Magnetic circuit partition decoupling type wheel hub motor, magnetic adjustment region design and hybrid cooling structure

Abstract

The application discloses a magnetic circuit partition decoupling type wheel hub motor for an electric vehicle, a magnetic field adjusting region design and a hybrid cooling structure, a permanent magnet is arranged on a d-axis, the utilization rate of the permanent magnet is improved, and output torque is improved; a suitable magnetic barrier is arranged on a q-axis, and uncontrollable self-leakage of the permanent magnet is reduced; a magnetic field adjusting region is constructed on a rotor, the mechanical strength of the rotor is improved, a main magnetic circuit and an auxiliary magnetic circuit are designed in a partition mode, the magnetic flux direction of the auxiliary magnetic circuit under different working conditions is changed by adjusting armature currents under different working conditions, and optimal distribution of d-q axis inductances under all working conditions is realized; a simple axial water channel is embedded at a stator winding with high heat, circumferential water channels and axial water channels jointly act, advantages are complementary, double-layer oil channels enable a rotating shaft and an inner surface of the stator to be fully cooled, a cooling mode of bidirectional circulation combined with upper and lower oil channels is adopted, the stator yoke is fully cooled under the action of gravity, water cooling and oil cooling are combined, and the overall heat dissipation effect of the stator is improved.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicles, and particularly relates to the structure of a hub motor for electric vehicles, the design of its key parameters, and its hybrid cooling structure. Background Technology

[0002] To reduce environmental pollution and alleviate resource scarcity, electric vehicles have become one of the main directions for the development of new energy vehicles. With increasingly complex driving environments and the existence of various operating conditions such as low-speed light load, heavy-load hill climbing, and high-speed cruising, more stringent performance requirements are being placed on the motors and drive systems of electric vehicles. Currently, permanent magnet hub motors are used in electric vehicles due to their advantages such as high power density, high integration, and strong flexibility. However, most of these motors have limited speed ranges, low efficiency in the high-speed weak magnetic region, and both high power density and high integration place higher demands on the motor's heat dissipation capabilities.

[0003] Chinese patent number 201610256109.0 proposes a hybrid excitation hub motor. By adding an extra excitation winding and adjusting the magnitude and direction of the current in the electric excitation winding, the air gap magnetic field of the motor can be flexibly adjusted and controlled, thereby widening the motor's speed range and increasing its torque density. However, the copper loss generated by the continuous electric excitation current significantly reduces the efficiency of the motor in the high-speed field weakening region, and the additional heat source increases the difficulty of motor heat dissipation.

[0004] Chinese patent number 202110127061.4 proposes a heat dissipation device for a high power density external rotor permanent magnet motor based on heat dissipation copper pipe technology. This device fully utilizes the high thermal conductivity of the copper pipes to quickly and efficiently transfer heat to the outside of the permanent magnet motor, keeping it within a suitable operating temperature range, preventing malfunctions, and ensuring the motor's safety and stability. However, copper pipes are expensive, resulting in high costs, and the connection quality at the copper pipe joints largely depends on the construction process, requiring high-quality workmanship.

[0005] This demonstrates that in-wheel motors still face challenges in terms of wide speed range and efficiency in the high-speed range, making it difficult to fully meet the diverse performance requirements of automotive drive motors under varying operating conditions. Furthermore, heat dissipation of highly integrated in-wheel motors remains a challenge. Therefore, addressing issues such as the difficulty in adjusting the air gap magnetic field, narrow speed range, and low efficiency in the high-speed, weak magnetic region of in-wheel motors to meet the diverse operating conditions of electric vehicles, as well as analyzing the heat distribution of in-wheel motors to solve overheating problems, is of great significance. Summary of the Invention

[0006] In view of the above problems, the objective of the present invention is to provide a magnetic circuit partition decoupling in-wheel motor, so as to meet the diverse performance requirements of vehicle drive motors under variable working conditions, and at the same time provide a design method for the in-wheel motor and a hybrid cooling structure thereof to solve the motor overheating problem,

[0007] To achieve the above objective, the technical solution adopted by the magnetic circuit partition decoupling in-wheel motor of the present invention is: 10 square magnetic barriers with centers on the d-axis and 10 trapezoidal magnetic barriers with centers on the q-axis are alternately embedded in the rotor along the circumferential direction, and one auxiliary magnetic circuit small rectangular permanent magnet that is not in contact with the corresponding square magnetic barrier is respectively arranged in the middle of both tangential sides of each square magnetic barrier, and both of the two auxiliary magnetic circuit small rectangular permanent magnets are magnetized along the inner and outer thickness directions with opposite magnetization directions; one main magnetic circuit large rectangular permanent magnet is fixedly embedded in the middle of each trapezoidal magnetic barrier 6, each main magnetic circuit large rectangular permanent magnet is magnetized along the inner and outer thickness directions, the magnetization directions of two adjacent main magnetic circuit large rectangular permanent magnets are opposite, and the magnetization direction of each main magnetic circuit large rectangular permanent magnet is the same as that of the two closest auxiliary magnetic circuit small rectangular permanent magnets; one strip-shaped magnetic barrier that is not in contact with both the trapezoidal magnetic barrier and the auxiliary magnetic circuit small rectangular permanent magnet is respectively arranged on each tangential side of each trapezoidal magnetic barrier; a magnetic regulating region is enclosed between the inner surface of the square magnetic barrier, the inner surface of the auxiliary magnetic circuit small rectangular permanent magnet and the inner surface of the rotor.

[0008] Preferably, the radial cross section of the square magnetic barrier is a square with four rounded corners, the radial cross section of the trapezoidal magnetic barrier is a trapezoid, and the bottom edge of the trapezoid faces outward while the top edge faces inward; the inner and outer surfaces of the main magnetic circuit large rectangular permanent magnet respectively overlap with the top edge and the bottom edge of the trapezoidal magnetic barrier, the inner and outer thickness of the main magnetic circuit large rectangular permanent magnet is greater than the thickness of the auxiliary magnetic circuit small rectangular permanent magnet, the tangential width of the main magnetic circuit large rectangular permanent magnet is greater than the width of the auxiliary magnetic circuit small rectangular permanent magnet, and the inner and outer thickness of the auxiliary magnetic circuit small rectangular permanent magnet is less than the thickness of the square magnetic barrier; the inner surface of the strip-shaped magnetic barrier overlaps with the inner surface of the rotor, and there are distances between the inner and outer surfaces of the square magnetic barrier and the trapezoidal magnetic barrier and the inner and outer surfaces of the rotor.

