Manufacturing of switched reluctance motors with variable wire twist ratios

Abstract

Manufacturing of switched reluctance motors with variable wire twist ratios The electric motor assembly includes a stator including a plurality of stator poles, each having 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 in a plurality of wire turns around the stator pole extending from the base end of the stator pole to the rotor end of the stator pole. The wire turns of the coil near the rotor end of the stator pole are twisted, and the wire turns of the coil near the base end of the stator pole are untwisted.

Description

[Technical Field]

[0001] The present application relates to an electric working machine, and more particularly to a technique for improving the performance and manufacturability of an electric motor for an electric working machine. [Background technology]

[0002] Large mobile work machines (e.g., wheel loaders) can be powered by one or more electric motors. An example of an electric motor is described in U.S. Patent Application No. 9,118,225. The electric motor is a switched reluctance motor that includes a stator with an electromagnetic coil. During operation, there are losses associated with the coils in the electric motor, generating undesirable heat. To reduce these losses, the wire turns of the coils are twisted. However, manufacturing coils with twisted wire turns presents challenges. Twisting the wire distorts the coil's shape, which makes it difficult to place the coil on the stator. Summary of the Invention

[0003] Large electric mobile work machines use large-capacity energy sources to drive one or more electric motors. While twisting the wire in the coil of an electric motor can improve the motor's performance, twisted coils are difficult to manufacture and difficult to assemble into electric motors with twisted wire.

[0004] An exemplary electric motor assembly for a work machine includes a stator including a plurality of stator poles, each having a base end and a rotor end opposite the base end, and an electromagnetic coil around each stator pole. The coil around each stator pole includes at least two conductive wires wound in multiple turns around the stator pole extending between the base end of the stator pole and the rotor end of the stator pole. The wire turns of the coil closer to the rotor end of the stator pole are twisted, and the wire turns of the coil closer to the base end of the stator pole are untwisted.

[0005] An exemplary method of forming an assembly for an electric motor includes forming an electromagnetic coil by winding at least two conductive wires in a plurality of turns wound transversely about a center of the coil such that the coil has a first side and a second side, twisting the wire turns of the coil near the first side of the coil and untwisting the wire turns of the coil near the second side of the coil, forming a plurality of electromagnetic coils, and positioning each coil on a stator pole of a stator having a plurality of stator poles, each stator pole having a rotor end and a base end, and each coil being positioned such that the first side of the coil is proximate the rotor end of the stator pole and the second side of the coil is proximate the base end of the stator pole.

[0006] An exemplary electric motor for a work machine includes a stator, a rotor, and a plurality of electromagnetic coils. The stator includes a plurality of stator poles, each having a base end and a rotor end opposite the base end, and a plurality of stator slots disposed between two of the stator poles. The rotor is disposed within the stator and includes a plurality of rotor poles extending toward the stator poles. Each of the electromagnetic coils is disposed around the stator pole and includes at least two conductive wires wound in a plurality of wire turns around the stator pole extending from the base end of the stator pole to the rotor end of the stator pole. The wire turns of the coil closer to the rotor end of the stator pole are twisted, and the wire turns of the coil closer to the base end of the stator pole are untwisted. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a front view showing an example of a work machine according to the present disclosure. FIG. [Figure 2] 1 is a schematic diagram illustrating a portion of an example of an electric motor for a work machine according to the present disclosure. [Figure 3] FIG. 10 is a schematic diagram illustrating a portion of another example of an electric motor for a work machine according to the present disclosure. [Figure 4] FIG. 2 is an end view of two stator poles and coils wound around the stator poles according to the present disclosure. [Figure 5]3 is a cross-sectional view of a stator pole, such as the stator pole shown as pole B+ in FIG. 2, and a coil wrapped around the stator pole, in accordance with the present disclosure. [Figure 6] FIG. 2 is a cross-sectional view of a wire turn of a coil according to the present disclosure. [Figure 7] 1 is a cross-sectional view of a group of conductive wires that can be wound to form an electromagnetic coil for an electric motor according to the present disclosure. [Figure 8] FIG. 1 is a flow diagram of an exemplary method of forming an assembly for an electric motor according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] SUMMARY OF THE DISCLOSURE Embodiments of the present disclosure relate to methods and apparatus for improving the efficiency of electric motors in work machines.

[0009] FIG. 1 illustrates an example of a machine 100 consistent with the present disclosure. In FIG. 1, the machine 100 includes a frame 102, wheels 104, implements 106, and a speed control system implemented in one or more on-board electronics, such as an electronic control unit or ECU. The exemplary machine 100 is a wheel loader. However, in other examples, the machine may be other types of machines associated with various industries, including, by way of example, construction, agriculture, forestry, transportation, material handling, waste management, marine, and stationary power. Thus, while some examples are described with reference to a wheel loader machine, embodiments consistent with the present disclosure are also applicable to other types of machines, including graders, scrapers, dozers, excavators, compactors, material handling vehicles such as dump trucks, ships, generators, and other exemplary machine types.

