Switched reluctance motor fabrication with variable wire twist rate

Abstract

An assembly for an electric motor, the assembly comprising: a stator comprising a plurality of stator poles, each stator pole comprising a base end and a rotor end opposite the base end; and an electromagnetic coil surrounding each stator pole. The coil surrounding each stator pole includes at least two conductive wires wound around the stator pole into a plurality of turns extending from the base end of the stator pole to the rotor end of the stator pole. The turns of the coil closer to the rotor end of the stator pole are twisted, and the turns of the coil closer to the base end of the stator pole are not twisted.

Description

Technical Field

[0001] This document relates to electric working machines and, more particularly, to techniques for improving the performance and manufacturability of electric motors for electric working machines. Background Art

[0002] Large mobile working machines (e.g., wheel loaders) may be driven by one or more electric motors. An example of an electric motor is described in U.S. Patent No. 9,118,225. The motor is a switched reluctance motor that includes a stator having electromagnetic coils. In operation, there are losses associated with the coils in the motor that can undesirably generate heat. The turns of the coils are twisted to reduce these losses. However, there are challenges in manufacturing coils with twisted turns. Twisting the wires can cause the coils to deform, making it difficult to place the coils on the stator. Summary of the invention

[0003] Electric large mobile work machines use a large amount of energy to drive one or more electric motors. Twisting the wires of the motor's coils improves the motor's performance, but twisted coils are difficult to manufacture and motors are difficult to assemble using coils with twisted wires.

[0004] An example assembly of an electric motor for a work machine includes: a stator including a plurality of stator poles, each stator pole including a base end and a rotor end opposite the base end; and an electromagnetic coil surrounding each stator pole. The coil surrounding each stator pole includes: at least two conductive wires, the at least two conductive wires being wound around the stator pole into a plurality of turns, the plurality of turns extending between the base end of the stator pole and the rotor end of the stator pole. The turns of the coil closer to the rotor end of the stator pole are twisted, and the turns of the coil closer to the base end of the stator pole are not twisted.

[0005] An example method of manufacturing an assembly for an electric motor includes: forming an electromagnetic coil by winding at least two conductive wires into a plurality of turns, the plurality of turns being wound transversely to the center of the coil so that the coil has a first side and a second side; twisting the turns of the coil closer to the first side of the coil and not twisting the turns of the coil closer to the second side of the coil; forming a plurality of electromagnetic coils; and arranging each coil on a stator pole of a stator having a plurality of stator poles. Each stator pole has a rotor end and a base end, and each coil is arranged so that the first side of the coil is closer to the rotor end of the stator pole and the second side of the coil is closer to the base end of the stator pole.

[0006] An example electric motor for a working machine includes a stator, a rotor, and a plurality of electromagnetic coils. The stator includes a plurality of stator poles and a plurality of stator slots, each stator pole includes a base end and a rotor end opposite to the base end, and each stator slot is located between two stator poles. The rotor is located in the stator and includes a plurality of rotor poles extending toward the stator pole. Each of the electromagnetic coils is arranged around the stator pole and includes at least two conductive wires, which are wound around the stator pole into a plurality of turns, and the plurality of turns extend from the base end of the stator pole to the rotor end of the stator pole. The coil includes: twisted turns closer to the rotor end of the stator pole; and untwisted turns closer to the base end of the stator pole. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a front view depicting an example work machine according to the present disclosure.

[0008] Figure 2 is a schematic diagram of a portion of an example of an electric motor for a work machine according to the present disclosure.

[0009] Figure 3 is a schematic diagram of a portion of another example of an electric motor for a working machine according to the present disclosure.

[0010] Figure 4 is an end view of two stator poles and a coil wound around the stator poles according to the present disclosure.

[0011] Figure 5 The stator pole according to the present disclosure and the stator pole (such as Figure 2 The stator pole shown is a cross-sectional view of a coil wound around it as pole B+).

[0012] Figure 6 is a cross-sectional view of turns of a coil according to the present disclosure.

[0013] Figure 7 is a cross-sectional view of a set of electrically conductive wires that may be wound to make an electromagnetic coil for an electric motor in accordance with the present disclosure.

