A stepped slot stator core and flat wire embedding method for improving slot fill rate

Abstract

The application discloses a stepped slot stator core and flat wire embedding method for improving slot filling rate, and belongs to the technical field of motors, which comprises a stator core, a first slot arranged on the top of the stator core and distributed along the circumference of the stator core, and a second slot arranged on the top of the stator core and staggered along the circumference with the first slot. The stepped slot structure is staggered along the circumference of the stator core by the first slot and the second slot, and a stepped boss with a sawtooth-shaped axial section is symmetrically arranged in each slot. Each slot independently provides two opposite limiting steps to produce a combined effect of circumferential constraint and radial extrusion on the flat wire. Since the sawtooth-shaped boss extends along the axial direction, the flat wire can be slid into along the axial direction without interference, avoiding the twisting or deviation of the flat wire during high-pressure embedding, and eliminating local stress concentration.

Description

Technical Field

[0001] This invention relates to the field of motor technology, and in particular to a stepped slot stator core and a method for embedding flat wires to improve slot fill factor. Background Technology

[0002] With the rapid development of new energy vehicles, industrial automation, and high-end equipment manufacturing, drive motors, as core power components, have seen their power density, energy efficiency, and thermal management performance become key indicators for measuring technological level. The stator core, as the core carrier of the motor's magnetic circuit and the supporting structure of the windings, directly determines the amount of copper wire filling and the level of resistance loss, thus affecting the motor's torque output and temperature rise. In the industry trend of pursuing high power density, maximizing the filling ratio of winding conductors within a limited stator volume, while simultaneously considering manufacturing feasibility and operational reliability, has become a critical technological bottleneck that urgently needs to be overcome in the motor manufacturing field.

[0003] In existing stator core technology, to balance leakage flux and ease of wire insertion, the industry generally adopts a semi-closed slot design. This structure limits leakage flux and provides an insertion channel for flat wires by setting a narrow neck structure at the top of the stator teeth. Some solutions attempt to enhance the friction between the flat wire and the slot wall by optimizing the roughness of the slot inner wall or adding small positioning protrusions. Other solutions use pre-forming processes to process the ends of the flat wires into irregular structures that match the shape of the slot to reduce insertion interference. For the needs of high power density motors, conventional design approaches often focus on increasing the amount of copper wire in a limited space, attempting to reduce resistance loss by increasing the material filling ratio.

[0004] However, in existing technologies, the inner walls of conventional semi-closed slots are mostly smoothly transitioned arcs or straight lines, providing only unidirectional radial restraint and failing to provide effective circumferential constraint on the conductor. During high-voltage winding, the flat wire, lacking circumferential positioning, is prone to twisting or shifting within the slot, causing the flat wire to be stressed to one side. This results in excessive concentration of contact pressure on the edge of the flat wire or one side wall of the slot, leading to localized stress concentration. This non-uniform stress state not only scratches the insulation layer of the flat wire, posing a risk of inter-turn short circuits, but also causes plastic deformation or micro-cracks in the silicon steel sheets of the stator core, severely affecting the mechanical strength and fatigue life of the core. Simultaneously, due to the lack of stable attitude control of the flat wire within the slot, it is difficult to achieve tight packing when multiple conductors are arranged side by side, resulting in a large number of irregular gaps remaining in the slot. This keeps the slot fill factor stagnant at a low level for a long time, making it difficult to meet the high torque output requirements of the motor. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a stepped slot stator core and a flat wire embedding method to improve slot fill factor.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a stepped slot stator core for improving slot fill factor, comprising: Stator core; The first slot is provided on the top of the stator core and is distributed at intervals along the circumference of the stator core; The second slot is located at the top of the stator core and is staggered with the first slot in the circumferential direction. Cooling holes are formed throughout the periphery of the stator core to allow cooling medium to circulate and remove heat. The stator core is configured such that the inner wall structures of the first slot and the second slot are arranged in a V-shape symmetrically. The opening of the first slot (2) faces the inner diameter direction of the stator core (1), and the opening of the second slot (3) faces the outer diameter direction of the stator core (1). The first slot and the second slot are each provided with symmetrically distributed limiting structures, so that the flat wire inserted into any slot can be limited by the two sides of the symmetrical structure in the slot, thereby achieving bidirectional constraint independently in a single slot and improving the slot fill factor.

[0007] In a preferred embodiment of the present invention, the limiting structure of the first slot is composed of symmetrically arranged first stepped bosses; the limiting structure of the second slot is composed of symmetrically arranged second stepped bosses.

[0008] In a preferred embodiment of the present invention, the first stepped boss and the second stepped boss are sawtooth-shaped in the axial section of the stator core.

[0009] In a preferred embodiment of the present invention, a cooling hole is provided through the periphery of the stator core, the cooling hole being arranged along the axial direction of the stator core and avoiding the magnetic circuit of the tooth section.

[0010] In a preferred embodiment of the present invention, the depths of the first slot and the second slot are adapted to the axial length of the stator core, and the slots maintain a constant cross-sectional shape along the axial direction.

[0011] Secondly, the present invention provides a method for inserting flat wires into a stepped slot stator core to improve slot fill factor, comprising the following steps: S1. Micro-forging is performed on the ends of the flat wire to form a guide slope that matches the serrated profile of the stepped groove. S2. Apply a lubricating layer to the surface of the flat wire and align the flat wire with the slot of the stator core so that the axis of the flat wire is parallel to the center line of the slot. S3. Apply pressure along the axial direction of the flat wire to make the flat wire pass through the multi-stage stepped boss in the first or second slot, and use the guide ramp to guide the flat wire to slide into the sawtooth slot. S4. Remove the axial pressure and use the elastic recovery of the flat wire itself and the geometric interference of the sawtooth shape to lock the flat wire in the groove in the radial direction. S5. Apply high-frequency micro-amplitude vibration to the stator core 1, and use the stress relaxation characteristics of metal to eliminate the micro-gap between the flat wire and the slot, forming an interference fit.

