YASA axial flux permanent magnet motor and oil cooling system and oil cooling method thereof

Abstract

The invention discloses an oil cooling system of a YASA axial flux permanent magnet motor, which comprises a semicircular oil duct arranged between a motor shell and a stator bracket outer check ring, a plurality of oil nozzles communicated between the semicircular oil duct and a stator inner cavity, a stator oil outlet communicated with the stator inner cavity, an oil guide opening and a rotor oil outlet, at least two oil guide openings are formed in the stator bracket and are correspondingly communicated between the two rotor inner cavities and the stator inner cavity; each rotor oil outlet is arranged in the corresponding rotor inner cavity in a matched mode. Compared with the prior art, on one hand, cooling oil flows in the stator inner cavity to take away heat on the surface of the winding, and on the other hand, the cooling oil in the stator inner cavity is guided into the rotor inner cavity through the oil guide opening, so that oil drops are thrown to high-temperature areas such as the axial end face of the stator, the surface of the permanent magnet and the surface of a rotor system, and the heat is effectively taken away; and the problem of over-high oil friction loss is also avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet motors, and in particular to a YASA axial flux permanent magnet motor and an oil cooling system and an oil cooling method thereof. Background Art

[0002] YASA axial flux permanent magnet motors, due to their compact structure, small size, light weight, high torque, and high power density, have been widely used in high-performance electric vehicles, industrial automation, and wind power generation. However, these motors generate a large amount of heat during operation. If this heat is not dissipated effectively and promptly, it will cause the motor temperature to rise, performance to decline, and even damage the insulation material, seriously affecting the motor's lifespan and reliability.

[0003] For the YASA axial flux permanent magnet motor with a dual-rotor single-stator structure, the stator is located between the two rotors and has no stator yoke. The double air gap has poor heat dissipation and large thermal resistance. In addition, the motor is in a high-performance state for a long time and has high heat generation power. Both air cooling and water cooling methods are difficult to meet the heat dissipation requirements.

[0004] In order to improve the heat dissipation effect, oil cooling is now widely used; for example, Figure 1 The oil cooling structure of the YASA axial flux permanent magnet motor shown in the figure forms a semicircular oil channel (1) between the motor housing and the outer retaining ring of the stator bracket, and a plurality of oil spray ports (2) are opened on the semicircular oil channel and connected to the inner cavity of the stator. The cooling oil is transported from the oil reservoir to the main oil inlet of the motor by an oil pump, and then enters the semicircular oil channel (1) and is squeezed into small droplets through the oil spray ports (2) to spray on the surface of the winding (9) to directly spray and cool the winding (9). Under the action of gravity, the cooling oil flows downward through the spacing of the winding (9). At the same time, to ensure that the cooling oil can fully wrap and take away the heat generated by the winding (9), a baffle is added at an appropriate position; finally, it flows into the return oil pipe through the stator oil outlet (3).

[0005] During use, the aforementioned oil-cooling structure has difficulty dissipating heat from the stator core and rotor system (including permanent magnets and rotor) in the YASA axial flux permanent magnet motor, as the yokeless stator core and rotor system (including permanent magnets and rotor) are unable to contact the cooling oil. This results in inefficient heat dissipation from the stator core and rotor system, which relies solely on natural convection within the rotor cavity. In particular, the stator core, a critical area where heat is highly concentrated, is significantly limited in its effective heat transfer due to the poor thermal conductivity of the air inside the motor and its compact spatial layout. Consequently, the highest temperatures generated by the motor during operation are often concentrated in the stator core, highlighting the shortcomings of existing oil-cooling technology. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide an oil cooling system and method for a YASA axial flux permanent magnet motor, so as to solve the problem of relatively poor heat dissipation capacity in the YASA axial flux permanent magnet motor in the prior art.

[0007] To achieve the above objectives, the first aspect of the present invention adopts the following technical solution: an oil cooling system for a YASA axial flux permanent magnet motor, comprising a semicircular oil passage disposed between a motor housing and an outer retaining ring of a stator bracket, a plurality of oil injection ports communicating with the semicircular oil passage and a stator inner cavity, and a stator oil outlet communicating with the stator inner cavity, and further comprising:

[0008] Oil guide openings, wherein the oil guide openings are provided on the stator support and there are at least two of them, and the oil guide openings are connected between the two rotor inner cavities and the stator inner cavity respectively;

[0009] The rotor oil outlet is provided with one rotor oil outlet in the inner cavity of each rotor.

