TW202201879A - Motor with maglev inner rotor capable of achieving the effects of reducing noises and increasing service life and keeping the shaft rod rotating stably - Google Patents

Abstract

The present invention relates to a motor with a maglev inner rotor. The motor includes a casing having an upper shaft hole and a lower shaft hole; a stator set installed in an accommodating space and comprising a wire seat and two stator magnets, wherein the wire seat is arranged in the casing, the two stator magnets are ring magnets, one of the stator magnets is arranged on one side surface of the casing adjacent to the periphery of the upper shaft hole, and the other stator magnet is arranged on one side surface of the casing adjacent to the periphery of the lower shaft hole; and a rotor set installed in the accommodating space and comprising a shaft rod and two rotor magnets, wherein the shaft rod rotatably penetrates through the upper shaft hole and the lower shaft hole, a protruded ring magnet is provided around the shaft rod, the position of the ring magnet is adjacent to the position of the wire seat, and the two rotor magnets are annular convex magnets and are respectively arranged on the two ends of the shaft rod. The adjacent surfaces on which the rotor magnet and the stator magnet are arranged have the same magnetic polarity and repel each other to maintain a gap in between to form a magnetic levitation phenomenon, so that the shaft rod and the stator set can be kept in the center of the casing in a stable rotation without contact, thereby achieving the effects of reducing noises and increasing service life.

Description

Motor with Maglev Inner Rotor

The present invention relates to a motor, in particular to a motor with a maglev inner rotor with a maglev structure.

Products of the prior art applied to the motor mechanism, one of which is a dust-proof DC fan such as TW M468704, which includes a base, a rotor element and a stator element, the base is fixedly connected to the rotor element, and the rotor element includes a shaft core and a fan The blade, the base is fixedly connected with the fan blade, the stator element includes a fan frame with a middle tube, a stator and a bearing, the shaft core is sleeved in the bearing, the bearing is fixedly installed inside the middle tube, and the stator sleeve is fixed outside the middle tube , The shaft core is positioned in it by the contact type bearing structure. When the fan starts to work, the shaft core runs at a high speed to drive the fan blades to rotate at a high speed.

However, in the motor mechanism of the aforementioned dust-proof DC fan, the bearing is a contact type bearing, and one of the contact type bearings is a relatively common ball bearing. The ball bearing mainly includes four components: outer ring, inner ring, ball and cage. , By placing the balls in the cage and setting them between the outer ring and the inner ring, the ball bearing has the effect of rolling friction, and under the long-term high-speed operation of the ball bearing, the ball is easy to generate noise due to friction. , the worn balls will generate more noise due to the loss of the true round surface and the contact surface of the outer ring or the inner ring, which will cause more noise, and also cause the center of the inner ring to be offset due to the generation of the gap, resulting in the sleeve The shaft core entering the inner ring vibrates, thereby reducing the operating efficiency of the motor and shortening the service life of the motor. Therefore, the overall structure of the motor mechanism in the prior art has the aforementioned problems and shortcomings, and needs to be improved.

In view of the shortcomings and deficiencies of the prior art, the present invention provides a motor with a magnetically levitated inner rotor, wherein two ends of the motor are respectively provided with stator magnets, two ends of the shaft are respectively provided with a rotor magnet, and the stator magnets are connected with the stator magnets. The rotor magnets are arranged to repel each other with the same poles to generate a magnetic levitation phenomenon, so that the shaft can be kept in the center of the housing for the purpose of stable rotation.

