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.
Worm gears enable compact gear design and high power density due to a high gear ratio within a single gear stage. However, they often show high sliding speeds within the tooth contact, resulting in high frictional heat and increased thermal stresses. Therefore, an exact calculation regarding efficiency and heat balance is essential in the early stages of gear design. Currently, no calculation method is available to automatically analyze worm gears with regard to efficiency and heat balance. The simulation program "WTplus" is widely used to calculate the efficiency and heat balance of gearbox systems containing cylindrical and bevel gears. The efficiency is determined by adding up load-dependent and no-load power losses of gears, bearings, seals and other rotating components. The calculation of the heat balance of the gearbox is based on the heat transfer between the single components, as well as heat dissipation to the environment. A suitable abstraction of the gearbox by nodal points is conducted for an efficient and accurate calculation of local temperatures using a thermal network model. The simulation program WTplus was extended to automatically analyze the efficiency and heat balance of various designs of worm gears. For this, new approaches for the calculation of load-dependent and no-load losses, as well as new algorithms for nodalization and node-linking, were developed and implemented. Moreover, essential formulas describing the thermal resistances were customized. Simulation results were validated with measurements from research and industry showing very close alignment for various operating points and gear designs.
The knowledge of component temperatures during transient operation conditions is essential for an optimal design of a gearbox. This is because critical peak temperatures limit the transferable power as well as the load capacity. Moreover, understanding the thermal behavior of the gearbox is key to improving its efficiency. Therefore, the Thermal Network Method (TNM) of the calculation program WTplus was extended to calculate component temperatures in gearboxes for transient operation conditions. Specifically, the TNM considers the component masses and specific heat capacities of each node modelling the gearbox structure. This enables the algorithm to compute a corresponding system of differential equations and thus determine the temperature change over time. Therefore, WTplus can be used to identify critical gearbox component temperatures during load cycles. The applied method was validated with measurements collected at the FZG gear efficiency test rig.
Gearbox housing geometry and oil guide plates strongly influence gearbox oil flow and interaction of oil with machine elements. Guided oil flow can increase gearbox efficiency and improve heat management. Recent research studies have demonstrated the potential of Computational Fluid Dynamics (CFD) simulations to predict the gearbox oil flow and no-load losses. Thereby, the influence of housing geometry and guide plates has rarely been addressed. This study focuses on a CFD analysis on the oil flow of a dip lubricated spur gear stage with a guide plate. Grid-based CFD models with different simulation setups were confronted and evaluated. Results show that the selection of the simulation setup with respect to the acceleration ramp and mesh size needs to address the considered object of investigation and the desired depth of information. An appropriate simulation setup shows great accordance with recordings of the oil distribution by a high-speed camera. A detailed analysis of the simulation results identified the contribution of different gear surface zones to the no-load gear loss torque. For the considered guide plate a strong interaction of oil flow and loss torque due to pressure forces on the tooth flank surface zones and due to shear forces on the front and tip circle surface zones of the gears was determined.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.