Magnetic eCVT could replace conventional hybrid mechanical eCVT with likely 1-2% fuel economy improvement and other benefits
|MAGSPLIT is intended to replace mechanical eCVTs with a combination motor/magnetic gear. Source: Magnomatics. Click to enlarge.|
At the SAE 2014 Hybrid & Electric Vehicle Technologies Symposium in San Diego, Chris Kirby, founder and Managing Director of UK-based Magnomatics, presented an overview of the company’s second-generation MAGSPLIT (Magnetic Power Split) eCVT system, a compact magnetic transmission designed to replace both the mechanical planetary gearset and motor/generator that form a typical hybrid powersplit system.
Preliminary testing results of a prototype of the magnetic eCVT presented at the conference suggest a likely 1-2% improvement in fuel consumption compared to a conventional hybrid system, along with the benefits of reduced system complexity, no lubrication, low battery charge swing (allowing either downsizing the battery or extending the life of the original size) and compact packaging. Much further testing and optimization remains to be done, Kirby noted.
Background. Magnomatics was founded in 2006 by a group of engineers from the University of Sheffield (UK) to commercialize magnetic gearing and motor technology developed there.
|Basic overview of Magnomatics magnetic gear and motor technology.|
Magnomatics has received funding from the UK’s Technology Strategy Board (TSB) for a number of projects investigating the application of its technology in hybrid systems. These include:
HiTED In wheel motor for bus/truck (Volvo, Kollmorgen, Magnet Applications);
HiUCV In wheel motor for refuse vehicle (Dennis Eagle, MIRA, Arnold Magnetics, MTL);
MCVT Magnetic eCVT for heavy duty vehicles (Volvo, Arnold Magnetics); and
MAGSPLIT Magnetic eCVT for passenger car (Ford, Romax Technology, Arnold Magnetics).
In 2012 Magnomatics secured £2.5 million (US$4.1 million) funding to develop magnetically geared motors and generators for the hybrid and electric vehicle market. £1.06 million (US$1.7 million) was provided by IP Group which was matched by Finance Yorkshire. Fusion IP also invested £366,000 (US$602,000) in the technology.
In August 2013, Magnomatics joined The Proving Factory to meet the medium-volume requirements of automotive customers for its MAGSPLIT power split device. (The Proving Factory is a UK collaborative project designed to bridge the market gap between technology developers making innovative, low-carbon “proof of concept” prototypes, and the need to develop vehicle manufacturer’s confidence in the new technology by providing volume supply.)
MAGSPLIT principle. MAGSPLIT essentially integrates the magnetic equivalent of a planetary gearset with a high-performance permanent magnet brushless motor. 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.
Magnomatics says that a typical installation would have MAGSPLIT mounted directly onto the crankcase of the internal combustion engine. The gear ratio is controlled by varying the electrical power flow through the motor/generator. This electrical energy is either transiently stored or directed back to the drive train via a second traction motor.
|Typical installation. The configuration offers a direct mechanical power flow path, a direct electrical path, and an indirect electrical path. Click to enlarge.|
This would allow the engine to operate over a narrow speed band offering peak efficiency while delivering a variable speed drive to the wheels.
The magnetic gear within the MAGSPLIT has a typical efficiency of 99.5% at rated load. Losses are associated with importing/exporting power through the electrical path (i.e. winding copper losses). However, the total efficiency over a typical drive cycle is >95%.
MAGSPLIT 2. With the MAGSPLIT 2 system, Magnomatics reduced the package to a dual rotor system by removing the two outer arrays of magnets (for the control rotor and the sun gear) and essentially creating an electromagnetic sun gear, Kirby said.
MAGSPLIT 2 provides a lot more control and flexibility of design, Kirby said, while reducing magnet material as well.
Magnomatics has created three prototypes based on the specification of a 200 N·m C-Class passenger car: the original MAGSPLIT 1 with three rotors; MAGSPLIT 2a with surface mount magnets, running about the same magnet grade as the original MAGSPLIT; and MAGSPLIT 2b with interior magnets (magnets embedded within the rotor. MAGSPLIT 2b has about 1.5 kilos of magnet material, compared to the original 3.3 kg of MAGSPLIT 1.