Research Of Vehicle Fan Clutch Driven By Shape Memory Alloy

Fan clutch is an important component of vehicle engine cooling system. Its property is asignificant factor to influence the heat dispersion and cooling performance. Electronic silicone oilvehicle fan clutch and Magneto-Rheology(MR) fluid fan clutch can’t adjust the fan speedintelligently according to the engine heat conditions. Furthermore, there are other disadvantages,such as the poor performance of torque transitive under high temperature, the easy-leaking behaviorof silicone oil, the perishable characteristics of Magneto-Rheological Fluid (MRF). Besides, theMRF fan clutch need extra power for excitation coil. Aiming to solve those problems, a new type ofintelligent fan clutch was designed. Furthermore, since the driving springs and bias-springs of theOffset&Round-trip type SMA spring actuator were designated, the operating temperature ofactuator wouldn’t be changed. To improve these disadvantages, the adjustable Offset&Round-triptype SMA spring actuator was designed. Its operating temperature was adjustable, which based onthe changing of the bias-pressure of bias-spring. Using the adjustable Offset&Round-trip typeSMA spring actuator as a drive unit, fan clutch possesses these advantages: simple structure, thesensitivity of temperature changes, the automatically adjustment of fan speed, the variable operatingtemperature. It is a excellent design that improve engine thermal conditions and performance,reduce power consumption of cooling fan and energy emission. This dissertation is composed of sixchapters and the main contents are as follows:In chapter1, the background and significance of this project were presented, the characteristicsof three kinds of fan clutch were compared. The development status of fan clutch was summarized,the SMA’s properties, such as shape memory effect and super-elastic, were introduced. After thesediscussions, the main objective of this research project is shown at the end of this chapter.In chapter2, the heat transfer analysis and calculation of engine cooling system wereimplemented. The heat emission and air flow of engine cooling system were calculated. With anengine and cooling system as example, the fan was selected and the fan’s torque and power werecalculated. Finally, the speed controlling technology of engine cooling fan was introduced.In chapter3, the fan clutch structure was designed. Based on the results of the heat transferanalysis of the cooling system, the capacity of fan clutch torque was calculated and the structure offan clutch was determined. The torque transfer model of fan clutch was established, the size of fanclutch friction plate was determined, the material and arrangement of driver spring were selected;combining Single-trip memory SMA springs and offset springs, the Offset&Round-trip type SMAspring actuator was designed. Based on Brinson’s one-dimensional constitutive model, the SMA spring’s model was derived, and the SMA spring and bias-spring were designed by analyzing themechanical behavior of the spring. The design and assembly of all other parts were completed andthe prototype was manufactured.In chapter4, fan clutch Modal analysis. The finite element software-ANSYS Workbench wasdescribed, the theory and process of modal analysis were introduced. The pretreatment of Modalanalysis, such as the finite element model, properties of material, contact conditions and constraintswere set. Meshing and solving automatically used the General Post-processor, the dynamicparameters of the model, such as previous ten natural frequencies and corresponding modes, wereobtained. Analyzing the influence of corresponding modes, comparing the results of modal analyses,the resonance characteristics of fan clutch under the excitation frequency in the engine have beenverified.In chapter5, the performance of fan clutch was studied. The relationship equation offorce-temperature and torque-temperature was derived, and the experiment result was applied toverify the equation. The relationship of displacement-temperature and force-temperature wereinvestigated, and the relationship of the actuator’s force-temperature and the fan clutch’storque-temperature under different biasing force were investigated. The results of experiments wasanalyzed, and the facts, that Round-trip driving can be achieved by using Single-trip SMA springs,was certified. The conclusion that the temperature of the fan clutch’s combine and separation couldbe adjusted effectively by adjusting biasing force, which was proved by the experiment.In chapter6, the major research work was elaborated. Future development was predicted inorder to provide references for the future research on this project.