Flanagan, Louis
(2022)
High-powered electric motorcycle integrated performance studies.
PhD thesis, University of Nottingham.
Abstract
Electric vehicles and low carbon technology are currently at the forefront of research due to the need to rapidly reduce global carbon emissions. Significant effort has been invested into the improvement of electric cars but comparatively little for electric motorcycles, especially high-performance electric motorcycles.
To achieve high-performance it is important to capture relevant design trade-offs and plan for vehicle optimisation prior to starting detailed design. These design trade-offs typically involve optimal sizing of the vehicle battery, electric motor, and motor drive, as well as the determination of the optimum lift-to-drag ratio. A full vehicle analysis including pertinent mechanical and electrical elements is required to perform this properly, as the system is highly interdependent. Existing models are shown to be lacking in key areas, notably the integration of an appropriate battery model, a realistic electric motor model (reflecting modern high-performance electric motorcycle design practices), and an appropriate tyre model, amongst other issues.
The work in this thesis builds and validates a full vehicle model of a modern high-performance electric motorcycle. This is accomplished by first developing a rigid body dynamics motorcycle model that includes a full tyre model, the effects of downforce, differing front and rear tyres, and front-wheel drive. Further work is then undertaken to increase the depth and suitability of the electric powertrain modelling for high-performance electric motorcycles. Here, the battery thermal and electrical responses are modelled as well as the powertrain torque response, including saturation and loss modelling of the motor, motor drive and final drive. To validate these models both motor dynamometer testing and battery cycle testing is performed. An accelerated battery testing procedure is also developed to reduce the time required to properly evaluate and characterise test cells for performance evaluation.
Having developed the vehicle model, a lap simulation procedure is then developed, implemented, and validated. Validation uses lap data acquired at multiple events including the Isle of Man TT Zero, Pikes Peak International Hillclimb (PPHIC) and Elvington Airfield Land speed record attempts. The lap simulation is then extended to include the effects of energy deployment strategy on lap time. This includes a different methodology for designs that are limited by the battery thermal performance and those that are not. This deployment strategy implementation is shown to significantly affect lap time.
The work continues with lap time simulations of the Isle of Man TT Zero and PPHIC, investigating the respective influence of energy management on battery sizing. This shows that it is important to include the energy management strategy into the design evaluation and that the energy management trade-offs are specific to each race event. Additionally, analysis shows that situations, where battery temperature management strategies dominate energy management strategies, should be avoided by the proper design of a battery cooling system. This is because the penalty associated with reducing battery temperature through power and velocity limitations is higher than that of including sufficient cooling.
The lap time sensitivity to mass, motor inertia, winglet lift-to-drag ratios and other design variables are explored with recommendations made for the Isle of Man TT Zero race and PPHIC. It is shown that by properly including representations of the underlying physics using a holistic modelling approach, and utilising a quantifiable objective, the relative contribution of individual elements can be quantified and directly compared. The significance of this from a full vehicle design standpoint is large as now vehicle development can be accurately targeted into areas that provide significant benefit. This can greatly improve the efficiency of the development process and the ultimate performance of the motorcycle.
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