Slot-free stator with end cover

Abstract

The invention provides a slot-free stator with an end cover. An electric machine is described, the electric machine comprising: a stator having a plurality of slots; and the insulating ring covers the end part of the stator. The insulating ring is characterized by a chamfered opening aligned with the slot, a peripheral ridge, and a well region extending from the ridge to the opening. A winding is wound within and extends away from the slot without a conventional slot liner.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to electric machine construction. BACKGROUND

[0002] Electric machines are used for propulsion in electric and hybrid electric vehicles (EVs and HEVs). These electric machines, which typically include permanent magnet (PM) synchronous motors or induction motors, convert electrical energy from a battery or fuel cell into mechanical energy to drive the vehicle wheels. SUMMARY

[0003] An electric machine includes a stator defining a plurality of slots, an insulating ring shrouding an end of the stator, and windings wound within and extending away from the slots. The insulating ring is designed with a plurality of chamfered openings aligned with the slots, a ridge around its perimeter, and a well region extending from the ridge to the chamfered openings. The windings are positioned within the slots such that the slots are free of traditional liners, allowing portions of the well region to be located between the windings. Additionally, an insulating compound covers the well region and fills the slots, providing both electrical insulation and mechanical stability.

[0004] Another embodiment of an electric machine features a stator having slots that are also free of liners, and windings wound directly within these slots. This design includes means for insulating the ends of the stator, preventing contact between the windings and the edges of the slots, to achieve effective insulation without traditional slot liners.

[0005] In a further embodiment, the electric machine includes a stator having slots that are free of liners, and a plastic end cap affixed to an end of the stator. The plastic end cap has a plurality of openings aligned with the slots that do not extend into the slots, a raised perimeter edge, and a recessed region extending from the edge to the openings. Hairpin windings are inserted into and extend from the slots such that portions of the plastic end cap are located between the stator and the hairpin windings. Additionally, a varnish is applied to fill the slots and be contained within the recessed region. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1A , Figure 1B and Figure 2 is a perspective partial assembled view of an electric machine.

[0007] Figure 3 is Figure 1A , Figure 1B and Figure 2 are cross-sectional side views of the electric machine of DETAILED DESCRIPTION

[0008] Embodiments are described herein. It should be understood, however, that the embodiments are merely examples and that other embodiments can be implemented in various alternative forms. The figures are not necessarily to scale and some features can be exaggerated to show details, while other features can be omitted or minimized to prevent the figures from becoming unclear. Therefore, specific structural and functional details disclosed are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to various embodiments.

[0009] Various features that are described in connection with any one of the figures can be combined with features from one or more of the other figures to produce embodiments that are not explicitly shown or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features can be provided by those of ordinary skill in the art in view of the teachings of the present disclosure to produce embodiments that are particularly suited to a certain application or implementations.

[0010] The design and operation of permanent magnet traction motors (PM motors) are central to modern electric propulsion systems for motor vehicles. These motors, characterized by a rotor embedded with permanent magnets and a stator with wound coils, can offer a mix of efficiency, power density, and performance characteristics.

[0011] PM motors can convert electrical energy into mechanical energy. This is primarily due to the presence of permanent magnets in the rotor, which generate a constant magnetic field without the need for additional energy input. The stator, which can include multiple windings of insulated wires, is supplied with alternating current (AC) from an inverter. This AC current generates a rotating magnetic field in the stator. The interaction between the rotating magnetic field of the stator and the static magnetic field of the rotor produces torque, causing the rotor to turn and thus drive the vehicle's wheels.

[0012] The control of PM motors is achieved through power electronics and algorithms. An inverter, which converts direct current (DC) from the vehicle's battery into the AC required by the motor, plays a role in this process. Modern inverters use techniques such as pulse width modulation (PWM) to control the voltage and frequency of the AC supply, thereby influencing the performance of the motor under various driving conditions. Field-oriented control (FOC) is a widely used strategy that allows independent control of the motor's torque and rotational speed by aligning the stator current with the rotor's magnetic field. Another control technique is direct torque control (DTC), which directly controls the motor's torque and flux. DTC provides dynamic response and efficiency by minimizing switching losses in the inverter. These control strategies are implemented using microprocessors and sensors that monitor the motor's operating parameters such as current, voltage, and rotor position. The integration of machine learning algorithms and predictive analytics can also enhance the performance of the motor.

