferably determines that the coolant pump is idling when an actual rotation speed of the coolant pump obtained by a rotation speed sensor is higher than a target rotation speed obtained from the ECU, and a difference between the two exceeds a predetermined value. 
     A pore clogging determination method according to an embodiment of the present invention is used in am engine cooling system. The engine cooling system includes: a first cooling passage passing through the inside of an engine; a second cooling passage branching from the first cooling passage and bypassing the engine; a coolant pump configured to circulate a coolant in the first and second cooling passages; a connection passage connecting an engine outlet of the first cooling passage to the second cooling passage; a switching valve disposed in the connection passage, configured to open and close the connection passage, and including a pore that allows a very small amount of coolant to flow through the connection passage; and a first temperature sensor configured to detect a coolant temperature at the engine outlet. The pore clogging determination method includes: a tentative determination step of tentatively determining clogging of the pore based on the degree of increase in the coolant temperature at the engine outlet, the coolant temperature being detected by the first temperature sensor at a cold start of the engine; an idling determination step of outputting a command to increase a rotation speed of the coolant pump and determining the presence or absence of idling in the coolant pump when the pore clogging has been tentatively determined at the tentative determination step; and a pore clogging finalization step of finalizing the determination of the pore clogging when it has been determined in the idling determination step that the coolant pump is not idling. 
     Advantages of the Invention 
     The present invention is effective in suppressing an erroneous determination of clogging of a pore that allows the coolant to flow in an engine cooling system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system diagram illustrating configurations of a pore clogging determination apparatus and an engine cooling system according to an embodiment of the present invention; 
         FIG. 2A  is an explanatory diagram illustrating a distribution of coolant temperatures inside an engine head; 
         FIG. 2B  is an explanatory diagram illustrating a flow of a coolant inside an engine block and an engine head, and a position of a temperature sensor; 
         FIG. 3  is a flowchart illustrating an operation of a pore clogging determination apparatus according to an embodiment of the present invention; 
         FIG. 4A  is a graph illustrating a change with time of a rotation speed of an engine; and 
         FIG. 4B  is a graph illustrating a change with time of a coolant temperature T 4  at an engine outlet when the engine is driven in a similar manner to  FIG. 4A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a pore clogging determination apparatus  70  of the present embodiment will be described with reference to the drawings. First, an engine cooling system  100  to which the pore clogging determination apparatus  70  of the present embodiment is applied will be described with reference to  FIG. 1 . As illustrated in  FIG. 1 , the engine cooling system  100  includes a first cooling passage  20  that passes through the inside of an engine  10 , a second cooling passage  30  that bypasses the engine  10 , and a coolant pump  14  that circulates a coolant in the first and second cooling passages  20  and  30 . 
     The coolant pump  14 , the engine  10 , a radiator  11 , and a thermostat  13  are connected in series in this order to the first cooling passage  20  from upstream. The engine  10  has a cooling passage therein and is cooled by the coolant. The radiator  11  cools the coolant having a temperature that has increased inside the engine  10 . The thermostat  13  opens and closes a flow of the coolant in the first cooling passage  20  depending on the coolant temperature. A first branch point  22  and a second branch point  28  are connected via the second cooling passage  30  that bypasses the engine  10 . The first branch point  22  exists between the engine  10  and the coolant pump  14  in the first cooling passage  20 . The second branch point  28  exists between the thermostat  13  and the coolant pump  14 . A third branch point  25  and a fourth branch point  31  are connected via a connecting pipe  40 . The third branch point  25  exists at an engine outlet pipe  24  in the first cooling passage  20 . The fourth branch point  31  exists between the first branch point  22  in the second cooling passage  30  and the second branch point  28 . A switching valve  50  is attached to the connecting pipe  40  and opens or closes the coolant flow in the connecting pipe  40 . An electromagnetic actuator controls open/close operations of the switching valve  50 .  FIG. 1  schematically illustrates an electromagnetic actuator  51 . A pore (micropore)  52  is provided at a center of a valve body of the switching valve  50  to allow the coolant to flow through the inside thereof even when the valve is in a closed state.  FIG. 1  schematically illustrates the pore (micropore)  52  as a pipe that bypasses the switching valve  50 . Note that the thermostat  13  and the switching valve  50  illustrated in  FIG. 1  both indicate the closed states thereof when the engine  10  is undergoing a cold start. The coolant pump  14  is driven by the electrical power of a motor  15 . A rotation speed sensor  16  that detects a rotation speed of the motor  15  is attached to the coolant pump  14 . Further, a temperature sensor  17  that detects the coolant temperature at an engine outlet is attached to the engine outlet pipe  24  of the first cooling passage  20 . 
