Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-07-20
2003-03-11
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156010, C029S596000, C029S598000
Reexamination Certificate
active
06531794
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to electric motors, and more particularly to brushless DC motors with permanent magnets.
Known brushless DC electric motors typically include a motor housing, a stator, and a rotor assembly. The stator includes a stator core having a bore therethrough. The rotor assembly is rotatably mounted in the housing, extends through the stator bore, includes a rotor core and a rotor shaft extending through the core. Typically, the rotor core has at least one permanent magnet mounted thereon. The housing includes a shell and two endshields and houses at least a portion of the rotor assembly. Electric motors also include at least one bearing sized to receive the rotor shaft. The endshields attach to ends of the housing shell and support the bearings. This particular construction is conventionally known as an “inner rotor” motor construction. The invention described herein pertains to motors with “inner rotor” motor construction, as well as motors with an inside out “outer rotor” motor construction.
During operation, the brushless DC motor utilizes electronic switching to provide torque. Typically, a motor controller receives a position feedback signal from a sensor inside the motor. The sensor ensures that excitation to the stator field always leads the permanent-magnet field to produce torque. The torque and power output of a DC motor are directly related to magnet energy level. More particularly, the amount of output is directly related to the residual induction level (Br) of the permanent magnets.
Sometimes, motor manufacturers fabricate a base motor and then develop a product line of motors with different outputs based upon the base motor but with different dimensions. For example, “stacking out” is a common method to vary the output. “Stacking out” means to increase the length of the motor depending upon output needs. However, changing the length of a motor requires different length parts and raises costs for the manufacturer.
Accordingly, a manufacturer must design, manufacture, and stock parts of varying dimensions to fabricate motors with different outputs forming a typical motor product line. Typical parts with varying dimensions include a stator, a stator core, a rotor shaft, a rotor core, and a motor housing. For example, 6-inch, 8-inch, and 10-inch rotor shafts might all be utilized in the same base motor to provide different output motors obtained from increasing lengths of stators and rotors. However, designing, manufacturing, and stocking 3 different length parts is more expensive than designing, manufacturing, and stocking 1 standardized part.
BRIEF SUMMARY OF THE INVENTION
A method for fabricating motors of different outputs using standardized parts includes fabricating standardized parts, ascertaining desired motor output, selecting at least one magnet from a group of interchangeable magnets to provide the desired output, and assembling a motor with the selected magnet and standardized parts such that the desired output is provided.
The interchangeable magnets have different Br values and, when interchanged in a motor, will vary the output of the motor. Since the selection is made after the standardized parts are fabricated, the output of the motor can be determined in the final stages of assembly and thus a motor manufacturer is able to respond quickly to market forces.
Accordingly, a method is provided to fabricate motors of different outputs using standardized parts wherein the output is changeable during final assembly. The invention described herein applies to motors with “inner rotor” motor construction, as well as motors with an inside out “outer rotor” motor construction.
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Hendershot et al., “Design of Brushless Permanent-Magnet Motors” Chap. 3, 1994.
Brahmavar Subhash M.
Erdman David M.
Harms Harold B.
Armstrong Teasdale LLP
Mullins Burton S.
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