Electric motor

Abstract

In one aspect, the present disclosure provides an electric motor including a stator and a rotor assembly including a rotor body and a pinion integrally formed as a single piece with the rotor body.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to co-pending U.S. Provisional Patent Application No. 63 / 319,075, filed March 11, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to electric motors, and more particularly to structures and methods for manufacturing electric motors using at least a powder metallurgy manufacturing process and optionally in combination with one or more other manufacturing processes. Background Technology

[0004] Tools (such as power tools) may include electric motors having a stator for generating a magnetic field and a rotor configured to rotate when the stator is energized. The rotor may be coupled to an output gear and a gearbox. The stator and rotor may each include multiple parts, which makes the assembly of the stator, rotor, and motor difficult. Utility Model Content

[0005] In one aspect, this disclosure provides an electric motor including a stator and a rotor assembly, the rotor assembly including a rotor body and a pinion integrally formed as a single piece with the rotor body.

[0006] In another separate aspect, the drive assembly includes an electric motor and a transmission. The electric motor includes: a stator comprising a stator core and a plurality of windings supported on the stator core; and a rotor assembly comprising a rotor body and a pinion coupled to and configured to rotate with the rotor body. The transmission includes: a transmission housing integrally formed as a single piece with the stator core; and a driven gear supported within the transmission housing and drivably coupled to the pinion to receive torque from the pinion.

[0007] In another separate aspect, the stator includes a stator core and a plurality of windings. The stator core includes: an annular portion having an inner circumferential surface and a plurality of first attachment features on the inner circumferential surface, the annular portion being made of a first material; and a plurality of tooth portions, each tooth portion having a second attachment feature configured to engage with a corresponding first attachment feature of the annular portion to combine the tooth portion with the annular portion, the tooth portion being made of a second material different from the first material. The plurality of windings are wound on the corresponding tooth portions of the stator core.

[0008] In another independent aspect, a method of manufacturing a rotor assembly of an electric motor includes providing a rotor body including a first axial end, an opposite second axial end, and a cavity defined between the first axial end and the second axial end. The method also includes providing a bulk magnetic material in a solid or liquid form and processing the magnetic material using one or more of a sintering, a bonding, or an injection molding process to form a solid magnetic body within the cavity.

[0009] Other features and aspects of the present technology will become apparent from consideration of the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a perspective view of a portion of an electric motor having a rotor body with an integral pinion gear.

[0011] Figure 2 is a perspective view of a portion of an electric motor having a rotor body with an integral pinion gear. Figure 1 is a cross-sectional view taken along section line 2-2 in Figure 1 .

[0012] Figure 3 is a perspective view of a stator core of an electric motor according to another embodiment.

[0013] Figure 4 is a perspective view of a stator core of an electric motor according to another embodiment. Figure 3 is a side view of the stator core of .

[0014] Figure 5 is an end view of the stator core of Figure 3 .

[0015] Figure 6 is an end view of the stator core of Figure 3 . is a cross-sectional view taken along section line 6-6 in Figure 4 .

[0016] Figure 7 is a perspective view of a rotor assembly having a rotor body with a plurality of cavities.

[0017] Figure 8 is an exemplary cross-sectional view illustrating a method for manufacturing a magnet within a cavity of a rotor body of Figure 7 .

[0018] Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. Also, it is to be understood that the terminology used herein is for the purpose of description and not of limitation. DETAILED DESCRIPTION

[0019] Figure 1 and Figure 2 A brushless electric motor 10 is shown including a stator 14 Figure 2 ) and a rotor assembly 18. The stator 14 and the rotor assembly 18 are each oriented along a longitudinal axis LA of the motor 10. The rotor assembly 18 is rotatable about the longitudinal axis LA upon startup of the motor 10. The rotor assembly 18 includes a rotor body 22 Figure 2 ) and a pinion gear 26 that is integrally formed as a single piece with the rotor body 22. A transition portion 28 can couple the pinion gear 26 to the rotor body 22. The transition portion 28 can be annularly shaped about the longitudinal axis LA, as shown in Figure 2 , or the transition portion 28 can be annularly shaped, cylindrically shaped, or otherwise shaped relative to the longitudinal axis LA. In the illustrated embodiment, the transition portion 28 extends axially in a direction parallel to the longitudinal axis LA. In other embodiments, the transition portion 28 can extend in different directions relative to the longitudinal axis LA. In some embodiments, the transition portion 28 functions as a rotor shaft to connect the rotor body 22 to the pinion gear 26. In embodiments that include the transition portion 28, the motor 10 need not include a rotor shaft (not shown).

