Andy Pye discovers how vibration attenuation can be achieved in a magnetically controlled variable transmission.
Magnomatics is a high-technology company formed in 2006 as a spin out from the University of Sheffield. The company specialises in the development of advanced magnetic transmission systems and high-torque electrical machines.
The company is commercialising novel products based upon highly efficient proprietary magnetic gear technology and is working with some of the world’s largest multinationals from a range of industries, including automotive, renewable energy, rail, aerospace, marine, and oil and gas.
Magnetic gears are contactless and therefore very efficient over a broad range of speeds. They are compact and also incorporate a torque fuse feature. They are especially suited to high torque, low speed applications and can also be adapted into a continuously variable hybrid transmission and power split device for automotive applications.
The MagSplit (Magnetically Controlled Variable Transmission) is a highly efficient electrically controlled power split device that can achieve a continuous range of gear ratios to match a fixed speed prime-mover to a variable load. It is used to ensure that the engine is operating at its maximum efficiency at any point in the drive cycle. It is also compact and can filter torsional vibrations from the engine, eliminating the need for torsional dampers.
The MagSplit differs from existing three-rotor power split systems, such as those in the Toyota and Ford product range, as it is a two-rotor system (input/output) with an entirely magnetic variator function. Variable speed mechanical output with a fixed input mechanical speed is achieved by exporting/importing electrical power through a set of control windings – splitting the power along a “variator” path.
With the outer PM control rotor held static, the magnetic gear has an intrinsic fixed ratio gear. By controlling the current flow through the stator control windings, the rotational speed of the PM control rotor is varied and hence the gear ratio can be controlled over a broad range about the intrinsic ratio by varying the speed of the outer array of magnets which become the high speed element of the gear. Through this speed control, the MagSplit is also capable of fully disconnecting the output drive. This is much simpler than using a mechanical planetary system where the speed of the sun gear must be controlled.
Aachen Acoustics Colloquium is one of the most important centres for development and research in automotive acoustics. The Colloquium takes place once a year and particularly addresses the latest methods and technologies in the fields of acoustics and vibrations of vehicles and drives.
During the Colloquium, Magnomatics presented a whitepaper entitled, ‘High Bandwidth Drivetrain Vibration Attenuation Using Electromagnetic Powersplit Transmission’, written by Stuart Calverley, Jeff Birchall and David Black, which outlines the performance of the company’s magnetic powersplit (MagSplit) system as a filter for torsional vibration.
The whitepaper reports on recent project work to demonstrate the significant reductions in drive train noise, vibration and harshness (NVH) inherent in a Magnomatics magnetic transmission system. Substantial system cost savings are validated by deleting incumbent vibration control components in conventional drivetrains.
During the course of this development at Magnomatics, a significant breakthrough has been achieved, whereby the unique properties of the MagSplit, and specifically the magnetic variator, were used to give near 100% attenuation of torsional vibration. This was measured on a custom-made dynamometer system with a synthesised vibration input. This is an unusually important result, since when exploited it will mean that the Magsplit will provide significant technical and commercial benefits, perhaps mounting to as much as $200 per vehicle, as a result of removing the Dual Mass Flywheel (DMF).
The engine test methodology currently under development involves coupling the engine operation with the Magsplit and to develop the prototype control methods and calibration techniques required to confirm that the DMF can indeed be deleted and the attendant benefits realised.