INCORPORATION BY REFERENCE 
   The disclosure of Japanese Patent Application No. 2003-096645 filed on Mar. 31, 2003 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The invention relates to an engine cooling device/method designed to cool an engine through circulation of cooling medium. 
   2. Description of Related Art 
   As an engine cooling device designed to cool an engine through circulation of cooling medium, a cooling device equipped with a heat-accumulating container has been known. A cooling device of this type causes cooling medium that has reached a high temperature by receiving heat from an engine to flow into a heat-accumulating container, and thereby makes it possible to thermally insulate and store the cooling medium. 
   As an engine cooling device equipped with a heat-accumulating container, there is known a device that is disclosed in Japanese Patent Application No. 10-77839 as an example of the related art. This cooling device is constructed as follows. 
   That is, a radiator passage and a bypass passage are provided as cooling medium passages for causing cooling medium to flow. The radiator passage is designed to cause cooling medium that has flown out from a body of an engine to flow into the body of the engine via a radiator. The bypass passage is designed to cause cooling medium that has flown out from the body of the engine to flow into the body of the engine without causing the cooling medium to flow via the radiator. 
   The bypass passage is provided with a control valve. The flow rate of cooling medium flowing through the bypass passage can be adjusted through control of the control valve. A cooling circuit for causing cooling medium to circulate is so constructed as to include the control valve, the radiator passage, and the bypass passage. 
   Further, as a cooling medium passage, there is provided a heat-accumulating passage that has a heat-accumulating container and that can be selectively connected to the cooling circuit. This heat-accumulating passage is connected to the cooling circuit, whereby a heat-accumulating circuit for causing cooling medium in the heat-accumulating container to circulate via the body of the engine is constructed. 
   In the aforementioned engine cooling device, when the engine is started, hot cooling medium in the heat-accumulating container is caused to flow into the engine by connecting the heat-accumulating passage to the cooling circuit. If the temperature of the cooling medium in the heat-accumulating container becomes lower than a predetermined temperature, the warm-up of the engine is promoted by disconnecting the heat-accumulating passage from the cooling circuit. 
   Whether cooling medium in the heat-accumulating container is supplied to the engine or the heat-accumulating passage is disconnected from the cooling circuit, the bypass passage is closed to prevent low-temperature cooling medium from being recirculate to the body of the engine. Thus, the warm-up performance of the engine is further enhanced. 
   In causing cooling medium in the heat-accumulating container to flow into the body of the engine, if cooling medium is caused to circulate with the bypass passage closed as in the case of the aforementioned related art, the following problem may arise. 
   That is, the flow resistance of cooling medium is increased by closing the bypass passage. Hence, the cooling medium cannot be guaranteed to flow through the cooling circuit and the heat-accumulating circuit at a sufficient flow rate. This results in a delay in warming up the engine. 
   SUMMARY OF THE INVENTION 
   An engine cooling device/method capable of suitably promoting the warm-up of an engine is provided as modes of implementing the invention. 
   This cooling device comprises a cooling circuit, a heat-accumulating passage, and a controller. The cooling circuit is so constructed as to include a radiator passage for causing cooling medium flowing from a body of an engine to flow into the body of the engine via a radiator, a bypass passage for causing cooling medium flowing out from the body of the engine to flow into the body of the engine without flowing via the radiator, and a control valve for controlling a flow rate of cooling medium flowing through the bypass passage. The heat-accumulating passage is provided with a heat-accumulating container for storing the cooling medium in a thermally insulated state, and constitutes a heat-accumulating circuit for causing the cooling medium in the heat-accumulating container to circulate via the body of the engine by being selectively connected to the cooling circuit. The controller i) completes the heat-accumulating circuit by connecting the heat-accumulating passage to the cooling circuit to supply the cooling medium in the heat-accumulating container to the body of the engine and opens the control valve to increase a flow rate of cooling medium flowing through the bypass passage, and then ii) disconnects the heat-accumulating passage from the cooling circuit and closes the control valve. 
   On the other hand, the engine cooling method comprises a step of causing cooling medium to flow through a cooling circuit that is so constructed as to include a radiator passage for causing cooling medium flowing from a body of an engine to flow into the body of the engine via a radiator, a bypass passage for causing cooling medium flowing out from the body of the engine to flow into the body of the engine without flowing via the radiator, and a control valve for controlling a flow rate of cooling medium flowing through the bypass passage, a step of causing the cooling medium to flow through a heat-accumulating passage that is provided with a heat-accumulating container for storing the cooling medium in a thermally insulated state and that constitutes a heat-accumulating circuit for causing the cooling medium in the heat-accumulating container to circulate via the body of the engine by being selectively connected to the cooling circuit, a step of completing the heat-accumulating circuit by connecting the heat-accumulating passage to the cooling circuit to supply the cooling medium in the heat-accumulating container to the body of the engine and opening the control valve to increase a flow rate of cooling medium flowing through the bypass passage, and a step of disconnecting the heat-accumulating passage from the cooling circuit and closing the control valve after opening the control valve. 
