Power tool with permanent magnet synchronous reluctance motor

Abstract

A power tool includes a housing and a motor assembly positioned within the housing. The motor assembly includes a rotor and a stator having a winding slot that receives a stator winding. The rotor includes a rotor body having a first slot positioned at a first distance from a center of the rotor body, a second slot positioned at a second distance from the center of the rotor body, and a third slot positioned at a third distance from the center of the rotor body. The first slot, the second slot, and the third slot curve about a common center. The rotor further includes a first magnet positioned within the first slot, a second magnet positioned within the second slot, and a third magnet positioned within the third slot.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 924,329, filed on October 22, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to power tools, and more particularly to power tools having permanent magnet motors. Summary of the Invention

[0004] The present disclosure provides a power tool comprising a housing and a motor assembly positioned within the housing. The motor assembly comprises a rotor and a stator, the stator having winding slots for receiving stator windings. The rotor comprises a rotor body having a first slot positioned at a first distance from a center of the rotor body and a second slot positioned at a second distance from the center of the rotor body. The first slot and the second slot are curved about a common center. The rotor further comprises a first magnet positioned within the first slot and a second magnet positioned within the second slot.

[0005] The present disclosure provides a motor assembly for a power tool, the motor assembly including a stator and a rotor, the stator having winding slots for receiving stator windings, the rotor including a rotor body having a first slot positioned at a first distance from a center of the rotor body and a second slot positioned at a second distance from the center of the rotor body. The first slot and the second slot each curve about a common point. The rotor further includes a first magnet positioned within the first slot and a second magnet positioned within the second slot.

[0006] In some aspects, the common point is located outside of the rotor body.

[0007] In some aspects, a first dimension is measured between a first end of the first slot and the outer peripheral surface of the rotor body, a second dimension is measured between a second end of the first slot and the outer peripheral surface of the rotor body, and the second dimension is equal to the first dimension.

[0008] In some aspects, a first dimension is measured between an end of the first slot and the outer peripheral surface of the rotor body, a second dimension is measured between an end of the second slot and the outer peripheral surface of the rotor body, and the second dimension is equal to the first dimension.

[0009] In some aspects, the span of the first magnet is in the range of 50% to 100% of the first slot.

[0010] In some aspects, the span of the first magnet is in the range of 50% to 56% of the first slot.

[0011] In some aspects, the first magnet spans 53% of the first slot.

[0012] In some aspects, the span of the second magnet is in the range of 33% to 100% of the second slot.

[0013] In some aspects, the span of the second magnet is in the range of 33% to 39% of the second slot.

[0014] In some aspects, the second magnet spans 36% of the second slot.

[0015] In some aspects, the third slot is positioned a third distance from the center of the rotor body, the third slot is curved about the common point, and the third magnet is positioned within the third slot.

[0016] In some aspects, the third magnet has a span in the range of 35% to 100% of the third slot.

[0017] In some aspects, the span of the third magnet is in the range of 35% to 41% of the third slot.

[0018] In some aspects, the third magnet spans 38% of the third slot.

[0019] In some aspects, the motor is configured to drive a cyclic load.

[0020] In some aspects, the motor provides more starting torque than a brushless DC motor of the same package size and provides a higher no-load speed than a brushless DC motor of the same package size.

[0021] In some aspects, a tool element is provided, and wherein the tool element is driven by a motor.

[0022] In some aspects, the stator includes at least twenty-four slots.

[0023] In some aspects, the rotor is a 4-pole rotor.

[0024] The present disclosure provides a power tool comprising a housing and a permanent magnet synchronous reluctance motor positioned within the housing. The permanent magnet synchronous reluctance motor comprises a stator having a stator winding, a rotor having a plurality of slots, and a magnet positioned in each of the plurality of slots. The power tool further comprises a tool element driven by the permanent magnet synchronous reluctance motor.

[0025] In some aspects, a permanent magnet synchronous reluctance motor provides more starting torque than a brushless DC motor of the same package size and provides a higher no-load speed than a brushless DC motor of the same package size.

