WO2022129710A1

WO2022129710A1 - Distributed vibration trap device, particularly for a stator or casing of a rotating electrical machine

Info

Publication number: WO2022129710A1
Application number: PCT/FR2021/051924
Authority: WO
Inventors: Olivier Sauvage; Gaël CHEVALLIER; Emeline SADOULET-REBOUL; Kévin JABOVISTE
Original assignee: Psa Automobiles Sa; Centre National De La Recherche Scientifique; Ecole Nationale Superieure De Mécanique & Des Microtechniques; Université de Franche-Comté; Université De Technologie De Belford-Montbeliard
Priority date: 2020-12-17
Filing date: 2021-11-03
Publication date: 2022-06-23
Also published as: FR3118110A1

Abstract

The device (PVD) is intended to be mounted on a circumferential external surface (SEC) of a cylindrical structure, such as a stator (ST) of a rotating electrical machine, the device being of the so-called "MTMD" type and comprising a plurality of elementary resonators (RE) which have natural frequencies (FP) within a predetermined frequency distribution. According to the invention, the device comprises a grid (GRD) which is made from a material having a resilience property and which is provided with a plurality of attachment points (PF) which form damping slabs (PA), the grid comprising a plurality of lattices (CR) in which the elementary resonators are formed, each lattice having a central vibration zone (CC) and arms (BR) which each support an attachment point at the end thereof, and each lattice having a rigidity/mass ratio which is adjusted in order to obtain the desired natural frequency.

Description

DESCRIPTION

TITLE OF THE INVENTION: VIBRATION TRAP DEVICE DISTRIBUTED IN PARTICULAR FOR A STATOR, OR CASING, OF A ROTATING ELECTRIC MACHINE

The present invention claims the priority of French application N ° 2013418 filed on 17.12.2020, the content (text, drawings and claims) of which is incorporated herein by reference.

The present invention generally relates to the passive filtering of noise and vibrations emitted by a generally cylindrical type structure such as a stator or a casing of a rotating electrical machine. More particularly, the invention relates to a distributed vibration trap device intended to equip a structure of the cylindrical type, such as a stator of a rotating electrical machine, in particular an electric traction motor in an electric vehicle, but not exclusively.

In an electric vehicle, the electric motor in operation is a source of annoying vibrations and noises which is likely to alter the acoustic comfort of the passengers. The noises generated by the electric motor are often of the so-called "siren" type, with multiple frequency harmonics, and are potentially very unpleasant for the passengers of the vehicle. The “siren” noises are linked to the electromagnetic operation of the electric motor, which produces dynamic stresses on its mechanical structure. The mechanical structure of the electric motor then vibrates under the effect of these dynamic forces and radiates noise.

In an electric motor and, more generally, in a rotating electric machine, the specific vibratory behavior of the stator, generally having an approximately cylindrical shape, is very influential on the vibro-acoustic behavior of the machine. This proper vibrational behavior, with the proper modes and the proper frequencies associated with it, determines the possible resonances of the structure.

A stator ST of a rotary electric traction machine, as used in an electric traction system of a motor vehicle, is represented by way of example in Fig.1. On the vibro-acoustic level, this stator ST can be seen, to the first order, as a portion of cylinder emitting vibrations essentially by its outer circumferential surface SEC, outer circumferential surface which is extended and coupled with the ambient air. Other vibrations transmitted to the body of the vehicle via the suspension elements of the machine can also cause a nuisance for the passengers of the vehicle.

With reference also to Figs.2 and 3, given the generally cylindrical shape of the stator of a rotating electrical machine, the specific vibration modes of the latter can be categorized according to a conventional nomenclature in which the number of antinodes and nodes vibration is counted in one direction. In Fig.2, different eigenmodes, from “0” to “3”, are represented and correspond to vibratory deformations in the radial direction. These modes "0" to "3" are the first of a series of eigenmodes characterized in the radial direction. The proper mode "0", called "breathing" mode or "breathing mode" in English, corresponds to a radial vibratory deformation which is uniform. The following eigenmodes “1”, “2” and “3” of Fig.2 have at least one high point and one low point of vibration in the radial direction and are ovalization and out-of-phase ovalization modes, and a triangular mode, respectively.

