WO2022070478A1

WO2022070478A1 - Methods and systems for bonding magnets to a rotor of an electric motor

Info

Publication number: WO2022070478A1
Application number: PCT/JP2021/011281
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; at least one magnet; and a plurality of isolators; where at least one of the plurality of isolators is placed between the rotor lamination stack and the at least one magnet; and where the at least one of the plurality of isolators provide a bond gap between the a least one magnet and the lamination stack and prevent electrical shorting.

Description

METHODS AND SYSTEMS FOR BONDING MAGNETS TO A ROTOR OF AN ELECTRIC MOTOR

　　Embodiments relate generally to electric motors and more particularly to bonding of magnets to a rotor 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 rotor with a rotor housing, a rotor lamination stack, at least one magnet, and a plurality of isolators. In one embodiment, at least one of the plurality of isolators may be placed between the lamination stack of the rotor and the magnets. In one embodiment, the at least one of the plurality of isolators may provide a bond gap between the at least one magnet and the lamination stack 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 view of a portion of the electric motor of FIG. 1;
[Fig. 3] FIG. 3 depicts a side perspective view of a rotor lamination stack of the motor of FIG. 2;
[Fig. 4] FIG. 4 depicts a top perspective view of a section of the lamination stack of FIG. 3;
[Fig. 5] FIG. 5 depicts a top perspective view of magnets of the electric motor of FIG. 2;
[Fig. 6] FIG. 6 depicts a top perspective view of a magnet bonded to the lamination stack of FIG. 4;
[Fig. 7] FIG. 7 depicts a top perspective view of a rotor lamination stack bonded to a rotor housing; and
[Fig. 8] FIG. 8 depicts a cross-sectional view of a magnet retention ring bonded to the rotor lamination stack and the rotor housing of FIG. 7 and to a plurality of magnets associated with the rotor lamination stack.

　　When mounting of magnets onto a rotor with glue, the magnets could create an electrical short in the lamination stacks of the rotor, due to features of the rotor and the coating on the magnets (e.g., conductive, nickel plating). In one embodiment, a plurality of isolators or "spacers" may be placed between the lamination stack of the rotor and the magnets. The spacers may provide a bond gap between the magnets and the 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 may be made of titanium, which is conductive. A large coefficient of thermal expansion (CTE) differential between materials may arise, such as a large CTE differential between the magnets and the rotor of the motor 110.

　　When mounting of the magnets on the rotor with glue, the magnets could create an electrical short in the lamination stacks, because of features of the rotor and the coating on the magnets (e.g., Nickel, which is conductive). In one embodiment, a plurality of isolators or "spacers" may be placed between the lamination stack of the rotor and the magnets. The spacers may provide a bond gap between the magnets 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 magnets from the rotor to prevent electrical shorts, but also for properly centering of the magnets (and other parts of the motor) into position during assembly of the motor. In one embodiment, the spacers may be electrically non-conductive to maintain a bond gap.

　　With respect to FIG. 2, a section of a rotor 112 of the motor 110 is illustrated. The rotor 112 may include a rotor housing 114, a rotor lamination stack 116, and at least one magnet 118. In one embodiment, the rotor lamination stack 116 may be made of iron and the rotor housing 114 may be made of titanium, which is electrically conductive. The magnets 118 may be Neodymium Iron Boron magnets, with nickel plating, which is electrically conductive.

　　In one embodiment, the lamination stack 116 may include a plurality of concave cavities 119 spaced evenly across the inner circumference of the rotor 112. The cavities may be shaped to accommodate a convex underside 120 of each magnet 118. In one embodiment, each magnet 118 has a curved top side 121 of large radius, allowing the magnets 118 to seat nearly flush with the inner circumference of the rotor 112. In one embodiment, within 6 hours or less, prior to bonding, the bond surfaces, e.g., the cavities 119 of the lamination stack 116 may be treated with a rust removal solution. The bonding surface may be maintained wet by re-applying the rust solution every 30 minutes or less, for 120 minutes or more, while taking care not to cause de-lamination. Visible spots on the back iron surface may be removed and the back iron surface is kept moist.

