Phoenix Turbine Builders Club

EV & HEV Basics

July 2007

Last month we talked about selecting a project car for an HEV retrofit. This month we'll cover the basics of EV's and HEV's so we'll be able to plan the conversion.

Electric vehicles (EV's) and hybrid-electric vehicles (HEV's) are very similar in a fundamental sense. They both have electric traction motors, and they both have some sort of stored energy -- like batteries. Beyond that, these systems and subsystems vary widely.

EV Conversions

Most electric conversions are centered around a series wound DC electric motor in the 96-120 volt region. They may use the vehicle's original flywheel -- directly coupled to the motor output shaft. The vehicle is left in third or fourth gear and started up under a load, to prevent over-revving and blowing the electric motor.

The battery packs are massive and heavy -- generally around 1200 pounds; the range and carrying capacity is greatly reduced, and battery life is short due to high discharge and depletion rates.

Since the motor torque and horsepower is controlled through high amperage electronic gates or switches, the cost of the controller is high, and heat-related failures are a problem. 

And while some people say that electric vehicles are "pollution free", they really are not. They displace or shift the pollution to power plant locations -- which usually burn coal in an old, highly polluting fashion. So much for electrics.

HEV Types and Limitations

Hybrids, on the other hand, have unlimited range (depending on fuel availability) and are generally lighter and just as utilitarian as older mechanical systems.

HEV's have a few things in common with EV's; they use an electric traction motor for some or all of their motive power, they have a (smaller) battery pack, and a power controller. They also come with an internal combustion engine and a generator/alternator to recharge the batteries. This is where commonality ends.

There are many types of HEV configurations, and varying degrees of hybridization. We'll look at just a couple of the more popular types for our discussion.

Probably the most well-known HEV is the Toyota Prius. There are also many "work-a-likes" such as the Ford SUV and Honda Civic -- but they all work about the same. These are parallel hybrids; the mechanical engine/ICE works in parallel with the electric motor to power the vehicle. The ICE charges the battery pack as it becomes depleted, and it also transfers mechanical torque to the wheels through a dual input transmission. The electric motor acts as an assist or power booster and only provides an economic advantage in city stop-and-go traffic. On the highway, most of the motive power comes from the ICE -- where it is most efficient. 

Due to the rather large engines they carry, today's hybrids are not very efficient overall. In fact, Europeans don't buy them, for the most part, because their diesel-powered compacts are far more efficient.

So if hybrid vehicles are not such a great way to go, why are we pursuing that direction? Well, there are hybrids, and then there are hybrids.

The GM Volt is an example of what we call a series hybrid. In a series system, the ICE spins a generator, which in turn charges a battery pack, which in turn powers the electric traction motor. There is no direct mechanical link between the fuel-burning engine and the wheels.

The problems with the Volt render it a car concept for some distant future use -- if at all. The traction motor is too large, the generator is too small, the power controller is too expensive, and the killer -- like with Tesla Motors -- is that they are waiting for some elusive new battery density discovery before making the car available to the mass market.

Fiero Project Description

So where are we going with all of this? To make a long story short, our design uses a very small fuel-burning engine, a relatively small, inexpensive battery pack, a smaller power controller, a properly sized generator, and a superior power management architecture. We are also including one critical component that none of the others use -- an APU or Auxiliary Power Unit -- to supply power wherever and whenever the system demands it.

Our system is being developed for a worldwide growing demand for a low-cost hybrid vehicle that will serve as both an urban commuter and a recreational vehicle or fun car.

As we go through this project, you will have to keep in mind that certain parts -- like the main engine -- will be removed, never to return, but there are other components that must go back into that space in a very compact, pre-determined manner.

Next month we will begin the first phase of our new HEV retrofit.