Abstract:
A method for controlling a fan in a vehicle includes comparing the current temperature of at least a first device and a second device to multiple temperature ranges for each of said devices and determining on the basis of said comparisons whether fan speed should be changed, increasing fan speed to a maximum fan speed if at least one of the comparisons indicates that the maximum fan speed is desired, increasing fan speed to a reference fan speed if at least one of the comparisons indicates that an increase in fan speed less than the maximum fan speed is desired, and decreasing fan speed to a reference fan speed if the comparisons indicate that a decrease in fan speed is desired.

Description:
BACKGROUND OF INVENTION 
       [0001]    The present invention relates generally to a fan located in a motor vehicle for transferring heat by convection from various components, devices or systems using an air stream produced by the fan. 
         [0002]    In a hybrid electric vehicle, or a vehicle whose power source is a fuel cell, or a vehicle having a conventional powertrain, a fan having variable speed and operating efficiency is used to maintain temperature in an acceptable range in various vehicle systems. Each system has a specific temperature range at which the system operates at optimum efficiency. The vehicle systems affected by operation of the fan may include engine coolant, transmission oil, power steering oil, engine oil, electric motor and power electronics coolant, fuel cell stacks, battery thermal systems, engine charge air coolers, and refrigerant or air conditioning. 
         [0003]    A need exists for a strategy that addresses the temperature requirements of the systems and controls the fan such that its energy consumption, fan power and fan noise are minimized. Preferably the control strategy will also minimize the combined energy consumption both of the fan and of other devices associated with the vehicle systems, such as a refrigerant compressor. 
         [0004]    The control strategy should also minimize noise, vibration and harshness (NVH) of the dynamic systems affected by fan operation. 
       SUMMARY OF INVENTION 
       [0005]    An embodiment contemplates a method for controlling a fan in a vehicle by comparing the current temperature of at least a first device and a second device to multiple temperature ranges for each of said devices and determining on the basis of said comparisons whether fan speed should be changed, increasing fan speed to a maximum fan speed if at least one of the comparisons indicates that the maximum fan speed is desired, increasing fan speed to a reference fan speed if at least one of the comparisons indicates that an increase in fan speed less than the maximum fan speed is desired, and decreasing fan speed to a reference fan speed if the comparisons indicate that a decrease in fan speed is desired. 
         [0006]    An advantage of an embodiment is the minimization of fan power consumption and fan noise over a wide range of operating modes, improve fuel efficiency, improve NVH, and incorporate control strategy to control front end fans to minimize energy consumption in hybrid, fuel cell and traditional vehicles to minimize fan power and fan noise. The increasing need to actively control temperatures of multiple vehicle systems (engine coolant, transmission oil, power steering oil, components in the engine compartment, engine oil, electric motor and power electric coolant, fuel cell stacks, battery thermal systems, charge air coolers, air conditioning), with each having a specific optimum control point for efficient point, is met. This control strategy controls fan speeds to minimize fan power to meet the cooling needs of each system and incorporate HVH controls to minimize fan noise to achieve vehicle requirements. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  is a logic flow diagram illustrating a fan speed control for a motor vehicle; 
           [0008]      FIG. 2  shows the control logic steps of the engine coolant control module shown in  FIG. 1 ; 
           [0009]      FIG. 3  shows the control logic steps of the refrigerant system fan speed request module shown in  FIG. 1 ; 
           [0010]      FIG. 4  shows the control logic steps of the NVH control module shown in  FIG. 1 ; and 
           [0011]      FIG. 5  shows the control logic steps of the fan efficiency control module shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , a series of tests  50 - 55  based on the number of components/subsystems requiring temperature control are made to determine, for each component or system, whether to set a flag that indicates a need to increase fan speed or to set another flag that indicates a need to decrease fan speed. In  FIG. 1 , the increase and decrease arrows represent the nature of the flag that is set, i.e., a need to increase or decrease fan speed for each system or component that would be cooled by an air stream produced by the fan. If an increase fan speed flag is set, a control algorithm determines whether to increase fan speed, the magnitude of the new speed, and the rate of the speed change. If a decrease fan speed flag is set, the control algorithm determines whether to decrease fan speed, the magnitude of the new speed, and the rate of the speed change. 
