Vehicle Design Summit Electric Hub Motor (V2)MotivationRequirements (Preliminary)ConstraintsPreliminary Design Choices Preliminary Design Choices (Continued)Preliminary Design Choices (Continued)Design VariablesDesign Variables (Continued)Design Variables (Continued)Design Variables (Continued)Stator Slot DesignMotor GeometryPerformance AnalysisFuture WorkLessons LearnedVehicle Design SummitElectric Hub Motor (V2)Eric ConnerHarvey TangMatthew PeddieMotivation• The AHPV from VDS 1.0 used an expensive, NGM electric hub motor, costing roughly $8000. (picture on right)• VDS 1.0 required a new electric hub motor to serve as both a replacement for the NGM motor, and as a stepping stone design for VDS 2.0.Requirements (Preliminary)• 10 kW continuous Power• 90%+ efficiency optimized for 45 miles an hour.• Motor weight less than 30 kg• Must interface with EV-C200 controller• Acceleration from 0-60 mph in less than 15 s.• Solar/Battery power must be used• Constant Torque with speed variationConstraints• Motor must fit between wheel and suspension arm, not interfere with other components• Motor cannot draw more power then controller can supply• Torque must not surpass limit of suspension arm bolt holePreliminary Design Choices • Design Choices Æ Why did we decide to design a 3-phase, axial gap, double sided, slotted, surface mounted brushless DC motor? Note, these design choices were made based on research, not simulated optimization.• Brushless Hub Motor Æ Comparison to Brush Hub Motor– higher efficiency and reliability (reduction of electromagneticinterference)– reduced noise – longer lifetime (no brush erosion)– However, more difficult to control (resolved by digital control)• Why 3-phase?– Excellent starting conditions with smooth rotation and low torque ripple Æ No structural resonance and induced mechanical stress–Flexible Æ Work with large variety of magnet configurations, winding configurations, and coil winding– Good conductor utilization Æ Higher phases give better utilization but are offset by increased numbers of leads and transistorsPreliminary Design Choices (Continued)• Why axial gap?– Spatial limitations Æ Motor must interface with suspension arm; fixed dimensions.– Axial Gap gives compact machine construction and short frame with much shorter rotor in axial direction, and thus less overall thickness– High power density.– High efficiency; no rotor copper losses due to permanent-magnet excitation.• Why double sided air gap?– The high attractive force between the rotor and the stator is counterbalanced by the use of a second stator. – Reduced copper and iron losses – Increased power density. – Increased cooling characteristicsPreliminary Design Choices (Continued)• Why slotted armature?– A motor with armature slots is more robust– Allowance for different winding structures– Although the slotted armature implies increased losses from flux ripple and tooth iron losses, the increased robustness is necessary to combat the mechanical stress.– Slotted armatures give higher airgap flux density levels using fewer permanent magnets.• Why surface mounted permanent magnets?– Much easier construction and manufacturing compared to interior permanent magnetsDesign Variables• How did we optimize our motors number of poles, stator slots, magnet span, coil turns, magnet grade, magnet skew and air gap length?• Maxwell3D was used as a means of running dynamic optimization Æ Program errors would not allow use of Maxwell’s optimization toolbox Æ Several configurations were analyzed separately so that various trends could be analyzed for an optimized engine• On the right is the sketch of the engine prior to the optimization of the design variablesDesign Variables (Continued)• The table on the right shows our final optimized engine and the values for each design variableDesign VariableOptimized ValuePole Number 8Stator Slots 18Magnet Grade NeFeBCoil Span 2Air Gap 1 mmStator Offset 15 Deg.Magnet Span 150 Deg.Magnet Skew 1 slot pitchWire Diameter .82 mmDesign Variables (Continued)• Pole Number Æ Smooth torque coupled with low speed generally implies large pole count• 8 poles decreases thickness of rotor yoke/stator yoke, decreasing overall diameter. • 8 poles minimizes flux leakage inside rotor• 8 poles increases the axial length of the stator and the end windings which reduces copper losses and increases efficiency• Stator Slots Æ Related to pole number; slot/pole number must be fraction to reduce cogging and skewing of poles or lamination stack. • 18 slots gives coil span of 2 Æ easier to manufacture• 18 slots reduces cogging torque• 18 slots reduces the length of the end windings and consequentlythe copper losses.• Air Gap Length Æ Increased length results in more overall losses while too small of a gap results in decreased power densityDesign Variables (Continued)• Magnet Grade Æ NeFeB has a larger energy-density then other magnets at a reasonable cost, increasing overall power density and torque• Stator offset Æ 15 degree offset of stators with each other was arrived at; compromise between elimination of some higher order harmonic components (decreases overall losses) and axial asymmetry which can cause pulsating axial force and create losses. • Magnet Skew Æ Skew can eliminate cogging torque as well as high-frequency components related to flux losses• Magnet Span Æ Span minimizes the pulsating torque, and in turn, cogging torque. • Wire Diameter Æ Optimized to turns per coil in the motor. Larger diameter gives less losses, however, less turns per coil. • Coil Span Æ Given by slot/poles, rounded down for short-pitching; gives an increased machine efficiency by reducing the end-turn lengths.Stator Slot Design• Previously defined Maxwell3D slot configuration for axial gap hub motors was used• Slot too deep or narrow Æ increased leakage • Slot width too large Æ slot tooth saturation• Slot top too open Æ cogging torque increases• Slot top too closed Æleakage will increase.Section SizeWedge Height1 mmBody Height8 mmOpening Width2.5 mmWedge Max Width6 mmBottom Width6 mmBottom Fillet3 mmOpening Height1 mmMotor GeometryComponent Size (mm)Inner Diameter252 mmOuter Diameter360 mmRotor Thickness36 mmAir Gap (x2) 1 mmStator Thickness (x2)8 mmFrame Thickness (x2)16 mmOverall Thickness86 mm• Although inner and outer radius are