[0012] In a preferred embodiment of the present invention, in step S1, the pressure of micro-forging is 5-20kN, the forging deformation is 3-8% of the thickness of the flat wire section, and the angle of the formed guide slope is 10-30°.

[0013] In a preferred embodiment of the present invention, in step S2, the lubricating layer is a molybdenum disulfide solid lubricant with a coating thickness of 5-20 μm.

[0014] In a preferred embodiment of the present invention, in step S3, the axial pressure is applied by a servo pressure head, with a pressure range of 200-800N and an indentation speed of 0.5-3mm / s.

[0015] In a preferred embodiment of the present invention, in step S5, the frequency of the high-frequency micro-amplitude vibration is 500-2000Hz, the amplitude is 2-15μm, and the vibration duration is 5-30s.

[0016] This invention addresses the shortcomings of the prior art and has the following beneficial effects: The stepped slot structure is arranged in a staggered pattern along the circumference of the stator core through the first and second slots. Each slot has a stepped boss with a serrated axial cross section. Each slot independently provides two limiting steps in opposite directions, which exert a combined effect of circumferential constraint and radial compression on the flat wire. Since the serrated boss extends axially, the flat wire can slide in axially without interference, avoiding twisting or displacement of the flat wire during high-voltage winding and eliminating local stress concentration. This close packing improves the slot fill factor, protects the insulation layer, and enhances the stiffness of the stator teeth.

[0017] By applying specific pressure and deformation to the ends of the flat wire during pretreatment, a guide slope that precisely matches the serrated slot is formed, and a lubricating layer is coated on the surface of the flat wire. This allows the flat wire to convert sliding friction into rolling tendency during the sliding process, reducing insertion resistance and eliminating friction peaks at the bends. Compared with the forced insertion process in the prior art, which is prone to damage to the insulation layer or jamming, this method effectively protects the integrity of the insulating varnish film on the surface of the flat wire, improves the yield of the assembly process, and ensures that the flat wire can accurately reach the predetermined position, achieving neat arrangement of conductors in the slot and providing process assurance for high slot fill factor.

[0018] By applying vibration energy of a specific frequency and amplitude to the stator core after the flat wire is in place, the stress relaxation characteristics of the metal are utilized to induce microscopic plastic deformation at the contact surface between the flat wire and the slot, thereby eliminating microscopic gaps and forming a tight interference fit. Compared with the problems of blocked heat conduction paths and easy generation of local hot spots in the existing technology, this method not only replaces the traditional macroscopic interference fit and avoids damage to the core structure caused by forced extrusion, but also opens up the conduction path of winding heat to cooling holes by compacting the contact surface, reducing motor temperature rise, improving the continuous overload capacity under high power density conditions, and consolidating the improvement of slot fill factor. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a perspective structural diagram of a preferred embodiment of the present invention; Figure 2 This is a top view of the stator core according to a preferred embodiment of the present invention; Figure 3 This is a partial enlarged view of the first stepped boss in a preferred embodiment of the present invention; Figure 4 This is a partial enlarged view of the second stepped boss in a preferred embodiment of the present invention; Figure 5 This is a flowchart of a preferred embodiment of the present invention.

[0020] In the diagram: 1. Stator core; 2. First slot; 21. First stepped boss; 3. Second slot; 31. Second stepped boss; 4. Cooling hole. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0023] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0024] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0025] like Figures 1-4 As shown, a stepped slot stator core for improving slot fill factor includes: Stator core 1; The first slot 2 is disposed on the top of the stator core 1 and is distributed at intervals along the circumference of the stator core 1; The second slot 3 is located on the top of the stator core 1 and is staggered with the first slot 2 in the circumferential direction; Cooling holes 4 are formed through the periphery of the stator core 1 to allow cooling medium to circulate and remove heat. The stator core 1 is configured such that the inner wall structures of the first slot 2 and the second slot 3 are arranged in a V-shape symmetrically. The opening of the first slot 2 faces the inner diameter direction of the stator core 1, and the opening of the second slot 3 faces the outer diameter direction of the stator core 1. The first slot and the second slot are each provided with symmetrically distributed limiting structures, so that the flat wire inserted into any slot can be limited by the two sides of the symmetrical structure in the slot, thereby achieving bidirectional constraint independently in a single slot and improving the slot fill factor.

[0026] The core inventive concept of this invention is that two kinds of V-shaped symmetrical slots are arranged alternately on the top of the stator core 1, and the openings of the first slot 2 and the second slot 3 face the inner diameter direction and the outer diameter direction of the stator core 1, respectively. Each slot is symmetrically provided with axial sawtooth stepped bosses, which can achieve bidirectional constraint on the flat wire in a single slot, thereby improving the slot fill factor.

[0027] Specifically, the stator core 1 is made of multiple silicon steel laminations with toothed grooves. Multiple cooling holes 4 are provided axially in the yoke region of the stator core 1. The cooling holes 4 are evenly distributed around the circumference of the stator core 1, and their cross-sectional shape is circular or elliptical. The cooling holes 4 serve as fluid channels for heat exchange, and their positions avoid the magnetic circuit saturation regions of the teeth and yoke.

[0028] Furthermore, the top of the stator core 1 is provided with a first slot 2 and a second slot 3, which are arranged alternately in the circumferential direction of the stator core 1; this staggered distribution design aims to optimize the magnetic circuit performance and manufacturing process of the stator core.

[0029] Specifically, the first slot 2 is disposed on the top of the stator core 1 and is distributed at intervals along the circumference of the stator core 1. Each first slot 2 includes a first stepped protrusion 21 symmetrically disposed on both sides of the slot. The first stepped protrusion 21 extends from the side wall of the slot into the slot, forming a limiting step in the first direction.