[0009] The technical solution adopted by the design method for the magnetic regulating region of the magnetic circuit partition decoupling in-wheel motor of the present invention is:

[0010] The radial thickness of magnetic flux leakage in the magnetic regulating region is calculated according to the formula The radial thickness of magnetic flux leakage l_ under low-speed and light-load working conditions is obtained rib-rated =2x_ rated w rib L a (R pm1 +R pm2 +2R g ) / (μ0(1-4R g +2R b )), x is the slope of the silicon steel sheet material with respect to the magnetic flux density-magnetic field strength curve, 0<x<90, μ0 is the magnetic permeability of air, w ribL is the width of the magnetization region. a R is the length of the motor shaft. pm1 The permanent magnet reluctance of the main magnetic circuit, R pm2 For the permanent magnet reluctance of the auxiliary magnetic circuit, R g For air gap reluctance, K ρ R is the salient pole ratio of the motor. b For magnetic barrier and magnetic reluctance, x_ rated The slope of the magnetic flux density-magnetic field strength curve for silicon steel sheet material under low-speed and light-load conditions;

[0011] 2) Based on the radial thickness l of leakage magnetic flux under low-speed and light-load conditions rib-rated The salient pole ratio K under low-speed heavy-load conditions was calculated. ρ _ min =2x_ heavy w rib L a (R pm1 +R pm2 +2R g ) / (μ0l_ rib-rated )+4R g -2R b salient pole ratio K under high-speed light load conditions ρ _ max =2x_ high w rib L a (R pm1 +R pm2 +2R g ) / (μ0l_ rib-rated )+4R g -2R b ;x_ heavy 、x_ high These represent the slopes of the magnetic flux density-magnetic field strength curves for silicon steel sheet materials under low-speed heavy-load and high-speed light-load conditions, respectively.

[0012] 3) Check if K is satisfied ρ _ min <1 and K ρ _ max >1, if so, then the radial thickness l of the magnetic leakage is... rib Meets the requirements;

[0013] 4) In step 3), if the radial thickness of the leakage magnetic field is l_ rib If it does not meet the requirements, adjust (R) pm1 +R pm The value of ) and magnetic barrier reluctance R b The size, according to the adjusted (R) pm1 +R pm The value of ) and magnetic barrier reluctance R b Calculate the new saliency ratio Kρ Based on the new salient pole ratio K ρ Repeat steps 1)-3) until the radial thickness of the leakage flux is l_ rib Until the requirements are met.

[0014] If K is not satisfied ρ _ min If the value is less than 1, then the magnetic barrier reluctance R will be reduced. b As the set difference increases, adjust (R) accordingly. pm1 +R pm The value of ) satisfies K ρ _ min <1; if K is not satisfied ρ _ max If the value is greater than 1, then the magnetic barrier reluctance R will be reduced. b As the set difference decreases, adjust (R) accordingly. pm1 +R pm The magnitude of the value of ) satisfies K ρ _ max >1, and repeat this process.

[0015] The technical solution adopted by the hybrid cooling structure of the magnetic circuit partition decoupling hub motor of the present invention is as follows: each tooth of the stator is fixedly embedded with an axial cooling water jacket composed of multiple U-shaped sleeves connected end to end. A through hole is opened in the middle of the U-shaped sleeve. One side wall of the U-shape of each U-shaped sleeve passes through the outer layer of a stator tooth along the axial direction. Each U-shaped sleeve spans two adjacent stator teeth. All stator teeth are continuously spanned by multiple U-shaped sleeves along the axial direction. The first end of the axial cooling water jacket is the inlet and the last end is the outlet. An inlet and an outlet are set at one end of the motor along the axial direction, which are respectively connected to the inlet and outlet of the axial cooling water jacket.

[0016] Preferably, a blind hole with one open end and the other closed is opened in the center of the rotating shaft. A fixed inner cylinder is coaxially fitted into the blind hole of the rotating shaft. The inlet end of the inner cylinder extends outward from the open end of the rotating shaft, and the outlet end does not contact the closed end of the rotating shaft. Multiple inner ring teeth are arranged at intervals along the axial direction on the inner sidewall of the rotating shaft, and multiple outer ring teeth are arranged at intervals along the axial direction on the outer sidewall of the inner cylinder. The outer ring teeth and inner ring teeth are staggered in the axial direction. The outer ring teeth do not contact the inner wall of the rotating shaft, and the inner ring teeth do not contact the outer wall of the inner cylinder. Cooling oil enters from the inlet of the inner cylinder and flows out from the open end of the rotating shaft.

[0017] Preferably, an inner annular sleeve and an outer annular sleeve are provided in the middle of the stator yoke. The inner annular sleeve and the outer annular sleeve have inlets at the top and outlets at the bottom, respectively. A hollow cylindrical upper sleeve connecting the two inlets is provided axially above the stator yoke, and a hollow cylindrical lower sleeve connecting the two outlets is provided axially below the stator yoke. Cooling oil enters from the hollow cylindrical upper sleeve and flows out from the hollow cylindrical lower sleeve under the action of gravity.

[0018] The beneficial effects of adopting the above technical solution in this invention are:

[0019] 1. The motor of this invention features a permanent magnet on the d-axis to improve its utilization rate and increase output torque; and a suitable magnetic barrier on the q-axis to reduce uncontrollable self-leakage of the permanent magnet. A magnetic adjustment region is constructed on the rotor, improving its mechanical strength and enabling high-speed operation. By adjusting the armature current under different operating conditions, the magnetic flux direction of the auxiliary magnetic circuit can be changed, achieving flexible adjustment and control of the magnetic flux and improving the motor's driving performance.

[0020] 2. This invention proposes a magnetic circuit partitioning and decoupling design method for the magnetic adjustment region, introducing two types of magnetic circuits: a main magnetic circuit and an auxiliary magnetic circuit. Compared with a single magnetic circuit, the addition of an auxiliary magnetic circuit increases the design and control dimensions of the magnetic flux. The partitioning design method, separating and decoupling the two magnetic circuits, facilitates precise design and control of each circuit separately. Furthermore, differentiated guiding designs based on the different design requirements of the two magnetic circuits better meet the diverse performance demands under different operating conditions, ensuring high motor output torque while widening the speed regulation range.

