You are here
E-Motors: Mounting Long Stators with Two RENCOL® Tolerance Rings
November 30th, 2020
Electrification in the automotive industry is being driven by the desire for lightweight systems to reduce running costs and also the move towards EVs to reduce CO2 emissions. In both cases it is important to have an e-motor that is as efficient as possible, otherwise the motor will have to be larger and heavier than necessary to accommodate the power requirements.
One factor that can cause a decrease in motor efficiency is misalignment of the stator, which leads to an inconsistent and unpredictable air gap, between the rotor and the stator. In addition, misalignment can cause excessive noise and premature wear.
Traditionally a solution to the misalignment issue is to switch from a thin to a wide tolerance ring (both shown in Figure 1). For larger motors with long stators, this comes with other problems as the large width of the tolerance ring requires more material to create the ring which increases weight and material cost. Additionally, a wide ring requires a long assembly stroke which increases the risk of metal particle generation, which can cause issues in electronic systems.
Figure 1. Stator mounted into the housing with: (left) a thin tolerance ring; (right) a wide tolerance ring
Rather than trying to create a sophisticated, expensive tolerance ring design that satisfies all the problems in stator mounting, it is sometimes more efficient to make two tolerance rings of different designs (SV at one end, HV at the other, as seen in Figure 2) that can be installed at either end of the long stator yoke with short assembly strokes leading to a smaller risk of particle generation (Figure 3).
Figure 2. Stator mounted into the housing with two tolerance rings, one SV and the other HV.
Figure 3. (left) The assembly stroke of a wide tolerance ring solution; (right) Shorter overall assembly strokes for the RENCOL® 2TR solution.
A two tolerance ring system, opens up new possibilities as different ring designs can be used at each end of the stator. For example, one end of the stator could be designed to have a high stiffness and high retention force while the second tolerance ring could have a low stiffness design to offer misalignment compensation as well as clearance and rattle free performance.
Applications that could benefit this system are, but not limited to; drive motors, hybrid drive motors, 48v systems, KERS, alternators, starter motors, oil pump motors, engine/battery cooling pump motors, e-turbos, electric scooter/bicycle/motorcycle and wiper motors.
For a more in-depth look at RENCOL® Tolerance Rings, please read What is a Tolerance Ring?