Abstract:
A driving load of a cooling fan unit is selectively determined from a plurality of predetermined loads corresponding to vehicle parameters including a coolant temperature and a vehicle speed. Also, on the basis of a plurality of coolant temperature ranges and a plurality of vehicle speed ranges. The cooling fan unit is driven with the determined driving load. The vehicle parameters preferably further include a refrigerant pressure and a state of an air/con switch.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority of Korean Application No. 10-2003-0025108, filed Apr. 21, 2003, the disclosure of which is incorporated fully herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    Generally, the present invention relates to a method and apparatus for controlling a cooling fan of a vehicle. More particularly, the present invention relates to a method and apparatus for optimally controlling a cooling fan of a vehicle in a variety of vehicle running states.  
         BACKGROUND OF THE INVENTION  
         [0003]    Typically, a vehicle is equipped with a radiator to exhaust heat generated by an engine. A cooling fan is mounted to the radiator so heat is expelled therefrom by active blowing of air. When a vehicle is equipped with an air conditioning system (referred to as “air/con” hereinafter), a condenser is disposed in the vicinity of the radiator for condensing refrigerant and for radiating heat therefrom. An additional cooling fan is provided for enhancing heat radiation of both of the radiator and the condenser.  
           [0004]    For stable running of the vehicle, the one or more cooling fans should be properly controlled in accordance with a running state of the vehicle. Therefore, research has been undertaken for determining an optimal controlling of the cooling fan in accordance with variable running states of the vehicle. For example, such a cooling fan can be controlled on and off according to a coolant temperature of an engine.  
           [0005]    As a further development, as is described in Laid Open Korean patent publication 2002-80980, the cooling fan can be controlled according to a temperature of a cabin room of a vehicle. Further information regarding controlling of a cooling fan of a vehicle can be found in Laid Open Korean patent publications 2000-21773 and 2002-93393. If a cooling fan can be better controlled in accordance with a running state of a vehicle than as yet known in the art, more stable operation of an engine and more stable running of the vehicle can be achieved.  
           [0006]    The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.  
         SUMMARY OF THE INVENTION  
         [0007]    An embodiment of the present invention provides a method and apparatus for controlling at least one cooling fan of a vehicle with stableness in engine operation and vehicle running.  
           [0008]    An embodiment of the apparatus for controlling a cooling fan unit of a vehicle includes a coolant temperature detector for detecting a coolant temperature and a vehicle speed detector for detecting a vehicle speed. The apparatus also includes a controller for controlling the cooling fan unit at least on the basis of the coolant temperature and the vehicle speed. The controller executes instructions for a method according to the present invention.  
           [0009]    According to another embodiment a method for controlling a cooling fan unit of a vehicle includes detecting a plurality of vehicle parameters including a coolant temperature and a vehicle speed, determining a driving load of the cooling fan unit corresponding to the vehicle parameters, and operating the cooling fan unit at the determined driving load. The driving load is selectively determined from a plurality of predetermined loads on the basis of a plurality of temperature ranges of the coolant temperature and a plurality of vehicle speed ranges.  
           [0010]    In a further embodiment, the plurality of temperature ranges are formed by at least one reference temperature selected from a plurality of predetermined temperatures. Also, the plurality of speed ranges are formed by at least one reference speed selected from a plurality of predetermined speeds.  
           [0011]    In a yet further embodiment, the vehicle is equipped with an air conditioning system including an air/con switch, and the at least one reference temperature and the at least one reference speed are selected on the basis of an on/off state of the air/con switch.  
           [0012]    In a yet further embodiment, the at least one reference temperature and the at least one reference speed are selected on the basis of an on/off state of the air/con switch and a refrigerant pressure in the air conditioning system.  
           [0013]    It is preferable that, in the case in which the air/con switch is off, the determining the driving load of the cooling fan unit determines the driving load as a smallest one of the predetermined loads when the coolant temperature lies in a first temperature range less than a first reference temperature. A load depending on comparison of the vehicle speed and a first reference speed when the coolant temperature lies in a second temperature range greater than or equal to the first reference temperature and less than a second reference temperature. A load depending on comparison of the vehicle speed and a second reference speed when the coolant temperature lies in a third temperature range greater than or equal to the second reference temperature and less than a third reference temperature. Also, a largest one of the predetermined loads when the coolant temperature lies in a fourth temperature range greater than or equal to the third reference temperature. In this case, it is preferable that the first reference temperature is less than 100° C., and the second reference temperature and the third reference temperature are greater than 100° C. In this case, it is also preferable that the first reference speed is smaller than the second reference speed.  
