Stator integrated oil-immersed cooling structure of axial flux motor and yokeless axial flux motor

Abstract

The application discloses a stator integrated oil-immersed cooling structure of an axial flux motor and a yokeless axial flux motor, and belongs to the technical field of drive motor thermal management. The application is used for solving the double problems of high-efficiency heat dissipation and high-reliability mechanical fixation of the stator of the yokeless axial flux motor. The stator support is in a spoke structure, and an internal cooling liquid flow channel network is integrated in the stator support, including an oil inlet, an annular shunt flow channel, an inner wall flow channel in the side wall of the stator slot and an oil outlet. Cooling oil is sprayed out through the spray outlet at the end of the inner wall flow channel and directly cools the winding. A flow guide baffle is arranged in the stator slot and used for guiding flow and supporting the winding. The inner side of the end cover is provided with an embedded positioning groove matched with the stator tooth and a supporting rib providing axial compression, so that three-dimensional locking of the stator assembly is realized. The end cover is provided with a thinning area close to the air gap side to optimize the magnetic circuit.

Description

Technical Field

[0001] This invention relates to the field of thermal management technology for drive motors, specifically to an axial flux permanent magnet synchronous motor, and more particularly to a stator-integrated oil-cooling structure for a yokeless axial flux motor. Background Technology

[0002] With the acceleration of global electrification, drive motors are constantly evolving towards higher torque density, higher power density, and lighter weight. Compared to radial flux motors, which are limited by traditional magnetic circuit structures and core utilization, axial flux permanent magnet motors, especially those with yokeless segmented armature topologies (such as the YASA structure), have shown significant advantages in achieving extremely high torque density, high efficiency, and compact axial structure by eliminating continuous stator yokes and using independent concentrated winding stator teeth. They have become an ideal choice for high-performance applications such as hub drives and flywheel energy storage.

[0003] However, these advantages come with more severe challenges in thermal management and mechanical fixation. In terms of thermal management, because the continuous metal yoke, the primary heat conduction path, is eliminated, the stator teeth and windings are thermally separated, making it difficult to effectively conduct the generated heat to the external casing via traditional pathways. Simultaneously, the dual-rotor stator structure and extremely small air gap design commonly used in these motors further restrict heat dissipation channels, causing heat to accumulate inside the stator assembly, especially at the windings. This easily leads to accelerated aging of the insulation material or irreversible demagnetization of the permanent magnets, severely limiting the motor's continuous output capacity and reliability. Currently, common air-cooling and liquid-cooling solutions for the casing have minimal cooling effect on the "hot spots" inside the yokeless stator due to the inefficient heat transfer paths, making it difficult to meet the high power density operation requirements.

[0004] In terms of structural fixation, the segmented stator core is subjected to significant radial, tangential, and axial stresses under complex alternating electromagnetic forces. Traditional potting adhesive fixation methods are prone to fatigue cracking and creep relaxation under long-term thermo-mechanical coupling loads, leading to a decrease in stator assembly stiffness and loss of positioning accuracy, which may in turn cause increased electromagnetic vibration and noise or even structural failure.

[0005] Direct oil cooling technology is considered an effective way to solve the heat dissipation problem of high power density motors, but when applied to yokeless axial flux motors, it still faces several technical challenges: First, if the cooling oil directly enters the narrow air gap, significant fluid friction (oil churning) losses will occur, leading to decreased efficiency and additional heat generation; second, if the existing flow channel design is not reasonable, a "dead zone" for cooling oil flow can easily form inside the windings, causing poor local heat dissipation; third, to achieve effective oil immersion cooling and sealing, complex additional sealing and piping components are often required, increasing system complexity and manufacturing costs. Furthermore, the internal space of the stator support, as the main load-bearing structure, is often not fully utilized in traditional designs, indicating potential for optimization.

