Abstract
In order to increase the power density of BEVs (Battery Electric Vehicles), high-speed concepts are being progressively developed. With increased speed, the power of the electrical machine can be maintained with reduced torque and therefore size, resulting in cost and package advantages. In the joint research project Speed4E with seven industrial and five university partners, such high-speed electromechanical powertrain is being developed and investigated. The electrical machines will run at a maximum rotational speed of 50,000 rpm in the test rig and 30,000 rpm in the test vehicle. The developed lubrication system for the Speed4E transmission aims for high efficiency and optimized heat balance, via a demand-oriented oil flow. In this context, this study investigates how an efficient lubrication system can be designed with respect to the holistic thermal management of the vehicle. Therefore, a hybrid lubrication consisting of dip and injection lubrication is realized. For the analysis and evaluation, efficiency calculations and CFD (Computational Fluid Dynamics) simulations of the oil distribution are presented.
Highlights
Different lubrication methods are available for transmissions depending on the application and requirements for lubrication and heat dissipation
In order to focus on the efficiency for different immersion depths and oil injection volume rates, six operating points are simulated and their efficiency behavior analyzed
Beneath the efficiency calculations the oil distribution inside the transmission with and without dip lubrication is simulated by Computational fluid dynamics (CFD)
Summary
Different lubrication methods are available for transmissions depending on the application and requirements for lubrication and heat dissipation. For high-speed transmissions, typically dip lubrication or injection lubrication is used [1,2,3]. Akin and Townsend [10] investigated the correlation between oil jet penetration depth and injection speed They conclude, that the deepest penetration depth, and the most effective lubrication and heat dissipation, is achieved when the injection speed is slightly higher than the circumferential speed of the gears. An injection lubrication system for all gear stages is not favorable as it could result in high constructive effort and pump power needed. Ji et al [25] investigated the oil flow inside a single-stage gearbox with the SPH method and pictured the influence of different immersion depths for dip lubrication on the oil distribution.
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