[0014] Figure 8 is a flow chart of an example of a method of manufacturing an assembly for an electric motor according to the present disclosure. DETAILED DESCRIPTION

[0015] Examples according to the present disclosure relate to methods and apparatus for improving the efficiency of an electric motor of a work machine.

[0016] Figure 1 An example machine 100 is depicted in accordance with the present disclosure. Figure 1In the embodiment of the present invention, machine 100 includes a frame 102, wheels 104, implements 106, and a speed control system implemented in one or more onboard electronic devices (e.g., an electronic control unit or ECU). The example machine 100 is a wheel loader. However, in other examples, the machine can be other types of machines related to various industries, including, for example, construction, agriculture, forestry, transportation, material handling, waste management, marine, stationary power, etc. Therefore, although some examples are described with reference to wheel loaders, examples according to the present disclosure are also applicable to other types of machines, including graders, scrapers, bulldozers, excavators, compactors, material handling vehicles such as dump trucks, ships, generator sets, and other example machine types.

[0017] Machine 100 includes a frame 102 mounted on four wheels 104, although in other examples, the machine may have more than four wheels. Frame 102 is configured to support and / or mount one or more components of machine 100. For example, machine 100 includes a housing 108 coupled to frame 102. Housing 108 may house, among other components, an electric motor to propel the machine over various terrains via wheels 104. In some examples, multiple electric motors are included in multiple housings at multiple locations of machine 100.

[0018] The machine 100 includes an implement 106 coupled to a frame 102 via a linkage assembly 110 that is configured to be actuated to articulate a bucket 112 of the implement 106. The bucket 112 of the implement 106 may be configured to transfer material, such as soil or debris, from one location to another. The linkage assembly 110 may include one or more cylinders 114 that are configured to be actuated, for example, hydraulically or pneumatically, to articulate the bucket 112. For example, the linkage assembly 110 may be actuated by the cylinders 114 to raise and lower and / or rotate the bucket 112 relative to the frame 102 of the machine 100.

[0019] Platform 116 is coupled to frame 102 and provides access to various locations on machine 100 for operational purposes and / or maintenance purposes. Machine 100 also includes an operator compartment 118, which may be open or enclosed and accessible via platform 116. Operator compartment 118 may include one or more control devices (not shown), such as a joystick, steering wheel, pedals, levers, buttons, switches, etc. The control devices are configured to enable an operator to control machine 100 and / or implement 106. Operator compartment 118 may also include an operator interface, such as a display device, an audio source, a light source, or a combination thereof.

[0020] The machine 100 can be used in a variety of industrial, construction, commercial or other applications. The machine 100 can be operated by an operator in an operator cabin 118. The operator can, for example, drive the machine 100 to and from different locations on the job site, and can also use the bucket 112 of the machine 106 to pick up and deposit loads of materials. As another example, operation by a remote operator and autonomous operation are contemplated. The machine 100 can be used to excavate a portion of the job site by actuating the cylinder 114 to articulate the bucket 112 via the connecting rod 110 to dig into and remove dirt, rocks, sand, etc. from a portion of the job site and deposit the load at another location. The machine 100 may include a battery compartment connected to the frame 102 and including a battery system 120. The battery system 120 is electrically connected to one or more motors of the machine 100.

[0021] Figure 2 It is used for operating machinery (such as Figure 1 Schematic diagram of an example portion of an electric motor 224 of a working machine 100 of the present invention. The example electric motor 224 is a switched reluctance motor that includes a stator 226 and a rotor 228 that is rotatable relative to the stator 226. The stator 226 includes eight stator poles 230, and the rotor 228 includes four rotor poles 232. The electric motor 224 may include Figure 2 Examples of different numbers of stator poles 230 and rotor poles 232 .

[0022] The stator 226 includes stator slots 234 between the stator poles 230. The stator slots 234 are open toward the rotor 228. The stator poles 230 and the stator slots 234 have a base end and a rotor end. The stator slots 234 each have a width that tapers or narrows from the base end to the rotor end. The shape of the stator 226 can be referred to as an open slot configuration.