More generally, a vibrational mode can result from the combination of several eigenmodes in different directions. Thus, a clean mode "i" of the family of clean modes in the radial direction of the stator can appear simultaneously with another clean mode "j" belonging to a family of clean modes in the longitudinal direction of the stator. One then speaks of compound eigenmode (i, j). It will therefore be understood that the terms -- eigenmode "0" -- used in the present application in fact covers a plurality of compound eigenmodes denoted by (0, j).

Fig.3 shows by way of example, in three-dimensional representation, a vibration mode comprising a natural mode "0" and in which the deformations have amplitudes which vary between a central zone ZC and end zones ZE of the stator.

In electrical machines used in automobiles, the natural frequency of mode "0" is generally quite high in the audible spectrum, of the order of one to several kilohertz (kHz), i.e. in a frequency range where human hearing acuity is maximum. In the modal vibratory behavior of the stator, it is this natural mode "0" which generates the most difficulties, with a "siren" type noise, and which is difficult to filter in practice.

In the state of the art, various solutions are known for reducing, in particular by damping, the vibrations in a structure such as a stator.

A usual solution is to use layers of viscoelastic damping materials which are prestressed between more rigid layers according to a technique called “sandwiches” or “constrained layers”. The damping of vibrations and a concomitant reduction in noise are obtained here thanks to the shear that the viscoelastic material undergoes when the stator deforms according to the targeted natural mode. However, this solution has the following main drawbacks: a) It is not very effective for the eigenbreath mode "0" because the deformations generated in this mode do not cause, or relatively little, shear in the viscoelastic layers, which reduces substantially the damping capacity; b) The elastomers usually used for the viscoelastic layers provide a damping effect which varies with the temperature, because their moduli of elasticity are very sensitive to it, which ultimately leads to a performance drift in the reduction of vibrations depending on the operating conditions of the rotating electric machine; c) The damping behavior of these elastomers is also very sensitive to the level of prestress. This requires precise assembly of the sandwiches, with low tolerances which are difficult to guarantee in mass production and generates significant costs.

Another state-of-the-art solution consists of using vibration traps. A simple and well-known vibration trap is the so-called "beater" trap, or "TMD" for "Tuned Mass Damper" in English, which functionally is a device of the "mass-spring-damper" type. Document JP5806057B2 discloses the use in a rotating electric machine of two beaters mounted on the outer circumferential surface of the machine. The two beaters are mounted with an angular offset, so as to correspond to a node and an anti-node of the vibration mode of the machine. In a first embodiment, each beater is formed of a damping elastic blade and a flyweight, the blade having one end fixed to the stator and a free end carrying the flyweight. In another embodiment, each beater is formed of a damping elastic blade assembled to a mass-forming portion and the assembly thus formed is fixed to the stator at both ends.

The device with two beaters proposed by JP5806057B2 has the disadvantage of introducing two secondary resonances close to the initial resonance frequency to be processed, on either side of the latter, which can prove to be very troublesome when the rev range of operation is extended, which is the case with a rotating electrical machine. Another drawback of this two beater device lies in the practical need to use a material with high intrinsic damping for the elastic blade of the beater in order to obtain a satisfactory result, which poses problems of implementation, cost and stability over time of the performance obtained.

Furthermore, vibration traps with several elementary resonators called “MTMD”, for “Multiple Tuned Mass Damper” in English, are also known, such as that disclosed by document WO2016/177961 A1 and designed to be mounted on a rotating structure. like a rotating shaft. Compared to a simple beater, an "MTMD" vibration trap has the advantage of an efficiency that extends over a range of frequencies. In an “MTMD” vibration trap, the frequencies of the various elementary resonators must be precisely adjusted in order to obtain a distribution of frequencies allowing the desired result to be achieved. The couplings between the different elementary resonators must also be adjusted for an optimal result. Replacing one or more flippers with an MTMD-type vibration trap can be wise to avoid the aforementioned major drawbacks of introducing secondary resonance and using material with high intrinsic damping.

