Induction motor with collar-reinforced end ring

Abstract

An induction motor having collar-reinforced end rings is disclosed. The induction motor includes a stator and a rotor. The stator is configured to generate a rotating magnetic field. The rotor is disposed inside the stator, separated from the stator by an air gap, and configured to rotate about an axis in response to the rotating magnetic field. The rotor includes a rotor core, a plurality of end rings, and a plurality of collars. The end rings are attached at opposite ends of the rotor core. Each end ring has one of a plurality of regions disposed outside the air gap. Each region has an outer surface. The collars are attached around the outer surface of each region under a pre-stressed condition. The pre-stressed condition is configured to maintain a compressive stress in the end rings at a maximum design rotational speed of the rotor.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a system and method for an induction motor with collar reinforced end rings. BACKGROUND

[0002] Die cast type induction motors have a rotor that rotates inside a stator. The rotor includes a plurality of laminations having slots that are held by end rings. Conductors fill the slots to create a cage configuration. Such cage induction machines are widely used in industrial applications. At high operating speeds, the rotor end rings can deform due to centrifugal stresses in the end rings. The deformation can cause the end rings to bulge, potentially leading to cracks. In severe cases, the bulging can cause the end rings to contact the inner wall of the stator.

[0003] It is desirable to design a technique for manufacturing and / or operating an induction motor with collar reinforced end rings. SUMMARY

[0004] An induction motor is provided herein. The induction motor includes a stator and a rotor. The stator is configured to generate a rotating magnetic field. The rotor is disposed inside the stator, separated from the stator by an air gap, and configured to rotate about an axis in response to the rotating magnetic field. The rotor includes a rotor core, a plurality of end rings, and a plurality of collars. The plurality of end rings are attached at opposite ends of the rotor core. Each of the plurality of end rings has one of a plurality of regions disposed outside the air gap. Each of the plurality of regions has an outer surface. The plurality of collars are attached around the outer surface of each of the plurality of regions under a pre-stressed condition. The pre-stressed condition is configured to maintain a compressive stress in the plurality of end rings at a maximum design rotational speed of the rotor.

[0005] In one or more embodiments of the induction motor, the rotor includes a plurality of conductors disposed within the rotor core and connected to the plurality of end rings. The plurality of conductors applies a centrifugal force to the plurality of end rings when the rotor rotates.

[0006] In one or more embodiments of the induction motor, the plurality of collars are configured to maintain the outer surface of each of the plurality of end rings at a constant outer diameter by containing the centrifugal force of the plurality of conductors when the rotor rotates.

[0007] In one or more embodiments of the induction motor, the plurality of conductors are manufactured from copper, the plurality of end rings are manufactured from aluminum, and the plurality of collars are manufactured from stainless steel.

[0008] In one or more embodiments of the induction motor, the plurality of conductors and the plurality of end rings are manufactured from copper, and the plurality of collars are manufactured from stainless steel.

[0009] In one or more embodiments of the induction motor, the plurality of collars reduce a tensile stress in the plurality of end rings to maintain a loop stress in the plurality of end rings when the rotor is rotating.

[0010] In one or more embodiments of the induction motor, each of the plurality of collars has an interference fit with a corresponding one of the plurality of end rings to establish a pre-stressed condition.

[0011] In one or more embodiments of the induction motor, the interference fit is a press fit or a shrink fit.

[0012] In one or more embodiments, the induction motor is part of a vehicle.

[0013] A method for operating an induction motor is provided herein. The method includes generating a rotating magnetic field with a stator and rotating a rotor about an axis in response to the rotating magnetic field. The rotor is disposed in an interior of the stator and separated from the stator by an air gap. The rotor includes a rotor core, a plurality of end rings attached at opposite ends of the rotor core, wherein each of the plurality of end rings has one of a plurality of regions disposed outside the air gap, and each of the plurality of regions has an outer surface, and a plurality of collars attached about the outer surface of each region of the plurality of end rings under a pre-stressed condition. The method further includes maintaining a compressive stress in the plurality of end rings at a maximum design rotational speed of the rotor with the plurality of collars.

[0014] In one or more embodiments of the method, the rotor includes a plurality of conductors disposed within the rotor core and connected to the plurality of end rings. The method further includes applying a centrifugal force to the plurality of end rings with the plurality of conductors when the rotor is rotating.

[0015] In one or more embodiments, the method includes maintaining the outer surface of each of the plurality of end rings at a constant outer diameter by suppressing the centrifugal force of the plurality of conductors with the plurality of collars when the rotor is rotating.

[0016] In one or more embodiments, the method includes reducing a tensile stress in the plurality of end rings to maintain a loop stress in the plurality of end rings using the plurality of collars when the rotor is rotating.

