Rotor cooling with thermally conductive material

Abstract

A rotor core for an electric machine includes a core stack comprising a plurality of identical laminated plates, each laminated plate including a plurality of magnet slots formed therein, the magnet slots of each laminated plate being axially aligned and adapted to support a plurality of permanent magnets therein, and a number of thermally conductive inserts extending axially through the core stack and adapted to conduct heat outward from an interior of the core stack toward a distal end of the core stack.

Description

Technical Field

[0001] This disclosure relates to a permanent magnet rotor for an electric motor used in automobiles. Background Technology

[0002] A permanent magnet motor is an AC motor that uses magnets embedded in or attached to the surface of the rotor. The magnets generate a constant magnetic flux, unlike induction motors which require a stator magnetic field connected to the rotor to generate flux. Permanent magnet motors can be divided into two main categories: surface permanent magnet motors (SPMs) and internal permanent magnet motors (IPMs). Both types of permanent magnet motors generate magnetic flux through permanent magnets fixed to or inside the rotor.

[0003] SPM motors have magnets fixed to the outside of the rotor surface. Due to this mechanical mounting, they are less mechanically strong than IPM motors. This reduced mechanical strength limits the motor's maximum safe mechanical speed. Additionally, these motors exhibit a very limited magnetic saliency ratio. The inductance measured at the rotor terminals is consistent regardless of the rotor position. Due to this near-uniform saliency ratio, SPM motor design relies heavily, if not entirely, on the magnetic torque component to generate torque.

[0004] IPM motors embed permanent magnets within the rotor itself. Unlike SPM motors, the placement of the permanent magnets gives IPM motors excellent mechanical properties, making them suitable for operation at very high speeds. These motors are also defined by their relatively high saliency ratio. Due to their saliency, internal permanent magnet motors have the ability to generate torque by utilizing the motor's magnetic properties and reluctance torque components. These characteristics are advantageous when using IPM motors in automotive applications.

[0005] In a permanent magnet motor, the magnetic flux is generated by a magnet. The magnetic flux field follows a specific path and can be enhanced or suppressed. Increasing or enhancing the magnetic flux field will allow the motor to temporarily increase torque production. Counteracting the magnetic flux field will cancel out the motor's existing magnetic field. A reduced magnetic field will limit torque production.

[0006] Permanent magnets are not permanent and their capabilities are limited. Certain forces can be applied to these materials to demagnetize them. In other words, the magnetism of permanent magnet materials can be removed. Permanent magnets can be demagnetized if the material is subjected to significant stretching or is allowed to reach very high temperatures.

[0007] High temperatures force the magnetic particles within a permanent magnet to be agitated. Magnetic dipoles are capable of withstanding a certain amount of thermal agitation. However, even when stored at room temperature, prolonged agitation will weaken the magnet's strength. Furthermore, all magnetic materials have a threshold known as the "Curie temperature," which defines the temperature at which thermal agitation causes complete demagnetization of the material.

[0008] A key property of stable magnetic materials is maintaining the rotation of all their domain atoms in the same direction. When a magnet is exposed to high temperatures, the balance between temperature and the magnetic atoms is disrupted, thus affecting their magnetism. In other words, tiny magnetic atoms themselves act like tiny magnets, collectively forming a huge magnetic field. When they are randomly oriented in different directions, the total magnetism is zero.