   According to the aforementioned cooling device and the aforementioned cooling method, when cooling medium in the heat-accumulating container is supplied to the body of the engine, the flow resistance of cooling medium is reduced through an increase in the flow rate of the cooling medium flowing through the bypass passage. Therefore, the flow rate of cooling medium flowing through the cooling circuit and the heat-accumulating circuit is increased. Because the cooling medium in the heat-accumulating container is thereby supplied to the body of the engine at an early stage, the warm-up of the engine can be promoted suitably. After the cooling medium in the heat-accumulating container has been supplied to the body of the engine, the heat-accumulating passage is disconnected from the cooling circuit and the control valve is closed. Therefore, the recalculation of low-temperature cooling medium to the body of the engine is restricted. Thereby, the temperature of the body of the engine can be suitably restrained from falling due to the low-temperature cooling medium. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned objects, features, advantages, technical and industrial significance of this invention will be better understood by reading the following detailed description of the exemplary embodiments of the invention, when considered in connection with the accompanying drawings, in which: 
       FIG. 1  is a schematic block diagram showing the overall construction of an engine cooling device as a concrete embodiment of the invention; 
       FIG. 2  is a flowchart showing a preheat process performed in the embodiment; 
       FIG. 3  is a flowchart showing a coolant circulation stoppage process performed in the embodiment; 
       FIG. 4  shows control patterns of the engine cooling device according to a cooling device cooling process when starting an engine in the embodiment; 
       FIG. 5  is a block diagram of a circulation pattern of coolant during a preheat mode in the engine cooling device of the embodiment; 
       FIG. 6  is a block diagram of a circulation pattern of coolant during a coolant circulation stoppage mode in the engine cooling device of the embodiment; 
       FIG. 7A  is a timing chart showing a control pattern that is realized as to operation/stoppage of the engine by a cooling device control process during start of the engine; 
       FIG. 7B  is a timing chart showing a control pattern that is realized as to the presence of an engine start request by the cooling device control process during the start of the engine; 
       FIG. 7C  is a timing chart showing a control pattern that is realized as to the opening of a flow rate control valve by the cooling device control process during the start of the engine; 
       FIG. 7D  is a timing chart showing a control pattern that is realized as to the opening/closing of an open-close valve by the cooling device control process during the start of the engine; 
       FIG. 7E  is a timing chart showing a control pattern that is realized as to the opening/closing of all ports of a three-way valve by the cooling device control process during the start of the engine; and 
       FIG. 7F  is a timing chart showing a control pattern that is realized as to the drive/stoppage of an electric water pump by the cooling device control process during the start of the engine. 
   


   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   In the following description, the invention will be described in more detail in terms of exemplary embodiments. 
   The overall construction of an engine cooling device having a function of cooling an engine E (engine body) is illustrated in FIG.  1 . 
   First of all, the functions of various components of the engine cooling device  1  will be described. A water pump  11  is driven through the engine E and force-feeds coolant. 
   A radiator  12  exchanges heat between coolant and outside air. 
   A throttle body  13  contains a throttle valve and adjusts the amount of intake air in accordance with the opening of the valve. 
   A heater core  14  exchanges heat between coolant and air for heating the interior of a vehicle compartment. The heat-exchanged air is supplied to the interior of the vehicle compartment through a heater. 
   An electric water pump  15  is driven through a battery and force-feeds coolant. 
   A heat-accumulating container  16  stores coolant and thermally insulates the coolant from air outside the container. Thus, the coolant is stored in the heat-accumulating container  16  while being held constant in temperature. 
   A coolant delivery pipe  17  causes coolant that has flown out from the heat-accumulating container  16  to flow into a cylinder head of the engine E. 
   A thermostat  21  operates in accordance with the temperature of coolant, and adjusts the flow rate of coolant flowing into a radiator  12 . When the thermostat  21  assumes a minimum opening (i.e., when the thermostat  21  is closed), the flow rate of coolant flowing into the radiator  12  is “0”. As the opening of the thermostat  21  approaches a maximum opening, the flow rate of coolant flowing into the radiator  12  increases. 
   A flow rate control valve  22  is continuously variable in opening and adjusts the flow rate of coolant flowing through a flow passage (bypass passage) for causing the coolant to circulate while bypassing the radiator  12 . When the flow rate control valve  22  assumes a minimum opening (i.e., when the flow rate control valve  22  is closed), the flow rate of coolant flowing through the flow passage is “0”. As the opening of the flow rate control valve  22  approaches a maximum opening, the flow rate of coolant flowing through the flow passage increases. 
   An open-close valve  23  can be switched to its open or closed state, and changes over the flow pattern of coolant in a flow passage (throttle passage) for causing the coolant to flow into a throttle body  13 . When the open-close valve  23  is in its open state, coolant is supplied to the throttle body  13 . On the other hand, when the open-close valve  23  is in its closed state, coolant is not supplied to the throttle body  13 . 
   A three-way valve  24  has three ports (i.e., a first port P 1 , a second port P 2 , and a third port P 3 ), and selectively changes over the circulation pattern of coolant by changing open-close states among the ports. 
   An electronic control unit (EMU)  3  comprehensively controls an injector INJ of the engine E, the electric water pump  15 , the flow rate control valve  22 , the open-close valve  23 , and the three-way valve  24 . The construction of the controller (control means) includes the EMU  3 . 
