Tall tyres, externally excited motor – Conti shows off its EV technology

To demonstrate its various solutions for electric vehicles, Continental has converted a bog-standard Renault Megane to a prototype electric vehicle. Around 40 components the company produces for electric vehicles have been integrated into the Megane, including the motor, battery, power electronics, displays and controls, all the peripheral devices for propulsion and charging and – most importantly for us – Conti.eContact tyres. Most of components used are already on the market or are ready to go into production.

“All the know-how that has flowed from all five of our divisions demonstrates that Continental has the technologies and systems expertise for electric cars. This is particularly significant as electrification of cars is becoming more and more of a reality,” commented Continental CEO Dr. Elmar Degenhart regarding the project.

Tyre diameter key to mileage boost

The Conti.eContact tyres fitted to the converted prototype were specifically developed for electric cars. Their unusual 195/55 R20 size and the aerodynamic rims used are not just there for looks, says Conti – The tyres exhibit 30 per cent less rolling resistance, extending range considerably. The tyres’ automatic tyre pressure monitoring system helps extend working life by ten per cent.

But the key factor for this boost in mileage is the Conti.eContact’s unusual diameter, states Continental. Deformation decreases when the tyre approaches the contact patch, resulting in greatly diminished rolling resistance. At the same time, the same load bearing is possible as with ordinary tyres. In addition, Continental has designed the sidewalls to reduce energy loss when the tyres deflect or top out. The sidewall dispenses with the usual edging and design elements, just like the very smooth and largely enclosed rims, in order to diminish wind resistance as much as possible.

The tread design features a combination of four longitudinal grooves, numerous sipes, an absence of transverse corrugations, and stiff tread ribs, all trimmed to provide lower rolling resistance and less tyre noise. Continental says it was also possible to achieve more precise handling characteristics and safer wet braking. The very low tyre contour prevents excess travel by the belt elements and therefore also lowers rolling resistance. Finally, the new tyre is lighter than previous designs.

Other features

Important as the tyres are to the prototype vehicle’s characteristics, they perform as part of a team. The team leader, so to speak, is arguably the externally excited synchronous motor fitted to the Renault, the likes of which the vehicle manufacturer has already fitted in thousands of its electric cars. The motor generates 70 kilowatts and maximum torque of 226 Newton metres, propelling the prototype from zero to 100 kilometres per hour in 11.9 seconds. Continental is the only manufacturer to mass produce an externally excited synchronous motor in the automotive industry. The company opines that this sort of motor has several major advantages compared with permanently excited electric motors: Externally excited motors make for high efficiency throughout all ranges of operation. Particularly at high rpm’s, regulation of the excitation current yields lower mutual inductance. This technical feature also serves to protect the motor. Yet another advantage is that no expensive rare earth metals are needed for the magnets.
 
The electric motor is coupled to an integrated single-gear transmission and a differential that includes a mechanical parking lock, power electronics and an electric vehicle controller. The second-generation power electronics stem from a flexible modular system. Even with the built-in DC/DC converter, the unit is some 30 per cent smaller than the first generation, making it one of the most compact components on the market. Power comes from a lithium-ion battery. Including its built-in management system, safety electronics, the crash sensor evSAT, and liquid cooling, the system weighs 154 kilogrammes, allowing installation in a sandwich floor without sacrificing any space. The battery pack has a nominal voltage of 355 volts and a capacity of 18 kilowatt hours, which gives the car a maximum range of 150 kilometres.

Continental Engineering Services (CES) completely gutted the base car and transformed it into an electric vehicle in just over six months. The prototype fulfils nearly every safety and quality requirement for a mass-produced car and is road legal.