motor-w-solutions - ME250 Design and Manufacturing I...

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ME250 Design and Manufacturing I Electric Motors
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Outline Introduction Operation principle Permanent magnet DC motors Summary 2
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Introduction Converts electrical power to mechanical power Electric power = current X voltage Mechanical power = force X velocity or torque X angular velocity Electrical power Mechanical power I , V F, v or T, 3
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Introduction Major types AC motor DC motor Stepper motor Linear motor 4
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Introduction Pros Available in smaller sizes than IC engines No exhaust gasses Less noise than IC engines Easy control of torque/speed by voltage/current Cons Lower power-weight ratio than IC engines Lower power-cost ratio than IC engines Batteries have lower energy density than fossil fuels atteries are more expensive than fossil fuels Batteries are more expensive than fossil fuels 5
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Operation principle Force on current-carrying wire in magnetic field ) ( B I F i F : Lorentz force vector [N]; perpendicular to both B and I . current [A] i : current [A] I : vector of wire in magnetic filed [m] B : vector of magnetic flux density [tesla] F F B B 6 I I
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Operation principle Voltage on moving wire in magnetic field I B v ) ( d e e ind : induced voltage; aka electromotive force (EMF) [V] ind v : velocity vector of wire [m/s] I : vector of wire in magnetic filed [m] v e ind B Flemming’s Right hand rule 7
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Operation principle A “free” current–carrying wire in magnetic field R B V in i i i e ind l F, v x x When the switch is on, the wire will experience a sudden increase of force from 0 to F. Then x x v e ind in the direction opposite to i . i F v 8 Eventually v reaches a constant velocity.
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Operation principle At steady-state, apply F load to slow down wire B l F, v x x F load Net force to F - F load x x v e ind i F v ventually aches a constant velocity again: 9 Eventually v reaches a constant velocity again: v new < v
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Operation principle Basic trend F load v F load v v F load Note: v is steady-state velocity. 10
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Operation principle Torque-speed curves of various DC motors ermanent Permanent Magnet Motor Series Motor Shunt Motor Compound Motor 11
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Permanent magnet DC motors Problem: cannot continue 360 revolution Permanent N S Magnet i n F N S i n F B i F B i + - Armature (Coil) + - F F F Cannot rotate rther!! 12 F further!!
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Permanent magnet DC motors Solution: mechanical brushes Gap switches the current direction and keeps the armature tating rotating. 13
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Permanent magnet DC motors Mechanical brushes in action ttp://www youtube com/watch?v Xi7o8cMPI0E 14 http://www.youtube.com/watch?v=Xi7o8cMPI0E
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Permanent magnet DC motors Internal assembly 15
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Permanent magnet DC motors Torque-current relationship 0 (for 0 ) T 0 0 (for 0) or ) A T i K T T i T i  ) ( B I F i T : motor torque [Nm] 0 (for TA A T Ki K K T : torque constant (motor specific) [Nm/A/weber] i A : armature current [A] : magnetic flux [weber] = [Tm 2 ] T 0 : torque loss (e.g. frictional) [Nm] 16
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This note was uploaded on 09/12/2011 for the course MECHENG 250 taught by Professor Stevis during the Winter '09 term at University of Michigan.

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motor-w-solutions - ME250 Design and Manufacturing I...

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