In order to achieve the above-mentioned purpose of the invention, the technical means adopted in the present invention is to design a motor with a magnetically levitated inner rotor, which includes: a casing, which has an upper shaft hole and a lower shaft hole, and an accommodating space is formed inside the casing; A stator group, which is installed in the accommodating space and arranged on the casing, the stator group includes a wire seat and two stator magnets, one end of the wire seat is arranged around the casing, and a plurality of sections are formed on the wire seat A slot, a coil is wound around the slot of the wire seat and a wire capable of outputting electric energy is connected. The two stator magnets are annular magnets and have an inner annular surface and an axial annular surface. One of the stator magnets is a ring magnet. is arranged on a side surface of the housing adjacent to the periphery of the upper shaft hole, and the other stator magnet is arranged on a side surface of the housing adjacent to the periphery of the lower shaft hole; A rotor set is installed in the accommodating space. The rotor set includes a shaft rod and two rotor magnets. The shaft rod is a rod body with one end rotatably passing through the upper shaft hole of the housing, and the other end rotatably passing through the upper shaft hole of the housing. Passing through the lower shaft hole, a ring-shaped magnet is protruded around the shaft rod, and the position of the ring-shaped magnet is adjacent to the position of the wire seat. The two rotor magnets are ring-shaped convex magnets and are respectively arranged at two ends of the shaft rod, Each of the rotor magnets has one side toroid and one end toroid, the outer diameter of the side toroid of the rotor magnet is smaller than the inner diameter of the inner toroid of the stator magnet, and the side toroid is opposite to the opposite toroid. The inner toroid of the stator magnet is adjacent to the same polarity position, and the end torus is adjacent to the opposite axial toroid of the stator magnet to the same polarity.

Further, in the motor with a magnetically levitated inner rotor, the rotor set further comprises two magnetic conductive sheets, the two magnetic conductive sheets are annular sheets with magnetic conductive iron and are respectively sleeved on the shaft The rod is fixed on both ends of the shaft rod, and each rotor magnet is sleeved on the shaft rod and fixed on each of the magnetic conductive sheet bodies.

Further, in the motor with a magnetically levitated inner rotor, the casing has a top case and a bottom cover, the top case has a lower opening, and the inner end surface of the top case is concavely formed with an upper portion a groove, the bottom surface of the upper groove is provided with an upper shaft hole, the bottom cover is a disk body and covers the lower opening of the casing, the inner end surface of the bottom cover is concavely formed with a bottom a groove, the bottom surface of the lower groove is provided with a lower shaft hole, and the two stator magnets are respectively located in the upper groove and the lower groove.

Further, the motor with a magnetic levitation inner rotor further comprises a guide casing and a fan blade, the guide casing is a hollow cylinder, and a fixing seat is formed inside, and one end of the casing is fixed The fan blade is sleeved and fixed on the end of the shaft which is located on the lower shaft hole.

Further, in the motor with a magnetically levitated inner rotor, the fan blade is formed with a slot portion, and a positioning magnet is protruded around the inner periphery of the opening of the slot portion, and the housing is located at the other end of the housing relative to the fixing seat. The groove is kept at a distance from the positioning magnet.

Further, the fixed seat includes a joint portion and a plurality of guide vanes, the joint portion is a hollow cylinder, the plurality of guide vanes are formed around the periphery of the joint portion, and one side of each guide vane is fixed extending from the inner side wall of the guide casing and toward one end of the guide casing.

Further, in the motor with a magnetically levitated inner rotor, a joint surface is formed in the joint portion, and a plurality of joint holes are formed on the joint surface, and a plurality of perforations penetrate through the peripheral surface of the upper groove of the top shell, and the line One end of the seat adjacent to the upper shaft hole is protruded around a plurality of fixing posts, the plurality of fixing posts are plastic posts and pass through the plurality of through holes and the plurality of joint holes, and the plurality of fixing posts are hot-melted and fixed on the joint surface.

Further, the motor with a magnetically levitated inner rotor further comprises a fixing ring piece, the fixing ring piece is an annular piece body and abuts against the other side surface of the joint surface relative to the casing, the fixing ring piece is an annular piece. A plurality of riveting holes are pierced through the ring piece, and a plurality of riveting posts are protruded around the end of the wire seat adjacent to the upper shaft hole at intervals, and the plurality of riveting posts pass through the plurality of perforations, the plurality of joint holes and the plurality of riveting holes and riveted to the fixing ring.

Further, in the motor with a magnetically levitated inner rotor, the axial inclination angle of the plurality of guide vanes is opposite to the axial inclination angle of the blades of the fan blade.

Further, in the motor with a magnetically levitated inner rotor, any two adjacent blades of the fan blade are partially overlapped in the axial direction.

The advantage of the present invention is that by setting the magnetic properties of the lateral toroid of the two rotor magnets and the magnetic properties of the inner toroid of the two stator magnets to be N poles, the magnetic properties of the end toroidal surfaces of the two rotor magnets and the axial toroidal magnetic properties of the two stator magnets are both N-poles. The magnetism is S-pole, so the same magnetic poles repel each other to form a magnetic levitation phenomenon, so that the shaft can keep stable rotation in the center of the casing, so as to reduce noise and increase the service life. There is a positioning magnet, which can generate a suction force with the casing, so it can increase the stability of the fan blade during the rotation process. The structural strength of the rotor magnets prevents damage during rotation.