[0023] The stator poles 230 may be grouped into two or more phase sets of the stator poles 230 corresponding to the number of phases (eg, two phases) of the switched reluctance motor. Figure 2 In the example of FIG. 1 , eight stator poles 230 are grouped in two phase sets, with four stator poles (labeled A+ and A-) grouped in one phase set and the other four stator poles (labeled B+ and B-) grouped in the other phase set. Each stator pole 230 has a conductive winding or electromagnetic coil 236 wound around it. The coils 236 positioned around the stator poles 230 of each phase set (A+, A- and B+, B-) are electrically connected. Non-conductive spacers 238 can be placed in the stator slots 234 between adjacent coils.

[0024] The rotor 228 has no windings or magnets. The rotor 228 may be formed as a stack of vertically laminated iron sheets. The rotor poles 232 may be grouped into diametrically aligned pairs.

[0025] In operation, the rotation of the rotor 228 of the switched reluctance motor is achieved by sequentially exciting adjacent groups of stator poles 230 by supplying current to the coils 236 of the stator poles 230. The excitation of the stator poles 230 generates a magnetic flux, to which the rotor poles 232 are attracted, tending to align the rotor poles 232 with the energized stator poles 230. When the rotor poles 232 are aligned with the energized stator poles 230, the DC current to the energized poles is terminated and then supplied to the next sequential stator poles 230. The rotor poles 232 are then attracted to the next sequential group of poles, which causes the rotor 228 to continue to rotate. This process continues during the operation of the switched reluctance motor. Torque is generated by the tendency of the rotor poles 232 to align with the energized stator poles 230. By synchronizing the excitation of consecutive stator poles 230 with the instantaneous position of the rotor poles 232, continuous torque can be generated. Although the concepts are described for a switched reluctance motor, the concepts can also be applied to a switched reluctance generator or any slotted electric machine.

[0026] Figure 3 is another example of a portion of the electric motor 324 . Figure 3 The example motor 324 in FIG. 1 is also a switched reluctance motor including a stator 326 and a rotor 328. In this example, the stator 326 is located inside the rotor 328, and the surrounding rotor 328 rotates around the inner stator 326. The coil 236 is arranged around the stator pole 330. The stator slot 334 has a Figure 2 The stator slots 234 have different shapes. Figure 3 In the embodiment, the stator slots 334 each have a width that tapers or narrows from the rotor end to the base end. Figure 2 As shown in the example of , continuous torque can be generated by synchronizing the excitation of continuous stator poles 330 with the instantaneous position of rotor poles 332.

[0027] Figure 4 An end view of two coils 236 arranged around adjacent stator poles 230 is shown. The stator poles 230 may include Figure 2 or Figure 3 The coil 236 includes at least two conductive wires wound into a plurality of turns 446 wound with a coil innermost portion 448. The coil innermost portion 448 contacts a side surface 450 of the stator pole 230. A non-conductive tape 452 may be used to hold the turns of the coil. The coil 236 is located in the stator slots 234 between the stator poles 230. Non-conductive spacers 238 may be placed in the stator slots 234 between adjacent coils 236.

[0028] Figure 5 is a stator pole 230 (such as Figure 2230 and a cross-sectional view of a stator pole 230 (designated as B+ in FIG. 1 ) and a coil 236 wound around the stator pole 230. In this example, the rotor is located within the stator. The coil 236 includes at least two conductive wires that are wound into a plurality of turns around the stator pole 230. The turns of the coil 236 extend from the base end of the stator pole 230 to the rotor end in the stator pole 230. Each stator slot 234 holds a portion of the coil 236 of the stator pole 230 and another portion of the coil 236 of the adjacent stator pole 230. The coil 236 has a plurality of longitudinal turns per unit length of turns of the stator pole 230. Because the stator slots 234 are tapered, the coil 236 has fewer turns per unit length at the rotor end of the stator pole 230 than at the base end of the stator pole 230. The turns of coil 236 closer to the rotor end of the stator pole are twisted, and the turns of coil 236 closer to the base end of stator pole 230 are not twisted. Figure 3 The coil shape of the stator 326 of the motor 324 is reversed because the coil slots 334 are reversed from the coil 236 , which has fewer turns per unit length at the base end of the stator pole 330 than at the rotor end of the stator pole 330 .

