Design of electric motors for new low-carbon vehicles.
Estimating Power and Torque Requirements for Variable Driving Conditions
Ever increasing numbers of electric automobiles, motorcycles, and scooters are being purchased by consumers to reduce environmental impact, and the market is only expanding. The motors used to power these vehicles, however, differ significantly from conventional internal combustion engines, meaning special attention must be paid to power and torque requirements to ensure successful operation. Edge Mobility Ltd engaged Xi as part of the UK Niche Vehicle Network program to develop analytical capabilities to assist in the design of electric motors for consumer motorcycles and scooters operating in a range of driving situations.
Analytical Calculations for Custom Drive Cycles
Electric motorcycles must operate for a wide range of weather conditions and road types. This means that a vehicle must be able to overcome headwinds, climb steep hills, or travel on rough road surfaces. It’s useful to vehicle and motor designers to understand exactly what forces are present at any time to determine what the engine must provide to keep the vehicle going. Factors defining a journey may include velocity, headwind, elevation, and incline, for example. A user-friendly computational tool can help streamline designers’ work in assessing the suitability of a given vehicle or motor for a given drive cycle.
Flexibility and Rapid Estimation for Accelerating Motor Design
Certain drive cycles are set out in various national and international test standards, especially for emissions testing. Many, however, don’t account for different driving styles – relaxed, aggressive and everything in between. Incline and elevation changes are also frequently ignored. Having a tool with which to import user-defined drive cycles allows the designer to validate power and torque results against existing, well-characterized benchmarks, while also allowing for estimation of motor suitability in other individualized driving situations. This lends confidence to the process and allows for significantly expanded and expedited design iterations.
Xi’s Role: Physics Modelling with MATLAB
Xi developed a model in MATLAB App Designer which reads in custom drive cycles, defined in terms of input parameters such as velocity, torque, headwind, elevation, road condition, etc… This graphical user interface (GUI) calculates results such as incline, road/tire friction force, aerodynamic drag, and motor power, amongst others. Indeed, a velocity profile may be provided, from which a torque profile may be calculated. Conversely, a torque profile may be provided, from which a velocity profile may be calculated. These calculations take into account all forces acting on the vehicle at all points during the simulated journey in order to return the derived results; these may then be plotted for visual inspection or exported to spreadsheet files for record-keeping or further external analysis.
How Xi Helped
The MATLAB App Designer provides the user with a custom front-end interface through which a user may define a journey, define a vehicle or plot forces acting over the course of the journey. The effects of uncertainties in input parameters on the calculated torque results were also handled. For example, the elevation, ambient headwind, or tire/road friction coefficients may not be perfectly known or may not be explicitly known at all. This GUI tool allows the user to apply engineering judgement to uncertainty estimates on input parameters, which are used to calculate an uncertainty profile associated with the resulting torque profile. This is a critical facet of the engineering design process.
Furthermore, GUIs such as this may be compiled into a standalone application, or, if the user has an active MATLAB license, the back-end code may also be updated and modified. The GUI is thus a user-friendly design tool for the motor engineer as well as a flexible platform for the software developer.
Skill Set Used
- MATLAB App Designer Tool for Graphical User Interface (GUI) Development
- Force, power and torque analysis of motorcycle journeys
- Comparison of baseline and custom drive cycles
- Uncertainty analysis for the engineering design process
- Data presentation and export
- Flexibility in the definition of input journeys and motorcycle/rider configurations
- Calculation of power and torque profiles for a wide range of vehicles, elevation profiles, velocity profiles.
- User-friendly interface for non-software engineers
- Expandable software platform that may incorporate new functionalities as projects progress
Part 2 - Real World Measurement
Please read here the second part of the case study. In this part we explain how Xi measured quantities such as speed, acceleration, suspension displacement, wind speed and tyre pressure of a motorcycle as it was ridden around a pre-determined drive cycle route. The collected data was analysed and used to refine a motorcycle model.