GB2554665A

GB2554665A - Damping vibrations of an electric supercharger

Info

Publication number: GB2554665A
Application number: GB1616705.8A
Authority: GB
Inventors: Nicholas Webster Matthew
Original assignee: Valeo Air Management UK Ltd
Current assignee: Valeo Air Management UK Ltd
Priority date: 2016-09-30
Filing date: 2016-09-30
Publication date: 2018-04-11
Also published as: GB201616705D0

Abstract

An electric supercharger comprises an electric motor assembly. The electric motor assembly includes a body 200 and a stator assembly 111 within the body. Between the body and the stator assembly, there is a damping layer 250 comprising a first constraining layer 260, a second constraining layer 280 and a constrained layer 270 between the first and second constraining layers. The constraining layers may be metal layers which are each 30-60 microns thick. The constrained layer may be a viscoelastic layer which is 0.1-0.4 millimetres thick. There may be a further resin layer. There may be a second damping layer comprising a third constraining layer and a constrained layer between the second and third constraining layers. Also disclosed is a method of damping vibrations in an electric supercharger by providing the abovementioned supercharger. The method may include heating the body to expand it and then inserting the stator assembly and damping layer. The method may include wrapping each layer successively around the stator assembly. The damping sheet may be provided as a pre-fabricated composite sheet.

Description

(54) Title of the Invention: Damping vibrations of an electric supercharger

Abstract Title: Constrained Layer Damping for the Vibrations of an Electric Supercharger (57) An electric supercharger comprises an electric motor assembly. The electric motor assembly includes a body 200 and a stator assembly 111 within the body. Between the body and the stator assembly, there is a damping layer 250 comprising a first constraining layer 260, a second constraining layer 280 and a constrained layer 270 between the first and second constraining layers. The constraining layers may be metal layers which are each 30-60 microns thick. The constrained layer may be a viscoelastic layer which is 0.1-0.4 millimetres thick. There may be a further resin layer. There may be a second damping layer comprising a third constraining layer and a constrained layer between the second and third constraining layers. Also disclosed is a method of damping vibrations in an electric supercharger by providing the abovementioned supercharger. The method may include heating the body to expand it and then inserting the stator assembly and damping layer. The method may include wrapping each layer successively around the stator assembly. The damping sheet may be provided as a pre-fabricated composite sheet.

250

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Figure 3

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Figure 1 (Prior Art)

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Figure 2 (Prior Art)

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Figure 4

Damping vibrations of an electric supercharger

Field of the Invention

The present invention concerns the damping of vibrations of an electric supercharger. More particularly, but not exclusively, this invention concerns providing passive constrained layer damping in an electric supercharger.

Background of the Invention

Electric superchargers typically provide a compressed air charge to an internal combustion engine by means of a compressor wheel on a drive shaft driven by an electric motor. Vibrations in the supercharger can cause undesirable noise, a phenomenon typically referred to as noise, vibration and harshness. One source of vibrations is vibration of the stator assembly within the supercharger body. One approach to damping those vibrations is to inject a two-part resin into the gap between the stator assembly and the supercharger body. However, it has been found to be difficult to get an even injection of resin, and resin, especially two-part resin, can be difficult to handle, apply and store. Moreover, even with injected resin, noise, vibration and harshness have been found to continue at an undesirable level.

The present invention seeks to mitigate the abovementioned problems.

Summary of the Invention

The present invention provides according to a first aspect, an electric supercharger comprising an electric motor assembly, the electric motor assembly including a body, and a stator assembly within the body, wherein, between the body and the stator assembly, there is a damping layer comprising a first constraining layer, a second constraining layer and a constrained layer between the first and second constraining layers.

