Abstract:
Cooling water is circulated at small flow rate of 1 to 5 L/min between a bypass passage and an engine without circulating the cooling water in an oil cooler before the warming-up of the engine is completed. After the warming-up is completed, the cooling water is supplied to the oil cooler so that the engine cooling water temperature is maintained at 95° C. to 110° C. Consequently, the no local boiling of the cooling water in the engine occurs to prevent the engine from being deformed locally due to heat. Thus, the warming-up of the engine can be promoted while preventing the heat of the engine from being absorbed by the ATF through the cooling water. After the warming-up is completed, the fuel consumption can be improved by reducing the friction loss of the engine oil.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cooling apparatus and, more particularly, to a cooling apparatus, for a liquid cooled internal combustion engine, such as a cooling apparatus for an automobile engine. 
     2. Description of the Related Art 
     Coolant for a liquid-cooled internal combustion engine is conventionally circulated by a pump that is driven by the engine. When the engine is started, the idling engine speed is increased both to warm-up the engine and to prevent the engine from stalling. For a coolant pump driven by the engine, the average flow rate of coolant increases because the speed of rotation of the pump increases as the engine picks up speed. Since heat transfer to the coolant increases as the average flow rate of the coolant increases, it is difficult to warm up the engine immediately after the engine is started. 
     To solve this problem, Japanese Kokai No. 8-14043 discloses a coolant pump driven by an electrical motor that is stopped when the engine is being warmed up. 
     However, stopping the coolant pump decreases the heat transfer to the coolant so that the coolant in the engine often boils locally. Local boiling of the coolant may cause the engine (cylinder head, cylinder block, etc.) to deform, thus damaging the engine. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to eliminate the drawbacks mentioned above by preventing damage to an engine (internal combustion engine) and promoting the warming-up of the engine. 
     To achieve the object, according to an aspect of the present invention, there is provided a cooling apparatus for a liquid-cooled internal combustion engine ( 10 ), comprising: a radiator ( 20 ) that cools coolant discharged from the engine bypasses the radiator ( 20 ) and returns to the engine ( 10 ); and a heat exchanger ( 90 ) that exchanges heat between coolant discharged from the engine ( 10 ) and a working oil; wherein when the temperature of the coolant discharged from the engine ( 10 ) is below a predetermined temperature, the flow rate of the coolant returned to the engine ( 10 ) is restricted to between 1 and 5 L/min, and the coolant discharged from the engine ( 10 ) is allowed to flow through the radiator ( 20 ) and the bypass passage ( 30 ) but not the heat exchanger ( 90 ); and when the temperature of the coolant discharged from the engine is above the predetermined temperature, the coolant discharged from the engine is allowed to flow through the radiator ( 20 ), the bypass passage ( 30 ), and the heater exchanger ( 90 ). 
     With this arrangement, when the temperature of the coolant is below a predetermined temperature, the coolant is circulated at small flow rate of 1 to 5 L/min between the bypass passage ( 30 ) and the liquid-cooled internal combustion engine ( 10 ) and, hence, it is possible to prevent the coolant in the liquid-cooled internal combustion engine ( 10 ) from boiling locally. 
     Moreover, it is possible to shorten the time necessary to complete the warming-up, in comparison with the circulation of the coolant at flow rate of 5 L/min or more. Consequently, the warming-up can be promoted while preventing the liquid-cooled internal combustion engine (cylinder head or cylinder block, etc.) from being deformed locally due to heat. 
     When the temperature of the coolant is below a predetermined temperature, the coolant is circulated at least between the liquid-cooled internal combustion engine ( 10 ) and the bypass passage ( 30 ) without passing in the oil heat exchanger ( 90 ) and, hence, it is possible to prevent the heat of the liquid-cooled internal combustion engine ( 10 ) from being absorbed by the working oil through the coolant. Therefore, the warming-up can be further promoted. 
     The oil heater exchanger ( 90 ) exchanges heat between working oil in a torque converter ( 80 ) for an automatic transmission and the coolant. 
     According to another aspect of the present invention, a cooling apparatus for a liquid-cooled internal combustion engine ( 10 ); comprising: a radiator ( 20 ) that cools coolant discharged from the engine ( 10 ) and returns the cooled coolant to the engine ( 10 ); a bypass passage ( 30 ) through which the coolant discharged from the engine ( 10 ) bypasses the radiator ( 20 ) and returns to the engine ( 10 ); and a heater exchanger ( 60 ) that exchange heat between coolant discharged from the engine ( 10 ) and ambient air; wherein before the engine is warmed-up of the engine, the flow rate of the coolant returned to the engine is restricted to between 1 and 5 L/min, and the coolant discharged from the engine ( 10 ) is allowed to flow through the radiator ( 20 ), the bypass passage ( 30 ) but not heat exchanger ( 60 ); and after the engine is warmed up, the coolant discharged by the engine is allowed to flow through the radiator ( 20 ), the bypass passage ( 30 ) and the heater exchanger ( 60 ). 