           [0014]    In another further embodiment, in the case in which the air/con switch is on and the refrigerant pressure lies in a range less than a first predetermined pressure and greater than or equal to a second predetermined pressure, the determining the driving load of the cooling fan unit determines the driving load as a smallest one of the predetermined loads when the coolant temperature lies in a first temperature range less than a first reference temperature. A load depending on comparison of the vehicle speed and a first reference speed when the coolant temperature lies in a second temperature range greater than or equal to the first reference temperature and less than a second reference temperature. A load depending on comparison of the vehicle speed and a second reference speed when the coolant temperature lies in a third temperature range greater than or equal to the second reference temperature and less than a third reference temperature. Also, a largest one of the predetermined loads when the coolant temperature lies in a fourth temperature range greater than or equal to the third reference temperature. In this case, it is preferable that the first reference temperature is less than 0° C., the second reference temperature is greater than or equal to 0° C. and less than 100° C., and the third reference temperature is greater than 100° C. In this case, it is preferable that the first reference speed is greater than the second reference speed.  
           [0015]    In another further embodiment, in the case in which the air/con switch is on and the refrigerant pressure is less than a predetermined pressure, the determining the driving load of the cooling fan unit determines the driving load as a smallest one of the predetermined loads when the coolant temperature lies in a first temperature range less than a first reference temperature. A load depending on comparison of the vehicle speed and a first reference speed when the coolant temperature lies in a second temperature range greater than or equal to the first reference temperature and less than a second reference temperature. Also, a largest one of the predetermined loads when the coolant temperature lies in a third temperature range greater than or equal to the second reference temperature. In this case, it is preferable that the first reference temperature is less than 0° C., and the second reference temperature is greater than 100° C.  
           [0016]    In another further embodiment, in the case in which the air/con switch is on and the refrigerant pressure is greater than or equal to a predetermined pressure, the determining the driving load of the cooling fan unit determines the driving load as a smallest one of the predetermined loads when the coolant temperature is less than a first reference temperature. A largest one of the predetermined loads when the coolant temperature is greater than or equal to the first reference temperature. In this case, it is preferable that the reference temperature is less than 0° C.  
           [0017]    In another further embodiment, the at least one reference temperature and the at least one reference speed are selected on the basis of whether the vehicle is equipped with an air conditioning system. In this case, it is preferable that, in the case in which the vehicle is not equipped with an air conditioning system, the determining the driving load of the cooling fan unit determines the driving load as a smallest one of the predetermined loads when the coolant temperature lies in a first temperature range less than a first reference temperature. A load depending on comparison of the vehicle speed and a first reference speed when the coolant temperature lies in a second temperature range greater than or equal to the first reference temperature and less than a second reference temperature. Also, a largest one of the predetermined loads when the coolant temperature lies in a third temperature range greater than or equal to the second reference temperature.  
           [0018]    In another further embodiment, an exemplary method according to an embodiment of the present invention further includes determining whether a detected vehicle parameter is abnormal, and the determining the driving load of the cooling fan unit determines the driving load on the basis of whether a vehicle parameter is abnormal and which vehicle parameter is abnormal.  
           [0019]    In this case, it is preferable that, in the case in which the vehicle speed is abnormal, the determining the driving load of the cooling fan unit determines the driving load using a value less than the first predetermined speed as the vehicle speed.  
           [0020]    It is also preferable that, in the case in which the coolant temperature is abnormal, the determining the driving load of the cooling fan unit determines the driving load as the largest one of the predetermined loads.  
           [0021]    It is also preferable that the vehicle is equipped with an air conditioning system including an air/con switch, and that the vehicle parameters further include a refrigerant pressure of the air conditioning system. In the case in which the refrigerant pressure is abnormal, the determining the driving load of the cooling fan unit determines the driving load as a smallest one of the predetermined loads when the coolant temperature lies in a first temperature range less than a first reference temperature. A load depending on comparison of the vehicle speed and a first reference speed when the coolant temperature lies in a second temperature range greater than or equal to the first reference temperature and less than a second reference temperature. A load depending on comparison of the vehicle speed and a second reference speed when the coolant temperature lies in a third temperature range greater than or equal to the second reference temperature and less than a third reference temperature. Also, a largest one of the predetermined loads when the coolant temperature lies in a fourth temperature range greater than or equal to the third reference temperature.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, read together with the description, serve to explain the principles of the invention in which:  
         [0023]    [0023]FIG. 1 is a block diagram showing an apparatus for controlling a cooling fan of a vehicle according to an embodiment of the present invention;  
         [0024]    [0024]FIG. 2 is a table showing a control pattern for each running state of a vehicle that is realized in a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention;  
         [0025]    [0025]FIG. 3A is a flowchart for showing a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention, the flowchart mainly relating to the case in which a refrigerant pressure is less than a first predetermined pressure and greater than or equal to a second first predetermined pressure;  
         [0026]    [0026]FIG. 3B is a flowchart for showing a process for controlling a cooling fan in a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention, especially when a refrigerant pressure is greater than or equal to a first predetermined pressure;  
         [0027]    [0027]FIG. 3C is a flowchart for showing a process for controlling a cooling fan in a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention, especially when a refrigerant pressure is less than a second first predetermined pressure;  
         [0028]    [0028]FIG. 3D is a flowchart for showing a process for controlling a cooling fan in a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention, especially when an air/con switch is turned off;  
         [0029]    [0029]FIG. 3E is a flowchart for showing a process for controlling a cooling fan in a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention, especially when an air conditioning system is not provided in a vehicle; and  
         [0030]    [0030]FIG. 3F is a flowchart for showing a process for controlling a cooling fan in a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention, especially when at least one sensor abnormally functions.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0031]    According to FIG. 1, an apparatus for controlling a cooling fan of a vehicle controls at least one of cooling fans  60  and  70 . The apparatus of this embodiment includes a vehicle speed detector  10 , a coolant temperature detector  20 , a refrigerant pressure detector  30 , an air/con switch (i.e., an air conditioning operation switch)  40 , and a controller  50 . In FIG. 1, the cooling fan unit  80  is shown as including two cooling fans, i.e., first and second cooling fans  60  and  70 . However the scope of the present invention should not be understood to be limited to the number of cooling fans. The spirit of the present invention may be applied to a case in which the cooling fan unit  80  includes only one cooling fan or more than 2.  
