Transmission Modeling for Optimization of Electric Powertrains

Abstract

Over the last decade, the number of electric vehicles (EVs) on the
world's roads has rapidly increased. Optimization of power consumption
in electric powertrains will, therefore, lead to reduced energy usage
in the road transport sector. EPOS, is a research project that aims
to optimize EV powertrains, with the objectives to minimize cost and
power consumption. As a part of the EPOS project, this thesis' purpose
was to develop an optimization tool for the mechanical transmissions in
EVs, with the objectives to minimize mass and power loss. The optimization
tool is intended to run millions of times, therefore a target for
execution time for the transmission optimizations was set. Models for
component size and efficiency were initially created with a high level
of detail, which was subsequently reduced in order to reach the target
for execution time. Fixed values for design variables and an iteration
based gear-set optimization model lead to successfully reaching the target,
but solutions were less optimized. The xed variables' impact on
the optimization result could be evaluated, by comparing the optimization
solutions while varying the number of xed design variables. The
optimal solution was determined with a scoring model, that compared
the optimization objectives in terms of energy consumption. It was
found that there was a signicant trade-o when minimizing mass and
power loss. Prioritization in the trade-o was important when deciding
on an optimal solution, in order to get the desired result. The nal
conclusion of this thesis was that the detail of component models and
the compromise between optimization objectives, have an important
role in attaining the most optimal transmission design.

Popular Abstract

Optimizing Gearboxes for Electric Cars

The environmental gain from switching to electric cars can be lost if there is much
power loss in the gearbox. Optimized gearbox designs can solve this problem, and
make electric cars better.

A project was carried out in order to determine the gearbox that gives electric cars the
longest driving range. The driving range is lowered by power loss in the gearbox, and also
if the gearbox is unnecessarily heavy. Therefore, it would be ideal to minimize the power
loss and minimize the weight of the gearbox. However, when optimizing the gearbox it
was found that there is a clear trade-o between low weight and low power loss, meaning
that it is not possible to get the best of both worlds.

The transition to electric vehicles has the potential to reduce greenhouse gas emissions.
In order for electric vehicles to reach the wider market it is important to reduce cost and increase driving range. This can be achieved by reducing power loss and weight of the
gearbox.

With high efficiency in a gearbox, the gears often become bigger and thus the volume
increases. The increased volume implies that more room is needed for the gearbox, which
takes space from the batteries. The size of the battery determines the driving distance,
just like the amount of fuel that ts in your gas car's tank will determine how far you can
drive. The driving range problem was supposed to be solved with a more ecient gearbox,
but instead the driving range would be shortened by the increased size of an ecient
gearbox. For this reason, it was crucial to nd the optimal balance between eciency and
size when selecting a gearbox for electric cars.

The work conducted can help electric car manufacturers to select a gearbox that results in
the best end product. Optimization of gearboxes can lead to electric cars with longer
driving distance, which is highly desired by consumers. Further, with an optimal gearbox
less energy goes to waste, which improves the environmental sustainability of electric cars.

This project is part of a research project called EPOS, which is a collaboration between
industry and academy. EPOS aims to provide knowledge in how electric vehicles should
be designed and implemented in society. The importance of the EPOS project is
highlighted by the fact that the Swedish Energy Agency is contributing as a sponsor.

In order to solve the problem in balancing weight and power loss, a gearbox optimization
tool was developed through computer programming. Since the program compares millions
of gearboxes, every gearbox needs to be calculated in a very short amount of time. The
program optimizes in steps, where unsuitable gearbox alternatives were eliminated early
on. This managed to reduce the time to optimize the millions of gearboxes from several
weeks to just a few hours.

• author: Lundborg, Jacob and Hulth Olsson, Johanna
• supervisor: Rikard Hjelm
• organization: Machine Elements
• course: MMEM01 20211
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Electric vehicle transmission, multi-objective optimization, mass minimization, power loss minimization
• language: English
• id: 9054193
• date added to LUP: 2021-06-14 15:47:15
• date last changed: 2021-06-14 15:47:15