     With this arrangement, when the temperature of the coolant is below a predetermined temperature, the coolant is circulated at small flow rate of 1 to 5 L/min between the bypass passage ( 30 ) and the liquid-cooled internal combustion engine ( 10 ) and, hence, it is possible to prevent the coolant in the liquid-cooled internal combustion engine ( 10 ) from boiling locally. 
     Moreover, it is possible to shorten the time necessary to complete the warming-up, in comparison with the circulation of the coolant at flow rate of 5 L/min or more. Consequently, the warming-up can be promoted while preventing the liquid-cooled internal combustion engine (cylinder head or cylinder block, etc.) from being deformed locally due to heat. 
     Since when the temperature of the coolant is below a predetermined temperature, the coolant is circulated at least between the liquid-cooled internal combustion engine ( 10 ) and the bypass passage ( 30 ) without passing in the heating heat exchanger ( 60 ), it is possible to prevent the heat of the liquid-cooled internal combustion engine ( 10 ) from being absorbed by the air through the coolant. Therefore, the warming-up can be further promoted. 
     In addition to the foregoing, when the temperature of the coolant is above a predetermined temperature, the coolant is circulated to the heating heat exchanger ( 60 ) and, hence, the warming-up can be quickly carried out by the coolant of high temperature when the ambient temperature is low. 
     According to still another aspect of the present invention, there is provided a cooling apparatus for a liquid-cooled internal combustion engine ( 10 ); comprising: a radiator ( 20 ) that cools coolant discharged from the engine ( 10 ) and returns the cooled coolant to the engine ( 10 ); a bypass passage ( 30 ) through which the coolant discharged from the engine ( 10 ) bypasses the radiator ( 20 ) and returns to the engine ( 10 ); and a heater exchanger ( 90 ) that exchange heat between coolant discharged from the engine ( 10 ) and a working oil; wherein when the temperature of coolant discharged from the engine is below a predetermined temperature, the flow rate of the coolant returned to the engine is restricted between 1 and 5 L/min, and the coolant discharged from the engine ( 10 ) is allowed to flow through only the radiator ( 20 ) and the bypass passage ( 30 ) but not the heater exchanger ( 90 ); when the temperature of the coolant is above the predetermined temperature, the coolant discharged from the engine is allowed to flow through the radiator ( 20 ), the bypass passage ( 30 ), and the oil heat exchanger ( 90 ); when the engine ( 10 ) is warmed up, the cooling liquid is circulated to the radiator ( 20 ) so that the temperature of the coolant is approximately in the range of 95° C. to 110° C. 
     With this structure, when the temperature of the coolant is below a predetermined temperature, the coolant is circulated at small flow rate of 1 to 5 L/min between the bypass passage ( 30 ) and the liquid-cooled internal combustion engine ( 10 ) and, hence, it is possible to prevent the coolant in the liquid-cooled internal combustion engine ( 10 ) from boiling locally. Moreover, it is possible to shorten the time necessary to complete the warming-up, in comparison with the circulation of the coolant at flow rate of 5 L/min or more. Consequently, the warming-up can be promoted while preventing the liquid-cooled internal combustion engine (cylinder head or cylinder block, etc.) from being deformed locally due to heat. 
     When the temperature of the coolant is below a predetermined temperature, the coolant is circulated at least between the liquid-cooled internal combustion engine ( 10 ) and the bypass passage ( 30 ) without passing in the oil heat exchanger ( 90 ) and, hence, it is possible to prevent the heat of the liquid-cooled internal combustion engine ( 10 ) from being absorbed by the working oil through the coolant. Consequently, the warming-up can be further promoted. 
     When the temperature of the coolant is above a predetermined value, the coolant is circulated to the oil exchanger ( 90 ) and, hence, when the temperature of the working oil is low, the working oil can be heated by the coolant of high temperature. 
     Consequently, not only can the warming-up can be promoted, but also the fuel consumption can be improved by increasing the temperature of the working oil to thereby reduce the friction loss thereof. 
     Since the control is made so that the temperature of the coolant is maintained in the range of 95° C. to 110° C. when the warming-up is completed, the fuel consumption can be further improved by increasing the temperature of the lubricant (engine oil) which is circulated in the liquid-cooled internal combustion engine ( 10 ) to thereby reduce the friction loss. 
     Note that the reference numerals of the components (means) recited above exemplarily correspond to those in embodiments of the invention which will be discussed below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a cooling apparatus according to a first embodiment of the present invention. 
