Types of Electric Vehicles

Electric cars are becoming more and more common. Indeed in a world of persistently high oil and gas prices people are looking for alternatives. With a new drivetrain and energy source comes a new lingo. The motoring public over the decades has adopted a vocabulary suited for internal combustion engines. A new vocabulary is starting to shape up to describe the electric world.

We can see three basic electric drivetrain configurations emerging. They lie along a continuum going from a pure electric vehicle to a normal gasoline powered vehicle. Going from the most similar to conventional cars to pure electric, we find these common configurations.

Hybrid Electric Vehicle (HEV)
Hybrid is the word used to describe a vehicle with both an electric and an internal combustion engine. The electricity is generated by the gasoline engine and there is no provision for plugging in the vehicle or otherwise charging it. The electric engine is used to capture energy generated by the Internal Combustion Engine (ICE) that would otherwise go to waste. One example is regenerative braking, in which the electric engine captures kinetic energy to slow the car down. In other designs the ICE is run at its most efficient speed and used to generate electricity which keeps the battery charged. Then an electric engine feeds off the battery to provide motive power for the vehicle. This works because the efficiency difference between running an ICE at its peak efficiency and average efficiency is greater than the losses involved in transferring the energy to electricity. Another technique is to switch the ICE off when idling. An electric engine feeding off of a battery does not have to turn over and waste fuel to idle. From the point of view of the driver, a hybrid is like a gasoline powered vehicle. The only way to fill it up is at the gas pump. All of the efficiency gains are internal and invisible.

Plug In Hybrid Electric Vehicle (PHEV)
Plug in hybrids are like hybrid vehicles in that they have a dual power train with both electric and internal combustion engines. However, the electric engine is designed to directly provide motive power instead of just help out the ICE. The gasoline powered ICE is present to extend range. It is possible to externally charge plug in hybrids. They have a capability to be plugged into an electricity socket. By charging the battery in this way and not exceeding the battery range, it is possible to avoid filling them with gasoline. This makes their electric nature obvious to the driver, who can tailor his driving and refueling habits to drastically cut back on the amount of gasoline pumped. Unlike hybrids, which take only gasoline as fuel, plug in hybrids give the owner the power to trade off the type of fuel to be used between electricity and gasoline.

Electric Vehicles (EV)
True electric vehicles do not have an internal combustion engine. They have a single power train based on one or more electric motors. Some designs have a single motor and others have individual motors for each wheel. The only way to refuel these is by plugging them in and charging them up. The design space for electric drive trains is quite large and still being explored. On the scale from ICE to electric EVs are the most advanced step furthest from our automotive engineering experience. Expect to see lots of progress here.

This seems to be the current vocabulary relating to the different electric configurations available and in development. Just so you can keep your EVs and PHEVs straight!

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