   Next, various sensors constituting a detection system of the engine cooling device  1  will be described. Various data detected through the detection system are input to the EMU  3 . 
   An engine coolant temperature sensor S 1  detects a temperature (engine coolant temperature The) of coolant for cooling the engine E. 
   A system switch S 2  detects a request to start the engine E. A request to start the engine E can be detected, for example, on the basis of a condition that the changeover position of an ignition switch be shifted to “ON” or a condition that a door be opened through a door open-close switch of the vehicle. 
   The EMU  3  monitors the amount of fuel injected from the injector IN. 
   Next, flow passages in the engine cooling device  1  will be described. 
   A first cooling passage R 1  connects the engine E to the first port P 1  of the three-way valve  24 . 
   A second cooling passage R 2  connects the engine E to the thermostat  21 . 
   A third cooling passage R 3  connects the first cooling passage R 1  to the radiator  12 . 
   A fourth cooling passage R 4  connects the radiator  12  to the thermostat  21 . 
   A fifth cooling passage R 5  connects the first cooling passage R 1  to the flow rate control valve  22 . 
   A sixth cooling passage R 6  connects the flow rate control valve  22  to the second cooling passage R 2  via the thermostat  21 . The sixth cooling passage R 6  is in communication with the second cooling passage R 2  whether the thermostat  21  is open or closed. 
   A seventh cooling passage R 7  connects the first cooling passage R 1  to the open-close valve  23 . 
   An eighth cooling passage R 8  connects the open-close valve  23  to the throttle body  13 . 
   A ninth cooling passage R 9  connects the throttle body  13  to the second cooling passage R 2  via the thermostat  21 . The ninth cooling passage R 9  is in communication with the second cooling passage R 2  whether the thermostat  21  is open or closed. 
   A tenth cooling passage R 10  connects the second port R 2  of the three-way valve  24  to the heater core  14 . 
   An eleventh cooling passage R 11  connects the heater core  14  to the second cooling passage R 2  via the thermostat  21 . The eleventh cooling passage R 11  is in communication with the second cooling passage R 2  whether the thermostat  21  is open or closed. 
   A twelfth cooling passage R 12  connects the third port P 3  of the three-way valve  24  to the electric water pump  15 . 
   A thirteenth cooling passage R 13  connects the electric water pump  15  to the heat-accumulating container  16 . 
   A fourteenth cooling passage R 14  connects the heat-accumulating container  16  to the coolant delivery pipe  17 . 
   The following cooling passages are constituted through the aforementioned cooling passages respectively. 
   The third cooling passage R 3  and the fourth cooling passage R 4  constitute a radiator passage. When the thermostat  21  is open, the radiator passage is open. On the other hand, when the thermostat  21  is closed, the radiator passage is closed. When the radiator passage is open, coolant flows via the radiator  12 . 
   The fifth cooling passage R 5  and the sixth cooling passage R 6  onstitute a bypass passage. When the flow rate control valve  22  is open, the bypass passage is open. On the other hand, when the flow rate control valve  22  is closed, the bypass passage is closed. When the bypass passage is open, coolant flows while bypassing the radiator  12 . 
   The seventh cooling passage R 7 , the eighth cooling passage R 8 , and the ninth cooling passage R 9  constitute a throttle passage. When the open-close valve  23  is open, the throttle passage is open. On the other hand, when the open-close valve  23  is closed, the throttle passage is closed. When the throttle passage is open, coolant flows via the throttle body  13 . 
   The tenth cooling passage R 10  and the eleventh passage R 11  constitute a heater passage. The heater passage can be selectively connected to the first cooling passage R 1  through control of the three-way valve  24 . When both the first and second ports P 1  and P 2  of the three-way valve  24  are open, the heater passage is connected to the first cooling passage R 1  (the heater passage is opened). On the other hand, when the first or second port P 1  or P 2  of the three-way valve  24  is closed, the heater passage is disconnected from the first cooling passage R 1  (the heater passage is closed). When the heater passage is open, coolant flows via the heater core  14 . 
   The twelfth cooling passage R 12 , the thirteenth cooling passage R 13 , and the fourteenth cooling passage R 14  constitute a heat-accumulating passage. The heat-accumulating passage can be selectively connected to the first cooling passage R 1  through control of the three-way valve  24 . When both the first and third ports P 1  and P 3  of the three-way valve  24  are open, the heat-accumulating passage is connected to the first cooling passage R 1  (the heat-accumulating passage is opened). On the other hand, when the first or third port P 1  or P 3  of the three-way valve  24  is closed, the heat-accumulating passage is disconnected from the first cooling passage R 1  (the heat-accumulating passage is closed). When the heat-accumulating passage is open, coolant flows via the heat-accumulating container  16 . 
   The following circulation circuits for causing coolant to circulate are constituted by the aforementioned respective cooling passages. 