[0030] Specifically, the second slot 3 is located on the top of the stator core 1 and is staggered with the first slot 2 along the circumferential direction. Each second slot 3 includes a second stepped protrusion 31 symmetrically arranged on both sides of the slot. The extension direction of the second stepped protrusion 31 is opposite to the first direction, forming a limiting step in the second direction.

[0031] It should be noted that, on the axial cross-section of the stator core 1, the cross-sections of the first stepped boss 21 and the second stepped boss 31 are both sawtooth-shaped. This axial sawtooth structure is a stepped design that extends along the axial direction of the slot, rather than a circumferential cross-section protrusion, which transforms the originally straight inner wall of the slot into a symmetrical irregular profile with multiple bends. The axial depth of the first slot 2 and the second slot 3 is adapted to the axial length of the stator core 1. The stepped structure maintains a constant cross-sectional shape along the entire axial direction so that the flat wire can be inserted axially. Moreover, the cross-sectional shape reserves a small gap to accommodate the elastic deformation of the flat wire, so that the flat wire can smoothly pass through the stepped area by its own elastic deformation when it is pressed in axially, avoiding rigid interference, so that the flat wire can be inserted axially.

[0032] It is understandable that when the flat wire is inserted into the first slot 2 or the second slot 3, the cross-section of the flat wire is rectangular, with its width direction corresponding to the circumferential width of the slot and its thickness direction corresponding to the radial depth of the slot. At this time, a single flat wire only needs to be inserted into one slot, and bidirectional constraint can be achieved by using the symmetrical two-sided bosses inside the slot. Since the sawtooth profile of the first stepped boss 21 and the second stepped boss 31 is a stepped structure extending axially, when the flat wire is pressed axially, the guide slope at its end can slide in step by step without causing circumferential interference. When the flat wire is embedded in the first slot 2, its two sides in the width direction are respectively limited by the two sides of the first stepped boss 21 inside the slot. When the flat wire is embedded in the second slot 3, its two sides in the width direction are respectively limited by the two sides of the second stepped boss 31 inside the slot. This prevents the flat wire from twisting or shifting circumferentially inside the slot, ensuring the neatness and tightness of multiple flat wires arranged side by side.

[0033] Specifically, the step depth, step width, and spacing between adjacent steps of the first slot 2 and the second slot 3 are adjusted according to the design target of the flat wire size and slot fullness; the stepped structure forms multi-point support in the radial direction: when the flat wire is fully embedded, the steps of the first step boss 21 and the second step boss 31 abut against different height positions of the flat wire, forming a radial constraint effect, and realizing dual positioning of the flat wire in the circumferential and radial directions.

[0034] In this embodiment, the staggered arrangement of the first slot 2 and the second slot 3 on the top of the stator core 1 constructs a stepped slot structure with bidirectional limiting capability, transforming the single radial limiting of the smooth slot in the prior art into a combined circumferential and radial limiting of the stepped slot. The limiting directions of the first slot 2 and the second slot 3 are opposite. When the flat wire is subjected to electromagnetic force or mechanical vibration, the displacement trend in either direction is suppressed by the stepped steps in the corresponding direction, ensuring the attitude stability of the winding during motor operation. The cooling hole 4 penetrates the yoke of the stator core 1 and maintains a preset distance from the stator slot. The heat generated by the winding is conducted to the yoke through the teeth and then carried away by the cooling medium in the cooling hole 4, forming a heat conduction path.

[0035] like Figure 5 As shown, a method for inserting flat wire into a stepped slot stator core to improve slot fill factor includes the following steps: S1. Micro-forging is performed on the ends of the flat wire to form a guide slope that matches the serrated profile of the stepped groove. S2. Apply a lubricating layer to the surface of the flat wire and align the flat wire with the slot of the stator core 1 so that the axis of the flat wire is parallel to the center line of the slot. S3. Apply pressure along the axial direction of the flat wire to make the flat wire pass through the multi-stage stepped boss in the first or second slot, and use the guide ramp to guide the flat wire to slide into the sawtooth slot. S4. Remove the axial pressure and use the elastic recovery of the flat wire itself and the geometric interference of the sawtooth shape to lock the flat wire in the groove in the radial direction. S5. Apply high-frequency micro-amplitude vibration to the stator core 1, and use the stress relaxation characteristics of metal to eliminate the micro-gap between the flat wire and the slot, forming an interference fit.

[0036] The core inventive concept of this invention is as follows: by micro-forging the end of the flat wire to form a guide slope that matches the serrated contour of the stepped slot, and by using a lubricating layer to reduce the pressing resistance, the flat wire is radially locked by elastic recovery and geometric interference of the serrated groove after axial pressing. Finally, high-frequency micro-amplitude vibration is used to eliminate micro gaps and form an interference fit, thereby achieving reliable insertion of the flat wire with high slot fill factor in the stepped slot structure.

[0037] In step S1, the embedded end of the flat wire is subjected to micro-forging pretreatment. The micro-forging process adopts cold molding. The end of the flat wire is placed in a mold with a preset cavity. The press applies extrusion pressure along the thickness or width direction of the flat wire, forcing the metal material at the edge of the flat wire end to undergo directional plastic flow, thereby forming a guide slope on both sides of the end that matches the serrated groove profile formed by the first groove 2 and the second groove 3.

[0038] The pressure range of micro-forging is 5-20kN, the forging deformation is controlled at 3-8% of the thickness of the flat wire section, and the angle of the formed guide slope is 10-30°.

[0039] When the flat wire contacts the groove corner, the guide ramp transforms sliding friction into a gradual wedging action, avoiding stress concentration caused by the flat wire edge directly impacting the stepped step; the contour of the mold cavity corresponds to the stepped corner of the sawtooth groove, ensuring that the inclination angle of the guide ramp matches the cutting angle of the groove step.