     FIG. 2 is a flow chart of the operation of the cooling apparatus according to the first embodiment of the present invention. 
     FIG. 3A is a graph showing the coolant temperature and the oil temperature as a function of time, and FIG. 3B is a graph showing a relationship between the engine speed as a function of time. 
     FIG. 4 is a schematic view of a conventional cooling apparatus. 
     FIG. 5 is a schematic view of a conventional cooling apparatus. 
     FIG. 6 is a bar graph showing the improvement of fuel consumption due to operation of the cooling apparatus according to the first embodiment of the present invention. 
     FIG. 7 is a schematic view of a cooling apparatus according to a second embodiment of the present invention. 
     FIG. 8 is a graph of the flow rate of coolant warming-up control mode and time necessary to warm up the engine. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the invention is discussed immediately below with reference to FIG. 1, a schematic of the first embodiment. In this embodiment, a cooling apparatus for a liquid-cooled internal combustion engine is used to cool an automobile engine. 
     In FIG. 1, Numeral  10  designates a liquid-cooled internal combustion engine (engine), Numeral  20  designates a radiator that cools a coolant that has been: discharged from the engine  10  and returns the cooled coolant to the engine  10 , and Numeral  21  designates a cooling fan for supplying cold air to the radiator  20 . 
     Numeral  30  designates a bypass passage through which coolant discharged from the engine  10  bypasses the radiator  20  and returns to the engine  10 ; Numeral  40  designates an electronic flow rate control valve Ad (referred to as the first valve) that controls the flow rates through both the radiator  20  and the bypass passage  30 ; Numeral  50  designates a coolant pump that is driven by the engine  10 . 
     Numeral  60  designates a heat exchanger (heater) that heats air to be discharged into a vehicle compartment by using the coolant (engine waste heat) as a heat source; Numeral  70  designates an electromagnetic valve (referred to as the second valve) that opens and closes a passage through which the coolant is supplied to the heater  60 ; Numeral  61  designates an air conditioning fan, which discharges cooled air into the vehicle compartment. 
     Numeral  80  designates a torque converter (fluid coupling) for an automatic transmission; and Numeral  90  designates an oil cooler (oil heat exchanger) that exchanges heat between the working oil of the torque converter  80  (automatic transmission fluid or ATF) and the coolant. 
     Numeral  101  designates a first coolant temperature sensor that is mounted within the bypass passage  30  adjacent the first valve  40  and Numeral  102  designates a second coolant temperature sensor that is mounted adjacent the inlet port of the pump  50  to sense the temperature of the coolant returned to the engine  10 . 
     Numeral  103  designates a pressure sensor that senses the suction negative pressure of the engine  10 ; Numeral  104  designates an engine speed sensor, which measures the speed of the engine  100 , and Numeral  105  designates an ambient temperature sensor which measures the temperature of the ambient air. 
     Signals from the sensors  101  through  105  and an ON/OFF signal from a start switch  106  of the vehicle&#39;s air conditioner are input to an electronic control unit (ECU)  100 , which controls the first and second valves  40  and  70  and the cooling fan  20  in accordance with predetermined programs. 
     The operations of the first and second valves  40  and  70  are discussed immediately below with reference to both the flow chart shown in FIG.  2  and the schematic shown in FIG.  1 . 
     When the engine  10  starts after the vehicle&#39;s ignition switch (not shown) is turned ON, the outputs of the speed sensor  104 , the pressure sensor  103 , the first and second coolant temperature sensors  101  and  102 , the ambient temperature sensor  105 , and the start switch  106  are read by the ECU  100 , as depicted by step S 100  in FIG.  2 . 
     The ECU  100  then calculates, the engine load using the engine speed and the suction negative pressure. 
     Based on the engine load thus obtained, the target temperature of the coolant (referred to as the target temperature Tmap), the flow rate of the coolant to be returned to the engine  10 , and the temperature of the coolant to be returned to the engine at which warm-up is deemed complete (referred to as the warm-up completion temperature Tw 1 ) are determined from a map (not shown) (S 110 ). 
     The temperature of the coolant flowing through the bypass passage  30  (referred to as the bypass coolant temperature Tb), which is measured by the first temperature sensor  101 , is compared with the warm-up completion temperature Tw 1 , which would be 100° C. of the coolant were pure water (S 120 ). 
     If the bypass coolant temperature Tb is less than the warm-up completion temperature Tw 1 , the engine load (as measured by the pressure sensor  103 ) is compared with a predetermined value R 0  (S 130 ). 
     If the measured engine load is less than the predetermined value R 0 , the second valve  70  is closed to prevent coolant from flowing to the oil cooler  90  and the warm-up control mode operation in which the coolant is circulated at least between the engine  10  and the bypass passage  30 . 