[0009] Higher temperatures cause magnetic domains to move faster and become more disordered. Depending on the degree of temperature increase, magnet strength may be temporarily reduced or permanently damaged. Conversely, cooling a magnet can give it a stronger magnetic field, where the magnet atoms vibrate less and the magnetic field becomes more stably focused in a given direction. Assuming the motor operates within its intended design window, the decrease in magnetic flux density is temporary and will begin to recover as the magnet cools. However, if the maximum temperature rating of the magnet is exceeded, partial demagnetization occurs, permanently altering the motor's performance. Therefore, while current motor rotors used in automotive applications fulfill their intended purpose, a new and improved rotor is needed, incorporating thermally conductive materials and cooling channels formed therein to more evenly distribute heat generated within the rotor core and reduce the maximum temperature the rotor core experiences. Summary of the Invention

[0010] According to several aspects of this disclosure, a rotor core for an electric motor in an automobile includes a core stack comprising a plurality of identical laminates, each laminate including a plurality of magnet slots formed therein, the magnet slots of each laminate being axially aligned and adapted to support a plurality of permanent magnets therein, and a plurality of thermal inserts extending axially through the core stack and adapted to conduct heat from the interior of the core stack outward toward the distal end of the core stack.

[0011] According to another aspect, each of the multiple thermally conductive inserts includes a single column that extends axially through the entire length of the core stack.

[0012] According to another aspect, each of the plurality of laminates includes a plurality of openings formed therein, wherein when the plurality of laminates are assembled to form a core stack, the plurality of openings in each of the plurality of laminates are axially aligned and define a plurality of axial cavities extending axially through the core stack, and each of the plurality of thermally conductive inserts includes a row of cast-in thermally conductive material in one of the plurality of axial cavities.

[0013] According to another aspect, each of the plurality of laminates includes a plurality of openings formed therein, wherein when the plurality of laminates are assembled to form a core stack, the plurality of openings in each of the plurality of laminates are axially aligned and define a plurality of axial cavities extending axially through the core stack, and each of the plurality of thermally conductive inserts includes a column of thermally conductive material inserted into one of the plurality of axial cavities.

[0014] According to another aspect, each of the multiple thermal inserts includes multiple column segments that are axially aligned and extend axially through the entire length of the core stack, with each column segment extending through a portion of the multiple laminates.

[0015] According to another aspect, each of the multiple thermal inserts includes multiple strips that are axially aligned and extend axially through the entire length of the core stack, with one strip of each of the multiple thermal inserts positioned within each of the multiple laminates.

[0016] According to another aspect, each of the multiple heat-conducting inserts includes a coolant channel that extends axially through the entire length of the rotor.

[0017] According to another aspect, the coolant passage within each of the plurality of heat-conducting inserts is connected to a central coolant supply source, wherein coolant is supplied to the coolant passage of each of the plurality of heat-conducting inserts at a first distal end of the rotor and exits the coolant passage of each of the plurality of heat-conducting inserts at a second distal end of the rotor.

[0018] According to another aspect, each of the plurality of thermally conductive inserts is positioned such that the distance between the outer edge of each of the plurality of thermally conductive inserts and any portion of any of the plurality of magnet slots is at least 2 mm, and the distance between the outer edge of each of the plurality of thermally conductive inserts and the inner diameter of the core stack is at least 2 mm.

[0019] Further areas of application will become apparent from the description provided herein. It should be understood that the specification and specific embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0020] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0021] Figure 1 This is a perspective view of the core stack of the rotor of an electric motor for use in an automobile, according to an exemplary embodiment.

[0022] Figure 2A yes Figure 1 An end view of an exemplary embodiment of the core stack shown;

[0023] Figure 2B yes Figure 2A A magnified view of a portion;

[0024] Figure 3A This is an end view of another exemplary embodiment of the chip stack;

[0025] Figure 3B yes Figure 3A A magnified view of a portion;

[0026] Figure 4 This is a schematic diagram of a rotor according to an exemplary embodiment, the rotor including coolant passages and a central cooling system;

[0027] Figure 5A yes Figure 1 An end view of an exemplary embodiment of the core stack shown, wherein the thermally conductive insert includes coolant channels formed therein;

[0028] Figure 5B yes Figure 5A A magnified view of a portion;

[0029] Figure 6A yes Figure 3A An end view of an exemplary embodiment of the core stack shown, wherein the thermally conductive insert includes coolant channels formed therein;

