Audi calls the A2 e-tron «the most efficient Audi ever», and it has now explained where much of that efficiency comes from. The answer is the APP350, the Volkswagen Group's rear-mounted permanent-magnet synchronous motor. It runs at 400 volts, delivers up to 350 Nm and was optimised for the group's MEB electric platform.
Key changes
- Silicon carbide inverter: Audi says the inverter now uses silicon carbide (SiC) MOSFETs instead of silicon-based transistors, reaching efficiencies above 97%. New software lowers the switching frequency at medium speeds and loads, the typical conditions of city and country driving.
- Thinner rotor laminations: More than 30% thinner than on the earlier APP310, which cuts iron losses.
- Delta stator winding: Switching the stator from a star to a delta layout, with fewer parallel branches, improves efficiency under partial load.
- Quieter running: The rotor segments are now staggered, which Audi says almost removes tonal noise when pulling away. The inverter also adds high-frequency harmonics to the motor current to cancel unwanted noise.
- Gearing and oil: Two ratios cover three outputs: 10.21:1 for the 125 kW and 140 kW versions and 11.53:1 for the 170 kW car. Finely machined gear teeth allow a very low-viscosity oil that reduces churning losses.
Automotive World points out that because the APP350 was built for the MEB platform, the gains are not limited to one Audi model. It also notes that using silicon carbide at 400 volts takes the material beyond the 800-volt platforms where it first caught on.