[0021] 3. This invention achieves optimal dq-axis inductance distribution under all operating conditions, that is, in low-speed, heavy-load conditions, the motor adopts positive inductance characteristics (L... d >L q This achieves the effects of increasing output torque and reducing the risk of irreversible demagnetization of permanent magnets; under high-speed and light-load conditions, the motor adopts reverse inductance characteristics (L... d <L q This achieves torque enhancement; under low-speed, light-load conditions, the motor employs a dq-axis inductance approximation design (L...). d =L q This technology enables smooth inductance transitions across all operating conditions and accelerates startup, meeting the diverse needs of electric vehicles under varying operating conditions.

[0022] 4. By adjusting the armature current under different operating conditions, the effective magnetic flux in the magnetization region is controlled, thereby changing the direction of the auxiliary magnetic circuit flux under different operating conditions, which improves the motor drive performance. Under low-speed heavy-load conditions, the q-axis current is large, saturating the magnetization region, which makes the auxiliary magnetic circuit form an effective magnetic circuit to increase torque; while under high-speed light-load conditions, the q-axis current is small, and the saturation degree of the magnetization region is low, which makes the auxiliary magnetic circuit form a leakage magnetic circuit to reduce magnetic flux and widen the speed regulation range.

[0023] 5. The hybrid cooling and heat dissipation structure of the motor proposed in this invention combines water cooling and oil cooling, with circumferential and axial water channels working together to complement each other. At the same time, since there are many heat sources in the motor, and the heat generated by each heat source is different and distributed in a non-centralized manner, the dual water channels and oil channels are dispersed in the housing, stator teeth, shaft and stator yoke, covering a large area of ​​heat-generating areas, comprehensively improving the heat dissipation efficiency of the hub motor cooling system and enhancing the heat dissipation effect.

[0024] 6. The hybrid cooling and heat dissipation structure has embedded axial water channels in the stator teeth and simple axial water channels in the stator windings where the heat is high. The temperature difference between the fluid and the wall is large, the convective heat transfer coefficient is large, and the heat dissipation efficiency is high. At the same time, the axial water channels dissipate heat evenly and there is no axial temperature gradient, which can prevent the winding insulation from aging due to high temperature and avoid unnecessary economic losses.

[0025] 7. The double-layer oil channels in the hybrid cooling and heat dissipation structure enable the shaft and the inner surface of the stator to be fully cooled. On the other hand, the double-layer oil channels in the stator core yoke adopt a cooling method that combines bidirectional flow with upper and lower oil channels. Under the action of gravity, the stator yoke is fully cooled, improving the overall heat dissipation effect of the stator. Attached Figure Description

[0026] Figure 1 This is a radial structural diagram of a magnetic circuit partitioned decoupled hub motor according to the present invention;

[0027] Figure 2 yes Figure 1 Enlarged view of the partial structure of the rotor and schematic diagram of permanent magnet magnetization;

[0028] Figure 3 This is the equivalent magnetic circuit diagram of the motor of the present invention;

[0029] Figure 4 yes Figure 2 The magnetic circuit diagram of the motor of the present invention under high-speed and light-load conditions;

[0030] Figure 5 yes Figure 2 The magnetic circuit diagram of the motor of the present invention under low-speed heavy-load conditions;

[0031] Figure 6 This is a full-condition distribution diagram of the motor of the present invention;

[0032] Figure 7 This is an enlarged schematic diagram showing the local structure and geometric dimensions of the rotor;

[0033] Figure 8 This is a magnetic field distribution diagram of the motor of the present invention under high-speed and light-load conditions;

[0034] Figure 9 This is a magnetic field distribution diagram of the motor of the present invention under low-speed heavy-load conditions;

[0035] Figure 10 This is a graph showing the torque and power distribution of the motor of the present invention at different speeds;

[0036] Figure 11 This is the motor efficiency map of the present invention;

[0037] Figure 12 This is a diagram showing the internal structure of the motor and the hybrid cooling structure disposed thereon according to the present invention.

[0038] Figure 13 for Figure 12 Enlarged 3D view of the inner layer oil passage structure;

[0039] Figure 14 This is a structural diagram of the motor of the present invention and the outer oil passage provided thereon;

[0040] Figure 15 This is an assembly diagram of the motor and the hybrid cooling structure disposed thereon according to the present invention.

[0041] Figure 16 To reflect Figure 15 Half-sectional view of the hollow cylindrical upper and lower sleeve structure;

[0042] Figure 17 This is a schematic diagram of the working structure of the oil passage in the hybrid cooling structure.

[0043] Figure 18 This is a comparison of the temperature convergence curves of the motor of the present invention under different heat dissipation conditions;

[0044] Figure 19 This is a comparison diagram of the torque characteristics of the motor of the present invention under different heat dissipation conditions.

[0045] In the diagram: 1. Rotor; 2. Stator; 3. Stator slot; 4. Armature winding; 5. Shaft; 6. Trapezoidal magnetic barrier; 7. Main magnetic circuit large rectangular permanent magnet; 8. Auxiliary magnetic circuit small rectangular permanent magnet; 9. Strip magnetic barrier; 10. Square magnetic barrier; 11. Housing; 12. Insulation layer; 13. Axial cooling water jacket; 14. Water inlet; 15. Water outlet; 16. Inner cylinder; 18. Inner ring tooth; 19. Outer ring tooth; 20. Hollow cylindrical upper sleeve; 21. Hollow cylindrical lower sleeve; 22. Outer annular sleeve; 23. Inner annular sleeve; 24. Oil drum. Detailed Implementation

[0046] See Figure 1 This invention discloses a magnetic circuit partitioned decoupled hub motor, comprising a rotor 1, a stator 2, and a shaft 5. The stator 2 and an end cover are fixedly connected together and mounted on a frame. The rotor 1 is coaxially fitted around the outside of the stator 2, and the stator 2 is coaxially fitted around the outside of the shaft 5. The rotor 1 and the shaft 5 are fixedly connected, driving the shaft 5 to rotate. Both the stator 2 and the rotor 1 are made of stacked silicon steel sheets of equal thickness, and the shaft 5 is made of non-magnetic material. The inner surface of the stator 2 has 36 stator slots 3 evenly distributed along the circumferential direction, and the armature winding 4 is placed in the stator slots 3. Inside the rotor 1, 10 square magnetic barriers 10 and 10 trapezoidal magnetic barriers 6 are staggered along the circumferential direction, with a trapezoidal magnetic barrier 6 between every two square magnetic barriers 10 and a square magnetic barrier 10 between every two trapezoidal magnetic barriers 6. The square magnetic barrier 10 has a square radial cross-section, and the trapezoidal magnetic barrier 6 has a trapezoidal radial cross-section, with the base of each trapezoid facing outward and the top facing inward. The four corners of each square magnetic barrier 10 are rounded. There are distances between the inner and outer surfaces of the square magnetic barrier 10 and the trapezoidal magnetic barrier 6 and the inner and outer surfaces of the rotor 1.