[0006] In summary, yokeless axial flux motors face two main challenges: interrupted heat dissipation paths and excessively high hotspot temperatures due to the lack of a continuous yoke in the stator; and unreliable fixation of the segmented stator assembly under complex electromagnetic forces. Therefore, an innovative integrated design scheme is urgently needed to collaboratively address the dual challenges of efficient stator heat dissipation and highly reliable mechanical fixation in yokeless axial flux motors, thereby fully unlocking their performance potential. Summary of the Invention

[0007] To address the dual challenges of efficient stator heat dissipation and highly reliable mechanical fixation in yokeless axial flux motors, this invention provides an integrated oil-immersed cooling structure for the stator of an axial flux motor and a yokeless axial flux motor.

[0008] In a first aspect, the present invention provides a stator integrated oil-immersed cooling structure for an axial flux motor, comprising:

[0009] Stator support 1, which has a network of coolant flow channels inside;

[0010] The stator core winding assembly 2 consists of multiple independent stator tooth cores distributed along the circumference and concentrated windings respectively mounted on each of the stator tooth cores. The stator core winding assembly 2 is fixed on the stator support 1.

[0011] A pair of end caps 3 are respectively encapsulated on both sides of the axial direction of the stator support 1 and the stator core winding assembly 2;

[0012] The coolant flow channel network has a spray outlet toward the winding for guiding coolant to the surface and gaps of the winding;

[0013] The inner side of the end cap 3 is provided with a positioning structure that matches the end shape of the independent stator tooth core, which is used to limit and press the stator core winding assembly 2 in the axial, radial and tangential dimensions.

[0014] Preferably, the stator support 1 is an integrally formed spoke-shaped structure, including an inner ring, an outer ring, and a plurality of radial spokes connecting the inner ring and the outer ring;

[0015] Stator slots are formed between adjacent radial spokes to accommodate the stator core winding assembly 2, the windings extending into the stator slots.

[0016] Preferably, the coolant flow channel network is integrated into the body of the stator support 1 and forms a complete coolant circulation path;

[0017] The coolant flow channel network includes:

[0018] Oil inlet 102 is provided on the inner ring of the stator support 1;

[0019] The distribution channel includes an annular oil inlet diversion channel 106 formed in the inner ring, and the oil inlet diversion channel 106 is connected to the oil inlet 102;

[0020] Multiple inner wall flow channels 111 are formed inside the radial spokes that constitute the sidewall of the stator slot, and are connected to the oil inlet diversion channel 106 through an inner wall inlet 107 provided in the inner ring. Each inner wall flow channel 111 is provided with an injection outlet 112 at its end.

[0021] The oil outlet channel includes an oil outlet channel 109 formed in the inner ring and parallel to the oil inlet diversion channel 106. One end of the oil outlet channel 109 is connected to the bottom area of ​​the stator slot through the oil outlet channel outlet 108, and the other end is connected to the oil outlet 103 provided on the inner ring.

[0022] The flow path of the cooling oil is as follows: it enters the oil inlet branch channel 106 from the oil inlet 102 for distribution, enters the corresponding inner wall channel 111 through each inner wall inlet 107, is sprayed out from the spray outlet 112 to cool the winding, and the oil that has absorbed heat flows into the oil outlet channel 109 through the oil outlet 108, and is finally discharged from the oil outlet 103.

[0023] Preferably, the distribution channel is sealed by an inner channel top cover 101 located at the end of the inner ring to form an annular oil distribution main pipe.

[0024] Preferably, the injection outlet 112 is a plurality of holes or slits distributed axially along the inner wall flow channel 111, with the opening direction pointing towards the winding in the stator slot.

[0025] Preferably, a flow guide baffle 104 is also provided in the stator slot. The flow guide baffle 104 is connected to the radial spokes that form the two opposite sidewalls of the stator slot. It is used to diffuse and guide the coolant from the injection outlet 112 into the gap of the winding, and at the same time provide lateral support to the winding.

[0026] The drainage baffle 104 has a layered or grid-like structure.

[0027] Preferably, the positioning structure on the end cap 3 includes:

[0028] The radial and tangential positioning part is a stator tooth embedding positioning groove 304 formed on the inner side of the end cover 3, and the end of the independent stator tooth core is embedded in the stator tooth embedding positioning groove 304.

