DISTRIBUTED VIBRATION TRAP DEVICE IN PARTICULAR FOR A STATOR OR CASING OF A ROTATING ELECTRIC MACHINE

Abstract

The device (PVD) is intended to be mounted on a circumferential outer surface (SEC) of a cylindrical type 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) having natural frequencies (FP) included in a determined frequency distribution. According to the invention, the device comprises a grid (GRD) formed from a material having an elastic property and provided with a plurality of fixing points (PF) forming damping blocks (PA), said grid comprising a plurality of crosspieces (CR) in which the elementary resonators are formed, each crosspiece having a central vibration zone (CC) and arms (BR) each supporting a fixing point at its end, and each crosspiece having a stiffness / mass ratio which is adjusted to obtain the desired natural frequency. Figure 4

Description

Title of the invention: DISTRIBUTED VIBRATION TRAP DEVICE IN PARTICULAR FOR A STATOR, OR CASING, OF A ROTATING ELECTRIC MACHINE

[0001] The present invention relates generally to the passive filtering of noise and vibrations emitted by a generally cylindrical 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 cylindrical structure, such as a stator of a rotating electrical machine, in particular an electric traction motor in an electric vehicle, but not exclusively.

[0002] In an electric vehicle, the electric motor in operation is a source of vibrations and annoying 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, operation which produces dynamic forces on the mechanical structure thereof. The mechanical structure of the electric motor then vibrates under the effect of these dynamic forces and radiates noise.

[0003] In an electric motor and, more generally, in a rotating electrical machine, the inherent vibrational behavior of the stator, generally having an approximately cylindrical shape, is very influential on the vibro-acoustic behavior of the machine. This inherent vibrational behavior, with the inherent modes and frequencies associated with it, determines the possible resonances of the structure.

[0004] A stator ST of a rotating electric traction machine, as used in an electric traction system of a motor vehicle, is shown as an example in [Fig.l]. From a vibro-acoustic point of view, this stator ST can be seen, to the first order, as a portion of a cylinder emitting vibrations essentially by its circumferential outer surface SEC, a circumferential outer surface which is extended and coupled with the ambient air. Other vibrations transmitted to the body of the vehicle via suspension elements of the machine can also cause a nuisance for the passengers of the vehicle, but are not considered here because they are outside the scope of the present invention.

[0005] Also referring to Figs. 2 and 3, taking into account the generally cylindrical shape of the stator of a rotating electrical machine, the natural vibration modes thereof can be categorized according to a conventional nomenclature in which the number antinodes and vibration nodes are counted along a direction.

[0006] In [Fig.2], different natural modes, from "0" to "3", are represented and correspond to vibrational deformations in the radial direction. These modes "0" to "3" form a family of natural modes in the radial direction. The natural mode "0", called "breathing mode" in English, corresponds to a radial vibrational deformation which is uniform. The following natural modes "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.

[0007] More generally, a vibrational mode can result from the combination of several natural modes in different directions. Thus, a natural mode “i” of the family of natural modes in the radial direction of the stator may appear simultaneously with another natural mode “j” belonging to a family of natural modes in the longitudinal direction of the stator. This is then referred to as a compound natural mode (i, j). It will therefore be understood that the terms — natural mode “0” — used in the present application in fact cover a plurality of compound breathing natural modes noted (0, j).

[0008] [Fig. 3] shows by way of example, in three-dimensional representation, a vibrational 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.

[0009] In electrical machines used in automobiles, the natural frequency of the "0" mode is generally quite high in the audible spectrum, of the order of one to several kilohertz (kHz), that is to say in a frequency range where human hearing acuity is maximum. In the modal vibration behavior of the stator, it is this "0" natural mode which generates the most noise pollution, with a "siren" type noise, and which is difficult to filter in practice.

[0010] In the state of the art, various solutions are known for reducing, in particular by damping, vibrations in a structure such as a stator.