   The first cooling passage R 1 , the second cooling passage R 2 , the radiator passage (the third cooling passage R 3  and the fourth cooling passage R 4 ), the bypass passage (the fifth cooling passage R 5  and the sixth cooling passage R 6 ), the throttle passage (the seventh cooling passage R 7 , the eighth cooling passage R 8 , and the ninth cooling passage R 9 ), and the heater passage (the tenth cooling passage R 10  and the eleventh cooling passage R 11 ) constitute a cooling circuit. 
   When coolant circulates through the radiator passage, heat is exchanged in the radiator  12  between the coolant and outside air. When coolant circulates through the bypass passage, radiation of heat from the coolant in the radiator  12  is restricted. When coolant circulates through the throttle passage, heat is exchanged between the throttle body  13  and the coolant. When coolant circulates through the heater passage, heat is exchanged in the heater core  14  between the coolant and air for heating the vehicle compartment. 
   The first cooling passage R 1  and the heat-accumulating passage (the twelfth cooling passage R 12 , the thirteenth cooling passage R 13 , and the fourteenth cooling passage R 14 ) constitute a heat-accumulating circuit. The heat-accumulating passage is connected to the cooling circuit (the first cooling passage R 1 ) through control of the three-way valve  24 , whereby the heat-accumulating circuit is constituted. 
   When coolant circulates through the heat-accumulating circuit, heat is exchanged between the coolant stored in the heat-accumulating container  16  and the engine E. When the open-close valve  23  is open, heat is further exchanged between the coolant stored in the heat-accumulating container  16  and the throttle body  13 . When both the first and second ports P 1  and P 2  of the three-way valve  24  are open, heat is further exchanged in the heater core  14  between the coolant stored in the heat-accumulating container  16  and air for heating the vehicle compartment. 
   In the engine cooling device  1  thus constructed, when the engine E is started, the heat-accumulating passage is opened to supply the engine E with coolant in the heat-accumulating container  16 , whereby the warm-up of the engine E can be promoted. 
   If coolant is caused to circulate with the bypass passage closed in causing coolant in the heat-accumulating container to flow into the engine, the flow resistance of the coolant increases, so that the flow rate of coolant flowing through the cooling circuit and the heat-accumulating circuit is not guaranteed to be sufficient. Hence, the performance of warm-up is adversely affected. 
   In the present embodiment, therefore, such apprehensions are dispelled by controlling the engine cooling device through a procedure that will be described below. 
   Hereinafter, “a cooling device control process during start of the engine” for controlling the driving pattern of the engine cooling device during start of the engine will be described with reference to  FIGS. 2 and 3 . This process is composed of “a preheat process” shown in FIG.  2  and “a coolant circulation stoppage process” shown in FIG.  3 . It is to be noted herein that the present process corresponds to the process performed through the control means of the invention. 
   Referring to  FIG. 2 , “the preheat process” will be described. This process is started upon detection of a request to start the engine E through the system switch S 2 , and is terminated after the performance of processing in steps S 101  to S 106  which will be described below. 
   It is determined whether or not an engine coolant temperature THwe is lower than a cold-state criterion temperature THwL (step S 101 ). That is, it is determined whether or not a condition THwe &lt;THwL is satisfied. 
   If the engine coolant temperature THwe is equal to or higher than the cold-state criterion temperature THwL, a shift to step S 106  is made without performing the processing in the following steps S 102  to S 105 . The cold-state criterion temperature THwL is used as a coolant temperature threshold indicating whether or not the engine E is in a cold state. That is, if the engine coolant temperature THwe is lower than the cold-state criterion temperature THwL, the engine E is in a cold state. 
   If the engine coolant temperature THwe is lower than the cold-state criterion temperature THwL, the following operations are performed (step S 102 ). 
   Namely, (a) the bypass passage is opened by fully opening the flow rate control valve  22  (i.e., by setting the opening thereof as a maximum opening), (b) the throttle passage is opened by opening the open-close valve  23 , (c) the heater passage is connected to the first cooling passage R 1  by opening the first and second ports P 1  and P 2  of the three-way valve  24 , and (d) the heat-accumulating passage is connected to the first cooling passage R 1  by opening the first and third ports P 1  and P 3  of the three-way valve  24 . 
   Coolant is caused to circulate through the bypass passage, the throttle passage, the heater passage, and the heat-accumulating passage by driving the electric water pump  15  (step S 103 ). The promotion of warm-up of the engine E through hot coolant (hot fluid) stored in the heat-accumulating container  16 , namely, so-called preheat is thereby realized. 
   It is determined whether or not a drive period Tpm for the electric warm pump  15  is equal to or longer than a predetermined period TpmX (step S 104 ). That is, it is determined whether or not a condition Tpm ≧TpmX is satisfied. If the condition is not satisfied, the processing in the aforementioned step S 104  is repeatedly performed. The predetermined drive period TpmX indicates a period that elapses before the hot coolant stored in the heat-accumulating container  16  is sufficiently supplied to the interior of the engine E, and can be set in accordance with the volume of the heat-accumulating container  16  or the size of the engine E. 
   If the drive period Tpm for the electric water pump  15  has become equal to or longer than the predetermined period TpmX (i.e., if preheat has been completed), the electric water pump  15  is stopped (step S 105 ). The circulation of coolant in the engine cooling device  1  is thereby stopped. 
