CVT-Based Full Hybrid Powertrain Offering High Efficiency at Lower Cost 2010-01-1313
In 2007 Punch Powertrain started the development of a full
hybrid powertrain concept based on its CVT. A performance and
efficiency analysis proved that a post-configuration offered the
best solution. In parallel to the mechanical and electrical
development an advanced, Matlab/Simulink® simulation system was
established. A robust powertrain strategy was developed and
implemented into the simulation system. Results show a potential of
30% to 70% fuel efficiency improvement depending on the cycle (type
approval and real-world cycles). A higher saving potential is
possible as a plug-in.
The fuel efficiency improvement is reached while meeting other
important targets. First of all, the powertrain cost premium needs
to match the saving. Next to keeping the transmission cost under
control the electric drive technology and the batteries are
cornerstones of the powertrain development. A dedicated switched
reluctance electric motor/generator is developed at a partner.
Switched reluctance combines high efficiency and dynamic behavior
with a low cost potential. Special care has been taken to iron out
some drawbacks like torque ripple and noise. LiFePO₄ is the
preferred battery chemistry. It offers the best combination of
performance and cost without the safety risk of classic lithium ion
or polymer cells.
Additionally, the powertrain size is very restricted. The
development team at Punch Powertrain managed to keep the powertrain
length, width and height within the size of the conventional
counterpart. This enables a straightforward integration into most
engine bays. As such, Punch Powertrain offers a fairly easy
hybridization path for conventional cars.
During the development project the search for auxiliary
components was a continuous effort to find affordable components
that do not jeopardize the development targets for mass, space and
efficiency. For most components a "hybrid compatible"
solution was found. The hydraulic pump for the transmission was one
exception. A parallel development was initiated during the
A demonstrator vehicle is being built to drive as EV mid 2009
and as full hybrid by the end of 2009. In parallel a second
powertrain will undergo a series of test on bench to validate and
optimize the powertrain strategy. By exchanging powertrain control
modifications between the demonstrator and the test bench
driveability will be guaranteed while further optimizing the fuel
economy. Experience from both test platforms will be used in the
industrialization project. This project will result in a
production-ready powertrain design as well as a flexible production
system for small to medium production series.