[0010] Machine 100 includes a frame 102 mounted on four wheels 104, although in other examples, machine 100 can 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 can house, among other components, an electric motor or the like for propelling the machine over various terrains via wheels 104. In some examples, multiple electric motors are included in multiple housings at multiple locations on machine 100.

[0011] Machine 100 includes an implement 106 coupled to frame 102 via linkage assembly 110, which is configured to actuate to articulate a bucket 112 of implement 106. Bucket 112 of implement 106 may be configured to transport material, such as dirt, from one location to another. Linkage assembly 110 may include one or more cylinders 114 that are configured to be hydraulically or pneumatically actuated, for example, to articulate bucket 112. For example, cylinders 114 may actuate linkage assembly 110 to raise, lower, and / or rotate bucket 112 relative to frame 102 of machine 100.

[0012] A platform 116 is coupled to the frame 102 and provides access to various locations on the machine 100 for operation and / or maintenance. The machine 100 also includes an operator's cab 118 that may be openable and accessible via the platform 116. The operator's cab 118 may include one or more controls (not shown), such as a joystick, a steering wheel, pedals, levers, buttons, switches, among other examples. The controls are configured to allow the operator to control the machine 100 and / or the implement 106. The operator's cab 118 may also include an operator interface, such as a display, an audio source, a light source, or a combination thereof.

[0013] Machine 100 may be used for a variety of industrial, construction, commercial, or other applications. Machine 100 may be operated by an operator within cab 118. The operator may, for example, drive machine 100 to and from various locations on a work site and may use bucket 112 of implement 106 to pick up and place loads of material. In yet another example, both remote operator operation and autonomous operation are contemplated. Machine 100 may excavate a portion of a work site by actuating cylinders 114 to articulate bucket 112 via linkage 110 to dig and remove dirt, rock, sand, etc. from one portion of the work site and deposit the load in another location. Machine 100 may include a battery compartment connected to frame 102 and containing battery system 120. Battery system 120 is electrically coupled to one or more electric motors of machine 100.

[0014] Figure 2 is a schematic diagram illustrating a portion of an example electric motor 224 for a work machine, such as work machine 100 of Figure 1. The example electric motor 224 is a switched reluctance motor that includes a stator 226 and a rotor 228 that is rotatable relative to stator 226. Stator 226 includes eight stator poles 230, and rotor 228 includes four rotor poles 232. Electric motor 224 may include a different number of stator poles 230 and rotor poles 232 than the example of Figure 2.

[0015] The stator 226 includes stator slots 234 between the stator poles 230. The stator slots 234 open toward the rotor 228. The stator poles 230 and the stator slots 234 have base ends and rotor ends. Each of the stator slots 234 tapers or decreases in width from the base end to the rotor end. The shape of the stator 226 may be referred to as an open slot configuration.

[0016] The stator poles 230 may be grouped into two or more phase sets of stator poles 230 corresponding to the number of phases (e.g., two) of the switched reluctance motor. In the example of FIG. 2, eight stator poles 230 are grouped into two phase sets, with four stator poles (labeled A+ and A-) grouped as one phase set and four stator poles (labeled B+ and B-) grouped as another phase set. Each stator pole 230 has a conductive winding or electromagnetic coil 236 wound around it. The coils 236, centered around the stator poles 230 of each group of phase sets (A+, A- and B+, B-), are electrically connected. Non-conductive spacers 238 may be placed in the stator slots 234 between adjacent coils.

[0017] The rotor 228 is devoid of windings and magnets. The rotor 228 may be formed as a stack of iron pieces stacked one on top of the other. Each rotor pole 232 may be grouped in a radially aligned pair.

[0018] During operation, rotation of the rotor 228 of the switched reluctance motor is achieved by sequentially energizing adjacent sets of stator poles 230 by supplying current to the coils 236 of the stator poles 230. The energization of the stator poles 230 generates magnetic flux that attracts the rotor poles 232, tending to align the rotor poles 232 with the energized stator poles 230. Once the rotor poles 232 and the energized stator poles 230 are aligned, the DC current to the energized poles is terminated and subsequently supplied to the next successive stator pole 230. The rotor poles 232 are then attracted to the next successive set of poles, thereby continuing rotation of the rotor 228. This process continues throughout 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. Continuous torque may be generated by synchronizing the energization of successive stator poles 230 with the instantaneous position of the rotor poles 232. Although the concepts are described with respect to switched reluctance motors, the concepts are also applicable to switched reluctance generators and any open-slot electric machine.

