A rim drive propeller motor structure

Abstract

The application relates to a rim drive propeller motor structure which comprises a rotor part, a stator part, a motor support and a permanent magnet part, the rotor part comprises a propeller and a rotor iron core arranged at the outer peripheral part of the propeller, the stator part comprises separately arranged annular array stator iron cores and stator windings respectively arranged on the stator iron cores, the motor support is composed of left and right mounting frames matched and connected, the stator part is fixedly arranged at the inner peripheral part of the motor support, the rotor part is rotationally connected to the inner middle part of the motor support, a plurality of permanent magnet insertion grooves are uniformly arranged at the outer peripheral part of the motor support and located between the adjacent stator iron cores, and the permanent magnet part comprises a plurality of permanent magnet inserts, each permanent magnet insert is inserted into the corresponding permanent magnet insertion groove. The propeller motor structure is rationally designed and convenient to disassemble, assemble and maintain.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ship electric propulsion, in particular to a rim drive propeller motor structure. BACKGROUND

[0002] With the needs of energy and environmental protection and smart ocean development, the ship electric propulsion system has been widely used, especially in various offshore and inland small ships and underwater submersibles. The propeller, as an important device, has always been valued by people, and new structures of propellers are constantly proposed. One typical structure is the integrated propeller with a rim structure.

[0003] The driving motor of the rim structure integrated propeller adopts a common radial flux inner rotor motor structure, the propeller is directly installed on the rotor, and the shaft connection link is cancelled, which is beneficial to improve the propeller efficiency and reduce the ship vibration. At the same time, the air gap of the structure is directly placed in the water, which does not need sealing treatment, the process is simple, and it is beneficial to heat dissipation. Due to the above advantages, the rim type integrated propeller has attracted widespread attention, and many practical structures have been proposed. However, the integrated propeller with a rim structure is prone to sand entering the air gap in actual application, which causes wear and even damage of the stator and rotor, and affects the application range of the rim type propeller. Generally, the rim propeller motor adopts an inner rotor structure, the permanent magnets are distributed on the surface of the rotor in a surface-mounted or embedded manner, the propeller is placed inside the rotor, and the bearings are placed inside the stator to fix the rotor part. In actual application, the rim propeller adopts magnetic sealing and other methods to prevent sand from entering the air gap, but the structure is relatively complex and compact, and at the same time, due to the influence of the magnetic attraction of the permanent magnet, the stator and rotor are difficult to disassemble, and maintenance is difficult. SUMMARY

[0004] The purpose of the present application is to provide a rim drive propeller motor structure, which is reasonable in design and convenient to disassemble and maintain.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a rim drive propeller motor structure, comprising a rotor part, a stator part, a motor support and a permanent magnet part, the rotor part comprises a propeller and a rotor core arranged on the outer peripheral part of the propeller, the stator part comprises a plurality of separated stator cores arranged in an annular array and a plurality of stator windings respectively wound on each stator core, the motor support is composed of a left mounting frame and a right mounting frame connected together, the stator part is fixedly installed on the inner peripheral part of the motor support, the rotor part is rotationally connected to the inner middle part of the motor support, a plurality of permanent magnet insertion slots are uniformly arranged on the outer peripheral part of the motor support and located between adjacent stator cores, and the permanent magnet part comprises a plurality of permanent magnet inserts, each permanent magnet insert is inserted into the corresponding permanent magnet insertion slot.

[0006] Further, the rotor part comprises a ring-shaped rotor core, a ring-shaped embedded connecting part, a propeller, a shaft sleeve and a rotating shaft, the rotor core is fixedly installed on the outer circumferential part of the embedded connecting part, the propeller is composed of a ring-shaped array of several propeller blades, the embedded connecting part is fixedly connected with the shaft sleeve located in the middle part through the propeller, and the shaft sleeve is fixedly installed on the rotating shaft.

[0007] Further, the stator core is an H-shaped laminated silicon steel sheet, the stator winding is wound on the corresponding H-shaped laminated silicon steel sheet in a ring winding method, the outgoing lines of each stator winding are respectively passed out of the winding outgoing hole on the motor support, and the wiring of the end part of the stator winding is performed outside the motor support.

