WO2022070476A1

WO2022070476A1 - Methods and systems for bonding a rotor lamination stack to a rotor housing of an electric motor

Info

Publication number: WO2022070476A1
Application number: PCT/JP2021/011279
Authority: WO
Inventors: Eric HARLAN; Zaher Daboussi; Matthew Todd Keennon
Original assignee: Hapsmobile Inc.
Priority date: 2020-09-30
Filing date: 2021-03-18
Publication date: 2022-04-07

Abstract

Systems, devices, and methods including: at least one electric motor, including: a rotor, including: a rotor housing; a rotor lamination stack; a plurality of spacers; where at least one of the plurality of spacers may be placed between the rotor lamination stack and the rotor housing; and where the at least one of the plurality of spacers may provide a bond gap between the at least one rotor lamination stack and the rotor housing and prevent electrical shorting.

Description

METHODS AND SYSTEMS FOR BONDING A ROTOR LAMINATION STACK TO A ROTOR HOUSING OF AN ELECTRIC MOTOR

　　Embodiments relate generally to electric motors and more particularly to bonding of a rotor lamination stack to a rotor housing of an electric motor.

Background

　　Unmanned aerial vehicles (UAVs) may function optimally at high altitude where the motor (or motors) of the UAVs may be exposed to extreme temperature ranges. Electric shorts may occur in the rotors of the motors over such extreme temperature ranges.

Summary

　　A system embodiment may include at least one electric motor. The at least one motor may include a stator with a rotor housing, a rotor lamination stack, and a plurality of spacers. In one embodiment, at least one of the plurality of spacers may be placed between the rotor lamination stack and the rotor housing. In one embodiment, the at least one of the plurality of spacers may provide a bond gap between the rotor lamination stack and the rotor housing and prevent electrical shorting.

　　The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. Like reference numerals designate corresponding parts throughout the different views. Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:
[Fig. 1] FIG. 1 depicts an unmanned aerial vehicle including an electric motor;
[Fig. 2] FIG. 2 depicts a side perspective exploded view of a rotor of the electric motor of FIG. 1, including a rotor lamination stack and a rotor housing;
[Fig. 3] FIG. 3 depicts a side perspective view of a portion of the assembled rotor of FIG. 2;
[Fig. 4] FIG. 4 depicts a bottom perspective view of a portion of the assembled rotor of FIG. 2 with injection holes in the rotor housing; and
[Fig. 5] FIG. 5 depicts a cross-sectional view of a magnet retention ring bonded to the rotor lamination stack and the rotor housing of FIG. 2 and to a plurality of magnets associated with the rotor lamination stack.

　　When mounting of a rotor lamination stack onto a rotor housing with glue, an electrical short in the lamination stack may occur, due to features of the rotor. More specifically, the rotor lamination stack and the rotor housing may be made of two different electrically conductive materials, such as iron and titanium. In one embodiment, a plurality of isolators or "spacers" may be placed between the rotor lamination stack and the rotor housing. The spacers may provide a bond gap between the rotor housing and the rotor lamination stack and prevent electrical shorting.

　　With respect to FIG. 1, an unmanned aerial vehicle (UAV) 100 with at least one motor 110 is depicted. UAVs are aircraft with no onboard pilot and may fly autonomously or remotely. In one embodiment, the UAV 100 is a high altitude long endurance aircraft. In one embodiment, the UAV 100 may have one or more motors 110, for example, between one and forty (40) motors, and a wingspan between 100 feet and 400 feet. In one embodiment, the UAV 100 has a wingspan of approximately 260 feet and is propelled by a plurality of propellers 140 coupled to a plurality of motors, for example, ten (10) electric motors, powered by a solar array covering the surface of the wing, resulting in zero emissions. In one embodiment, the UAV 100 may weigh approximately 3,000 lbs.

