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Hydraulic Hybrid System> Could EPA's new technology one day mean more mileage for> you? by Cathy Nikkel I've seen a similar concept in use in Australia. The rear axle had another output shaft that would spin (or be spun by) a hydraulic pump. That pump transferred fluid from a storage tank to a pressure vessel and was used for braking and acceleration assistance. Must have been in a Popular Mechanics over twenty + years ago.