How do Hydraulic Hybrid vehicles differ from hybrid electric vehicles?
Hydraulic Hybrid vehicles and Hybrid Electric vehicles (HEV) each have their own set of advantages and disadvantages. HEVs have been first to market, are able to support other on-board electrical needs, are quiet, and because of higher energy density, can support longer engine-off operation. HHVs have higher power density, which ensures greater recovery of otherwise wasted braking energy and provides greater power boost. HHVs use lower cost components and do not require high voltage batteries. Most HEVs store energy by charging a battery system, although some use an ultra-capacitor system. HEVs use electric motors to deliver stored energy to the wheels. HHVs store energy by pumping hydraulic fluid into a high pressure storage vessel called an accumulator. The accumulator contains nitrogen gas which is compressed (or pressurized) up to 5000 psi when the accumulator is full. HHVs use this compressed gas to force hydraulic fluid through a hydraulic motor to deliver power to the wheels.
