Electric Hybrid Cars and their Power Trains

Faced with uncertainties such as fossil fuel shortages, global warming and air quality, automakers are not letting their guard down, if only to retain control of the future and not be forced one day to turn to a third party to meet these environmental demands. The idea of a hybrid vehicle, an old concept dating back to the early twentieth century, is making a comeback. This is a vehicle that combines two different energy sources: an engine using a fossil or derived fuel (gasoline, diesel, natural gas for vehicles, hydrogen, etc.) and an electric motor. There are two main types of hybridization:

• the "parallel" hybrid, which alternates or combines two energy sources;

• the "series" hybrid, which always runs on electric power, with thermal energy only backing up the electric motor in the same way as a generator. Batteries can be recharged from a household socket or while driving, using an alternator.

The advantage of hybridization lies in its ability to reduce fossil fuel consumption and hence CO ₂ emissions, insofar as the combustion engine does not run continuously, but mainly at speeds where efficiency is most favorable. It also results in the advantages of electric propulsion in dense traffic areas, where pollution levels are high, while the range problems encountered with "all-electric" vehicles disappear.

Technically reliable, hybrid vehicles have two major drawbacks:

• the dual motorization induces an excess weight which penalizes its autonomy and performances;

• its cost is relatively higher than a conventional motorization.

These disadvantages, combined with a desire to optimize the industry and make their mark, have led automakers to develop other versions of hybrids, usually with the same objective in mind: to "sacrifice their electric share". For example, Toyota's Prius, the first hybrid vehicle to be launched on the market, only ran on electric power between 0 and 20 km/h, during power calls and when reversing. Honda's Insight never runs in pure electric mode, its battery's main function being to recover energy from braking.

Since then, things have moved on very quickly, and this article will begin by presenting the basics of hybrid theory, which will help us to understand this complex world where the possibilities for arbitration between technologies must take into account environmental, economic and usage criteria, because in the end it's the customer who will judge the relevance of the choice.

All these points will be discussed, and the hydrogen fuel cell...