[0011] A common solution is to use layers of viscoelastic damping materials that are prestressed between more rigid layers using a technique known as "sandwiches" or "constrained layers". Vibration damping and a concomitant reduction in noise are achieved here through the shearing that the viscoelastic material undergoes when the stator deforms according to the targeted natural mode. This solution, however, has the following main drawbacks:

[0012] a) It is not very effective for the natural breathing mode “0” because the deformations generated in this mode do not cause, or very little, shear in the viscoelastic layers, which substantially reduces the damping capacity;

[0013] b) The elastomers usually used for viscoelastic layers provide damping that varies with temperature, which leads to a performance drift in vibration reduction depending on the operating conditions of the rotating electrical machine;

[0014] c) The damping behavior of these elastomers is also very sensitive to the prestress level. This requires precise assembly of the sandwiches, with low tolerances which are difficult to guarantee in large-scale production and generates significant costs.

[0015] Another solution of the state of the art 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 electrical machine of two beaters mounted on the circumferential outer 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 weight, the blade having one end fixed on the stator and a free end carrying the weight.In another embodiment, each beater is formed from a resilient damping blade assembled to a mass-forming portion and the assembly thus formed is fixed to the stator at two ends.

[0016] The two-beater device proposed by JP5806057B2 has the disadvantage of introducing two secondary resonances close to the initial resonant frequency to be treated, on either side of the latter, which can prove very troublesome when the operating speed range is extended, which is the case with a rotating electrical machine. Another disadvantage of this two-beater device lies in the need in practice 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.

[0017] Furthermore, vibration traps with several elementary resonators known as “MTMDs”, for “Multiple Tuned Mass Damper” in English, are also known, such as the one disclosed by document WO2016 / 177961A1 and designed to be mounted on a rotating structure such as a rotating shaft. Compared to a simple beater, an “MTMD” vibration trap has the advantage of an efficiency that extends over a frequency range. In an “MTMD” vibration trap, the frequencies of the different elementary resonators must be precisely adjusted in order to obtain a frequency distribution that makes it possible to achieve the desired result. The couplings between the different elementary resonators must also be adjusted for a desired result. optimal. Replacing one or more beaters with an MTMD type vibration trap may be advisable to avoid the major disadvantages mentioned above of introducing secondary resonance and using material with high intrinsic damping.

[0018] It is desirable to provide a vibration trap device of the "MTMD" type suitable for equipping a generally cylindrical structure, such as a stator of a rotating electrical machine, and providing an effective reduction of vibrations due to breathing resonance of the structure, as well as a reduced cost and easy implementation for large-scale production, and good robustness in the face of disparities and drifts.

[0019] According to a first aspect, the invention relates to a distributed vibration trap device intended to be mounted on a circumferential outer surface of a cylindrical type structure, the device being of the so-called "MTMD" type and comprising a plurality of elementary resonators having natural frequencies included in a determined frequency distribution. According to the invention, the device comprises a grid formed from a material having an elastic property and provided with a plurality of fixing points forming damping blocks, the grid comprising a plurality of crosspieces in which the plurality of elementary resonators are formed, each crosspiece having a central vibration zone and arms each supporting a fixing point at its end, and each crosspiece having a stiffness / mass ratio which is adjusted to obtain the desired natural frequency.

[0020] According to a particular embodiment, the crosspiece comprises at least one part modified by removal or addition of material, allowing an adjustment of the natural frequency of the elementary resonator.

[0021] According to another particular embodiment, the fixing points forming shock-absorbing blocks comprise a shock-absorbing material.

[0022] 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%.

[0023] According to yet another particular embodiment, the damping material is an adhesive material.

[0024] According to yet another particular embodiment, the grid is a metal grid.

[0025] According to yet another particular embodiment, the grid is obtained from a metal sheet.

[0026] According to yet another particular embodiment, the grid has a rectangular mesh and cross-shaped crosspieces.

[0027] The invention also relates to a cylindrical type structure comprising a A distributed vibration trap device, as briefly described above, mounted on a circumferential outer surface, and a rotating electrical machine comprising the distributed vibration trap device mounted on a circumferential outer surface of a stator of the machine.

