The present invention relates generally to electromagnetic actuators, and more particularly, to a stator lamination and outer housing of an actuator.
The desirability of and need for a rotary electromagnetic actuators has been recognized for years. A factor in the effectiveness of rotary electromagnetic actuators is the ability of the actuator to convert electromagnetic forces into useful output torque. That is, the efficiency of the actuator in converting electromagnetic forces into useful output torque is of primary importance. In some rotary actuator designs, a significant factor in this conversion is the presence of undesired air gaps in the actuator, and more specifically, the presence of air gaps between an outer enclosure and a stator in the actuator. For rotary actuators in which a magnetic flux path is formed by a rotor, a stator lamination stack, and an outer enclosure, such undesired air gaps greatly reduce the torque output of the actuator and lead to significant inefficiency in converting electromagnetic forces into useful output torque by creating undesirable reluctance. Useful output torque is maximized when the stator-armature gap provides a flux path having a minimal reluctance.
In an effort to minimize or eliminate this undesirable air gap, the interface between the stator lamination stack and an inner surface of the outer housing needs to be a precision line-to-line fit to eliminate a performance-reducing air gap. In an effort to form this line-to-line fit, current technology relies on a method to heat outer enclosure to expand its inner diameter in order to press the stator lamination into the enclosure. That is, the outer circular enclosure is heated to a desired temperature, and then the stator lamination stack is pressed into the outer enclosure. As the outer enclosure cools, it creates a press fit between the two parts. Such a process, however, is complex and costly, and additionally, may not always form an adequate line-to-line fit at desired locations in the actuator so as to form an efficient flux path.
In another commonly used method, the outer enclosure is made from sheet metal that is wrapped around the stator lamination stack. An additional adhesive may be employed to form a solid connection between the outer enclosure and the stator laminations to prevent unwanted rotation or axial translation therebetween. However, such an adhesive can function as an undesirable air gap and increase reluctance. Furthermore, application of the outer enclosure in such a manner results in a seam within the enclosure, which leaves the actuator unsealed.
Therefore, a need exists for a stator lamination design and method of positioning the stator lamination within an outer enclosure is efficient and cost effective. Additionally, it is desired that such a stator lamination design and construction method assures a line-to-line fit between the stator lamination stack and outer enclosure so as to eliminate a performance reducing air gap therebetween and form an efficient magnetic flux path.