Drives and Controls Magazine
UK-developed hybrid Mini will hit 100km/h in 4.5s
Published:  01 September, 2006

UK-developed hybrid Mini will hit 100km/h in 4.5s

A British electric motor maker has developed a hybrid-electric version of the BMW Mini One which, it says, will hit 100km/h in 4.5s, reach a top speed of 240km/h, achieve a fuel consumption of 2.9 litres/100km (80 mpg), and travel for 1,500km before needing to be refuelled. Hampshire-based PML Flightlink has spent several years working on the technology incorporated in the hybrid Mini, which is driven by four 750Nm brushless permanent magnet motors — one in each wheel hub.

The water-cooled 24-phase, 1,800 rpm, motors are based on PML Flightlink`s pancake motor technology. They are driven by 120kW water-cooled IGBT inverters, built into each motor and capable of delivering 480A at 450V. Together, each motor and drive weigh just 24kg.

The 480kW developed by the four motors is more than six times higher than the 75kW of the Mini`s original engine — which weighs almost twice as much as they do.

The original engine has been replaced by a 15kg two-cylinder internal combustion engine, linked to a generator, that delivers 15kW continuously, or 20kW peaks. Energy from the generator is stored in a 70Ah lithium-polymer battery and an 11-Farad "ultra capacitor", which can deliver up to 700A and can release and absorb energy ten times faster than a battery.

The vehicle has no gears, mechanical drive train, or brakes — the braking is performed by the motors, which recover the energy to charge the battery and ultra-capacitor. The control software includes functions such as traction control and anti-skid braking (which can be applied during acceleration, as well as deceleration).

Each IP65-protected wheel motor is controlled independently, although they are linked to each other via a CANbus network and decide 100 times a second how to share the torque, depending on the current road and vehicle conditions.

The hybrid Mini made its public debut at the recent London Motor Show. Working with a customer, Synergy Innovations, PML Flightlink has built two prototypes, There are no plans to put the vehicle into production at this stage.

The prototypes are not road-legal at present and the performance figures are based on workshop tests, but Chris Newman, PML Flightlink`s sales manager, describes them as "conservative". The company is hoping to demonstrate the hybrid in action at a forthcoming show in Japan, and to have a road-legal version ready during the first quarter of next year.

Newman says that there has been tremendous interest in the Mini`s technology since the Motor Show and PML Flightlink is talking to potential partners, including volume car manufacturers.

Newman describes the in-motor inverter as the most important technological breakthrough. He points out that a 120kW inverter would "normally be the size of a fridge". There is "nothing else like it on the market," he says. The technology is designed to continue running even if there are up to 27 internal failures.

PML Flightlink is using similar motor and inverter technologies in other applications such as direct-drive winches and propeller drives for boats.

Siemens is also working on a drive system based on in-wheel motors.