[0008] Further, the stator part comprises 3n stator cores, the stator windings on the 3n stator cores are divided into three phases, n stator windings in each phase are connected in parallel, and the neutral points of each stator winding are connected; the outgoing lines comprise two end outgoing lines of the stator winding, the two end outgoing lines are simultaneously passed out of the same winding outgoing hole to the outside of the motor support; one end outgoing line of all the stator windings is divided into three phases, n outgoing lines in each phase are respectively connected with external three-phase A, B and C, and the other end outgoing line is simultaneously short-circuited together to form a star connection.

[0009] Further, the stator part comprises 24 stator cores, the stator windings on the 24 stator cores are divided into three phases, and 8 stator windings in each phase are connected in parallel.

[0010] Further, the motor support is a concentric ring structure in which left and right mounting frames are oppositely connected together; the mounting frame comprises a ring-shaped part, an end face outer circumferential part, an end face connecting frame, an end face disc part and a bearing, one end of the ring-shaped part is connected with the outside of the end face outer circumferential part, the other end of the ring-shaped part is nested and matched with the ring-shaped part of the other mounting frame, the inside of the end face outer circumferential part is connected with the end face disc part located in the middle part through the end face connecting frame, the bearing is fixedly installed in the middle part of the end face disc part, and the rotating shaft in the middle part of the rotor part is rotatably connected with the bearings in the middle parts of the left and right mounting frames.

[0011] Further, the outer peripheral portion of the end surface of the mounting frame is annularly provided with a plurality of concave-shaped support seats matching the number of the stator cores to support the stator cores; the middle portion of the support seat is provided with a winding insertion slot to accommodate the stator winding arranged in the middle portion of the stator core; the permanent magnet support slot is arranged between the adjacent support seats to support the permanent magnet insert when it is inserted; the first positioning hole penetrating the outer peripheral portion of the end surface is arranged on the support seat, and the second positioning hole is arranged on the stator core to fix and install each stator core between the left and right mounting frames through the positioning fastener; the winding lead-out hole penetrating the outer peripheral portion of the end surface is arranged on the winding insertion slot; and the annular portion of the mounting frame is uniformly provided with a plurality of permanent magnet insertion slots between the adjacent support seats.

[0012] Further, the permanent magnet insert comprises a plug-in part and a magnetic steel, and the magnetic steel is embedded in the front portion of the plug-in part, and the plug-in part is adapted to the shape of the permanent magnet insertion slot.

[0013] Compared with the prior art, the present application has the following beneficial effects: the present application proposes a wheel rim drive propeller motor structure convenient to disassemble and maintain, aiming at the problems that the propeller of the wheel rim drive is easy to enter sand and gravel, and the structure of the ordinary wheel rim drive propeller is compact and inconvenient to maintain; the propeller motor structure adopts an integrated structure, the propeller is directly installed on the rotor, the power loss of the connecting shaft is reduced, and special sealing treatment is not required; the permanent magnet of the structure is located on the stator side and can be independently disassembled and installed from the side; the structure adopts the disassembly mode of disassembling the permanent magnet first when disassembling, and the motor can be conveniently disassembled without special tools; therefore, the wheel rim drive propeller motor structure is conducive to solving the problems of difficult assembly of the integrated propeller and difficult maintenance after sand and gravel enter the air gap during use, and has strong practicability and broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a schematic diagram of the wheel rim drive propeller motor structure of the embodiment of the present application;

[0015] Figure 2 is a schematic diagram of the structure of the rotor portion in the embodiment of the present application;

[0016] Figure 3 is a schematic diagram of the inductance L1 and L2 under the condition that the stator and rotor are not aligned in the embodiment of the present application;

[0017] Figure 4 is a schematic diagram of the structure of the stator portion in the embodiment of the present application;

[0018] Figure 5 is a schematic diagram of the structure of the motor support in the embodiment of the present application;

[0019] Figure 6is a structural schematic diagram of the mounting rack in the embodiment of the present application;

[0020] Figure 7 is a schematic diagram of the mounting process of the stator part and the motor support in the embodiment of the present application;

[0021] Figure 8 is a schematic diagram of the mounting process of the permanent magnet part in the embodiment of the present application;

[0022] Figure 9 is a schematic diagram of the rim drive propeller motor in the embodiment of the present application. DETAILED DESCRIPTION

[0023] The present application will be further described below in conjunction with the drawings and embodiments.