In use, when the electric motor assembly vibrates, the constraining layers act to increase shear strains experienced by the constrained layer. Consequently, an amount of energy is dissipated, which provided damping of the vibrations. The use of a constrained layer sandwiched between two constraining layers is known as Passive constrained layer damping (PCLD damping). It is known to use PCL damping of extensive planar sheets, such as aircraft wings. The inventor is not aware that anyone has previously proposed applying PCL damping to electric superchargers. Moreover, the use of PCL damping in a s/c has been found to be especially beneficial in the context of a motor in an electric supercharger.

The body may be, for example a casting, a pressed steel body or a machined body.

The electric motor may be a switched reluctance motor. Noise vibration and harshness issues can be more severe for a switched reluctance motor than for a permanent magnet motor. The switched reluctance operation causes cyclic loading of the motor. In particular, the switching of electromagnetic fields in a switched reluctance motor can cause deformations of the stator, which in turn cause vibrations. The benefits of providing the damping layer have been found to be most noticeable at resonant frequencies, in particular resonances at high frequencies, such as those seen in the motor excitation of the switched reluctance motor in an electric supercharger. The 8^th order harmonic (i.e. the frequency 8 times the rotational frequency of the rotor) is believed to be particularly problematic. For example, for a motor operating at 60k rpm, there is expected to be a particularly strong vibration at 8 kHz.

The electric motor may be a permanent magnet motor.

The constrained layer may be bonded to the first and second constraining layers.

The first constraining layer may be a metal layer, for example a foil layer, for example steel or aluminium. The second constraining layer may be a metal layer, for example a foil layer, for example steel or aluminium.

The constrained layer may be a viscoelastic layer.

The viscoelastic material may be, for example, a rubber (e.g. a silicone rubber or a neoprene rubber); a room-temperature vulcanization (RTV) elastomer; an amorphous polymer; and a semi-crystalline polymer. Many suitable viscoelastic materials will be known to the skilled person. The viscoelastic material may be selected to optimise damping at a pre-selected frequency, for example a frequency at which unwanted vibrations are known to occur (for example a resonance frequency).

The damping layer may comprise one or more further layer between the first constraining layer and the stator assembly. The damping layer may comprise one or more further layer between the second constraining layer and the body. The (or at least one of the) further layers may be a viscoelastic layer. The (or at least one of the) further layers may be a resin layer. The resin layer may be an injected resin layer. The resin layer may be a two-part silicone elastomer. The resin layer may be heat cured.

The further layers may comprise a second damping layer comprising a third constraining layer and a constrained layer between the second and third constraining layer. The further layers may comprise still further damping layers, each damping layer including a constrained layer between two constraining layers .

The electric motor assembly may further include constraints preventing or reducing longitudinal movement of the stator. The constraints may be, for example, washers or rubber seals.

The viscoelastic layer may be at least 0.1 mm thick, more preferably at least 0.15 mm thick, still more preferably at least 0.2 mm thick. The viscoelastic layer may be less than 0.4 mm thick, more preferably less than 0.35 mm thick, still more preferably less than 0.3 mm thick.

The metal layer may be at least 30 microns thick, more preferably at least 40 microns thick, still more preferably at least 45 microns thick. The metal layer may be less than 60 microns thick, more preferably less than 50 microns thick, still more preferably less than 45 microns thick.

The (or at least one of the) further layers may be at least 0.5 mm thick, more preferably at least 0.75 mm thick, still more preferably at least 1 mm thick. The (or at least one of the) further layers may be less than 3 mm thick, more preferably less than 2.5 mm thick, still more preferably less than 2 mm thick.

The electric motor assembly may include a rotor within the stator assembly.

According to a second aspect of the invention there is also provided a method of damping vibrations in an electric supercharger comprising an electric motor assembly, the electric motor assembly including a body, and a stator assembly within the body, the method comprising providing between the body and the stator assembly, a damping layer comprising a first constraining layer, a second constraining layer and a constrained layer between the first and second constraining layers.

The method may include heating the body to expand it and inserting the stator assembly and the damping layer within the expanded body.