         [0013]    The devices and systems whose temperatures are tested may include engine coolant  50 , transmission oil temperature (TOT)  51 , charge air cooler (CAC)  52 , low temperature loop  53 , battery coolant temperature  54 , and refrigeration system fan  55 . The low temperature loop is a coolant loop having an operating temperature lower that the engine cooling system. A vehicle may include multiple low temperature loops for cooling power electronics, electric motors, engine charge air, a hybrid battery, fuel cell stack, etc. 
         [0014]      FIG. 2  illustrates that the decision block  50  for the engine cooling system includes two normal coolant temperature range tests  60  to determine (1) whether engine coolant temperature is greater than a normal maximum reference temperature, and (2) whether engine coolant temperature is less than a normal minimum engine coolant temperature range. If the result of test  60  (1) is logically true, a flag is set at  61  indicating that fan speed is to be increased by a weighting factor. If the result of test  60  (2) is logically true, a flag is set at  62  indicating that fan speed is to be decreased by a weighting factor. If result of test  60 (1) and  60 (2) is false, neither flag is set. 
         [0015]    Decision block  50  further includes intermediate coolant temperature range test  64 , which determines whether current engine coolant temperature is in a range between a maximum intermediate reference temperature and a minimum intermediate reference temperature. If the result of test  64  is logically true, a flag is set at  63  indicating a bypass of efficiency and ramp-up limit optimization. 
         [0016]    If the result of test  64  is false, no flag is set, indicating that an efficiency and ramp-up limit optimization is to be performed at step  57 , and control advances to step  66 . 
         [0017]    At step  68 , a test is made to determine whether the efficiency and ramp-up limit optimization bypass flag has been set for any of the devices being tested at steps  50 - 54 . If the result of test  68  is false for any of the devices tested at  50 - 54 , a fan speed ramp-up flag is set at step  69  for the respective device, before steps  70 - 76  are executed. 
         [0018]    If the result of test  68  is true for each of the devices tested at  50 - 54 , no fan speed ramp-up is performed and control advances to step  57 . 
         [0019]    Decision block  50  further includes a maximum fan mode test  66 , which determines whether current engine coolant temperature is in a range between a maximum high reference temperature and a minimum high reference temperature. If the result of test  66  is logically true, a flag is set at  67  indicating that fan speed is to be increased to its maximum speed, otherwise no flag is set. 
         [0020]    Each of the tests  51 - 54  for corresponding devices, components and systems comprises the series of tests described with reference to  FIG. 2 . Therefore, one flag will be set for each of the first two tests  60 (1) and  60 (2), a flag may be set for test  64 , and a flag may be set for test  66 . 
         [0021]    Referring again to  FIG. 1 , a test is made at step  70  to determine whether any fan speed full-on flag  67  is set. If the result of test  72  is true, at  71  fan speed is increased to its maximum speed. 
         [0022]    If the result of test  70  is false, control advances to step  72  where a test is made to determine whether any fan speed ramp-up flag is set as a result of executing step  57 , as described below with reference to  FIG. 5 . If any fan speed ramp-up flag is set, the result of test  72  is true and fan speed is increased at step  73  by a calibrated factor based on the device whose fan speed ramp-up flag is set. 
         [0023]    If the result of test  72  is false, control advances to step  74  where a test is made to determine whether each fan speed decrease flag  62  for each device  50 - 54  is set. If the result of test  74  is true, fan speed is decreased at  75  by a calibrated factor. 
         [0024]    If the result of test  74  is false, control advances to step  76  where a test is made to determine whether any fan speed increase flag  61  is set for any of the devices tested at steps  50 - 54 . If the result of test  74  is true, the increased fan speed is determined at step  77  as a factor of current fan speed. The rate of change of fan speed is determined at steps  78  and  82 . 
         [0025]    If the result of test  76  is true, vehicle speed is determined at  78 , and a desired rate of change of fan speed  80  is determined from a function  82 , which is indexed by vehicle speed and a value attributed to the device or devices that require an increase in fan speed. Fan speed is changed at  84  at the desired rate of change  80  and the algorithm is exited at step  85 . 
         [0026]    At step  98 , a test is made to determine whether the fan noise is greater than the fan noise limit. If the result of test  98  is true, control advances to step  100  to determine whether a fan speed increase flag has been set at any one of steps  73 ,  75 ,  77 . If the test at step  100  is false, at step  102 , a test is made to determine whether the slope of function  94  is negative for the current fan speed. 
