The durability of the suspension system is a critical component in the development of a vehicle because it is consistently and directly exposed to dynamic loads while the vehicle is in motion. In most cases, attempts are made to improve the durability of a vehicle suspension system by changing the shapes of its parts and components. However, the authors propose to improve the overall durability performance of a vehicle suspension system by modifying the compliance of the elastomeric bushings, which pivotally connect the lower control arm to the vehicle frame. It is relatively easy and cost effective to change the compliance of the bushing components because they are made of rubber or elastomeric materials. The following procedure was used for the present analysis. Firstly, dynamic loads were obtained based on a multi-body dynamic analysis while the vehicle was driven on a virtual proving ground test. Secondly, the stress distribution of the vehicle suspension system was calculated using finite element analysis to obtain an optimal combination of the elastomeric bushing compliance and provide the maximum improvement to the stress distribution on the basis of a robust design approach. Finally, the durability performance of each component in the vehicle suspension system was evaluated using quasi-static durability analyses. The fatigue life of the optimal model was improved by 36—39 per cent when the knuckle and lower control arm passed over bumps, and by 30—41 per cent when they passed over potholes. The proposed optimal design process to improve the elastomeric bushing compliance made it easy to evaluate and improve the durability performance of the vehicle suspension system in the initial stages of the vehicle development process.
The number of used batteries is expected to dramatically increase in the near future due to the expansion of the electric vehicle (EV) market globally. Accordingly, the Korean government has improved the supporting structures for the recycling system for used batteries, and in particular, in the field of repurposing, various studies are being conducted with a focus on effective evaluation methods that can secure the performance and safety of batteries after use. The repurposing of used batteries is mostly adapted in the field of energy storage systems for normally used EV batteries and a total inspection before repurposing is required due to battery characteristics that can vary depending on the operational environments of and accidents involving medium- and large-sized batteries for EVs and energy storage systems (ESSs) that have been occurring continuously for the past few years. Therefore, this paper investigates the operating mechanisms of the internal resistance test method and implements a test device for middle- and large-sized cells and packs. Based on the proposed test method, the internal resistance of nickel manganese cobalt (NMC)-type commercial large batteries is analyzed according to the SOC (state of charge), SOH (state of health), ambient temperature, and connection degradation of batteries. The distribution degrees of the alternative current (AC) internal resistance (IR) and direct current (DC) internal resistance (IR) measurement methods under state of health (SOH) test conditions are about 7% and 50%. It was found that the DC IR measurement method is more effective in diagnosing battery cell degradation. The distribution degree of DC IR measurements for the degraded connection condition shows an increase of less than 1% regardless of the state of charge (SOC), while the distribution degree of the AC IR measurements shows an increase of up to 319%, indicating that the AC IR method is more effective than the DC IR method in identifying connection degradation. It is confirmed that the proposed method is effective in internal resistance measurement and safety evaluations for the repurposing of batteries.
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