The technical means adopted by the present invention to achieve the predetermined purpose of the invention are further described below with reference to the drawings and preferred embodiments of the present invention.

Please refer to FIG. 1 , the motor with a magnetically levitated inner rotor of the present invention includes a casing 10 , a stator group 20 , a rotor group 30 , a guide casing 40 , a fan blade 50 and a fixed ring piece 60.

Referring to FIGS. 1 to 4 , the casing 10 is a hollow cylindrical body with an accommodating space. In this embodiment, the casing 10 has a top casing 11 and a bottom cover 12 , and the top casing 11 is formed with a The upper surface 111 and the lower opening 112, the inner side surface of the upper surface 111 of the top case 11 is concavely formed with an upper groove 113, the bottom surface of the upper groove 113 is provided with an upper shaft hole 114, and the upper surface 111 of the top case 11 is formed. A plurality of perforations 115 penetrate through the periphery of the upper groove 113 , and a plurality of engaging portions 116 are protruded from the periphery of the lower opening 112 of the top case 11 ; The inner surface of the bottom cover 12 is concavely formed with a lower groove 121, the bottom surface of the lower groove 121 is provided with a lower axis hole 122, and the inner surface of the bottom cover 12 is penetrated with a plurality of engaging holes 123, and the engaging holes 123 surround the space Passing through the periphery of the bottom cover 12 , the engaging portions 116 of the top case 11 and the engaging holes 123 of the bottom cover 12 are combined and fixed to each other.

The stator group 20 is installed in the accommodating space of the casing 10. The stator group 20 includes a wire seat 21 and two stator magnets 22. The wire seat 21 is a hollow cylindrical body composed of silicon steel sheets and one end is disposed on the casing 10. The other end of the base 21 is arranged on the bottom cover 12, a plurality of slits 211 are formed on the base 21, and a coil is wound around the slits 211 of the base 21 and is connected with a wire capable of outputting electrical energy (not shown in the figure). In this embodiment, a plurality of fixing posts 212 and a plurality of riveting posts 213 are protruded around one end of the wire seat 21 adjacent to the upper shaft hole 114 at intervals, and the fixing posts 212 are plastic posts for welding and fixing. The post 213 is used for riveting and fixing, but it is not limited thereto. The fixing method can be changed according to the user's needs, as long as the function of fixing the wire seat 21 can be achieved.

Please refer to FIG. 2 , FIG. 4 and FIG. 5 , the two stator magnets 22 have the same structure and shape, so the stator magnet 22 is used as an example for illustration. The stator magnet 22 is a ring magnet and has an inner ring surface 221 and an axial ring Surface 222 , in this embodiment, the stator magnet 22 is disposed in the upper groove 113 of the casing 10 at the periphery of the upper shaft hole 114 , and the other stator magnet 22 is disposed in the lower groove 121 of the bottom cover 12 at the bottom The peripheral edge of the shaft hole 122 .

The rotor assembly 30 is installed in the accommodating space of the casing 10 . The rotor assembly 30 includes a shaft rod 31 , two magnetic conductive sheets 32 and two rotor magnets 33 . The upper shaft hole 114, the other end rotatably penetrates the lower shaft hole 122 of the bottom cover 12, a ring magnet 311 is protruded around the surface of the shaft 31, and the position of the ring magnet 311 is adjacent to the position of the wire seat 21 for connecting with The magnetic field of the seat 21 causes the shaft 31 to rotate after the magnetic field induction; two ends and keep a distance from the ring magnet 311 .