[0024] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as would be commonly understood by one of ordinary skill in the art to which the present application belongs.

[0025] It should be noted that the terms used herein are only for the purpose of describing the specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a presence of a feature, step, operation, device, component, and / or combinations thereof.

[0026] As shown in Figures 1-9 The present embodiment provides a rim drive propeller motor structure, which comprises a rotor part, a stator part, a motor support and a permanent magnet part. The rotor part comprises a propeller R403 and a rotor core R401 arranged on the outer periphery of the propeller. The stator part comprises a plurality of separate stator cores T102 arranged in an annular array and a plurality of stator windings T101 respectively wound on each stator core. The motor support is composed of a left mounting rack and a right mounting rack connected together. The stator part is fixedly installed on the inner periphery of the motor support. The rotor part is rotatably connected to the inner middle part of the motor support. The outer periphery of the motor support is uniformly provided with a plurality of permanent magnet insertion slots between adjacent stator cores. The permanent magnet part comprises a plurality of permanent magnet inserts, each of which is inserted into a corresponding permanent magnet insertion slot.

[0027] As shown in Figure 2As shown, the rotor part includes an annular rotor core R401, an annular embedded connecting part R402, a propeller R403, a shaft sleeve R404 and a rotating shaft R405, the rotor core R401 is fixedly installed on the outer peripheral part of the embedded connecting part R402, the propeller R403 is composed of a plurality of propeller blades in annular array, the embedded connecting part R402 is fixedly connected with the shaft sleeve R404 located in the middle part through the propeller R403 to form an integral whole, and the shaft sleeve R404 is fixedly installed on the rotating shaft R405. In this structure, the rotor part only has a core without winding and permanent magnet.

[0028] Meanwhile, the structure reduces the thickness of the rotor tooth part and the yoke part by increasing the number of pole pairs, thereby reducing the thickness of the rotor part.

[0029] In order to reduce the size of the rotor tooth part and the yoke part, the structure adopts a multi-pole design idea. Generally, the more the number of poles, the more complex the motor, but the increase of the number of poles is conducive to reducing the size of the tooth part. In the literature about flux switching motor, the analysis of modulated magnetic field is often carried out from the perspective of magnetic motive force distribution, and the rotor part is idealized in these analyses, that is, it is considered that the distance between the rotor slot and the stator is far, and the magnetic flux cannot directly reach the rotor slot part from the stator tooth part. This assumption requires a higher rotor tooth part, which obviously occupies the space of the rotor part and is not suitable for rim-driven propellers. During the displacement of the rotor within one pole pitch, the electromagnetic torque T e can be described as the differential of the magnetic co-energy (assuming that the current i is constant):

[0030]

[0031] wherein the magnetic co-energy W is a function of the winding current i and the rotor displacement angle, and is also the integral of the flux linkage ψ with respect to the current.

[0032]

[0033] Therefore, the electromagnetic torque can be described by the current and the inductance as:

[0034]

[0035] When the rotor displacement angle changes within one rotor pole pitch, the winding inductance changes between L min and L max , thereby generating an electromagnetic torque, the greater the difference between L min and L max , the greater the electromagnetic torque. When the material and other factors are determined, L max is mainly related to the air gap g between the stator and the rotor teeth, considering the underwater working characteristics of the propeller, the air gap g cannot be too small. L min is related to the distance h rThe greater the distance, the greater the magnetic reluctance when the rotor and stator magnetic poles are misaligned. min The smaller the value, the more conducive it is to increasing torque, but the higher the rotor teeth, the more propeller space it occupies.

[0036] Normally h r It is more than 10 times the air gap g, but this is unsuitable for rim drives because rim drive motors typically have a large air gap. For example, if the air gap is taken as 2mm, and calculated at 10 times, h r Also 20mm, which will take up a lot of space for propeller distribution.

