Patent Application
20170229931
The present invention relates generally to electric motors, and more particularly to laminations for making an electric motor stator.
In a system with an electric motor, it is desirable to keep the torque constant of the motor as linear as possible when the motor is subjected to high intermittent torque demands. If the torque constant rolls off (i.e., degrades and becomes non-linear) and the motor laminations have not reached magnetic saturation, then additional current may be supplied to the motor to compensate for the degraded torque constant. However, if the iron in the motor laminations has reached magnetic saturation, then roll off of the torque constant cannot be compensated for by increasing the current.
To accomplish a linear torque constant over a specified operating torque range, the iron associated with the stator must be sufficient to support the necessary magnetic flux levels. Therefore, the motor laminations are designed with enough iron so that the torque constant remains linear over the expected operating torque range. However, adding ferrous material to the laminations takes away physical space available for the motor windings. As the physical space for the motor windings is decreased, the motor resistance increases, which causes additional heating and changes the motor's time constant.
Applicant has designed a motor having an optimal torque constant linearity. The design uses conventional circular laminations onto which windings are inserted. Although suitable torque constant linearity is achieved, the motor is not cost effective to manufacture in high production volumes. To enable this motor to be manufactured in high volumes in a cost effective manner, a manufacturing process was adopted whereby the laminations are formed as straight line laminations and then rolled to form a circular stator after the copper windings are installed. In the straight line laminations, the fingers that receive the copper windings are arranged as a plurality of parallel fingers spaced apart from one another by slot areas along a longitudinal axis of the laminations. The winding step is performed while the fingers are parallel and there is easy access and space for winding machinery. The wound laminations are then rolled into a circular configuration in which the fingers extend radially toward a central axis of the motor. This process maximizes the amount of copper winding in the slot areas allocated for copper, and therefore minimizes the overall axial length of the motor for a given motor constant.
Winding the laminations while they are straight and then rolling the wound laminations into a circular stator requires that a back iron region of the laminations be configured with bendable hinge features between the fingers. The hinge features are formed by adding voids in the laminations so that adjacent fingers of the lamination are connected by a thin strip of lamination material acting as the hinge feature. However, providing the hinge features reduces the amount of material in the back iron region of the laminations, thus causing the torque constant to roll off at lower torque demands than the conventional circular lamination version of the motor.
Therefore, it is an object of the present invention to provide a rollable motor lamination that does not compromise torque constant linearity relative to a comparable circular motor lamination.
In an embodiment of the present invention, a motor lamination defines a plurality of finger segments spaced along a longitudinal axis, and a plurality of hinge segments respectively between adjacent pairs of the finger segments. Each finger segment has a reference center, a back iron region, and a finger projecting from the back iron region along a finger axis extending perpendicular to the longitudinal axis of the lamination. The back iron region includes a pair of lateral edges each extending in a respective radial direction relative to the reference center of the finger segment, and a pair of inner edges each extending from the finger to an associated one of the lateral edges. Each inner edge is non-arcuate in shape. For example, the inner edge may have a first straight edge portion extending perpendicular to the radial direction of the associated lateral edge. When the lamination is rolled into circular form, each first straight edge portion aligns with another first straight edge portion of an adjacent finger segment, such that the rolled lamination has a plurality of non-arcuate inner edges bounding slot areas for the motor windings. The resulting inner edge configuration provides extra back iron material in the lamination to compensate for back iron material omitted to define the hinge segments and maintain a desired torque constant linearity.
The invention is also embodied by an electric motor stator that comprises a stack of laminations defining a ring-shaped back iron and a plurality of angularly-spaced fingers separated by a plurality of angularly-spaced slot areas, wherein each of the fingers extends radially inward from the back iron toward a central axis of the stack along a respective radial finger axis and each of the slot areas has a respective radial slot axis. The back iron has a plurality of inner edges each extending between an angularly adjacent pair of the fingers and bounding an associated one of the slot areas. In accordance with the invention, each of the inner edges includes at least one non-arcuate edge portion. The inner edges may have a plurality of straight edge portions. For example, the each inner edge may have a pair of straight transition portions connected by a bridge portion. The bridge portion may also be straight, and may extend perpendicular to the radial slot axis of the associated slot area. By configuring the inner edges in this way, extra back iron material is provided for mitigating torque constant roll off.
The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which:
Lamination 10 is cut from a sheet of lamination material. The shape of lamination 10 defines a plurality of finger segments 12 spaced along the longitudinal axis 11, and a plurality of hinge segments 14 respectively between adjacent pairs of finger segments 12. Each finger segment 12 has a reference center 13, a back iron region 16, and a finger 18 projecting from back iron region 16 along a finger axis 19 extending perpendicular to longitudinal axis 11.
Reference is also made to
Referring again to
As may be seen in
The novel configuration of inner edges 24 departs from traditional use of an inner edge that is simply a circular arc from one finger to the next to provide extra back iron material at regions 46 associated with hinge segments 14, thereby making up for the loss of back iron material due to formation of hinge segments 14. By mitigating torque constant roll off affects, the present invention allows for use of straight line laminations 10 for more efficient stator production without sacrificing torque constant linearity.
While the invention has been described in connection with exemplary embodiments, the detailed description is not intended to limit the scope of the invention to the particular forms set forth. The invention is intended to cover such alternatives, modifications and equivalents of the described embodiment as may be included within the scope of the invention.