[0019] FIG. 3 is another example of a portion of an electric motor 324. The exemplary electric motor 324 in FIG. 3 is also a switched reluctance motor including a stator 326 and a rotor 328. In this example, the stator 326 is inside the rotor 328, and the surrounding rotor 328 rotates around the internal stator 326. The coils 236 are disposed around the stator poles 330. The stator slots 334 have a different shape than the stator slots 234 in FIG. 2. In FIG. 3, each of the stator slots 334 tapers in width or decreases in size from the rotor end to the base end. As in the example of FIG. 2, continuous torque may be generated by synchronizing the energization of successive stator poles 330 with the instantaneous position of the rotor poles 332.

[0020] FIG. 4 shows an end view of two coils 236 arranged around adjacent stator poles 230. The stator poles 230 can be included in either the stator of FIG. 2 or FIG. 3. The coils 236 include at least two conductive wires wound around a plurality of wire turns 446 around which an innermost coil portion 448 is wound. The innermost coil portion 448 contacts a side surface 450 of the stator pole 230. A non-conductive tape 452 may be used to hold the wire turns of the coils. The coils 236 are positioned in stator slots 234 between the stator poles 230. A non-conductive spacer 238 may be positioned in the stator slots 234 between adjacent coils 236.

[0021] FIG. 5 is a cross-sectional view of a stator pole 230, such as the stator pole 230 designated B+ in FIG. 2, and a coil 236 wound around the stator pole 230. In this example, a rotor is disposed within the stator. The coil 236 includes at least two conductive wires wound in multiple wire turns around the stator pole 230. The wire turns of the coil 236 extend from the base end of the stator pole 230 to the rotor end of the stator pole 230. Each stator slot 234 holds a portion of the coil 236 of its own stator pole 230 and a portion of the coil 236 of the adjacent stator pole 230. The coil 236 has multiple longitudinal wire turns per length of the stator pole 230. Due to the narrower stator slots 234, the coil 236 has fewer wire turns per length at the rotor end of the stator pole 230 than at the base end of the stator pole 230. The wire turns of the coil 236 near the rotor end of the stator pole are twisted and the wire turns of the coil 236 near the base end of the stator pole 230 are untwisted. The coil slots 334 are reversed with the coil 236 having fewer wire turns per length at the base end of the stator pole 330 than at the rotor end of the stator pole 330, so the coil geometry is reversed relative to the stator 326 of the electric motor 324 of FIG. 3.

[0022] Twisting the wire turns of a coil can improve efficiency and reduce heat losses. However, twisting all of the wire turns of coil 236 results in a larger coil because adjacent twisted wires may not be as closely packed. This allows the coil to be curved rather than flat. During a conduction cycle when the coil is energized, the maximum magnetic flux in the coil is near the gap between the stator poles 230 and the rotor poles 232. Twisting only the wire in the coil closest to the rotor end improves efficiency and results in a coil that is easier to manufacture and place in stator 226.

[0023] 5 shows a portion of a coil 236 that includes twisted wire turns 237 and untwisted wire turns 239. In the example of FIG. 5, less than half of the wire turns are twisted. In some examples, approximately half of the wire turns (e.g., 40-60% of the wire turns) are twisted.

[0024] FIG. 6 is a cross-sectional view of some of the wire turns of coil 236. Wire turns within the rectangles are closer to the rotor ends and are twisted. Wire turns outside of the rectangles are not twisted. The numbers within the circles reflect the order in which the wire turns are formed when winding the coil. FIG. 6 illustrates that the wire twist does not have to be sequential across the wire turns. Instead, the wire twist may stop and start multiple times in the winding of coil 236.

[0025] The wires closer to the rotor end may have 1 twist per turn and the wires closer to the proximal end have 0 twists per turn. The number of twists per turn may be different from the number of twists per turn. The number of twists per turn may be, but is not limited to, from 0.5 twists per turn to 2 twists per turn, while the wires closer to the proximal end still have 0 twists per turn.

[0026] 7 is a cross-sectional view of a conductive wire that can be wound to form coil 236. The wire may be an insulated wire that can include insulation 740 and a conductive wire. The conductive wire may include multiple metal strands 742 within insulation 740. In this example, seven wires enter insulation 740.

[0027] Industrial Applicability 8 is a flow diagram of an example method 800 of forming an assembly for an electric motor. In block 805, an electromagnetic coil is formed by winding at least two conductive wires into a plurality of wire turns wound transversely to the center of the coil. The coil is formed having a first side and a second side. The wire may be an insulated wire having a plurality of metallic strands within an insulator.