[0017] In one or more embodiments of the method, the induction motor is part of a vehicle.

[0018] A method for manufacturing an induction motor is provided herein. The method includes attaching a plurality of end rings at opposite ends of a rotor core of a rotor. Each of the plurality of end rings has one of a plurality of regions. Each of the plurality of regions has an outer surface. The method includes inserting the rotor inside a stator and separated from the stator by an air gap such that each of the plurality of regions is disposed outside the air gap. The stator is configured to generate a rotating magnetic field. The rotor is rotatable about an axis in response to the rotating magnetic field. The method further includes attaching a plurality of collars about the outer surface of each of the plurality of regions under a pre-stressed condition. The pre-stressed condition is configured to maintain a compressive stress in the plurality of end rings at a maximum design rotational speed of the rotor.

[0019] In one or more embodiments, the method includes disposing a plurality of conductors within the rotor core and connecting the plurality of conductors to the plurality of end rings. The plurality of conductors apply a centrifugal force to the plurality of end rings when the rotor is rotating.

[0020] In one or more embodiments, the method includes creating the pre-stressed condition by interference fitting the plurality of collars to the plurality of end rings.

[0021] In one or more embodiments of the method, the interference fit is a press fit of the plurality of collars around the plurality of end rings.

[0022] In one or more embodiments of the method, the interference fit includes heating the plurality of collars, positioning the plurality of collars around the plurality of end rings, and cooling the plurality of collars.

[0023] In one or more embodiments of the method, the interference fit includes cooling the plurality of end rings, positioning the plurality of collars around the plurality of end rings, and warming the plurality of collars.

[0024] The present invention also discloses the following technical solutions:

[0025] Scheme 1. An induction motor comprising:

[0026] a stator configured to generate a rotating magnetic field; and

[0027] a rotor disposed inside the stator, separated from the stator by an air gap, and configured to rotate about an axis in response to the rotating magnetic field, the rotor comprising:

[0028] a rotor core;

[0029] a plurality of end rings attached at opposite ends of the rotor core, wherein each of the plurality of end rings has one of a plurality of regions disposed outside the air gap, and each of the plurality of regions has an outer surface; and

[0030] a plurality of collars attached around the outer surface of each of the plurality of regions under a prestressed condition, wherein the prestressed condition is configured to maintain compressive stresses in the plurality of end rings at a maximum design rotational speed of the rotor.

[0031] Scheme 2. The induction motor of Scheme 1, wherein the rotor further comprises a plurality of conductors disposed within the rotor core and connected to the plurality of end rings, wherein the plurality of conductors impart centrifugal forces to the plurality of end rings when the rotor rotates.

[0032] Scheme 3. The induction motor of Scheme 2, wherein the plurality of collars are configured to maintain the outer surface of each of the plurality of end rings at a constant outer diameter by suppressing the centrifugal forces of the plurality of conductors when the rotor rotates.

[0033] Scheme 4. The induction motor of Scheme 2, wherein the plurality of conductors are manufactured from copper, the plurality of end rings are manufactured from aluminum, and the plurality of collars are manufactured from stainless steel.

[0034] Scheme 5. The induction motor of Scheme 2, wherein the plurality of conductors and the plurality of end rings are manufactured from copper, and the plurality of collars are manufactured from stainless steel.

[0035] Scheme 6. The induction motor of Scheme 1, wherein the plurality of collars reduce tensile stresses in the plurality of end rings to maintain hoop stresses in the plurality of end rings when the rotor rotates.

[0036] Scheme 7. The induction motor of Scheme 1, wherein each of the plurality of collars has an interference fit with a corresponding one of the plurality of end rings to establish the prestressed condition.

[0037] Scheme 8. The induction motor of Scheme 7, wherein the interference fit is a press fit or a shrink fit.

[0038] Scheme 9. The induction motor of Scheme 1, wherein the induction motor is part of a vehicle.

[0039] Scheme 10. A method for operating an induction motor, the method comprising:

[0040] generating a rotating magnetic field with a stator;

[0041] rotating the rotor about an axis in response to the rotating magnetic field, wherein the rotor is disposed in an interior of the stator and separated from the stator by an air gap, the rotor comprising:

[0042] a rotor core;

[0043] a plurality of end rings attached at opposite ends of the rotor core, wherein each of the plurality of end rings has one of a plurality of regions disposed outside the air gap, and each of the plurality of regions has an outer surface; and

[0044] a plurality of collars attached about the outer surface of each region of the plurality of end rings under a pre-stressed condition; and

[0045] maintaining compressive stresses in the plurality of end rings at a maximum design rotational speed of the rotor with the plurality of collars.