[0013] Noise, vibration, and harshness (NVH) characteristics are a consideration in the design and operation of PM motors. While these motors are generally quieter than internal combustion engines, they can produce high frequency noise due to electromagnetic interactions and mechanical components. Minimizing NVH requires specific design of the motor’s components and mounting system, as well as the use of sound-damping materials.

[0014] Integration of PM motors within a broader vehicle system involves several factors. For example, regenerative braking is a feature that allows the motor to act as a generator during deceleration, converting kinetic energy back into electrical energy and recharging the battery. This not only improves energy efficiency, but also extends the driving range.

[0015] Placement of PM motors within a vehicle can also impact performance and design flexibility. Some designs place the motor centrally with the transmission and drive shaft to distribute power to the wheels. However, in-wheel motor designs, where the motor is directly integrated into the wheel hub, are becoming increasingly popular. In-wheel motors can eliminate the need for traditional drivetrain components, reducing mechanical losses and allowing for more flexible vehicle designs in certain scenarios. However, this can also introduce other issues.

[0016] Traditional random winding techniques are being replaced by other methods, such as hairpin winding, which uses rectangular wire instead of the conventional round wire. This technique can enhance the packing density of the winding, reducing electrical resistance and improving efficiency. Hairpin winding can also improve the thermal performance of the motor by providing better heat dissipation paths.

[0017] Thermal management maintains the performance and lifespan of PM motors. High power density and continuous operation generate heat, which, if not managed, can lead to degradation of the magnets and insulating materials. Cooling systems are commonly used, with liquid cooling being effective for high-performance applications. Liquid cooling involves circulating a coolant through channels in the motor housing that absorb and dissipate heat.

[0018] The choice of permanent magnet material impacts the performance of PM motors. Rare-earth magnets, such as neodymium iron boron (NdFeB) and samarium cobalt (SmCo), are widely used due to their high magnetic strength and resistance to demagnetization. In particular, NdFeB magnets offer some of the highest energy densities among commercially available magnets, making them a choice for high-performance applications.

[0019] The geometry of the rotor, including the shape and arrangement of the magnets, impacts the efficiency and torque characteristics of the motor. Common designs include surface-mounted magnets, where the magnets are attached to the surface of the rotor, and interior permanent magnets, where the magnets are embedded within the rotor. Surface-mounted designs are easier to manufacture and offer high power density, but can be more susceptible to demagnetization and mechanical stress in certain scenarios. Interior designs can provide better protection for the magnets and offer improved performance at high speeds, but their production can be more complex.

[0020] The stator typically includes a laminated core (laminations) with slots that house the windings (e.g., copper windings). These windings are arranged to generate a magnetic field. Selecting the proper wire gauge, insulation material, and winding technique is relevant. One of the components in a conventional stator design is the slot liner, which protects the windings during the stator assembly wire insertion process and insulates the windings from the core and prevents short circuits. The slot liner is typically made of a high-temperature, high dielectric strength material such as Nomex or Mylar.

[0021] The installation of the slot liner involves inserting the liner into the stator slots prior to placing the copper windings. This can be done manually or using automated machinery, depending on the manufacturing scale and precision requirements. The slot liner should fit tightly within the slots to provide uniform insulation and support for the windings. Any gaps or misalignments can lead to electrical leakage or reduced insulation effectiveness.

[0022] Here, an arrangement is presented in which the slot liner is replaced with a stator core end cap. By eliminating the slot liner, additional space within the slots is available. This space can be used for various purposes, such as in-slot cooling, increased wire (e.g., copper) slot fill, and / or increased varnish fill, thereby potentially enhancing the overall performance and efficiency of the motor.

[0023] Referring to Figure 1A , Figure 1B and Figure 2 , the motor 10 includes, among other things, a stator 12 defining a plurality of slots 14, windings 16, and an end cap 18. The stator 12 is a core component of the motor 10 that is configured to hold the windings 16 and to act as a magnetic circuit that enhances the efficiency of the magnetic field generated by the windings 16. In some examples, the stator 12 is made of laminated iron or other ferromagnetic material, which helps to direct and focus the magnetic field produced by the windings 16.

[0024] The stator 12 includes a series of slots 14 designed to accommodate the windings 16. The windings 16 are positioned within the slots 14 without the use of traditional slot liners, allowing for a more compact configuration. The slots 14 are devoid of any internal liners that are typically used to insulate the windings 16 from the stator 12. Instead, an insulating end cap 18 or insulating ring is placed at the end of the stator 12.