[0030] Figure 6B yes Figure 6A A magnified view of a portion;

[0031] Figure 7A yes Figure 6A An end view of an exemplary embodiment of the core stack shown, wherein the coolant channels include radially outwardly extending portions;

[0032] Figure 7B yes Figure 7A A magnified view of a portion;

[0033] Figure 8A This is a perspective view of a one-piece thermal conductive insert according to an exemplary embodiment;

[0034] Figure 8B This is a perspective view of a thermally conductive insert including column segments according to another exemplary embodiment; and

[0035] Figure 8C This is a perspective view of a core stack according to another exemplary embodiment, wherein one laminate of the core stack is partially removed and the core stack includes multiple rows of multiple thermally conductive inserts. Detailed Implementation

[0036] The following description is merely exemplary in nature and is not intended to limit this disclosure, application, or use.

[0037] See Figure 1The rotor core 10 for an electric motor in an automobile includes a core stack 12, which comprises a plurality of identical laminates 14. The rotor core 10 originates from an electric motor within the automobile, such as, but not limited to, a starter motor, alternator, starter / generator, or other electric motor. Each laminate 14 is made of a ferrous material, such as, but not limited to, steel or non-oriented electrical steel. The laminates 14 are arranged adjacent to each other along a central axis 16 to define the core stack 12.

[0038] See Figure 2A Each laminate 14 includes a plurality of holes 17 formed therein. The laminates 14 are aligned relative to each other along a central axis 16 such that the holes 17 of each laminate 14 are axially aligned with corresponding holes 17 in adjacent laminates 14 to define a plurality of magnet slots 18. The magnet slots 18 extend axially through the core stack 12 parallel to the central axis 16. The magnet slots 18 are adapted to support a plurality of permanent magnets therein.

[0039] exist Figure 1 and Figure 2A In the exemplary embodiment shown, the core stack 12 includes eight sets of symmetrical magnet slots 18, which are uniformly spaced circumferentially around the core stack 12. Each set of magnet slots 18 includes four V-shaped magnet slots 18. Each set of magnet slots 18 also defines an outer magnetic inductance 20, a middle magnetic inductance 22, and an inner magnetic inductance 24. The outer, middle, and inner magnetic inductances 20, 22, and 24 provide paths for the electrical flux current during operation of the rotor core 10.

[0040] See Figure 1 , Figure 2A and Figure 2B The core stack 12 includes a plurality of thermally conductive inserts 26 extending axially through the core stack 12. The thermally conductive inserts 26 are adapted to conduct heat from the interior of the core stack 12 outward toward the distal ends of the core stack 12. More specifically, the thermally conductive inserts 26 are associated with each set of magnet slots 18. As shown, the core stack 12 includes eight thermally conductive inserts 26. The thermally conductive inserts 26 are made of a high thermal conductivity material that conducts heat away from the permanent magnets located within the magnet slots 18 and the outer, middle, and inner magnetic inductances 20 and 22, and 24. This heat is then conducted axially through the thermally conductive inserts 26 toward the distal ends 28, 30 of the core stack 12 to distribute heat more evenly throughout the core stack 12 and reduce the maximum temperature experienced at any point within the core stack 12.

[0041] See Figure 2A and Figure 2BIn one exemplary embodiment, the thermally conductive inserts 26 are generally elliptical in shape. As shown, eight thermally conductive inserts are circumferentially spaced evenly around the core stack 12, positioned between eight sets of magnet slots 18 and radially inward. To facilitate efficient heat transfer, the thermally conductive inserts 26 are positioned near the magnet slots 18; however, to maintain the structural integrity of the core stack 12 and avoid interference with the magnetic field, a minimum distance is preferred. In one exemplary embodiment, each of the plurality of thermally conductive inserts 26 is positioned such that the distance 32 between the outer edge 34 of each of the plurality of thermally conductive inserts 26 and any portion of any of the plurality of magnet slots 18 is at least 2 mm. Furthermore, the distance 36 between the outer edge 34 of each of the plurality of thermally conductive inserts 26 and the inner diameter 38 of the core stack 12 is at least 2 mm.