[0028] 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:

[0029] [Fig-1] [Fig. 1] is a perspective view of a stator of a rotating electric traction machine of the type present in an electric vehicle.

[0030] [Fig.2] [Fig.2] schematically shows different natural modes of vibration producing radially in a generally cylindrical structure like the stator of [Fig.l].

[0031] [Fig.3] [Fig.3] shows, in three-dimensional representation, an example of a natural breathing mode “0” in a stator, in which deformations occur whose amplitudes vary in the longitudinal direction.

[0032] [Fig.4] [Fig.4] is a simplified perspective view of a structure overall cylindrical, such as a stator, equipped with a distributed vibration trap device of the invention.

[0033] [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.

[0034] [Fig.6] [Fig.6] is a top plan view of a grid used in the manufacture of the distributed vibration trap device of [Fig.4].

[0035] [Fig.7] [Fig.7] is a plan view of an elementary resonator included in the distributed vibration trap device of [Fig.4].

[0036] [Fig.8] [Fig.8] is a sectional view of the elementary resonator of [Fig.7].

[0037] [Fig.9] [Fig.9] is a sectional view showing various modifications made to an elementary resonator crosshead to adjust its natural frequency.

[0038] With reference to Figs. 4 to 9, a particular embodiment of a PVD distributed vibration trap device according to the invention is now described below.

[0039] With particular reference to [Fig. 4], the distributed vibration trap device PVD is here mounted on a stator ST, shown 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 an electric vehicle. The PVD device is designed to cover the circumferential outer surface SEC of the stator ST, partially or completely depending on the application.

[0040] The PVD distributed vibration trap device is generally presented as a grid GR which is curved and fixed on the circumferential outer surface SEC of the stator ST. Typically, the PVD device is fixed by gluing on the SEC surface, by fixing points PF, as will appear more clearly later. A plurality of elementary resonators RE juxtaposed next to each other are formed from the crosspieces CR of the grid GR.

[0041] The PVD distributed vibration trap device is an “MTMD” type device formed by the plurality of juxtaposed RE elementary resonators and is designed to process the “0” breathing natural mode, 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 dozen RE elementary resonators, and preferably a few hundred RE elementary resonators for a better result.

[0042] Also referring to [Fig. 5], the elementary resonators RE are each functionally equivalent to a “mass-spring-damper” device having its own natural resonance frequency. Thus, adjacent resonators REn and RE(n+1) can be tuned to different natural resonance frequencies FPn and FP(n+1). The vibrational displacement DV of an elementary resonator RE is essentially in the radial direction DR of the stator ST, following the normal to the circumferential outer surface SEC. The plurality of elementary resonators RE provide an optimal frequency distribution of resonance frequencies centered substantially on the frequency of the breathing natural mode “0” to be treated. The spatial distribution of the resonators RE on the circumferential outer surface SEC and the distribution of the associated natural frequencies will be determined optimally depending on the applications.

[0043] 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 an elastic property. Typically, it is made from a metal sheet, by material removal techniques known for mass production, such as cutting, stamping, forging, casting or others. The material of the GR grid will be chosen essentially according to the elasticity and mass characteristics sought for the resonators. Steels and other metals may typically be chosen for the material of the GR grid.

[0044] As best seen in [Fig.6], in the described embodiment, 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 RB 1 and a second ribbon RB2 at a central crossing point PC. The fixing points PF are regularly distributed in the first and second ribbons RB 1 and RB2. A fixing point PF is arranged in each portion of the ribbons RB 1 and RB2 between two adjacent central crossing points PC, at the midpoint between the two adjacent points PC.

[0045] With reference to [Fig.7] showing a resonator RE in top view, the crosshead CR comprises a central vibration zone CC including the central crossing point PC and four arms BR projecting crosswise from the central vibration zone CC. The arms BR of a crosshead CR are formed by the portions of the ribbons RB1, RB2, between the central vibration zone CC and the four fixing points PF. The fixing points PF are thus supported at the ends of the arms BR which are distant from the central crossing point PC.

