Rotor core with improved heat conduction

Abstract

The present subject matter relates to a rotor assembly (100) that includes a rotor core (102) having a central axis (108), coaxially coupled to a rotor shaft (106) The rotor core (102) includes a stack of laminations (104) mounted on the rotor shaft (106). Each lamination from the stack of laminations (104) is provided with a central hole through which the rotor shaft (106) is passed. Further, one or more oblong holes (110) is arranged around the central hole. In addition, a filler material (112) is filled in the one or more oblong holes (110). The filler material (112) is composed of thermally conductive material.

Description

ROTOR CORE WITH IMPROVED HEAT CONDUCTIONFIELD OF INVENTION

[0001] The present subject matter relates to a rotor core with improved heat conduction. Specifically, it addresses advancements in rotary electrical machines, particularly for automotive applications, focusing on enhancing thermal management within the stack of laminations.BACKGROUND

[0002] Rotary electrical machines are widely used in automotive applications and very much so as traction motor. Rotary electrical machines generate considerable about of heat during operation, especially if applied as traction motor for hybrid or electric vehicles where high motor output is expected. Normally, a rotor of the rotary electrical machine generate heat due to eddy current loss and hysteresis loss which occur in an iron core thereof, and therefore, components of said machine deteriorate due to temperature rise. Accordingly, drive time of the rotary electrical machine needs to be controlled to suppress temperature rise. Moreover, heat generated within the rotary electrical machine may lead to excessive wear due to thermal expansion. It is therefore important that the internal components of the rotary electrical machine, such as rotor, be cooled efficiently. It is desirable that cooling of the rotary electrical machine is achieved whilst considering size and weight constraints.

[0003] Typically, the rotor of a rotary electrical machine consists of a stack of laminations, each featuring holes that serve to relieve stress during the assembly process and ensure consistent contact pressure during high RPM operation. This design is critical for maintaining the structural integrity of the rotor under dynamic conditions. The rotor shaft is equipped with a coolant flow system that effectively cools the rotor during operation. However, the presence of these holes in the laminations significantlyimpedes heat transfer between the rotor shaft — where the coolant flows — and the stack itself. This obstruction can lead to localized overheating within the rotor assembly, adversely affecting performance and efficiency.

[0004] Therefore, the technical problem to be solved by the present subject matter is how to enhance heat transfer between the rotor shaft and the rotor with oblong holes in the laminations while maintaining effective stress relief and contact pressure during high RPM operation.SUMMARY OF THE INVENTION

[0005] The present subject matter seeks to solve the above- mentioned technical problem in conventional rotor assemblies. The rotor assembly described herein is designed for use in rotary machines intended for driving motor vehicles, specifically as a traction motor for electric vehicles (EVs). However, the rotor assembly described herein also make it applicable in various other fields, including industrial machinery, aerospace applications, and renewable energy systems.

[0006] The present subject matter relates to a rotor assembly comprising: a rotor core having a central axis, coaxially coupled to a rotor shaft, said rotor core comprising: a stack of laminations, mounted on the rotor shaft, wherein each lamination from the stack of laminations is provided with a central hole through which the rotor shaft is passed, and wherein one or more oblong holes is arranged around the central hole; and a filler material composed of thermally conductive material filled in one or more oblong holes. By filling the one or more oblong holes with the filler material, the rotor assembly effectively captures and dissipates heat, preventing overheating and ensuring optimal operational temperatures. The rotor core is therefore configured with improved heat conduction.

[0007] According to an example, the rotor shaft comprises a hollow structure in which cooling medium flows. Heat absorbed by the fillermaterial is transferred to the rotor shaft, where it can be carried away by the cooling medium, thus maintaining safe operating temperatures and enhancing overall efficiency.

[0008] According to an example of the present subject matter, the filler material is a thermal interface material (TIM). TIM significantly enhances the thermal management capabilities of the rotor assembly, promoting efficient operation and extending the lifespan of a rotary machine in which the rotor assembly is applied. The TIM filled in the one or more oblong holes may be selected from the group consisting of thermal pad, thermal gel, and varnish.

