Abstract:
An engine cooling system includes a liquid-to-air heat exchanger having an associated fan and a pump forcing convection and a controller communicating with the fan and the pump, the controller increasing fan speed in response to a first gradient in heat transfer rate to power exceeding a second gradient in heat transfer rate to power for increasing pump speed, and increasing pump speed when the second gradient is greater than the first gradient. The controller may increase the pump speed in response to a desired increase in heat transfer rate. The first gradient may be based on a gradient in heat transfer rate to air flow from a map of heat exchanger performance. The second gradient may be based on a gradient in heat transfer rate to coolant from a map of heat exchanger performance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Divisional of U.S. application Ser. No. 12/879,630 filed Sep. 10, 2010, the disclosure(s) of which is hereby incorporated in its entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to providing a desired cooling level in a liquid-to-air heat exchanger in an energy efficient manner. 
       BACKGROUND 
       [0003]    In most production vehicles, the water pump that causes engine coolant to circulate through the engine and radiator is driven by the engine and the speed of the pump is dictated by the rotational speed of the engine. To ensure that there is sufficient coolant flow at the most demanding operating condition, the amount of flow at most operating conditions is higher than necessary. To improve control over the pump speed, the pump is decoupled from the engine and is either driven by an electric motor, driven by a variable speed clutch, hydraulically driven, or driven by some other actively controllable means. The electrically driven variant is particularly suited to a vehicle with a significant capacity for electrical power generation such as a hybrid electric vehicle. 
         [0004]    It is common for a fan to be provided to direct air flow across the fins and tubes of the radiator. The fan is commonly electrically driven, although it too may be driven by a variable speed clutch, hydraulically driven, or driven by some other actively controllable means. The flow across the radiator is due to movement of the vehicle and the fan. 
         [0005]    When an increase in heat transfer rate is indicated, the fan speed or the coolant pump speed may be increased. 
       SUMMARY 
       [0006]    According to an embodiment of the disclosure, the choice of increasing the fan speed or increasing the pump speed is determined so that the power consumed is minimized. The broad concept is that dQ/dP, the gradient in heat transfer rate to power, is determined for both the fan and the pump at the present operating condition. The one with the higher gradient is the one that is commanded to increase speed. 
         [0007]    A method to control cooling in a liquid-to-air heat exchanger with a fan and a pump forcing convection is disclosed including: determining a first gradient in heat transfer rate to fan power associated with adjusting fan speed, determining a second gradient in heat transfer rate to pump power associated with adjusting pump speed, and adjusting one of fan speed and pump speed based on the gradients. The method may further include determining whether a change in heat transfer is indicated and the adjusting one of fan speed and pump speed is further based on such change in heat transfer being indicated. The fan speed is increased when the first gradient is greater than the second gradient and an increase in heat transfer is indicated. The pump speed is increased when the second gradient is greater than the first gradient and an increase in heat transfer is indicated. The fan speed is decreased when the second gradient is greater than the first gradient and a decrease in heat transfer is indicated. The pump speed is decreased when the first gradient is greater than the second gradient and a decrease in heat transfer is indicated. The liquid is a coolant typically comprising water and ethylene glycol. The liquid is contained within a duct and the air may or may not be ducted. The liquid-to-air heat exchanger is called a radiator and the first and second gradients are determined by: evaluating a radiator performance relationship with radiator performance as a function of liquid coolant and air flows and/or velocities and transforming the radiator performance relationship into a heat transfer performance relationship with heat transfer rate as a function of liquid coolant and air flows and/or velocities. Radiator performance information may take one of several forms including: effectiveness, heat transfer per unit temperature difference between the bulk coolant and air flow streams entering the radiator, or any other suitable manner to capture performance. The performance relationships may be expressed as lookup tables, graphs, or empirical formulas. The first gradient is determined for increased fan speed and the second gradient is determined for increased pump speed when an increase in heat transfer is indicated. The first gradient is determined for decreased fan speed and the second gradient is determined for decreased pump speed when a decrease in heat transfer is indicated. 
         [0008]    A method to control cooling in a liquid-to-air heat exchanger with a fan and a pump forcing convection is disclosed that includes determining a first gradient in heat transfer to power for increasing fan speed, determining a second gradient in heat transfer to power for increasing pump speed, increasing fan speed when the first gradient is greater than the second gradient, and increasing pump speed when the second gradient is greater than the first gradient. The method may further include determining whether an increase in heat transfer is desired. The choice of increasing fan speed and/or pump speed is further based on such a determination that an increase in heat transfer is desired. The first gradient is determined based on determining a gradient in heat transfer rate to air flow from a map of radiator performance and determining a gradient in air flow to fan power and the second gradient is determined based on determining a gradient in heat transfer rate to coolant flow from a map of radiator performance and determining a gradient in coolant flow to pump power. 