[0047] like Figure 2 As shown, the center of the square magnetic barrier 10 is on the d-axis, and the center of the trapezoidal magnetic barrier 6 is on the q-axis. A small rectangular permanent magnet 8 for auxiliary magnetic circuits is positioned at the midpoint of each side of the square magnetic barrier 10 along the tangential direction. These two small rectangular permanent magnets 8 are not in contact with the square magnetic barrier 10. The two small rectangular permanent magnets 8 have identical structures and are tangentially symmetrical with respect to the center and q-axis of the trapezoidal magnetic barrier 6. The width direction of the two small rectangular permanent magnets 8 is tangential, and their thickness direction is along the inside-outside direction. Both small rectangular permanent magnets 8 are magnetized along their inside-outside thickness directions, and the magnetization directions are opposite to each other. The thickness of the small rectangular permanent magnets 8 is less than the thickness of the square magnetic barrier 10.

[0048] Each trapezoidal magnetic barrier 6 has a main magnetic circuit large rectangular permanent magnet 7 fixedly embedded in its center. The width of the main magnetic circuit large rectangular permanent magnet 7 is tangential and smaller than the top edge of the trapezoidal magnetic barrier 6. The thickness of the main magnetic circuit large rectangular permanent magnet 7 is along the inward and outward directions of the motor, and its thickness is equal to the trapezoidal height of the trapezoidal magnetic barrier 6. The inner and outer surfaces of the main magnetic circuit large rectangular permanent magnet 7 overlap with the top and bottom edges of the trapezoidal magnetic barrier 6, respectively. Each main magnetic circuit large rectangular permanent magnet 7 is magnetized along its inner and outer thickness directions, and the magnetization directions of two adjacent main magnetic circuit large rectangular permanent magnets 7 are opposite. Along the circumference, the magnetization direction of each main magnetic circuit large rectangular permanent magnet 7 is the same as that of the two closest auxiliary magnetic circuit small rectangular permanent magnets 8. The thickness of the main magnetic circuit large rectangular permanent magnet 7 is greater than the thickness and width of the auxiliary magnetic circuit small rectangular permanent magnets 8.

[0049] A strip magnetic barrier 9 is provided on both sides of the tangential direction of each trapezoidal magnetic barrier 6. The strip magnetic barrier 9 separates the trapezoidal magnetic barrier 6 from the small rectangular permanent magnet 8 of the auxiliary magnetic circuit. The strip magnetic barrier 9 does not contact either the trapezoidal magnetic barrier 6 or the small rectangular permanent magnet 8 of the auxiliary magnetic circuit. The inner surface of the strip magnetic barrier 9 overlaps with the inner surface of the rotor 1, and the outer surface of the strip magnetic barrier 9 is outside the outer surface of the trapezoidal magnetic barrier 6 and the small rectangular permanent magnet 8 of the auxiliary magnetic circuit.

[0050] See Figure 3 Since the main magnetic circuit is formed by the large rectangular permanent magnet 7 and the auxiliary magnetic circuit is formed by the small rectangular permanent magnet 8, a partitioned design is adopted for the main and auxiliary magnetic circuits, and these two types of magnetic circuits are separated and decoupled. The main magnetic circuit is loop A formed by two adjacent large rectangular permanent magnets 7, rotor 1, stator 2, and air gap. The auxiliary magnetic circuit is loop B formed by a square magnetic barrier 10 and two small rectangular permanent magnets 8 on both sides.

[0051] For the main magnetic circuit A of the permanent magnet, firstly, the shape of the large rectangular permanent magnet 7 in the main magnetic circuit can be rationally designed to improve its utilization rate and increase the output torque; secondly, a suitable trapezoidal magnetic barrier 6 can be added to reduce the uncontrollable self-leakage magnetic flux of the permanent magnet, thereby increasing the output torque and helping to achieve the partitioning of the magnetic circuit. For the auxiliary magnetic circuit B of the permanent magnet: the area enclosed by the inner surface of the square magnetic barrier 10, the inner surface of the small rectangular permanent magnet 8 in the auxiliary magnetic circuit, and the inner surface of the rotor 1 is the "magnetic adjustment area". A variable magnetic flux design method is introduced for the magnetic adjustment area. By adjusting the armature current under different operating conditions, the effective magnetic flux of the magnetic adjustment area is controlled, thereby changing the direction of the magnetic flux in the auxiliary magnetic circuit under different operating conditions, thus improving the motor drive performance. Specifically: see Figure 4 As shown, under low-speed, heavy-load conditions, the q-axis current is relatively large, saturating the magnetizing region and causing the auxiliary magnetic circuit to form an effective magnetic circuit to increase torque. (See also...) Figure 5As shown, under high-speed and light-load conditions, the q-axis current is small and the saturation degree of the magnetic adjustment region is low, which causes the auxiliary magnetic circuit to form a leakage magnetic circuit to reduce the magnetic flux and widen the speed adjustment range.

[0052] See Figure 6 This diagram illustrates the optimal distribution of the dq-axis inductance of the electric motor under all operating conditions. To meet the diverse needs of electric vehicles under varying operating conditions, the optimal dq-axis inductance distribution is achieved across all operating modes. Electric vehicles exhibit several typical operating conditions, including "low-speed light load, heavy-load hill climbing, and high-speed cruising." The motor speed under these typical operating conditions is divided into two speed regions from low to high: the low-speed region (0-n). rated and high-speed area n rated -n max ; where n rated For the rated speed, n max The maximum speed is defined; the motor torque under typical operating conditions is divided into two torque regions from low to high: the light load region 0-T. rated and heavy load area T rated -T peak Among them, T rated For the rated torque, T peak The peak torque is used; therefore, motors under typical operating conditions can be divided into the "low-speed, light-load" region based on speed-torque [(0-n rated ),(0-T rated "Low-speed heavy load" region [(0-n rated ),(T rated -T peak )], and the "high-speed light-load" area [(n rated -n max ),(0-T rated Furthermore, the optimal distribution of dq-axis inductance under all operating conditions is: L in the low-speed, light-load region d =L q L in low-speed heavy-load area d >L q and L in high-speed light-load areas d <L q .

