Potentials to Reduce the Energy Consumption of Electric Vehicles in Urban Traffic

By means of a parameter study using a detailed backwards facing model of the longitudinal vehicle dynamics, the design of the transmission ratio in battery electric vehicles (BEV) is analyzed for different driving cycles and it is shown that the electric consumption in urban operation can be significantly reduced by up-speeding the electric machine (EM) using a high 1st transmission ratio. But this potential currently remains unused in fixed-speed BEV due to various additional driving requirements of extra-urban driving with higher vehicle speeds. For this reason, multi-speed BEV are further investigated as a solution to the conflicting design objectives. An additional parameter study for multi-speed BEV with two transmission ratios shows further potentials for the reduction of electric consumption both in urban and extra-urban driving scenarios. Furthermore, the more complex "Two-Drive-Transmission" (TDT) concept is investigated as a multi-speed BEV powertrain with two downsized EMs instead of one high-power EM and it is compared with the other BEV variants using a comparative optimization approach. The TDT uses low-cost and energetically efficient shifting devices based on the technology of an automated manual transmission with simple dog clutches without friction surfaces, allowing shifting without interruption of traction force. Dynamic programming is applied as operational strategy for all simulations considering shifting losses to achieve a benchmarking of the potentials of fixed-speed and multi-speed BEV

Dimensionless Process Development for Lattice Structure Design in Laser Powder Bed Fusion

Laser powder bed fusion enables the fabrication of complex components such as thin-walled cellular structures including lattice or honeycomb structures. Numerous manufacturing parameters are involved in the resulting properties of the fabricated component and a material and machine-dependent process window development is necessary to determine a suitable process map. For cellular structures the thickness, which correlates with the process parameters, directly influences the mechanical properties of the component. Thus, dimensionless scaling laws describing the correlation between strut thickness, process parameters, and material properties enable predictive lattice structure design for laser powder bed fusion. This contribution develops material independent dimensionless allometric scaling laws for both single track and contour exposure to enable process-driven design of lattice structures in laser powder bed fusion. The theory derived with dimensional analysis is validated for the powder alloys stainless steel alloy 1.4404, nickel alloy 2.4856, aluminum alloy AlSi10Mg and Scalmalloy AlMgSc. The results can be used for the process-driven design of lattice structures and dense material obtaining high precision in the micrometer range or economic production with high melt pool width

Material and process invariant scaling laws to predict porosity of dense and lattice structures in laser powder bed fusion

Scaling laws represent an efficient way to describe complex physical phenomena efficiently and reliably by simplified relative quantities, which are holistic in the sense that they are invariant to changes in scale and therefore often universal. During part manufacturing in laser powder bed fusion additive manufacturing several such complex physical phenomena arise leading to unstable melt pool behavior and part porosity. Correlating processing parameters with melt pool quantities and eventually part properties such as porosity computationally efficiently can enable real-time build failure detection and process adaption leading to zero scrap rates in additive manufacturing. The efficient and reliable process-property correlation for dense materials is an ongoing field of research, whereas architected cellular and lattice structures, which are becoming more and more relevant in the context of additive manufacturing are rarely considered in this regard. In this contribution, a dimensionless number and the corresponding scaling law are derived to describe the correlation between porosity and process parameters for components manufactured by laser powder bed fusion. The scaling law is tested and validated for the commonly used alloys Ti-6Al-4V and AlSi10Mg on both dense and lattice structures regarding its suitability to predict the type and amount of porosity in additively manufactured components. The objective of this work is to foster reliable and predictable part quality and enable quality-driven build rate optimization