Electric Supercar Uses Closed-loop Cooling

Hethel, Norfolk, England

A prototype all-electric Lotus Elise, powered by two internal, oil-cooled, brushless dc motors, weighs just 875 kg. Simulations predict a 30-70 mph time of five seconds for the vehicle and a range of 120 miles.

Made by Zytek Automotive Ltd., the motors are mounted on lightweight aluminum single-ratio Zytek gearboxes. Each weighs 13 kg. and the two together produce a total of 200 bhp (brake horsepower), or 150 kW. A closed-loop, presurized cooling system for the motors employs a comventional transformer oil that flows through slots in the stator laminations, and over the windings. This approach removes heat produced in the stator winding by FR losses. Zytek claims the motor is the first production EV motor to use this technique to cool critical components.

Power for the motors comes from a 300 V nickel cadmium battery pack. Engineers selected nickel cadmium technology to ensure steady voltage throughout most of the discharge cycle. Recharge to 95% capacity will require 60 minutes. An electroic control system made by Zytek coordinates all power-related functions and provides both regenerative braking and traction control.

Vehicle running gear, bodywork, and the extruded and bonded aluninum chassis are retained from the starndard Elise. In the future, passenger compartment heating will be provided using heat from the motor cooling oil, which is cooled by the starndard Elise radiator.