Spin Me Around! How epoxy-enhanced e-engines enable high performing e-cars!

Background The increasing need to lower humanity’s CO2-footprint requires, next to other initiatives, the development of alternative mobility concepts such as electric vehicles. In order to transition from a combustion engine powered car to an electric one there are three main components needed: Besides the energy source (e.g. battery pack), and the control unit, an electric drive is required.  Electric drives exist since the late 19th century and have been a key to industrialisation. The first e-car was already invented in 1888 by German engineer Andreas Flocken from Coburg, who fitted a high wheeled carriage with an e-engine and batteries, boasting 0.7 KW power output, which was able to get the “car” to accelerate to 10 km/h!



Because the use requirements for an EV-motor are significantly different from a stationary drive used in industrial manufacturing, automotive producers spend significant resources in R&D to develop high performing e-engines with reduced energy consumption to boost achievable mileage.   The basic principle of all traction motors (= e-motors) is the creation of a rotating magnetic field in the stator, the rotor has to follow. The easiest way to create a constant magnetic field in the rotor, which interacts with the rotating one is the use of permanent magnets. To produce highly efficient permanent magnets, rare earth metals are necessary and today China effectively has a quasi-global monopoly. To avoid dependency on permanent magnets, two main alternative concepts are considered, induction- and external-exited motors. In both cases the rotor magnetic field is electrically induced.

The efficiency of such motors increases with the rotational speed (rpm). Due to the high rotational speeds it becomes imperative to solidly fix the wires of the rotor coil (external-excited motor) in place to avoid an unbalance which could destroy the motor. It should be noted that the coil temperature in operation reaches 150 to 200°C (!) depending on the electric current density applied. Therefore, a high glass transition* (Tg) system providing mechanical strength at operation temperature with excellent crack resistance is indispensable.

The main challenges in the design of appropriate epoxy rotor coil encapsulation system are to achieve the targeted glass transition temperature (Tg) of greater than 190°C within a fairly short cure cycle of only 3 hours at max. 190°C. On top of that, the minimum fracture toughness to obtain a crack resistant encapsulation under tough automotive testing conditions needs to be met as well. This challenge has been mastered by close collaboration of chemical and automotive engineers. Once again, epoxies have made their mark and shown their prowess in supporting the transition to a low-carbon, more sustainable, more environmentally friendly society!

*Glass transition temperature = temperature range where the properties of a material change due to a phase change from a hard, glassy state to a more rubbery, amorphous state. In epoxy polymers exceeding the Tg would result in a gradual loss of mechanical properties