[0020] In other embodiments, the pinion gear 26 can be integrally formed with the rotor body 22 in other ways during a common manufacturing process. For example, both the rotor body 22 and the pinion gear 26 can be individually mechanically coupled with a rotor shaft, but formed simultaneously using similar manufacturing processes (e.g., powder metallurgy processes). In such embodiments where the pinion gear 26 and the rotor body 22 are formed simultaneously (e.g., integrally formed with the connection to the rotor shaft), the pinion gear 26 is coupled with the rotor body 22 by the rotor shaft for co-rotation with the rotor body.

[0021] The impeller 30 can be overmolded (as shown in Figure 2 ) or otherwise coupled to the rotor body 22. The impeller 30 is configured to generate airflow in response to rotation of the rotor body 22. Optionally, the rotor body 22 can include a mating element, a mating surface, a plurality of mating elements, or a plurality of mating surfaces to engage (i.e., clamp or snap into) the impeller 30 to the rotor body 22 during assembly. Such mating elements or mating surfaces can be disposed proximate the second axial end 22b of the rotor body 22. The mating elements or mating surfaces can include any type of mechanical connection, including but not limited to a press-fit key and keyway, a pin, a fastener, a welded connection, etc. Optionally, the impeller 30 can be integrally formed as a single piece with the rotor body 22 during a powder metallurgy process that constructs the rotor body 22. Alternatively, the impeller 30 can be formed as a separate piece from the rotor body 22, but with a separate manufacturing process (e.g., another powder metallurgy process) that constructs the rotor body 22.

[0022] The stator 14 includes a stator core 34 and a plurality of windings 38 supported on the stator core 34. The stator core 34 and stator windings 38 are shown schematically in Figure 2 The pinion gear 26 is configured to drive (i.e., directly drive without additional gears attached or otherwise fixed to the rotor body 22) a driven gear (not shown) of the transmission 46. The driven gear is driveably coupled to the pinion gear 26 and is configured to receive torque from the pinion gear. The driven gear is supported within a transmission housing 50 of the transmission 46. The driven gear can engage the ring gear 42 of the transmission 46. The driven gear functions as a rotational output of the transmission 46. The driven gear can be positioned within the transmission housing 50. The transmission 46 can be a single-stage or multi-stage transmission. The combination of the electric motor 10 and the transmission 46 can be referred to as a drive assembly 12.

[0023] The rotor assembly 18 can be formed through a powder metallurgy process. During a powder metallurgy process, a metal is melted and atomized into a powder form, leaving a pure metal or metal alloy and water or gas. A blend of the powdered metal and / or metal alloy is prepared. The blend can optionally include lubricants, elements, and / or other additives. The powder mixture is filled and pressed into a negative shape of the final part, referred to as a die. The mixture is compacted under a pressure of, for example, between 200-1500 MPa. Any binder remaining in the mixture is burned off, and the resulting part is heated. The resulting part is heated and / or pressurized to create diffusion and / or solid-state bonding between the particles of the blend. The amount and duration of heating and / or pressurizing varies depending on the alloy composition of the blend. Additionally or alternatively, the rotor assembly 18 can be formed in part through an additional or finalizing process of the powder metallurgy process, which can include pressing and / or sintering of the powder (e.g., in a soft magnetic composite [e.g., “SMC”] process). Such powder metallurgy processes can include, but are not limited to, casting, crush milling, aligned pressing, sintering, slicing, quenching, cold pressing, hot pressing, hot deformation, surface treatment, coating finishes, magnetization, and / or machining of the rotor assembly 18. In other embodiments, the powder metallurgy process forming the rotor assembly 18 (e.g., the rotor body 22 and pinion gear 26) can include a compression and / or injection molding process.