[0046] Scheme 11. The method of Scheme 10, wherein the rotor further comprises a plurality of conductors disposed within the rotor core and connected to the plurality of end rings, the method further comprising:

[0047] applying centrifugal forces to the plurality of end rings with the plurality of conductors when the rotor is rotating.

[0048] Scheme 12. The method of Scheme 11, further comprising:

[0049] maintaining the outer surface of each of the plurality of end rings at a constant outer diameter by suppressing the centrifugal forces of the plurality of conductors with the plurality of collars when the rotor is rotating.

[0050] Scheme 13. The method of Scheme 10, further comprising:

[0051] reducing tensile stresses in the plurality of end rings to maintain hoop stresses in the plurality of end rings using the plurality of collars when the rotor is rotating.

[0052] Scheme 14. The method of Scheme 10, wherein the induction motor is part of a vehicle.

[0053] Scheme 15. A method for manufacturing an induction motor, the method comprising:

[0054] attaching a plurality of end rings at opposite ends of a rotor core of a rotor, wherein each of the plurality of end rings has one of a plurality of regions, and each of the plurality of regions has an outer surface;

[0055] inserting the rotor inside the stator and separating the rotor from the stator by an air gap, such that each of the plurality of regions is disposed outside the air gap, wherein the stator is configured to generate a rotating magnetic field and the rotor is rotatable about an axis in response to the rotating magnetic field; and

[0056] attaching a plurality of collars about the outer surface of each of the plurality of regions under a pre-stressed condition, wherein the pre-stressed condition is configured to maintain compressive stresses in the plurality of end rings at a maximum design rotational speed of the rotor.

[0057] Scheme 16. The method of scheme 15, further comprising:

[0058] disposing a plurality of conductors within the rotor core; and

[0059] connecting the plurality of conductors to the plurality of end rings, wherein the plurality of conductors impart a centrifugal force to the plurality of end rings when the rotor is rotating.

[0060] Scheme 17. The method of scheme 16, further comprising:

[0061] generating the pre-stressed condition by interference fitting the plurality of collars to the plurality of end rings.

[0062] Scheme 18. The method of scheme 17, wherein the interference fit is a press fit of the plurality of collars about the plurality of end rings.

[0063] Scheme 19. The method of scheme 17, wherein the interference fit comprises:

[0064] heating the plurality of collars;

[0065] positioning the plurality of collars about the plurality of end rings; and

[0066] cooling the plurality of collars.

[0067] Scheme 20. The method of scheme 17, wherein the interference fit comprises:

[0068] cooling the plurality of end rings;

[0069] positioning the plurality of collars about the plurality of end rings; and

[0070] warming the plurality of collars.

[0071] The above features and advantages and other features and advantages of the present disclosure are readily apparent from the following detailed description of the best modes for carrying out the present disclosure when taken in connection with the accompanying drawings. Attached Figure Description

[0072] Figure 1 It is a schematic plan view illustrating the context of a vehicle according to one or more exemplary embodiments.

[0073] Figure 2 This is a schematic cross-sectional view of an induction motor according to one or more exemplary embodiments.

[0074] Figure 3 It is a schematic partially exploded perspective view of a rotor according to one or more exemplary embodiments.

[0075] Figure 4 This is a schematic cross-sectional view of a portion of an end ring according to one or more exemplary embodiments.

[0076] Figure 5 This is a schematic enlarged partial cross-sectional view of a sample from an end ring according to one or more exemplary embodiments.

[0077] Figure 6 It is a graph of radial pressure estimation at the inner diameter of the end ring on a rotor according to one or more exemplary embodiments.

[0078] Figure 7 It is a graph showing the estimation of circumferential stress on a rotor according to one or more exemplary embodiments.

[0079] Figure 8 It is a flowchart of an operation method according to one or more exemplary embodiments.

[0080] Figure 9 This is a flowchart of a method for manufacturing an induction motor according to one or more exemplary embodiments.

[0081] Figure 10 This is a flowchart of a method for attaching a collar to an end ring according to one or more exemplary embodiments.

[0082] Figure 11 This is a flowchart of another method for attaching a collar to an end ring according to one or more exemplary embodiments. Detailed Implementation

[0083] Embodiments of the present disclosure provide a design, an operating method, and a method for manufacturing an induction motor that utilizes a thin-walled collar around the outer diameter of a rotor end ring. The collar on the outer diameter experiences high centrifugal forces and stresses at high rotational speeds (e.g., > 12,000 revolutions per minute). The centrifugal forces are generated by the rotor conductors and by the enclosed mass of the end ring. In various embodiments, the conductors are copper bars overcast by aluminum end rings. The collar can be manufactured from stainless steel and then press fit or heat shrink fit onto the end ring. The stainless steel collar allows the use of high electrical conductivity pure aluminum or pure copper in high speed mixing rotors.