         [0032]    The vehicle speed detector  10  detects a current running speed (i.e., vehicle speed V) of the vehicle and sends it to the controller  50 . In the case in which the vehicle is equipped with a manual transmission, a conventional sensor that detects a rotation speed of a transfer driven gear of the manual transmission can be used as the vehicle speed detector  10 . In the case in which the vehicle is equipped with an automatic transmission, a conventional PG-B (pulse generator-B) sensor can be used as the vehicle speed detector  10 .  
         [0033]    The coolant temperature detector  20  detects a temperature of a coolant (i.e., coolant temperature T) for cooling of an engine (not shown) and sends it to the controller  50 . The refrigerant pressure detector  30  detects a compression pressure of a refrigerant (referred to as a refrigerant pressure P hereinafter) when the air/con is operated and sends it to the controller  50 . The air/con switch  40  detects an on/off signal regarding operation of the air/con (or including interior temperature of the vehicle), and sends it to the controller  50 . The controller  50  controls operation of the cooling fans  60  and  70  on the basis of information obtained by the detectors  10 ,  20 , and  30 .  
         [0034]    A control pattern of the cooling fan unit  80  according to an embodiment of the present invention is hereinafter described in detail with reference to FIG. 2, with respect to each running state of a vehicle. FIG. 2 is a table showing a control pattern for each running state of a vehicle that is realized in a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention. According to an embodiment of the present invention, first and second predetermined speeds V 1  and V 2  (e.g., V 1 =45 Km/h, V 2 =80 Km/h) are used as reference speeds for differentiating a plurality of vehicle speed ranges.  
         [0035]    In addition, reference temperatures for differentiating a plurality of temperature ranges are chosen from first, second, third, and fourth predetermined temperatures T 1 , T 2 , T 3 , and T 4  (e.g., T=−30° C., T 2 =95° C., T 3 =102° C., T 4 =105° C.) in accordance with each running state of the vehicle. Such a choice for reference temperatures at each running state is described below. When the coolant temperature T is less than the first predetermined temperature T 1 , the cooling fan unit  80  is always controlled to remain stopped. When the air/con switch  40  is turned on, the cooling fan unit  80  is controlled dependent on the refrigerant pressure P.  
         [0036]    Firstly, a control pattern of the cooling fan unit  80  for a case in which the refrigerant pressure P is greater than or equal to a first predetermined pressure P 1  (e.g., 18 kgf/cm 2 ) is explained in detail hereinafter. In this case, when the coolant temperature T is less than the first predetermined temperature T 1 , the cooling fan unit  80  is controlled to remain stopped as was described above. To the contrary, when the coolant temperature T is greater than or equal to the first predetermined temperature T 1 , the cooling fan unit  80  is driven with a high load, e.g., by simultaneously operating the first; and second cooling fans  60  and  70 . That is, in this case, the first predetermined temperature T 1  becomes a reference temperature to form a plurality of temperature ranges.  
         [0037]    Next, a control pattern of the cooling fan unit  80  for a case in which the refrigerant pressure P is less than the first predetermined pressure P 1  and greater than or equal to a second first predetermined pressure P 2  (e.g., 18 kgf/cm 2 &gt;P≧13 kgf/cm 2 ) is explained in detail hereinafter. In this case, a control pattern of the cooling fan unit  80  is dependent on the vehicle speed V. In this case, the first, second, and third predetermined temperatures T 1 , T 2 , and T 3  become reference temperatures to form a plurality of temperature ranges.  