Please refer to FIG. 4 and FIG. 5 , the two rotor magnets 33 are annular convex magnets and are respectively sleeved on the two ends of the shaft 31 and fixed on the two magnetic conductive sheets 32 . The two rotor magnets 33 have the same structure and shape, so the One of the rotor magnets 33 is illustrated as an example. The rotor magnet 33 has a side toroid 331 and an end toroid 332 . The outer diameter of the side toroid 331 of the rotor magnet 33 is smaller than the inner diameter of the inner toroid 221 of the stator magnet 22 . , the lateral annular surface 331 is located at the position of the inner annular surface 221 when the rotor magnet 33 passes through the annular hole of the stator magnet 22 at the position of the lateral annular surface 331 . The inner toroid 221 has the same polarity and is adjacent in position, and the end torus 332 of the rotor magnet 33 and the axial toroid 222 of the stator magnet 22 have the same polarity and are adjacent to each other;

Please refer to FIG. 5 , in this embodiment, the magnetic properties of the lateral toroid 331 of the rotor magnet 33 and the magnetic properties of the inner toroid 221 of the stator magnet 22 are both N poles, and the magnetic properties of the end torus 332 of the rotor magnet 33 are the same as those of the stator. The magnetic properties of the axial annular surface 222 of the magnet 22 are both S poles, but not limited to this, and the magnetic properties of the lateral annular surface 331 of the rotor magnet 33 and the inner annular surface 221 of the stator magnet 22 are both S poles. The magnetism of the end toroidal surface 332 of the magnet 33 and the magnetism of the axial toroidal surface 222 of the stator magnet 22 are both N poles. With the aforementioned magnetic pole polarity configuration, the rotor magnets 33 at the two ends of the shaft 31 are respectively connected to the two adjacent stator magnets 22 . Repel each other and maintain a gap, so that the shaft 31 of the rotor group 30 and the stator group 20 do not contact each other.

Please refer to FIGS. 2 , 3 , 4 and 6 , the diversion casing 40 is a hollow cylinder with a fixed seat 41 formed therein, and one end of the top shell 11 is fixed on the fixed seat 41 . In this embodiment, In the example, the fixed seat 41 includes a joint portion 411 and a plurality of guide vanes 414. The joint portion 411 is a hollow cylinder with a joint surface 412 formed therein, and a plurality of joint holes 413 are formed around the joint surface 412. The fixing column 212 on the 21 penetrates through the through hole 115 on the top shell 11 and the engaging hole 413 of the fixing seat 41 and is fixed on the engaging surface 412 by thermal fusion; the plurality of guide fins 414 are formed around the periphery of the engaging portion 411, and each guide The sheet 414 is a piece, one side of which is fixed on the inner side wall of the guide casing 40 and extends toward one end of the guide casing 40 .

Please refer to FIG. 1 , FIG. 3 and FIG. 7 , the fan blade 50 is a structure with a plurality of blades that can push the fluid, which is fixed to one end of the shaft 31 located at the lower shaft hole 122 , and the fan blade 50 is formed with a groove 51 , A positioning magnet 52 is protruded around the inner periphery of the opening of the groove portion 51 . The other end of the casing 10 relative to the fixing seat 41 is located in the groove portion 51 of the fan blade 50 and maintains a distance from the positioning magnet 52 . The axial inclination of the vanes is opposite to the axial inclination of the guide vanes 414 on the fixed seat 41 , and any two adjacent vanes on the fan blade 50 partially overlap in the axial direction to improve the flow and pressure of the propelled fluid.

Please refer to FIG. 1 , FIG. 3 , and FIG. 6 , the fixing ring piece 60 is an annular piece and is abutted against the other side of the joint surface 412 relative to the casing 10 , and a plurality of riveting holes are pierced through the fixing ring piece 60 61. The riveting posts 213 on the wire seat 21 respectively penetrate through the through holes 115 of the top shell 11, the engaging holes 413 of the fixing seat 41 and the riveting holes 61 on the fixing ring sheet 60 and are riveted on the fixing ring sheet 60 so that the wire seat is 21 and the fixing ring piece 60 can be clamped and fixed on the fixing base 41 .

The present invention can be implemented as a motor that pushes fluid. Please refer to FIG. 1 , FIG. 3 and FIG. 5 . The overall assembly process is as follows. The top shell 11 and the guide shell 40 can be integrated by plastic injection molding technology. Assemble the stator group 20 and the rotor group 30 in the top case 11 respectively, cover the bottom cover 12, weld and fix the bottom cover 12 on the top case 11, and fix the fixing posts 212 on the top case 11 and riveting posts by hot-melting 213 is riveted and fixed on the fixed ring sheet 60, and finally the fan blade 50 is riveted and welded to the shaft 31 and fixed on the shaft 31; when in use, an external power is input to the coil through a wire to generate N pole and S pole. The magnetic field changes, and then drives the shaft 31 to drive the fan blades 50 to rotate and push the fluid, so as to achieve the effect that the motor of the present invention can output power. The magnetism is N-pole, the magnetism of the end annular surface 332 of the rotor magnet 33 and the magnetism of the axial annular surface 222 of the stator magnet 22 are both S-pole, so the magnetic poles repel each other to form a magnetic levitation phenomenon, so that the shaft 31 can be kept in the casing The center 10 rotates stably without contacting the housing 10 .