[0026] In some aspects, the plurality of slots are curved.

[0027] In some aspects, the magnets within each slot of the plurality of slots span less than 56% of the slot.

[0028] In some aspects, the permanent magnet synchronous reluctance motor includes at least twenty-four winding slots formed in the stator, and the rotor includes at least four poles.

[0029] Before explaining any embodiment in detail, it should be understood that the embodiments are not limited in their application to the configuration details and component arrangements set forth in the following description or shown in the following figures. The embodiments can be practiced or implemented in a variety of different ways. It should also be understood that the wording and terminology used herein are for illustrative purposes only and should not be considered restrictive. The use of "comprising," "including," or "having" and variations thereof is intended to encompass the items listed below and their equivalents, as well as additional items. Unless otherwise specified or limited, the terms "mount," "connect," "support," and "couple" and variations thereof are used broadly and encompass direct and indirect mounting, connection, support, and coupling.

[0030] In addition, it should be understood that embodiments may include hardware, software, and electronic components or modules, which, for the purposes of discussion, may be shown and described as if most components were implemented only in hardware. However, a person of ordinary skill in the art will recognize, based on a reading of this detailed description, that in at least one embodiment, the electronic-based aspects may be implemented in software (e.g., stored on a non-transitory computer-readable medium) that is executable by one or more processing units (e.g., a microprocessor and / or an application-specific integrated circuit ("ASIC")). Thus, it should be noted that embodiments may be implemented using a plurality of hardware- and software-based devices and a plurality of different structural components. For example, the "server," "computing device," "controller," "processor," etc. described in the specification may include one or more processing units, one or more computer-readable media modules, one or more input / output interfaces, and various connectors (e.g., a system bus) connecting components.

[0031] Relative terms used in conjunction with quantities or conditions, such as "about", "approximately", "substantially", etc., will be understood by those of ordinary skill in the art to include the value described and have the meaning dictated by the context (e.g., the term includes at least the degree of error associated with measurement precision, the tolerance associated with a particular value [e.g., manufacturing, assembly, use, etc.], etc.). Such terms should also be considered to disclose a range defined by the absolute values ​​of the two endpoints. For example, the expression "about 2 to about 4" also discloses a range of "2 to 4". Relative terms can refer to plus or minus a certain percentage of the indicated value (e.g., 1%, 5%, 10% or more).

[0032] It should be understood that although some of the drawings show hardware and software located within a particular device, these depictions are for illustrative purposes only. The functions described herein as being performed by one component can be performed in a distributed manner by multiple components. Similarly, the functions performed by multiple components can be merged and performed by a single component. In some embodiments, the components shown can be combined or divided into separate software, firmware and / or hardware. For example, logic and processing can be distributed between multiple electronic processors rather than being located in and performed by a single electronic processor. Regardless of how the hardware and software components are combined or divided, they can be located on the same computing device, or can be distributed between different computing devices connected by one or more networks or other suitable communication links. Similarly, components described as performing specific functions can also perform additional functions not described herein. For example, a device or structure that is "configured" in a certain manner is configured at least in that manner, but can also be configured in a manner that is not explicitly listed.

[0033] Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Various power tool applications with cyclical loads that require high starting torque and high no-load speed are demonstrated.

[0035] Figure 2 yes Figure 1 A diagram of an example of a cyclic load applied to a power tool, illustrating torque as a function of angular position.

[0036] Figure 3 A graph showing the electrical characteristics of a conventional motor as a function of torque, with various operating points identified relative to the power tool load.

[0037] Figure 4 A graph showing the torque capability of a power tool motor as a function of angular position, where the minimum torque requirement level is determined.

[0038] Figure 5 is a cross-sectional view of a permanent magnet synchronous reluctance machine ("PMSRM") according to embodiments described herein.

[0039] Figure 6 yes Figure 5 A partial enlarged view of the PMSRM.