It is desirable to provide a vibration trap device of the "MTMD" type suitable for equipping a structure of the generally cylindrical type, such as a stator of a rotating electrical machine, and providing an effective reduction of the vibrations due to the resonance in breathing of the structure. , as well as reduced cost and easy implementation for mass production, and good robustness in the face of disparities and drifts. According to a first aspect, the invention relates to a distributed vibration trap device intended to be mounted on an outer circumferential surface of a structure of the cylindrical type, the device being of the so-called "MTMD" type and comprising a plurality of elementary distributed resonators spatially on the outer circumferential surface and having natural frequencies included in a determined frequency distribution. According to the invention, the device comprises a grid formed from a material having a property of elasticity and provided with a plurality of fixing points forming damping blocks, the grid comprising a plurality of crosspieces in which are formed the plurality elementary resonators, each brace having a central vibration zone and arms each supporting a fixing point at its end, and each brace having a stiffness/mass ratio which is adjusted to obtain the desired natural frequency.

According to a particular embodiment, the determined frequency distribution covers a determined interval of frequencies comprising the resonance frequency associated with the "0" mode, called breathing mode, of the cylindrical-type structure.

According to a particular embodiment, the length of the determined interval of frequencies is between 0.5% and 100% of the value of the resonance frequency associated with mode 0 called breathing.

According to a particular embodiment, the frequency distribution is linear and regular around the resonance frequency associated with the "0" mode, called breathing mode, of the cylindrical-type structure.

According to a particular embodiment, the spider comprises at least one part modified by removal or addition of material, allowing an adjustment of the natural frequency of the elementary resonator.

According to another particular embodiment, the fixing points forming damping blocks comprise a damping material. This damping material provides the dissipation function to the elementary resonators.

According to yet another particular embodiment, the damping material is selected so as to obtain an effective damping of the elementary resonators of the order of one to ten%.

According to yet another particular embodiment, the damping material is an adhesive material.

According to yet another particular embodiment, the grid is a metallic grid.

According to yet another particular embodiment, the grid is obtained from a metal sheet.

According to yet another particular embodiment, the grid has a rectangular mesh and cross braces. The invention also relates to a cylindrical type structure comprising a distributed vibration trap device, as described briefly above, mounted on a circumferential outer surface, and a rotating electric machine comprising the distributed vibration trap device mounted on a surface outer circumferential of a stator of the machine.

Other advantages and characteristics of the present invention will appear more clearly on reading the detailed description below of several particular embodiments of the invention, with reference to the appended drawings, in which:

[Fig.1] Fig.1 is a perspective view of a stator of a rotary electric traction machine of the type present in an electric vehicle.

[Fig.2] Fig.2 schematically shows different eigenmodes of vibration occurring radially in a generally cylindrical structure like the stator of Fig.1.

[Fig.3] Fig.3 shows, in three-dimensional representation, an example of natural breathing mode “0” in a stator, in which deformations occur whose amplitudes vary in the longitudinal direction.

[Fig.4] Fig.4 is a simplified perspective view of a generally cylindrical structure, such as a stator, equipped with a distributed vibration trap device of the invention.

[Fig.5] Fig.5 is a simplified cross-sectional view showing a functionally equivalent diagram of a generally cylindrical structure, such as a stator, equipped with a distributed vibration trap device of the invention.

[Fig.6] Fig.6 is a top plan view of a grid used to fabricate the distributed vibration trap device of Fig.4.

[Fig.7] Fig.7 is a plan view of an elementary resonator included in the distributed vibration trap device of Fig.4.

[Fig.8] Fig.8 is a sectional view of the elementary resonator of Fig.7.

[Fig.9] Fig.9 is a sectional view showing various modifications made to an elementary resonator spider to adjust its natural frequency.

With reference to Figs.4 to 9, there is now described below a particular embodiment of a PVD distributed vibration trap device according to the invention.

Referring more particularly to FIG. 4, the PVD distributed vibration trap device is here mounted on a stator ST, represented schematically, which forms a generally cylindrical structure. The stator ST is for example that of a rotating electrical machine, such as an electric traction motor in a electric vehicle. The PVD device is designed to cover the outer circumferential surface SEC of the ST stator, partially or entirely depending on the application.

The distributed vibration trap device PVD is generally presented as a grid GR which is curved and fixed on the outer circumferential surface SEC of the stator ST. Typically, the PVD device is fixed by bonding to the SEC surface, by fixing points PF, as will appear more clearly subsequently. A plurality of elementary resonators RE juxtaposed next to each other are formed from crosspieces CR of grid GR.