[0053] See Figure 3 This invention proposes a targeted design method for the magnetic adjustment region, and the key parameter for designing the magnetic adjustment region is the leakage magnetic radial dimension, that is, the leakage magnetic radial thickness l_ between the inner surface of the square magnetic barrier 10 and the inner surface of the rotor 1. rib To conduct precise design, the specific design method is as follows:

[0054] 1) Based on magnetic permeability μ s (B rib ), width of the magnetization region w rib Radial thickness l_rib , the leakage reluctance R of the magnetic flux regulation region can be calculated according to the following formula rib :

[0055]

[0056] wherein, μ s (B rib ) is the magnetic permeability, μ0 is the air magnetic permeability, B rib is the magnetic flux density of the magnetic flux regulation region, which is a variable quantity related to current, x is the slope of the magnetic flux density-magnetic field strength curve of the silicon steel sheet material, which is a variable quantity related to the magnetic flux density B rib , the slope x changes as the magnetic flux density changes, 0<x<90, the magnetic permeability μ s (B rib ) changes as the slope x changes; μ r is the relative magnetic permeability, S is the area through which the magnetic flux passes, w rib is the width of the magnetic flux regulation region, L a is the axial length of the motor; it can be known from formula (1) that the leakage reluctance R of the magnetic flux regulation region rib changes as the armature current changes.

[0057] 2) Calculate the salient pole ratio K of the motor based on the leakage reluctance R of the magnetic flux regulation region rib ρ :

[0058]

[0059] wherein, R pm1 is the permanent magnet reluctance of the main magnetic circuit, R pm2 is the permanent magnet reluctance of the auxiliary magnetic circuit, R g is the air gap reluctance, R b is the magnetic barrier reluctance.

[0060] 3) The radial leakage flux thickness l_ of the magnetic flux regulation region can be derived according to formula (1) and formula (2) rib :

[0061]

[0062] 4) Under the working condition of low speed and light load, since the d-q axis inductance L of the motor d =L q , that is, the salient pole ratio K ρ (i d ,i q )=1, at this time the radial leakage flux thickness l_ rib is a fixed value l_ rib-rated , it can be obtained according to formula (3):

[0063] l_​rib-rated =2x_ rated w rib L a (R pm1 +R pm2 +2R g ) / (μ0(1-4R g +2R b )),

[0064] Where, x_ rated This represents the slope of the magnetic flux density-magnetic field strength curve for silicon steel sheet material under low-speed and light-load conditions.

[0065] Then, based on the radial thickness l_ of leakage flux under low-speed and light-load conditions rib-rated Verify the radial thickness l_ of the leakage flux under low-speed, light-load conditions. rib =l_ rib-rated Can the dimensions guarantee that the motor meets the dq axis inductance L under low-speed, heavy-load conditions? d >L q That is, the salient pole ratio K ρ <1, while also ensuring that L is met under high-speed and light-load conditions. d <L q That is, the salient pole ratio K ρ >1. The specific method for verifying whether the requirements are met is as follows:

[0066] Based on formula (3), the salient pole ratio K of the motor under low-speed heavy-load conditions is derived. ρ _ min =2x_ heavy w rib L a (R pm1 +R pm2 +2R g ) / (μ0l_ rib-rated )+4R g -2R b , where x_ heavy Let K be the slope of the magnetic flux density-magnetic field strength curve for silicon steel sheet material under low-speed, heavy-load conditions. The saliency ratio K of the motor under high-speed, light-load conditions is also derived. ρ _ max =2x_ high w rib L a (R pm1 +R pm2 +2R g ) / (μ0l_ rib-rated )+4R g -2R b , where x_ high Let K be the slope of the magnetic flux density-magnetic field strength curve for silicon steel sheet material under high-speed, light-load conditions; as long as K is at this point... ρ_ min <1 and K ρ _ max >1, i.e., leakage magnetic radial thickness l_ rib The requirements are met.

[0067] 5) If in step 4), the salient pole ratio K ρ _ min and K ρ _ max If the design requirements cannot be met, return to step 2 and readjust (R). pm1 +R pm The value of ) and magnetic barrier reluctance R b The size, and according to the readjusted (R) pm1 +R pm The value of ) and magnetic barrier reluctance R b Calculate the new saliency ratio K ρ Based on the new salient pole ratio K ρ Repeat steps 3)-5) until K is satisfied. ρ _ min <1 and K ρ _ max >1, radial thickness of magnetic flux leakage l_ rib Until the requirements are met. Specifically:

[0068] If the salient pole ratio K under the low-speed heavy-load condition in step 5) is ρ _ min The requirement was not met, i.e., K was not satisfied. ρ _ min If R is less than 1, then R needs to be adjusted. b As the set difference increases, adjust (R) accordingly. pm1 +R pm The magnitude of the value of ) to satisfy K ρ _ min <1. If the saliency rate K is under the high-speed cruise condition in step 5), ρ _ max The requirement was not met, i.e., K was not satisfied. ρ _ max If R > 1, then R needs to be adjusted. b As the set difference decreases, adjust (R) accordingly. pm1 +R pm The magnitude of the value of ) to satisfy K ρ _ max >1; Repeat this process until the design requirements are met.

[0069] Furthermore, the setting of the magnetic adjustment area of ​​rotor 1 also improves the mechanical strength of rotor 1, making high-speed operation of the motor possible. By setting the strip magnetic barrier 9, the uncontrollable self-leakage magnetic flux of the small rectangular permanent magnet 8 in the auxiliary magnetic circuit is reduced, the output torque is improved, and it also helps to realize the partition design of the two magnetic circuits.