[0040] Figure 6A is a partially enlarged view of a PMSRM according to another embodiment described herein.

[0041] Figure 7 It is a conventional interior permanent magnet ("IPM") motor with Figure 5A graph comparing the speed, output power, and efficiency of a permanent magnet synchronous reluctance motor. DETAILED DESCRIPTION

[0042] Power tools that include electric motors to drive fans, pumps, compressors, and the like experience variable load conditions. For example, one load condition might require high starting torque, while a second load condition might require high idle speed. Furthermore, load conditions can be cyclical. Therefore, the electric motor must be appropriately sized to meet the various load requirements of the power tool.

[0043] refer to Figure 1 , various power tools are shown (e.g., a wire cutter 10, a wire cutter 14, and an air pump 18). In alternative embodiments, the power tool can be an electric crimper, a knockout tool, a pump (hydraulic, air, or water), a deployment tool, a punching tool, or any other similar power tool. The power tools 10, 14, 18 have a large starting torque requirement when operating in an application and have a cyclic load (i.e., a repetitive load curve) once the power tool motor has reached normal operating speed. The power tools 10, 14, 18 each include a housing 12, 16, 20 and a driven tool element (i.e., a working element). For example, depending on the application of the power tool, the tool element can be a claw 21, a pliers, a cutter 22, a drill bit, a piston, a crimper, a punch, etc.

[0044] refer to Figure 2 , the first pump torque curve 24 and the second pump torque curve 26 are shown in inch-pounds as a function of rotational position (e.g., degrees) at a given maximum operating pressure. When utilizing a pump in a power tool application, the pump piston reciprocates, slowly increasing pressure. During normal operation, the motor requires very little power due to the motor's rotational storage of energy and the cyclical nature of the load. In other words, normal operation of the pump is a high speed, low torque situation. In contrast, when the pump is stopped and maximum pressure is acting on the piston, a large amount of torque is required (i.e., a high starting torque). During use, the pump piston may be just Figure 2 The peak torque shown is stopped before the tool is turned on again, so that a very large starting torque is required. Therefore, the power tools 10, 14, 18 must include motors that are sized to accommodate various worst-case load conditions, which may result in expensive and oversized motors.

[0045] refer to Figure 3 , shows the pump load condition of a conventional power tool having a brushless DC ("BLDC") motor such as an interior permanent magnet ("IPM") motor. In other words, Figure 3 The electrical characteristics of a conventional IPM motor in a pump application are shown. Specifically, Figure 3 The efficiency 30, output power 34, current 38 and speed 42 of the IPM motor are shown as a function of torque. Figure 3 , various torque levels corresponding to various pump operating points are shown as vertical lines. In particular, low torque during pressure buildup and connecting rod extension, high speed no-load condition 46, average load condition 50, peak load condition 54, and stall load condition 58 (e.g., pressure relief at maximum pressure, or starting torque) are shown as being outside the capabilities of conventional motors. The majority of the motor's operation is in no-load condition 46 or heavy load starting 58.

[0046] refer to Figure 4 , shows the variation of the motor stall torque (in inch ounce-force) as a function of rotational position. In particular, the motor torque 62 at a first operating voltage (e.g., 19.5 volts) and the motor torque 66 at a second operating voltage (e.g., 17.5 volts) vary with rotational position (degrees). As described above, in some cases, the pump piston may stall at a high compression stroke and the motor may be in a rotational position that does not produce enough torque to be able to start. In other words, the horizontal line 70 represents the minimum torque requirement to achieve normal starting at maximum pressure. In the embodiment shown, the horizontal line 70 is 76 ounce-inches (oz-in) and represents the peak load at maximum pressure. If the motor torques 62, 66 drop below the horizontal line 70, a possible stall point 72 ( Figure 4 ), and the power tool may not start properly. As a result, power tool designs include motors that are larger and more powerful than what is typically required for most tool use. In other words, providing high starting torque in power tools driven by IPM motors comes at the expense of increased tool size, cost, and efficiency.

