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.
This coating protects the magnets from exposure to environmental influences. Other established methods of joining, such as mechanical clamping of magnets, are reaching their limits in terms of motor function and production process. Adhesive bonding, on the other hand, meets all these requirements.
Bonding is also advantageous for other motor concepts beyond joining magnets and lamination stacks. It can be used to join the shaft and rotor or the stator and housing. Adhesives can prevent fretting or contact corrosion. They are also impact-resistant, which is essential for the high dynamic forces in electric motors.
The vibration-damping characteristics of adhesives helps reduce noise and provides acoustic improvement. Their homogeneous stress distribution helps compensate for thermal stress that may be generated due to different coefficients of thermal expansion between the stator and housing.
Gap-filling properties help prevent slippage and play in the area surrounding the shaft. Often, bonding allows for lower manufacturing costs, since a high level of automation can be used.
Apart from these assembly applications, adhesives are also used for casting sensitive components in electric motors to protect them from humidity, aggressive media and mechanical stress.
Read more: Assembling EV Motors With Adhesive