   In step S 106 , the following operations are performed. 
   Namely, (a) the bypass passage is closed by fully closing the flow rate control valve  22  (i.e., by setting the opening thereof as a minimum opening), (b) the throttle passage is closed by closing the open-close valve  23 , (c) the heater passage is disconnected from the first cooling passage R 1  by closing the first and second ports P 1  and P 2  of the three-way valve  24 , and (d) the heat-accumulating passage is disconnected from the first cooling passage R 1  by closing the first and third ports P 1  and P 3  of the three-way valve  24 . The present process is terminated after the aforementioned operations have been completed. 
   Thus, according to the preheat process, when the engine E is started in a cold state (i.e., during cold start of the engine E), hot fluid in the heat-accumulating container  16  is supplied to the engine E while the flow rate control valve  22 , the open-close valve  23 , and the three-way valve  24  are all open. In other words, during cold start of the engine E, preheat is carried out after all the valves that can be controlled through the EMU  3  have been opened. 
   If the hot fluid stored in the heat-accumulating container  16  has sufficiently been supplied to the interior of the engine E and if the engine E has been warmed up in comparison with a cold state during start thereof (i.e., during warm start of the engine E), the respective cooling passages of the engine cooling device  1  are closed to stop the circulation of coolant. 
   Referring to  FIG. 3 , the coolant circulation stoppage process will be described. This process is started upon start of the engine E, and is terminated after the performance of processing in steps S 201  and S 202  which will be described below. 
   It is determined whether or not a cumulative value of fuel injection amounts from the start of the engine E up to now (a fuel injection amount cumulative value FiA) is equal to or larger than a predetermined cumulative value FiX (step S 201 ). That is, it is determined whether or not a condition FiA ≧FiX is satisfied. The predetermined cumulative value FiX is used as a fuel injection amount threshold cumulative value indicating whether or not the engine E has just been started. Namely, if the injection amount cumulative value is smaller than the predetermined cumulative value FiX, the engine E has just been started. 
   If the engine E has just been started (i.e., if the injection amount cumulative value FiA is smaller than the predetermined cumulative value FiX), the processing in the aforementioned step S 201  of determination is repeatedly performed at intervals of a predetermined period. At this moment, the flow rate control valve  22 , the open-close valve  23 , and the three-way valve  24  are controlled according to the following pattern. Namely, (a) the flow rate control valve  22  is held fully closed, (b) the open-close valve  23  is held closed, (c) the first and second ports P 1  and P 2  of the three-way valve  24  are held closed, and (d) the first and third ports P 1  and P 3  of the three-way valve  24  are held closed. 
   If the injection amount cumulative value FiA has become equal to or larger than the predetermined cumulative value FiX, the engine cooling device  1  is restored to normal control (step S 202 ). That is, the flow rate control valve  22 , the open-close valve  23 , and the three-way valve  24  are controlled in accordance with the operational state of the engine E or the like. 
   Thus, according to the coolant circulation stoppage process, before the injection amount cumulative value FiA becomes equal to or larger than the predetermined cumulative value FiX after the engine E has been started, the flow rate control valve  22 , the open-close valve  23 , and the three-way valve  24  are held closed, whereby the circulation of coolant in the engine cooling device  1  is stopped. 
   Referring now to  FIG. 4 , the control patterns of the engine cooling device  1  according to the cooling device control process ( FIGS. 2 and 3 ) during start of the engine will be summarized. 
   If a condition [1] shown below is satisfied in starting the engine E, the engine cooling device  1  is controlled through a preheat mode that will be described later. On the other hand, if one of conditions [2] to [4] shown below is satisfied in starting the engine E, the engine cooling device  1  is controlled through a coolant circulation stoppage mode that will be described later. 
   [1] That the engine E be started in a cold state (the engine coolant temperature The be lower than the cold-state criterion temperature THwL) and that preheat have not been completed (the drive period Tpm for the electric water pump  15  be shorter than the predetermined period TpmX). 
   [2] That the engine E be started in a cold state (the engine coolant temperature The be lower than the cold-state criterion temperature THwL) and that preheat have been completed (the drive period Tpm for the electric water pump  15  be equal to or longer than the predetermined period TpmX). 
   [3] That the engine E be started in a hot state (the engine coolant temperature The be equal to or higher than the cold-state criterion temperature THwL). 
   [4] That the engine E have just been started (the fuel injection amount cumulative value FiA be smaller than the predetermined cumulative value FiX). 
   In the preheat mode, (a) the flow rate control valve  22  is fully opened, (b) the open-close valve  23  is opened, (c) all the ports of the three-way valve  24  are opened, and (d) the electric water pump  15  is driven. The engine cooling device  1  is controlled according to these patterns. 
   In the coolant circulation stoppage mode, (a) the electric water pump  15  is stopped, (b) the flow rate control valve  22  is fully closed, (c) the open-close valve  23  is closed, and (d) all the ports of the three-way valve  24  are closed. The engine cooling device  1  is controlled according to these patterns. 
   In any of the aforementioned respective control modes, the thermostat  21  is basically held closed. 