[0084] By incorporating a thin-walled collar on the outer diameter of the end ring, the maximum rotational speed of a die cast hybrid induction rotor is improved. The collar enables the end ring to withstand higher hoop stresses and centrifugal forces compared to existing designs based on low strength materials. For example, a pure aluminum or pure copper end ring alone is susceptible to distortion from large rotational stresses caused by the high peripheral velocity of the rotor. The stresses in a hybrid rotor can be greater due to the inertia of the copper bar type conductors incorporated in the rotor. The thin-walled collar of a hybrid induction rotor allows the rotor to reach higher rotational speeds specified for electric vehicles. Implementing an induction motor in an electric vehicle also reduces the reliance on permanent magnet electric motors. Hoop stress is a force applied circumferentially (perpendicular to the axis of rotation) in both directions on the parts of a cylinder.

[0085] Reference Figure 1 shows a schematic plan view of an environment of a vehicle 80, in accordance with one or more example embodiments. The vehicle 80 generally includes a rechargeable energy storage system 90, a transmission 92, a wiring harness 94, and an induction motor 100.

[0086] The vehicle 80 implements a motor-based machine. The vehicle 80 can include, but is not limited to, a mobile object such as an automobile (e.g., an electric vehicle or a hybrid vehicle), a truck, a motorcycle, a boat, a train, and / or an airplane. In some embodiments, the vehicle 80 can include a stationary object such as a backup power system and / or an industrial machine. Other types of vehicles 80 can be implemented to meet design criteria for a particular application.

[0087] The rechargeable energy storage system 90 implements a battery pack. The rechargeable energy storage system 90 typically operates to store energy used by the induction motor 100. In charging mode, the rechargeable energy storage system 90 can receive current from a generator and / or an external source. In discharging mode, the rechargeable energy storage system 90 can supply current to the induction motor 100. The rechargeable energy storage system 90 may include multiple battery modules electrically connected in series and / or parallel between the positive and negative terminals of the battery pack. In various embodiments, the rechargeable energy storage system 90 can provide an approximate 200 to 1,000 volt DC (direct current) potential between the positive and negative terminals of the battery pack. Other battery voltages may be implemented to meet the design criteria of a specific application. The rechargeable energy storage system 90 may be physically and electrically connected to a wiring harness 94.

[0088] The transmission 92 implements a torque control mechanism. The transmission 92 typically operates to transmit mechanical torque from the induction motor 100 to the wheels of the vehicle 80. In various embodiments, the transmission 92 may implement gear transmission. In other embodiments, the transmission 92 may implement a continuously variable transmission (CVT).

[0089] Wiring harness 94 implements a wire harness. Wiring harness 94 is typically operated to carry power between rechargeable energy storage system 90 and induction motor 100. In operation, power can flow along wiring harness 94 from rechargeable energy storage system 90 to induction motor 100.

[0090] An induction motor 100 is implemented as a drive motor for a vehicle 80. The induction motor 100 typically operates to provide rotation and torque to drive the wheels of the vehicle 80. The electricity consumed by the induction motor 100 can be provided by a rechargeable energy storage system 90. The induction motor 100 typically has a stator and a rotor. The rotor may be disposed within the stator and separated from the stator by an air gap.

[0091] refer to Figure 2 The diagram shows a schematic cross-sectional view of an example embodiment of an induction motor 100 according to one or more exemplary embodiments. The induction motor 100 generally includes a stator 102 and a rotor 106.

[0092] Stator 102 implements an induction motor stator. Stator 102 typically operates to cause rotor 106 to rotate. Stator 102 may include multiple windings and multiple laminations extending inward toward rotor 106. Multiphase alternating current driven through the windings typically establishes a rotating magnetic field 104. The inner diameter of stator 102 and the outer diameter of rotor 106 are separated by an air gap 108.

[0093] A rotating magnetic field 104 is generated by the stator 102. The rotating magnetic field 104 rotates about the axis 110 at a synchronous speed (e.g., Ns). The synchronous speed Ns is variable by changing the frequency of the alternating current.

[0094] The rotor 106 implements an induction motor rotor. The rotor 106 is disposed in the interior of the stator 102. The rotor 106 can include a rotor core 112, a plurality of end rings 114a-114b, a plurality of collar rings 120a-120b, and a plurality of conductors 122a-122n. The rotor 106 is generally operative to convert the rotating magnetic field 104 into mechanical motion about the axis 110. The rotor 106 rotates at a rotor speed (e.g., Nr) that is less than the synchronous speed Ns. The rotor 106 generally has a maximum design rotational speed (e.g., ω max ) at which the rotor 106 can operate without self-induction damage.