　　In one embodiment, after removing all visible oxides the lamination stack 116 (e.g., the entire back iron) and housing 114 may be rinsed with deionized or distilled water and dry water with lint free wipes, swabs or compressed air. To further remove any moisture, the lamination stack 116 may be placed in a 150 F oven for an hour. In another embodiment, to further remove any moister, the lamination stack 116 may be dried with a fan or a warm air forced air heater for 30 minutes prior to bonding.

　　In one embodiment and with respect to FIG. 3, a spacer 124 may be adhered at opposite ends of a cavity 119 of the lamination stack 116. In one embodiment, the spacers 124 are strips of electrically non-conductive Kapton tape. In one embodiment, the Kapton spacers 124 may be used to center the rotor 112 in the housing 114, and to prevent metal-to-metal contact between the rotor lamination stack 116 and the magnets 118.

　　In one embodiment, the spacers 124 may be placed equally around the rotor lamination stack 116 and to a known thickness to create a bond gap. More specifically, two identical rings of Kapton tape, one corresponding to either end of a magnet 118, may be applied around each outer edge of the lamination stack 116. In one embodiment, the Kapton tape spacers 124 are 2mm polyamide Kapton tape with a 1/8 inch width. 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 nickel plating of the magnets 118, 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 bond gap of approximately 0.0035 inches to 0.007 inches.

　　With respect to FIG. 4, an individual cavity 119 is shown with a section of one of the annular rings of Kapton tape at one end of the cavity 119 and a section of the other annular ring of Kapton tape at the opposite end of the cavity 119.

　　Prior to adherence of the magnet 118 to the cavity 119, the magnets 118 may be grit blasted to ensure the magnets 118 have a relatively rough surface, as shown in FIG. 5. Additionally, masking tape pieces may be applied and removed to all surfaces of each magnet 118 to pull off iron particles, or other foreign object damage. This process may be continued until there are no visible particles on each magnet.

　　With respect to FIG. 6, a magnet 118 is shown with a single layer nickel plating. In one embodiment, the back iron cavity 119 and the magnet 118 are coated with epoxy and adhered to one another. In one embodiment, the epoxy is Hysol 9360 epoxy.

　　With respect to FIG. 7, the rotor 112 may be slid into the titanium housing 114 after the bonding preparation process described above. The 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 8, a magnet retention ring 130 is applied to the lamination stack 116, the rotor housing 114, and the magnets 118. 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;
　　　　　　　　at least one magnet; and
　　　　　　　　a plurality of isolators;
　　　　　　wherein at least one of the plurality of isolators is disposed between the rotor lamination stack and the at least one magnet; and
　　　　　　wherein the at least one of the plurality of isolators provide a bond gap between the at least one magnet and the lamination stack to prevent electrical shorting.
　　The system of claim 1, wherein the rotor lamination stack includes a plurality of concave cavities spaced evenly across the inner circumference of the rotor.
　　The system of claim 2, wherein the cavities are shaped to accommodate a convex underside of each magnet.
　　The system of claim 2 or 3, wherein the cavity and the magnet are coated with epoxy and adhered to one another.
　　The system of claim 4, wherein the epoxy is Hysol 9360 epoxy.
　　The system of any one of claims 1 to 5, wherein the rotor comprises spacers which are adhered at opposite ends of the cavity of the rotor lamination stack.
　　The system of claim 6, wherein the spacers are strips of electrically non-conductive Kapton tape.
　　The system of any one of claims 1 to 7, wherein the rotor further comprises a magnet retention ring which is applied to the lamination stack, the rotor housing, and the magnets.
　　The system of claim 8, 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 11, 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 8, the magnetic retention ring is made of cold-compliant rated, Hysol 9360 epoxy.