[0029] The axial clamping part is a stator end support rib 303 protruding from the inner side of the end cover 3;

[0030] The stator end support rib 303 is constructed in any of the following ways:

[0031] (a) Abutting against the end face of the stator core winding assembly 2;

[0032] (b) Abutting against the end face of the stator support 1;

[0033] (c) Simultaneously abutting against the end face of the stator core winding assembly 2 and the end face of the stator support 1.

[0034] Preferably, the end cap 3 has a thinning region 301 in the area corresponding to the motor air gap;

[0035] The wall thickness of the thinning region 301 is 0.3 mm to 0.5 mm.

[0036] Preferably, the stator support 1 is made of high-strength aluminum alloy or special engineering plastic.

[0037] In a second aspect, the present invention provides a yokeless axial flux motor, comprising the stator integrated oil-immersed cooling structure of the aforementioned axial flux motor; and

[0038] Two rotors 4 are respectively disposed on both sides of the stator integrated oil-immersed cooling structure.

[0039] The beneficial effects of this invention are:

[0040] 1. Excellent heat dissipation and high power: Through the design of the internal wall flow channels and outlets, the cooling oil is forced into the depths of the windings, directly flushing and cooling the stator windings, achieving impact cooling. The flow guide baffles ensure that the oil flow covers the winding surface, eliminating thermal dead zones. This effectively solves the problem of difficult stator heat dissipation in yokeless axial flux motors, thereby significantly improving the motor's thermal management limits and sustainable power density.

[0041] 2. Stable structure and long service life: Through the stator tooth embedding positioning groove on the end cover and the stator end support rib, combined with the flow guide baffle of the stator bracket, three-dimensional locking (axial, radial, and tangential) of the stator segment core is achieved. This provides extremely high structural rigidity, effectively resisting vibration, impact, and complex electromagnetic forces during vehicle operation, solving the problem of unstable stator assembly fixation, and significantly enhancing the mechanical reliability of long-term operation.

[0042] 3. Compact size and high efficiency: The cooling channels are directly integrated inside the stator support, eliminating the need for complex external piping and sealing, saving valuable internal space in the motor, resulting in a compact structure and high integration. Simultaneously, the thinning design of the end cap optimizes the magnetic circuit, reduces the effective magnetic gap, helps improve magnetic flux density and torque density, and reduces eddy current losses.

[0043] 4. Superior Overall Performance: This invention cleverly utilizes the internal space of the stator support to construct a cooling network and achieves mechanical locking through end caps. This integrated design enhances heat dissipation and structural strength while achieving comprehensive performance optimization, enabling the motor to possess both high power density and high reliability. Attached Figure Description

[0044] Figure 1 This is an exploded view of the stator assembly provided in an embodiment of the present invention.

[0045] Figure 2 This is a three-dimensional structural diagram of the stator support.

[0046] Figure 3 This is a cross-sectional view of the stator support.

[0047] Figure 4 This is an axial top view of the stator assembly after assembly.

[0048] Figure 5 This is a magnified view of the flow channel details of a single stator support unit.

[0049] Figure 6 This is a partial sectional view of the flow channel structure inside the stator support.

[0050] Figure 7 This is an external side view of the end cap.

[0051] Figure 8 This is an inner side view of the end cap.

[0052] In the diagram: 1. Stator support; 101. Inner flow channel top cover; 102. Oil inlet; 103. Oil outlet; 104. Drainage baffle; 105. Stator support bolt hole; 106. Oil inlet branch flow channel; 107. Inner wall inlet; 108. Oil outlet; 109. Oil outlet; 110. Flow channel between support and winding; 111. Inner wall flow channel; 112. Injection outlet; 2. Stator core winding assembly; 3. End cover; 301. Thinning zone; 302. End cover bolt hole; 303. Stator end support rib; 304. Stator tooth embedding positioning groove; 4. Rotor. Detailed Implementation

[0053] 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.

[0054] This invention aims to solve the dual challenges of efficient heat dissipation and highly reliable mechanical fixation of the stator in a yokeless axial flux motor, and provides an integrated solution.