[0095] The air gap 108 can provide a physical gap between an inner surface of the stator 102 and an outer surface of the rotor 106. The size of the air gap 108 between the stator 102 and the rotor 106 can be less than one millimeter (mm). In some embodiments, the size of the air gap 108 can be less than 0.5 mm (e.g., 0.2 mm to 0.45 mm). Other sizes of the air gap 108 can be implemented to meet design criteria for a particular application.

[0096] The rotor core 112 implements a central portion of the rotor 106. The rotor core 112 is operative to rotate about the axis 110 at the rotor speed Ns. The rotor core 112 can transfer mechanical torque generated by the rotor 106 to the transmission 92.

[0097] The end rings 114a-114b implement electrical connections attached at opposite ends of the rotor core 112. The end rings 114a-114b physically and electrically connect the conductors 122a-122n at opposite longitudinal ends of the conductors 122a-122n. The end rings 114a-114b have respective regions 116a-116b disposed outside the air gap 108. Each region 116a-116b has an outer surface 118a-118b. The end rings 114a-114b generally cast over the outer ends of the conductors 122a-122n. In various embodiments, the end rings 114a-114b are manufactured from aluminum or copper. Other materials can be used to meet design criteria for a particular application.

[0098] The collar rings 120a-120b implement thin-walled compression rings. The collar rings 120a-120b are attached about respective outer surfaces 118a-118b within the regions 116a-116b of the end rings 114a-114b under a pre-stressed condition. The pre-stressed condition is configured to maintain the outer surfaces 118a-118b of the end rings 114a-114b in a substantially parallel orientation with the axis 110 at the maximum design rotational speed ω maxCompression stresses in the end rings 114a-114b are maintained. The pre-stressed condition can be achieved by shrink fitting the collars 120a-120b onto the end rings 114a-114b.

[0099] The conductors 122a-122n implement electrical conductors. The conductors 122a-122n are disposed within the rotor core 112 around an outer circumference of the rotor core 112. The conductors 122a-122n are physically and electrically connected to the end rings 114a-114b. The rotating magnetic field 104 is configured to induce currents in the end rings 114a-114b and the conductors 122a-122n as the rotating magnetic field 104 cuts through the conductors 122a-122n. The induced currents cause the rotor 106 to rotate. As the rotor 106 rotates, the conductors 122a-122n exert centrifugal forces to the end rings 114a-114b.

[0100] Referring to Figure 3 , a schematic, partially exploded perspective view of an example implementation of the rotor 106 is shown in accordance with one or more example embodiments. The rotor core 112 includes the conductors 122a-122n disposed between the end rings 114a-114b. The first end ring 114a has a first region 116a on a first outer surface 118a. The second end ring 114b has a second region 116b on a second outer surface 118b. A second collar 120b is disposed around the second outer surface 118b of the second end ring 114b within the second region 116b. Likewise, a first collar 120a (see Figure 2 ) is disposed around the first outer surface 118a of the first end ring 114a within the first region 116a.

[0101] The collars 120a-120b shrink fit (or press fit) onto the end rings 114a-114b of the die cast hybrid rotor 106 to improve the rotational performance of the induction motor 100. The die cast hybrid rotor 106 can be an aluminum rotor or a copper rotor. The collars 120a-120b can be high strength stainless steel collars.

[0102] The collars 120a-120b are installed on the end rings 114a-114b under a pre-stressed condition to permit high speed operation of the rotor 106. The collars 120a-120b provide the low strength pure aluminum or low strength pure copper end rings 114a-114b with the ability to resist centrifugal loads exerted at a specified high rotational speed. The high strength stainless steel collars 120a-120b shrink fit and / or press fit onto the end rings 114a-114b to induce compression stresses that overcome centrifugal tensile stresses on the aluminum die cast or copper die cast end rings 114a-114b, particularly the forces generated by the conductors 122a-122n that form the multi-material cage configuration.

[0103] Referring to Figure 4FIG. 1 shows a schematic cross-sectional view of an example portion of a first end ring 114a according to one or more example embodiments. A portion of a first collar 120a is shown mounted on the first end ring 114a.

[0104] The end rings 114a-114b rotate at an angular velocity (ω) and are subjected to a radial pressure (e.g., centrifugal force P) caused by the centrifugal effect of the conductors 122a-122n in the lamination slots and the rotating mass of the end rings 114a-114b at a sample radius (e.g., r). A hoop tension (e.g., F) is established due to rotation. The collars 120a-120b exert a compressive pressure (e.g., C) to prevent the end rings 114a-114b from bulging against the radial pressure P and the hoop tension F.