[0010] Technical principle:

[0011] The inventors state that those skilled in the art would not consider introducing cooling oil into the rotor cavity to dissipate heat, as direct contact between the rotor system and the cooling oil would result in high oil friction losses. However, the present application introduces a cooling oil channel into a semicircular oil channel, where the cooling oil is squeezed into small droplets through an oil nozzle and sprayed onto the winding surface for direct cooling. Under the influence of gravity, the cooling oil flows downward through the winding gap, ensuring that the cooling oil can fully envelop and remove the heat generated by the winding. At the same time, the cooling oil in the stator cavity is introduced into the rotor cavity through the oil guide opening, and the oil amount in the rotor cavity is kept constant within a certain range. When the rotor system rotates at a certain speed, the rotation of the rotor system will cause the cooling oil attached to its surface to produce a strong centrifugal splashing effect, and the oil droplets are thrown to high-temperature areas such as the axial end face of the stator, the surface of the permanent magnet and the surface of the rotor system, thereby enhancing the cooling coverage range; after completing the heat exchange, the splashed oil droplets will be discharged through the rotor oil outlet to take away the heat; at the same time, the problem of excessive oil friction loss is avoided, which is unexpected by technicians in this field.

[0012] The second aspect of the present invention adopts the following technical solution: a method for oil cooling of a YASA axial flux permanent magnet motor, using the oil cooling system of the YASA axial flux permanent magnet motor described in the first aspect of the present invention, comprising:

[0013] Supplying cooling oil to the inner cavity of the stator, and controlling the oil accumulation rate of the inner cavity of the stator to always be not less than a first preset threshold, and the oil pressure to always be not less than a second preset threshold;

[0014] directing cooling oil from the stator inner cavity into the rotor inner cavity through the oil guide opening, and adjusting the oil amount in the rotor inner cavity to be maintained within a third preset threshold range;

[0015] The rotor is driven to rotate at a speed not lower than a fourth preset threshold value, so that the cooling oil in the inner cavity of the rotor is splashed and cooled under the action of centrifugal force.

[0016] The third aspect of the present invention adopts the following technical solution: a YASA axial flux permanent magnet motor, comprising an oil cooling system of the YASA axial flux permanent magnet motor as described in the first aspect of the present invention.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The oil cooling system and oil cooling method of the present invention supply cooling oil to the stator inner cavity. On the one hand, the cooling oil flows in the stator inner cavity to take away the heat from the winding surface. On the other hand, the cooling oil in the stator inner cavity is introduced into the rotor inner cavity through the oil guide opening. In combination with the oil accumulation rate, oil pressure, oil volume in the rotor inner cavity and rotor speed limit of the stator inner cavity, it is ensured that the oil droplets are thrown to high-temperature areas such as the stator axial end face, the permanent magnet surface and the rotor system surface, thereby effectively taking away the heat and avoiding the problem of excessive oil friction loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the oil cooling structure of the YASA axial flux permanent magnet motor in the background technology ( Figure 1 The direction of the arrow in the middle is the direction of cooling oil flow);

[0020] Figure 2 A schematic structural diagram of a YASA axial flux permanent magnet motor in the present invention;

[0021] Figure 3 for Figure 2 Schematic diagram of the local structure;

[0022] Figure 4 A schematic diagram of the partial structure of the oil cooling structure of a YASA axial flux permanent magnet motor in the present invention ( Figure 4 The direction of the arrow in the middle is the direction of cooling oil flow);

[0023] Figure 5 Schematic diagram of the arrangement of four oil guide opening designs on the stator bracket in the present invention;

[0024] Figure 6 Graph showing the cooling oil distribution under four oil guide opening design conditions at rated speed in the present invention;

[0025] Figure 7 This is a comparison chart of the cooling performance of the present invention under four oil guide opening design conditions;

[0026] Figure 8 The steady-state temperature field obtained by the oil-cooling structure of the YASA axial flux permanent magnet motor in the background technology;

[0027] Figure 9 This is the steady-state temperature field obtained by the oil cooling system of the YASA axial flux permanent magnet motor using an oil guide opening of 1*1.5 mm in the present invention.