[0047] More specifically, in order to increase the torque capability of the BLDC motor (e.g., starting torque), the size of the motor is increased (e.g., increasing the motor diameter or the motor length). However, increasing the size of the BLDC motor increases the size and cost of the entire power tool. In addition, increasing the size of the BLDC motor to accommodate the worst-case load scenario (e.g., starting conditions) will result in the motor being oversized for most of the remaining power tool operating requirements (e.g., non-starting conditions). Finally, increasing the starting torque capability of the BLDC motor will have the counterproductive effect of also reducing the no-load speed. Reducing the no-load speed is undesirable because once the motor has reached operating speed, it is desirable for the motor to operate as fast as possible in order to complete the task as quickly as possible.

[0048] refer to Figure 5, the power tools 10, 14, 18 include a motor assembly positioned within the housing 12, 16, 20. In the illustrated embodiment, the motor assembly is a permanent magnet synchronous reluctance motor (PMSRM) 74. In other words, the power tools 10, 14, 18 include a permanent magnet synchronous reluctance motor 74 positioned within each housing 12, 16, 20 and operable to drive tool elements. In particular, Figure 5 A cross-sectional view of a PMSRM 74 is shown. The permanent magnet synchronous reluctance machine (PMSRM) 74 may also be referred to as a permanent magnet assisted synchronous reluctance machine (PMaSRM), a permanent magnet synchronous reluctance motor, or a permanent magnet assisted synchronous reluctance motor. The permanent magnet synchronous reluctance machine 74 may operate as a motor or a generator.

[0049] The PMSRM 74 includes a stator 78 and a rotor 82. The stator 78 includes a stator body 86 having teeth 90 that define winding slots 94 that receive stator windings 98. In the illustrated embodiment, the teeth 90 extend radially inward. In some embodiments, the stator body 86 is a single solid ferromagnetic piece. In other embodiments, the stator body 86 is formed as a stack of stator laminations. In the illustrated embodiment, the stator 78 includes twenty-four winding slots 94. In other embodiments, the stator 78 includes twenty-five or more winding slots 94. In other embodiments, the stator 78 includes twenty-three or fewer winding slots 94. In some embodiments, the stator includes six or more winding slots 94. The stator winding can be a distributed winding across multiple teeth 90, which allows multiple winding slots 94 to be used per pole. In some embodiments, the stator includes twelve or more winding slots 94.

[0050] Continue to refer Figure 5The rotor 82 includes a rotor body 102 having curved slots 106A, 106B, and 106C (i.e., arcuate slots) formed therein. In some embodiments, the rotor body 102 is a single solid ferromagnetic piece. In other embodiments, the rotor body 102 is formed as a stack of rotor laminations. The rotor 82 includes a first slot 106A, a second slot 106B, and a third slot 106C. The first slot 106A is different in size from the second slot 106B, and the second slot 106B is different in size from the third slot 106C. In the illustrated embodiment, the first slot 106A is larger than the second slot 106B, and the second slot 106B is larger than the third slot 106C. In the illustrated embodiment, the rotor body 102 includes four sets of three slots 106A, 106B, and 106C (i.e., a total of twelve slots). In other words, the rotor 82 is a four-pole rotor. In other embodiments, the rotor 82 includes five or more poles. In further alternative embodiments, rotor 82 includes three or fewer poles. Slots 106A, 106B, 106C can operate as flux barriers. In the illustrated embodiment, slots 106A, 106B, 106C are partially empty and configured as air flux barriers. In other embodiments, slots 106A, 106B, 106C are at least partially filled with flux barrier material. In some embodiments, two or fewer slots define each rotor pole.