　　Embodiments of the present application disclose electric motors. The embodiments may in particular be directed to brushless motors, such as brushless DC motors. A brushless DC motor may consist of two main parts, a stator and a rotor. Generally speaking, a brushless DC motor is a collection of electromagnets on the stator with permanent magnets attached on the movable rotor. The motor can be either an in-runner (magnets on the inside of the coils) or an out-runner (magnets outside the coils). For an in-runner motor, the rotor is a permanent magnet with two poles, while the stator consists of coils. Through application of a desired current, the coils will generate a magnetic field that will attract permanent magnets of the rotors. If each coil is activated one after another, the rotor will keep rotating because of the force interaction between permanent magnets and the electromagnet. In turn, an out-runner brushless motor has the permanent magnets outside the electromagnets. In one embodiment, the motor 110 may be a three-phase inverter powered permanent magnet motor, which may propel a UAV for extended flight. In one embodiment, the motor 110 is an out-runner motor. In another embodiment, the motor 110 is an in-runner motor.

　　Flying at an altitude of approximately 65,000 feet above sea level and above the clouds, the UAV 100 is designed for continuous, extended missions of up to months without landing. The motor 110 may function optimally at high altitude where the motor may be exposed to temperatures between 40 ℃ and -85 ℃, and provides for considerable periods of sustained flight of the UAV 100 without recourse to land.

　　The rotor may include a lamination stack, which is a package of individual sheets separated by electrically insulating layers to suppress eddy current losses under dynamic magnetic loading. Generally speaking, electric shorts may occur in the lamination stack of the rotor over such extreme temperature ranges described above. More specifically, the rotor lamination stack may be made of iron and the rotor housing may be made of titanium, which are both electrically conductive. A large coefficient of thermal expansion (CTE) differential between materials may arise, such as a large CTE differential between the rotor lamination stack and the rotor housing of the motor 110.

　　When mounting of the rotor lamination stack onto the rotor housing with glue, an electrical short in the lamination stacks may occur, because of features of the rotor. More specifically, the rotor lamination stack and the rotor housing may be made of two different electrically conductive materials, such as iron and titanium. In one embodiment, a plurality of isolators or "spacers" may be placed between the rotor lamination stack and the rotor housing. The spacers may provide a bond gap between the rotor housing and the lamination stack and prevent electrical shorting. In one embodiment, the spacers may be made of tape, such as Kapton tape. Kapton is a polyimide film that remains stable across a wide range of temperatures. In one embodiment, the spacers not only provide for isolating of the rotor lamination stack from the rotor housing to prevent electrical shorts, but also for properly lamination stack into position during assembly of the motor. In one embodiment, the spacers may be electrically non-conductive to maintain a bond gap between the rotor lamination stack from the rotor housing.

　　With respect to FIG. 2, a rotor 112 of the motor 110 is illustrated. The rotor 112 may include a rotor housing 114 and a rotor lamination stack 116. In one embodiment, the rotor lamination stack 116 may be made of iron strips, such as cobalt-iron or nickel-iron strips and the rotor housing 114 may be made of titanium. In one embodiment, the rotor lamination stack 116 and the rotor housing 114 are electrically conductive.

　　The lamination stack 116 may include a plurality of concave cavities 119 spaced evenly across the inner circumference of the rotor lamination stack 116. The cavities may be shaped to accommodate a plurality of nickel-plated magnets (not shown).

　　In one embodiment, a plurality of spacers 124 may be spaced equally around an outer surface 123 of the rotor lamination stack 116. In one embodiment, 8 spacers 124 may be spaced equally around the outer surface 123. In one embodiment, the spacers 124 are strips of electrically non-conductive Kapton tape. In one embodiment, the spacers 124 may be made of a known thickness to create a bond gap. In one embodiment, the Kapton tape spacers 124 have a 0.125 inch width and are 0.003 inches thick. In one embodiment, the Kapton tape spacers 124 may be used to center the rotor lamination stack 116 in the rotor housing 114, and to prevent metal-to-metal contact between the rotor lamination stack 116 and the rotor housing 114, hence, preventing electrical shorting, because the lamination stack 116 in the rotor housing 114 are both electrically conductive.

　　In one embodiment, low pressure compressed air may be applied to blow off the lamination stack 116 after the Kapton tape spacers 124 are adhered in place.

　　A large coefficient of thermal expansion (CTE) differential between materials may arise, such as a large CTE differential between the iron rotor lamination stack 116 and the titanium housing 114 of the motor 110. The spacers 124 provide a bond gap between the magnets 118 and the lamination stack 116, thereby prevent electrical shorting. In one embodiment, the Kapton tape spacers 124 provide a 0.004 inch thick bond gap.

