Peugeot unveils hydraulic, air-hybrid 80 mpg car | ExtremeTech

Auto manufacturer?Peugeot?Citroen has teamed up with Bosch to create a hybrid car that uses hydraulics to capture and transfer energy. For city driving it is estimated that the car will be able to get up to 80% of the energy for locomotion from regenerative braking. It will also get over 80 miles per gallon (2.9?liters?of fuel per 100?kilometers) while emitting 69 grams of carbon dioxide per kilometer.

The?Peugeot,? due out in 2016, will be the first major implementation of hybrid fluid power in a car. UPS trucks, which typically go through a lot of stop-start cycles, have used similar systems to reclaim energy from braking to great success. Until now, for smaller vehicles including electric hybrids, it has made more sense to use electric regenerative braking. The technology is being called Hybrid Air, although the real role for air appears just to be that of a compressible fluid to back the hydraulic power conversion.

Integrated into the drivetrain is a matched hydraulic pump and motor which in addition to acting as a hydrostatic drive (essentially a continuously variable transmission) transmitting power derived directly from the engine, it also extracts the energy generated during braking. This energy is then stored within a system of tanks acting as the familiar ?accumulator? in a hydraulic system. Usually an accumulator has an air bladder filled with nitrogen that is compressed by the hydraulic fluid within a giant piston.

Any time a fluid is compressed, significant heat is generated, and in many circumstances this would make such a system less efficient than an equivalent electric system. These disadvantages are seemingly offset by virtue of the fact that batteries typically cannot absorb or deliver power on the scale that stopping a large vehicle necessitates. Unless additional mechanisms like fast-charging supercapacitors are added to the loop, energy will be going to waste on a hard brake.

A true ?all-air? vehicle would just have a huge tank and expand the stored air in its cylinders to extract power. Hybrid versions based on this concept are also being explored by other auto manufacturers, and indeed big rigs effectively control the airflow in their cylinders using brake retarders for additional, albeit lossy, stopping power. For the present time however, the compact form of hydraulic power conversion is already a mature technology. Hydraulic motors and pumps with radial piston configurations and variable displacement can now make pressure conversions very efficient.

Friction in hydraulic system generates significant heat and in designs like the UPS truck (pictured above), dual accumulators and coolers are employed to let the vehicle operate at high duty cycles. On the scale of a compact car, where hydraulic lines are thinner and pumps are smaller, passive radiation of this heat may in fact suffice allowing the system to be much simpler.

There are clearly a lot of variables to consider when comparing fluid and electric hybrid technologies. With a direct on-board source of reliable fluid power, total redesigns of vehicles may even by possible allowing systems like traditional hydraulic brakes or radiators to be integrated into one larger unit. It will be interesting to see just how well the Peugeot design performs when it comes to market. Perhaps the risks of gas under pressure will prove to be more palatable than high voltage ? but then again, with experience as our guide, there are likely to be a few unforeseen details that will emerge between now and 2016.

Now read: Why hybrids are dying: Gas engines are good enough on mpg, plug-ins are sexier

Source: http://www.extremetech.com/extreme/146450-peugeot-unveils-hydraulic-air-hybrid-80-mpg-car?utm_source=rss&utm_medium=rss&utm_campaign=peugeot-unveils-hydraulic-air-hybrid-80-mpg-car

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