The method may include wrapping the first constraining layer around the stator assembly, wrapping the constrained layer around the first constraining layer, and wrapping the second constraining layer around the constrained layer. The method may include bonding the constrained layer to the first and second constraining layers. Alternatively, the method may include providing the damping layer as a pre-fabricated composite sheet. The method may include the step of wrapping the pre-fabricated sheet around the stator assembly.

The method may include providing further layer between the first constraining layer and the stator assembly. The method may include providing a further layer between the second constraining layer and the body. The method may include injecting the one or more further layer, which may be a viscoelastic layer, for example a resin layer.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa .

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 is a sectional perspective view of a known supercharger;

Figure 2 is a perspective view of part of a Switched Reluctance Motor (SRM) for a known electric supercharger;

Figure 3 is a schematic cross-sectional view of a body and stator assembly from an electric motor assembly according to a first example embodiment of the invention; and

Figure 4 is a schematic cross-sectional view of a body and stator assembly from an electric motor assembly according to a second example embodiment of the invention.

Detailed Description

Figure 1 is a sectional perspective view of a known electric supercharger 109, disclosed in UK patent publication GB2508647. The electric supercharger 109 includes a housing in the form of a body 200 (in this example an aluminium casting) and an electric drive assembly having a motor 101 comprising a stator assembly 111 with stator segments 103, and a rotor 111a, and a control unit 112 in the form of a Printed Circuit Board (PCB) located to the rear of the motor 101.

There is a small gap 210 between the stator assembly 111 and the body 200. In the known electric supercharger discussed above, the small gap is injected with a twopart resin to provide damping of vibrations of the stator ass emb1y 111.

Power to the electric motor 101 and control unit 112 is supplied by a lead/acid battery (not shown) charged by an alternator (not shown) associated with an engine. The drive assembly is arranged to drive the compressor element 114, in the form of a compressor wheel, via the shaft 113. The shaft 113 is supported by a front bearing assembly 116a and a rear bearing assembly 116b.

In common with known superchargers, the supercharger 109 receives air through the inlet 117. The compressor element 114 then compresses the inlet air and expels it into the radial chamber 119 and through the outlet (not shown).

Figure 2 shows a perspective view of an example of the stator assembly 111 of the switched reluctance motor 101, suitable for use in the prior art arrangement of Figure 1. The stator assembly of Figures 2 is disclosed in GB2510382.

The stator assembly 111 comprises six stator segments 103 arranged in a circle. Each segment 103 is formed by a coil of wire (winding) 108 (only the ends of which tend to be visible in Figure 2) wrapped around a metallic core 127. The segments 103 can be divided into pairs of diametrically opposite segments 103A-C, each segment 103 in the pair being arranged to form an opposite pole to the other when energised by a control module (not shown). Within each pair of segments 103A-C,

- 8 the winding for forming one pole is indicated by the light-coloured wires, and the winding for forming the opposing pole is indicated by dark-coloured wires.

The cores 127 are held together by a steel former

220 .

In the known damping arrangement discussed above, the steel former 220 is held in place within the body 200 and compresses the core 127 together. There is a small gap 210 between the body 200 and the metal former 220, into which gap the two-part resin is injected.

Figure 3 is a schematic cross-sectional view of a body and stator assembly from an electric motor assembly according to a first example embodiment of the invention. In this arrangement the stator assembly is as described above, but has a novel and innovative damping arrangement.

In the example embodiment of Fig.3, the gap 210 between the body 200 and the metal former 220 of the stator assembly is annular. It is filled with an annular damping layer 250. In the damping layer 250 there is an annular first constraining layer, in the form of a 50 micron thick inner aluminium foil 260, and an annular second constraining layer, in the form of a 50 micron thick outer aluminium foil 280. Sandwiched between the first constraining layer and the second constraining layer is a constrained layer in the form of a 0.25 mm thick annular viscoelastic layer 270.