         [0009]    A cooling system for an automotive engine includes a radiator coupled to an engine cooling circuit in which the engine is disposed, a fan forcing air past the radiator, a pump disposed in the cooling circuit, and an electronic control unit electronically coupled to the fan and the pump. The electronic control unit commands the fan and/or the pump to change operating speed when an adjustment in heat transfer rate is indicated. In some situations, the adjustment in heat transfer may be realized by increasing either the fan speed or the pump speed. The electronic control unit determines which of the fan and the pump to command based on a first gradient of heat transfer rate to power for adjusting fan speed and a second gradient of heat transfer rate to power for adjusting pump speed. The fan and the pump may be electrically driven, driven by a variable speed clutch, hydraulically driven, or driven by some other actively controllable means. The system may have various sensors and actuators coupled to the electronic control unit including: an ambient temperature sensor electronically coupled to the electronic control unit, an engine coolant sensor electronically coupled to the engine coolant circuit, and a vehicle speed sensor electronically coupled to the electronic control unit. The first and second gradients may further be based on inputs from the sensors which include the ambient temperature, the engine coolant temperature, and the vehicle speed. 
         [0010]    The fan speed is commanded to increase when the first gradient is greater than the second gradient and an increase in heat transfer is indicated. The pump speed is commanded to increase when the second gradient is greater than the first gradient and an increase in heat transfer is indicated. The fan speed is commanded to decrease when the second gradient is greater than the first gradient and a decrease in heat transfer is indicated. The pump speed is commanded to decrease when the first gradient is greater than the second gradient and a decrease in heat transfer is indicated. The amount of the fan speed increase or decrease and the amount of the pump speed increase or decrease is based on an amount of a change in heat transfer rate that is indicated. In some situations, both fan and pump speeds may be increased simultaneously. These situations may include situations when increasing one or the other in isolation may not provide the desired increase in heat transfer performance. Further, in these situations, the aforementioned logic may be utilized to determine the speed increase for each actuator so as to realize the least combined usage of energy between them for increasing heat transfer by changing both fan and pump speed simultaneously. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic of an automotive coolant system; 
           [0012]      FIG. 2  is a graph of radiator coolant flow and pump power as a function of pump speed; 
           [0013]      FIG. 3  is a graph of radiator airflow and fan power as a function of fan speed; 
           [0014]      FIGS. 4 and 5  are flowcharts according to embodiments of the present disclosure; and 
           [0015]      FIG. 6  is a graph illustrating ranges at which fan or pump usage is preferred by performing a power analysis. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0017]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated and described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations consistent with the present disclosure, e.g., ones in which components are arranged in a slightly different order than shown in the embodiments in the Figures. Those of ordinary skill in the art will recognize that the teachings of the present disclosure may be applied to other applications or implementations. 
         [0018]    According to an embodiment of the disclosure, the decision to increase the speed of a fan or a pump associated with a liquid-to-air heat exchanger is based on evaluating the gradient in heat transfer to power input, dQ/dP. 
         [0019]    One example of a liquid-to-air heat exchanger to which the present disclosure applies is commonly called a radiator. Although the predominant heat transfer mode associated with the radiator is actually convection, it is commonly referred to as a radiator. For convenience and simplicity, the liquid-to-air heat exchanger is referred to as a radiator in the following description. 
         [0020]    In  FIG. 1 , a vehicle  10  having four wheels  12 , an internal combustion engine  14 , and a radiator  16  for providing cooling for engine  14  is shown. A liquid coolant, typically a mixture of water and ethylene glycol, is provided to a water jacket cast in engine  14  by a pump  18 . Typically, pump  18  is driven by engine  14 . However, in some applications, pump  18  is either electrically driven, driven by a variable speed clutch, hydraulically driven, or driven by some other actively controllable means so that pump  18  can be operated partially or fully independently of engine rotational speed. A fan  20  which is either electrically driven, driven by a variable speed clutch, hydraulically driven, or driven by some other actively controllable means is provided proximate radiator  16 . Air is forced across radiator  16  due to vehicle speed and/or fan  20 . 
         [0021]    An electronic control unit (ECU)  30  is coupled to a variety of sensors and actuators, which may include, but is not limited to: ambient air temperature sensor  32 , engine coolant temperature sensor  34 , engine  14 , water pump  18 , fan  20 , vehicle speed sensor  36 , and other sensors and actuators  38 . 
         [0022]    For a radiator having a particular architecture and deploying specific heat transfer media, a map of its heat transfer performance characteristics can be determined experimentally, analytically, or by a combination of the two. The resultant heat transfer performance map may take on the form of a dimensionless, heat-exchanger effectiveness. An example two-dimensional lookup table is shown in Table 1 in which the heat transfer media are engine coolant and air and the effectiveness is based on the flows and/or resultant velocities of the two heat transfer media: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Radiator Effectiveness 
               