[0024] Such compression and / or injection molding processes forming the rotor assembly 18 can utilize soft magnetic composite (e.g., “SMC”) material. In such embodiments, the rotor assembly 18 can additionally or alternatively be formed in part by utilizing soft magnetic composite powder. In such a powder metallurgy process including soft magnetic composite powder, iron (Fe) or other magnetized particles having a magnetic insulation coating can be combined with other powders forming the rotor assembly 18. Heat treatment of such a powder metallurgy process including soft magnetic composite (e.g., “SMC”) powder can be performed at relatively lower temperatures to preserve the iron (Fe) or other magnetic coating of the rotor assembly 18. When utilizing soft magnetic composite powder, different metal and / or alloy powders of the blend forming the rotor assembly 18 can be selected.

[0025] The rotor assembly 18 includes a rotor body 22 and an integrally formed pinion gear 26, which has a number of advantages over traditional rotor assemblies that press fit a pinion gear 26 to a separately formed motor output shaft. The rotor assembly 18 effectively reduces the part count, complexity, and assembly time (e.g., duration) of the motor 10. As discussed above, the rotor assembly 18 can include a rotor body 22 having a shaft, or alternatively, the rotor body 22 can not include a dedicated shaft, classifying the rotor body 22 as a “shaftless rotor.” The pinion gear 26 can be correspondingly configured depending on the desired connection to a driven gear (not shown). For example, the pinion gear 26 can be configured as a spur gear, bevel gear, etc. The pinion gear 26 can be configured to have a desired number of gear teeth to adjust the gear ratio between the pinion gear 26 and the driven gear (not shown). The rotor assembly 18 can include a hollow core 48 to conserve material, which in turn reduces the cost of the rotor assembly 18. In Figure 2 In the example embodiment, the hollow core 48 is positioned on a radially inner side of the rotor body 22 facing the longitudinal axis LA. In the illustrated embodiment, the hollow core 48 generally corresponds to the volume that would typically accept a rotor shaft.

[0026] Figure 2Further shown is a bearing 54 positioned between the rotor body 22 and a stationary portion of the ring gear 42 and / or the transmission housing 50. More specifically, the bearing 54 is positioned radially between a bearing mounting surface 58 of the rotor body 22 and a hub 62 of the ring gear 42. The rotor body 22 includes a first axial end 22a and an opposite second axial end 22b. The first axial end 22a is positioned closer to the pinion gear 26 than the second axial end 22b. The second axial end 22b is positioned closer to the impeller 30 than the first axial end 22a. In the illustrated embodiment, the bearing mounting surface 58 is positioned adjacent the first axial end 22a. In other embodiments (not shown), the bearing mounting surface 58 (or an additional bearing mounting surface 58 and bearing 54) can be positioned closer to the second axial end 22b than the first axial end 22a. In either embodiment, the bearing mounting surface 58 can align and / or center the rotor body 22 with the longitudinal axis LA.

[0027] Other embodiments of the rotor body 22 are possible. For example, the pinion gear 26 can be positioned between the first axial end 22a and the second axial end 22b of the rotor body 22. In contrast, the illustrated pinion gear 26 is positioned axially outward of the first axial end 22a and is connected to the first axial end 22a by the transition portion 28. This can effectively shrink the axial length of the motor 10 along the longitudinal axis LA. In other embodiments, the length of the transition portion 28 can be reduced and / or removed entirely, such that the first axial end 22a is coupled directly or closer to the pinion gear 26. Another example rotor body 22 can include surface permanent magnets (SPMs) mounted on a radially outermost surface of the rotor body 22. This is in contrast to a rotor body 22 that includes interior permanent magnets (IPMs) mounted on a radially inner portion of the rotor body 22, within the bounds of the radially outermost surface of the rotor body 22.

