The MAGSPLIT® Hybrid Transmission
The Magsplit transmission device splits propulsion power magnetically. In operation, it offers greater efficiency with superior NVH compared to the alternatives. As a power split, the launch quality is smooth and tunably progressive, whether driving purely electrically or with the combustion engine. As electrification proliferates, hybrids must continue to offer a competitive driving experience and, for Chinese customers, this magnetic
Mr. Andrew Chapman, Powertrain Attribute Leader, Changan UK R&D Centre Limited
Issue: #December 2017
The Magsplit device
The conventional powersplit has an input from a combustion engine and an e-machine into a mechanical epicyclic gear arrangement. The Magsplit combines the epicyclic and e-machine functions into one device. The device comprises an outer stator and two concentric rotors. The inner rotor has a magnetic field that is, in the current development, generated using permanent magnets and is connected directly to the device output. The secondary rotor, connected to the combustion engine, is positioned in what would be the air gap in a conventional emachine and has circumferentially alternating materials of high and low permeability. The torque ratio of the device is determined by the ratio of inner and secondary poles.
The transmission arrangement
The transmission arrangement is from then on familiar enough but with the package constraints applied for Changan C/D segment products forcing the second e-machine onto a parallel axis. The transmission length is short at 345 mm with scope to optimise the flywheel and end winding spaces. The secondary rotor acts as a simple single mass flywheel with the magnetic gearing isolating the drivetrain mechanical gears from torsional vibrations.
Figure 1 The Magsplit device Figure 2 Transmission exploded view
This isolation is possible because the reaction torque for the engine input is provided by the magnetic field of the stator which has zero mechanical inertia. The resultant magnetic field can therefore be placed with precision to counter the torsional oscillations induced by the reciprocating engine. This ability complements engine down speeding and dethrottling techniques which further improve powertrain efficiency. Changan UK is in collaboration with Magnomatics, Romax Technology, The University of Sheffield and CMCL Innovations, with financial support from Innovate UK, to progress the design and test of the transmission and powertrain system. The integrated powertrain will be manufactured and tested during 2018.
System sizing & vehicle performance
The transmission initial system sizing process starts with the use of the proprietary Magnomatics sizing tool which was utilised to check for performance against Changan requirements. The system supports 0 – 100 km/h acceleration times of <8 seconds when coupled to a combustion engine with a 200Nm torque capability and meets standard gradeability demands.
The Romax developed methodology for rapid concept transmission design and evaluation in conventional, hybrid, and electric vehicles was utilised to inform the early design. In addition to simulating five different drivetrain layouts, sensitivity studies were carried out to evaluate the effect on fuel consumption of changes to magnetic and mechanical ratios, control strategy, and component efficiencies. Romax uses a statistical approach to drive cycle simulation which directly considers speed-acceleration operating points in place of a speed vs time profile, and a single calculation over the operation space in place of a separate calculation for each timestep.