             
          
           
               
                   
                 Airlow: Standard Air Velocity (m/s) 
               
             
          
           
               
                   
                 1.20 
                 1.60 
                 2.00 
                 2.40 
                 2.80 
                 3.20 
                 3.60 
                 4.00 
                 4.40 
                 4.80 
               
               
                   
                   
               
             
          
           
               
                 Coolant 
                 0.50 
                 0.826 
                 0.765 
                 0.710 
                 0.660 
                 0.616 
                 0.577 
                 0.542 
                 0.511 
                 0.483 
                 0.458 
               
               
                 flow 
                 0.75 
                 0.852 
                 0.799 
                 0.749 
                 0.704 
                 0.663 
                 0.626 
                 0.592 
                 0.561 
                 0.534 
                 0.508 
               
               
                 [kg/s] 
                 1.00 
                 0.866 
                 0.818 
                 0.772 
                 0.729 
                 0.690 
                 0.654 
                 0.621 
                 0.592 
                 0.564 
                 0.539 
               
               
                   
                 1.25 
                 0.875 
                 0.830 
                 0.786 
                 0.746 
                 0.708 
                 0.673 
                 0.641 
                 0.612 
                 0.585 
                 0.560 
               
               
                   
                 1.50 
                 0.881 
                 0.838 
                 0.797 
                 0.757 
                 0.721 
                 0.687 
                 0.656 
                 0.627 
                 0.600 
                 0.576 
               
               
                   
                 1.75 
                 0.900 
                 0.863 
                 0.827 
                 0.792 
                 0.758 
                 0.726 
                 0.696 
                 0.668 
                 0.642 
                 0.618 
               
               
                   
                 2.00 
                 0.911 
                 0.879 
                 0.847 
                 0.816 
                 0.786 
                 0.757 
                 0.729 
                 0.703 
                 0.678 
                 0.655 
               
               
                   
                 2.25 
                 0.918 
                 0.890 
                 0.861 
                 0.833 
                 0.805 
                 0.778 
                 0.752 
                 0.728 
                 0.704 
                 0.682 
               
               
                   
                 2.50 
                 0.923 
                 0.898 
                 0.871 
                 0.845 
                 0.819 
                 0.794 
                 0.770 
                 0.747 
                 0.725 
                 0.703 
               
               
                   
                 2.75 
                 0.927 
                 0.903 
                 0.879 
                 0.855 
                 0.830 
                 0.807 
                 0.784 
                 0.762 
                 0.740 
                 0.720 
               
               
                   
               
             
          
         
       
     
         [0023]    The heat transfer rate is related to effectiveness: 
         [0000]        Q=ε*C *ν*( T   coolant,in   −T   air,in )
 