[0025] The insulating ring 18 features a plurality of chamfered openings 20 aligned with the slots 14 of the stator 12. These openings facilitate the insertion of the windings 16 into the slots 14 through the end cap 18. The end cap 18 also includes a ridge 22 around its perimeter and a well region 24 extending from the ridge 22 to the chamfered openings 20. The ridge 22 serves to contain and secure an insulating compound 26 within the well region 24.

[0026] The windings 16 are arranged such that portions of the well region 24 are located between the windings 16 and the stator 12, providing some degree of separation and additional insulation. This configuration facilitates insulation of the windings 16 from the stator 12 even without a traditional slot liner. Because the stator 12 is without a slot liner, the windings 16 can have straight extensions 28 (i.e., portions of each of the windings 16 that protrude straight from an outer edge of a corresponding slot 14 before being bent, beyond and away from the outer edge), which are reduced (e.g., less than 2.5 millimeters) relative to arrangements that use a slot liner, which can be torn by the windings.

[0027] Referring to Figure 3 Once the windings 16 are positioned within the slots 14 and over the well region 24 of the insulation ring 18, an insulating compound 26 is applied. This insulating compound 26 fills the slots 14 and covers the well region 24, forming a cohesive insulation layer. In this example, the insulating compound 26 is applied such that it is flush with the top of the ridge 22. This filling and covering approach provides both electrical insulation and mechanical stability for the windings 16.

[0028] The windings 16 shown in the figures can be hairpin windings, random windings, shaped coil windings, lap windings, wave windings, concentrated windings, distributed windings, fractional slot windings, bar windings, single layer windings, double layer windings, etc.

[0029] The nested hairpin winding is a hairpin-shaped wire arranged in a specific, tightly packed configuration within the slots 14 to optimize space utilization and electrical performance. The hairpin winding is a preformed rectangular or square cross-section wire that is bent into a "hairpin" shape, with each hairpin having two straight legs connected by a bend. The straight sections of the hairpins are inserted into the slots 14, and their ends are welded together to form a continuous winding around the stator 12. In the nested configuration, the hairpin windings are placed within the slots 14 in a tightly packed, interleaved manner. "Nested" refers to the way the hairpins are positioned relative to each other, thereby reducing the gap size and increasing the number of conductors in a given space. This arrangement can involve layering the hairpins such that they fit tightly together within each of the slots 14, typically in multiple layers. Advantages of the nested hairpin winding include increased slot fill factor, improved thermal management, enhanced mechanical stability, and reduced eddy currents and losses. By nesting the hairpins, the amount of conductive material within each of the slots 14 can be maximized, resulting in a higher slot fill factor and increased electrical efficiency by reducing the resistance of the winding 16. The tight packing of the winding 16 allows for better thermal conduction and dissipation, as the hairpins can be in direct contact with the stator 12 and each other. The interleaved arrangement also provides mechanical support and reduces movement or vibration of the winding during operation, thereby enhancing the durability and reliability of the electric machine 10. Additionally, the use of rectangular or square conductors in the hairpin winding can reduce eddy current losses compared to traditional round wire windings, particularly when the winding is nested to minimize the gap.

[0030] The insulating rings 18 can be made of plastic, providing insulating properties while being easy to manufacture and install. However, other materials can be used, including composite materials, ceramics, metal alloys with insulating coatings, thermoset polymers, thermoplastic plastics with fillers, rubber compounds, epoxy systems, etc. Each material offers unique advantages, such as enhanced thermal stability or mechanical strength, depending on the specific requirements of the application.

[0031] The insulating compound 24 can be a varnish as previously mentioned. However, other materials can be used, including epoxy resins, silicone compounds, polyurethane resins, polyester resins, impregnating gels, thermoplastic insulating materials, ceramic insulators, fluoropolymer coatings, mica-based insulating materials, etc. These materials offer various benefits, such as improved thermal management, mechanical protection, and enhanced electrical insulation, to meet different application needs and environmental conditions.

[0032] While the foregoing describes exemplary embodiments, these embodiments are not intended to cover all possible forms thereof. Language used in the specification is descriptive, not limiting, and it is understood that modifications can be made without departing from the spirit and scope of the disclosure.

[0033] As previously described, features of various embodiments can be combined to produce further embodiments of the application that can not be expressly described or illustrated. While certain embodiments can be described as providing advantages or being preferred over other embodiments or prior art implementations, a person having ordinary skill in the art will recognize that some features or properties can be adjusted to provide for desired overall system properties, depending on the specific application and implementation. These properties can include, but are not limited to, strength, durability, marketability, appearance, packaging, size, maintainability, weight, manufacturability, and ease of assembly. Embodiments that are considered less desirable in one or more properties are therefore not outside the scope of the present disclosure and can be suitable for particular applications.

