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Volvo: Kers is better than batteries

Date: 14 August 2014   |   Author: Tristan Young

Free energy is an impossibility, but a new system called Flybrid looks like it could be a low-cost way of improving the emissions and fuel consumption of almost any car. Tristan Young investigates what could be revolutionary technology

An average modern car can accelerate from 0-60mph in around 12 seconds; however, the same car is also capable of going from 60-0mph in less than three seconds.

According to Doug Cross, the chief technology officer at Torotrak, this demonstrates both where energy can be harvested from to help improve a car's efficiency and a need for Flybrid system his company is developing.

Flybrid uses F1-developed technology, in the form of Kinetic Energy Recovery System (KERS), to capture energy when a car slows and then use it to drive the wheels when needed. The result is a boost in power and a cut in fuel use, plus a subsequent emissions improvement.

The principle of capturing braking energy and then using it as power isn't new - hybrid cars have been doing it for years - but the difference with conventional KERS is that instead of converting the braking energy into electricity, storing it in batteries and thenusing that to power an electric motor driving the wheels, Flybrid KERS stores the power mechanically in a flywheel.

To capture energy, when a driver presses the brake pedal (or just lifts off the accelerator), a special set of gears slow the car by putting the deceleration energy into spinning a flywheel to speeds of up to 60,000rpm. Then to drive the car forward, the gearing is reversed and power is sent to the wheels.


There are several advantages for the Flybrid system over a battery and motor system. Firstly, it adds just 80kg to the weight of a car, compared with several hundred kilos of batteries and motor. The system is also compact and can be installed in a car without compromising interior space, plus it's made of easily obtainable materials - mainly steel and carbon fibre - too. As a result, the system is also expected to be relatively low cost when put into production. Early predictions put it  as cheap as £500.

In percentage terms, the savings achieved depend on the car in which the system is installed and the size of the car's engine. In a 245hp petrol Volvo S60, Flybrid KERS adds 80hp and improves fuel consumption by 25%. However, the same 80hp system could easily be used in conjunction with a much less powerful car to provide a greater economy improvement. Indeed, Torotrak has built and tested a supermini with a 40hp diesel engine and a 90hp Flybrid system, which was capable of 0-60mph in seven seconds, yet only produced 58g/km of CO2.

Install the system in a 60mpg car and improve its economy by 25% to 75mpg and some basic sums show that as a £500 option it would pay for itself within 25,000 miles at current fuel prices.

The disadvantage of Flybrid is that, unlike a battery-based storage system, it will only store energy
for about 20 minutes. This means that an initial 'charging' (by braking or setting the system to capture energy under constant power) of the system is needed the first time you drive.

The other downside is that, at least in the prototype Volvo we sampled, the system is noisy. However, Torotrak engineers claim this noise would be removed in a production car.
The first production use of a Flybrid system is expected to be in a bus in the coming months, with the first production car-based system expected in a Lotus Exige in the next year or two.
However, it's thought that it would take between three and four years for a Flybrid system to appear in a higher-volume vehicle that is more likely to appeal to fleets and business car drivers.

What's it like to drive?

Torotrak is working with Volvo on Flybrid and has fitted an 80hp system to an S60 T5 model, which produces 245hp from the conventional petrol engine. The engine drives the front wheels,
while the Flybrid system powers the rear wheels.

BusinessCar was given the opportunity to test the prototype on track. Initial impressions are that, aside from the large touchscreen tablet computer mounted to the dash, the car is like any other automatic to drive. Only the whirring whine noise from the flywheel and gearing made it obvious that something other than the engine was at work.

The energy recovery and delivery is completely automatic. For those that have driven a hybrid car with heavy brake-energy regeneration, the feel of the brakes is good, and the blending of real braking and slowing through energy recovery is perhaps better.

More noticeable is the performance boost. Without the Flybrid system activated the best we could manage on a damp track was a 0-60mph time of 7.6 seconds. With the Flybrid system activated, and only two thirds full, we achieved 5.8 seconds.

While fleets will be more interested in economy improvements than 0-60mph times, these figures obviously show the gains possible.