[0055] Please see Figure 1 The exploded view of the stator assembly of the yokeless axial flux motor provided in the embodiment of the present invention clearly shows the assembly relationship of the left and right end covers, stator support, stator winding assembly and outer rotor.

[0056] The core of this invention lies in a stator integrated oil-immersed cooling structure, which mainly consists of the following parts: a stator support 1, a stator core winding assembly 2, and a pair of end caps 3 located on both sides of its axial direction. When applied to a complete machine, this stator structure is held by two rotors 4 from both sides, forming a typical yokeless axial flux (such as YASA) motor topology.

[0057] I. Stator Support: The load-bearing frame for integrated cooling channels

[0058] The stator support 1, as the skeleton of the entire stator assembly, is designed to possess both high structural rigidity and the ability to integrate complex flow channels. For example... Figure 2 and Figure 3The diagram shows a three-dimensional structural schematic of the stator support 1 and a cross-sectional structural schematic from another angle. The stator support 1 is preferably made of high-strength aluminum alloy using 3D printing, or integrally molded using special engineering plastics via injection molding. Its main body exhibits a spoke-shaped topology, consisting of an inner ring, an outer ring, and multiple radial spokes connecting them. These spokes provide primary structural support, while their internal space is cleverly designed as cooling oil delivery channels.

[0059] More importantly, stator slots for accommodating the stator core winding assembly 2 are naturally formed between adjacent radial spokes. For example... Figure 4 As shown, it is an axial top view of the stator assembly after assembly, and the flow direction of the cooling oil in the gap between the bracket and the winding can be clearly seen (indicated by the arrow).

[0060] The present invention integrates a three-dimensional coolant flow channel network into the body of the stator support 1. Figure 3 This complex internal flow channel network is shown in detail. Specifically, the network includes:

[0061] Oil inlet 102 and oil outlet 103: respectively located on stator bracket 1, used to connect to external cooling oil circulation system.

[0062] Distribution channel: Includes oil inlet distribution channel 106 located in the inner ring area. This channel has an annular structure, and its top is sealed by the inner channel top cover 101, thereby forming an annular oil distribution manifold to ensure that the cooling oil pressure entering from the oil inlet 102 is evenly distributed.

[0063] Multiple inner wall channels 111: These channels are formed inside the radial spokes that form the sidewalls of the stator slots. Each inner wall channel 111 is connected to the aforementioned annular oil distribution manifold (i.e., the oil inlet branch channel 106) via an inner wall inlet 107 formed on the inner annular wall.

[0064] Jet outlet 112: such as Figure 5 and Figure 6 (As shown in the enlarged view of the stator support flow channel and the partial cross-sectional view of the inner wall flow channel), multiple spray outlets 112 are distributed axially at the ends of each inner wall flow channel 111. This design allows the cooling oil flow to accelerate in the narrow flow channel 111 and then be sprayed out at high speed from the outlets 112 in a "sprinkler" shape.

[0065] Oil outlet channel: including oil outlet channel 109, which is also integrated in the inner ring area and runs parallel to the oil inlet branch channel 106. One end of the oil outlet channel 109 is connected to the bottom area of ​​each stator slot through the oil outlet channel outlet 108, and the other end converges to the oil outlet 103.

[0066] The cooling process is as follows: Cooling oil is pumped in through inlet 102, first entering the annular inlet distribution channel 106 to ensure uniform oil pressure. Subsequently, the oil enters the corresponding inner wall channels 111 through each inner wall inlet 107. Due to the change in the channel cross-sectional area, the oil flow is accelerated, and finally, it is vertically sprayed from the jet outlet 112 onto the sides and internal gaps of the stator winding 2. This impact jet perpendicular to the heating surface greatly thins the thermal boundary layer, achieving an extremely high local heat transfer coefficient. After the jet covers the winding, the oil flows through all the inter-turn gaps of the coil under the guidance of the flow, absorbing heat and increasing its temperature. Finally, under the action of gravity and pressure difference, it collects at the oil outlet 108 at the bottom of the stator slot, and is discharged from the oil outlet 103 via the oil outlet channel 109, completing the cooling cycle.