   Referring now to  FIGS. 5 and 6 , the operation and effect achieved by “the cooling device control process during start of the engine” ( FIGS. 2 and 3 ) will be described.  FIG. 5  shows a pattern according to which coolant circulates when the engine cooling device  1  is controlled through the preheat mode.  FIG. 6  shows a pattern according to which coolant circulates when the engine cooling device  1  is controlled through the coolant circulation stoppage mode. In  FIGS. 5 and 6 , cooling passages indicated by solid lines represent those through which coolant flows, arrows represent directions in which coolant flows, and cooling passages indicated by broken lines represent those through which coolant does not flow. 
   Referring to  FIG. 5 , the operation and effect achieved by the preheat mode will be described. 
   When the engine cooling device  1  is controlled through the preheat mode, the electric water pump  15  causes coolant to circulate while the bypass passage, the throttle passage, and the heater passage as well as the heat-accumulating passage are open. Therefore, the coolant flows through all the cooling passages but the radiator passage. 
   At this moment, since coolant circulates via the heat-accumulating passage, the hot fluid stored in the heat-accumulating container  16  is supplied to the engine E. Also, because the bypass passage, the throttle passage, and the heater passage are open, the flow resistance of coolant is reduced. 
   The flow rate of the hot fluid supplied to the engine E from the heat-accumulating container  16  thereby increases, and the hot fluid in the heat-accumulating container  16  flows into the engine E at an early stage. Therefore, the warm-up of the engine E is promoted suitably. 
   Referring to  FIG. 6 , the operation and effect achieved by the coolant circulation stoppage mode will be described. 
   When the engine cooling device  1  is controlled through the coolant circulation stoppage mode, the radiator passage, the bypass passage, the throttle passage, the heater passage, and the heat-accumulating passage are closed. Therefore, coolant does not circulate through any of the cooling passages. 
   Thus, after hot fluid in the heat-accumulating container  16  has been supplied into the interior of the engine E sufficiently, low-temperature coolant is not recirculate to the engine E. Therefore, the warm-up of the engine E is promoted more suitably. 
   When the engine E is started in a hot state and even if the engine E has just been started, low-temperature coolant is not recirculate to the engine E. Therefore, the warm-up of the engine E is promoted more suitably. 
   Referring now to  FIG. 7 , one example of the control pattern of the engine cooling device  1  according to “the cooling device control process during start of the engine” will be described. It is assumed that a request to start the engine E is detected through a vehicle-door opening operation based on a door open-close switch at a time t 71  (see FIG.  7 B). 
   If it is assumed herein that the engine coolant temperature THwe is lower than the cold-state criterion temperature THwL, the following operations (a) to (d) are performed (see  FIGS. 7C  to  7 F). 
   That is, (a) the flow rate control valve  22  is fully opened, (b) the open-close valve  23  is fully opened, (c) all the ports of the three-way valve  24  are opened, and (d) the electric water pump  15  is driven. 
   Coolant is thereby caused to circulate with its flow resistance having been reduced. As a result, the hot fluid in the heat-accumulating container  16  is supplied to the engine E at an early stage. 
   If it is assumed that the drive period Tpm for the electric water pump  15  becomes equal to or longer than the predetermined period TpmX at a time t 72 , the following operations (a) to (d) are performed (see  FIGS. 7C  to  7 F). 
   That is, (a) the electric water pump  15  is stopped, (b) the flow rate control valve  22  is fully closed, (c) the open-close valve  23  is fully closed, and (d) all the ports of the three-way valve  24  are closed. 
   The circulation of low-temperature coolant to the engine E is thereby stopped. As a result, the warm-up of the engine E is promoted suitably. 
   If it is assumed that the engine E is started at a time t 73 , the flow rate control valve  22 , the open-close valve  23 , and the three-way valve  24  are held closed until the fuel injection amount cumulative value FiA becomes equal to or larger than the predetermined cumulative value FiX (see  FIGS. 7A and 7C  to  7 E). 
   Because the circulation of coolant is thereby stopped, the warm-up of the engine E is promoted suitably. 
   If it is assumed that the fuel injection amount cumulative FiA becomes equal to or larger than the predetermined cumulative value FiX at a time t 74 , the flow rate control valve  22 , the open-close valve  23 , and the three-way valve  24  are thereafter controlled in accordance with the operational state of the engine E ( FIGS. 7C  to  7 E). 
   As described above in detail, beneficial effects as cited below are gained from the engine cooling device of the embodiment. 
   (1) In the present embodiment, if hot fluid in the heat-accumulating container  16  is supplied to the engine E on the ground that the engine coolant temperature The is lower than the cold-state criterion temperature THwL before the operation of starting the engine E, the bypass passage, the throttle passage, and the heater passage as well as the heat-accumulating passage are opened. The flow resistance of coolant is thereby reduced, and the hot fluid in the heat-accumulating container  16  is supplied to the engine E at an early stage. Therefore, the warm-up of the engine E can be promoted suitably. 
   (2) The aforementioned process (1) is performed before the operation of starting the engine E. Therefore, the engine E can be warmed up at an earlier stage. 
