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CVT-Based Full Hybrid Powertrain Offering High Efficiency at Lower Cost
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 12, 2010 by SAE International in United States
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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 project.
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.
CitationDebal, P., Faid, S., Tricoche, L., and Bervoets, S., "CVT-Based Full Hybrid Powertrain Offering High Efficiency at Lower Cost," SAE Technical Paper 2010-01-1313, 2010, https://doi.org/10.4271/2010-01-1313.
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