The PVD distributed vibration trap device is a device of the “MTMD” type formed by the plurality of juxtaposed elementary resonators RE and is designed to preferentially process the natural breathing mode “0”, but not exclusively. The juxtaposed RE elementary resonators have between them frequency tunings or detunings which are optimized as a whole for the overall efficiency of the PVD device. Thus, depending on the applications, the PVD device may comprise one or several tens of elementary resonators RE, and preferably a few hundred elementary resonators RE for a better result. The plurality of elementary resonators RE are spatially distributed over the outer circumferential surface.

With reference also to FIG. 5, the elementary resonators RE are each functionally equivalent to a “mass-spring-damper” device having its own resonant frequency. Thus, adjacent resonators REn and RE(n+1) can be tuned to different resonant natural frequencies FPn and FP(n+1). The vibratory displacement DV of an elementary resonator RE takes place essentially in the radial direction DR of the stator ST, following the normal to the outer circumferential surface SEC. The plurality of elementary resonators RE provide an optimal frequency distribution of resonance frequencies covering a determined interval of frequencies centered substantially on the resonance frequency of the natural breathing mode “0” to be processed. The length of the determined interval of frequencies can be between 0.5% and 100% of the value of the resonance frequency associated with mode 0 called breathing. For example for a "0" mode at 4000Hz, this gives an interval of length, in other words a spread going from 20 Hz (i.e. [3990-4010] Hz if centred) to 4000Hz (i.e. [2000 - 6000] Hz if centred) . The spatial distribution of the resonators RE on the outer circumferential surface SEC and the distribution of the associated eigenfrequencies will be determined optimally depending on the applications.

The GR grid used in this particular embodiment to form the PVD distributed vibration trap device is shown flat in Fig.6. This GR grid is made of a material having a property of elasticity. Typically, it is made from a metal sheet, by material removal techniques known for mass production, such as cutting, stamping, forging, foundry or others. The material of the grid GR will be chosen essentially according to the characteristics of elasticity and mass sought for the resonators. Steels and other metals may typically be chosen for the GR grid material. As best seen in FIG. 6, in the example embodiment described, the grid GR of the PVD device is made with a rectangular mesh, more precisely, a square mesh here. The grid GR comprises a plurality of first and second ribbons, RB1 and RB2, arranged perpendicularly. Each crosspiece CR is formed by a crossing between a first ribbon RB1 and a second ribbon RB2 at a central crossing point PC. The attachment points PF are regularly distributed in the first and second ribbons RB1 and RB2. An attachment point PF is arranged in each portion of the strips RB1 and RB2 between two adjacent central crossing points PC, at the level of the midpoint between the two adjacent points PC.

With reference to FIG. 7 showing a resonator RE in plan view, the spider CR comprises a central vibration zone CC including the central crossing point PC and four arms BR projecting in a cross from the central vibration zone CC. The arms BR of a spider CR are formed by the portions of the strips RB1, RB2, between the central vibration zone CC and the four fixing points PF. The attachment points PF are thus supported at the ends of the arms BR which are distant from the central crossing point PC.

With reference also to Fig.8 showing a sectional view AA of the resonator RE of Fig.7, the attachment points PF each here comprise a through hole OR drilled in the ribbon RB1, RB2, and a point of glue forming a PA fixing damping block. The through-hole OR helps with a more robust mechanical fixing between the tape RB1, RB2, and the shock-absorbing block of fixing PA.

The PA fixing dampers are made here of an adhesive material with a low intrinsic loss factor, such as epoxy resin, Araldite® glue and others. PA fixing damping blocks provide structural damping and are able to withstand low amplitude deformations without alteration.

In the invention, the damping pads of fixing PA make it possible to obtain an individual damping of each of the elementary resonators RE. It should be noted that a low effective modal damping, of the order of one to a few percent (%), will be sufficient for the RE resonators to operate with good efficiency. In the invention, this characteristic of low effective modal damping of RE resonators makes it possible to dispense with the use of an elastomer with a high intrinsic loss factor, in favor of resins, glues and other materials with a low loss factor. intrinsic loss and which offer the advantage of a more convenient practical use and more stability in particular in temperature and humidity.

By way of comparison, the damping required in the invention is approximately one order of magnitude lower than that required for one or more “TMD” beaters.

