Electric cars

The internal combustion engine has been around for hundreds of years, and although the original pioneers of this technology would hardly recognise a modern engine, the fundamental principles have remained the same. Improvements in efficiency, power output and refinement have been made at an astonishing rate, but propulsion systems have now entered a rapid and crucial stage of evolution. Fossil fuel powered cars are becoming increasingly unfashionable and the motoring industry has responded to customer concerns about the environment.

The beautiful Lightning GT: an electric supercar
Lightning GT

Introduction

Billions of dollars are being invested throughout the world in the technologies which will power the next generation of consumer vehicles - and this is a very exciting prospect. Countless start-up technology companies are competing for their innovations to be adopted by the big players, resulting in a wide diversity of potential options for the car of tomorrow. Here we examine whether electricity could be the fuel of choice for the next generation of sportscars.

So what are the main pros and cons?

There are a lot of reasons to like electric motors - the technology is proven and relatively advanced, they have massive torque and are much more efficient in turning stored energy into motion. The French land speed record breaking TGV train used motors on each carriage for propulsion and it wasn't exactly sluggish.

However, the train did have one distinct advantage over an electric car - a limitless supply of electricity supplied through the overhead cables. Batteries are the weak link at the moment, they're heavy, slow to charge on domestic power, and only provide limited range. Tesla currently use a huge bank of laptop batteries as their power source which isn't exactly cutting edge, but the technology is gradually catching up. When it does, here's a summary of what we have to look forward to…

Motor layouts

Single motor

The single motor design has been the first to be adopted due to the similarity with existing cars - a large individual motor can sit where the engine used to be, and powers two or four wheels via some differentials and drive shafts. This layout works well, and minimises the need for complex control electronics, however there is another way…

Multiple motors

Several smaller, lighter motors can be used to power each wheel individually (as used in the beautiful Lightning GT). These motors can be mounted inboard or even inside the wheels. This removes the need for any differentials and other transmission components and allows much greater control of each individual wheel. Cars using this layout can have much greater flexibility in terms of design and aerodynamics, and will benefit from more accurate traction control systems (discussed below).

Performance overview

Acceleration

Acceleration where electric motors excel. They have huge amounts of torque all available from a standstill, and have no need for a clutch or gearbox, so no valuable seconds will be lost fumbling for second gear. Great news for your quarter mile times!

Top speed

Top speed isn't so great - as you go faster, you consume energy at an exponential rate and this drains batteries quickly. Most electric cars will have artificially limited top speeds to maintain decent driving range. Don't expect any Veyron beating high speed runs.

Weight

Batteries are currently pretty heavy, but can be distributed in a flexible manner which means the mass can be kept close to the ground (creating a low centre of gravity), and spread equally between the front and rear (for more balanced handling). Electric cars do not require heavy conventional gearboxes due to the increased rev range of the power plant, and in-wheel motors remove the need for almost all driveline components, saving weight significantly.

Driveline and traction systems

This is where things start to get interesting - although many electric cars will use a single large electric motor as an engine substitute, some manufacturers are experimenting with several smaller motors which power each wheel individually. Suddenly traditional traction systems such as limited slip differentials, launch control, and brake-based traction control are out of the window. Torque can be divided much more accurately between each wheel depending on the conditions and driver inputs, leading to the best possible grip and performance.

Noise

Not exactly exciting to listen to. Artificial 'sound generators' exist but these may put off the purists. A genuine, decent sounding motor needs consideration.

Maintenance

With only a few moving parts, electric motors have greatly reduced maintenance requirements. There is much less wear and tear, no reliance on an oil reservoir and very little that can go wrong.

Regenerative braking

Finally onto regenerative braking, which is already used in some hybrids, regenerative braking allows some of the energy lost during braking to be captured by using the motor in reverse as a generator - simply reversing the polarity allows the motor to generate braking force and help recharge the batteries.

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