[0028] The reference numerals in the drawings of the specification include: semicircular oil channel 1, oil injection port 2, stator oil outlet 3, oil guide opening 4, rotor oil outlet 5, stator bracket 6, rotor 7, permanent magnet 8, winding 9, stator 10. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below through specific embodiments:

[0030] like Figure 2 、 Figure 3 as well as Figure 4 As shown, an embodiment of the present invention proposes an oil cooling system for a YASA axial flux permanent magnet motor, including a semi-circular oil channel 1 arranged between the motor casing and the outer retaining ring of the stator bracket 6, a plurality of oil injection ports 2 connected to the semi-circular oil channel 1 and the stator inner cavity, and a stator oil outlet 3 connected to the stator inner cavity, and also including an oil guide opening 4 and a rotor oil outlet 5. The oil guide openings 4 are opened on the stator bracket 6 and there are at least two of them. The oil guide openings 4 are correspondingly connected between the two rotor inner cavities and the stator inner cavity; the rotor oil outlet 5 is provided in each rotor inner cavity.

[0031] In this embodiment, the semi-circular oil channel 1 is connected to a main oil inlet, and an oil pump is used to transport cooling oil from the oil reservoir to the main oil inlet. The cooling oil is then introduced into the semi-circular oil channel 1 and squeezed into small droplets through the oil spray port 2 to spray on the surface of the winding 9 to directly spray cool the winding 9; under the action of gravity, the cooling oil flows downward through the spacing between the windings 9, ensuring that the cooling oil can fully wrap and take away the heat generated by the windings 9; then the cooling oil flows into the return oil pipe through the stator inner cavity oil outlet for reuse.

[0032] At the same time, the cooling oil in the stator cavity is introduced into the rotor cavity through the oil guide opening 4, and the oil amount in the rotor cavity is kept constant within a certain range. When the rotor 7 rotates at a certain speed, the rotation of the rotor 7 will cause the cooling oil attached to its surface to produce a strong centrifugal splashing effect, and the oil droplets are thrown to high-temperature areas such as the axial end face of the stator 10, the surface of the permanent magnet 8 and the surface of the rotor 7, thereby enhancing the cooling coverage; after completing the heat exchange, the splashed oil droplets will flow into the return oil pipe through the rotor oil outlet 5 for reuse.

[0033] In this embodiment, there is one oil guide opening 4 between each of the rotor inner cavity and the stator inner cavity, and the rotor oil outlet 5 is located at the bottom of the motor housing and the oil guide openings 4 are all arranged on the bottom side of the stator bracket 6; at the same time, the aperture ratio of the oil guide opening 4 to the rotor oil outlet 5 is 3:8. Specifically, the aperture of the oil guide opening 4 is 1.5 mm, and the aperture of the rotor oil outlet 5 is 4 mm.

[0034] During the research and development process, the number and position of the oil guide openings were optimized as follows:

[0035] When the total oil intake of the cooling system is constant, how to distribute the cooling oil flow according to the heating characteristics of this type of high-power density motor to achieve the best heat dissipation effect is the key to oil circuit design, and the number and position of the oil guide openings directly determine the cooling oil flow distribution in the stator cavity and the rotor cavity. Therefore, the present invention optimizes the overall heat dissipation performance of the motor by comparing and analyzing the number and position of the oil guide openings, and minimizes the energy consumption of this process (mainly due to the oil friction loss caused by the direct contact between the rotor system and the cooling oil). Four oil guide opening design situations are designed, such as Figure 5 shown.

[0036] Under the four oil guide opening designs, the cooling oil distribution in the inner cavity of the single-side rotor at the rated speed of the motor (3800rpm) is as follows: Figure 6 As shown in the figure, when there is only one oil guide opening and the aperture is 1.5 mm (this can be expressed as 1*1.5 mm; other cases can be written similarly), the cooling oil forms a semi-ring on the radial outer surface of the rotor. The depth of the cooling oil in the rotor cavity just contacts the radial outer surface of the rotor, and the axial end surface of the stator is evenly covered by the oil film. When the number of oil guide openings is increased from one to two, the oil volume in the rotor cavity increases, and the rotor system becomes oil-immersed, which increases the contact area between the cooling oil and the rotor system. When the number of oil guide openings reaches three, the cooling oil is immersed to half the radial length of the permanent magnets, and the contact area between the rotor back plate and the cooling oil further expands. When the number of oil guide openings is increased to four, the gap between the rotor yoke back plate and the inner wall of the casing, as well as the air gap, is almost completely filled with oil. Due to gravity, the cooling oil accumulates more at the lower horizontal end, resulting in greater stator wetness in this area. However, the high level of oil infiltration alone cannot directly determine the cooling performance, as excessive oil accumulation can lead to a sharp increase in oil friction losses, resulting in frictional heat generation. Therefore, to accurately measure cooling performance, the convective heat transfer coefficient (CHTC) at each stator end face must be analyzed.