         [0000]    where Q is the heat transfer rate in W, c is the effectiveness, C is the heat capacity of the lower heat capacity fluid in J/kg-K, v is the mass flow rate of the lower heat capacity fluid in kg/s, T coolant,in  is the temperature of engine coolant as it enters the radiator in K, and T air,in  is the temperature of the air as it approaches the radiator in K. From the above equation, the heat transfer as a function of fluid flows can be computed and an example of which is shown in Table 2: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Heat Transfer in Watts 
               
             
          
           
               
                   
                 Airlow: Standard Air Velocity (m/s) 
               
             
          
           
               
                   
                 1.20 
                 1.60 
                 2.00 
                 2.40 
                 2.80 
                 3.20 
                 3.60 
                 4.00 
                 4.40 
                 4.80 
               
               
                   
                   
               
             
          
           
               
                 Coolant 
                 0.50 
                 10573 
                 13058 
                 15141 
                 16900 
                 18400 
                 19694 
                 20820 
                 21803 
                 22674 
                 23451 
               
               
                 flow 
                 0.75 
                 10907 
                 13640 
                 15992 
                 18028 
                 19803 
                 21363 
                 22740 
                 23965 
                 25062 
                 26046 
               
               
                 [kg/s] 
                 1.00 
                 11084 
                 13957 
                 16467 
                 18668 
                 20609 
                 22332 
                 23868 
                 25249 
                 26489 
                 27617 
               
               
                   
                 1.25 
                 11197 
                 14160 
                 16777 
                 19090 
                 21147 
                 22984 
                 24632 
                 26119 
                 27469 
                 28692 
               
               
                   
                 1.50 
                 11284 
                 14305 
                 16996 
                 19392 
                 21535 
                 23458 
                 25189 
                 26759 
                 28187 
                 29490 
               
               
                   
                 1.75 
                 11516 
                 14737 
                 17649 
                 20275 
                 22648 
                 24799 
                 26751 
                 28525 
                 30148 
                 31635 
               
               
                   
                 2.00 
                 11656 
                 15008 
                 18082 
                 20895 
                 23469 
                 25833 
                 27998 
                 29992 
                 31828 
                 33523 
               
               
                   
                 2.25 
                 11750 
                 15190 
                 18378 
                 21324 
                 24049 
                 26566 
                 28900 
                 31058 
                 33066 
                 34931 
               
               
                   
                 2.50 
                 11816 
                 15320 
                 18591 
                 21639 
                 24475 
                 27119 
                 29576 
                 31873 
                 34014 
                 36016 
               
               
                   
                 2.75 
                 11865 
                 15419 
                 18756 
                 21880 
                 24804 
                 27542 
                 30106 
                 32504 
                 34760 
                 36871 
               
               
                   
               
             
          
         
       
     
         [0024]    In an automotive application, the air provided to the radiator may or may not be ducted and the temperature may be ambient temperature. In some applications, however, the temperature of the air is heated upstream of the radiator, i.e., it is exposed to other heat loads prior to being supplied to the radiator. In the automotive application, the velocity of the air blowing across the radiator is based on several factors including both the speed of the fan and the velocity of the vehicle. Temperatures may be inferred from provided engine sensors, such as engine coolant temperature and ambient temperature where applicable. Coolant velocity or mass flowrate is based on the pump speed and system architecture. Additional modeling may be required to account for the factors specific to the particular application and the particular present operating condition. The results of these models may be utilized in the ECU, or the models may themselves reside in the ECU and may be exercised in real time to provide the necessary information. 
         [0025]    Next, gradients of heat transfer vs. fluid flow, dQ/dv can be determined for each of the fluids, as shown in Tables 3 and 4: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Gradient of Heat Transfer Versus Coolant Flow (Delta Heat 
               
               
                 Transfer)/(Delta Coolant Flow in units of (W-s/kg) 
               
             
          
           
               
                   
                 Airlow: Standard Air Velocity (m/s) 
               
             
          
           
               
                   
                 1.20 
                 1.60 
                 2.00 
                 2.40 
                 2.80 
                 3.20 
                 3.60 
                 4.00 
                 4.40 
                 4.80 
               
               
                   
                   
               