[0046] Also referring to [Fig.8] showing a sectional view AA of the resonator RE of [Fig.7], the fixing points PF each here comprise a through hole OR drilled in the ribbon RB1, RB2, and a point of glue forming a fixing damping pad PA. The through hole OR helps to provide a more robust mechanical fixing between the ribbon RB1, RB2, and the fixing damping pad PA.

[0047] The PA fixing damping blocks are made here of an adhesive material with a low intrinsic loss factor, such as epoxy resin, Araldite® glue and others. The PA fixing damping blocks provide structural damping and are capable of withstanding low amplitude deformations without alteration.

[0048] In the invention, the PA fixing damping blocks make it possible to obtain individual damping of each of the elementary resonators RE. It will 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 low effective modal damping characteristic of the 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 intrinsic loss factor and which offer the advantage of more convenient practical use and greater stability, particularly in temperature and humidity.

[0049] For comparison, the damping required in the invention is approximately one order of magnitude lower than that required for one or more “TMD” beaters.

[0050] Alternatively, in the case where the influence of temperature must be greatly limited, the PA fixing damping blocks may be made of an organic material having a minimal intrinsic loss factor, then taking advantage of friction as a source of dissipation to grant the RE resonators an effective modal damping of the order of one to a few percent (%).

[0051] In the resonator RE, the vibration is established in the central vibration zone CC of the crosshead CR having a certain mass. The central vibration zone CC vibrates perpendicular to the circumferential outer 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 crosshead CR. The fixing damping blocks PA allow the crosshead CR to be raised relative to the surface SEC, which provides a clearance space ED under the crosshead CR for the vibration of the central vibration zone CC.

[0052] In addition to their function of mechanically fixing the grid GR on the circumferential outer surface SEC of the stator ST, the fixing points PF with their fixing damping blocks PA fulfill a damping function in the resonators RE. In this embodiment, each fixing point PF is shared for the fixing of two adjacent crosspieces CR and thus participates in the aforementioned damping function for the two corresponding adjacent resonators RE.

[0053] Alternatively, a grid having a mesh pattern other than a rectangular pattern and leading to another type of cross, different from a cross, may be used in certain embodiments of the invention.

[0054] 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 uniform frequency distribution is generally sought for the PVD device, on either side of the natural frequency of the breathing natural mode “0” to be treated. In the PVD device, the calculated frequency distribution is obtained by adjusting the natural frequency FP of each of the resonators RE.

[0055] Of course, if several natural breathing modes "0" (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.

[0056] To tune the resonators RE to their natural frequency, it will be possible to proceed typically by removing or adding material in the crosspieces CR, but not exclusively. We will act on both the stiffness distribution of the crosspieces and the mass distribution to adjust the frequency distribution, knowing that the natural frequency of a crosspiece evolves substantially like the stiffness / mass ratio. Thus, a modification of the dimensions of the arms BR of the crosspieces 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 can pose more diff- fictional.

[0057] Examples E1 to E4 in [Fig.9] illustrate different methods that can be used for adjusting the natural frequencies FP of the resonators RE. Generally speaking, this adjustment can be obtained by adding or removing material in the crosspiece CR, but not exclusively.

[0058] In example E1, the natural frequency FP1 of a resonator RE1 is adjusted by adding material AM in the central vibration zone CC of its crosspiece CRI, so as to increase the mass of the central vibration zone CC.

[0059] In examples E2 to E4, material removals 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 of these, respectively, in particular by modifying the stiffness of the arms BR. In example E2, notches EH are made in two arms BR of the crosspiece CR2. In example E3, the same reduction profile of the initial width LA of the arms BR of the crosspiece CR3 is obtained by material removal. In example E4, the material removals in the arms BR of the crosspiece CR3 are made in a similar manner to example E3, except at the junction of these with the central vibration zone CC where different curvatures CB 1 and CB2 are introduced.