[0105] Referring to Figure 5 FIG. 2 shows a schematic enlarged partial cross-sectional view of an example sample 124 from the first end ring 114a according to one or more example embodiments. The first end ring 114a has an inner radius (e.g., Ri), an outer radius (e.g., Ro), and a constant outer diameter (e.g., D). The sample 124 at a sample radius r between the inner radius Ri and the outer radius Ro of the end ring 114a can be considered. The sample 124 generally has a sample radial thickness (e.g., δr) and a sample angular width (e.g., δθ).

[0106] The radial stress (e.g., σ r and the tangential stress (σ r + δσ r ) and the tangential stress (σ θ ) (inertial stress) affect the deformation of the first end ring 114a made of either a low-strength pure aluminum material or a low-strength pure copper material. If the inner radius Ri and / or the outer radius Ro of the first end ring 114a changes when rotating at a uniform angular velocity, then deformation occurs. Deformation generally causes small parts to crack and separate from the first end ring 114a. Similar situations exist for the second end ring 114. Thus, the collars 120a-120b are utilized to prevent deformation and thus maintain the integrity of the end rings 114a-114b.

[0107] Referring to Figure 6 FIG. 3 shows a chart 140 of an example radial pressure estimate at the inner diameter of an end ring (e.g., 114a) on the rotor 106 according to one or more example embodiments. An axis 142 of the chart 140 shows rotational speed in kilo revolutions per minute. An axis 144 of the chart 140 shows radial pressure in mega Pascals (MPa). A line 146 illustrates the yield strength of pure aluminum. The yield strength line 146 is slightly less than 8 MPa.

[0108] The estimated hoop stress of the end ring (e.g., 114a) without a collar is shown as typical stress points 166a-166n. The typical stress points 166a-166n can indicate that the end ring 114a experiences positive (expansion) hoop stress at speeds greater than 10,000 revolutions per minute. The estimated hoop stress of the end ring 114a with the collar 120a installed is shown as improved stress points 168a-168n. The improved stress points 168a-168n can indicate that the end ring 114a experiences negative (compression) hoop stress at speeds up to and above 20,000 revolutions per minute. The collar installed under pre-stressed conditions permits the end ring of the rotor to operate at higher speeds than the end ring operates without a collar.

[0109] Referring to Figure 7 FIG. 16 shows a graph 160 of example hoop stress estimates on the rotor 106, in accordance with one or more example embodiments. An axis 162 of the graph 160 shows speed in thousands of revolutions per minute. An axis 164 of the graph 160 shows hoop stress in megaPascals (MPa).

[0110] The estimated hoop stress of the end ring (e.g., 114a) without a collar is shown as typical stress points 166a-166n. The typical stress points 166a-166n can indicate that the end ring 114a experiences positive (expansion) hoop stress at speeds greater than 10,000 revolutions per minute. The estimated hoop stress of the end ring 114a with the collar 120a installed is shown as improved stress points 168a-168n. The improved stress points 168a-168n can indicate that the end ring 114a experiences negative (compression) hoop stress at speeds up to and above 20,000 revolutions per minute. The collar installed under pre-stressed conditions permits the end ring of the rotor to operate at higher speeds than the end ring operates without a collar.

[0111] Referring to Figure 8 FIG. 18 shows a flowchart of an example method of operation 180, in accordance with one or more example embodiments. The method of operation (or process) 180 is performed by the induction motor 100. The method 180 includes a step 182, a step 184, a step 186, a step 188, a step 190, and a step 192. This sequence of steps is shown as a representative example. Other sequences of steps can be implemented to meet the criteria of a particular application.

[0112] In step 182, the stator 102 generates a rotating magnetic field 104. In step 184, the rotating magnetic field 104 causes the rotor 106 to rotate about the axis 110. In step 186, the rotation of the end rings 114a-114b and the conductors 122a-122n apply centrifugal forces to the end rings 114a-114b and the collar 120a-120b.

[0113] In step 188, the high-strength collar 120a-120b maintains compressive stresses in the regions 116a-116b of the low-strength end rings 114a-114b at the maximum design rotational speed of the rotor 106. In step 190, the collar 120a-120b also maintains the outer surfaces 118a-118b of the end rings 114a-114b at a constant diameter D. In step 192, the collar 120a-120b reduces tensile stresses in the end rings 114a-114b to maintain hoop stresses in the end rings 114a-114b. Generally, steps 188, 190, and 192 are performed simultaneously.