[0051] In addition, rotor 82 includes permanent magnets 110A, 110B, 110C positioned within slots 106A, 106B, 106C. In the illustrated embodiment, permanent magnets 110A, 110B, 110C are curved to correspond to the arcuate shape of slots 106A, 106B, 106C. The magnet material may include sintered or bonded ferrite, ceramic ferrite, ceramic, or neodymium iron boron (NdFeB). Bonded neodymium can be injection molded from the front of the motor, while sintered neodymium is cut from a single block of material. With bonded neodymium, the material can be magnetized after injection, which greatly improves manufacturability and produces less waste. Additionally, plastic inserts in the magnet slots can be used to achieve less than 100% slot fill, which provides cost savings while still allowing electrical functionality.

[0052] refer to Figure 6First slot 106A is located a first distance R1 from a center 112 of rotor body 102, second slot 106B is located a second distance R2 from center 112, and third slot 106C is located a third distance R3 from center 112. Center 112 in the illustrated embodiment is the axis of rotation of rotor 82. First slot 106A, second slot 106B, and third slot 106C curve around a common point 107. In other words, second slot 106B partially nests within first slot 106A, and third slot 106C partially nests within second slot 106B. In the illustrated embodiment, common point 107 is located outside of rotor body 102. Specifically, common point 107 is located on teeth 90 of stator 78. In other words, slots 106A, 106B, and 106C are concave and curve around point 107, which is located radially outward from outer circumferential surface 103 of rotor body 102.

[0053] Continue to refer Figure 6 The ends of the slots 106A, 106B, and 106C are spaced equidistantly from the outer circumferential surface 103 of the rotor body 102. For example, a first dimension D1 measured between the first end 108A of the first slot 106A and the outer circumferential surface 103 and a second dimension D2 measured between the second end 108B of the first slot 106A and the outer circumferential surface 103 are approximately the same distance. Similarly, a third dimension D3 measured between the first end 108C of the second slot 106B and the outer circumferential surface 103 and the first dimension D1 are approximately the same distance. In other words, the distances D1-D6 from any end 108A-108D of each of the slots 106A, 106B, and 106C are positioned so as to be approximately the same distance relative to the outer circumferential surface 103 of the rotor body 102.

[0054] Continue to refer Figure 6, a first magnet 110A is positioned within the first slot 106A, a second magnet 110B is positioned within the second slot 106B, and a third magnet 110C is positioned within the third slot 106C. In the illustrated embodiment, magnets 110A, 110B, and 110C are positioned at the center of slots 106A, 106B, and 106C, respectively. Magnets 110A, 110B, and 110C do not fill the entire slots 106A, 106B, and 106C. For example, the span S1 of the first slot 106A around the common point 107 is approximately 110 degrees, while the span S2 of the first magnet 110A around the common point 107 is approximately 58 degrees. Therefore, the span of the first magnet 110A ranges from approximately 50% to approximately 56% of the span of the first slot 106A. In the illustrated embodiment, the span of the first magnet 110A is approximately 53% of the span of the first slot 106A. Similarly, the span S3 of the second slot 106B around the common point 107 is approximately 103 degrees, while the span S4 of the second magnet 110B around the common point 107 is approximately 37 degrees. Therefore, the span of the second magnet 110B ranges from approximately 33% to approximately 39% of the span of the second slot 106B. In the illustrated embodiment, the span of the second magnet 110B is approximately 36% of the span of the second slot 106B. Similarly, the span S5 of the third slot 106C around the common point 107 is approximately 81 degrees, while the span S6 of the third magnet 110C around the common point 107 is approximately 31 degrees. Therefore, the span of the third magnet 110C ranges from approximately 35% to approximately 41% of the span of the third slot 106C. In the illustrated embodiment, the span of the third magnet 110C is approximately 38% of the span of the third slot 106C. Thus, the magnets 110A-110C within each of the plurality of slots 106A-106C span less than approximately 56% of the slot.