         [0038]    When the vehicle speed V is less than the first predetermined speed V 1 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a low load by operating a selective one of the first and second cooling fans  60  and  70 ; and (3) in the case in which the coolant temperature T is not less than the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0039]    When the vehicle speed V is not less than the first predetermined speed V 1  but is less than the second predetermined speed V 2 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature Ti but is less than the second predetermined temperature T 2 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped; (3) in the case in which the coolant temperature T is not less than the second predetermined temperature T 2  but is less than the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a low load by operating a selective one of the first and second cooling fans  60  and  70 ; and (4) in the case in which the coolant temperature T is not less than the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0040]    When the vehicle speed V is greater than or equal to the second predetermined speed V 2 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the third predetermined temperature T 3 , again, the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped; and (3) in the case in which the coolant temperature T is not less than the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0041]    Subsequently, a control pattern of the cooling fan unit  80  for a case in which the refrigerant pressure P is less than the second first predetermined pressure P 2  is explained in detail hereinafter. In this case, a control pattern of the cooling fan unit  80  is dependent on the vehicle speed V. In this case, the first and third predetermined temperatures T 1  and T 3  become reference temperatures to form a plurality of temperature ranges.  
         [0042]    When the vehicle speed V is less than the first predetermined speed V 1 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as-described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a low load by operating a selective one of the first and second cooling fans  60  and  70 ; and (3) in the case in which the coolant temperature T is greater than or equal to the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0043]    When the vehicle speed V is not less than the first predetermined speed VI but is less than the second predetermined speed V 2 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the third predetermined temperature T 3 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped; and (3) in the case in which the coolant temperature T is greater than or equal to the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0044]    When the vehicle speed V is greater than or equal to the second predetermined speed V 2 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the third predetermined temperature T 3 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped; and (3) in the case in which the coolant temperature T is greater than or equal to the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0045]    In the above, control patterns of the cooling fan unit  80  are explained with respect to cases in which the air/con switch  40  is turned on, and hereinafter, a control pattern for a case in which the air/con switch  40  is turned off is explained in detail. In this case, controlling of the cooling fan unit  80  depends only on the vehicle speed V and the coolant temperature T. In this case, the second, third, and fourth predetermined temperatures T 2 , T 3 , and T 4  become reference temperatures to form a plurality of temperature ranges.  
         [0046]    When the vehicle speed V is less than the first predetermined speed V 1 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the second predetermined temperature T 2 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped; (3) in the case in which the coolant temperature T is not less than the second predetermined temperature T 2  but is less than the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a low load by operating a selective one of the first and second cooling fans  60  and  70 ; and (4) in the case in which the coolant temperature T is greater than or equal to the third predetermined temperature T 3 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0047]    When the vehicle speed V is not less than the first predetermined speed V 1  but is less than the second predetermined speed V 2 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the second predetermined temperature T 2 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped; (3) in the case in which the coolant temperature T is not less than the second predetermined temperature T 2  but is less than the fourth predetermined temperature T 4 , the cooling fan unit  80  is driven with a low load by operating a selective one of the first and second cooling fans  60  and  70 ; and (4) in the case in which the coolant temperature T is greater than or equal to the fourth predetermined temperature T 4 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0048]    When the vehicle speed V is greater than or equal to the second predetermined speed V 2 , the same as when the vehicle speed V is not less than the first predetermined speed V 1  but is less than the second predetermined speed V 2 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped as described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the fourth predetermined temperature T 4 , the two cooling fans  60  and  70  of the cooling fan unit  80  are controlled to remain stopped; and (3) in the case in which the coolant temperature T is greater than or equal to the fourth predetermined temperature T 4 , the cooling fan unit  80  is driven with a high load by simultaneously operating the cooling fans  60  and  70 .  
         [0049]    In the above, control patterns of the cooling fan unit  80  were explained with respect to-cases in which the vehicle is equipped with an air/con system, and hereinafter a control pattern for a case in which the vehicle is not equipped with an air/con system is explained in detail. In this case, the refrigerant is not provided in the vehicle, so the controlling of the cooling fan unit  80  depends only on the vehicle speed V and the coolant temperature T. In addition, a vehicle is usually provided with only one cooling fan (e.g., cooling fan  60 ) when an air conditioning system is not provided therewith. Therefore, in this case, the object that is controlled according to an embodiment of the present invention is only the first cooling fan  60 . In this case, the second and fourth predetermined temperatures T 2  and T 4  become reference temperatures to form a plurality of temperature ranges.  
         [0050]    When the vehicle speed V is less than the first predetermined speed V 1 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature Ti, the cooling fan  60  of the cooling fan unit  80  is controlled to remain stopped as was described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the second predetermined temperature T 2 , again, the cooling fan  60  of the cooling fan unit  80  is controlled to remain stopped; and (3) in the case in which the coolant temperature T is greater than or equal to the second predetermined temperature T 2 , the cooling fan unit  80  is driven with a high load by operating the first cooling fan  60  with a high load.  