[0060] In the examples described above, the different shapes of the arms of the crosspieces, allowing the optimal distribution of natural frequencies of the resonators, are obtained by modifying the arms which are initially identical for having been obtained in a grid, like that of [Fig.6], manufactured with uniform patterns and meshes. It will be noted that, in other embodiments, different shapes of arms may be produced during the manufacture of the grid, for example, by using punch tools having slightly different patterns from each other.

[0061] Generally speaking, 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 “0” breathing modes of the generally cylindrical structure to be treated.

[0062] The invention is of great interest for dealing with noise pollution originating 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 vibrations. These primary sources of noise and vibrations set in motion a casing of the machine, or stator, which radiates and / or transmits noise. Reducing noise and vibrations at the level of the primary sources themselves is not always possible given certain engineering constraints or limitations imposed by physics. It is then relevant to reduce vibrations as close as possible to the primary sources as is possible thanks to the distributed vibration trap device according to the invention.

[0063] The “0” breathing mode is a potentially highly emissive mode and is known by those skilled in the art to be difficult to treat by devices attached externally to a casing. Indeed, the swelling / expansion movements generated in this “0” mode are the opposite of the shear movements which allow effective treatment by known viscoelastic sandwich type solutions having a vibration damping function. Unlike these known solutions, the distributed vibration trap device according to the invention provides genuine damped elementary traps capable of treating the noises and vibrations originating from the swelling / expansion movements of the “0” mode.

[0064] 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.

[0065] Furthermore, in addition to the effective treatment of the breathing natural mode "0", 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 a further reduction of harmful vibrations and noise. The damping of these other natural modes will be obtained by a shearing effect of the prestressed material of the fixing damping blocks in the elementary resonators.

[0066] Compared to a conventional TMD mixer, the vibration trap device of the invention has less sensitivity to manufacturing dispersions and drifts due to operating conditions, such as temperature, humidity and the like. Furthermore, the added masses are potentially less significant and no harmful secondary resonances are introduced.

[0067] 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.

[0068] The invention is not limited to the particular embodiments which have been described here by way of example. Those skilled in the art, depending on the applications of the invention, will be able to make various modifications and variants falling within the scope of protection of the invention.

Claims

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 and comprising a plurality of elementary resonators (RE) having natural frequencies (FP) included in a determined frequency distribution, characterized in that it comprises a grid (GR) formed of a material having an elastic property and provided with a plurality of fixing points (PF) forming damping blocks (PA), said grid comprising a plurality of crosspieces (CR) in which 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 fixing point (PF) at its end, and each said crosspiece (CR) having a stiffness / mass ratio which is adjusted to obtain the desired natural frequency (PF),the frequency distribution covering a determined interval of frequencies including the resonance frequency associated with the “0” mode known as breathing mode of the cylindrical type structure.,

2. Device according to claim 1, characterized in that a said crosspiece (CR) comprises at least one modified part (CC, BR) by removal or addition of material, allowing an adjustment of the natural frequency (FP) of said elementary resonator (RE).

3. Device according to claim 1 or 2, characterized in that said fixing points (FP) forming shock-absorbing blocks (PA) comprise a shock-absorbing material.

4. Device according to claim 3, 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%.

5. Device according to claim 3 or 4, characterized in that said damping material is an adhesive material.

6. Device according to any one of claims 1 to 5, characterized in that said grid (GR) is a metal grid.

7. Device according to claim 6, characterized in that said grid (GR) is obtained from a metal sheet.

8. Device according to any one of claims 1 to 7, characterized in that said grid has a rectangular mesh and cross-shaped crosspieces (CR).

9. Cylindrical type structure (ST) characterized in that it comprises a distributed vibration trap device (PVD) according to any one of claims 1 to 8 mounted on a circumferential outer surface (SEC) of the structure.

10. Rotating electrical machine characterized in that it comprises a distributed vibration trap device (PVD) according to any one of claims 1 to 8 mounted on a circumferential outer surface (SEC) of a stator (ST) of said machine.

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