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Storage and Transfer

Hybrid Technology


It is now over 15 years since the launch of the first mass production full hybrid vehicle.


Toyota launched the Prius in Japan during 1997 and rolled it out worldwide in 2000. This has since been followed by the Auris, as well as a number of hybrid models from rival manufacturers ranging from Honda to Porsche.

The current generation of full hybrid vehicles have one major drawback – namely the cost and efficiency of the battery packs. No battery lasts forever, not even rechargeable batteries. Over time, the acid in the battery stratifies, meaning it loses its ability to hold its charge.

This issue has led many critics to dismiss these hybrid systems as a ‘stepping-stone’ rather than the future of personal transport. So what’s next for the hybrid?

Air Power

PSA group thinks it has the answer in the form of its 2008 Hybrid Air concept, which dispenses with the expensive lithium-ion battery packs of the current crop of hybrids. Some critics have lauded it as a car that will run on fresh air while others have panned it as pie in the sky.

While certainly innovative, Hybrid Air is a combination of tried and tested technologies - a petrol-powered internal combustion engine, a hydraulic motor and pump, compressed air storage tanks and an automatic transmission. The prototype is similar in design to Peugeot-Citroën’s existing hatchback models.

The biggest difference you will see when examining the chassis, is the four-foot long, blue tank running down the centre, affectionately referred to by the design engineers as the ‘scuba tank’. The tank holds around 20 litres of compressed nitrogen and some hydraulic fluid. During acceleration, compressed air is released, forcing fluid through the hydraulic pump and into the motor to drive the wheels.

[Andrew can we use images from here, do we have the rights or can you find an alternative image? http://www.psa-peugeot-citroen.com/en/inside-our-industrial-environment/innovation-and-rd/hybrid-air-an-innovative-full-hybrid-gasoline-system-article ]

The system uses energy from the vehicles regenerative braking system to operate the motor and the pump. Every time the vehicle brakes or decelerates, a reversible hydraulic pump compresses the nitrogen and releases it when the vehicle next accelerates in air or hybrid power mode.

So, exactly how much power does the air-fuelled motor produce? Well, at present, not much. Early prototypes were named Kiwi One and Kiwi Two as the energy stored within the air tanks was equivalent to the amount of energy that you would find inside a Kiwi.[1]

The air-powered mode is intended for stop-start driving in urban areas and will run from a standing start up to 43 mph. Depending on traffic, this mode will be active between 60 and 80% of urban driving time, making a big contribution to fuel efficiency and increasing MPG figures considerably. PSA is currently citing a fuel economy of around 81 miles per gallon.[2] In hybrid mode the air powered motor will boost power and torque during acceleration.

As well as being cheaper to run than its rival hybrids, the Hybrid Air should also be cheaper to buy thanks to the absence of any advanced battery technology. PSA also claims that its take on hybrid will be less expensive to service than traditional hybrids like the Prius, thanks to the simplicity of its components.

In reality, the design is still in its conceptual stage and design engineers concede that more work is needed on the hydraulic and braking systems. Only time will tell if the Hybrid Air concept is a road-worthy reality but the French car manufacturer certainly thinks so and plans to have it on the road by 2016.



Kinetic energy recovery systems, or KERS, are nothing new either. They have been around for years in the world of motorsport, but there has always been a question mark over whether or not the technology could be made relevant to road cars.

With its racing history, you might expect KERS to make its road debut in a Ferrari or Mercedes, yet it looks like Volvo could be the first to put the technology into a mass produced car. In fact, the Swedish marque has already fitted this system on the rear axle of an S60.

Put simply, Volvo’s KERS captures energy lost through braking and stores it in a carbon fibre flywheel that is attached to the rear axle. The front wheels are driven by the internal combustion engine while the rear wheels are driven by the KERS.

Under braking, the S60’s four-cylinder engine is shut off and the flywheel gathers rotational energy, spinning at up to 60,000 RPM. This energy is then used to accelerate the vehicle when it is time to move once again. It can also be used to power the vehicle once it reaches cruising speed. The flywheel's rotation is transferred to the rear wheels via a specially designed transmission.

Like the KERS systems used in Formula 1, Volvo’s KERS provides up to 80 bhp. [3] As with other hybrid systems the greatest fuel saving is achieved in urban environments, where driving is predominantly stop-start over short distances.



A supercapacitor (or supercap for short) is a power-storage device that stores energy by loading an electrical charge onto two electrodes. The larger and closer these electrodes are, the more energy they can store.

It takes just a few seconds to charge and discharge these clever storage devices. What’s more, they can withstand many hundreds of thousands of charging cycles. All of this makes them the perfect technology for the kind of energy-capture applications that exploit brief charging, such as regenerative braking.

This type of energy storage is commonly used in hybrid buses and trams all over the world where it is used to assist acceleration and to power accessories like air conditioning, automatic windows and passenger doors.

And now, Toyota has employed this same technology in its racing fleet. The company claims that the rapid burst of power from its supercapacitor energy storage system helped propel them to victory several times in the 2012 FIA World Endurance Championship series.

Toyota doesn’t expect to replace the Prius with a new supercap system anytime soon. But sources from the company’s racing division do believe that there are real world applications for the technology and that it has potential as a complementary system, providing power to accelerate from a stop, or providing bursts of power during acceleration.

The market has shown acceptance to hybrid engines, so there should be a steady flow of car manufacturers changing to hybrid engines in a wider range of vehicles. GS Batteries and Remy are already at the forefront of the technology by supplying AGM batteries and rotating electrics that are used for the current stop-start technologies. So watch this space for new technology advances that could develop the aftermarket in the future.  


[1] Guardian online March 2013

[2] Guardian online March 2013

[3] Autoblog online F1 style Kers system April 2013


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