[0009] According to another example of the present subject matter, the filler material is a conductive foam. For instance, the conductive foam is copper foam.

[0010] According to yet another example of the present subject matter, the filler material is transformer oil. Upon application of the transformer oil into the one or more oblong holes, an efficient transfer of heat from the rotor core is achieved whilst maintaining optimal operating temperatures of the rotor assembly.

[0011] Rotor assembly as claimed in any one of the preceding claims, wherein the one or more oblong holes are elliptical in shape and are arranged in a circular pattern around the central hole, and the position of each oblong hole is radially offset from the central axis by a fixed radial distance. By maintaining a consistent distance from the central axis, each oblong hole contributes to an even distribution of the filler material.

[0012] Rotor assembly as claimed in the preceding claim, wherein each oblong hole is elongated in a circular path that follows the curvature of the circular pattern. By virtue of elongation, the one or more oblong holes can accommodate a greater volume of filler material.

[0013] Rotor assembly as claimed in the preceding claim, wherein one or more oblong holes in each lamination coincide with the one or more oblong holes formed in adjacent laminations in the rotor core. This alignment of each lamination in the stack of laminations creates a continuous pathway through the rotor core, allowing for effective thermal management. The configuration of these coinciding one or more oblong holes enables the filling the filling material throughout the entire rotor core.

[0014] Rotor assembly as claimed in any one of the preceding claims, wherein each lamination comprises a second plurality of holes arranged in a circular pattern around the central hole, said second plurality of holes adapted to receive permanent magnets, and wherein said second plurality of holes is arranged at a radial distance from the central axis than the radial distance of the one or more oblong holes from the central axis.BRIEF DESCRIPTION OF DRAWINGS

[0015] The features, aspects, and advantages of the present invention will be better understood with regard to the following description and accompanying figures. The description refers to the annexed drawings, wherein:

[0016] FIG. 1A is an isometric view of a rotor assembly, configured in accordance with the present subject matter;

[0017] FIG. 1 B is a cross-sectional view of the rotor assembly shown in FIG. 1A, configured in accordance with the present subject matter;

[0018] FIG. 2A is an isometric view of a rotor core of the rotor assembly, configured in accordance with an aspect of the present subject matter; and

[0019] FIG. 2B is a top view, depicting a single lamination of the rotor core, configured in accordance with an example of the present subject matter.

[0020] The figures are not necessarily to scale, and the size of some parts may be exaggerated to clearly illustrate the example shown. Moreover, the drawings provide examples and / or examples consistent with the description, however, the description is not limited to the examples and / or examples provide in the drawings.DETAILED DESCRIPTION

[0021] In the description that follows, reference is made to accompanying drawings, which form part thereof, and in which is shown by way of illustration specific implementations in which the invention maybe practiced. These implementations are described in sufficient detail to enable that skilling in the art to practice the invention, and it is to be understood that the implementations may be combined, or that other implementations may be utilized, and that structural and logical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

[0022] The present subject matter relates to a rotor assembly. More particularly, the present subject matter relates to a rotor assembly for use in automotive applications. FIG. 1A illustrates such a rotor assembly 100 in an isometric view, configured in accordance with the present subject matter. FIG. 1 B is cross sectional view of the rotor assembly 100 shown in FIG. 1A. Particularly, FIG. 1 B illustrates a cross-section of the rotor assembly 100, taking along a plane (not shown) that passes through the central axis 108. The rotor assembly 100 includes a rotor core 102 having a central axis 108. The rotor core is coaxially coupled to a rotor shaft 106.The rotor core 102 includes a stack of laminations 104 mounted on the rotor shaft 106. Each lamination from the stack of laminations 104 is provided with a central hole, which the rotor shaft 106 is passed. One or more oblong holes 110 is arranged around this central hole. Further, a filler material 112 is filled in the one or more oblong holes 110. This filler material 112 is composed of thermally conductive material.

