ORGANIZACIONES ESTUDIADAS EN INDEPENDENCIA

Even when it starts moving, other than the absence of a tailpipe and the low levels of noise, there is very little to pick in between. So what is an EV and how different is it from other vehicles? Figure 10.2 illustrates the fundamental differences between an EV and an ICE powered vehicle. In an ICE vehicle, the energy source (fuel) is stored in a tank, which is hydraulically (pipes) connected to the ICE. Fuel is pumped to the ICE, which in turn transforms the chemical energy of the fuel into kinetic energy. Due to the revving characteristics of the ICE (see Figure 10.4 in the following sec- tion), a gearbox is necessary before the kinetic energy reaches the driven wheels. In an EV, energy is stored in a charged battery, which is electrically linked to the motor. The motor—through an intermediate inverter, in the case of an AC motor—trans- forms the electrical current from the battery to kinetic energy transmitted directly to the driven wheels.

The above applies to ‘pure’ electric vehicles. However, already from the mid- 1990s, mass-produced hybrid gasoline–electric vehicles made their appearance

Inverter Charger Kinetic energy Fuel Power Kinetic energy Current Power Gearbox Motor Battery E ICE Tank

FIGURE 10.2 Fundamental differences between an internal combustion engine (ICE) vehi- cle and an electric vehicle (EV).

(see Figure 10.3). The idea was to employ a small electric motor alongside the ICE in order to reduce fuel consumption. The motor also acts as a generator, charging the battery under braking. Thus, energy otherwise wasted as heat (brake disks or drums), is now partly recovered, transformed to current and stored in the battery. In a hybrid, the battery is usually many times smaller than in a pure EV. Accordingly, the effects of electric power are limited. For that reason, plug-in hybrids have been developed. At the time this manuscript was written, no plug-in hybrids were available in the mass market; however, a number of them were expected within a year. What makes them special is the fact that they bring hybrids closer to pure EVs. Battery size is significantly increased, and instead of relying on the—limited—recovered energy while decelerating, a charger is in place and the battery can be charged in the same way as a pure EV. Thus, short-distance trips can be completed on electric power only, while the ICE takes over when the battery is depleted.

Using components similar to those in a plug-in hybrid—albeit a different arrange- ment which brings it closer to a ‘pure’ EV, instead of driving the wheels when the battery is depleted, range-extender EVs employ an ICE only as generator to charge the battery. This is an even more niche, however promising, powertrain solution (again at the time of this manuscript). The obvious benefit: optimisation of the ICE to work only as generator results in improved efficiency (engine always revs at its optimum range). Another rare powertrain solution is the hydrogen/fuel cell electric vehicle; the addition of fuel cells to an EV platform and the replacement of the bat- tery with a hydrogen tank turns a vehicle into a water-producing factory (for details, see Appleby, 1988). Of course, there are practical obstacles to the generalisation

Tank E Hybrid _Plug-in Tank Battery Battery Charger Gearbox Gearbox Charger ICE ICE Motor Motor Kinetic energy Fuel Power Current

of this exciting technology and only a single example of such vehicle is currently available in the market.

Table 10.1 presents a summary of the key characteristics of electric and hybrid electric vehicles. The classification should not be seen as absolute; we already wit- nessed the thin line between plug-in hybrid and range-extender EVs. Let us not forget that hybrids themselves partly are electric vehicles. For the purpose of understand- ing the relative merits of each solution and its impact on driving ergonomics and human–machine interaction (HMI) however, it is useful and should be sufficiently valid. Starting from the right column, we have hybrids and plug-in hybrids. Both of these types use an electric motor alongside the ICE, as illustrated on Figure 10.3 above. Both hybrids tend to have lower emissions than their ICE counterparts, how- ever in reality this is very much dependent on driving style and behaviour. On the other hand, by retaining the fuel tank of the equivalent ICE vehicle, they can store high amounts of (chemical) energy. Therefore, they often match or exceed an ICE vehicle’s range. The plug-in type may exhibit further increased efficiency depending on how use determines work ratios between ICE and electric motor. Next to the plug-in hybrids, range-extender EVs appear more efficient, thanks to the improved efficiency of their generator compared to an ICE used to drive wheels. This is because, unlike an ICE driving wheels, a generator can spin constantly at its optimum frequency to charge the battery. In addition, range-extenders often (but not always) have a larger battery. This allows them to work as emission-free EVs for lon- ger periods of time. Again, the above may often not be realised, depending on how a vehicle is driven. The fuel cell EV, like the range-extender, uses a generator to pro- duce electricity and power the motor. That is where the similarities end however, as the fuel cells do not ‘burn fuel’. They allow hydrogen to react with oxygen from the air and produce water. Electrical current is also released during the reaction and that is what goes to the motor that drives the wheels. Thus, a decent-sized hydrogen tank is required; however, due to the chemical properties of hydrogen (gas/low density even in liquid form) and current efficiency of fuel cells, a same-size hydrogen tank TABLE 10.1

Basic Characteristics of Electric and Hybrid Electric Vehicles

Electric Hybrid

Power source Battery Fuel cell Battery +

generator (fuel) Gasoline/diesel + battery Gasoline/diesel (+ battery)

Powertrain Electric motor Electric motor Electric motor ICE + electric

motor

ICE (+ electric motor)

Efficiency High High High–medium Medium Medium

Energy capacity at given volume

Low Medium Medium–high High High

Conventional name Pure EV Hydrogen vehicle Range extender EV

provides shorter range than a fuel tank for the equivalent ICE. The main hindrance to fuel cell generalisation is availability and accessibility to hydrogen in a usable form. By contrast, electric power is virtually everywhere; ‘pure’ EVs can draw power from most sockets in modern houses, shops, offices, workshops and car parks. In addition, like all EVs, they enjoy the super-efficiency and driver-friendly proper- ties (see next section) of the electric motor. Thus, they consume minimum energy for a given distance. Their weakness lies in the energy capacity of batteries, which can store many times less energy in the same volume as a fuel tank. Ratios are not fixed, vary from fuel to fuel and depend on many parameters, however it is fair to say that with current lithium-ion technology, it would take a few decades of same-size bat- tery packs to store the equivalent energy stored in a gasoline tank.