First 18-meter electric bus in China powered by TM4 SUMO HD powertrain with external rotor motor technology
China’s first 18-meter battery electric bus has been put into service in Beijing. The Foton AUV 18-meter Harmony City BJ6180 is powered by a TM4 SUMO HD electric powertrain with a maximum torque of 3,500 N·m (2,581 lb-ft), 1600 N·m (1,180 lb-ft) continuous.
The SUMO HD is designed to interface with standard rear differentials without the need for an intermediate gearbox. Its direct drive / gearless approach makes it a good match for high-duty platform and commercial vehicle applications. The system features TM4’s external rotor motor technology (in which the rotor rotates on the outside of the stator). The external rotor motor technology delivers higher power density, high torque density, and increased long-term reliability than a similar motor with an internal rotor, according to TM4.
Electric motor torque is the product of the magnetic force and the length of the radius of the magnetic flux; the farther the magnetic flux is from the axle, the more torque is generated. For a given motor diameter, the external rotor topology has a longer radius than any other topology, and thus generates more torque with less material.
The 336 kg LSM280 motor in the SUMO HD system delivers 250 kW peak, 170 kW continuous power. The high number of poles and rounded magnet shape of the TM4 motor enables a lighter rotor and stator (reduced back iron) and thinner magnets that use a smaller amount of magnetic material. Near sinusoidal current and voltage generate fewer harmonic frequencies resulting in higher efficiency. Peak system efficiency of the SUMO HD is 95%.
The stator uses rectangular copper windings (bar wound) which provide a better fill factor than round copper and reduce the winding head length. Compactness and thermal management is improved, as well as efficiency. (A GM study found that bar winding lowers winding resistance 30% or more, lowering overall losses when compared to conventional wire wound types. Bar wound motors also have 50% or more greater heat dissipation area when compared to stranded wound types. Earlier post.)
The 215 kW/h lithium iron phosphate pack from Beijing Pride Energy Technology Ltd. Co. give the bus has a range of 100 km (62 miles). With a loading capacity of 143 passengers, the 18-meter vehicle features a light-weight monocoque structure with low-floor access.
Foton AUV also introduced advanced noise insulation technology, which reduces vehicle noise. Compared with other electric buses at present, Foton AUV 18-meter bus is six to eight decibels lower in noise.
Prestolite E-Propulsion Systems (PEPS), a 50/50 joint-venture between Prestolite Electric Beijing Limited and TM4 Inc., has been working closely with Foton for the electrification of the 12- and 18-meter New Energy Bus platforms; PEPS leverages TM4’s licensed technologies in Asia.