     The pore clogging determination apparatus  70  is a computer that includes a CPU and a storage unit therein. The temperature sensor  17  and the rotation speed sensor  16  are connected to the apparatus. The data detected, by each sensor is input to the pore clogging determination apparatus  70 . Also, the motor  15  that drives the coolant pump  14 , and the electromagnetic actuator  51  for the switching valve  50 , are connected to an ECU  60  that controls overall operations of the engine  10 , independent of the pore clogging determination apparatus  70 . A rotation speed command signal or a motor drive duty ratio signal for the motor  15  is input from the ECU  60  to the pore clogging determination apparatus  70 . 
     When the ECU  60  starts the engine  10  in the state illustrated in  FIG. 1 , the ECU  60  simultaneously starts the motor  15  that drives the coolant pump  14 , thereby starting the coolant pump  14 . At this time, the thermostat  13  and the switching valve  50  are each closed. Accordingly, the coolant circulates as indicated by arrows in  FIG. 1 , in the order of the coolant pump  14 , a discharge pipe  21 , the first branch point  22 , an engine inlet pipe  23 , the engine  10 , the engine outlet pipe  24 , the third branch point  25 , the pore (micropore)  52 , the fourth branch point  31 , the second branch point  28 , and returns to the coolant pump  14 . Simultaneously, the coolant circulates while bypassing the engine  10 , in the order of the coolant pump  14 , the first branch point  22 , the second branch point  28 , and back to the coolant pump  14 . 
     The following describes, with reference to  FIGS. 2A and 2B , how the coolant temperature inside the engine changes between a case where the coolant is flowing through the pore (micropore)  52  illustrated in  FIG. 1  and a case where the coolant is not flowing through the micropore  52  because the pore is clogged. When the coolant flows through the micropore  52 , the coolant flows into the inside of an engine block via the engine inlet pipe  23  illustrated in  FIG. 2B , flows through an engine head illustrated in  FIG. 2B , and then flows out to the outside of the engine head via the engine outlet pipe  24  connected to the engine head. As illustrated by a dashed line b in  FIG. 2A , when the coolant flows into the inside of the engine  10 , the temperature of the coolant is increased by the heat of the engine  10  and then keeps increasing slowly as it flows downstream. Then, the temperature of the coolant reaches a temperature T 1  at the position of the temperature sensor  17  provided at the engine outlet pipe  24 . On the other hand, when the coolant does not flow through the inside of the engine  10  due to the clogged pore (micropore)  52 , the temperature of the coolant settling inside the engine  10  is increased by the heat of the engine  10  as illustrated by a solid line a in  FIG. 2A . In contrast, the temperature of the coolant settling in the vicinity of the engine outlet pipe  24 , where the heat from the engine  10  has not been transmitted as much, does not increase largely, staying at a temperature T 0  lower than the temperature T 1  as illustrated in  FIG. 2A . That is, the temperature of the coolant at the engine outlet pipe  24  after the cold start of the engine is lower in a case where the coolant does not flow inside the engine  10  (where the pore (micropore)  52  is clogged), than in a case where the coolant flows inside the engine  10  (where the pore (micropore)  52  is not clogged). The pore clogging determination apparatus  70  of the present embodiment tentatively determines clogging of the pore (micropore)  52  based on the above-described principle. 
     Hereinafter, operations of the pore clogging determination apparatus  70  according to the present embodiment will be described with reference to  FIG. 3 . As shown at step S 101  in  FIG. 3 , the cold start of the engine  10  by the ECU  60  also starts the motor  15  for the coolant pump  14 , thereby starting the coolant pump  14 . As previously described with reference to  FIG. 1 , the thermostat  13  and the switching valve  50  are closed at the time of cold start of the engine. Accordingly, the coolant circulates as indicated by arrows in  FIG. 1 , in the order of the coolant pump  14 , the discharge pipe  21 , the first branch point  22 , the engine inlet pipe  23 , the engine  10 , the engine outlet pipe  24 , the third branch point  25 , the pore (micropore)  52 , the fourth branch point  31 , the second branch point  28 , and returns to the coolant pump  14 . Simultaneously, the coolant circulates while bypassing the engine  10 , in the order of the coolant pump  14 , the first branch point  22 , the second branch point  28 , and back to the coolant pump  14 . 