[0055] refer to Figure 6A The rotor 82A includes a rotor body 102 having curved slots 106A, 106B, 106C (ie, arcuate slots) formed therein. Figure 682A is similar to rotor 82, with similar reference numerals used to denote similar structures. Rotor 82A differs from rotor 82 in that rotor 82A includes permanent magnets 111A, 111B, and 111C positioned throughout slots 106A, 106B, and 106C. In the illustrated embodiment, permanent magnets 110A, 110B, and 110C are curved to correspond to the arcuate shape of slots 106A, 106B, and 106C, and span 100% of slot spans S1, S2, and S3. In other words, magnet 111A extends from end 108A to end 108B of slot 106A. Similarly, magnet 111B extends from end 108C to end 108D of slot 106B, and magnet 111C extends from end 108E to end 108F of slot 106C. In other embodiments, the span of the magnets 111A, 111B, 111C may be less than 100% of the corresponding slot 106A, 106B, 106C.

[0056] refer to Figure 7 , the capabilities of the PMSRM 74 are compared to a conventional IPM motor of the same size. In other words, the comparison between the PMSRM 74 and a conventional IPM motor is made with motors having the same package size (i.e., volumetric space). First, the IPM motor speed 114 is compared to the PMSRM speed 118. At low torque (i.e., no-load conditions), the PMSRM speed 118 is higher than the IPM motor speed 114. In the illustrated embodiment, the PMSRM speed 118 at low torque is approximately 30% higher than the IPM motor speed 114 at low torque. Second, the IPM motor power 122 is compared to the PMSRM power 126. At high torque levels, the PMSRM power 126 is higher than the IPM power 122 because the PMSRM 74 is able to produce more torque than a similarly sized IPM motor. In the illustrated embodiment, the PMSRM 74 produces approximately 25% more torque than the IPM motor. Third, the IPM motor efficiency 130 is compared to the PMSRM efficiency 134. Under high torque conditions, the PMSRM efficiency 134 is higher than the IPM motor efficiency 130, while under low torque conditions, the PMSRM efficiency 134 is similar to the IPM motor efficiency 130. Thus, the PMSRM 74 offers advantages in terms of relative speed, torque, power, and efficiency compared to a conventional IPM motor of the same package size.

[0057] Compared to other BLDC motor types, including IPM motors, of the same package size, power tools 10, 14, 18 that include the PMSRM 74 allow for improvements in two important operating conditions (i.e., starting torque and no-load speed) without unnecessarily increasing size and cost. With the PMSRM 74, the power tool can be made smaller if necessary, or the additional torque capacity can increase the success margin for extreme starting situations (e.g., during a cold start with a less viscous hydraulic fluid being pumped). The permanent magnet synchronous reluctance motor 74 provides more starting torque than a BLDC motor of the same package size and provides a higher no-load speed than a BLDC motor of the same package size.

[0058] In addition to improved operating characteristics, the PMSRM 74 also contains less rare earth magnet material than similar IPM designs. In some embodiments, the PMSRM 74 contains 50% of the magnets found in conventional IPM designs of the same package size. Magnetic materials are expensive and subject to fluctuations in financial markets. Therefore, reducing the required magnet material is desirable for long-term cost and planning purposes.

[0059] Although the disclosure has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the disclosure as described. Various features and advantages are set forth in the appended claims.

Claims

1. A power tool comprising: case; a motor assembly positioned within the housing, the motor assembly comprising: a stator having winding slots for receiving stator windings, and a rotor comprising a rotor body having a first slot positioned a first distance from a center of the rotor body and a second slot positioned a second distance from the center of the rotor body, the first slot and the second slot each being curved about a common point; wherein the rotor further comprises a first magnet positioned in the first slot and a second magnet positioned in the second slot; wherein the span of the first magnet is in the range of 50% to 56% of the first slot, and the span of the second magnet is in the range of 33% to 39% of the second slot.

2. The power tool according to claim 1, wherein: The common point is located outside the rotor body.

3. The power tool according to claim 1, wherein: a first dimension measured between a first end of the first slot and an outer peripheral surface of the rotor body; a second dimension measured between a second end of the first slot and the outer peripheral surface of the rotor body; and The second size is equal to the first size.

