Applications:

1. Original motor with ceramic ferrite magnets

Previously this motor has employed a two-pole field system using arc-shaped anisotropic ceramic ferrite magnets (shown at right in light blue) and a laminated rotor containing a "lap-connected" winding (shown in red). Two-dimensional finite element analysis ("FEA") is used to determine the field throughout the magnetic circuit for the motor under normal load conditions, the regions of high flux line density (and high color intensity) being close to saturation: rotor teeth at the d-axis and stator housing at the q-axis.

2. Motor with original rotor and injection-molded Neo magnets

Using an economy grade of powder, and by careful selection of the powder loading (60% by volume in this case) and the magnets' radial thickness, it is possible to substitute the ceramic ferrite arcs with injection-molded Neo to provide almost exactly the same air gap flux per pole and flux density distribution.  The FEA at right clearly demonstrates a comparable field distribution to the previous case.  This means that the physical attributes of the bonded magnet are gained while using exactly the same rotor laminations and winding.  Only the inner diameter of the motor housing should be reduced to match the reduction in the magnets' thickness, so the outer diameter of the motor may likewise be reduced (as illustrated here). 

While this is a very convenient method of replacing ceramic ferrite while retaining the same motor torque constant, it really does not utilize the full potential of bonded Neo to also provide improved motor performance.  This is illustrated below.

3. New 2-pole motor with compression-molded Neo magnets

Because the volumetric loading of powder in a compression-molded magnet is inherently higher still (typically 78%), it will not be possible to perform the motor's re-design without allowing the flux per pole to increase.  However, the same motor torque constant can be achieved by reducing the number of conductors in the rotor winding.  This, in turn, allows the diameter of the laminated rotor to be reduced and its "teeth" to be widened, which is needed to prevent their saturation in the now higher flux per pole.

As illustrated by the demagnetization curves shown above, this compression-molded Neo magnet achieves much superior magnetic properties and a higher energy product than the injection-molded Neo magnet (which exceeds that for the anisotropic ceramic ferrite).  This allows the outer diameter of the motor to be further reduced, so the performance advantage this motor has over the original ferrite design (since torque constant was kept the same) is a total weight saving of approximately 30%.

In this example of a typical automobile accessory motor, the 30% weight saving would indeed be a valuable benefit.  However, other applications may prefer to retain the original motor volume and utilize the higher available magnet energy product to increase the motor's torque constant (output power).

4. New 4-pole motor with compression-molded Neo ring magnet

But if motor weight is truly to be minimized using the compression-molded Neo material, then a four-pole field system in a ring magnet provides a better overall solution (at least for a motor of this size).  The single piece ring magnet easily provides the simplest and most robust stator assembly, allowing the pole number to increase without adding components.  In this example, four poles provide essentially the same total air gap flux as the previous two-pole case, but the maximum flux in the motor housing is halved, allowing its thickness also to be halved by further reducing the housing's outer diameter. 

With regard to the laminated rotor, its number of slots is likewise increased from eight to ten in this example, but more importantly the four-pole layout doubles the number of electrical paths through the "lap"-connected winding.  The conductors are therefore thinner than before, leading to a more densely-packed winding and a better motor efficiency.