             
          
           
               
                 Coolant 
                 0.50 
                 1336 
                 2327 
                 3404 
                 4514 
                 5613 
                 6674 
                 7677 
                 8650 
                 9552 
                 10379 
               
               
                 flow 
                 0.75 
                 711 
                 1269 
                 1902 
                 2559 
                 3224 
                 3876 
                 4514 
                 5135 
                 5705 
                 6285 
               
               
                 [kg/s] 
                 1.00 
                 450 
                 812 
                 1237 
                 1689 
                 2150 
                 2607 
                 3055 
                 3480 
                 3922 
                 4299 
               
               
                   
                 1.25 
                 348 
                 580 
                 879 
                 1208 
                 1552 
                 1897 
                 2226 
                 2559 
                 2871 
                 3194 
               
               
                   
                 1.50 
                 926 
                 1726 
                 2610 
                 3531 
                 4454 
                 5364 
                 6249 
                 7063 
                 7844 
                 8578 
               
               
                   
                 1.75 
                 563 
                 1085 
                 1732 
                 2477 
                 3284 
                 4135 
                 4990 
                 5869 
                 6718 
                 7554 
               
               
                   
                 2.00 
                 374 
                 730 
                 1186 
                 1720 
                 2317 
                 2934 
                 3608 
                 4265 
                 4954 
                 5630 
               
               
                   
                 2.25 
                 266 
                 519 
                 853 
                 1259 
                 1708 
                 2211 
                 2702 
                 3259 
                 3791 
                 4340 
               
               
                   
                 2.50 
                 194 
                 396 
                 657 
                 962 
                 1314 
                 1692 
                 2119 
                 2525 
                 2984 
                 3419 
               
               
                   
                 2.50 
                 194 
                 396 
                 657 
                 962 
                 1314 
                 1692 
                 2119 
                 2525 
                 2984 
                 3419 
               
             
          
           
               
                   
                 2.75 
                 Forward difference not available 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Gradient of Heat Transfer Versus Air Flow (Delta Heat 
               
               
                 Transfer)/(Delta Air Flow in units of (W-s/kg) 
               
             
          
           
               
                   
                 Airlow: Standard Air Velocity (m/s) 
               
             
          
           
               
                   
                 1.20 
                 1.60 
                 2.00 
                 2.40 
                 2.80 
                 3.20 
                 3.60 
                 4.00 
                 4.40 
                 4.80 
               
               
                   
                   
               
             
          
           
               
                 Coolant 
                 0.50 
                 6213 
                 5208 
                 4397 
                 3750 
                 3236 
                 2815 
                 2457 
                 2178 
                 1942 
                 For- 
               
               
                 flow 
                 0.75 
                 6833 
                 5880 
                 5091 
                 4437 
                 3899 
                 3442 
                 3064 
                 2742 
                 2459 
                 ward 
               
               
                 [kg/s] 
                 1.00 
                 7181 
                 6276 
                 5502 
                 4853 
                 4307 
                 3841 
                 3453 
                 3099 
                 2821 
                 differ- 
               
               
                   
                 1.25 
                 7407 
                 6542 
                 5784 
                 5140 
                 4592 
                 4121 
                 3718 
                 3375 
                 3057 
                 ence not 
               
               
                   
                 1.50 
                 7552 
                 6728 
                 5990 
                 5356 
                 4808 
                 4327 
                 3926 
                 3570 
                 3259 
                 avail- 
               
               
                   
                 1.75 
                 8052 
                 7280 
                 6566 
                 5933 
                 5376 
                 4880 
                 4435 
                 4058 
                 3717 
                 able 
               
               
                   
                 2.00 
                 8379 
                 7685 
                 7032 
                 6437 
                 5908 
                 5414 
                 4984 
                 4589 
                 4239 
               
               
                   
                 2 25 
                 8602 
                 7969 
                 7366 
                 6810 
                 6294 
                 5836 
                 5394 
                 5020 
                 4662 
               
               
                   
                 2.50 
                 8759 
                 8178 
                 7620 
                 7091 
                 6609 
                 6143 
                 5742 
                 5353 
                 5005 
               
               
                   