     In the warm-up control mode, the first valve  40  limits the coolant flow through the engine  10  to between 1 and 5 L/min, which range is narrower than the conventional range of (10 to 15 L/min) (S 140 , S 150 ). 
     If the measured bypass coolant temperature Tb is greater than the warm-up completion temperature Tw 1 , so that warm-up is deemed completed, or if the engine load is greater than the predetermined value R 0 , so that the warm-up control mode operation is no longer necessary, the second valve  70  is opened to allow the coolant to flow through the oil cooler  90 . A high temperature control mode operation is the coolant temperature, as measured by the second coolant temperature sensor  103 , is limited to the range 95 to 110° C. (S 160 , S 170 ). 
     The advantages of the first embodiment are described immediately below. 
     For low coolant temperatures, 1 to 5 L/min of coolant flows through the engine  10 , which is sufficient to prevent local boiling of coolant in the engine  10 . FIG. 8 shows the empirical relationship between the coolant flow rate in the warm-up control mode and the time needed to warm-up a 2000 cc (displacement) engine. When the coolant flow rate is 1 L/min, engine warm-up requires approximately 88% of the time required when the coolant flow rate is 15 L/min; when the coolant flow rate is 5 L/min engine warm-up requires approximately 98% of the time required when the coolant flow rate is 15 L/min. Thus, the time required to warm-up the engine decreases with coolant flow rate for flow rates less than 5 L/min. Such low flow rates are, however, sufficient to prevent heat-induced deformation of the engine  10  (cylinder head, cylinder block, etc.) 
     Moreover, when the coolant temperature is less than the warm-up completion temperature Tw 1 , the coolant is allowed to flow through the oil cooler  90 . Since the temperature of the coolant does not decrease due to heat transfer from the coolant to the ATF, the time required to warm-up the engine is further shortened. 
     FIG. 3A shows the empirical variation of the coolant temperature at the outlet of the engine and the oil temperature at the outlet of the oil cooler. In FIG. 3A, “A” represents the conventional cooling apparatus shown in FIG. 4, “B” represents the conventional cooling apparatus shown in FIG. 5, and “C” represents the cooling apparatus according to the first embodiment of the present invention. FIG. 4 depicts a conventional in which the first valve  40  is replaced with a thermostat that controls the opening of a flow control valve that utilizes the volume change of a wax material. FIG. 5 depicts a conventional cooling apparatus in which the oil cooler  90  is mounted in the radiator  20 . 
     FIG. 3A shows that the temperature of coolant discharged from the engine quickly reaches 80° C., the temperature at which the fuel injection control mode is switched from a start control mode to a normal control mode. FIG. 3B depicts the time dependence of the vehicle speed when the coolant temperature evolves as shown in FIG.  3 A. 
     Since coolant flows through the oil cooler  90  only when the coolant temperature exceeds the warm-up completion temperature Tw 1 , high-temperature coolant may be used to heat the ATF when the temperature of the ATF is low. 
     Therefore, not only can the engine be warmed-up more quickly, but the fuel consumption of the vehicle can also be improved by using the high-temperature coolant to warm the ATF thereby reduce the friction loss. In this embodiment, coolant flows through the oil cooler  90  only when the coolant temperature exceeds 100° C. and, hence, the temperature difference between the ATF and the coolant can be increased. Consequently, the temperature of the ATF can be rapidly increased, as shown by FIG.  3 A. 
     After the engine is warmed-up, engine coolant temperature is maintained between 95° C. and 110° C. and, hence, the fuel consumption can be improved by increasing the temperature of the lubricant (engine oil) to thereby reduce the friction loss, as may be seen in FIG.  6 . 
     In FIG. 6 “A” represents the conventional cooling apparatus shown in FIG. 4; “B” represents to the conventional cooling apparatus shown in FIG. 5; and “C” represents the cooling apparatus according to the first embodiment of the present invention. 
     A second embodiment of the present invention will be discussed below. In the second embodiment shown in FIG. 7, the first valve  40  and the second valve  70  are replaced with a single valve  45 . 
     The present invention can readily be modified as follows. In the first and second embodiments, the temperature of the coolant that flows through the oil cooler  90  was taken to be the same as the temperature at which engine warm-up is deemed complete. However, these two temperatures may be allowed to differ. 
     Moreover, although an oil cooler that exchanges heat between the ATF and the coolant is used in the first and second embodiments, an oil cooler that exchanges heat between the engine oil and the coolant can also be used. Furthermore, although the coolant pump  50  driven by the engine  10  is used in the first and second embodiments, a coolant pump driven by an electric motor can also be used.