[0028] Figure 3 to Figure 6 The stator 14 is shown in dashed lines. The stator core 34 can be fixed or coupled integrally with the transmission housing 50. In such embodiments that include the stator 14 fixed or coupled integrally with the transmission housing 50, the stator core 34 can engage the standoff 70 of the transmission housing 50. The stator core 34 can be positioned adjacent (e.g., annularly within and closer to the longitudinal axis LA than) the annular boss 74 of the rotor body 22. In the illustrated embodiment, the standoff 70 protrudes radially outward from the transmission housing 50. The standoff 70 can serve as a connection portion that fixes the transmission housing 50 to the stator 14, such that the transmission housing 50 and the stator core 34 can be integrally formed as a single piece.

[0029] In the illustrated embodiment, the rotor body 22 includes an annular boss 74 that protrudes axially from a location along the longitudinal axis LA corresponding to the first axial end 22a of the rotor body 22. The illustrated annular boss 74 is radially aligned relative to the longitudinal axis LA when compared to the bearing 54. That is, a normal line extending radially outward from the axis LA bisects both the bearing 54 and the boss 74.

[0030] In other embodiments, the transmission housing 50 and the stator core 34 can be integrally formed. Such a connection between the transmission housing 50 and the stator 14 can better group components together for meshing between the pinion gear 26 and driven gears (not shown) and / or other gears of the transmission 46. Further, such a connection can be adjusted to shorten an axial length of the motor 10 along the longitudinal axis LA.

[0031] Figure 3 A stator core 100 is illustrated. As will be described in detail below, the stator core 100 is a hybrid or composite body formed of a variety (e.g., plurality) of materials having different material properties, which can improve efficiency of a motor including the stator core 100. In some embodiments, the stator 14 can include the stator core 100. As Figure 5 As illustrated in the middle, the stator core 100 includes an annular portion (i.e., an annular yoke) 104 having an inner circumferential surface 104a, an outer circumferential surface 104b opposite the inner circumferential surface 104a, a first axial end 104c, and a second axial end 104d opposite the first axial end 104c. The stator core 100 further includes a plurality of tooth portions 108. The inner circumferential surface 104a includes a plurality of recesses (i.e., a plurality of “first attachment features”) 112. In the illustrated embodiment, the recesses 112 are “T-shaped.” The recesses 112 extend in a direction between the first axial end 104c and the second axial end 104d of the stator core 100. As shown in the middle, for example, the “T-shaped” generally describes a cross-sectional shape of the recesses 112 perpendicular to the longitudinal axis LA. The recesses 112 can be dovetail-shaped or other shapes. The tooth portions 108 each include a mating finger 116 (i.e., a “second attachment feature”). The mating finger 116 of each tooth portion 108 is configured to mate with a recess 112 of the annular portion 104 of the stator core 100. Accordingly, the tooth portions 108 and the annular portion 104 can be combined in assembly of the stator core 100. In the illustrated embodiment, the mating finger 116 can be aligned with one of the recesses 112, and the tooth portion 108 can be translated into position along the longitudinal axis LA. In some embodiments, the mating finger 116 can engage the recess 112 in a press-fit arrangement, where the mating finger 116 must be forced into engagement with the recess 112. In other embodiments, the mating finger 116 can engage the recess 112 in a snap-fit arrangement, where the mating finger 116 is configured to snap into engagement with the recess 112. Figure 4 As shown in the middle, for example, the “T-shaped” generally describes a cross-sectional shape of the recesses 112 perpendicular to the longitudinal axis LA. The recesses 112 can be dovetail-shaped or other shapes. The tooth portions 108 each include a mating finger 116 (i.e., a “second attachment feature”). The mating finger 116 of each tooth portion 108 is configured to mate with a recess 112 of the annular portion 104 of the stator core 100. Accordingly, the tooth portions 108 and the annular portion 104 can be combined in assembly of the stator core 100. In the illustrated embodiment, the mating finger 116 can be aligned with one of the recesses 112, and the tooth portion 108 can be translated into position along the longitudinal axis LA. In some embodiments, the mating finger 116 can engage the recess 112 in a press-fit arrangement, where the mating finger 116 must be forced into engagement with the recess 112. In other embodiments, the mating finger 116 can engage the recess 112 in a snap-fit arrangement, where the mating finger 116 is configured to snap into engagement with the recess 112. Figure 5In the illustrated embodiment, the toothed portion 108 may axially protrude from the first axial end 104c and the second axial end 104d of the annular portion 104 along the longitudinal axis LA. Figure 6 and Figure 6 The windings 38 are further shown, which are wound around the tooth portion 108.