                 2.75 
                 8885 
                 8341 
                 7810 
                 7310 
                 6845 
                 6409 
                 5996 
                 5639 
                 5277 
               
               
                   
               
             
          
         
       
     
         [0026]    The pump power and coolant flow are shown as a function of pump speed in  FIG. 2  for a given set of vehicular operating conditions. Similarly, fan power and relative air flow rate are plotted as a function of fan speed in  FIG. 3  for the same set of vehicular operating conditions. The data plotted in  FIGS. 2 and 3  may be generating using models, may come from test data, or a combination of the two. In the case of airflow, the complicated influences of ram air and air side heat rejection may be included in the model. From the data in  FIGS. 2 and 3 , a relationship between pump power vs. coolant flow (Table 4A) and a relationship between fan power vs. air flow (Table 5) can be determined: 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 4A 
               
             
             
               
                   
               
               
                 Radiator Coolant Flow as a Function of Pump Power 
               
             
          
           
               
                   
                 Coolant Flow (kg/s) 
                 Pump Power (W) 
               
               
                   
                   
               
             
          
           
               
                   
                 0.50 
                 31.8 
               
               
                   
                 0.75 
                 84.5 
               
               
                   
                 1.00 
                 167.7 
               
               
                   
                 1.25 
                 287.4 
               
               
                   
                 1.50 
                 452.2 
               
               
                   
                 1.75 
                 675.6 
               
               
                   
                 2.00 
                 980.9 
               
               
                   
                 2.25 
                 1414.6 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Air Flow as a Function of Fan Power 
               
             
          
           
               
                   
                 Air flow (m/s) 
                 Fan Power (W) 
               
               
                   
                   
               
             
          
           
               
                   
                 2.40 
                 47.1 
               
               
                   
                 2.80 
                 174.1 
               
               
                   
                 3.20 
                 352.7 
               
               
                   
                 3.60 
                 587.1 
               
               
                   
                 4.00 
                 889.5 
               
               
                   
                 4.40 
                 1282.4 
               
               
                   
                   
               
             
          
         
       
     
         [0027]    Based on the data in the tables above, gradients in coolant flow to pump power and air flow to fan power can be determined, as in Tables 6 and 7: 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Gradient in coolant flow as a function of coolant flow. 
               
             
          
           
               
                   
                   
                 (Delta Coolant Flow/ 
               
               
                   
                 Coolant Flow 
                 Delta Pump Power) 
               
               
                   
                 (kg/s) 
                 (W-s/kg) 
               
               
                   
                   
               
               
                   
                 0.50 
                 4.748E−03 
               
               
                   
                 0.75 
                 3.003E−03 
               
               
                   
                 1.00 
                 2.089E−03 
               
               
                   
                 1.25 
                 1.517E−03 
               
               
                   
                 1.50 
                 1.119E−03 
               
               
                   
                 1.75 
                 8.188E−04 
               
               
                   
                 2.00 
                 5.765E−04 
               
               
                   
                 2.25 
                 NA 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Gradient in air flow as a function of air flow. 
               
             
          
           
               
                   
                   
                 (Delta Airflow/ 
               
               
                   
                 Air Flow 
                 Delta Fan Power) 
               
               
                   
                 (Std. m/s) 
                 (W-s/kg) 
               
               
                   
                   
               
               
                   
                 2.40 
                 3.150E−03 
               
               
                   
                 2.80 
                 2.240E−03 
               
               
                   
                 3.20 
                 1.706E−03 
               
               
                   
                 3.60 
                 1.323E−03 
               
               
                   
                 4.00 
                 1.018E−03 
               
               
                   
                 4.40 
                 NA 
               
               
                   
                   
               
             
          
         
       
     
         [0028]    At this point, dQ/dv and dv/dP are known for each fluid. From these, two values of dQ/dP, i.e., for coolant and air, can be determined. Examples of these tables are shown in Tables 8 and 9: 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Gradient of Heat Transfer as a Function of Pump Power (W/W) 
               
             
          
           
               
                   
                 Airlow: Standard Air Velocity (m/s) 
                   
               
             
          
           
               
                   