[0037] Therefore, this invention increases the torque by increasing the number of pole pairs, which reduces h. r The effect of parameters on torque. As the number of pole pairs increases, when the stator and rotor poles are misaligned, the angular distance between the stator and rotor poles is small. In this case, increasing h... r It cannot effectively reduce L min .like Figure 3 As shown, at this time, both inductors L1 and L2 are related to h. r Regarding this, we can derive the following using approximate theoretical derivation:

[0038]

[0039] Where p = b ps / 2, which is half the width of the stator teeth, h c Where h is the distance between the stator and rotor teeth, and K is a coefficient determined by the core length and the number of winding turns. It can be seen that as the number of pole pairs increases, h... c Decreasing h causes L1 to increase and L2 to decrease. On the other hand, as h... r Increasing the value of h, while reducing L2, will also increase L1 between the stator and rotor teeth. To obtain a more ideal h... r The value can be differentiated with respect to L1+L2, and the differential term can be set to zero to obtain the corresponding h. r The expression is:

[0040]

[0041] That is, h r The height should be greater than It is evident that increasing the number of pole pairs also helps to reduce the stator tooth width, which ultimately helps to reduce the rotor tooth height. Typically, flux-switching motors have equal tooth slot widths, containing two teeth, one slot, and one magnet within one pole pitch. Assuming they have the same width, the stator inner radius is r, and the stator pole number is p, then the tooth width is 2πr / p / 4. Therefore, according to equation (7):

[0042]

[0043] In practice, h can be determined based on process and application requirements. r, the pole number range can be obtained. After the pole number logarithm design is adopted, the ratio of the rotor tooth height to the air gap size does not need to be kept large, and at this time, the torque promotion is mainly realized through the electromagnetic torque of the more number of tooth portions. In the example of the application, the stator inner diameter is 171mm, the air gap is set to 3mm considering the propeller processing technology, the rotor tooth height is 4mm, and p>15 can be obtained through calculation. Here, only the lower limit value of p is approximately given, and in actual cases, the simulation situation should also be comprehensively considered.

[0044] In the application, the stator part adopts a detachable permanent magnet design to achieve the purpose of convenient disassembly and maintenance. In order to achieve this purpose, the structure is realized through the following structure design: (1) the stator core adopts a separated stator core design; (2) the stator winding adopts a ring winding, so that the winding does not pass through the magnetic steel, and the detachable permanent magnet does not affect the fixation of the winding; (3) a support and fixation mechanism of the stator core and the stator winding is designed on the motor support; (4) the permanent magnet has a detachable structure design.

[0045] As shown in Figure 4 , the stator core T102 is an H-shaped laminated silicon steel sheet, and 3n independent H-shaped laminated silicon steel sheets are arranged in a circumferential ring array. The stator winding T101 is wound on the corresponding H-shaped laminated silicon steel sheet by a ring winding method, and the lead-out wires T105 of each stator winding T101 are respectively led out from the winding lead-out hole K309 on the motor support, and the wiring T104 of the end portion of the stator winding is performed outside the motor support. In this structure, the winding adopts a ring winding method, which has the disadvantage of increasing the winding, which increases the area outside the stator, but has little effect on the rim structure propeller. The advantage of this winding method is that the winding does not pass through the magnetic steel, which does not affect the disassembly of the magnetic steel, and at the same time, since half of the winding is outside the stator, it is more conducive to heat dissipation, especially in underwater application scenarios, in addition, it is also convenient for winding, which is conducive to improving the slot fill rate.

[0046] In this structure, each stator core T102 is provided with a positioning hole T103 for mounting the stator core on the motor support. It can be fixed with the motor support by inserting a pin, a bolt, etc.

[0047] In this embodiment, the stator part includes 24 stator cores, and the stator windings on the 24 stator cores are divided into three phases, 8 stator windings per phase are connected in parallel, and the neutral points of each stator winding are connected. Figure 4 As shown in the lead-out wire T105, the lead-out wire T105 actually includes two end lead-out wires of the stator winding, and the two end lead-out wires are simultaneously led out from the same winding lead-out hole K309 to the outside of the motor support. After the two end lead-out wires of all stator windings are led out to the outside of the motor support, one end of the lead-out wire is divided into three phases, 8 lead-out wires per phase are connected, and the other end of the lead-out wire is simultaneously short-circuited together to form a star connection. The three-phase wiring and the wiring of the other end of the short-circuited stator winding are wound in a ring structure, as shown in Figure 4The end winding T104 is not actually a wire, but is formed by winding a plurality of wires as described above.