[0023] According to the present subject matter, the filler material 112 can absorb heat generated at the rotor core 102, which occurs due to electromagnetic losses and friction during rotation. During operation of the rotor assembly 100, as the rotor core 102 spins, the rotor core 102 generates heat that can lead to thermal stress on various components in a rotary machine in which the rotor assembly 100 is provided. The filler material 112 within the one or more oblong holes 110 manage this heat by facilitating efficient thermal transfer. As heat is absorbed by the filler material 112, the filler material 112 conducts this thermal energy away from the rotor core, thereby reducing localized hot spots and promoting uniform temperature distribution across the rotor assembly 100.

[0024] In addition, the rotor shaft 106 may include a hollow structure 118 (shown in FIG. 1 B), allowing cooling medium such as air or liquid cooling to flow through. This flow of cooling medium in the hollow structure 118 further aids in carrying heat away from the rotor core 102. Therefore, in an example where the rotor shaft 106 includes the hollow structure 118, the combination of the filler material 112 in the one or more oblong holes 110 and cooling medium in the rotor shaft 106 creates an effective thermal management system.

[0025] According to an example of the present subject matter, the filler material 112 is a thermal interface material (TIM). TIM exhibits high thermal conductivity, ensuring that heat generated during operation is efficiently conducted away from the rotor core 102. Further, TIM has lowthermal resistance thereby minimizing barriers to heat flow, facilitating effective thermal management within the rotor assembly 100. Furthermore, TIM is configured to fill microscopic gaps that could hinder heat transfer. During installation of TIM into the one or more oblong holes 110, uniform coverage without excessive dripping or spreading is possible, as it allows for precise application.

[0026] According to another example of the present subject matter, the filler material 112 is a conductive foam. The conductive foam is a copper foam, for instance. The installation of conductive foam can be tailored to fit into the one or more oblong holes 110 through various methods such as die-cutting, adhesive backing, layering, or compression fitting.

[0027] According to yet another example of the present subject matter, the filler material 112 is transformer oil. This transformer oil, commonly also known as ‘insulation oil’, can facilitate cooling of the rotor core 102.

[0028] FIG. 2A is an isometric view of the rotor core 102 of the rotor assembly 100, configured in accordance with an aspect of the present subject matter. FIG. 2B is a top view, depicting a single lamination of the rotor core 102, configured in accordance with an example of the present subject matter.

[0029] According to an aspect of the present subject matter, the one or more oblong holes 110 are elliptical in shape and arranged in a circular pattern around a central hole 200 through which the rotor shaft 106 passes. Further, each oblong hole is radially offset from the central axis 108 by a fixed radial distance. It can also therefore be said that the one or more oblong holes 110 is arranged about the central axis 108. Within the meaning of the present subject matter, the word “radial” refers to a direction that extends outward from the central axis 108, said direction being perpendicular to the central axis 108. Therefore, in the circular pattern ofthe one or more oblong holes 110, “radially offset” refers to any point that is located at a distance from the center axis 108 along a straight line. Further, “fixed radial distance,” indicates that the one or more oblong holes 110 are each positioned at the same distance that is radially offset from the central axis 108.

[0030] According to the present subject matter, the circular pattern is indicated by a circular path 116 around the central axis 108. The circular path 116 serves to visually represent the arrangement of the one or more oblong holes in the rotor core 102. This circular path 116 signifies rotational symmetry, illustrating how each oblong hole is positioned uniformly around the central hole 200. Moreover, the circular path 116 emphasizes that the one or more oblong holes 110 are strategically arranged at equal angular intervals, rather than being randomly placed. Therefore, the circular path 116 follows the curvature of the circular pattern.

[0031] According to an aspect of the present subject matter, the one or more oblong holes 110 are elongated in a direction following the circular path 116. By virtue of elongation, the one or more oblong holes 110 can accommodate a greater volume of filler material 112.