In the example embodiment of Fig. 4, the annular gap 210 between the body 200 and the metal former 220 of the stator assembly is again filled with an annular damping layer 250'. The damping layer 250' has the same structure as the damping layer 250 of the example of Fig. 3, save that there is a further viscoelastic layer 290, formed by injecting two-part resin between the body 200 and the outer aluminium foil 280, to form a 1 mm thick annular resin layer.

In use, the stator assembly 220 vibrates. The vibrations cause shear stresses between the (constrained) viscoelastic layer 27 and the (constraining) inner aluminium foil 260 and outer aluminium foil 280. The shear stresses dissipate some of the vibrational energy, thus reducing the amount of vibrational energy transmitted from the stator assembly 220 to the body 200. In the example embodiment of Fig. 4, the further viscoelastic layer 290 provides further damping, of a conventional kind.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

In the example embodiments of Fig. 3 and 4, the various components are shown as having annular crosssections. In practice, the components will generally not be strictly annular, as seen for example in Fig. 2, in which the metal former 220 is substantially annular but has a non-circular inner face, structured to receive the six core 127, and a non-circular outer face, including grooves 300.

The example embodiments of Figs. 3 and 4 show a viscoelastic layer sandwiched between two metal foil layers, with a further resin layer in the example of Fig.

4. In some alternative embodiments further layers can be provided. In general, it can be expected that each viscoelastic layer will be generally thinner than the resin layer(s) and be sandwiched by metal layers, whereas each resin layer will be generally thicker and not necessarily sandwiched; however, embodiments in which there are layers having a different structure from that are also within the scope of the present invention, which is limited only by the scope of the independent claims set out below.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. An electric supercharger comprising an electric motor assembly, the electric motor assembly including a body, and a stator assembly within the body, wherein, between the body and the stator assembly, there is a damping layer comprising a first constraining layer, a second constraining layer and a constrained layer between the first and second constraining layers.

2. An electric supercharger as claimed in claim 1, in which the electric motor is a switched reluctance motor.

3. An electric supercharger as claimed in claim 1 or claim 2, in which the first constraining layer and/or the second constraining layer is a metal layer.

4. An electric supercharger as claimed in claim 3, in which the metal layer is at least 30 microns thick and is less than 60 microns thick.

5. An electric supercharger as claimed in any preceding claim, in which the constrained layer is a viscoelastic layer .

6. An electric supercharger as claimed in claim 5, in which the viscoeclastic layer is at least 0.1 mm thick and is less than 0.4 m thick.

7. An electric supercharger as claimed in any preceding claim, in which the damping layer comprises one or more further layer between the first constraining layer and the stator assembly and/or between the second constraining layer and the body.

8. An electric supercharger as claimed in claim 7, in which the, or at least one of the, further layers is a resin layer.

9. An electric supercharger as claimed in claim 7 or claim 8, in which the, or at least one of the, further layers comprises a second damping layer, comprising a third constraining layer and a constrained layer between the second and third constraining layers.

10. A method of damping vibrations in an electric supercharger comprising an electric motor assembly, the electric motor assembly including a body, and a stator assembly within the body, the method comprising providing between the body and the stator assembly, a damping layer comprising a first constraining layer, a second constraining layer and a constrained layer between the first and second constraining layers.

11. A method as claimed in claim 10, including heating the body to expand it and inserting the stator assembly and the damping layer within the expanded body.

12. A method as claimed in claim 10 or claim 11, including wrapping the first constraining layer around the stator assembly, wrapping the constrained layer around the first constraining layer, and wrapping the second constraining layer around the constrained layer.

13. A method as claimed in claim 12, including bonding the constrained layer to the first and second constraining layers.

14. A method as claimed in claim 10 or claim 11, including providing the damping layer as a pre-fabricated composite sheet.

15. A method as claimed in claim 14, including the step of wrapping the pre-fabricated sheet around the stator assembly.

16. A method as claimed in any of claims 10 to 15, the method including providing a further layer between the first constraining layer and the stator assembly and/or between the second constraining layer and the body.

17. A method as claimed in claim 16, the method including injecting the one or more further layer

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