[0040] In step S2, a lubricating layer is coated on the surface of the flat wire after micro-forging. The coating process of the lubricating layer can be dip coating, spray coating or brush coating, so that the solid lubricant is uniformly attached to the outer surface of the flat wire and forms a continuous film. The lubricating layer is a molybdenum disulfide solid lubricant with a coating thickness of 5-20 μm.

[0041] The function of the lubricating layer is to fill the micro-depressions on the surface of the flat wire and isolate the flat wire from direct contact with the inner wall of the slot. It continuously provides a friction-reducing effect during the pressing process, reducing the risk of damage to the insulation layer of the flat wire caused by repeated friction of the multi-step stepped slot.

[0042] After coating, place the flat wire on the positioning fixture and adjust the axis of the flat wire to be parallel to the center line of the slot 1 of the stator core. The positioning fixture can be equipped with a guide sleeve or a centering clamp to ensure the initial posture of the flat wire.

[0043] In step S3, a servo pressure head is used to apply pressure axially to the flat wire, which passes through the stepped groove area of ​​the first groove 2 or the second groove 3; wherein, the axial pressure range is 200-800N, and the pressing speed is 0.5-3mm / s.

[0044] During the pressing process, the guide slope at the end of the flat wire first touches the stepped structure of the first slot 2 or the second slot 3. Under the guidance of the slope, the flat wire undergoes a slight elastic bend and slides in along the inner wall of the serrated slot.

[0045] In step S4, after the flat wire reaches the predetermined bottom position of the groove, the axial pressure is removed. The elastic deformation accumulated by the flat wire during the pressing process is restored. The restoration trend is affected by the geometric interference of the first step boss 21 and the second step boss 31 on the inner wall of the sawtooth groove. The flat wire is held in the radial direction by multiple steps, realizing radial mechanical locking. The flat wire can maintain a stable position in the groove without the need for additional filling groove wedges.

[0046] Specifically, during the pressing process, there is an interference of 0.01-0.08mm between the flat wire and the stepped boss, and the flat wire undergoes controllable elastic deformation. After the pressure is removed, the flat wire elastically recovers 0.005-0.03mm, forming multi-point interference contact with the sawtooth bend, generating a radial clamping force sufficient to resist the electromagnetic force of the motor.

[0047] In step S5, after the flat wire is radially locked, a high-frequency micro-amplitude vibration is applied to the stator core 1 as a whole. The vibration excitation can be achieved by fixing the stator core 1 to a vibration platform, which is driven by a piezoelectric ceramic vibrator or an electromagnetic vibrator to generate controlled vibration along the axial or radial direction of the stator core 1; wherein, the frequency of the high-frequency micro-amplitude vibration is 500-2000Hz, the amplitude is 2-15μm, and the vibration duration is 5-30s.

[0048] Vibrational energy is transmitted through the main structure of stator core 1 to every contact interface between the flat wire and the inner wall of the slot.

[0049] Under alternating vibration loads, the protrusions at the microscale of the contact interface gradually undergo plastic yielding due to cyclic stress. The protrusion material fills the adjacent micro-valve, utilizing the stress relaxation characteristics of metallic materials to eliminate the micro-gap remaining after assembly.

[0050] After continuous vibration, the contact between the flat wire and the stator core 1 slot wall changes from multi-point contact to surface contact, forming an interference fit, thereby reducing the contact thermal resistance between the winding and the core and establishing a low thermal resistance path for the conduction of winding heat to cooling hole 4.

[0051] To further simplify and make the present invention achieve its objectives and effects, the present invention will be further illustrated in conjunction with the following specific embodiments and comparative examples, but the present invention is not limited to the scope of the embodiments described herein.

[0052] It should be noted that the raw materials used in the examples and comparative examples are described below: Molybdenum disulfide solid lubricant: pour point -30℃, specific gravity 0.86, grade 32, purchased from Shenzhen Youborui Trading Co., Ltd.

[0053] Example 1: S1. The ends of the flat wire are micro-forged using cold molding. The micro-forging pressure is 12kN, the forging deformation is 5.5% of the thickness of the flat wire cross section, and the angle of the resulting guide slope is 20°. S2. Coat the surface of the flat wire with molybdenum disulfide solid lubricant with a coating thickness of 12μm; align the flat wire with the slot of stator core 1 and use a centering fixture to ensure that the axis of the flat wire is parallel to the center line of the slot; S3. A servo pressure head is used to apply pressure along the axial direction. The pressure value is 500N and the pressing speed is 1.8mm / s, so that the flat wire passes through the first slot 2 or the second slot 3. The guide slope guides the flat wire to slide smoothly into the sawtooth slot. S4. Remove the axial pressure. The elastic recovery of the flat wire itself and the combined effect of the sawtooth geometric interference make the flat wire lock in the groove in the radial direction. S5. Apply high-frequency micro-amplitude vibration to stator core 1. The vibration frequency is 1200Hz, the amplitude is 8μm, and the vibration duration is 18s. Utilize the stress relaxation characteristics of metal to eliminate micro-gap in the contact surface and form an interference fit.

[0054] Example 2: This example is basically the same as Example 1, except that the coating thickness of the lubricating layer in step S2 is different. Specifically, in step S2, the lubricating layer is a molybdenum disulfide solid lubricant with a coating thickness of 5 μm.

[0055] Example 3: This example is basically the same as Example 1, except that the coating thickness of the lubricating layer in step S2 is different. Specifically, in step S2, the lubricating layer is a molybdenum disulfide solid lubricant with a coating thickness of 20 μm.

[0056] Example 4: This example is basically the same as Example 1, except that the pressing speed in step S3 is different. Specifically, in step S3, the axial pressure is applied by the servo head, the pressure value is 500N, and the pressing speed is 0.5mm / s.