[0070] like Figure 7 As shown, to reduce uncontrollable self-leakage magnetic flux and meet mechanical strength requirements, the tangential (width) distance between the square magnetic barrier 10 and the auxiliary magnetic circuit small rectangular permanent magnet 8 is d1; the tangential (width) distance between the auxiliary magnetic circuit small rectangular permanent magnet 8 and the strip magnetic barrier 9 is d2; and the tangential (width) distance between the strip magnetic barrier 9 and the trapezoidal magnetic barrier 6 is d3, satisfying d1 = d2 = d3 = 0.5 mm. To better achieve the separation of the main magnetic circuit and the auxiliary magnetic circuit, the minimum distance between the outer surface of the strip magnetic barrier 9 and the outer surface of the auxiliary magnetic circuit small rectangular permanent magnet 8 is C1 = 2.5 mm, and the tangential width of the strip magnetic barrier 9 itself is C2 = 3 mm. To improve the torque output of the main magnetic circuit and the auxiliary magnetic circuit, the minimum radial distance between the inner surface of the main magnetic circuit large rectangular permanent magnet 7 and the inner surface of the rotor 1 is y1 = 3 mm, and the minimum radial distance between the inner surface of the auxiliary magnetic circuit small rectangular permanent magnet 8 and the inner surface of the rotor 1 is y2 = 7 mm.

[0071] See Figure 8 The magnetic field distribution diagram of the magnetic circuit partitioned decoupled permanent magnet hub motor of the present invention under high-speed and light-load conditions is shown in the figure. Figure 9 The magnetic field distribution diagram of the magnetic circuit partitioned decoupled permanent magnet hub motor of the present invention under low-speed heavy-load conditions shows that, under high-speed light-load conditions, almost all the magnetic flux of the main permanent magnet circuit passes through the air gap into the stator 2 to ensure torque output. Only a small portion of the magnetic flux of the auxiliary magnetic circuit flows into the stator 2, with most forming a self-loop between the poles. This achieves "self-weakening of the permanent magnet" in the high-speed region, reducing the weakening current component i. d The corresponding weakening of magnetic copper loss improves the operating efficiency in the high-speed range. In the "low-speed heavy-load" condition, the large armature current will saturate the magnetizing region. At this time, the auxiliary magnetic circuit basically passes through the air gap and enters the stator, which improves the output torque of the motor.

[0072] See Figure 10 The torque and power distribution curves of the motor of the present invention at different speeds show that the maximum speed of the motor can reach 5 times the rated speed, and the rated torque is relatively large, indicating that the motor achieves high torque at low speed and wide speed range at high speed.

[0073] See Figure 11 The efficiency map of the motor of the present invention shown shows that the motor has a maximum efficiency of 96%, and the area with an efficiency greater than 90% reaches 85%, indicating that the motor achieves wide-area high efficiency.

[0074] See Figure 12 and Figure 13The motor of this invention is also equipped with a hybrid cooling structure, which uses water channels and oil channels. The water channels and oil channels are not made of copper pipes, but are made of aluminum. Aluminum has a high surface heat transfer coefficient and can dissipate heat quickly. Due to its physical properties, aluminum profiles can be processed into various shapes and cross-sections, which is convenient, quick and cost-effective.

[0075] A water channel is fixedly embedded in each tooth of the stator 2, using an axial cooling water jacket 13 as the water channel. The axial cooling water jacket 13 is composed of multiple U-shaped sleeves connected end to end, with a through hole in the middle of each U-shaped sleeve. The U-shaped sleeves pass through the outer layer of the stator teeth along the axial direction of the motor. One side wall of the U-shape of each U-shaped sleeve passes through the outer layer of one stator tooth, so that each U-shaped sleeve spans two adjacent stator teeth. All stator teeth are formed by multiple U-shaped sleeves continuously spanning each other along the axial direction, forming the axial cooling water jacket 13 on the outer layer of the stator teeth. The first end of the axial cooling water jacket 13 is the inlet, and the last end is the outlet. Each tooth surface of the stator 2 is covered with an insulating layer 12, and the U-shaped side wall of the U-shaped sleeve is in contact with the insulating layer 12. An inlet 14 and an outlet 15 are provided at one end of the motor's axial direction, which are respectively connected to the inlet and outlet of the axial cooling water jacket 13. Cooling water enters the axial cooling water jacket 13 from the inlet 14 and flows out from the outlet 15.

[0076] Oil passages are embedded in the middle of the rotating shaft 5 and the stator core yoke of the stator 2, and are divided into inner and outer layers. The inner oil passage is located in the inner cavity of the rotating shaft 5, and a blind hole with one open end and the other closed is opened in the middle of the rotating shaft 5. The fixed inner cylinder 16 is an axially continuous cylindrical shape, coaxially fitted in the blind hole of the rotating shaft 5. The outer diameter of the inner cylinder 16 is smaller than the inner diameter of the blind hole in the middle of the rotating shaft 5. The inlet end of the inner cylinder 16 extends outward from the open end of the rotating shaft 5, and the outlet end of the inner cylinder 16 does not contact the closed end of the rotating shaft 5, leaving an oil passage.

[0077] On the inner wall of the rotating shaft 5, a plurality of inner ring teeth 18 are arranged at intervals along the axial direction. On the outer wall of the inner cylinder 16, a plurality of outer ring teeth 19 are arranged at intervals along the axial direction. The outer ring teeth 19 and the inner ring teeth 18 are staggered in the axial direction. The outer ring teeth 19 do not contact the inner wall of the rotating shaft 5, and the inner ring teeth 18 do not contact the outer wall of the inner cylinder 16. Furthermore, the outer diameter of the outer ring teeth 19 is larger than the inner diameter of the inner ring teeth 18. In a preferred embodiment of the present invention, the number of outer ring teeth 19 is one more than the number of inner ring teeth 18, and the outer ring teeth 19 are located closest to both ends of the rotating shaft 5.

[0078] In the inner oil passage, the cooling oil flows as follows: The cooling oil enters through the inlet of the inner cylinder 16, passes through the through hole in the middle of the inner cylinder 16, and flows from the outlet of the inner cylinder 16 through the closed end of the rotating shaft 5. Due to the rotation of the rotating shaft 5, the cooling oil is thrown into the gap between the rotating shaft 5 and the inner cylinder 16, flowing sequentially through each outer ring tooth 19, the gap between the outer ring tooth 19 and the inner ring tooth 18, and then through the inner ring tooth 18, until it flows out from the open end of the rotating shaft 5, i.e., the oil outlet, and finally into the oil tank. The multi-tooth oil passage formed by the outer ring tooth 19 and the inner ring tooth 18 increases the length of the cooling oil's flow path, carrying away more heat.