[0037] Comparison of cooling performance under four oil guide opening designs, such as Figure 7 As shown. Figure 7As shown in (a), the CHTC of the winding surface under the 1*1.5mm oil guide opening is 793W / (m 2 ·K), the average CHTC of the stator surface is 212W / (m 2 ·K), the average CHTC of the permanent magnet surface is 214W / (m 2 ·K). However, with the oil guide opening of 4*1.5mm, the average CHTC of the winding surface dropped to 618W / (m 2 ·K), the average CHTC of the stator surface is increased to 465W / (m 2 ·K), the average CHTC of the permanent magnet surface is also increased to 321W / (m 2 K. Figure 7 As shown in (b), with an oil guide opening of 1*1.5mm, the oil friction loss at the rated speed of 3800rpm is 1387W, and the oil friction loss at the peak speed of 6000rpm reaches 3895W; with an oil guide opening of 4*1.5mm, the oil friction loss at the rated speed of 3800rpm is 2245W, and the oil friction loss at the peak speed of 6000rpm is as high as 7514W.

[0038] Research results show that the greater the number of oil-conducting openings on the stator bracket, the more cooling oil will flow from the stator cavity, the greater the convective heat transfer coefficient between the stator and permanent magnet surfaces, and the correspondingly better heat dissipation. However, increasing the number of oil-conducting openings also results in a significant increase in oil friction losses, and the winding spray cooling effect also deteriorates due to the reduced cooling oil distribution. Therefore, from a comprehensive perspective, the number of oil-conducting openings should not be too large. After comprehensively weighing factors such as motor performance indicators and process manufacturing costs, the final choice was to use oil-conducting openings sized 1 by 1.5 mm, located on the bottom side of the stator bracket.

[0039] like Figure 8 As shown, the steady-state temperature field obtained by the oil-cooling structure of the YASA axial flux permanent magnet motor in the background technology can be concluded that: the maximum temperature of the winding is 151.3°C, the maximum temperature of the stator core is 156.6°C, the maximum temperature of the permanent magnet is 119.5°C, and the maximum temperature of the rotor is 119.5°C.

[0040] like Figure 9As shown in the figure, the steady-state temperature field obtained by the oil cooling system of the YASA axial flux permanent magnet motor with a 1*1.5mm oil guide opening in this application shows that the stator heat dissipation efficiency is 8.15 times that of the background art, and the permanent magnet heat dissipation efficiency is 1.62 times that of the background art. The maximum temperatures of the windings, stator core, permanent magnets, and rotor are 123.3°C, 95.6°C, 72.4°C, and 72.4°C, respectively. Compared with the technical solution in the background art, the maximum temperatures of the windings, stator core, permanent magnets, and rotor have all decreased significantly, by 28K, 61K, 47.1K, and 47.1K, respectively.

[0041] The oil cooling system of this invention significantly improves the overall heat dissipation efficiency of the YASA axial flux permanent magnet motor, reduces motor failure rates, and enhances motor reliability and sustained output capacity. It also offers excellent cooling performance and simple manufacturing processes, making it suitable for YASA axial flux permanent magnet motors of various sizes.

[0042] like Figure 2 As shown, according to another embodiment of the present invention, a YASA axial flux permanent magnet motor oil cooling method, using an oil cooling system of a YASA axial flux permanent magnet motor as described in the above embodiment, includes: supplying cooling oil to a stator inner cavity, and controlling the oil accumulation rate of the stator inner cavity to always be not less than a first preset threshold value, and the oil pressure to always be not less than a second preset threshold value; guiding the cooling oil in the stator inner cavity into the rotor inner cavity through an oil guide opening, and adjusting the oil amount in the rotor inner cavity to be maintained within a third preset threshold value range;

[0043] The rotor is driven to rotate at a speed not lower than a fourth preset threshold value, so that the cooling oil in the inner cavity of the rotor is splashed and cooled under the action of centrifugal force.

[0044] The first preset threshold is set based on the stator winding temperature rise characteristics, and the second preset threshold is achieved through closed-loop control of the oil pump pressure. Specifically, the first preset threshold is an oil accumulation rate of no less than 90%, and the oil pump pressure is 0.2-0.5 MPa, ensuring that the second preset threshold is an oil pressure of no less than 0.15 MPa. The fourth preset speed threshold must meet the minimum critical speed at which cooling oil splashes and covers the entire heat dissipation surface of the rotor permanent magnets. Specifically, the third preset threshold is 100-300 mL, and the fourth preset threshold is a rotor speed of no less than 500 rpm.

