Novel Test Methods for Electric Transmission Fluid Development
Yungwan Kwak and Christopher Cleveland
Afton Chemical Corporation, Richmond, VA
May 19th, 2022
76th STLE Annual Meeting & Exhibition, Orlando, FL
Introduction
Performance Requirements of Electric Drivetrain Fluid (EDF)
New eMobility Tests
Various Cu corrosion types, connectors, magnets and magnet wires, plastic materials.
Summary
The Drive to Electric Drivetrain Fluid (EDF)
Speed of change is high Risk is therefore high OEMs interest in:
Cooling performance
Efficiency
Material Compatibility
Mechanical protection • Antiwear • Bearing
OEMs are investing ~ $300 billion in the coming years to develop and launch electric vehicles. As resources shift to electric vehicle development, investment in traditional powertrains is decreasing.
Some OEMs are even questioning if Hybrids are a sustainable strategy
Major Components in eDrives
Electric Motor Power Electronics Reduction
Converts electrical to mechanical energy
Converts DC (battery) to AC (motor / generator)
Gear set reducing high rpm of eMotor to suitable output. Single or 2-3 speed
Compact system bringing these components together.
Allows each wheel independent speed (for cornering etc)
Electric Drive Unit Requires Optimized ETF
Electrical Properties
Fresh electrical conductivity
Electrical conductivity after aging
Dielectric breakdown voltage
Cooling Performance
Material Compatibility
Copper and other yellow mtls.
Plastics/insulation materials
Elastomers/seals
Water contamination
Thermal conductivity
Specific heat capacity
Oxidation
Mechanical Protection
Extreme Pressure
Pitting
Wear (Gear & Bearing)
Protection under electrification
Efficiency
Friction
Viscometrics
Thermal property
eMobility Tests to be Discussed
Various Cu Corrosion Tests: Static and Electrified Condition
Conventional Cu Corrosion Tests: Vapor and Liquid Phase Test
Vapor phase test
Cu corrosion behaves differently in vapor and liquid phase
No correlation between the amount of Cu dissolved and visual rating
Severe Cu leaching can cause hardware issue
Visual ratings are misleading for Cu corrosion
Cu corrosion under electrification and material compatibility important
Liquid phase test
Copper Corrosion Test via Printed Circuit Board
Test condition
1 mV supply and 150 °C
Monitor resistance change over time
Liquid, interface, and vapor phase
Easy set up
Fluid A
Fluid B
Fluid C
Electrified Cu Corrosion Test via Printed Circuit Board
Test condition
10 V DC 0.5 mm electrode gap 150 °C
Monitors conductive layer
Evaluates 3 phases
Realtime evaluation
Easy set up
Low Voltage Connector Test
Assess conductive deposit on the connector pins under electrified condition
Liquid phase and vapor phase evaluation
12 DC voltage applied
Condition: 500 h, 1000 h, or longer at 150 °C
Conditions and parts selected with OEM and Tiers
Results of Low Voltage Connector Test
Good fluid @ 1000 hours
Bad fluid @ 500 hours
Bad fluid confirmed conductive deposit formation via resistance change
Clear differences between fluid chemistry/formulation
Degree of non-conductive deposit
Nature of S chemistry
V. P.
L. P.
Fresh
h
A B C D
Polyesterimide resin/varnish
20mm x 50 mm x 3 mm
Cured 1h at 150 °C
Aging tested in 150 °C
Color darkening
(lighter) A > C > D > B (darker)
Fluid chemistry important
Type of S more important
S content not critical Other various components
Plastic Material Compatibility Test
150 °C / 336 hour
Fresh A B C
Materials’ compatibility varies with fluid chemistry, material type, and water content
Permanent Magnet Test
Aged at 150 °C
Magnet strength decreased
20 – 28% No meaningful fluid contribution
Corrosion of surface (less) B < A < C (more)
Fluid chemistry affected corrosion not magnet strength
Magnet typically not direct contact in eMotor
Breakdown Voltage of Magnet Wire
Thermal rating of 200 °C magnet wire (twisted pair)
Aging conditions
150 °C in a pressure tube
Aging time and water content affect performance
Fluid chemistry and formulation important
Partial Discharge Property of Magnet Wires
PD or corona discharge occurs when sufficiently strong electric filed applied, generating localized hot, fluorescent, and audible discharge
Typically, PDIV is much lower than BDV
Dependent on type of insulation and thickness of insulation
Aging of magnet wire deteriorate PD performance
Takes long time to see differences without added water
Concept demonstrates that we can screen for compatibility
Discrimination between good and bad fluids
Fluid formulations can be adjusted to improve compatibility Diversity of designs means divergent needs
New requirements on top of all conventional requirements
The optimum solution will differ for each OEM
Working closely with expert partners is the best way to develop optimized ETF technology
Close collaborations with OEMs/Tiers
• Conditions and parts relevant to the OEM applications
Salute industry activity