[0079] like Figure 14 , 15 As shown in Figure 16, an outer oil passage is provided in the stator yoke of stator 2. This outer oil passage consists of two annular sleeves along the diameter direction, namely an inner annular sleeve 23 and an outer annular sleeve 22, both embedded in the middle of the stator core yoke. Inlets are opened at the top of the inner annular sleeve 23 and the outer annular sleeve 22, and outlets are opened at the bottom. Near the two inlets, a hollow cylindrical upper sleeve 20 is axially arranged above the stator yoke to connect the two inlets. Near the two outlets, a hollow cylindrical lower sleeve 21 is axially arranged below the stator yoke to connect the two outlets. Figure 15 and Figure 16 .

[0080] In the inner and outer annular sleeves, the flow path of the cooling oil is as follows: the cooling oil enters from the hollow cylindrical upper sleeve 20, and under the action of gravity, flows through the inner annular sleeve 23 and the outer annular sleeve 22 at the same time, flows downward from the hollow cylindrical lower sleeve 21, and finally flows into the oil drum.

[0081] like Figure 17 As shown, the cooling oil in the three-layer oil passage all originates from oil tank 24, which stores the cooling oil. Two oil pumps are installed in oil tank 24, positioned above the cooling oil. The hollow cylindrical upper sleeve 20 is connected to the first oil pump via a pipe, pumping the cooling oil into the inner annular sleeve 23 and the outer annular sleeve 22. The hollow cylindrical lower sleeve 21 is connected to the oil tank 24 via a pipe. The inlet of the inner cylinder 16 is connected to the second oil pump via a pipe, pumping the cooling oil into the inner oil passage. Oil flowing out from the outlet of the rotating shaft 5 directly enters the oil tank 24. Preferably, the inlet of the inner cylinder 16 and the outlet of the rotating shaft 5 extend into the oil tank 24. The stationary inner cylinder 16, like the stator 2, is fixedly connected to the housing 11. A bearing connects the outlet of the rotating shaft 5 to the wall of the oil tank 24, ensuring that the rotation of the rotating shaft 5 is not affected.

[0082] like Figure 18The temperature convergence curve of the motor of the present invention, as shown, indicates that the motor reaches a steady-state temperature after 25 iterations. Compared to the initial motor, i.e., the motor without the hybrid cooling structure described in this invention, after embedding the axial cooling water jacket 13 in the stator teeth, the steady-state temperature decreases from 170.2℃ to 151.3℃. Further adding an inner oil channel further reduces the steady-state temperature to 126.4℃. Adding an inner annular sleeve 23 and an outer annular sleeve 22 further reduces the temperature to 89.1℃. This demonstrates that the hybrid cooling structure for hub motors proposed in this invention has excellent heat dissipation performance.

[0083] See Figure 19 The torque characteristics of the motor of the present invention under different heat dissipation conditions are shown. It can be seen that, compared to the initial motor, the torque of the motor with only the axial cooling water jacket 13 increases from 102 Nm to 105 Nm. After adding an inner oil channel, the torque further increases to 107 Nm, and after adding an outer oil channel, the torque increases to 113 Nm. It is evident that the hybrid cooling structure for hub motors proposed in this invention improves the torque performance of the motor due to its superior heat dissipation effect.

Claims

1. A magnetic circuit partitioned decoupled hub motor, wherein the rotor (1) is coaxially sleeved outside the stator (2), characterized in that: The rotor (1) contains 10 square magnetic barriers (10) centered on the d-axis and 10 trapezoidal magnetic barriers (6) centered on the q-axis, interlaced along the circumferential direction. Each square magnetic barrier (10) has a small rectangular permanent magnet (8) of the auxiliary magnetic circuit that is not in contact with it on both sides along the tangential direction. Both auxiliary rectangular permanent magnets (8) are magnetized along the inner and outer thickness directions and the magnetization directions are opposite. A large rectangular permanent magnet (7) of the main magnetic circuit is fixedly embedded in the middle of each trapezoidal magnetic barrier (6). All are magnetized along the inner and outer thickness directions. The magnetization directions of two adjacent main magnetic circuit large rectangular permanent magnets (7) are opposite. The magnetization directions of each main magnetic circuit large rectangular permanent magnet (7) and the two closest auxiliary magnetic circuit small rectangular magnetic barriers (8) are the same. Each trapezoidal magnetic barrier (6) has a strip magnetic barrier (9) on each side of its tangential direction that does not contact the trapezoidal magnetic barrier (6) or the auxiliary magnetic circuit small rectangular permanent magnet (8). The inner surface of the square magnetic barrier (10), the inner surface of the auxiliary magnetic circuit small rectangular permanent magnet (8) and the inner surface of the rotor (1) form a magnetic adjustment area.

2. The magnetic circuit partitioned decoupled hub motor according to claim 1, characterized in that: The radial cross-section of the square magnetic barrier (10) is a square with rounded corners on all four sides. The radial cross-section of the trapezoidal magnetic barrier (6) is trapezoidal with the base facing outward and the top facing inward. The inner and outer surfaces of the main magnetic circuit large rectangular permanent magnet (7) overlap with the top and bottom edges of the trapezoidal magnetic barrier (6), respectively. The inner and outer thickness of the main magnetic circuit large rectangular permanent magnet (7) is greater than the thickness of the auxiliary magnetic circuit small rectangular permanent magnet (8), and the tangential width is greater than the width of the auxiliary magnetic circuit small rectangular permanent magnet (8). The inner and outer thickness of the auxiliary magnetic circuit small rectangular permanent magnet (8) is less than the thickness of the square magnetic barrier (10). The inner surface of the strip magnetic barrier (9) overlaps with the inner surface of the rotor (1). There is a distance between the inner and outer surfaces of the square magnetic barrier (10) and the trapezoidal magnetic barrier (6) and the inner and outer surfaces of the rotor (1).

3. The magnetic circuit partitioned decoupled hub motor according to claim 1 or 2, characterized in that: The tangential width distance d1 between the square magnetic barrier (10) and the small rectangular permanent magnet (8) of the auxiliary magnetic circuit, the tangential width distance d2 between the small rectangular permanent magnet (8) of the auxiliary magnetic circuit and the strip magnetic barrier (9), and the tangential width distance d3 between the strip magnetic barrier (9) and the trapezoidal magnetic barrier (6) satisfy d1=d2=d3=0.5mm; the minimum distance between the outer surface of the strip magnetic barrier (9) and the outer surface of the small rectangular permanent magnet (8) of the auxiliary magnetic circuit is 2.5mm, the tangential width of the strip magnetic barrier (9) is 3mm, the minimum radial distance between the inner surface of the large rectangular permanent magnet (7) of the main magnetic circuit and the inner surface of the rotor (1) is 3mm, and the minimum radial distance between the inner surface of the small rectangular permanent magnet (8) of the auxiliary magnetic circuit and the inner surface of the rotor (1) is (7)mm.