[0048] As shown in Figures 5-7 The motor support is a concentric ring structure formed by left and right mounting frames being connected together in a facing and nesting manner. This structure can ensure that the two mounting frames have a good concentric state during installation. The mounting frame K300 is composed of a ring portion, an end face outer peripheral portion, an end face connecting frame K304, an end face disc portion K307 and a bearing K306. One end of the ring portion is connected to the outer side of the end face outer peripheral portion, and the other end of the ring portion is nested with the ring portion of the other mounting frame. The inner side of the end face outer peripheral portion is connected to the end face disc portion K307 located in the middle thereof through the end face connecting frame K304. The bearing K306 is fixedly installed in the middle of the end face disc portion K307. The rotating shaft R405 in the middle of the rotor portion is rotatably connected to the bearings K306 in the middle of the left and right mounting frames. There are mounting screw holes K308 on the end face disc portion K307, which are used for installing a hub cap. In this embodiment, the end face connecting frame K304 is a cross-shaped connecting frame, and the outer shape thereof is designed in a streamline shape to reduce fluid resistance.

[0049] A plurality of concave support seats K303 are arranged in a ring shape on the end face outer peripheral portion of the mounting frame K300, and the number of the support seats K303 matches the number of the stator cores, so as to support the stator cores. The support seat K303 has a winding placement slot K301 in the middle, which is used for accommodating the stator winding arranged in the middle of the stator core. Permanent magnet support grooves K302 are arranged between adjacent support seats K303, so as to support the permanent magnet insert when the permanent magnet insert is inserted. First positioning holes K305 are arranged on the support seat K303 and penetrate the end face outer peripheral portion. Second positioning holes T103 are arranged on the stator core T102 correspondingly, so as to fix and install each stator core between the left and right mounting frames through a positioning fastener A101. Winding lead-out holes K309 are arranged on the winding placement slot K301 and penetrate the end face outer peripheral portion. A plurality of permanent magnet insertion grooves are uniformly arranged on the ring portion of the mounting frame and located between adjacent support seats.

[0050] As shown in Figure 8 The permanent magnet insert includes a plug-in part P202 and a magnetic steel P203. The magnetic steel P203 is embedded in the front part of the plug-in part P202, and the plug-in part P202 is adapted to the shape of the permanent magnet insertion groove. Threaded holes P201 are arranged on the left and right ends of the plug-in part P202, so as to lock the left and right ends of the permanent magnet insert on the left and right mounting frames through a threaded fastener.

[0051] In the above structure, the core, the motor support and the magnetic steel are in a seawater immersion environment, and need to be coated with anticorrosive paint.

[0052] The rim drive integrated propeller structure provided by the embodiment is a 24-pole stator 20-pole rotor structure. During installation, the stator and rotor parts are installed first, and then the permanent magnet part is installed. During assembly of the stator part, the 24 stator cores are first wound, and then the stator cores and stator windings are installed on the motor support through bolts and positioning holes, as shown in FIG. 10. Figure 7 After the winding lead-out wire T105 passes through the winding lead-out hole K309 on the motor support, the end connection is performed outside the motor support. After the stator and rotor parts are installed and fixed, the permanent magnet is installed from the side of the motor support, as shown in FIG. 11. Figure 8 Then the motor outer shell is installed to protect the winding ends and improve the hydrodynamic performance. During disassembly, the permanent magnet part is disassembled first, and then the stator and rotor parts are disassembled. When sand enters the air gap and needs to be cleaned, the motor outer shell is first disassembled, and then the permanent magnets are taken out one by one. After the permanent magnets are disassembled, there is no magnetic attraction between the stator and rotor, and the rotor part can be easily taken out to clean the sand that may exist in the air gap. After cleaning is completed, the above steps are repeated to easily reinstall the motor. It can be seen that the present application does not need special tools to quickly disassemble the propeller, and after cleaning the sand, the permanent magnet is installed again, which can be very convenient for disassembly and maintenance.

