The development of today's powertrains focuses on the
reduction of CO₂ emissions. Therefore several new technologies for
internal combustion engines have been established. A further
tendency is the successive electrification of powertrains in hybrid
vehicles. However, these trends lead to increasing system costs
which are a very important aspect at the market segment of compact
cars.
At the Institute of Internal Combustion Engines of the Technical
University of Munich a drivetrain concept for urban and commuter
traffic is under development. It is based on a lean-burn air-cooled
two-cylinder natural gas engine which is combined with a hydraulic
hybrid system.
The paper contains detailed information about the engine as well
as the hybrid vehicle powertrain in parallel structure. Particular
characteristics and innovations of the hydraulic hybrid system
compared to systems known so far are shown. The size of the
hydraulic pump is chosen in consideration of low pump losses and
suitable torque in combination with the engine map. Furthermore,
the paper puts emphasis on the selection of the hydraulic storage
type regarding system efficiency, complexity and package.
Subsequent to the description of the hybrid system, the results of
an entire vehicle simulation of the parallel hydraulic hybrid
powertrain are presented and discussed.
In summary, the paper describes concept, design and simulation
results of a two-cylinder natural gas engine combined with an
innovative hydraulic hybrid system in parallel structure.