In the aforementioned process, since the inner periphery of the opening of the slot 51 of the fan blade 50 is protruded with a positioning magnet 52, the positioning magnet 52 can generate a suction force with the casing 10, so that the fan blade 50 can increase the number of fan blades 50 during the rotation process. Bottom stability.

In the aforementioned process, since the magnetic conductive sheet 32 is provided, the magnetic field interference caused by the rotor magnet 33 and the ring magnet 311 can be avoided, and the magnetic conductive sheet 32 fixed on the shaft 31 can increase the structural strength of the rotor magnet 33 . Avoid damage during rotation.

In the foregoing process, since the guide plate 414 is provided on the fixed seat 41 , the fluid can have a pressurization and flow guide function when flowing through the guide plate 414 , so as to increase the flow rate and pressure of the fluid.

In the aforesaid process, since the fixing ring piece 60 is provided, the wire seat 21 and the top shell 11 can be fixed on the joint surface 412 of the guide casing 40 by riveting, so as to achieve a more stable effect.

The above is only a preferred embodiment of the creation, and does not limit the creation in any form. Although the creation has been disclosed as a preferred embodiment, it is not intended to limit the creation. Those of ordinary knowledge, within the scope of the technical solution of the creation, can make some changes or modifications by using the technical content disclosed above as equivalent embodiments of equivalent changes, but any content that does not depart from the technical solution of the creation, according to this The technical essence of the creation Any simple modifications, equivalent changes and modifications made to the above embodiments still fall within the scope of the technical solution of the creation.

10: Shell 11: Top shell 111: Upper surface 112: Bottom opening 113: Upper groove 114: Upper shaft hole 115: perforation 116: Engagement part 12: Bottom cover 121: Bottom groove 122: Bottom shaft hole 123: snap hole 20: stator group 21: Wire seat 211: Slotting 212: Fixed column 213: Riveted column 22: Stator magnet 221: inner torus 222: Axial Torus 30: Rotor set 31: Axle 311: Ring Magnet 32: Magnetic sheet body 33: Rotor magnet 331: Lateral Torus 332: End toroid 40: diversion shell 41: Fixed seat 411: Joint 412: Joint Surface 413: Engagement hole 414: deflector 50: fan blade 51: Groove 52: Positioning magnet 60: Fixed ring piece 61: Riveting hole

FIG. 1 is a perspective sectional view of the present invention. Figure 2 is a front cross-sectional view of the present invention. Figure 3 is an exploded view of the present invention. Figure 4 is a partial exploded view of the present invention. FIG. 5 is an enlarged partial cross-sectional view of the present invention. Figure 6 is a top view of the present invention. Figure 7 is a bottom view of the present invention.

10: Shell

11: Top shell

112: Bottom opening

113: Upper groove

114: Upper shaft hole

12: Bottom cover

121: Bottom groove

122: Bottom shaft hole

20: stator group

21: Wire seat

211: Slotting

213: Riveted column

22: Stator magnet

30: Rotor set

31: Axle

311: Ring Magnet

32: Magnetic sheet body

33: Rotor magnet

40: diversion shell

41: Fixed seat

411: Joint

414: deflector

50: fan blade

51: Groove

52: Positioning magnet

60: Fixed ring piece

61: Riveting hole

Claims (10)