4. The power tool according to claim 1, wherein: a first dimension measured between an end of the first slot and an outer peripheral surface of the rotor body; a second dimension is measured between an end of the second slot and the outer peripheral surface of the rotor body; and The second size is equal to the first size.

5. The power tool according to claim 1, wherein: The span of the first magnet is 53% of the first slot.

6. The power tool according to claim 1, wherein: The span of the second magnet is 36% of the second slot.

7. The power tool according to claim 1, wherein: The rotor further includes a third slot located a third distance from the center of the rotor body, the third slot curving about the common point; and a third magnet is positioned within the third slot.

8. The power tool according to claim 7, wherein: The span of the third magnet is in the range of 35% to 100% of the third slot.

9. The power tool according to claim 8, wherein: The span of the third magnet is in the range of 35% to 41% of the third slot.

10. The power tool according to claim 9, wherein: The span of the third magnet is 38% of the third slot.

11. The power tool according to claim 1, wherein: The motor is configured to drive a cyclic load.

12. The power tool of claim 1, further comprising a tool element, and wherein: The tool element is driven by the motor.

13. The power tool according to claim 1, wherein: The stator includes at least twenty-four slots.

14. The power tool according to claim 1, wherein: The rotor is a 4-pole rotor.

15. A power tool comprising: case; a permanent magnet synchronous reluctance motor positioned within the housing, the permanent magnet synchronous reluctance motor including a stator having a stator winding and a rotor having a plurality of slots, and a magnet positioned within each of the plurality of slots; and a tool element driven by the permanent magnet synchronous reluctance motor; wherein the plurality of grooves are curved, and The magnet in at least one slot of the plurality of slots has a span between 33% and 39% of the slot.

16. The power tool according to claim 15, wherein: The span of the magnet within each slot of the plurality of slots is less than 56% of the slot.

17. The power tool according to claim 15, wherein: The permanent magnet synchronous reluctance motor includes at least twenty-four winding slots formed in the stator, and the rotor includes at least four poles.

18. A motor assembly for a power tool, the motor assembly comprising: a stator having winding slots for receiving stator windings; as well as a rotor comprising a rotor body having a first slot positioned at a first distance from a center of the rotor body and a second slot positioned at a second distance from the center of the rotor body; the first slot and the second slot each being curved about a common point; wherein the rotor further comprises a first magnet positioned in the first slot and a second magnet positioned in the second slot, and wherein the span of the first magnet is in the range of 50% to 56% of the first slot, and the span of the second magnet is in the range of 33% to 39% of the second slot.

19. The motor assembly of claim 18, wherein: The common point is located outside the rotor body.

20. The motor assembly of claim 18, wherein: a first dimension measured between a first end of the first slot and an outer peripheral surface of the rotor body; a second dimension measured between a second end of the first slot and the outer peripheral surface of the rotor body; and The second size is equal to the first size.

21. The motor assembly of claim 18, wherein: a first dimension measured between an end of the first slot and an outer peripheral surface of the rotor body; a second dimension is measured between an end of the second slot and the outer peripheral surface of the rotor body; and The second size is equal to the first size.

22. The motor assembly of claim 18, wherein: The span of the first magnet is 53% of the first slot.

23. The motor assembly of claim 18, wherein: The span of the second magnet is 36% of the second slot.

24. The motor assembly of claim 18, wherein: The rotor further includes a third slot located a third distance from the center of the rotor body, the third slot curving about the common point; and a third magnet is positioned within the third slot.

25. The motor assembly of claim 24, wherein: The span of the third magnet is in the range of 35% to 100% of the third slot.

26. The motor assembly of claim 25, wherein: The span of the third magnet is 38% of the third slot.

27. The motor assembly of claim 18, wherein: The motor is configured to drive a cyclic load.

28. The motor assembly of claim 18, further comprising a tool element, and wherein: The tool element is driven by the motor.

29. The motor assembly of claim 18, wherein: The stator includes at least twenty-four slots.

30. The motor assembly of claim 18, wherein: The rotor is a 4-pole rotor.

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