[0067] II. Drainage baffle: Dual function of guiding and supporting flow

[0068] like Figure 2 and Figure 6 As shown, a current-guiding baffle 104 is also provided in the stator slot, downstream of the winding. This baffle is connected to the radial spokes that form the two opposite sidewalls of the stator slot and has a dual core function:

[0069] 1. Fluid Guiding: As a fluid guiding component, it precisely diverts and guides the oil flow ejected from the injection outlet 112, ensuring that it flows closely against the winding surface and that the oil flow fills all winding gaps to completely eliminate heat dissipation dead zones. At the same time, its layered or grid-like structure can induce turbulence in the fluid, disrupting the laminar boundary layer and further improving the heat transfer coefficient.

[0070] 2. Mechanical support: As a mechanical structure, it is in direct contact with the stator winding 2, providing tangential support for the winding and stator core, effectively preventing them from twisting or displacing under the action of electromagnetic forces (such as Lorentz force).

[0071] III. End Cap: Integrated design for sealing, positioning, and magnetic circuit optimization

[0072] End cap 3 not only plays a key role in sealing the oil chamber, but also integrates innovative mechanical positioning features and electromagnetic optimization design. Figure 7 and Figure 8 These are the outer and inner side views of end cap 3, respectively.

[0073] like Figure 8 As shown, two key mechanical positioning features are provided on the inner side of end cap 3:

[0074] Stator tooth mounting and positioning grooves 304: These grooves are radially distributed and their shape perfectly matches the end face (tooth) shape of the stator core. During assembly, the core end is directly embedded into the groove, thereby converting the tangential shear force acting on the stator teeth into compressive stress in the end cap material. This achieves strict limitation on the radial and tangential displacement of the stator core and significantly improves torsional reliability.

[0075] Stator end support ribs 303: These support ribs are also radially distributed, and their positions precisely correspond to the spokes and winding ends of the stator bracket 1. When the end cover 3 is locked by bolts (corresponding to bolt holes 302 and 105), the support ribs 303 apply axial preload to the stator structure to prevent the stator lamination core from loosening under axial magnetic attraction, thus providing reliable axial support.

[0076] like Figure 7 As shown, a thinning region 301 is specially designed on the side of the end cover 3 near the motor air gap (outer side). The plane of this region is lower than the outer perimeter, controlling the wall thickness to an extremely thin range of 0.3mm to 0.5mm. This "thinning" design brings two major benefits:

[0077] 1. Optimized magnetic circuit: The thickness of the end cover on the air gap side is reduced, making the stator core end face closer to the rotor magnet, thereby reducing magnetic resistance and improving the effective air gap magnetic flux density and the motor torque density.

[0078] 2. Suppressing losses: When the end cap is made of metal, this thinning design can significantly reduce the cross-sectional area of ​​the eddy current path induced by the alternating magnetic field, thereby effectively suppressing eddy current losses.

[0079] IV. Summary of Overall System Integration and Advantages

[0080] By assembling the aforementioned stator integrated oil-immersed cooling structure with the two rotors 4, a complete yokeless axial flux motor is formed (see...). Figure 1 This invention achieves the following comprehensive benefits through the ingenious combination of an integrated flow channel and end cap positioning features:

[0081] Extremely high heat dissipation efficiency: Through precise injection and forced guidance by the baffle, the cooling oil reaches the heat source directly and covers the entire surface, eliminating fluid dead zones.

[0082] Excellent structural stability: The positioning groove of the end cover, the support rib and the baffle of the bracket work together to achieve three-dimensional locking of the stator assembly, which has strong vibration and impact resistance.

[0083] Compact and highly integrated: Built-in flow channels save space and increase power density.

[0084] Optimized electromagnetic performance: The thinned end cap area reduces magnetic reluctance and eddy current loss.