[0034] According to the present application, there is provided an electric machine having a stator defining a plurality of slots, an insulating ring shrouding an end of the stator, wherein the insulating ring defines a plurality of chamfered openings aligned with the slots, a ridge around a perimeter of the insulating ring, and a well region extending from the ridge to the chamfered openings, windings wound within the slots and extending away from the slots such that the slots are unlined and portions of the well region are between the windings, and an insulating compound covering the well region and filling the slots.

[0035] According to an embodiment, the insulating compound covers the well region such that a top of the ridge and the insulating compound are flush with one another.

[0036] According to an embodiment, the windings are hairpin windings.

[0037] According to an embodiment, the hairpin windings are nested hairpin windings.

[0038] According to an embodiment, the windings are wound within the slots and extend away from the slots such that the portions of the well region are between the stator and the windings.

[0039] According to an embodiment, the windings have a straight extension of less than 2.5 millimeters.

[0040] According to an embodiment, the insulating ring is plastic.

[0041] According to an embodiment, the insulating compound is a varnish.

[0042] According to an embodiment, the insulating compound is an epoxy.

[0043] According to the invention, there is provided an electric machine having a stator defining a plurality of slots, windings wound within the slots without slot liners, and a device for insulating an end of the stator and preventing contact between the windings and edges of the slots.

[0044] According to embodiments, the invention further features an insulating compound filling the slots and a coating portion of the device.

[0045] According to embodiments, the device is further for containing the insulating compound.

[0046] According to embodiments, the windings are hairpin windings.

[0047] According to embodiments, the windings have a straight extension of less than 2.5 millimeters.

[0048] According to the invention, there is provided an electric machine having a stator defining a plurality of slots without liners, a plastic end cap attached to an end of the stator, wherein the plastic end cap defines a plurality of openings aligned with the slots, a raised perimeter edge, and a recessed area extending from the raised perimeter edge to the openings, hairpin windings inserted into and extending from the slots such that portions of the plastic end cap are between the stator and the nested hairpin windings, and a varnish contained within the recessed area and filling the slots.

[0049] According to embodiments, the hairpin windings have a straight extension of less than 2.5 millimeters.

[0050] According to embodiments, the hairpin windings are nested hairpin windings.

Claims

1. An electric machine comprising: a stator defining a plurality of slots; an insulating ring shrouding an end of the stator, wherein the insulating ring defines a plurality of chamfered openings aligned with the slots, a ridge around a perimeter of the insulating ring, and a well region extending from the ridge to the chamfered openings; windings wound within and extending away from the slots such that the slots are unlined and portions of the well region are between the windings; and an insulating compound covering the well region and filling the slots.

2. The electric machine of claim 1, wherein the insulating compound covers the well region such that a top of the ridge and the insulating compound are flush with each other.

3. The electric machine of claim 1, wherein the windings are hairpin windings.

4. The electric machine of claim 3, wherein the hairpin windings are nested hairpin windings.

5. The electric machine of claim 1, wherein the windings are wound within and extend away from the slots such that the portions of the well region are between the stator and the windings.

6. The electric machine of claim 5, wherein the windings have a straight extension of less than 2.5 millimeters.

7. The electric machine of claim 1, wherein the insulating ring is plastic.

8. The electric machine of claim 1, wherein the insulating compound is varnish.

9. The electric machine of claim 1, wherein the insulating compound is epoxy.

10. An electric machine comprising: a stator defining a plurality of slots; windings wound within the slots without slot lining; and a device for insulating an end of the stator and preventing contact between the windings and edges of the slots.

11. The electric machine of claim 10, further comprising an insulating compound filling the slots and a coated portion of the device.

12. The electric machine of claim 11, wherein the device is further for containing the insulating compound.

13. The electric machine of claim 10, wherein the windings are hairpin windings.

14. The electric machine of claim 10, wherein the windings have a straight extension of less than 2.5 millimeters.

15. An electric machine comprising: a stator defining a plurality of slots without lining; a plastic end cap attached to an end of the stator, wherein the plastic end cap defines a plurality of openings aligned with the slots, a raised perimeter edge, and a recessed region extending from the raised perimeter edge to the openings; hairpin windings inserted into the slots and extending from the slots such that portions of the plastic end cap are between the stator and the nested hairpin windings; and varnish contained within the recessed region and filling the slots. ​ ​

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