     As shown at step S 102  in  FIG. 3 , the pore clogging determination apparatus  70 , following the starting of the engine  10 , detects an initial temperature T 40  of the coolant in the engine outlet pipe  24  using the temperature sensor  17 . Next, the pore clogging determination apparatus  70  waits until a predetermined time period has elapsed, as shown at step S 103  in  FIG. 3 . The predetermined time period may be a time period needed for a coolant temperature T 4  at the engine outlet to increase to a predetermine temperature when the pore (micropore)  52  is not clogged. This time period may be about three or five minutes, for example. 
     As illustrated in  FIGS. 4A and 4B , after the cold start of the engine  10  at time t 1 , when the pore (micropore)  52  is not clogged and the coolant is flowing inside the engine  10  and the engine outlet pipe  24 , the coolant temperature T 4  at the engine outlet starts increasing at time t 2  from the initial temperature  140 , and keeps increasing to reach a temperature T 41  at time t 4  after the predetermined time period has elapsed, as illustrated by a dashed line c in  FIG. 4B . In contrast, when the pore (micropore)  52  is clogged and the coolant is not flowing inside the engine  10  or inside the engine outlet pipe  24 , the coolant temperature T 4  at the engine outlet remains at the initial temperature T 40  until time t 3 , and the temperature detected by the temperature sensor starts increasing at time t 3  as illustrated by a solid line d in  FIG. 4B . Thereafter, the temperature keeps increasing to reach a temperature T 42  at the predetermined time t 4 . The temperature T 42 , however, is lower than the coolant temperature T 41  at the engine outlet when the pore (micropore)  52  is not clogged. Also, as illustrated by a solid line e in  FIG. 4B , when the first cooling passage  20  has no coolant therein or the time is immediately after injection of the coolant, the coolant pump  14  idles even with the motor  15  running. As a result, no coolant flows in the first and second cooling passages. Therefore, increase in the coolant temperature T 4  at the engine outlet is delayed in a similar manner to the case where the coolant is not flowing due to the clogged pore (micropore)  52 . That is, comparing the case where the pore (micropore)  52  is clogged and the case where the coolant pump  14  is idling, the rates of the temperature increase in the coolant temperature T 4  at the engine outlet are substantially equal, as illustrated in the solid lines a and e in  FIG. 4B . 
     The pore clogging determination apparatus  70  detects the coolant temperature T 4  at the engine outlet again at time t 4  after the predetermined time period has elapsed, as shown at step S 104  in  FIG. 3 . The pore clogging determination apparatus  70  then calculates a temperature difference ΔT 4 =(T 4 −T 40 ), which is the difference between the initial temperature T 40  and the coolant temperature T 4  at the engine outlet at the predetermined time t 4 , as shown at step S 105  in  FIG. 3 . When the temperature difference ΔT 4  is equal to or more than a predetermined threshold ΔTS (the case where ΔT 4  is not less than ΔTS), the pore clogging determination apparatus  70  determines as NO at step S 106  in  FIG. 3  and then finishes executing the program based on a determination that the pore (micropore)  52  is not clogged (normal determination) as shown at step S 113  in  FIG. 3 . 
     When the temperature difference ΔT 4  is less than the predetermined threshold ΔTS at step S 106  in  FIG. 3 , the pore clogging determination apparatus  70  determines as YES at step S 106  in  FIG. 3  and moves to step S 107  in  FIG. 3 . As described above, the rates of the temperature increase with respect to the time in the coolant temperature T 4  at the engine outlet are substantially equal between the case where the pore (micropore)  52  is clogged and the case where the coolant pump  14  is idling. Therefore, it is difficult at this stage to determine whether this is the case where actual clogging of the pore (micropore)  52  is occurring as illustrated by the solid line a in  FIG. 4B  or the case where the idling coolant pump  14  is hindering the coolant from flowing through the pore (micropore)  52  as illustrated by the solid line e in  FIG. 4B , even with the presence of the delayed increase in the coolant temperature T 1  at the engine outlet. Therefore, the pore clogging determination apparatus  70  tentatively determines that the pore (micropore)  52  is clogged and then moves to step S 108  in  FIG. 3 . 