[0057] Example 5: This example is basically the same as Example 1, except that the pressing speed in step S3 is different. Specifically, in step S3, the axial pressure is applied by the servo head, the pressure value is 500N, and the pressing speed is 3mm / s.

[0058] Example 6: This example is basically the same as Example 1, except that the frequency of the high-frequency micro-amplitude vibration in step S5 is different. Specifically, in step S5, the frequency of the high-frequency micro-amplitude vibration is 500Hz, the amplitude is 8μm, and the vibration duration is 18s.

[0059] Example 7: This example is basically the same as Example 1, except that the frequency of the high-frequency micro-amplitude vibration in step S5 is different. Specifically, in step S5, the frequency of the high-frequency micro-amplitude vibration is 2000Hz, the amplitude is 8μm, and the vibration duration is 18s.

[0060] Comparative Example 1: This comparative example is basically the same as Example 1, except that the wire embedding process adopts existing conventional processes, and the specific steps are as follows: S1. The ends of the flat wire are not micro-forged, and the original cut end face is maintained. S2. The flat wire surface is not coated with a molybdenum disulfide lubricating layer. The flat wire is directly aligned with the slot of the stator core 1 so that the axis of the flat wire is parallel to the center line of the slot. S3. Apply pressure along the axial direction of the flat wire to make the flat wire pass through the first groove 2 or the second groove 3, and control the pressing speed at 0.5-3mm / s. S4. After removing the axial pressure, embed a traditional insulating slot wedge at the top of the slot for radial fixation. S5. No high-frequency micro-amplitude vibration treatment is applied; the wire embedding assembly is completed directly.

[0061] Comparative Example 2: This comparative example is basically the same as Example 1, except that the micro-forging process of the flat wire end is omitted in step S1. The remaining steps are the same as in Example 1. Specifically, step S1 is: the flat wire end is not micro-forged, and the original cut end face is maintained.

[0062] Comparative Example 3: This comparative example is basically the same as Example 1, except that: in step S4, instead of using elastic recovery and geometric interference for radial locking, a traditional slot wedge is used for fixing. Specifically, step S4 is: after removing the axial pressure, a traditional insulating slot wedge is inserted into the top of the slot of the stator core 1, and the slot wedge applies radial clamping force to the flat wire to achieve fixing.

[0063] Comparative Example 4: This comparative example is basically the same as Example 1, except that the high-frequency micro-amplitude vibration processing in step S5 is omitted. The specific steps are as follows: S1. Micro-forging is performed on the ends of the flat wire. The micro-forging pressure is 12kN, the forging deformation is 5.5% of the thickness of the flat wire section, and the angle of the resulting guide slope is 20°. S2. Coat the surface of the flat wire with a solid lubricant of molybdenum disulfide with a coating thickness of 12μm, and align the flat wire with the slot of the stator core 1 so that the axis of the flat wire is parallel to the center line of the slot. S3. Apply pressure along the axial direction to the flat wire, with a pressure value of 500N and a pressing speed of 1.8mm / s, so that the flat wire passes through the first slot 2 or the second slot 3, and use the guide slope to guide the flat wire to slide into the sawtooth slot. S4. Remove the axial pressure and use the elastic recovery of the flat wire itself and the geometric interference of the sawtooth shape to lock the flat wire in the groove in the radial direction. S5. Complete the wire embedding without applying high-frequency micro-vibration treatment.

[0064] Comparative Example 5: This comparative example is basically the same as Example 1, except that the coating thickness of the lubricating layer in step S2 is lower than the lower limit of the preferred range. Specifically, step S2 is: applying molybdenum disulfide solid lubricant to the surface of the flat wire with a coating thickness of 2 μm, and aligning the flat wire with the slot of the stator core 1 so that the axis of the flat wire is parallel to the center line of the slot.

[0065] Comparative Example 6: This comparative example is basically the same as Example 1, except that the coating thickness of the lubricating layer in step S2 is higher than the upper limit of the preferred range. Specifically, step S2 is: applying molybdenum disulfide solid lubricant to the surface of the flat wire with a coating thickness of 30 μm, and aligning the flat wire with the slot of the stator core 1 so that the axis of the flat wire is parallel to the center line of the slot.

[0066] Comparative Example 7: This comparative example is basically the same as Example 1, except that the pressing speed in step S3 is lower than the lower limit of the preferred range. Specifically, step S3 is: applying pressure along the axial direction to the flat wire, with a pressure value of 500N and a pressing speed of 0.2mm / s, so that the flat wire passes through the first slot 2 or the second slot 3, and using the guide slope to guide the flat wire to slide into the sawtooth slot.

[0067] Comparative Example 8: This comparative example is basically the same as Example 1, except that the pressing speed in step S3 is higher than the upper limit of the preferred range. Specifically, step S3 is: applying pressure along the axial direction to the flat wire, with a pressure value of 500N and a pressing speed of 8mm / s, so that the flat wire passes through the first slot 2 or the second slot 3, and using the guide slope to guide the flat wire to slide into the sawtooth slot.

[0068] Comparative Example 9: This comparative example is basically the same as Example 1, except that the high-frequency micro-amplitude vibration frequency in step S5 is lower than the lower limit of the preferred range. Specifically, step S5 is: applying high-frequency micro-amplitude vibration to the stator core 1, with a vibration frequency of 300Hz, an amplitude of 8μm, and a vibration duration of 18s, using the stress relaxation characteristics of metal to eliminate the micro gap between the flat wire and the slot contact surface, forming an interference fit.

[0069] Comparative Example 10: This comparative example is basically the same as Example 1, except that the high-frequency micro-amplitude vibration frequency in step S5 is higher than the upper limit of the preferred range. Specifically, step S5 is: applying high-frequency micro-amplitude vibration to the stator core 1, with a vibration frequency of 3000Hz, an amplitude of 8μm, and a vibration duration of 18s, using the stress relaxation characteristics of metal to eliminate the micro gap between the flat wire and the slot contact surface, forming an interference fit.

