Bearings and mechanical tolerances
The unglamorous parts that keep the rotor spinning true for hundreds of thousands of kilometres.
- Explain bearings and mechanical tolerances at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
A traction motor's air gap is often under a millimetre, so the bearings that centre the rotor inside it must hold extraordinarily tight tolerances for the life of the vehicle.
In depth
Bearing locations
Explore where the bearings sit relative to the rotor and shaft.
Electrical bearing damage
High-frequency PWM switching can induce voltage on the rotor shaft relative to the housing. If that voltage discharges through the thin oil film of a bearing, it creates tiny electrical discharge machining pits — a pattern engineers call fluting, visible as parallel grooves on the bearing race.
Diagnose: unusual bearing noise
Work through a scenario involving an intermittent whine from a drive unit.
Growling noise increases with speed
A technician reports a growling noise from the drive unit that gets louder with vehicle speed and does not change with steering input.
Key takeaways
- Bearings hold the rotor centred to tolerances measured in microns.
- High-frequency inverter switching can induce damaging shaft currents.
- Fluting damage is a recognisable symptom pointing to electrical bearing discharge.
Confirm you've read through and we'll count it toward your progress.