     The pore clogging determination apparatus  70  checks whether idling of the coolant pump  14  has ever been checked for as shown at step S 108  in  FIG. 3 . In the case where idling in the coolant pump  14  has been checked for once, the pore clogging determination apparatus  70  moves to step S 110  of  FIG. 3 . When no idling in the coolant pump  14  is detected on that occasion, the pore clogging determination apparatus  70  determines that the first and second cooling passages  20  and  30  are filled with the coolant and that the delayed increase in the coolant temperature T 4  at the engine outlet has been caused by the clogged pore (micropore)  52  at the switching valve  50 . The pore clogging determination apparatus  70  finalizes a pore clogging determination, namely, an abnormal determination, as shown at step S 111  of  FIG. 3 , and then displays a failure indication on a diagnostic device or the like. When idling of the coolant pump  14  is detected on that occasion, on the other hand, the pore clogging determination apparatus  70  moves to step S 112  in  FIG. 3  and cancels the tentative determination of pore clogging made at step S 107  in  FIG. 3 , not displaying any failure indication on the diagnostic device. 
     Meanwhile, when it is determined at step S 108  in  FIG. 3  that idling of the coolant pump  14  has not been checked for, the pore clogging determination apparatus  70  executes a process for checking for idling of the coolant pump shown in step S 109  in  FIG. 3 . The pore clogging determination apparatus  70  outputs, to the ECU  60  illustrated in  FIG. 1 , a signal to increase the drive duty ratio or a signal to increase the rotation speed command value (target rotation speed) of the motor  15  for the coolant pump  14 . Simultaneously, the pore clogging determination apparatus  70  obtains, from the ECU  60 , the increased drive duty ratio or the increased rotation speed command value (target rotation speed) for the motor  15 . Also, the pore clogging determination apparatus  70  obtains the actual rotation speed of the motor  15  by using the rotation speed sensor  16 . The pore clogging determination apparatus  70  compares both values, and when the actual rotation speed of the motor  15  is more than the rotation speed command value (target rotation speed), and the difference between the two exceeds a predetermined threshold ΔRS, determines that the coolant pump  14  is idling. On the other hand, when the difference between the actual rotation speed of the motor  15  and the rotation speed command value (target rotation speed) does not exceed the predetermined threshold ΔRS, the pore clogging determination apparatus  70  determines that the coolant pump  14  is not idling. Subsequently, when the coolant pump  14  is idling, the pore clogging determination apparatus  70  determines as YES at step S 110  in  FIG. 3 , and moves to step S 112  in  FIG. 3 , where the apparatus cancels the tentative determination of pore clogging made at step S 107  in  FIG. 3 , not displaying any failure indication on the diagnostic device. In contrast, when the coolant pump is not idling, the pore clogging determination apparatus  70  determines as NO at step S 110  in  FIG. 3 , and moves to step S 111  in  FIG. 3  to finalize the pore clogging determination (abnormal determination) and then displays a failure indication on the diagnostic device or the like. 
     As described above, when determining clogging of the pore  52  based on the rate of increase in the coolant temperature T 4  at the engine outlet, the pore clogging determination apparatus  70  of the present embodiment initially checks whether the delayed increase in the coolant temperature T 4  at the engine outlet has been caused by the idling of the coolant pump  14  and then finalizes the abnormality determination of the pore clogging, making it possible to suppress an erroneous determination of the pore clogging and enhance reliability of the pore clogging determination. 
     In the above-described embodiment, the clogging of the pore (micropore)  52  has been determined based on whether the temperature difference ΔT 4  between the coolant temperature T 4  at the engine outlet at a predetermined time t 4  and the initial temperature T 40  is equal to or more than the predetermined threshold ΔTS. Alternatively, the clogging of the micropore  52  may be determined, for example, by comparing a temperature increase rate per predetermined time period (ΔT 4 /(t 4 −0)) and a predetermined temperature increase rate.