Heat Analysis And Application Research On Speed Control Pre-resistor Of Engine Cooling Fan

Eelectronic fan driven by direct current brush motor is mainly applied in entry level passenger car,with speed adjusted by pre-resistor in series connection.In the field,it is serious once fan stall(locked-rotor)happens.In high speed mode the motor might be over heated.In low speed mode the thermal fuse of resistor should be opened in time.Sometimes the vehicle even ends with thermal event.It is very important for engineer to understand the thermal behavior of pre-resistor to make sure safe application of pre-resistor in electronic fan.Application engineer wants to understand the risk of different fan stall condition and the facts as basis to select proper type of motor and resistor,define proper structure for mounting of pre-resistor and select proper material of fan and shroud.The thesis aims on safe application of pre-resistor,studies on thermal behavior of the pre-resistor,clarifies how heat transfers from resistor to shroud and main influence factor for temperature rising of shroud when fan stall in low mode.The main contents of the research are as following:(1)Three types of thermal simulation model for resistor in fan stall in low mode condition have been established and compared with test results.The models reflect real structure of pre-resistor but are simplified,reflect different angle and positioning depth of the pre-resistor in system layout.The models could calculate with different ambient temperature and load.By comparing with real test results,the thermal simulation models are reliable.(2)Based on calibrated thermal simulation models,different boundary conditions of fan stall in low mode are calculated,including different types of resistor,load,ambient temperature and angle,positioning depth of resistor in system layout.The temperature rising curve of shroud and open time of thermal fuse are captured,visualized and compared with melting temperature of specific material of shroud(PP or PA glass fiber reinforced).By comparing with temperature rising on shroud,main mode of heat transfer from resistor to shroud are clarified.Possible measures to lower down temperature rising of shroud are studied.(3)Design rules for resistor application in engine cooling fan towards thermal behavior are summarized.Temperature rising curve of shroud and open time of fuse when fan stall in low mode are provided,under different load and ambient temperature.With the input from system engineer regarding power consumption on resistor under different ambient temperature,application engineer can quickly estimate open time of fuse and temperature rising of shroud in stall condition.It is the basis for application engineer to select right type of motor,resistor and material for fan and shroud.In the end,the thesis makes proposals for further study in next step.