[0045] The above-mentioned control of the oil accumulation rate in the stator cavity to always be no less than 90% and the oil pressure in the stator cavity to always be no less than 0.15MPa ensures that the cooling oil in the stator cavity can effectively enter the rotor cavity through the oil guide opening. Furthermore, by adjusting the pressure and flow of the oil pump, the oil volume in the rotor cavity is controlled to be maintained between 100 and 300mL. At the same time, the rotor speed is no less than 500rpm, which can form a uniform oil film on the rotor surface and produce sufficient splashing during rotation. Specifically, the high-speed rotation of the rotor causes the oil adhering to its surface to produce a strong centrifugal splashing effect, and the oil droplets are thrown toward high-temperature areas such as the axial end face of the stator, the surface of the permanent magnets, and the surface of the rotor, thereby enhancing the cooling coverage. After completing the heat exchange, the splashed oil droplets will return to the oil return pipe through the rotor oil outlet and then return to the oil reservoir. After cooling, they are recycled again to ensure continuous cooling effect.

[0046] This design optimizes the oil distribution in the rotor cavity while ensuring the spray cooling of the winding, maximizing the overall heat dissipation efficiency of the motor while avoiding excessive oil friction losses.

[0047] like Figure 2 and Figure 3 As shown, according to another embodiment of the present invention, the YASA axial flux permanent magnet motor includes an oil cooling system of the YASA axial flux permanent magnet motor as described in the above embodiment, which has its advantages.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An oil cooling system for a YASA axial flux permanent magnet motor, comprising a semicircular oil channel disposed between the motor housing and the outer retaining ring of the stator support, a plurality of oil injection ports communicating between the semicircular oil channel and the stator inner cavity, and a stator oil outlet communicating with the stator inner cavity, characterized in that: Also includes: Oil guide openings, wherein the oil guide openings are provided on the stator support and there are at least two of them, and the oil guide openings are connected between the two rotor inner cavities and the stator inner cavity respectively; The rotor oil outlet is provided with one rotor oil outlet in the inner cavity of each rotor.

2. The oil cooling system of a YASA axial flux permanent magnet motor according to claim 1 is characterized in that: There is one oil guide opening between each of the rotor inner cavity and the stator inner cavity.

3. The oil cooling system of a YASA axial flux permanent magnet motor according to claim 2, characterized in that: The rotor oil outlet is located at the bottom of the motor housing and the oil guide openings are all arranged on the bottom side of the stator bracket.

4. The oil cooling system of a YASA axial flux permanent magnet motor according to claim 3 is characterized in that: The ratio of the aperture of the oil guide opening to the aperture of the rotor oil outlet is 3:

8.

5. The oil cooling system of the YASA axial flux permanent magnet motor according to claim 4 is characterized in that: The diameter of the oil guide opening is 1.5 mm, and the diameter of the rotor oil outlet is 4 mm.

6. An oil cooling method for a YASA axial flux permanent magnet motor, characterized in that: An oil cooling system for a YASA axial flux permanent magnet motor according to any one of claims 1 to 5, comprising: Supplying cooling oil to the inner cavity of the stator, and controlling the oil accumulation rate of the inner cavity of the stator to always be not less than a first preset threshold, and the oil pressure to always be not less than a second preset threshold; directing cooling oil from the stator inner cavity into the rotor inner cavity through the oil guide opening, and adjusting the oil amount in the rotor inner cavity to be maintained within a third preset threshold range; The rotor is driven to rotate at a speed not lower than a fourth preset threshold value, so that the cooling oil in the inner cavity of the rotor is splashed and cooled under the action of centrifugal force.

7. The oil cooling method for a YASA axial flux permanent magnet motor according to claim 6, characterized in that: The first preset threshold is set according to the temperature rise characteristics of the stator winding, and the second preset threshold is achieved through closed-loop control of the oil pump pressure.

8. The oil cooling method for a YASA axial flux permanent magnet motor according to claim 7, characterized in that: The first preset threshold is that the oil accumulation rate is not less than 90%, and the second preset threshold is that the oil pressure is not less than 0.15 MPa.

9. The oil cooling method for a YASA axial flux permanent magnet motor according to claim 6, characterized in that: The third preset threshold is 100-300 mL, and the fourth preset threshold is that the rotor speed is not less than 500 rpm.

10. A YASA axial flux permanent magnet motor, characterized in that: An oil cooling system comprising a YASA axial flux permanent magnet motor as claimed in any one of claims 1 to 5.

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