[0114] Referring to Figure 9 FIG. 1 shows an example induction motor 100 in accordance with one or more example embodiments. The motor 100 includes a stator 102 and a rotor 106. The stator 102 includes a stator core 104. The rotor 106 includes a rotor core 112 and end rings 114a-114b. The rotor 106 also includes a collar 120a-120b and conductors 122a-122n. The motor 100 is shown in a cross-sectional view taken along a plane that is perpendicular to an axis 110 of the motor 100.

[0115] In step 202, the laminations can be attached to the rotor core 112. In step 204, the conductors 122a-122n can be disposed in the slots of the laminations within the rotor core 112. In step 206, at opposite ends of the rotor core 112 of the rotor 106, end rings 114a-114b are attached to the conductors 122a-122n. Each end ring 114a-114b has a respective region 116a-116b. Each region 116a-116b has a respective outer surface 118a-118b.

[0116] In step 208, the rotor 106 is inserted inside the stator 102 and separated from the stator 102 by the air gap 108 such that at least a portion of each region 116a-116b is disposed outside the air gap 108. In step 210, a collar 120a-120b is attached around the outer surface 118a-118b of each region 116a-116b under a pre-stressed condition. The pre-stressed condition is configured to maintain a compressive stress in the end ring 114a-114b at a maximum design rotational speed of the rotor 106. The pre-stressed condition is achieved by interference fitting the collar 120a-120b to the end ring 114a-114b. After the interference fit, the diameter of the collar 120a-120b increases slightly from a relaxed diameter (e.g., D 轴环 ) and the diameter of the end ring 114a-114b decreases slightly from a relaxed diameter (e.g., D 端部环 ). An assembled diameter (e.g., D 组装 ) at the interface between the collar 120a-120b and the end ring 114a-114b can be greater than the relaxed diameter of the collar 120a-120b and less than the relaxed diameter of the end ring 114a-114b (D 轴环 < D 组装 < D 端部环 ). In step 212, an end shield can be attached to provide a protective cover on opposite ends of the rotor 106.

[0117] Referring to Figure 10 , a flowchart of an example step 210a to attach the collar 120a-120b on the end ring 114a-114b is shown, in accordance with one or more example embodiments. Step 210a can be a variation of step 210 to interference fit the collar 120a-120b by shrink fitting the collar 120a-120b. Step (or process) 210a can be performed with ordinary induction motor manufacturing tools. Step 210a includes step 222, step 224, and step 226.

[0118] In step 222, the collar 120a-120b can be heated to expand the inner radius. In step 224, the expanded collar 120a-120b is positioned around the end ring 114a-114b at the region 116a-116b. In step 226, the collar 120a-120b is cooled. The cooling generally causes the inner radius of the collar 120a-120b to shrink and establish the pre-stressed condition on the end ring 114a-114b.

[0119] Referring to Figure 11, a flowchart showing example steps 210b to attach the collar 120a-120b on the end ring 114a-114b, in accordance with one or more example embodiments. The steps 210b can be a variation of the steps 210 to interference fit the collar 120a-120b by shrink fitting the end ring 114a-114b. The steps (or process) 210b can be performed with common induction motor manufacturing tools. The steps 210b include step 242, step 244, and step 246.

[0120] In step 242, the rotor 106 is cooled to reduce the outer radius of the end ring 114a-114b. In step 244, the collar 120a-120b is positioned around the end ring 114a-114b at the region 116a-116b. In step 246, the rotor 106 is warmed to expand the outer radius of the end ring 114a-114b. The warming generally causes the outer diameter of the end ring 114a-114b to expand and establish a pre-stressed condition on the collar 120a-120b. In various embodiments, the interference fit can be achieved with a combination of press fitting the collar 120a-120b to the end ring 114a-114b, heating the collar 120a-120b for shrink fitting, and / or cooling the end ring 114a-114b for shrink fitting.

[0121] While the best mode has been described in detail with respect to specific embodiments of the disclosure, those skilled in the art who attach significance to the precharacterizing part of the claims will realize that other alternative designs and embodiments in accordance with the disclosure are possible and fall within the scope of the appended claims.

Claims

1. An induction motor, comprising: The stator is configured to generate a rotating magnetic field; as well as A rotor, disposed inside the stator, separated from the stator by an air gap, and configured to rotate about an axis in response to the rotating magnetic field, the rotor comprising: Rotor core; A plurality of end rings are attached to opposite ends of the rotor core, wherein each of the plurality of end rings has one of a plurality of regions disposed outside the air gap, each of the plurality of regions having an outer surface, and the outer surface being aligned with the inner diameter of the air gap; and Multiple collars are attached to the outer surface of each of the multiple regions outside the air gap under prestressed conditions, wherein the prestressed conditions are configured to maintain compressive stress in the multiple end collars at the maximum design speed of the rotor, and the multiple collars extend radially beyond the outer diameter of the air gap.

