Huddersfield, UK--More applications may be opening up for axial airgap motors. This motor design is not new--it was invented in Switzerland in the late 1940s--and it already fulfills many tasks in the fractional horsepower range. However, when taken beyond this range a number of design constraints must be considered if the motor is to be mass produced. A Brook Hansen company, Electrodrives Ltd., now claims to have overcome these difficulties.
Electrically, the axial airgap motor is similar to other ac motors, but it has disk-shaped stator/rotor cores which are placed adjacent to one another with flux linkage across an axial airgap. A significant axial force develops between stator and rotor when energized, and the resulting attraction force acts to close the working airgap between the two components. This affects rotor bearing durability which, in contrast to other motor designs, must satisfy high thrust demands due to the magnetic attraction.
Thermal behavior also differs from conventional motors. As a proportion of its volume, the stator presents less surface area in direct contact with the stator mounting. This is a disadvantage for thermal dissipation when compared with a squirrel-cage motor and its diecast aluminum-ribbed frame. On the other hand, the rotor is not positioned deep inside the stator as with conventional motors. Consequently, it is possible to achieve competitive output coefficients.
Electrodrives employs an automated process for the product consistency demanded by the volume OEMs. Unlike squirrel-cage induction motors where both stator and rotor are formed from individually punched steel laminations, the axial airgap cores are produced from a tightly formed coil of steel strip. The geometry and manufacturing processes involved permit an efficient use of materials, minimizing waste. Such savings offset the motor's somewhat higher bearing cost.
"Principle applications," says Rick Robbins, Product Manager at Brook Hansen, "are those where a short, squat design is essential." He quotes polishers, floor cleaners, and hoists as possible uses in a power range up to 2.2 kW.