[0070] Performance testing: The wiring methods of Examples 1-7 and Comparative Examples 1-10 were subjected to performance tests in sequence, including slot fill rate, insulation layer damage rate, contact thermal resistance, maximum indentation resistance, and assembly yield. The results are shown in Table 1.

[0071] Slot fill factor: After completing the winding and vibration treatment, the stator core 1 is dried to constant weight, and the total mass of the flat wire is weighed using an electronic balance. Subsequently, the stator core 1 was immersed in dichloromethane and subjected to ultrasonic vibration to completely remove the flat wire insulation layer. After removing the core, rinsing and drying it, the mass of the core body alone was weighed. , and The difference is the total mass of all flat copper conductors; based on the density of copper being 8.89 g / cm³. 3 Calculate the total volume of the copper conductor After removing the flat wire, fill each slot with low-viscosity silicone rubber. After curing, remove the molded part, measure the volume of each slot using the drainage method, and sum the volumes to obtain the total volume of the slots. Slot fill rate is calculated as follows: Each stator core was measured three times, and the average value was taken.

[0072] Insulation damage rate: This was conducted after winding was completed and before vibration treatment. The stator core 1 was fixed to a rotating worktable, and a stereomicroscope was used to observe each flat wire's exposed end and the portion extending axially from both ends of the slot segment by segment, focusing on checking for scratches, indentations, peeling, or cracks in the insulation layer. For suspected damaged areas, a scanning electron microscope was used for further confirmation and photographic recording. The number of flat wires with insulation damage was counted. The total number of flat wires embedded in the stator core 1 is Insulation layer damage rate according to Calculation. Each experiment was repeated three times, and the average breakage rate was taken as the final data.

[0073] Contact thermal resistance: Using the steady-state heat flow method, the stator core 1, after being wound and vibrated, was placed in a constant-temperature environmental chamber, with the ambient temperature controlled at 25±0.5℃. Deionized water at a constant temperature of 20℃ and a flow rate of 1L / min was circulated through the cooling holes 4 of the stator core 1, while a constant current was simultaneously applied from both ends of the flat wire winding to generate 10W of Joule heat power. T-type thermocouples with an accuracy of ±0.1℃ were embedded on the winding surface near the slot outlet and 1mm from the inner wall of the slot on the core teeth, and connected to a multi-channel data acquisition instrument. When the temperature fluctuation did not exceed 0.2℃ within 30 minutes, it was considered to be in a steady state, and the surface temperature of the winding was recorded. internal temperature of the iron core and heating power Calculate contact thermal resistance Calculate the value in K / W; measure each sample three times and take the average value.

[0074] Maximum indentation resistance: This is measured on an automatic wire inserting machine. The machine integrates high-precision pressure and displacement sensors with a sampling frequency of 100Hz. The flat wire, after micro-forging and lubrication, is aligned with the designated slot of the stator core 1 via a feeding mechanism. The servo indenter is then activated and moves axially downward at a constant speed of 1.8mm / s. After the end of the indenter contacts the end face of the flat wire, pressure and displacement values ​​are recorded until the flat wire is fully inserted into the slot and its end face is flush with the end face of the core. The maximum pressure peak value during the entire indentation process is extracted from the pressure-displacement curve, which is the maximum indentation resistance of the flat wire. Ten flat wires are randomly selected from each stator core 1 for measurement, and the arithmetic mean is calculated as the maximum indentation resistance of the sample.

[0075] Assembly yield: A batch of 50 stator cores assembled consecutively is considered as one batch. Throughout the entire winding process, including micro-forging, lubrication coating, axial pressing, radial locking after depressurization, and high-frequency micro-vibration treatment, two operators jointly inspect and record any defects. Defects include: pressing force exceeding 1000N triggering an alarm; height difference between the flat wire end face and the core end face exceeding ±0.5mm; axial movement or loosening of the flat wire after depressurization; visible damage to the insulation layer after vibration; and any abnormality that prevents subsequent assembly from being completed. If any of these conditions occurs, the slot corresponding to that flat wire is counted as one defect. If any one of the flat wires in a core is defective, the entire core is considered non-conforming. Let the number of qualified cores be... The total number of iron cores is Assembly yield rate according to Each embodiment or comparative example was tested in at least three batches, and the average value was taken.

[0076] Table 1: Performance test results of the wire embedding methods in Examples 1-7 and Comparative Examples 1-10 Group Slot fill rate (%) Insulation layer damage rate (%) Contact thermal resistance (K / W) Maximum indentation resistance (N) Assembly yield (%) Example 1 82.5 0.6 0.38 420 98.5 Example 2 81.2 1.3 0.44 485 95.8 Example 3 82.9 0.4 0.35 375 99.2 Example 4 82.7 0.5 0.37 398 98.7 Example 5 81.5 1.1 0.41 465 97.0 Example 6 81.9 0.7 0.46 425 97.5 Example 7 83.0 0.5 0.34 418 98.9 Comparative Example 1 71.5 9.0 0.92 780 80.0 Comparative Example 2 78.0 3.8 0.49 640 90.0 Comparative Example 3 75.5 0.9 0.43 425 95.5 Comparative Example 4 80.8 0.7 0.70 422 96.5 Comparative Example 5 78.5 2.8 0.51 595 92.0 Comparative Example 6 80.0 1.6 0.54 345 93.5 Comparative Example 7 82.1 0.6 0.39 415 98.0 Comparative Example 8 79.2 3.0 0.47 570 91.5 Comparative Example 9 81.0 1.2 0.62 425 95.0 Comparative Example 10 81.3 2.0 0.45 428 94.0 A comparison between Example 1 and Comparative Example 1 reveals that: Comparative Example 1 employs conventional processes without micro-forging of the flat wire ends, without applying a lubricating layer, and without applying high-frequency vibration. The flat wire ends retain the sharp edges formed by the original cutting, directly impacting the stepped corner of the stepped groove during pressing, resulting in stress concentration at the contact point and a peak pressing resistance of 780N. This impact load causes extensive scratching and peeling of the insulation layer on the flat wire surface, with a breakage rate of 9.0%. Simultaneously, the dry friction without a lubricating layer causes the flat wire to twist circumferentially within the groove, preventing tight packing and leaving irregular gaps within the groove, resulting in a groove fill factor of only 71.5%. Without high-frequency vibration post-treatment, the flat wire maintains a multi-point discrete contact state with the groove wall, the actual contact area being less than 30% of the apparent area, and the air gap causing a contact thermal resistance as high as 0.92K / W.