                 2.40 
                 2.80 
                 3.20 
                 3.60 
                 4.00 
               
               
                   
                   
               
             
          
           
               
                 Coolant 
                 0.50 
                 21.43 
                 26.65 
                 31.69 
                 36.45 
                 41.06 
               
               
                 flow 
                 0.75 
                 7.69 
                 9.68 
                 11.64 
                 13.56 
                 15.42 
               
               
                 [kg/s] 
                 1.00 
                 3.53 
                 4.49 
                 5.45 
                 6.38 
                 7.27 
               
               
                   
                 1.25 
                 1.83 
                 2.36 
                 2.88 
                 3.38 
                 3.88 
               
               
                   
                 1.50 
                 3.95 
                 4.98 
                 6.00 
                 6.99 
                 7.90 
               
               
                   
                 1.75 
                 2.03 
                 2.69 
                 3.39 
                 4.09 
                 4.81 
               
               
                   
                 2.00 
                 0.99 
                 1.34 
                 1.69 
                 2.08 
                 2.46 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Gradient of Heat Transfer as a Function of Fan Power (W/W). 
               
             
          
           
               
                   
                 Airlow: Standard Air Velocity (m/s) 
                   
               
             
          
           
               
                   
                 2.40 
                 2.80 
                 3.20 
                 3.60 
                 4.00 
               
               
                   
                   
               
             
          
           
               
                 Coolant 
                 0.50 
                 11.81 
                 7.25 
                 4.80 
                 3.25 
                 2.22 
               
               
                 flow 
                 0.75 
                 13.98 
                 8.73 
                 5.87 
                 4.05 
                 2.79 
               
               
                 [kg/s] 
                 1.00 
                 15.29 
                 9.64 
                 6.55 
                 4.57 
                 3.15 
               
               
                   
                 1.25 
                 16.19 
                 10.28 
                 7.03 
                 4.92 
                 3.44 
               
               
                   
                 1.50 
                 16.87 
                 10.77 
                 7.38 
                 5.19 
                 3.63 
               
               
                   
                 1.75 
                 18.69 
                 12.04 
                 8.33 
                 5.87 
                 4.13 
               
               
                   
                 2.00 
                 20.28 
                 13.23 
                 9.24 
                 6.59 
                 4.67 
               
               
                   
               
             
          
         
       
     