[0042] See Figure 3A and Figure 3B In another exemplary embodiment, each thermally conductive insert 26 includes a portion 40 extending radially outward toward the outer diameter 42 of the core stack 12 between the plurality of sets of magnet slots 18. In another exemplary embodiment, each of the plurality of thermally conductive inserts 26 is positioned such that the distance 32 between the outer edge 34 of any portion of each of the plurality of thermally conductive inserts 26 (including the radially outwardly extending portion 40) and any portion of any of the plurality of magnet slots 18 is at least 2 mm. Furthermore, the distance between the outer edge 34 of any portion of the plurality of thermally conductive inserts 26 (including the radially outwardly extending portion 40) and the outer diameter 42 of the core stack 12 is at least 2 mm.

[0043] See Figure 4 In one exemplary embodiment, each of the plurality of thermally conductive inserts 26 includes a coolant channel 44 extending axially through the entire length 46 of the core stack 12. The coolant channel 44 within each of the plurality of thermally conductive inserts 26 is connected to a central coolant supply source 48. Coolant is supplied at a first distal end 28 of the core stack 12 into the coolant channel 44 of each of the plurality of thermally conductive inserts, flows axially through the thermally conductive insert 26 as indicated by arrow 50, and exits the coolant channel 44 of each of the plurality of thermally conductive inserts 26 at a second distal end 30 of the core stack.

[0044] See Figure 5A and Figure 5B In one exemplary embodiment, the heat-conducting insert 26 is a generally elliptical tube that defines a smaller elliptical coolant channel 44 therein. See also Figure 6A and Figure 6BIn another exemplary embodiment, the thermally conductive insert 26 includes a generally elliptical tube defining a smaller elliptical coolant channel 44 therein, and the thermally conductive insert 26 also includes a portion 40 extending radially outward toward the outer diameter 42 of the core stack 12 between the plurality of sets of magnet slots 18. See also Figure 7A and Figure 7B In another exemplary embodiment, the thermally conductive insert 26 is generally elliptical in shape, including a portion 40 extending radially outward toward the outer diameter 42 of the core stack 12. The coolant channel 44 also includes a portion 52 extending radially outward within the portion 40 of the thermally conductive insert 26 toward the outer diameter 42 of the core stack 12. In all embodiments, the coolant channel 44 is entirely defined by the thermally conductive insert 26.

[0045] See Figure 8A In one exemplary embodiment, each thermally conductive insert 26 includes a single row 26' extending axially along the entire length 46 of the core stack 12. See again Figure 2B In one exemplary embodiment, each of the plurality of laminates 14 includes a plurality of openings 54 formed therein. When the plurality of laminates 14 are assembled to form a core stack 12, the plurality of openings 54 within each of the plurality of laminates 14 are axially aligned and define a plurality of axial cavities 56 extending axially through the core stack 12. Each of the plurality of thermally conductive inserts 26' includes a row of cast thermally conductive material within one of the plurality of axial cavities 56. In another exemplary embodiment, each of the plurality of thermally conductive inserts 26' includes a row of thermally conductive material that is machined or cast on the exterior of the core stack 12 and inserted into one of the plurality of axial cavities 56 after the core stack 12 is formed. The one-piece thermally conductive inserts 26' combined with the coolant channel 44 have the advantage of providing a sealed coolant path from a first distal end 28 of the core stack 12 to a second distal end 30 of the core stack 12. This eliminates the possibility of coolant leakage from the core stack 12 between the laminates 14.

