Within the ModulED project, the consortium developed an innovative electric powertrain to reach new performances in term of power, comfort and cost reduction.
The powertrain developed is modular. Modularity implies that the different subsystems can easily be assembled and disassembled. This allows an easy exchange of parts in case of repair but also the development of other powertrain configurations with little extra effort. For example, the transmission design is based on a two-speed technology but allows an ease of integration of a single speed design, with a minimal amount of new parts.
Figure 1: Modular electric powertrain
The ModulED electric powertrain is fully integrated, with motor, inverter, transmission and cooling into a compact unit. This high level of integration offers clear advantages for OEMs. The integration eliminates several parts and simplifies others. This results into a lower cost powertrain. The assembly of this powertrain into a vehicle involves only one unit and the simplified interfacing with the vehicle involves only the powertrain suspension, the drive shafts, high voltage and low voltage cabling and cooling. The smaller assembly effort also results in a cost saving.
Figure 2: Compact integrated electric powertrain
The high level of integration also resulted in a compact unit. The size of the powertrain is comparable to electric powertrains of a previous generation that do not include the inverter and offer substantially lower power. The small powertrain volume allows its use as an e-axle driving the rear wheels. In case of front wheel drive vehicles, the compact powertrain leaves space for a frunk.
The ModulED transmission
The ModulED electric powertrain has an efficient two speed transmission. During the development process high efficiency was a key requirement for the transmission configuration selection, gear design and bearing configuration and selection. The result is a 25% reduction of simulated losses when compared to earlier single speed designs.
Further efficiency gains are realized with an oil pump free concept using gravity for oil distribution. Additionally, the gear switching mechanism only requires energy during actuation. This comes at the expense of a short torque interruption. The powertrain control will make these torque interruptions as smooth as possible.
The ModulED Cooling
Although electric powertrains have a much smaller heat rejection than conventional powertrains an effective cooling system is required to guarantee the long life of the power electronic components and the magnetic strength of the permanent magnet material. Due to the compact integration of the ModulED powertrain it was a challenge to develop the cooling system. The use of 3D-CFD was a big help to reach an effective design.
Figure 3: Coolant flow pattern in inverter and motor
The cooling system of the ModulED powertrain also contributes to the powertrain efficiency. By using several parallel cooling channels both for the inverter cooling and the motor cooling the pressure drop in the cooling system is kept quite low. This allows using a small, low power water pump even when the powertrain operates at high power.