         [0027]      FIG. 3  illustrates in greater detail the control steps of the refrigerant system fan speed request  55 , which is executed immediately after step  54  as shown in  FIG. 1 . At step  120 , the on/off operating state of the compressor of the refrigerant system is checked. If the compressor is off, control moves to step  56 . 
         [0028]    But if the compressor is on, at step  122  a test is performed to determine whether the compressor speed has a high variation due to changes in engine speed. If the compressor speed variation is greater than a reference variation in compressor speed, control advances to step  56  and the refrigerant system fan speed request  55  is skipped. If the compressor speed variation is less than the reference speed variation, the magnitude of power required currently to drive both the compressor and the fan is calculated at step  124 , and stored in electronic memory at step  126 . 
         [0029]    Experience shows that increasing fan speed can reduce the load on the compressor. Therefore, fan speed is increased at  128 , a new total power required to drive the compressor and fan at its increased speed is calculated at step  130  and is stored in electronic memory at step  132 . 
         [0030]    The rate at which the new total power required to drive the compressor and fan is changing with respect to time is determined at step  134  and is used as an index to determine a desired gain from function  136 . The desired gain is set at step  138  and stored in electronic memory for use at steps  140 ,  142 . The desired gain is the desired time rate of change of fan speed. 
         [0031]    A test is performed at step  144  to determine whether the total power that is stored at step  126  is greater than the total power that is stored at step  132 . If the result of test  144  is true, a change in fan speed is calculated at step  140  from the product of the change in fan speed and the desired gain. A flag indicating an increase in fan speed is set at  146  with a calibrated weighting factor. 
         [0032]    If the result of test  144  is false, a change in fan speed is calculated at step  142  from the product of the change in fan speed and the desired gain. A flag indicating a decrease in fan speed is set at  148  with a calibrated weighting factor. 
         [0033]      FIG. 4  illustrates control steps for optimizing NVH represented by the NVH module  56  of  FIG. 1 . If the test at step  190  indicates that the fan is on, control advances to step  192  to determine the current fan noise from a function  194 , which is indexed by current fan speed. The target fan noise limit appears in graph  194  as a horizontal line. 
         [0034]    The target fan noise limit may be a dynamic value determined from function  196 , whose independent variables include vehicle speed, engine speed and the current gear produced by a transmission. The target fan noise limit may depend on these and other variables including throttle position, fan speed, engine speed, and engine coolant temperature. NVH is optimized at  198  by either increasing or decreasing fan speed by a calibrated factor. 
         [0035]    At  200 , a test is made to determine whether current fan noise is greater than the target fan noise limit. If the result of test  200  is true, control passes to step  202 , where a test is made to determine if a fan speed increase flag  73 ,  75 ,  77  is set. 
         [0036]    If the result of test  202  is false, at step  204  a test is made to determine whether the slope of the fan noise function  194  is negative for the current fan speed. 
         [0037]    If the result of test  204  is true, at step  206  fan speed is decreased by a factor and control advances to step  68 . But if the result of test  204  is false, indicating that the slope of function  194  is positive for the current fan speed, control advances to step  68  without increasing fan speed. 
         [0038]    If the result of test  200  is false indicating that fan noise is less than the fan noise limit, or the result of test  202  is true indicating that a fan speed increase flag is set, at step  208  a higher fan speed having a lower noise than the corresponding fan speed limit is determined, e.g., from function  194 . At step  210 , fan speed is increased to the fan speed determined in step  208  and control advances to step  68 . 
         [0039]      FIG. 5  illustrates the steps of the fan efficiency module  57  of  FIG. 1 . If the test at step  250  indicates that the fan is off, control advances to step  70 . But if the test at step  250  indicates that the fan is on, control advances to step  252  to determine from function  254  whether the slope of fan efficiency is negative for the current fan speed. If the efficiency slope is positive, fan speed is decreased at step  256  by a calibrated weighting factor. If the efficiency slope is negative, fan speed is decreased at step  258  by a calibrated weighting factor. In this way, fan speed is changed to an optimized fan speed, at which electric power consumption required to drive the fan is reduced. 
         [0040]    Throughout the description, the term “fan” applies to a blower that produces an air stream. The terms “device” and “system” applies to a component whose temperature is affected by the speed and temperature of the air stream. 
         [0041]    While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.