[0032] According to yet another aspect of the present subject matter, each lamination in the rotor core 102 includes a second plurality of holes 114. This second plurality of holes 114 are also arranged in a circular pattern around the central hole 200. The second plurality of holes 114 are adapted to receive permanent magnets (not shown) that contribute to increases heat generation at the rotor core 102. The second plurality of holes 114 is arranged at a radial distance from the central axis 108. The aforementioned radial distance of the second plurality of holes 114 is larger than the radial distance at which the one or more oblong holes 110 are disposed from the central axis 108. The ‘radial distance’ refers to the radial offset, of the one or more oblong holes 110 and / or the second plurality ofholes 114 with respect to the central axis 108. Therefore, by virtue of the filler material 112, heat generated by permanent magnets are also effectively absorbed by the filler material 112 and then transferred to the cooling medium in the rotor shaft 106.

[0033] According to an aspect of the present subject matter, each lamination in the stack of laminations 104 is features the one or more oblong holes 110, which are specifically configured to coincide with the one or more oblong holes formed in adjacent laminations within the stack of laminations 104. This alignment of each lamination in the stack of laminations 104 creates a continuous pathway through the rotor core 102, allowing for effective thermal management. The configuration of these coinciding one or more oblong holes enables the filling the filling material 112 throughout the entire rotor core 102.

[0034] According to an aspect of the present subject matter, the rotor assembly 100 is configured to rotate in a rotary machine (not shown). The rotor assembly 100 interacts with a stator that include stator windings adapted to generate a stator magnetic field. The rotor assembly 100 is arranged coaxially to the stator and configured to generate a rotor magnetic field that interacts with the stator magnetic field to product a torque or power. The rotary machine may be applied in a motor vehicle to create traction to move motor vehicle. Though the present subject matter speaks of applying the rotor assembly and hence the rotary electrical machine in automobile applications, it can be understood that the application can extend to various other industries and may be used in fans, blowers, machine tools, turbines, pumps, compressors, rolling mills, movers, paper mills, etc.

[0035] Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subjectmatter. It is therefore contemplated that such modifications can be made without departing from the scope of the present subject matter is defined.

Claims

We Claim:

1. Rotor assembly (100) comprising: a rotor core (102) having a central axis (108), coaxially coupled to a rotor shaft (106), said rotor core (102) comprising: a stack of laminations (104), mounted on the rotor shaft (106), wherein each lamination from the stack of laminations (104) is provided with a central hole (200) through which the rotor shaft (106) is passed, and wherein one or more oblong holes (110) is arranged around the central hole (200); and a filler material (112) composed of thermally conductive material filled in one or more oblong holes (110).

2. Rotor assembly (100) as claimed in claim 1 , wherein the filler material (112) is a thermal interface material (TIM).

3. Rotor assembly (100) as claimed in the preceding claim, wherein the TIM is selected from the group consisting of thermal pad, thermal gel, and varnish.

4. Rotor assembly (100) as claimed in claim 1 , wherein the filler material (112) is a conductive foam.

5. Rotor assembly (100) as claimed in the preceding claim, wherein the conductive foam is copper foam.

6. Rotor assembly (100) as claimed in claim 1 , wherein the filler material (112) is transformer oil.

7. Rotor assembly (100) as claimed in any one of the preceding claims, wherein the one or more oblong holes (110) are elliptical in shape and are arranged in a circular pattern around the central hole (200), andthe position of each oblong hole (110) is radially offset from the central axis (108) by a fixed radial distance.

8. Rotor assembly (100) as claimed in the preceding claim, wherein each oblong hole (110) is elongated in a circular path that follows the curvature of the circular pattern.

9. Rotor assembly (100) as claimed in the preceding claim, wherein one or more oblong holes (110) in each lamination (104) coincide with the one or more oblong holes (110) formed in adjacent laminations in the rotor core (102).

10. Rotor assembly (100) as claimed in any one of the preceding claims, wherein each lamination comprises a second plurality of holes (114) arranged in a circular pattern around the central hole (200), said second plurality of holes (114) adapted to receive permanent magnets, and wherein said second plurality of holes (114) is arranged at a radial distance from the central axis (108) than the radial distance of the one or more oblong holes (110) from the central axis (108).

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