[0077] A comparison of Example 1 and Comparative Example 2 reveals that: Comparative Example 2 did not perform micro-forging on the ends of the flat wire, resulting in zero deformation. The ends of the flat wire retained the sharp edges from the original cutting. These edges formed line contact with the stepped corners of the slot during pressing, leading to highly concentrated contact stress. The peak stress exceeded the shear strength of the insulation layer on the surface of the flat wire, causing the insulation layer to be planed off in strips by the edges, resulting in a breakage rate of 3.8%. Simultaneously, due to the absence of a guide ramp, the flat wire lacked tangential force guidance when crossing the first step, causing the flat wire axis to deviate from the center line of the slot. When multiple flat wires were arranged side-by-side, they were squeezed and twisted against each other, preventing tight stacking and resulting in a slot fill rate of 78.0%. After depressurization, the elastic recovery direction of the flat wire was inconsistent with the normal direction of the serrated steps of the slot, weakening the radial locking effect and resulting in an assembly yield of 90.0%.

[0078] A comparison between Example 1 and Comparative Example 3 reveals that Comparative Example 3 underwent micro-forging, but the deformation amount deviated from the stated range. With a deformation amount of 2%, only a small rounded corner was formed at the end of the flat wire. The radius of the rounded corner was smaller than the radius of curvature of the stepped corner of the slot, failing to produce an effective wedging guide effect. The flat wire still impacted the step with an almost sharp edge, and the local stress concentration was not adequately relieved. The maximum indentation resistance was 640N, and the insulation layer damage rate was 0.9%. With a deformation amount of 10%, the copper material at the end of the flat wire underwent excessive plastic deformation, increasing dislocation density and forming dislocation entanglements and vacancy defects, thus reducing the material's elastic limit. After the axial pressure was removed, the elastic recovery at the end of the flat wire was insufficient, failing to form a tight geometric interference with each level of the serrated step. The radial locking force weakened, the slot fill factor was 75.5%, and the assembly yield was 95.5%. In Example 1, the 5.5% deformation amount resulted in a guide slope angle of 20°, ensuring both the wedging guide effect and maintaining the elastic recovery capability.

[0079] A comparison of Example 1 and Comparative Example 4 reveals that Comparative Example 4 omits the high-frequency micro-amplitude vibration post-processing step. Its micro-forging, lubrication, and pressing steps are the same as in Example 1, with a maximum pressing resistance of 422 N. However, due to the absence of vibration, an uneven contact interface still exists on the microscale between the flat wire surface and the inner wall of the slot, with the actual contact area accounting for 10% to 30% of the apparent area, and the gap filled with air. The thermal conductivity of air is approximately 0.026 W / (m·K), while that of steel is approximately 50 W / (m·K). The contact thermal resistance is 0.70 K / W, meaning the heat generated by the winding cannot be effectively conducted to the stator core 1 and cooling holes 4 through the contact interface.

[0080] A comparison of Examples 1 / 2-3 and Comparative Examples 5-6 reveals that the molybdenum disulfide solid lubricant possesses a hexagonal layered structure with an interlayer shear strength below 10 MPa. Under indentation pressure, the molybdenum disulfide grains align along the sliding direction, forming a continuous transfer film that transforms the friction interface into a molybdenum disulfide-molybdenum disulfide contact, reducing the friction coefficient to 0.05-0.08. In Comparative Example 5, the lubricant layer thickness is 2 μm, and the film cannot form a continuous coverage; local areas show direct copper-steel contact, resulting in a friction coefficient exceeding 0.3, a maximum indentation resistance of 595 N, and an insulation layer breakage rate of 2.8%. In Comparative Example 6, the lubricant layer thickness is 30 μm. Excess lubricant is squeezed and aggregated under high pressure, forming agglomerates. These agglomerates generate three-body abrasive wear between the flat wire and the groove wall, resulting in an insulation layer breakage rate of 1.6%. Simultaneously, the agglomerates hinder precise positioning of the flat wire, leading to a groove fill factor of 80.0%. Both the 12 μm thickness in Example 2 and the 20 μm thickness in Example 3 can form a complete and not excessive lubricating film, with the 20 μm thickness reducing the maximum indentation resistance to 375 N.

[0081] A comparison of Examples 1 / 4-5 and Comparative Examples 7-8 reveals that the pressing speed affects material deformation behavior and lubricant film formation. In Comparative Example 7, with a speed of 0.2 mm / s, the lubricant film was fully formed, but prolonged pressure could induce creep in the flat wire, affecting the elastic recovery accuracy after pressure release, resulting in an assembly yield of 98.0%. In Comparative Example 8, with a speed of 8 mm / s, the pressing process involved dynamic impact loading. The yield strength of the flat wire material increased instantaneously due to strain rate sensitivity, and the lubricant did not have time to spread and orient itself, leading to the disruption of the boundary lubrication state. Under high-speed impact, the contact time between the flat wire edge and the groove step was only a few milliseconds, converting energy into localized heat and elastic stress waves. The instantaneous temperature at the contact point could exceed the glass transition temperature of the insulation layer by approximately 150°C, causing the insulation layer to soften and tear, resulting in a breakage rate of 3.0%. The impact load also induced plastic buckling of the silicon steel sheet edge of the stator core 1, resulting in an assembly yield of 91.5%. The speeds of 0.5 mm / s in Example 4 and 3 mm / s in Example 5 are both within the range, with 0.5 mm / s resulting in an insulation layer breakage rate of 0.5%.

