Biographie
Abstract
All new electric vehicles sold in the US require an 8-year/100,000 mile (160,000 km) battery warranty. Electric vehicle batteries are complex mechanical structures that support dynamic masses, and transmit loads and vibration through many thousands of joints and components. Fatigue failure therefore presents a significant risk to the overall reliability of the battery system. The design requirement over a population of electric vehicles is frequently expressed in terms of a statistical reliability target; for example: “Over a warranty period of 8 years/100,000 miles, I require greater than 95% reliability (i.e. fewer than 5% failures), with no less than 90% confidence in my estimation.” This paper considers how digital simulation along with physical component testing and statistical reliability analysis, are used to support the fatigue design requirement and thereby reduce a company’s exposure to unacceptable warranty risk. The paper addresses the following challenges: The advantages of ‘Stochastic Design’ concepts over more traditional ‘Deterministic Design’.- Statistical methods for characterising the variability in customer usage severity.
- Statistical methods for quantifying the effect of uncertainty in fatigue life simulation.
- The roles of simulation alongside physical testing in providing both simulation parameters, and verification of the simulation model.
- The statistical comparison of fatigue simulation with physical tests – especially in considering the limited number of physical tests usually performed, and the wide variability associated with fatigue failure.
- The scaling of many in/dependent failure modes when representing the overall reliability of a complex battery system using ‘System-of-Systems’ reliability simulation methods.
The paper demonstrates how simulation, properly verified using suitably improved physical testing, (consisting of additional measurements and run to failure in an efficient manner), may be used to validate the reliability design requirements for complex structural systems – “SV&V – Simulation, Verification & Validation”.
The significance of this approach extends beyond electric vehicle battery systems to any complex system where a high confidence in fatigue reliability is required.