[0028] In block 810, not all turns of wire are twisted. The wire turns of the coil near the first side of the coil are twisted and the wire turns of the coil near the second side of the coil are untwisted. In some examples, approximately half of the turns of the wire (e.g., the top half of the turns) include twists in the wire. In variations, less than half of the turns include twists in the wire. In some examples, twisting the wire turns of the wire includes twisting the wire once per turn. In some examples, twisting the wire includes twisting the wire turns such that the number of twists ranges from, but is not limited to, 0.5 twists per turn to 2 twists per turn.

[0029] In block 815, multiple such coils are formed. In block 820, each of the coils is positioned on a stator pole of a stator having multiple stator poles. Each stator pole has a rotor end and a base end. Each coil is positioned such that a first side of the coil is near the rotor end of the stator pole and a second side of the coil is near the base end of the stator pole. The coil may be positioned in a stator slot adjacent to the stator pole. The stator slot may be tapered, narrower at the rotor end and wider at the base end. The coil may have fewer wire turns on the first side of the coil than the second side of the coil to accommodate the width change. Conversely, the stator slot may be tapered, wider at the rotor end and narrower at the base end. The coil may have more wire turns on the first side of the coil than the second side of the coil to accommodate the width change. Non-conductive spacers may be positioned in the stator slots between adjacent coils.

[0030] A coil in which all wire turns are not twisted reduces the coil leg thickness and coil leg height compared to a coil in which all wire turns are twisted, thereby simplifying coil manufacturing while still retaining the advantages of a coil using twisted wire. Also, preventing torsion twisting of the coil improves coil shape, which makes it easier to position the coil on the stator pole and eliminates the need to cold-press the coil into the correct shape. A coil in which all wire turns are not twisted reduces contact stress between strands and reduces wire crossovers, thereby extending service life compared to a coil with all twisted wire turns. It also reduces coil resistance and increases coil contact area, which improves coil cooling. While the concept has been described with respect to an electric motor, the concept is also applicable to generators.

[0031] Unless expressly excluded, the use of a singular form to describe a component, structure, or operation does not exclude the use of a plurality of such components, structures, or operations, or their equivalents. Use of singular terms ("a," "an," "the," and "at least one") or the term "one or more" and similar referents in the context of describing the present invention (particularly in the context of the claims below) should be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Use of the term "at least one" followed by 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 construed to mean one 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 indicated herein or clearly contradicted by context. Similarly, the word "or" as used herein refers to any possible permutation of a set of items. For example, the phrase "A, B, or C" refers to at least one of A, B, C, or any combination thereof, such as any of a plurality of any items such as A; B; C; A and B; A and C; B and C; A, B, and C; or A and A; B, B, and C; A, A, B, C, and C.

[0032] The above detailed description is intended to be illustrative and not restrictive. Accordingly, the scope of the present disclosure should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. a stator (226) including a plurality of stator poles (230), each having a base end and a rotor end opposite the base end; An electromagnetic coil (236) around each stator pole, the electromagnetic coil (236) including at least two conductive wires wrapped in a plurality of wire turns (446) around the stator pole extending between the base end of the stator pole and the rotor end of the stator pole; 1. An assembly for an electric motor (224), wherein the wire turns (237) of the coil near the rotor end of the stator pole are twisted and the wire turns (239) of the coil near the base end of the stator pole are untwisted.

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

3. 2. The assembly of claim 1, wherein the number of turns of wire in the coil near the rotor end of the stator pole comprises a number of twists per turn in a range from 0.5 twists per turn to 2 twists per turn, and the number of turns of wire in the coil near the base end of the stator pole comprises 0 twists per turn.

4. The assembly of claim 1 , wherein approximately half of the turns of the wire are twisted.

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

6. 2. The assembly of claim 1, wherein the at least two conductive wires are insulated wires including an insulator (740) and a plurality of metal strands (742) within the insulator.

7. 2. The assembly of claim 1, wherein the coil has fewer wire turns per length of the stator pole at the rotor end of the stator pole than at the base end of the stator pole.

8. forming an electromagnetic coil (236) by winding at least two conductive wires in a plurality of wire turns (446) wound transversely around a coil center; twisting the wire turns of the coil near the first side of the coil and untwisting the wire turns of the coil near the second side of the coil; forming a plurality of said electromagnetic coils; a first end of the stator pole and a second end of the stator pole, the first end of the stator pole being closer to the rotor end of the stator pole and the second end of the stator pole being closer to the base end of the stator pole.

9. The method of claim 8 , wherein twisting the wire turns proximate the first side of the coil comprises twisting the wire turns once per turn.

10. 9. The method of claim 8, wherein twisting the wire turns proximate the first side of the coil comprises twisting to a twist per turn in the range of 0.5 turns per turn to 2 turns per turn.

Images