4. A method for designing the magnetic adjustment region of a magnetic circuit partitioned decoupled hub motor as described in claim 1, characterized in that: 1) Calculate the radial thickness of magnetic flux leakage in the magnetic field regulation region Obtain the radial thickness l_ of magnetic flux leakage under low-speed light-load operating conditions rib-rated =2x_ rated w rib L a (R pm1 +R pm2 +2R g ) / (μ0(1-4R g +2R b )), which is a fixed value; x is the slope of the magnetic flux density-magnetic field strength curve for the silicon steel sheet material, 0<x<90, μ0 is the magnetic permeability of air, w rib is the width of the magnetic field regulation region, L a is the axial length of the motor, R pm1 is the permanent magnet reluctance of the main magnetic circuit, R pm2 is the permanent magnet reluctance of the auxiliary magnetic circuit, R g is the air gap reluctance, K ρ is the saliency ratio of the motor, R b is the magnetic barrier reluctance, x_ rated is the slope of the magnetic flux density-magnetic field strength curve for the silicon steel sheet material under low-speed light-load operating conditions; 2) Based on the radial thickness l of leakage magnetic flux under low-speed and light-load conditions rib-rated The salient pole ratio K under low-speed heavy-load conditions was calculated. ρ _ min =2x_ heavy w rib L a (R pm1 +R pm2 +2R g ) / (μ0l_ rib-rated )+4R g -2R b salient pole ratio K under high-speed light load conditions ρ _ max =2x_ high w rib L a (R pm1 +R pm2 +2R g ) / (μ0l_ rib-rated )+4R g -2R b ;x_ heavy 、x_ high These represent the slopes of the magnetic flux density-magnetic field strength curves for silicon steel sheet materials under low-speed heavy-load and high-speed light-load conditions, respectively. 3) Check if K is satisfied ρ_min <1 and K ρ_max >1, if so, then the radial thickness l of the magnetic leakage is... rib Meets the requirements; 4) In step 3), if the radial thickness of the leakage magnetic field is l_ rib If it does not meet the requirements, adjust (R) pm1 +R pm The value of ) and magnetic barrier reluctance R b The size, according to the adjusted (R) pm1 +R pm The value of ) and magnetic barrier reluctance R b Calculate the new saliency ratio K ρ Based on the new salient pole ratio K ρ Repeat steps 1)-3) until the radial thickness of the leakage flux is l_ rib Until the requirements are met.

5. The magnetic adjustment region design method according to claim 4, characterized in that: In step 4), if K is not satisfied... ρ_min If the value is less than 1, then the magnetic barrier and magnetic reluctance R will be reduced. b As the set difference increases, adjust (R) accordingly. pm1 +R pm The value of ) satisfies K ρ_min <1; if K is not satisfied ρ_max If the value is greater than 1, then the magnetic barrier reluctance R will be reduced. b As the set difference decreases, adjust (R) accordingly. pm1 +R pm The magnitude of the value of ) satisfies K ρ_max >1, and repeat this process.

6. A hybrid cooling structure for a magnetic circuit partitioned decoupled hub motor as described in claim 1, characterized in that: Each tooth of the stator (2) is fixedly fitted with an axial cooling water jacket (13) consisting of multiple U-shaped sleeves connected end to end. The U-shaped sleeves have a through hole in the middle. One side wall of the U-shape of each U-shaped sleeve passes through the outer layer of a stator tooth along the axial direction. Each U-shaped sleeve spans two adjacent stator teeth. All stator teeth are continuously spanned by multiple U-shaped sleeves along the axial direction. The first end of the axial cooling water jacket (13) is the inlet and the last end is the outlet. One end of the motor's axial direction is provided with an inlet (14) and an outlet (15), which are connected to the inlet and outlet of the axial cooling water jacket (13) respectively.

7. The hybrid cooling structure according to claim 6, characterized in that: A blind hole with one end open and the other end closed is opened in the middle of the rotating shaft (5). The fixed inner cylinder (16) is coaxially fitted in the blind hole of the rotating shaft (5). The inlet end of the inner cylinder (16) extends outward from the open end of the rotating shaft (5), and the outlet end does not contact the closed end of the rotating shaft (5). Multiple inner ring teeth (18) are arranged at intervals along the axial direction on the inner side wall of the rotating shaft (5), and multiple outer ring teeth (19) are arranged at intervals along the axial direction on the outer side wall of the inner cylinder (16). The outer ring teeth (19) and the inner ring teeth (18) are arranged alternately in the axial direction. The outer ring teeth (19) do not contact the inner wall of the rotating shaft (5), and the inner ring teeth (18) do not contact the outer wall of the inner cylinder (16). Cooling oil enters from the inlet of the inner cylinder (16) and flows out from the open end of the rotating shaft (5).

8. The hybrid cooling structure according to claim 6 or 7, characterized in that: An inner annular sleeve (23) and an outer annular sleeve (22) are provided in the middle of the yoke of the stator (2). The inner annular sleeve (23) and the outer annular sleeve (22) have inlets at the top and outlets at the bottom. A hollow cylindrical upper sleeve (20) connecting the two inlets is provided axially above the yoke of the stator (2). A hollow cylindrical lower sleeve (21) connecting the two outlets is provided axially below the yoke of the stator. Cooling oil enters from the hollow cylindrical upper sleeve (20) and flows out from the hollow cylindrical lower sleeve (21) under the action of gravity.

9. The hybrid cooling structure according to claim 8, characterized in that: The hollow cylindrical upper sleeve (20) is connected to the first oil pump, and the hollow cylindrical lower sleeve (21) is connected to the oil drum (24) through a pipe. The inlet of the inner cylinder (16) is connected to the second oil pump through a pipe. The inlet of the inner cylinder (16) and the outlet of the rotating shaft (5) extend into the oil drum (24).

10. The hybrid cooling structure according to claim 7, characterized in that: The outer diameter of the outer ring tooth (19) is larger than the inner diameter of the inner ring tooth (18). The number of outer ring teeth (19) is one more than that of inner ring teeth (18). The outer ring teeth (19) are located near both ends of the rotating shaft (5).

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