Rujian Fu

Vibration-Induced Changes in the Contact Resistance of High Power Electrical Connectors for Hybrid Vehicles

Relatively little is known about the fretting mechanism of high power connectors used in hybrid vehicles, even though the vehicles are widely being introduced to the market. This paper experimentally investigates the fretting mechanisms of silver-plated high power connectors caused by vibrations. In order to emulate operational and environmental effects, a test stand was designed that is capable of measuring electrical contact resistance (ECR), relative displacement and connector temperature. The experimental results show that the variation of ECR of connectors subject to vibration is primarily due to periodic changes of contact area caused by relative motion between the contact interfaces, rather than other fretting corrosions. This finding was reinforced by observing a good correlation between relative motion and the increase of ECR under vibration. When a vibration stops, the ECR decreased to a value that is slightly larger than the original value. A surface analysis shows no obvious corrosion until the coating is worn away. In addition, the effect of high current on the fretting mechanism is also investigated.

Modeling and Analysis of Vibration-Induced Changes in Connector Resistance of High Power Electrical Connectors for Hybrid Vehicles

High power connectors used in hybrid vehicles are exposed to vibrations that cause changes in connector resistance. When vibration starts, the connector resistance increases temporarily and oscillates. When vibration stops, the connector resistance returns to a value that is similar to the original state. In this paper, finite element models are developed to analyze this phenomenon and compared with experimental results. A two-dimensional finite element model was developed to predict the motions at any location of the connector system. A contact spring present between the female and male parts of the connector is modeled in three dimensions and used to analyze the time response. The analysis shows that the relative displacement is closely related to the changes of connector resistance during vibration, and the models can be used to improve connector design and ensure better performance and reliability.

Modeling of SEI Formation Based on a Electrochemical Reduced Order Model for Li(MnNiCo)O2/Carbon Polymer Battery

Experimental investigations conducted on a large format lithium ion polymer battery have revealed that one of the major factors causing capacity and power fade is the formation and growth of solid electrolyte interphase (SEI), particularly at anode during charging, which consumes lithium ions and electrolytes. As a result, internal resistance increases. The SEI formed at the graphite anode surface protects the electrode from being decomposed by electrolyte solvent initially, but its growth leads to a gradual capacity and power fade. This phenomenon is described by Butler- Volmer equation that is incorporated into an electrochemical reduced order model. The model consists of coupled physics-based partial differential equations that mimic the lithium ion intercalation reactions and the solvent reduction reactions that produce SEI. The developed reduced order model is validated experimentally at different current rates. Simulation results of the SEI resistance with respect to cycle numbers, as well as the changes of the corresponding electrochemical parameters, are presented.