         [0029]    Based on the data in Tables 8 and 9, the more efficient device, fan or pump, can be commanded to increase output to respond to a demand for additional cooling. For example, if the present coolant flow is 1.25 kg/s and the present air velocity is 2.8 m/s, dQ/dP for the pump is 2.36 and for the fan, 10.28. In this example, the fan provides the greater heat transfer rate for the same input power. 
         [0030]    The selection of which device to actuate to provide improved heat transfer is described above in terms of two-dimensional lookup tables. However, this is a non-limiting example. The determination can be based on data in graphical form, a set of empirical relationships of the data, a comprehensive model including all of the relevant factors, or any other suitable alternative. In regards to the above discussion, heat transfer leading to energy being removed from the coolant is considered to be positive and power supplied to the device (either fan or pump) is considered to be positive. 
         [0031]    A flow chart showing both increases and decreases in heat transfer rate is shown in  FIG. 5  and starts in  120 . Control passes to  122  in which it is determined if an increase or decrease in heat transfer rate is indicated. In one embodiment, only a heat transfer rate change exceeding a threshold level is enough to rise to the level of indicating a change in pump or fan speed. I.e., some hysteresis can be built in to avoid continuous changes in pump and/or fan speed. If the desired level of heat transfer change exceeds the threshold and it is determined in block  122  that an increase in heat transfer rate is warranted, control passes to block  124  to determine both values of dQ/dP. In embodiments where the liquid-to-air heat exchanger is a radiator, the values of dQ/dP may be determined by evaluating a radiator performance relationship with radiator performance as a function of liquid coolant and air flows and/or velocities and transforming the radiator performance relationship into a heat transfer performance relationship with heat transfer rate as a function of liquid coolant and air flows and/or velocities, as illustrated at block  125 . As the branch including blocks  124 ,  126 ,  128 , and  130  is the same as blocks  104 ,  106 ,  108 , and  110 , no further discussion of this branch is provided. If it is determined in block  122  that a decrease in heat transfer rate is warranted, control passes to  134  to determine both values of dQ/dP. The values of dQ/dP may, for example, be determined as illustrated in block  125  and discussed above. The two values are compared in block  136 . If dQ/dP for the pump is greater than dQ/dP for the fan, control passes to block  140  where fan speed is decreased. Otherwise control passes to block  138  in which pump speed is decreased. After any of the changes in fan or pump speed, i.e., in block  128 ,  130 ,  138 , or  140 , control passes back to block  122 . 
         [0032]    The discussion above focuses on selecting the appropriate actuator to employ to meet a demand for additional cooling. It is also within the scope of the present disclosure to select the appropriate device to reduce heat transfer. In this case, dQ is negative and dP are negative because the rate of heat transfer is decreasing as well as the power input decreasing. In this situation, the device which has the lesser dQ/dP associated with it is the one that is commanded to reduce speed. The determination of the gradients dQ/dP for this situation can be determined analogously as for the situation where an increased heat transfer rate is indicated. 
         [0033]    A flow chart showing both increases and decreases in heat transfer rate is shown in  FIG. 5  and starts in  120 . Control passes to  122  in which it is determined if an increase or decrease in heat transfer rate is indicated. In one embodiment, only a heat transfer rate change exceeding a threshold level is enough to rise to the level of indicating a change in pump or fan speed. I.e., some hysteresis can be built in to avoid continuous changes in pump and/or fan speed. If the desired level of heat transfer change exceeds the threshold and it is determined in block  122  that an increase in heat transfer rate is warranted, control passes to block  124  to determine both values of dQ/dP. As the branch including blocks  124 ,  126 ,  128 , and  130  is the same as blocks  104 ,  106 ,  108 , and  110 , no further discussion of this branch is provided. If it is determined in block  122  that a decrease in heat transfer rate is warranted, control passes to  134  to determine both values of dQ/dP. The two values are compared in block  136 . If dQ/dP for the pump is greater than dQ/dP for the fan, control passes to block  140  where fan speed is decreased. Otherwise control passes to block  138  in which pump speed is decreased. After any of the changes in fan or pump speed, i.e., in block  128 ,  130 ,  138 , or  140 , control passes back to block  122 . 
         [0034]    In the embodiment in  FIG. 5 , a change in speed is commanded to one or the other of the pump and the fan. However, it is possible to determine a condition in which both are changed with the same constraint that the power increase is the minimum possible. If the computation interval is sufficiently short, the small changes in heat transfer to one or the other becomes essentially similar to combinations of changes to the two. Also, if the computation interval is short, the resulting changes in pump, or fan, speed are small steps. 
         [0035]    The data in Tables 8 and 9 can be utilized to determine a region in which the gradient in dQ/dP is equal for the fan and the pump, shown as  150  in  FIG. 6 . An increase in heat transfer is to be provided by the fan if the present operating condition falls above the line and to be provided by the pump if the present operating condition falls above the line. In operation, the algorithm will cause the operating condition to remain close to line  150 . 
         [0036]    The tables above are shown for a specific arrangement and a specific set of operating conditions. The tables are updated continuously to reflect present conditions by a real time running model, results from such a model, test data, or a suitable combination. Also, in the above tables, coolant is provided as a mass flowrate and airflow as a velocity. However, any measure of flow can be used for either: mass flowrate, volumetric flowrate, velocity, as examples. As described herein, sensors may be used to provide input to models. However, there is a desire to minimize the sensor set to reduce cost. Thus, some of the quantities used in the models may be inferred based on sensor signals, actuator settings, or inferred from other sensor signals. 
         [0037]    While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. Where one or more embodiments have been described as providing advantages or being preferred over other embodiments and/or over background art in regard to one or more desired characteristics, one of ordinary skill in the art will recognize that compromises may be made among various features to achieve desired system attributes, which may depend on the specific application or implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described as being less desirable relative to other embodiments with respect to one or more characteristics are not outside the scope of the disclosure as claimed. 
         [0038]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments that may not be specifically illustrated or described.