   (3) In the present embodiment, if hot fluid in the heat-accumulating container  16  is sufficiently supplied to the engine E before the operation of starting the engine E, the bypass passage, the throttle passage, the heater passage, and the heat-accumulating passage are closed. The circulation of low-temperature coolant to the engine E is thereby stopped. Therefore, the engine E can be suitably restrained from being lowered in temperature by low-temperature coolant. 
   (4) In the present embodiment, if the engine coolant temperature The is equal to or higher than the cold-state criterion temperature THwL before the operation of starting the engine E, the bypass passage, the throttle passage, the heater passage, and the heat-accumulating passage are closed. The circulation of low-temperature coolant is thereby stopped. Therefore, the engine E can be suitably restrained from being lowered in temperature by low-temperature coolant. 
   (5) In the present embodiment, before the fuel injection amount cumulative value FiA becomes equal to or larger than the predetermined cumulative value FiX after the engine E has been started, the warm-up operation of the engine E is performed with the bypass passage, the throttle passage, the heater passage, and the throttle passage being closed. The circulation of coolant is thereby stopped. Therefore, the warm-up of the engine E can be promoted suitably. 
   The aforementioned embodiment may be suitably modified and can also be implemented as embodiments that will be described hereinafter. 
   In the aforementioned embodiment, the following determination process can also be added to the preheat process (FIG.  2 ). That is, it is determined immediately before or after step S 101  “whether or not the temperature of coolant in the heat-accumulating container  16  (i.e., a heat-accumulating container coolant temperature THwt) is equal to or higher than a predetermined criterion temperature”. In this case, (a) if the heat-accumulating container coolant temperature THwt is equal to or higher than the predetermined criterion temperature, the processing starting from step S 102  are sequentially performed. On the other hand, (b) if the heat-accumulating container coolant temperature THwt is lower than the predetermined criterion temperature, the processing in step S 106  is performed while omitting the processing in steps S 102  to S 105 . The construction as described herein makes it possible to appropriately promote the warm-up of the engine E. 
   In the aforementioned embodiment, the following determination processing can also be added to the preheat process (FIG.  2 ). That is, it is determined immediately before or after step S 101  “whether or not the temperature of coolant in the heat-accumulating container  16  (i.e., the heat-accumulating container coolant temperature THwt) is equal to or higher than the engine coolant temperature THwe”. In this case, (a) if the heat-accumulating container coolant temperature THwt is equal to or higher than the engine coolant temperature THwe, the processing starting from step S 102  are sequentially performed. On the other hand, (b) if the heat-accumulating container coolant temperature THwt is lower than the engine coolant temperature THwe, the processing in step S 106  is performed while omitting the processing in steps S 102  to S 105 . The construction as described herein prevents the low-temperature coolant stored in the heat-accumulating container  16  from being supplied to the engine E. As a result, the warm-up performance of the engine E can be suitably restrained from deteriorating. 
   In the aforementioned embodiment, it is determined whether or not the engine coolant temperature The is lower than the cold-state criterion temperature THwL, and the processing in steps S 102  to S 105  (preheat) are performed when this condition is satisfied. However, the invention is not limited to this construction. Namely, it is also appropriate to omit the determination processing in step S 101  and to perform the processing starting from step S 102  every time the engine E is started. The construction as described herein eliminates the necessity to monitor the engine coolant temperature THwe prior to the implementation of preheat. In consequence, the preheat process is simplified. 
   In the aforementioned embodiment, preheat is carried out on the ground that the engine coolant temperature THwe is lower than the cold-state criterion temperature THwL. However, the invention is not limited to this construction. Namely, preheat may also be carried out on the ground that the engine coolant temperature THwe is lower than an outside air temperature. 
   In the aforementioned embodiment, the cold-state criterion temperature THwL is used in the determination processing of step S 101 . However, the cold-state criterion temperature THwL can be suitably changed to any temperature “that is equal to or higher than an outside air temperature and that is lower than a coolant temperature indicating the completion of warm-up of the engine E”. 
   In the aforementioned embodiment, it is determined that the engine E has just been started, on the ground that the fuel injection amount cumulative value FiA is smaller than the predetermined cumulative value FiX. However, the invention is not limited to this construction. Namely, it may also be determined that the engine E has just been started on the ground that the engine coolant temperature THwe is lower than the predetermined temperature. 
   In the aforementioned embodiment, it is determined that the engine E has just been started, on the ground that the fuel injection amount cumulative value FiA is smaller than the predetermined cumulative value FiX. However, the invention is not limited to this construction. Namely, it may also be determined that the engine E has just been started, on the ground that the elapsed time after completion of the start of the engine E is shorter than a predetermined elapsed time. 
   In the aforementioned embodiment, a request to start the engine E can be detected on the basis of the condition that “the changeover position of the ignition switch be shifted to “ON”” or the condition that “the door be opened through the door open-close switch of the vehicle”. However, the detection of a request to start the engine can be determined on the basis of other suitable conditions as well as the conditions exemplified in the aforementioned embodiment. For instance, a request to start the engine may also be detected on the basis of a condition “that the changeover position of the ignition switch be shifted to “START””. 
