The main goal of a motor designer is to maximise motor ouput ratings while minimizing its mass. Since its inception, Dana TM4 has chosen the external rotor design for its permanent magnet surface-mounted electric motors. TM4 MOTIVETM and TM4 SUMOTM electric powertrain systems are based on this topology.
Compared to rotor-centric permanent magnet motors, the external rotor motor topology (where the rotor rotates on the outside of the stator) has a greater magnetic flux.
Dana TM4 PM external rotor technology results in:
- Higher power density
- Higher torque density
- Increased long-term reliability
Increased effective air gap radius:
- The torque of an electric motor is the product of the magnetic force and the length of the radius of the magnetic flux. Thus, the farther the magnetic flux is from the axle, the more torque is generated.
- In a set diameter, the external rotor topology has a longer radius than any other topology, thus generating more torque with less material.
Surface permanent magnet technology
A motor with a high number of poles and a rounded magnet shape allows for:
- Lighter rotor and stator (reduced back iron)
- Near sinusoidal current and voltage generates fewer harmonic frequencies resulting in higher efficiency
- Thinner magnets that use a smaller amount of magnetic material
- Low cogging torque