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PRAZE Electric Scooter
PML have developed a prototype electric scooter - with high profile European partners including Peugeot and with support from the European Commission - called the PRAZE project.
The aim of the PRAZE project was to improve the efficiency of the “battery powered electric scooter”, and create “Personal Zero Emission Transport for the City of the Future”.
From the point of view of the end user, the main constraints limiting the take up of electric scooters were defined as: High cost compared with thermal engine scooter, low distance range, the heavy weight of vehicles, and difficulties with charging, e.g. for individuals living in apartments. Overcoming these constraints would be the aims of the design partners and would define the success of the PRAZE project.
Advances in vehicle performance were to be achieved through research and development of enabling technologies, namely the motor drive system, batteries and chassis. PML were tasked with developing a new drive system for the scooter, and the project management of PRAZE.
During the initial phase of PRAZE, two versions of motor drive systems were developed; the first prototype in-wheel scooter to be tested produced a maximum torque of 120Nm, exceeding the target of 100Nm. This presented some scope to reduce the size and weight of the motor. Subsequently a smaller motor was then specified, built, laboratory tested and fitted to another prototype vehicle. The rating of the smaller motor was increased further through improvements to the ventilation system.
A detailed weight assessment revealed that even with a further iteration/ optimised design, considering all possible weight reduction possibilities; the existing topology of motor would not reach the required target for safe handling.
A comprehensive review into possible alternative motor topologies then concentrated on two main contenders, namely the brushless printed stator and the single tooth topology.
Both motor topologies were prototyped and tested, culminating in the single tooth topology being selected as the most suitable for taking into pre-production.
Subsequent work resulted in PML developing a patented in-wheel motor topology that not only optimised power-to-weight, but through its revolutionary construction, utilising the same tooth for different motor sizes, maximised the exploitation potential of the motor in different applications.
Refining the design of the mechanical interlocking system was a significant factor and formed the main embodiment of the patent. Various schemes were investigated before the final version was agreed. Key was good mechanical interlocking that minimised electromagnetic flux saturation possibilities for different motor sizes.
Design for low cost manufacture resulted in a motor design with only three mechanical cast/machined components. Earlier split-rim designs, where the tyre mounted directly on to the outside of the motor, which had a removable lip, were rejected in favour of a motor design that could be integrally attached to a standard wheel. This had the benefit of allowing the vehicle manufacturer to keep their standard wheel rims and enabling the motor to be designed with thinner components, as it no longer took the full strain and shocks applied to the outside of the wheel.
The in-wheel motor also offers the scooter designer the benefit of greater space on the vehicle body, which can translate to increased size of the helmet / luggage compartment under the seat.
Throughout the course of the project a total of four scooters were built:
Two scooters were fitted with the first generation of in-wheel motor and subsequently two more were fitted with a lower weight, second-generation in-wheel motor. The later scooters were fully equipped with lights, indicators and horn etc. and were fully roadworthy.
The next generation of PRAZE scooter, equipped with “designed for production” system components, is expected to present significant commercial and performance advantages.
With ever-increasing legislation in cities reducing the number of polluting vehicles, the PRAZE scooter is truly poised to become the city transport of the future.
The main results of the PRAZE project can be summarized as follows:
Four prototype demonstrator vehicles were developed, which exceeded the project performance requirements, with peak motor efficiencies of 82% @ 20Nm and 76% @ 80Nm (PML)
Mathematical models were derived to determine the maximum un-sprung weight for an electric scooter rear wheel. (Peugeot)
Development of a Ni-Zn battery without any toxic components and a charge profile of less than 5 hours (Sorapec)
The In-wheel motor drive system was advanced by the design of a lower weight, higher efficient, compact controller capable of operating over a battery voltage range from 24V to 72V (PML)
In-wheel motor weight was dramatically reduced with the innovative single tooth motor topology, culminating in an design for manufacture weight of 11.88Kg (PML)
An investigation report was compiled into Infrastructure and regulations, indicating that the PRAZE scooter will have a significant impact in our cities as a zero emission vehicle (Citelec)
A technical evaluation has been completed together with a Project Web-site and presentation of published papers (Citelec)
For more information on the PRAZE scooter project, please visit the web site at www.praze.org
For more information on the in-wheel motor and drive system, please email PML.
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Tel: +86 (0) 592 2650865, 2650868, Fax: +86 (0) 592 2650869, E-mail:sales@pml.com.cn
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