[0029] Twisting the wires of the coils can improve efficiency and reduce losses that generate heat. However, twisting all the turns of the coil 236 results in a larger coil because adjacent twisted wires may not be placed so closely together. This may cause the coil to be bent instead of flat. During the conduction cycle when the coil is energized, the maximum magnetic flux in the coil is closer to the gap between the stator pole 230 and the rotor pole 232. Twisting only the wires in the coils closer to the rotor end can improve efficiency and make the coils easier to manufacture and place in the stator 226.

[0030] Figure 5 A portion of coil 236 including twisted turns 237 and untwisted turns 239 is shown. Figure 5 In some examples, less than half of the turns are twisted. In some examples, substantially half of the turns (e.g., 40% to 60% of the turns) are twisted.

[0031] Figure 6 is a cross-sectional view of some of the turns of the coil 236. The turns within the rectangle are closer to the rotor end and are twisted. Those turns not within the rectangle are not twisted. The numbers within the circles reflect the order in which the turns are formed when the coil is wound. Figure 6 It is shown that the twisting of the wire may not be performed sequentially on the turns. Instead, the twisting of the wire may be stopped and started during the winding of the coil 236, and the twisting of the wire may be performed at different times.

[0032] The wires closer to the rotor end may have one twist per turn, and the wires closer to the base end may have zero twists per turn. The number of twists per turn may be different from one twist per turn. The number of twists per turn may be, but is not limited to, one-half twist per turn to two twists per turn, but the wires closer to the base end may still have zero twists per turn.

[0033] Figure 7 236. The wire may be an electrically insulated wire that may include an insulating layer 740 and a conductive wire. The conductive wire may include a plurality of metallic wire strands 742 within the insulating layer 740. In this example, seven strands of wire are within the insulating layer 740.

[0034] Industrial Applicability

[0035] Figure 8 8 is a flow chart of an example of a method 800 for manufacturing an assembly for an electric motor. At block 805, an electromagnetic coil is formed by winding at least two conductive wires into a plurality of turns, the turns being wound with an orientation transverse to a center of the coil. The coil is formed to have a first side and a second side. The wire may be an electrically insulated wire including an insulating layer having a plurality of metal strands within the insulating layer.

[0036] At block 810, less than all of the turns are twisted. The turns of the coil closer to the first side of the coil are twisted, and the turns of the coil closer to the second side of the coil are not twisted. In some examples, substantially half of the turns (e.g., the upper half of the turns) include twisting of the wires. In variants, less than half of the turns include twisting of the wires. In some examples, the wires in the twisted turns include twisting the wires once per turn. In some examples, the twisted wires include twisting turns so that the number of twists per turn is in the range of twisting half of the turns per turn to twisting twice per turn, but is not limited thereto.

[0037] At box 815, a plurality of such coils are formed. At box 820, each of the coils is disposed on a stator pole of a stator having a plurality of stator poles. Each stator pole has a rotor and a base end. Each coil is disposed so that a first side of the coil is closer to the rotor end of the stator pole and a second side of the coil is closer to the base end of the rotor pole. The coil may be disposed in a stator slot near the stator pole. The stator slot may be tapered, narrower at the rotor end and wider at the base end. There may be fewer turns on the first side of the coil than on the second side of the coil to accommodate changes in width. Conversely, the stator slot may be tapered, wider at the rotor end and narrower at the base end. There may be more turns on the first side of the coil than on the second side of the coil to accommodate changes in width. | Non-conductive spacers may be disposed in stator slots between adjacent coils.