[0032] like Figure 3 As best shown, the toothed portion 108 includes a mating finger 116, a skirt segment 108a connected to and extending radially outward from the mating finger 116, a protruding segment 108b extending radially inward from the mating finger 116, and an end segment 108c extending circumferentially outward from the protruding segment 108b opposite to the skirt segment 108a. The skirt segment 108a may abut the inner circumferential surface 104a of the annular portion 104. The protruding segment 108b may leave sufficient space within the stator core 100 to receive a rotor assembly, such as the rotor assembly 18 of the motor 10.

[0033] 120 (overmolded parts) Figure 5 , Figure 6 and Figure 6 It can be applied to the stator core 100. The overmolded part 120 can be applied to the first axial end 104c and the second axial end 104d of the annular portion 104. Figure 3 As best shown, the overmolding member 120 can be applied to the inner circumferential surface 104a, the skirt segment 108a, each lateral side of each protruding segment 108b, and the radially opposite portion of the end head segment 108c to the longitudinal axis LA. In other words, the overmolding member 120 can be disposed on each surface between adjacent tooth portions 108. The overmolding member 120 can be applied to different components of the stator core 100. For example, as Figure 7 As shown, the overmolding member 120 may be disposed on at least one of the first axial end 104c and the second axial end 104d. Optionally, the overmolding member 120 may comprise a soft magnetic composite material.

[0034] The tooth portions 108 and the annular portion 104 can be made of different materials. The annular portion 104 can be made of a first material, such as a soft magnetic composite material. Such a soft magnetic composite material can be magnetized and demagnetized. In other words, the magnetic properties of the first material are not permanent. Such a soft magnetic composite material can not be able to handle the high magnetic flux densities that the tooth portions 108 can require. Accordingly, the tooth portions 108 can be made of a second material, such as M19 (i.e., a silicon steel composite or “electrical steel” that provides low core losses, which can include low carbon steel alloyed with silicon), that is capable of handling high magnetic flux densities. In some embodiments, the second material (e.g., M19) is configured to handle higher magnetic flux densities than the first material (e.g., soft magnetic composite material). In the illustrated embodiment, the second material is different than the first material. The tooth portions 108 can exhibit higher losses due to switching frequencies. This hybrid component and material stator core 100 can take advantage of the strengths of each material and more efficiently produce magnetic flux through the windings 38. Ultimately, this provides designers with the opportunity to obtain the relevant material properties of the annular portion 104 and the tooth portions 108. Further, the tooth portions 108 can be pre-wound with the windings 38 through a bobbin. The bobbin winding can more efficiently apply the windings 38 to the tooth portions 108 (i.e., the application can be faster and more windings 38 can be applied around each tooth portion 108), resulting in higher slot fill of the windings 38 in the stator core 100. The higher slot fill of the windings 38 increases the overall efficiency of the motor 10. Additionally or alternatively, a soft magnetic composite (SMC) material can be molded (e.g., as an overmold, such as overmold 120) and / or pressed onto and / or around the tooth portions 108 to improve the bonding (e.g., the electro-mechanical bonding as well as the mechanical coupling) between the tooth portions 108 and the annular portion 104 and / or between the windings 38 and the tooth portions 108.

[0035] Figure 1 A rotor assembly 300 is illustrated for use in a motor, such as the motor 10 of Figure 2 and Figure 8 The rotor assembly 300 includes a rotor body 304 having a first axial end 304a and an opposite second axial end 304b. The rotor body 304 includes a plurality of cavities 312 in the rotor body. Each cavity 312 extends between the first axial end 304a and the second axial end 304b of the rotor body 304. The cavities 312 are also circumferentially arranged about the longitudinal axis LA. An impeller 314 can be secured to the second axial end 304b of the rotor body 304 by any suitable mechanical connecting means. For example, as described above, the impeller 314 can include any type of mating element or mating surface, including but not limited to a press-fit key and keyway, a pin, a fastener, a welded connection, etc., to secure the impeller 314 to the second axial end 304b of the rotor body 304.