   In the aforementioned embodiment, the open-close valve  23  is opened to open the throttle passage if preheat has not been completed in starting the engine E in a cold state. However, the invention is not limited to this construction. Namely, the open-close valve  23  is closed even if preheat has not been completed in starting the engine E in a cold state. It is also appropriate that the throttle valve be thereby closed. 
   In the aforementioned embodiment, if preheat has not been completed in starting the engine E in a cold state, the flow rate control valve  22  is fully opened to open the bypass passage. However, the invention is not limited to this construction. Namely, if preheat has not been completed in starting the engine E in a cold state, the flow rate control valve  22  may also be set at any opening between its maximum opening and its minimum opening to open the bypass passage. In short, the control pattern of the flow rate control valve can be suitably changed as long as the flow rate of coolant flowing through the bypass passage is increased when the coolant is caused to circulate through the heat-accumulating circuit in starting the engine E in a cold state. 
   In the aforementioned embodiment, if preheat has not been completed in starting the engine E in a cold state, the first and second ports P 1  and P 2  of the three-way valve  24  are opened to open the heater passage. However, the invention is not limited to this construction. The heater passage may also be closed by closing the second port P 2  of the three-way valve  24  if preheat has not been completed in starting the engine E in a cold state. 
   In the aforementioned embodiment, the thermostat  21  that operates in accordance with the temperature of coolant is used. However, the invention is not limited to this construction. It is also possible to employ an electronic thermostat capable of electrically controlling the release state of a valve. In the construction as described herein, the electronic thermostat is opened to open the radiator passage if preheat has not been completed in starting the engine E in a cold state, whereby the flow resistance of coolant can further be reduced. If any one of the above-mentioned conditions (2) to (4) is satisfied, the recalculation of low-temperature coolant to the engine E can be avoided by closing the electronic thermostat. 
   In the aforementioned embodiment, the throttle passage is provided with the open-close valve  23 . However, the invention is not limited to this construction. Namely, a flow rate control valve whose opening is continuously variable can also be provided in place of the open-close valve  23 . 
   In the aforementioned embodiment, the bypass passage is provided with the flow rate control valve  22 . However, the invention is not limited to this construction. Namely, an open-close valve that can be switched to either its open state or its closed state can also be provided in place of the flow rate control valve  22 . 
   In the aforementioned embodiment, the preheat process is started in response to a request to start the engine E. However, the invention is not limited to this construction. Namely, the preheat process may also be started in response to the start of the engine E. The construction as described herein makes it possible to start the coolant circulation stoppage process after the preheat process has been completed. 
   In the aforementioned embodiment, the preheat process is started in response to a request to start the engine E. However, the invention is not limited to this construction. The preheat process may also be started immediately after the engine E has been started. The construction as described herein makes it possible to start the coolant circulation stoppage process after the preheat process has been completed. 
   In the aforementioned embodiment, the heat-accumulating passage is connected to or disconnected from the cooling circuit through control of the three-way valve  24 . However, the invention is not limited to this construction. Namely, it is also appropriate that the heat-accumulating passage be provided with an open-close valve, a flow rate control valve or the like and be connected to or disconnected from the cooling circuit through control of the open-close valve, the flow rate control valve or the like. 
   In the aforementioned embodiment, the invention is embodied on the assumption that the engine cooling device  1  exemplified in  FIG. 1  is to be used. However, the construction of the engine cooling device is not limited to the construction exemplified in the embodiment but can be any suitable construction. In short, as long as the cooling device is provided with a cooling circuit composed of a radiator passage, a bypass passage, and a flow rate control valve for controlling the flow rate of coolant flowing through the bypass passage, and with a heat-accumulating passage that includes a heat-accumulating container and that constitutes a heat-accumulating circuit by being selectively connected to the cooling circuit, it is possible to provide the cooling device with any construction. 
   In the aforementioned embodiment, the engine cooling device  1  is controlled during start of the engine E through the cooling device control process performed in starting the engine. However, the cooling device control process performed in starting the engine is not limited to the construction exemplified in the embodiment. In short, the control pattern can be suitably modified as long as it is constructed such that a heat-accumulating circuit is completed by connecting a heat-accumulating passage to a cooling circuit in starting an engine, that a bypass passage is opened through control of a control valve, that the heat-accumulating passage is disconnected from the cooling circuit after coolant in a heat-accumulating container has been supplied to the engine, and that the bypass passage is closed through control of the control valve. 
   While the invention has been described with reference to the exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the exemplary embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.
The invention provides an engine cooling device capable of suitably promoting the warm-up of an engine. This engine cooling device comprises a cooling circuit and a heat-accumulating passage. The cooling circuit is composed of a radiator passage, a bypass passage, and a flow rate control value for controlling the flow rate of coolant flowing though the bypass passage. The heat-accumulating passage is provided with a heat-accumulating container, and constitutes a heat-accumulating circuit for causing coolant in the heat-accumulating container to circulate via the engine. The cooling device completes the heat-accumulating circuit by connecting the heat-accumulating passage to the cooling circuit to supply the cooling medium in the heat-accumulating container to the body of the engine, opens the flow rate control valve to increase a flow rate of cooling medium flowing though the bypass passage, then disconnects the heat-accumulating passage from the cooling circuit, and closes the flow rate control valve.