Hybrid‐Electric Vehicles & Regenerative Braking
Cool technology? Or marketing tool?
Ken Stanton, PhD
Engineering Education
Dept. of Mechanical Engineering
How does hybridization improve MPG?
Downsize engine & run in more efficient zones
Electric motor torque & efficiency
Aerodynamics (not unique to hybrids, though)
Plug‐in for electric power recharge
Regenerative braking
So what is “regenerative braking?”
Is it a special technology added to HEVs?
Or is it just a marketing tool?
How electric motors work
Force in opposite directions, around a rotational object, creates torque
Force is from 2 magnetic fields interacting
Can be 2 magnets, 1 magnet & 1 coil, or 2 coils
Permanent magnets can’t be “controlled”
But we need to control an electric motors’
torque & speed
Coils can act like magnets AND are controllable
Direction and magnitude of electricity determines magnetic field
direction and magnitude
How electric motors work
Electrical energy ‐> Mechanical energy (rotational)
Also…
Mechanical energy ‐> Electrical energy
Flux Linkage
Flux linkage λ
= ∫B dS = BA
λ
= NBA for multiple turns
ϕ = BA for uniform field λ
= Nϕ
λ
= NBA cos θ
most complete equation
Also, λ
= Li
for coil flowing current
Back EMF
Bring it all together…
Vehicle is in motion ‐> kinetic energy
Wheels rotate with vehicle ‐> rotational energy
Wheels rotate electric motor
Motor rotation induces current in coils ‐> electrical energy
Induction creates opposing torque ‐> braking
Current is rectified (to DC) and sent to batteries ‐> stored electrical energy (in chemical form)
= Regenerative Braking
Controlling regenerative braking force
In conclusion…
Regenerative braking is just a property of electric motors
Benefits:
Reduces use of mechanical brakes (waste heat, materials)
Doesn’t require extra equipment
Recovers kinetic energy
Recharges batteries
Ken Stanton, PhD Research Scientist Mechanical Engineering Colorado State University [email protected]
Questions?