[0046] See Figure 8B In another exemplary embodiment, each insert 26 includes a plurality of column segments 26”, which are axially aligned and extend axially along the entire length 46 of the core stack 12. As shown, the insert 26 includes three column segments 26”. Each column segment 26” extends through a portion of the plurality of laminates 14 and extends axially end-to-end through the entire length 46 of the core stack 12 when inserted into it. See also Figure 8CIn one exemplary embodiment, one of the laminates 14 is partially removed from the core stack 12. Each insert 26 includes a plurality of axially aligned strips 26”' extending axially along the entire length 46 of the core stack 12. The thickness of each strip 26”' is approximately the same as the thickness of one laminate 14. One strip 26”' of each insert 26 is positioned within each laminate 14. When the laminates 14 are axially aligned along the central axis 16 of the core stack 12, the strips 26”' are arranged to form a thermally conductive insert 26. As shown, each laminate 14 includes eight strips 26”' located therein. When the laminates 14 are axially aligned along the central axis 16 of the core stack 12, the strips 26”' are arranged to form eight thermally conductive inserts 26.

[0047] The rotor core disclosed herein has the advantage of distributing heat generated within the rotor core more evenly throughout the entire rotor core and reducing the maximum temperature the rotor core experiences. This increases the efficiency of magnetic flux within the rotor core, allowing motors using the rotor core disclosed herein to provide the same motor torque as rotor cores using larger permanent magnets, thereby reducing rotor core cost and improving rotor core packaging characteristics. Alternatively, motors using the rotor core disclosed herein will exhibit increased motor torque, power, and operating speed compared to motors with permanent magnets of similar size without heat-conducting inserts.

[0048] The description in this disclosure is merely exemplary in nature, and any changes that do not depart from the spirit of this disclosure are intended to be within its scope. Such changes should not be considered as a departure from the scheme and scope of this disclosure.

Claims

1. A rotor core for an electric motor used in an automobile, comprising: Core stack, the core stack comprising a plurality of identical laminates; Each laminate includes a plurality of magnetic slots formed therein, the magnetic slots of each laminate being axially aligned and adapted to support a plurality of permanent magnets therein; and Multiple thermally conductive inserts extend axially through the core stack and are adapted to conduct heat from the interior of the core stack outward toward the distal end of the core stack; Each of the plurality of heat-conducting inserts includes a coolant channel disposed inside each of the plurality of heat-conducting inserts and extending axially through each of the plurality of heat-conducting inserts.

2. The rotor core of claim 1, wherein each of the plurality of thermally conductive inserts comprises a single row extending axially through the entire length of the core stack, and wherein, The coolant channel extends axially through the entire length of the core stack.

3. The rotor core of claim 2, wherein each of the plurality of laminates includes a plurality of openings formed therein, wherein when the plurality of laminates are assembled to form the core stack, the plurality of openings in each of the plurality of laminates are axially aligned and define a plurality of axial cavities extending axially through the core stack, and each of the plurality of thermally conductive inserts includes a column of cast-in thermally conductive material in one of the plurality of axial cavities.

4. The rotor core of claim 2, wherein each of the plurality of laminates includes a plurality of openings formed therein, wherein when the plurality of laminates are assembled to form the core stack, the plurality of openings in each of the plurality of laminates are axially aligned and define a plurality of axial cavities extending axially through the core stack, and each of the plurality of thermally conductive inserts includes a column of thermally conductive material inserted into one of the plurality of axial cavities.

5. The rotor core of claim 1, wherein the coolant passage within each of the plurality of heat-conducting inserts is connected to a central coolant supply source, wherein coolant is supplied into the coolant passage of each of the plurality of heat-conducting inserts at a first distal end of the rotor and exits the coolant passage of each of the plurality of heat-conducting inserts at a second distal end of the rotor.

6. The rotor core of claim 1, wherein each of the plurality of thermally conductive inserts is positioned such that the distance between the outer edge of each of the plurality of thermally conductive inserts and any portion of any of the plurality of magnet slots is at least 2 mm, and the distance between the outer edge of each of the plurality of thermally conductive inserts and the inner diameter of the core stack is at least 2 mm.

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