2. The induction motor of claim 1, wherein, The rotor further includes a plurality of conductors disposed within the rotor core and connected to the plurality of end rings, wherein, when the rotor rotates, the plurality of conductors apply centrifugal force to the plurality of end rings.

3. The induction motor of claim 2, wherein, The plurality of collars are configured to maintain the outer surface of each of the plurality of end rings at a constant outer diameter by suppressing the centrifugal force of the plurality of conductors when the rotor rotates.

4. The induction motor of claim 2, wherein, The plurality of conductors are made of copper, the plurality of end rings are made of aluminum, and the plurality of collars are made of stainless steel.

5. The induction motor according to claim 2, wherein, The plurality of conductors and the plurality of end rings are made of copper, and the plurality of collars are made of stainless steel.

6. The induction motor according to claim 1, wherein, When the rotor rotates, the plurality of collars reduce the tensile stress in the plurality of end rings to maintain the circumferential stress in the plurality of end rings.

7. The induction motor according to claim 1, wherein, Each of the plurality of collars has an interference fit with a corresponding one of the plurality of end rings to establish the prestress condition.

8. The induction motor according to claim 7, wherein, The interference fit is either a compression fit or a contraction fit.

9. The induction motor according to claim 1, wherein, The induction motor is part of a vehicle.

10. A method for operating an induction motor, the method comprising: A rotating magnetic field is generated using the stator; The rotor rotates about an axis in response to the rotating magnetic field, wherein the rotor is disposed inside the stator and separated from the stator by an air gap, the rotor comprising: Rotor core; A plurality of end rings are attached to opposite ends of the rotor core, wherein each of the plurality of end rings has one of a plurality of regions disposed outside the air gap, each of the plurality of regions having an outer surface, and the outer surface being aligned with the inner diameter of the air gap; and A plurality of collars, attached under prestressed conditions to the outer surface of each region of the plurality of end rings outside the air gap, wherein the plurality of collars extend radially beyond the outer diameter of the air gap; and The multiple shaft collars are used to maintain the compressive stress in the multiple end rings at the maximum design speed of the rotor.

11. The method according to claim 10, wherein, The rotor further includes a plurality of conductors disposed within the rotor core and connected to the plurality of end rings, and the method further includes: When the rotor rotates, centrifugal force is applied to the multiple end rings using the multiple conductors.

12. The method of claim 11, further comprising: When the rotor rotates, the outer surface of each of the plurality of end rings is kept at a constant outer diameter by using the plurality of collars to suppress the centrifugal force of the plurality of conductors.

13. The method of claim 10, further comprising: When the rotor rotates, the plurality of collars are used to reduce the tensile stress in the plurality of end rings in order to maintain the circumferential stress in the plurality of end rings.

14. The method of claim 10, wherein, The induction motor is part of a vehicle.

15. A method for manufacturing an induction motor, the method comprising: Multiple end rings are attached to opposite ends of the rotor core of the rotor, wherein each of the multiple end rings has one of a plurality of regions, and each of the plurality of regions has an outer surface; The rotor is inserted into the stator and separated from it through an air gap, such that each of the plurality of regions is disposed outside the air gap, wherein the outer surface of each of the plurality of end rings is aligned with the inner diameter of the air gap, the stator is configured to generate a rotating magnetic field, and the rotor is capable of rotating about an axis in response to the rotating magnetic field; and When the rotor is within the stator, a plurality of collars are attached to the outer surface of each of the plurality of regions outside the air gap under prestress conditions, wherein the prestress conditions are configured to maintain compressive stress in the plurality of end collars at the maximum design speed of the rotor, and the plurality of collars extend radially beyond the outer diameter of the air gap.

16. The method of claim 15, further comprising: Multiple conductors are arranged inside the rotor core; as well as The plurality of conductors are connected to the plurality of end rings, wherein, when the rotor rotates, the plurality of conductors apply centrifugal force to the plurality of end rings.

17. The method of claim 16, further comprising: The prestress condition is generated by interfering the plurality of collars with the plurality of end rings.

18. The method according to claim 17, wherein, The interference fit is a press fit between the plurality of collars and the plurality of end rings.

19. The method of claim 17, wherein, The interference fit includes: Heating the plurality of collars; Positioning the plurality of collars around the plurality of end rings; and Cool the plurality of collars.

20. The method of claim 17, wherein, The interference fit includes: Cooling the plurality of end rings; Positioning the plurality of collars around the plurality of end rings; and This warms up the plurality of collars.

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