[0085] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A stator integrated oil-immersed cooling structure for an axial flux motor, characterized in that, include: Stator support (1) has a network of coolant channels inside it; The stator core winding assembly (2) consists of multiple independent stator tooth cores distributed along the circumference and concentrated windings respectively mounted on each of the stator tooth cores. The stator core winding assembly (2) is fixed on the stator support (1). A pair of end caps (3) are respectively encapsulated on both sides of the stator bracket (1) and the stator core winding assembly (2); The coolant flow channel network has a spray outlet toward the winding for guiding coolant to the surface and gaps of the winding; The inner side of the end cap (3) is provided with a positioning structure that matches the end shape of the independent stator tooth core, which is used to limit and press the stator core winding assembly (2) in the three dimensions of axial, radial and tangential.

2. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 1, characterized in that, The stator support (1) is an integrally formed spoke-shaped structure, including an inner ring, an outer ring, and multiple radial spokes connecting the inner ring and the outer ring; Stator slots are formed between adjacent radial spokes to accommodate the stator core winding assembly (2), the winding extending into the stator slots.

3. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 2, characterized in that, The coolant flow channel network is integrated into the body of the stator support (1) and forms a complete coolant circulation path; The coolant flow channel network includes: An oil inlet (102) is provided on the inner ring of the stator support (1); The distribution channel includes an annular oil inlet branch channel (106) formed in the inner ring, the oil inlet branch channel (106) being connected to the oil inlet (102); Multiple inner wall flow channels (111) are formed inside the radial spokes that constitute the sidewall of the stator slot, and are connected to the oil inlet branch flow channel (106) through the inner wall inlet (107) provided in the inner ring. The end of each inner wall flow channel (111) is provided with the injection outlet (112). The oil outlet channel includes an oil outlet channel (109) formed in the inner ring and parallel to the oil inlet diversion channel (106). One end of the oil outlet channel (109) is connected to the bottom area of ​​the stator slot through the oil outlet channel outlet (108), and the other end is connected to the oil outlet (103) provided on the inner ring. The flow path of the cooling oil is as follows: it enters the oil inlet branch channel (106) from the oil inlet (102) for distribution, enters the corresponding inner wall channel (111) through each inner wall inlet (107), is sprayed out from the spray outlet (112) to cool the winding, and the oil after absorbing heat flows into the oil outlet channel (109) through the oil outlet (108) and is finally discharged from the oil outlet (103).

4. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 3, characterized in that, The distribution channel is sealed by an inner channel top cover (101) located at the end of the inner ring to form an annular oil distribution main pipe.

5. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 3, characterized in that, The injection outlet (112) is a plurality of holes or slits distributed axially along the inner wall flow channel (111), with the opening direction pointing towards the winding in the stator slot.

6. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 2, characterized in that, The stator slot is also provided with a flow guide baffle (104), which is connected to the radial spokes that form the two opposite sidewalls of the stator slot. It is used to diffuse and guide the coolant from the injection outlet (112) into the gap of the winding, and at the same time provide lateral support to the winding. The drainage baffle (104) has a layered or grid-like structure.

7. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 1, characterized in that, The positioning structure on the end cap (3) includes: The radial and tangential positioning part is a stator tooth mounting positioning groove (304) formed on the inner side of the end cover (3), and the end of the independent stator tooth core is embedded in the stator tooth mounting positioning groove (304); The axial pressing part is a stator end support rib (303) protruding from the inner side of the end cover (3). The stator end support rib (303) is constructed in any of the following ways: (a) Abutting against the end face of the stator core winding assembly (2); (b) Abutting against the end face of the stator support (1); (c) Simultaneously abutting against the end face of the stator core winding assembly (2) and the end face of the stator support (1).

8. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 7, characterized in that, The end cap (3) has a thinning area (301) in the region corresponding to the motor air gap. The wall thickness of the thinning region (301) is 0.3 mm to 0.5 mm.

9. The stator integrated oil-immersed cooling structure of an axial flux motor according to claim 1, characterized in that, The stator support (1) is made of high-strength aluminum alloy or special engineering plastic.

10. A yokeless axial flux motor, characterized in that, Including a stator integrated oil-immersed cooling structure for an axial flux motor as described in any one of claims 1 to 9; and Two rotors (4) are respectively disposed on both sides of the stator integrated oil-immersed cooling structure.

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