Document
National Aeronautics and Space Administration
NASA’s Magnetic Gearing Research for
Electrified Aircraft Propulsion
Dr. Justin Vivake Thomas
Scheidler Asnani Tallerico
NASA Glenn Research Center
Materials and Structures Division
Rotating and Drive Systems Branch
AIAA/IEEE Electric Aircraft Technologies Symposium Cincinnati, OH www.nasa.gov July 12, 2018
Outline
• Motivation • Principles of operation • Technology development at NASA • Future work • Conclusions National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Motivation
• NASA set goals for aircraft efficiency, emissions, reliability, and noise [1] • Parallel large & small aircraft development • Economic benefit of alternative propulsion • Electrified aircraft propulsion is a key enabler • Most concepts use direct drive • Geared drives are almost always mass optimal Direct drive Geared drive + Simpler + Optimized motor & fan − Non - optimal − More complex motor and/or fan motor − Potentially less reliable gearbox motor fan fan National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Motivation
Mechanical gearing Magnetic gearing Pros Pros + High / very high + Non - contact torque/mass + No lubrication ( specific torque ) + Low maintenance + High / very high + Easily integrated in efficiency electric machines + Mature technology + Potentially low vibration Cons Cons − Unknown limits on specific − Contact - related wear & torque & efficiency failure − Magnet temperature limit − Requires lubrication system(s ) − Individual magnet interaction weaker than 1 gear tooth pair − Routine & costly maintenance − Strong tonal vibration & cabin noise National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Background
Key historical developments st • 1901 – 1 invention • <1960s – primarily electromagnets • 1966 – SmCo magnets invented Data from • 1983 – NdFeB magnets invented • 2001 – Concentric magnetic gear (CMG) d mathematics Mechanical Analogous concentric Why we selected CMG planetary magnetic gear gear • Concentric input & output is most logical for most concepts • High specific torque • Easily integrated in electric machines National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Principles of Operation
o • Example: 4:1 gear ratio, 24 pole pairs in ring (15 wavelength) , 6 magnets per pair 1 pole pair (1 wavelength) Fundamental of ring o Closed loops indicate magnetic flux path, color indicates radial component of flux National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Principles of Operation
o • Example: 4:1 gear ratio, 24 pole pairs in ring (15 wavelength) , 6 magnets per pair Fundamental of ring Pole pieces Modulated o Ring wavelength o Modulated wavelength Closed loops indicate magnetic flux path, color indicates radial component of flux 𝑁 = 𝑁 + 𝑁 modulator ring sun National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Principles of Operation
Ring Modulator Fundamental sun and modulated ring field Fundamental ring and Sun modulated sun field Key Coupling path == Leakage path == • Key design variables 𝑁 𝑁 ring ring 𝐺𝑅 = 1 + 𝐺𝑅 = 𝑁 • # of magnetic pole pairs (“teeth”) 𝑁 sun sun • # magnets • Radial thickness of components & air gaps National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Research Needs
R&D needs in the field • Understand scaling • Thermal management • Data at higher speeds – efficiency, continuous operation • Enhanced high - speed efficiency • Advancement of other configurations • Shaft angle change • Combining inputs • Higher ratios National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Technology Development at NASA
2 - 1/2 year project • Create fundamental understanding • C ompare to mechanical gearing for aerospace applications Focus areas • Phase 1 – specific torque • Phase 2 – efficient high - speed operation • Phase 3 – motor/gear integration Progress • Phase 1 was recently completed.
