Fuel Economy Benefits of a Flywheel & CVT Based Mechanical Hybrid for City Bus and Commercial Vehicle Applications 2009-01-2868
Hybrid drivetrain systems are becoming increasingly prevalent in Automotive and Commercial Vehicle applications and have also been introduced for the 2009 Formula1 motorsport season. The F1 development has the clear intent of directing technical development in motorsport to impact the key issue of fuel efficiency in mainstream vehicles.
In order to promote all technical developments, the type of system (electrical, mechanical, hydraulic, etc) for the F1 application has not been specified.
A significant outcome of this action is renewed interest and development of mechanical hybrid systems comprising a high speed composite flywheel and a full-toroidal traction drive Continuously Variable Transmission (CVT).
A flywheel based mechanical hybrid has few system components, low system costs, low weight and dispenses with the energy state changes of electrical systems producing a highly efficient and power dense hybrid system.
Due to the system simplicity, the mechanical hybrid delivers a measured 72% ‘round trip’ efficiency in approximately half the package, half the weight and a quarter of the cost of an electric hybrid system.
Torotrak have assisted in the development of the flywheel based mechanical hybrid applying the Series Production full-toroidal traction drive technology in CVT format for use within motorsport but also as a technology for mainstream vehicle applications
For the mainstream applications, either the high speed / low mass flywheel or a more conventional higher mass / lower speed flywheel can be utilised. The mechanical hybrid system is now being developed for multiple automotive applications including a Government sponsored project with Jaguar Cars Ltd.
Due to the ‘stop / start’ transient duty cycle, the flywheel based mechanical hybrid system is particularly well suited to City Bus applications and can be extended to larger Commercial Vehicle applications.
This paper describes the flywheel based mechanical hybrid system, the simulation results of applying the flywheel hybrid to a City Bus and the powertrain arrangement for the flywheel hybrid system, energy storage requirements, system efficiencies, energy savings and hence fuel economy improvements.