[0053] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can use the disclosed technical content to make changes or modifications to equivalent embodiments. However, any simple modification, equivalent change and modification made to the above embodiments without departing from the technical solution of the present application, according to the technical essence of the present application, still falls within the protection scope of the present application.

Claims

1. A rim-driven propeller motor structure, characterized in that, The device includes a rotor section, a stator section, a motor bracket, and a permanent magnet section. The rotor section includes a propeller and a rotor core disposed on the outer periphery of the propeller. The stator section includes separate stator cores arranged in a ring array and stator windings respectively wound on each stator core. The motor bracket is composed of left and right mounting brackets connected together. The stator section is fixedly mounted on the inner periphery of the motor bracket, and the rotor section is rotatably connected to the middle of the inner part of the motor bracket. The outer periphery of the motor bracket has multiple permanent magnet slots evenly distributed between adjacent stator cores. The permanent magnet section includes multiple permanent magnet inserts, each of which is inserted into a corresponding permanent magnet slot. The rotor part includes an annular rotor core, an annular embedded connecting part, a propeller, a bushing, and a rotating shaft. The rotor core is fixedly installed on the outer periphery of the embedded connecting part. The propeller is composed of several propeller blades arranged in an annular array. The embedded connecting part is fixedly connected to the bushing located in the middle of the propeller. The bushing is fixedly installed on the rotating shaft.

2. The rim-driven propeller motor structure according to claim 1, characterized in that, The stator core is made of H-shaped laminated silicon steel sheets. The stator windings are wound on the corresponding H-shaped laminated silicon steel sheets using a ring winding method. The lead wires of each stator winding pass through the winding lead holes on the motor bracket and are connected at the ends of the stator windings on the outside of the motor bracket.

3. The rim-driven propeller motor structure according to claim 2, characterized in that, The stator section includes 3n stator cores, and the stator windings on the 3n stator cores are divided into three phases. The n stator windings of each phase are connected in parallel, and the neutral points of each stator winding are connected. The lead wires include the lead wires at both ends of the stator windings. The lead wires at both ends pass through the same winding lead-out hole to the outside of the motor bracket. One end of all stator windings is divided into three phases, with n lead wires for each phase, which are connected to the external three phases A, B, and C respectively. The other end of the lead wires are short-circuited together to form a star connection.

4. The rim-driven propeller motor structure according to claim 3, characterized in that, The stator section includes 24 stator cores, and the stator windings on the 24 stator cores are divided into three phases. The eight stator windings of each phase are connected in parallel, and the neutral points of each stator winding are connected.

5. The rim-driven propeller motor structure according to claim 1, characterized in that, The motor bracket is a concentric ring structure consisting of two mounting brackets, left and right, nested together. Each mounting bracket consists of an annular portion, an outer peripheral portion of the end face, an end face connecting bracket, an end face disc portion, and a bearing. One end of the annular portion is connected to the outer side of the outer peripheral portion of the end face, and the other end of the annular portion is nested with the annular portion of another mounting bracket. The inner side of the outer peripheral portion of the end face is connected to the end face disc portion located in its middle through the end face connecting bracket. The bearing is fixedly installed in the middle of the end face disc portion. The two ends of the rotating shaft in the middle of the rotor portion are rotatably connected to the bearings in the middle of the left and right mounting brackets, respectively.

6. The rim-driven propeller motor structure according to claim 5, characterized in that, The mounting bracket has multiple U-shaped support seats arranged in a ring around its outer periphery, matching the number of stator cores, to support the stator cores. Each support seat has a winding insertion slot in its center to accommodate the stator winding wound in the middle of the stator core. Permanent magnet support slots are provided between adjacent support seats to support the permanent magnet inserts when they are inserted. Each support seat has a first positioning hole penetrating the outer periphery of its end face, and each stator core has a corresponding second positioning hole, allowing the stator cores to be fixed between the left and right mounting brackets using positioning fasteners. The winding insertion slots have winding lead-out holes penetrating the outer periphery of their end faces. Multiple permanent magnet slots are evenly distributed on the annular portion of the mounting bracket between adjacent support seats.

7. The rim-driven propeller motor structure according to claim 1, characterized in that, The permanent magnet insert includes a plug and a magnet, the magnet being embedded in the front of the plug and the plug being adapted to the shape of the permanent magnet slot.

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