         [0051]    When the vehicle speed V is not less than the first predetermined speed V 1  but is less than the second predetermined speed V 2 , the same as when the vehicle speed V is less than the first predetermined speed V 1 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature T 1 , the cooling fan  60  of the cooling fan unit  80  is controlled to remain stopped as was described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the second predetermined temperature T 2 , again, the cooling fan  60  of the cooling fan unit  80  is controlled to remain stopped; and (3) in the case in which the coolant temperature T is greater than or equal to the second predetermined temperature T 2 , the cooling fan unit  80  is driven with a high load by operating the first cooling fan  60  with a high load.  
         [0052]    When the vehicle speed V is not less than the second predetermined speed V 2 , (1) in the case in which the coolant temperature T is less than the first predetermined temperature Ti, the cooling fan  60  of the cooling fan unit  80  is controlled to remain stopped as was described above; (2) in the case in which the coolant temperature T is not less than the first predetermined temperature T 1  but is less than the fourth predetermined temperature T 4 , again, the cooling fan  60  of the cooling fan unit  80  is controlled to remain stopped; and (3) in the case in which the coolant temperature T is greater than or equal to the fourth predetermined temperature T 4 , the cooling fan unit  80  is driven with a high load by operating the first cooling fan  60  with a high load.  
         [0053]    A method for controlling a cooling fan according to an embodiment of the present invention is hereinafter described in detail with reference to FIGS. 3A to  3 F. FIG. 3A is a flowchart for showing a method for controlling a cooling fan of a vehicle according to an embodiment of the present invention, the flowchart mainly relating to the case in which the refrigerant pressure P is less than a first predetermined pressure and greater than or equal to a second first predetermined pressure. As shown in FIG. 3A, when an engine of a vehicle is started, the controller  50  detects information regarding a running state of the vehicle, that is, information regarding the vehicle speed V, the coolant temperature T, and the refrigerant pressure P at step S 302 , and at the step S 305  the controller  50  determines if any detector  10 ,  20 , or  30  malfunctions.  
         [0054]    A malfunction of a detector may be determined on the basis of whether an output signal of the detector lies within a predetermined permitted range. Processes that are executed when any detector is determined to malfunction at the step S 305  are described later in detail with reference to FIG. 3F.  
         [0055]    When all detectors  10 ,  20 , and  30  are found to function normally at the step S 305 , the controller  50  determines at step S 308  whether the vehicle is equipped with an air conditioning system. The existence of an air conditioning system may be determined on the basis of, e.g., whether an air/con switch is provided to the vehicle, i.e., whether a signal is received from an air/con switch. Processes that are executed when the vehicle is not equipped with an air conditioning system are described later in detail with reference to FIG. 3E.  
         [0056]    When the vehicle is equipped with an air conditioning system, the controller  50  determines at step S 310  whether an air/con switch  40  is turned on. Processes that are executed when the air/con switch  40  is not turned on, i.e., when the air/con switch  40  remains at an off state, are described later in detail with reference to FIG. 3D. When the air/con switch  40  is turned on, the controller  50  determines at step S 315  whether the refrigerant pressure P of the air conditioning system is greater than or equal to the second first predetermined pressure P 2  and less than the first predetermined pressure P 1 .  
         [0057]    When the refrigerant pressure P does not lie in the range of the second first predetermined pressure P 2  to the first predetermined pressure P 1 , the controller  50  determines at step S 390  whether the refrigerant pressure P is greater than or equal to the first predetermined pressure P 1 . Processes that are executed when the refrigerant pressure P is greater than or equal to the first predetermined pressure PI at the step S 390  are described later in detail with reference to FIG. 3B.  
         [0058]    In addition, processes that are executed when the refrigerant pressure P is found to be not greater or equal to the first predetermined pressure P 1  at the step S 390  (that is, when the refrigerant pressure P is less than the second first predetermined pressure P 2 ) are described later in detail with reference to FIG. 3C.  
         [0059]    Hereinafter, processes regarding the case in which the refrigerant pressure P lies in the range of the second first predetermined pressure P 2  to the first predetermined pressure P 1  (S 315 -yes) are described in detail.  
         [0060]    Firstly at step S 325 , the controller  50  determines whether the coolant temperature T is less than the first predetermined temperature T 1 , and then at step S 330 , it determines to stop the cooling fan unit  80  in the case in which the coolant temperature T is less than the first predetermined temperature T 1 .  
         [0061]    When the coolant temperature T is not less than the first predetermined temperature T 1  at step S 325 , the controller  50  determines at step S 335  whether the coolant temperature T lies in a range greater than or equal to the first predetermined temperature T 1  and less than the second predetermined temperature T 2 .  
         [0062]    When the coolant temperature T lies in the range greater than or equal to the first predetermined temperature T 1  and less than the second predetermined temperature T 2 , the controller  50  determines at step S 340  whether the vehicle speed V is greater than or equal to the first predetermined speed V 1 .  
