Hybrid Hydraulic System

A hybrid hydraulic vehicle (HHV) is one that typically includes an internal combustion engine (ICE) which is coupled to a hydraulic pump which powers a hydraulic pump motor. Energy is stored in one or more accumulators in the form of compressed air, typically nitrogen. The vehicle is propelled when the pump motor is provided hydraulic power either directly from the pump motor or from the accumulator. Air in the accumulator is compressed by the hydraulic pump or by the pump motor during regenerative braking.

The two main advantages of a hybrid hydraulic system are: 1. It allows for power from a small ICE to be combined with that of an accumulator to provide power for short periods of time equal to that of a much larger engine. Because the small engine in a HHV is not coupled directly to the drivetrain, it can be run with its throttle fully open at its speed of optimum efficiency at all times. In a conventional vehicle with a larger engine that provides the same acceleration, the engine must run at speeds proportional to gear ratios in a transmission and rarely runs at peak efficiency. 2. Kinetic energy from the vehicle can be converted to stored energy in the accumulator during via regenerative braking when the pump motor is run in reverse an takes energy from the wheels and stores it in the accumulator.

A series HHV is currently being considered for the Open Source Car. Animations explaining how a series HHV works are provided by the EPA here: http://www.epa.gov/oms/technology/research/how-it-works.htm --Crank 18:23, 24 April 2011 (PDT)