[0082] A comparison of Examples 1 / 6-7 and Comparative Examples 9-10 reveals that the frequency of high-frequency micro-amplitude vibration determines the activation efficiency of stress relaxation. Comparative Example 9, with a frequency of 300Hz, suffers from insufficient vibration energy to overcome the interatomic potential barrier. Dislocations at the micro-bumps cannot be initiated or their movement distance is too short, resulting in only elastic deformation of the material without plastic flow, failing to effectively fill micro-gaps, and a contact thermal resistance of 0.62K / W. Comparative Example 10, with a frequency of 3000Hz, has a vibration wavelength close to the characteristic dimensions of the stator core 1, such as tooth width or slot depth, exciting structural resonance or elastic wave standing wave reflection. The vibration energy distribution is uneven: the amplitude at nodes is close to zero, with no relaxation effect; the amplitude at antinodes is amplified, potentially exceeding the material's fatigue limit, initiating micro-cracks in the flat wire or stator core 1. The insulation layer exhibits fatigue cracking under repeated alternating stress, with a failure rate of 2.0%. In Example 6, a frequency of 500Hz resulted in a contact thermal resistance of 0.46K / W, and in Example 7, a frequency of 2000Hz resulted in a contact thermal resistance of 0.34K / W. Both maintained a low breakage rate and a high assembly yield.

[0083] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A stepped slot stator core for improving slot fill factor, characterized in that, include: Stator core (1); The first slot (2) is provided on the top of the stator core (1) and is distributed at intervals along the circumference of the stator core (1); The second slot (3) is located on the top of the stator core (1) and is staggered with the first slot (2) in the circumferential direction; Cooling holes (4) are opened through the periphery of the stator core (1) to allow the cooling medium to flow and carry away heat; The stator core (1) is configured such that the inner wall structures of the first slot (2) and the second slot (3) are arranged in a V-shape symmetrical arrangement. The opening of the first slot (2) faces the inner diameter direction of the stator core (1), and the opening of the second slot (3) faces the outer diameter direction of the stator core (1). The first slot (2) and the second slot (3) are each provided with symmetrically distributed limiting structures, so that the flat wire inserted into any slot can be limited by the two sides of the symmetrical structure in the slot, thereby achieving bidirectional constraint independently in a single slot and improving the slot fill factor.

2. The stepped slot stator core for improving slot fill factor according to claim 1, characterized in that: The limiting structure of the first slot (2) is composed of symmetrically arranged first stepped bosses (21); the limiting structure of the second slot (3) is composed of symmetrically arranged second stepped bosses (31).

3. A stepped slot stator core for improving slot fill factor according to claim 2, characterized in that: The first stepped boss (21) and the second stepped boss (31) are serrated in the axial section of the stator core (1).

4. A stepped slot stator core for improving slot fill factor according to claim 1, characterized in that: Cooling holes (4) are provided through the periphery of the stator core (1). The cooling holes (4) are arranged along the axial direction of the stator core (1) and are arranged away from the magnetic circuit of the tooth.

5. A stepped slot stator core for improving slot fill factor according to claim 1, characterized in that: The depths of the first slot (2) and the second slot (3) are adapted to the axial length of the stator core (1), and the slots maintain a constant cross-sectional shape along the axial direction.

6. A method for flat wire insertion into a stepped slot stator core to improve slot fill factor, based on the stepped slot stator core for improving slot fill factor as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Micro-forging is performed on the ends of the flat wire to form a guide slope that matches the serrated profile of the stepped groove. S2. Apply a lubricating layer to the surface of the flat wire and align the flat wire with the slot of the stator core so that the axis of the flat wire is parallel to the center line of the slot. S3. Apply pressure along the axial direction of the flat wire to make the flat wire pass through the multi-stage stepped boss in the first or second slot, and use the guide ramp to guide the flat wire to slide into the sawtooth slot. S4. Remove the axial pressure and use the elastic recovery of the flat wire itself and the geometric interference of the sawtooth shape to lock the flat wire in the groove in the radial direction. S5. Apply high-frequency micro-amplitude vibration to the stator core to eliminate the micro-gap between the flat wire and the slot by utilizing the stress relaxation characteristics of the metal, thus forming an interference fit.

7. The method for flat wire embedding of a stepped slot stator core to improve slot fill factor according to claim 6, characterized in that: In step S1, the pressure of micro-forging is 5-20kN, the forging deformation is 3-8% of the thickness of the flat wire section, and the angle of the formed guide slope is 10-30°.

8. The method for flat wire embedding of a stepped slot stator core to improve slot fill factor according to claim 6, characterized in that: In step S2, the lubricating layer is a molybdenum disulfide solid lubricant with a coating thickness of 5-20 μm.

9. A method for inserting flat wire into a stepped slot stator core to improve slot fill factor according to claim 6, characterized in that: In step S3, the axial pressure is applied by a servo pressure head, with a pressure range of 200-800N and an indentation speed of 0.5-3mm / s.

10. A method for inserting flat wire into a stepped slot stator core to improve slot fill factor according to claim 6, characterized in that: In step S5, the frequency of the high-frequency micro-amplitude vibration is 500-2000Hz, the amplitude is 2-15μm, and the vibration duration is 5-30s.

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