         [0063]    When the vehicle speed V is greater than or equal to the first predetermined speed V 1 , the controller  50  determines to stop the cooling fan unit  80  at step S 345 . When the vehicle speed V is less than the first predetermined speed V 1 , the: controller  50  determines to operate the cooling fan unit  80  with a low load at step S 350 .  
         [0064]    The operation of the cooling fan unit  80  with a low load may be realized by operating only a part of the cooling fans included in the cooling fan unit  80 . As an example, one cooling fan (e.g., the cooling fan  60 ) of the two cooling fans  60  and  70  may be operated to realize such a low load operation of the cooling fan unit  80 . Alternatively, when the rotation speed of the cooling fans can be controlled, the rotation speed may be changed to low to realize such a low load operation of the cooling fan unit  80 .  
         [0065]    Referring back to the step S 335 , when the coolant temperature T does not lie in the range greater than or equal to the first predetermined temperature T 1  and less than the second predetermined temperature T 2 , the controller  50  determines at step S 355  whether the coolant temperature T lies in a range greater than or equal to the second predetermined temperature T 2  and less than the third predetermined temperature T 3 .  
         [0066]    When the coolant temperature T lies in the range greater than or equal to the second predetermined temperature T 2  and less than the third predetermined temperature T 3 , the controller  50  determines at step S 360  whether the vehicle speed V is greater than or equal to the second predetermined speed V 2 .  
         [0067]    When the vehicle speed V is greater than or equal to the second predetermined speed V 2 , the controller  50  determines to stop the cooling fan unit  80  at step S 365 . When the vehicle speed V is less than the second predetermined speed V 2 , the controller  50  determines to operate the cooling fan unit  80  with a low load at step S 370 .  
         [0068]    Referring back to the step S 355 , when the coolant temperature T does not lie in the range greater than or equal to the second predetermined temperature T 2  and less than the third predetermined temperature T 3 , that is, when the coolant temperature T is greater than or equal to the third predetermined temperature T 3 , the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 385 .  
         [0069]    The operation of the cooling fan unit  80  with a high load may be realized by operating all the cooling fans included in the cooling fan unit  80 . Alternatively, when the rotation speed of the cooling fans can be controlled, the rotation speed may be changed to high to realize such a high load operation of the cooling fan unit  80 .  
         [0070]    When a driving load of the cooling fan unit  80  is determined (i.e., as one of “stop”, “low load”, and “high load”) according to the coolant temperature T and the vehicle speed V at steps S 330 , S 345 , S 350 , S 365 , S 370 , and S 385 , the controller  50  operates the cooling fan unit  80  with such determined driving load at step S 395 .  
         [0071]    Subsequently, the controller  50  proceeds to the step S 302 , so the controlling state of the cooling fan unit  80  can remain optimal in accordance with a running state of the vehicle even though the running state may change while the vehicle is running.  
         [0072]    Hereinafter, processes regarding the case in which the refrigerant pressure P is greater than or equal to the first predetermined pressure P 1  at the step S 390  are described in detail with reference to FIG. 3B. In this case, an air conditioning system is equipped to a vehicle and the air conditioning system is operated such that the refrigerant pressure P becomes high. That is, the air conditioning system is operated with a high load. In this case, firstly at step S 425 , the controller  50  determines whether the coolant temperature T is less than the first predetermined temperature T 1 , and then at step S 430 , it determines to stop the cooling fan unit  80  in the case in which the coolant temperature T is less than the first predetermined temperature T 1 .  
         [0073]    When the coolant temperature T is not less than the first predetermined temperature T 1  at step S 325 , the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 435 . When a driving load of the cooling fan unit  80  is determined according to the coolant temperature T and the vehicle speed V at steps S 430  and S 435 , the controller  50  operates the cooling fan unit  80  with such determined driving load at step S 495 .  
         [0074]    Subsequently, the controller  50  proceeds to the step S 302 , so the controlling state of the cooling fan unit  80  can remain optimal in accordance with a running state of the vehicle even though the running state may change while the vehicle is running.  
         [0075]    Hereinafter, processes regarding the case in which the refrigerant pressure P is found to be not greater or equal to the first predetermined pressure P 1  at the step S 390  (that is, when the refrigerant pressure P is less than the second first predetermined pressure P 2 ) are described in detail with reference to FIG. 3C.  
         [0076]    Firstly at step S 525 , the controller  50  determines whether the coolant temperature T is less than the first predetermined temperature T 1 , and then at step S 530 , it determines to stop the cooling fan unit  80  in the case in which the coolant temperature T is less than the first predetermined temperature T 1 .  
         [0077]    When the coolant temperature T is not less than the first predetermined temperature T 1  at step S 525 , the controller  50  determines at step S 535  whether the coolant temperature T lies in a range greater than or equal to the first predetermined temperature T 1  and less than the third predetermined temperature T 3 .  