A motor with a magnetically levitated inner rotor, comprising: a casing, which has an upper shaft hole and a lower shaft hole, and an accommodating space is formed inside the casing; A stator group, which is installed in the accommodating space and arranged on the casing, the stator group includes a wire seat and two stator magnets, one end of the wire seat is arranged around the casing, and a plurality of sections are formed on the wire seat A slot, a coil is wound around the slot of the wire seat and a wire capable of outputting electric energy is connected. The two stator magnets are annular magnets and have an inner annular surface and an axial annular surface. One of the stator magnets is a ring magnet. is arranged on a side surface of the housing adjacent to the periphery of the upper shaft hole, and the other stator magnet is arranged on a side surface of the housing adjacent to the periphery of the lower shaft hole; A rotor set is installed in the accommodating space. The rotor set includes a shaft rod and two rotor magnets. The shaft rod is a rod body with one end rotatably passing through the upper shaft hole of the housing, and the other end rotatably passing through the upper shaft hole of the housing. Passing through the lower shaft hole, a ring-shaped magnet is protruded around the shaft rod, and the position of the ring-shaped magnet is adjacent to the position of the wire seat. The two rotor magnets are ring-shaped convex magnets and are respectively arranged at two ends of the shaft rod, Each of the rotor magnets has one side toroid and one end toroid, the outer diameter of the side toroid of the rotor magnet is smaller than the inner diameter of the inner toroid of the stator magnet, and the side toroid is opposite to the opposite toroid. The inner toroid of the stator magnet is adjacent to the same polarity position, and the end torus is adjacent to the opposite axial toroid of the stator magnet to the same polarity. The motor with a magnetically levitated inner rotor as claimed in claim 1, wherein the rotor set further comprises two magnetic-conductive sheet bodies, the two magnetic-conductive sheet bodies are annular sheet bodies with a magnetically conductive iron material and are respectively sleeved on the shaft The rod is fixed on both ends of the shaft rod, and each rotor magnet is sleeved on the shaft rod and fixed on each of the magnetic conductive sheet bodies. The motor with a magnetically levitated inner rotor as claimed in claim 1 or 2, wherein the casing has a top casing and a bottom cover, the top casing has a lower opening, and the inner end surface of the top casing is concavely formed There is an upper groove, the bottom surface of the upper groove is provided with an upper shaft hole, the bottom cover is a disk body and covers the lower opening of the casing, and the inner end surface of the bottom cover is concavely formed with A lower groove, the bottom surface of the lower groove is provided with a lower shaft hole, and the two stator magnets are respectively located in the upper groove and the lower groove. The motor with a magnetic levitation inner rotor according to claim 3, further comprising a guide casing and a fan blade, the guide casing is a hollow cylinder, and a fixing seat is formed inside, and one end of the casing is fixed The fan blade is sleeved and fixed on the end of the shaft which is located on the lower shaft hole. The motor with a magnetically levitated inner rotor according to claim 4, wherein a slot is formed on the fan blade, a positioning magnet is protruded around the inner periphery of the opening of the slot, and the housing is located at the other end of the housing relative to the fixing seat. The groove is kept at a distance from the positioning magnet. The motor with a magnetically levitated inner rotor as claimed in claim 5, wherein the fixed seat comprises a joint portion and a plurality of guide vanes, the joint portion is a hollow cylinder, and the plurality of guide vanes are formed around the periphery of the joint portion , one side of each guide plate is fixed on the inner side wall of the guide casing and extends toward one end of the guide casing. The motor with a magnetically levitated inner rotor as claimed in claim 6, wherein a joint surface is formed in the joint portion, a plurality of joint holes are formed on the joint surface, and a plurality of perforations penetrate through the peripheral surface of the upper groove of the top case, and the line One end of the seat adjacent to the upper shaft hole is protruded around a plurality of fixing posts, the plurality of fixing posts are plastic posts and pass through the plurality of through holes and the plurality of joint holes, and the plurality of fixing posts are hot-melted and fixed on the joint surface. The motor with a magnetically levitated inner rotor as claimed in claim 7, further comprising a fixing ring piece, the fixing ring piece is an annular piece and abuts against the other side of the joint surface relative to the housing, the fixing ring piece is an annular piece. A plurality of riveting holes are pierced through the ring piece, and a plurality of riveting posts are protruded around the end of the wire seat adjacent to the upper shaft hole at intervals, and the plurality of riveting posts pass through the plurality of perforations, the plurality of joint holes and the plurality of riveting holes and riveted to the fixing ring. The motor with a magnetically levitated inner rotor as claimed in claim 8, wherein the axial inclination angle of the plurality of guide vanes is opposite to the axial inclination angle of the blades of the fan blade. The motor with a magnetically levitated inner rotor according to claim 9, wherein any two adjacent blades of the fan blade partially overlap in the axial direction.

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