[0036] Figure 8 A method for manufacturing a rotor assembly 300 is illustrated. A rotor body 304 is provided, comprising a first axial end 304a, an opposite second axial end 304b, and at least one cavity 312 between the first axial end 304a and the second axial end 304b. An aggregate magnetic material (such as magnetic powder 316) is inserted into the cavity 312. The magnetic powder 316 is sintered and magnetized to form a solid magnetic body, such as a magnetic rod, within the cavity 312. The powder 316 may additionally be applied to the cavity 312 by another process (e.g., bonding) to form the magnetic rod. Additionally or alternatively, the powder 316 may be in liquid or melt form and injection molded into the cavity 312 to form the magnetic rod. Alternatively, the magnetic rod may be inserted into the cavity 312 after injection molding. Similarly, the magnetic rod may be a pressed magnet comprising magnetic powder 316 and a binder, the magnetic powder and binder being pressed together to increase the filling ratio of the magnetic powder 316 to the binder. The magnetic powder 316 can be subjected to a second treatment using one or more of a second sintering, second bonding, or second injection molding process. The second sintering, second bonding, and second injection molding processes can be the same as or different from the first sintering, bonding, or injection molding of the magnetic powder (e.g., magnetic powder 316). The resulting magnetic rod can form an internal permanent magnet. The magnetic rod can be shaped into a rectangular prism, a prism with another cross-sectional geometry, or any other feasible three-dimensional shape.

[0037] Returning to the example of magnetic powder 316 being positioned within cavity 312, as follows... ​As shown, the magnetic powder 316 can be suspended within the cavity 312, between the molds 320. In the illustrated embodiment, one mold 320 is applied to the first axial end 304a of the rotor body 304, while the other mold 320 is applied to the second axial end 304b of the rotor body 304. Force is applied to each mold 320 along arrows Al and A2, respectively, to compress the magnetic powder 316 within the cavity 312. The molds 320 can apply pressure to the powder 316 to form a magnetic bar. Several cycles of pressing and refilling the powder 316 within the cavity 312 can be required to achieve sufficient compaction of the powder 316 to form the resulting magnetic bar. In other words, the insertion of the magnetic powder 316 within the cavity 312 and sintering of the magnetic powder 316 can be repeated to incrementally form the magnetic bar within the cavity 312. In some embodiments, the multiple filling and pressing operations can produce a segmented magnet within the same cavity 312. The segmented magnet can have, for example, opposite polarities along the longitudinal axis LA. In forming the segmented magnet, a second aggregate magnetic material having a second polarity can be positioned within the cavity 312 with a first magnetic material having a first polarity opposite the second polarity. The tool(s) controlling the operation of the molds 320 can also be configured to align the powder 316 within the cavity 312. Additionally or alternatively, a heating element 324 can be positioned adjacent to the rotor body 304. The heating element 324 can apply heat to the rotor body 304, and thus to the magnetic powder 316, to form the magnetic bar. This sintering process of the rotor assembly 300 can fix the resulting magnetic bar in place within the cavity 312, and can eliminate the need for expensive separately produced magnets.

[0038] While the application has been described in detail with reference to certain preferred embodiments thereof, alterations and modifications of the application will be readily apparent to those of ordinary skill in the art.

[0039] Various features and advantages of the application are set forth in the following claims.

Claims

1. An electric motor, the electric motor comprising: a stator; and a rotor assembly comprising a rotor body and a pinion gear integrally formed with the rotor body as a single piece. The rotor body and the pinion gear are formed by a powder metallurgy process.

2. The electric motor of claim 1, wherein, The powder metallurgy process comprises at least pressing and sintering.

3. The electric motor of claim 2, wherein, The powder metallurgy process comprises soft magnetic composites.

4. The electric motor of claim 2, wherein, 5. The electric motor of claim 1, further comprising: an impeller, and a mating element disposed on the rotor body, the mating element configured to couple the impeller to the rotor body. The rotor assembly comprises an impeller integrally formed with the rotor body and the pinion gear, the impeller configured to generate an airflow in response to rotation of the rotor body.

6. The electric motor of claim 1, wherein, ​

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