2.3.1- BASIC CONCEPTS

The electric motor is an electromechanical device which transforms an electric current into kinetic power. It is composed by two main parts: the stator, which is fixed on the machine, and the rotor, which receives the torque caused by the magnetic field generated from the electric flow and shares the movement with the rotating part; in the case of the EV, the rotating parts are the wheels. Both stator and rotor allow magnets or electromagnets (copper coils which produce a magnetic field when they are fed by electricity) whose repulsion and attraction creates a movement, the kinetic energy of which is used to move the car.

Once the poles of the rotating magnets enter in contact with their static opposites, the firsts remain quiet (figure 1).

Figure 1

If, in example, the rotating magnet switched its polarity because of an electric current (that happens in DC brushed motors), the repulsion between it and the static ones would produce a rotating movement with a certain torque and speed, obtaining kinetic energy (figures 2-3). Once the magnet returned to a stable position, the cycle would restart.

Figure 2	Figure 3

Graphic source: VORKOETTER, Stefan. How Electric Motors Work. [Online] Stefanv.com. [Cited: October 2, 2009.] <http://www.stefanv.com/rcstuff/qf200212.html>.

2.3.2- PERFORMANCE IN THE EV

The vehicles that use an electric motor have a different functioning from the internal combustion counterpart. This is a brief analysis of the EV characteristics (including both battery electric vehicles and fuel cell vehicles) in comparison to the ones of the ICV:

•  BEHAVIOUR UNDER OPERATION; ENERGY CONSUMPTION

The electric propulsion system has a certain particularity that differs to the performance of the classic internal combustion: while this last, by design, requires being functioning at idle and spending fuel continuously even stopped (and consequently wasting it), the electric engine stops consuming electricity as soon as the driver retires the pressure on the accelerator pedal; this fact supposes an important efficiency increase under in-city or dense traffic circulation. Furthermore, the EV doesn't require startup when it is turned on and, due to the intrinsic characteristics of the electric motor, the requirement of a gearbox disappears.

In small private cars the differences between the acceleration and speed of the electric and the internal combustion motors are virtually not relevant. EVs, like ICVs, can be designed to work under any type of conditions depending on the interest of the end-user (in BEVs the limitations related to this issue are generally linked to a lack of performance of the battery system). The operation noise of an EV is in the order of ten times lower than the one of an ICV owing to the inexistence of explosions. This fact is also especially prominent during the starting, which is completely silent. Additionally there are no vibrations, since the electric motor is not alternative but rotational.

Focusing the attention on the efficiency, it is noticeable that while the average internal combustion car yields around the 15% of the input, the electric one has an efficiency of more than 80%.

•  ATHMOSPHERIC POLLUTION

In the opposite way to the combustion of carbon-based fuels, which produces hazardous releases to the atmosphere, the electric engine doesn't emit any toxic compound in the place where it is operating. In the practice, this fact would lead to sensible improvement of the air quality in urban areas and zones with intense traffic.

•  MAINTENANCE

Electric engines for EVs are structurally simpler than their counterparts. This fact leads to a minor maintenance cost due to the lower wearing of the mechanical parts, as well as a notable increase of the motor life span. In fact, the element which requires the greater preservation cost in any EV is the power supplying system (the batteries on the BEV and the fuel cell stack on the FCV).