[0038] A coil having less than all of the turns of the twisted coil reduces the coil leg thickness and coil leg height compared to all of the turns of the twisted coil, making it easier to manufacture the coil, but still providing the benefits of a coil having twisted wire. It also improves the shape of the coil by preventing torsional twisting of the coil, which makes it easier to place the coil on the stator pole and does not require the coil to be cold-pressed into an improved shape for placement. A coil having less than all of the turns of the twisted coil reduces inter-strand contact stress and reduces strand crossing, thereby increasing the operating life of the coil compared to a coil in which all of the turns are twisted. It also reduces coil resistance and improves coil contact area, thereby improving cooling of the coil. Although these concepts are described with respect to electric motors, these concepts can also be applied to generators.

[0039] Unless expressly excluded, the use of the singular to describe a component, structure, or operation does not exclude the use of a plurality of such components, structures, operations, or their equivalents. In the context of describing the present invention (particularly in the context of the appended claims), the use of the terms "one" and "an" and "said" and "at least one" or the term "one or more" and similar indicators should be interpreted as covering the singular and the plural, unless otherwise specified herein or clearly contradicted by the context. The use of the term "at least one" after a list of one or more items (e.g., "at least one of A and B" or "one or more of A and B") should be interpreted as meaning an item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B; A, A and B; A, B and B), unless otherwise specified herein or clearly contradicted by the context. Similarly, the word "or" used herein refers to any possible arrangement of a group of items. For example, the phrase "A, B or C" means at least one of A, B, C or any combination thereof, such as any of the following: A; B; C; A and B; A and C; B and C; A, B and C; or a plurality of any items such as A and A; B, B and C; A, A, B, C and C; and so on.

[0040] The above detailed description is intended to be illustrative rather than limiting. The scope of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. An assembly for an electric motor (224), the assembly comprising: A stator (226), the stator comprising a plurality of stator poles (230), each stator pole comprising a base end and a rotor end opposite the base end; and an electromagnetic coil (236) surrounding each stator pole, the coil surrounding each stator pole comprising: at least two conductive wires, the at least two conductive wires being wound around the stator pole into a plurality of turns (446), the plurality of turns extending between the base end of the stator pole to the rotor end of the stator pole; and The turns (237) of the coil closer to the rotor end of the stator pole are twisted, and the turns (239) of the coil closer to the base end of the stator pole are not twisted.

2. The assembly of claim 1 wherein turns of the coil closer to the rotor end of the stator pole include one twist per turn and turns of the coil closer to the base end of the stator pole include zero twists per turn.

3. The assembly of claim 1 , wherein the turns of the wire at the rotor end of the coil closer to the stator pole include a number of twists per turn that ranges from one-half twist per turn to two twists per turn, and the turns of the wire at the base end of the coil closer to the stator pole include zero twists per turn.

4. The assembly of claim 1 wherein substantially half of said turns of said electrical wire are twisted.

5. The assembly of claim 1 wherein less than half of said turns of said wire are twisted.

6. The assembly of claim 1, wherein the at least two electrically conductive wires are electrically insulated wires comprising an insulating layer (740) and a plurality of metallic wire strands (742) within the insulating layer.

7. The assembly of claim 1 wherein the coil has a certain number of turns per unit length of the stator pole, and the coil has fewer turns per unit length at the rotor end of the stator pole than at the base end of the stator pole.

8. A method of manufacturing a component of an electric motor (224), the method comprising: forming an electromagnetic coil (236) by winding at least two electrically conductive wires into a plurality of turns (446), the plurality of turns being wound transversely to a center of the coil, wherein the coil has a first side and a second side; twisting turns of the coil closer to the first side of the coil, and not twisting turns of the coil closer to the second side of the coil; forming a plurality of said electromagnetic coils; as well as Each of the plurality of coils is disposed on a stator pole (230) of a stator (226) having a plurality of stator poles, each stator pole having a rotor end and a base end, and each coil is disposed so that the first side of the coil is closer to the rotor end of the stator pole and the second side of the coil is closer to the base end of the stator pole. 9 . The method of claim 8 , wherein twisting the turns closer to the first side of the coil comprises twisting the turns once per turn.

10. The method of claim 8, wherein twisting the turns closer to the first side of the coil comprises twisting the turns to have a number of twists per turn in a range of one-half twist per turn to two twists per turn.

Images