         [0078]    When the coolant temperature T lies in the range greater than or equal to the first predetermined temperature T 1  and less than the third predetermined temperature T 3 , the controller  50  determines at step S 540  whether the vehicle speed V is greater than or equal to the first predetermined speed V 1 .  
         [0079]    When the vehicle speed V is greater than or equal to the first predetermined speed V 1 , the controller  50  determines to stop the cooling fan unit  80  at step S 545 . When the vehicle speed V is less than the first predetermined speed V 1 , the controller  50  determines to operate the cooling fan unit  80  with a low load at step S 550 .  
         [0080]    Referring back to the step S 535 , when the coolant temperature T does not lie in the range greater than or equal to the first predetermined temperature T 1  and less than the third predetermined temperature T 3 , i.e., when the coolant temperature T is greater than or equal to the third temperature T 3 , the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 555 .  
         [0081]    When a driving load of the cooling fan unit  80  is determined according to the coolant temperature T and the vehicle speed V at steps S 430 , S 545 , S 550 , and S 555 , the controller  50  operates the cooling fan unit  80  with such determined driving load at step S 595 . Subsequently, the controller  50  proceeds to the step S 302 , so the controlling state of the cooling fan unit  80  can remain optimal in accordance with a running state of the vehicle even though the running state may change while the vehicle is running.  
         [0082]    Hereinafter, processes regarding the air/con switch  40  not being turned on, (i.e., the case in which the air/con switch  40  remains at an off state) are described in detail with reference to FIG. 3D.  
         [0083]    Firstly at step S 625 , the controller  50  determines whether the coolant temperature T is less than the second predetermined temperature T 2 , and then at step S 630 , it determines to stop the cooling fan unit  80  in the case in which the coolant temperature T is less than the second predetermined temperature T 2 .  
         [0084]    When the coolant temperature T is not less than the second predetermined temperature T 2  at step S 625 , the controller  50  determines at step S 635  whether the coolant temperature T lies in a range greater than or equal to the second predetermined temperature T 2  and less than the third predetermined temperature T 3 .  
         [0085]    When the coolant temperature T lies in the range greater than or equal to the second predetermined temperature T 2  and less than the third predetermined temperature T 3 , the controller  50  determines at step S 640  whether the vehicle speed V is greater than or equal to the second predetermined speed V 2 .  
         [0086]    When the vehicle speed V is greater than or equal to the second predetermined speed V 2 , the controller  50  determines to stop the cooling fan unit  80  at step S 645 . When the vehicle speed V is less than the second predetermined speed V 2 , the controller  50  determines to operate the cooling fan unit  80  with a low load at step S 650 .  
         [0087]    Referring back to the step S 635 , when the coolant temperature T does not lie in the range greater than or equal to the second predetermined temperature T 2  and less than the third predetermined temperature T 3 , the controller  50  determines at step S 655  whether the coolant temperature T lies in a range greater than or equal to the third predetermined temperature T 3  and less than the fourth predetermined temperature T 4 .  
         [0088]    When the coolant temperature T lies in the range greater than or equal to the third predetermined temperature T 3  and less than the fourth predetermined temperature T 4 , the controller  50  determines at step S 660  whether the vehicle speed V is greater than or equal to the second predetermined speed V 2 .  
         [0089]    When the vehicle speed V is greater than or equal to the second predetermined speed V 2 , the controller  50  determines to stop the cooling fan unit  80  at step S 665 .  
         [0090]    When the vehicle speed V is less than the second predetermined speed V 2 , the controller  50  determines at step S 670  whether the vehicle speed V lies in a range greater than or equal to the first predetermined speed V 1  and less than the second predetermined speed V 2 .  
         [0091]    When the vehicle speed V lies in the range greater than or equal to the first predetermined speed V 1  and less than the second predetermined speed V 2 , the controller  50  determines to operate the cooling fan unit  80  with a low load at step S 675 . When the vehicle speed V does not lie in the range greater than or equal to the first predetermined speed V 1  and less than the second predetermined speed V 2 , the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 680 .  
         [0092]    Referring back to the step S 655 , when the coolant temperature T does not lie in the range greater than or equal to the third predetermined temperature T 3  and less than the fourth predetermined temperature T 4 , that is, when the coolant temperature T is greater than or equal to the fourth predetermined temperature T 4 , the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 685 .  
         [0093]    When a driving load of the cooling fan unit  80  is determined according to the coolant temperature T and the vehicle speed V at steps S 630 , S 645 , S 650 , S 665 , S 675 , S 680 , and S 685 , the controller  50  operates the cooling fan unit  80  with such determined driving load at step S 695 . Subsequently, the controller  50  proceeds to the step S 302 , so the controlling state of the cooling fan unit  80  can remain optimal in accordance with a running state of the vehicle even though the running state may change while the vehicle is running.  