　　With respect to FIG. 3, the rotor lamination stack 116 may be slid into the rotor housing 114 after a bonding preparation process, wherein the lamination stack 116 may have a liquid oxide removal treatment and the rotor housing 114 may be grit blasted. An epoxy, such as Hysol 9360 epoxy, may be injected into a plurality of injection holes 128 that are located around the circumference of the housing 114. In one embodiment, the housing 114 has 40 injection holes 128. With respect to FIG. 4, the assembled rotor 112 is shown with an epoxy applicator 129 for applying the epoxy into the injection holes of the rotor housing 114 to secure the rotor lamination stack 116 to the rotor housing 114.

　　With respect to FIG 5, a magnet retention ring 130 is applied to the lamination stack 116, the rotor housing 114, and a plurality of magnets 118, such as Neodymium Iron Boron magnets adhered to the lamination stack 116. More specifically, the magnetic retention ring 130 may be an epoxy fillet with a wall portion 131 adhered to an outer edge 132 of the rotor lamination stack 116 and to an outer edge 134 of the magnets 118. In one embodiment, the wall portion 131 is 0.10 inches thick. The magnetic retention ring 130 may further include a land portion 133 adhered to the outer edge 132 and a top surface 136 of the rotor housing 114. In one embodiment, the land portion 133 is 0.05 inches thick. In one embodiment, the magnetic retention ring 130 is made of cold-compliant rated, Hysol 9360 epoxy. In one embodiment, less than 2 grams of epoxy is required to form the magnetic retention ring 130.

　　It is contemplated that various combinations and/or sub-combinations of the specific features and aspects of the above embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments may be combined with or substituted for one another in order to form varying modes of the disclosed invention. Further, it is intended that the scope of the present invention is herein disclosed by way of examples and should not be limited by the particular disclosed embodiments described above.

Claims

　　A system comprising:
　　　　at least one electric motor, comprising:
　　　　　　a rotor, comprising:
　　　　　　　　a rotor housing;
　　　　　　　　a rotor lamination stack; and
　　　　　　　　a plurality of spacers;
　　　　　　wherein at least one of the plurality of spacers is disposed between the rotor lamination stack and the rotor housing; and
　　　　　　wherein the at least one of the plurality of spacers provide a bond gap between the at least one rotor lamination stack and the rotor housing to prevent electrical shorting.
　　The system of claim 1, wherein the rotor hausing and the rotor lamination stack are electrically conductive.
　　The system of claim 1 or 2, wherein the rotor lamination stack includes concave cavities spaced evenly across the inner circumference of the rotor lamination stack.
　　The system of claim 3, wherein the concave cavities are shaped to accommodate a plurality of nickel-plated magnets.
　　The system of any one of claims 1 to 4, wherein the rotor lamination stack is made of iron strips.
　　The system of claim 5, wherein the rotor lamination stack is made of cobalt-iron strips.
　　The system of claim 5, wherein the rotor lamination stack is made of nickel-iron strips.
　　The system of claim 5, wherein the rotor hausing is made of titanium.
　　The system of any one of claims 1 to 8, wherein the plurality of spaces is spaced equally around an outer surface of the rotor lamination stack.
　　The system of any one of claims 1 to 9, wherein the at least one of the plurality of spacers is made of tape.
　　The system of claim 10, wherein the at least one of the plurality of spacers is made of Kapton tape.
　　The system of any one of claims 1 to 11, wherein the rotor further comprises a magnet retention ring which is applied to the lamination stack, the rotor housing, and a plurality of magnets.
　　The system of claim 12, wherein the magnets are Neodymium Iron Boron magnets adhered to the lamination stack.
　　The system of claim 12, the magnetic retention ring is an epoxy fillet with a wall portion adhered to an outer edge of the rotor lamination stack and to an outer edge of the magnets.
　　The system of claim 14, the magnetic retention ring includes a land portion adhered to the outer edge and a top surface of the rotor housing.
　　The system of clam 12, the magnetic retention ring is made of cold-compliant rated, Hysol 9360 epoxy.