As a variant, in the case where the influence of the temperature must be greatly limited, the PA fixing damper blocks could be made of an organic material having a minimal intrinsic loss factor, then taking advantage of friction as a source dissipation to give the RE resonators an effective modal damping of the order of one to a few percent (%). In the resonator RE, the vibration is established in the central zone of vibration CC of the spider CR having a certain mass. The central vibration zone CC vibrates perpendicularly to the outer circumferential surface SEC, in the radial direction DR of the stator ST. The elastic stiffness necessary for the vibration of the central vibration zone CC is provided by the arms BR of the spider CR. The PA fixing damping pads allow the crosspiece CR to be raised in relation to the SEC surface, which provides a clearance space ED under the crosspiece CR for the vibration of the central vibration zone CC.

In addition to their function of mechanical fixing of the grid GR on the outer circumferential surface SEC of the stator ST, the fixing points PF with their damping pads of fixing PA perform a damping function in the resonators RE. In this exemplary embodiment, each attachment point PF is pooled for the attachment of two adjacent crosspieces CR and thus participates in the aforementioned damping function for the two corresponding adjacent resonators RE.

As a variant, a grid having a mesh pattern other than a rectangular pattern and leading to another type of spider, different from a cross spider, could be used in certain embodiments of the invention.

The optimal frequency distribution of the PVD distributed vibration trap device is determined by various vibration calculations known to those skilled in the art. An approximately linear and regular frequency distribution is generally sought for the PVD device, on either side of the natural frequency of the natural breathing mode “0” to be processed. In the PVD device, the calculated frequency distribution is obtained by adjusting the natural frequency FP of each of the resonators RE.

Of course, if several "0" natural breathing modes (several natural frequencies) are present and must be processed, several corresponding frequency distributions will be calculated and implemented in the PVD distributed vibration trap device.

To tune the resonators RE to their own frequency, it is possible to proceed typically by removing or adding material in the crosspieces CR, but not exclusively. We will act both on the distribution of the stiffnesses of the spiders and the mass distribution to adjust the frequency distribution, knowing that the natural frequency of a spider evolves substantially like the stiffness/mass ratio. Thus, a modification of the dimensions of the arms BR of the braces makes it possible to determine different stiffness/mass ratios and, consequently, different natural frequencies. Preferably, it is the width of the arms BR, or their width profile, which will be modified, rather than their thickness, the modification of which may pose more difficulties.

Examples E1 to E4 in Fig.9 illustrate different methods that can be used for adjusting the natural frequencies FP of the resonators RE. In general, this adjustment can be obtained by adding or removing material in the crosspiece CR, but not exclusively. In example E1, the natural frequency FP1 of a resonator RE1 is adjusted by adding material AM to the central vibration zone CC of its spider CR1, so as to increase the mass of the central vibration zone CC.

In examples E2 to E4, removals of material are made in the arms BR of the crosspieces CR2 to CR4 of the resonators RE2 to RE4 to adjust the natural frequencies FP2 to FP4 thereof, respectively, in particular by modifying the stiffness of the arms BR. In example E2, notches EH are made in two arms BR of cross brace CR2. In example E3, the same reduction profile of the initial width LA of the arms BR of the spider CR3 is obtained by removing material. In example E4, the removal of material in the arms BR of the spider CR3 are carried out in a similar way to example E3, except at the junction of these with the central zone of vibration CC where different curvatures CB1 and CB2 are introduced.

In the examples described above, the different shapes of the arms of the crosspieces, allowing the optimum distribution of natural frequencies of the resonators, are obtained by modifying the arms which are initially identical for having been obtained in a grid, such as that of FIG. 6, Manufactured uniform pattern and mesh. It will be noted that, in other embodiments, different arm shapes may be produced during the manufacture of the grid, for example, by using punch tools having slightly different patterns from one another.

In general, the elementary resonators of the vibration trap device of the invention may take different forms insofar as they behave as a whole like an “MTMD” device with respect to one or more eigenmodes of breathing “0” of the generally cylindrical structure to be treated.

The invention is of great interest for dealing with the noise pollution which comes from a machine, in particular from an electric traction motor in an electric vehicle. The machine contains internal mechanisms which are the primary sources of noise and vibration. These primary sources of noise and vibration set in motion a casing of the machine, or stator, which radiates and/or transmits noise. Reducing noise and vibration at the very level of primary sources is not always possible given certain engineering constraints or limitations imposed by physics. It is then relevant to reduce the vibrations as close as possible to the primary sources, as is possible thanks to the distributed vibration trap device according to the invention.