• Two prototypes were developed to understand specific torque National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Prototype 1 (PT - 1)
Specific torque • Goal: To gain design & manufacturing experience • 2D simulation : 31 Nm/kg • Loosely tailored to X - 57 high - lift propulsors 35% reduction • Ø152 mm (6 in), ~4:1 speed reduction, 4500 rpm • Measurement : 20 Nm/kg • Off - the - shelf magnets • Limited design optimization Demonstration of gear ratio Design • 3D printed structures Ring Lessons learned • COTS magnets lead to large Modulator gaps between magnets in the sun • Magnetic forces can deform/damage the structures during assembly Sun National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Prototype 2 (PT - 2)
Specific torque • Goal: Maximize specific torque • 2D simulation : 61 Nm/kg • Multi - stage parametric study 23% reduction • Custom - shaped magnets • Measurement : 47 Nm/kg (>2X PT - 1) Design Prototype Lessons learned • Magnetic gap thickness fundamentally limits 1 pole pair specific torque • Mechanical design features that enable thinner magnetic gaps can improve specific torque 1 pole pair National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Prototype Performance
PT - 1 PT - 2 Performance compared to Torque (Nm) aircraft transmissions 2D simulation 53.0 178 Measurement 34.0 134.8 Rotorcraft (TRL 9) Mass (kg) Fixed wing (TRL 9) Active 1.0 (59 %) 1.7 (59 %) Magnetic (TRL 3) Structural 0.7 (41 %) 1.2 (41 %) Total 1.7 2.868 Specific torque (Nm/kg) 2D simulation 31 61 Measured 20 47 𝜏 / 𝑚 =18.3 ∙ 𝜏 • Specific torque is only 3 % less than an aircraft gearbox ^0.193 • Conclusive comparison requires more data & higher TRL • Thermal & dynamic considerations neglected so far PT - 2 (measured) Specific torque (Nm/kg) • Can reduce mass with smaller air gaps & better structural PT - 1 (measured) integration 1 100 10,000 1,000,000 • Simultaneously need high specific torque & high efficiency Torque (Nm) • Scaling to other torque levels is unknown at this point Data courtesy of Dr. Tim Krantz (NASA GRC) National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Test Rig Development
• Motivation : comprehensive characterization of CMG needed & very sparse description of experiments in literature • Purpose: study components of electrified drivetrain • Rotating system driven by 30 kW motor Test section High - speed disc coupling (1 of 2) Motor Bearing housing Eddy current Precision torque (1 of 2) dynamometer transducer (1 of 2) National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Test Rig Development
Specialized features 1. Adaptability – support table permits wide variety of test articles (including those with parallel offset between input & output shafts) ● 2. Very high precision – efficiency calculated from output/input mechanical power < ± 0.02% ● uncertainty in measured torque & speed couplings that impose low forces when misaligned ● ● 3. Dynamic measurement – sensors with 6 kHz bandwidth couplings with zero backlash ● lightweight & stiff components vibration isolation table National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Test Rig Development
• Controlled parameters : motor’s speed & Key specifications dynamometer’s torque Max torque (continuous) 16 Nm • Eddy current dynamometer Input Max speed 22,000 rpm • Suitable for emulating moderate to high Max power (continuous) 30 kW speed propellers (~1,000 to 4,000 rpm) Max torque (continuous) 100 Nm • Disc couplings: several benefits, but low Output Max speed 15,000 rpm * misalignment capability Max power (continuous) 30 kW • Measurements Torque ± 0.02% • Torque (capacity, ripple, & response to Measurement uncertainty at Average efficiency ± 0.11% overload) nominal state** Instantaneous efficiency ± 0.13% • Speed Measurement bandwidth 6 kHz • Transverse vibration * with minor balancing • Temperature (bearings & prototype) ** not including parasitic losses or the effect of misalignment • Bearing loss vs speed measured & subtracted National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Future Work
Phase 2 – enable high efficiency at high speeds • Data • Speed dependence of torque , efficiency, vibration , & temperature • Design • Reduce driving mechanism for eddy currents • Unconventional solutions for magnet & pole piece containment • Materials • Alternative or laminated magnetic materials • Electrically - insulating, thermally - conductive structural materials Phase 3 – integration in electric motors • Focus : motor - to - rotor stages of the quadrotor and tiltwing • Explore several topologies from literature National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Conclusions
• Studied torque - to - mass ratio of concentric magnetic gear • Designed, built, and statically tested 2 prototypes • PT - 1 – rapid build, understand design & fabrication issues • PT - 2 – nearly optimized torque - to - mass ratio • Key conclusions from NASA’s Phase 1 (understand & improve specific torque) • Strong coupling between mechanical & magnetic designs • Magnetic performance limited by mechanical features & min. gap size • Concentric magnetic gears are viable, at least for lower torque applications (e.g., emerging electrified short haul aircraft ) • Improvement relies on reducing air gaps, better integration, lighter structures • Developed a new 30 kW (40 hp) rotating test rig to study components of electrified drivetrains • Test a wide variety of test articles • Directly measure mechanical efficiency with very high precision • Measure dynamic responses and vibration National Aeronautics and Space Administration Magnetic Gearing Research at NASA
Acknowledgements
• NASA Revolutionary Vertical Lift Technology (RVLT) Project • NASA Internal Research & Development Project
References
st 1. Constantinides , S., “The demand for rare Earth materials in permanent magnets,” Proc. of 51 Conf. of Metallurgists, Niagra Falls, Canada, 2012.
National Aeronautics and Space Administration Magnetic Gearing Research at NASA
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