Assembling EV Motors With Adhesive

Electric motors in cars are omnipresent, but they are also well hidden. In today’s late model vehicles, more than 30 motors are typically used to power a variety of applications, including ABS pumps, central locking systems, exterior mirrors, seat adjusters, window regulators and windshield wipers.

However, from a technical point of view, the most exciting aspect of electric motors are the ones used for the drivetrain in mild hybrids, full hybrids, plug-ins and purely electric cars. Even hydrogen-powered heavy-duty trucks need electric traction motors.

Electric motors are typically assembled with adhesives, because they provide impact resistance. Bonding also provides vibration-damping characteristics for noise reduction.

Externally excited synchronous motors have windings in the stator and rotor that are energized. The power density of these devices tends to be lower than that of other motor designs, while wear tends to be higher due to the use of carbon brushes. Electric vehicles with these motors, like the BMW iX3, do not require magnets.

Induction motors, another important AC drive, tend to have a lower power density and operate without magnets. These types of motors are found in the Audi e-tron and the Tesla Model S, Model Y and Model 3.

Permanent magnet motors have the highest power density. This applies especially to motors equipped with internal permanent magnets (IPM), which are found in EVs such as the Porsche Taycan. The magnets offer strong performance. However, because of the natural monopolies that surround the mining and sale of rare-earth magnets, they tend to be expensive and can be difficult to source.

Better Joining With Adhesives
As different as each of these concepts are, they share something in common: EV motors are becoming smaller and more powerful, while their efficiency continues to improve. To achieve performance goals, engineers must consider many things, including lamination design, an optimal embedding of the magnets into the lamination stack, and leaving the smallest gap possible between the magnet and coil.

Each of these things increases assembly challenges. Adhesive bonding is a great joining option, because it plays a different role depending on the motor concept. Bonding is especially important when fixing the magnets of IPMs.

For example, a progressive reduction in motor size leads to tightened manufacturing tolerances, which drives up costs. In addition, rare-earth magnets are susceptible to corrosion, which is why they receive a passivation, nickel or epoxy resin coating. It is critical that the coating not be damaged during mounting.

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