         [0094]    Hereinafter, processes regarding the case in which the vehicle is not equipped with an air conditioning system are described in detail with reference to FIG. 3E. Firstly at step S 725 , the controller  50  determines whether the coolant temperature T is less than the second predetermined temperature T 2 , and then at step S 730 , it determines to stop the cooling fan unit  80  in the case in which the coolant temperature T is less than the second predetermined temperature T 2 .  
         [0095]    When the coolant temperature T is not less than the second predetermined temperature T 2  at step S 725 , the controller  50  determines at step S 735  whether the coolant temperature T lies in a range greater than or equal to the second predetermined temperature T 2  and less than the fourth predetermined temperature. T 4 . When the coolant temperature T lies in the range greater than or equal to the second predetermined temperature T 2  and less than the fourth predetermined temperature T 4 , the controller  50  determines at step S 740  whether the vehicle speed V is greater than or equal to the second predetermined speed V 2 . When the vehicle speed V is greater than or equal to the second predetermined speed V 2 , the controller  50  determines to stop the cooling fan unit  80  at step S 745 . When the vehicle speed V is less than the second predetermined speed V 2 , the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 750 .  
         [0096]    Referring back to the step S 735 , when the coolant temperature T does not lie in the range greater than or equal to the second predetermined temperature T 2  and less than the fourth predetermined temperature T 4 , the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 755 .  
         [0097]    When a driving load of the cooling fan unit  80  is determined according to the coolant temperature T and the vehicle speed V at steps S 730 , S 745 , S 750 , and S 755 , the controller  50  operates the cooling fan unit  80  with such determined driving load at step S 795 . Subsequently, the controller  50  proceeds to the step S 302 , so the controlling state of the cooling fan unit  80  can remain optimal in accordance with a running state of the vehicle even though the running state may change while the vehicle is running.  
         [0098]    Hereinafter, processes regarding the case in which any detector is determined to malfunction at the step S 305  are described in detail with reference to FIG. 3F. When any detector of the detectors  10 ,  20 , and  30  is determined to malfunction at step S 305 , the controller  50  determines at step S 810  whether it is the vehicle speed detector  10  that malfunctions.  
         [0099]    The step S 810  implies that the controller  50  determines whether the detected vehicle speed V is abnormal. The malfunction of the vehicle speed detector  10  and the abnormality of the detected vehicle speed V may be determined on the basis of whether the detected vehicle speed V lies within a predetermined normal speed range. When the vehicle speed detector  10  is found to malfunction, the controller  50  supposes and sets the vehicle speed V as a value (e.g., 40 Km/h) less than the first predetermined speed V 1  at step S 815  and proceeds to the subsequent step S 308 .  
         [0100]    When the vehicle speed detector  10  does not malfunction, the controller  50  determines at step S 820  whether it is the coolant temperature detector  20  that malfunctions. The step S 820  implies that the controller  50  determines whether the detected coolant temperature T is abnormal. The malfunction of the coolant temperature detector  20  and the abnormality of the detected coolant temperature T may be determined on the basis of whether the detected coolant temperature T lies within a predetermined normal temperature range.  
         [0101]    When the coolant temperature detector  20  is found to malfunction, the controller  50  determines to operate the cooling fan unit  80  with a high load at step S 825 , and then the controller  50  operates the cooling fan unit  80  with a high load at step S 895 . Subsequently, the controller  50  proceeds to the step S 302 , so the controlling state of the cooling fan unit  80  can remain optimal in accordance with a running state of the vehicle even though the running state may change while the vehicle is running.  
         [0102]    When the coolant temperature detector  20  does not malfunction, the controller  50  determines at step S 830  whether it is the refrigerant pressure detector  30  that malfunctions.  
         [0103]    The step S 820  implies that the controller  50  determines whether the detected refrigerant pressure P is abnormal. The malfunction of the refrigerant pressure detector  30  and the abnormality of the detected refrigerant pressure P may be determined on the basis of whether the detected refrigerant pressure P lies within a predetermined normal pressure range.  
         [0104]    When the refrigerant pressure detector  30  is found to malfunction, the controller  50  controls the cooling fan unit  80  the same as when the air/con switch  40  is turned off, so the control process proceeds to a node D (refer to FIG. 3D). If the refrigerant pressure detector  30  does not malfunction, the controller  50  proceeds to the step S 308 .  
         [0105]    As described above, according to an embodiment of the present invention, one or more cooling fans of a vehicle are optimally controlled on the basis of a variety of vehicle parameters such as the coolant temperature T, the vehicle speed V, and the refrigerant pressure P, and therefore, more stable operation of an engine and more stable running of a vehicle are achieved at a variety of running circumstances of the vehicle. Furthermore, even if one or more detectors are malfunctioning, the cooling fans are still appropriately controlled.  
         [0106]    While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.