The "0" natural breathing mode is a mode that is potentially very emissive and known by those skilled in the art as being difficult to process by devices attached externally to a casing. Indeed, the swelling/dilation movements generated in this “0” mode are the opposite of the shearing movements which allow effective treatment by known solutions of the viscoelastic sandwich type having a vibration damping function. Unlike these known solutions, the distributed vibration trap device according to the invention provides real damped elementary traps capable of processing the noises and vibrations originating from the swelling/dilation movements of the “0” mode. The distributed vibration trap device according to the invention is effective for automotive applications in which frequencies typically of a few hundred to a few thousand Hertz must be processed.

Moreover, in addition to the effective processing of the "0" natural breathing mode, the vibration trap device of the invention can be designed so as to also provide damping of one or more other natural modes of the generally cylindrical structure, thus providing an additional reduction in vibrations and harmful noise. The processing of these other eigenmodes will be obtained by a shearing effect of the prestressed material of the fixing damper blocks in the elementary resonators.

Compared to a conventional TMD beater, the vibration trap device of the invention has less sensitivity to manufacturing dispersions and drifts due to operating conditions, such as temperature, humidity and others. In addition, the added masses are potentially less important and it is possible to eliminate harmful secondary resonances.

Another appreciable advantage of the vibration trap device of the invention lies in the fact that it can be manufactured with inexpensive materials. In addition, the cost of implementing the device of the invention is reduced.

The invention is not limited to the particular embodiments which have been described here by way of example. The person skilled in the art, depending on the applications of the invention, may make various modifications and variants falling within the scope of protection of the invention.

Claims

1. Distributed vibration trap device (PVD) intended to be mounted on a circumferential outer surface (SEC) of a cylindrical-type structure (ST), said device (PVD) being of the so-called "MTMD" type comprising a plurality of elementary resonators (RE) spatially distributed on the outer circumferential surface (SEC) and having natural frequencies (FP) included in a determined frequency distribution, characterized in that they comprise a grid (GR) formed from a material having a of elasticity and provided with a plurality of fixing points (PF) forming damping blocks (PA), the said grid comprising a plurality of crosspieces (CR) in which the said plurality of elementary resonators (RE) are formed, each said crosspiece (CR) having a central vibration zone (CC) and arms (BR) each supporting a said attachment point (PF) at its end, and each said spider (CR) having a stiffness/mass ratio which is adjusted for r obtaining the desired natural frequency (PF).

2. Device according to claim 1, characterized in that the determined frequency distribution covers a determined interval of frequencies comprising the resonant frequency associated with the "0" mode called breathing mode of the cylindrical type structure.

3. Device according to claim 2, characterized in that the length of the determined interval of frequencies is between 0.5% and 100% of the value of the resonant frequency associated with mode 0 called breathing.

4. Device according to one of the preceding claims, characterized in that the frequency distribution is linear and regular around the resonance frequency associated with the "0" mode, called breathing mode, of the cylindrical-type structure.

5. Device according to one of the preceding claims, characterized in that the device (PVD) comprises at least ten elementary resonators (RE).

6. Device according to one of the preceding claims, characterized in that a said spider (CR) comprises at least one modified part (CC, BR) by removing or adding material, allowing an adjustment of the natural frequency (FP) of said elementary resonator (RE).

7. Device according to one of the preceding claims, characterized in that said fixing points (FP) forming damping blocks (PA) comprise a damping material.

8. Device according to claim 7, characterized in that said damping material is selected so as to obtain an effective damping of said elementary resonators (RE) of the order of one to ten%.

9. Device according to claim 7 or 8, characterized in that said damping material is an adhesive material.

10. Device according to any one of the preceding claims, characterized in that said grid (GR) is a metal grid.

11. Device according to the preceding claim, characterized in that said grid (GR) is obtained from a metal sheet.

12. Device according to any one of the preceding claims, characterized in that said grid has a rectangular mesh and cross braces (CR).

13. Cylindrical type structure (ST) characterized in that it comprises a distributed vibration trap device (PVD) according to any one of preceding claims mounted on a circumferential outer surface (SEC) of the structure. Rotating electrical machine characterized in that it comprises a distributed vibration trap device (PVD) according to any one of Claims 1 to 12 mounted on a circumferential outer surface (SEC) of a stator (ST) of the said machine.