Yard Hostler Hydraulic Hybrid Combo Video [transcript]

An EPA production

These vehicles improve fuel economy from forty to over one hundred percent,

Without costly materials to reduce weight, 

Without loss in performance and occasionally enhancing it 

They have better fuel efficiency during city driving,

and upwards of forty percent less emissions.

Additionally, the extra cost build them in high volume can be regained within
 two to three years from fuel savings alone. 

These vehicles will be cleaner and more efficient when powered with advanced
 engines, some eventually eliminating the need for fossil fuels entirely. 

These are, series hydraulic hybrids, created by the Clean Automotive Technology
 program, by the Environmental Protection Agency.


The secrets of hydraulic hybrids

There are three key design features to making full series hydraulic hybrids so
 fuel efficient:

The first feature is hydraulic regenerative braking. Hydraulic hybrid components
 can capture and reuse 70% of the energy normally lost during braking, which is
 far above what is possible with other regenerative braking technologies. 

The second feature is extensive engine off operation.  Because series hydraulic
 hybrids rely on power stored in the accumulator to drive, rather than power
 generated directly by the engine, the engine can be shut off whenever it is not
 needed and in typical city driving the engine could be off up to half of the
 time.

The third and final feature is optimum engine control. When power from the
 engine is finally needed, the engine can be run always at its most efficient
 point, to convert the most power from the fuel burned. 


This is how a full series hydraulic hybrid works
  
When the drive pedal is pressed, pressurized nitrogen, stored in the high
 pressure tank or accumulator, pushes hydraulic fluid through the pump/motor
 which then, acting as a motor, uses the pressure to turn the wheels. The now
 unpressurized fluid is stored in the low pressure tank or reservoir.  
  
When the vehicle has been cruising and the usable high pressure fluid drops
 beneath a certain level, the engine turns on.  The engine is connected to a
 hydraulic pump, which pressurizes the low pressure fluid for the pump/motor to
 continue to turn the wheels.  Any excess high pressure fluid, produced by the
 engine-pump, is stored in the high pressure accumulator.  
  
When the brake pedal is pressed, the engine shuts off and the pump/motor slows
 the vehicle down by using the vehicle's kinetic energy to pressurize fluid
 pumping it back into the high pressure accumulator.  When the driver wants to
 accelerate again, only the saved energy will be used to turn the wheels. 

This technology was created through the Clean Automotive Technology Program, by
 the Environmental Protection Agency.