WO2019203817A1

WO2019203817A1 - Electric turbocharger magnet decoupling

Info

Publication number: WO2019203817A1
Application number: PCT/US2018/028125
Authority: WO
Inventors: Charles KURLE; Allan Kelly; Tyler GARRARY
Original assignee: Borgwarner Inc.
Priority date: 2018-04-18
Filing date: 2018-04-18
Publication date: 2019-10-24

Abstract

A magnet assembly used with an electric turbocharger having a plurality of magnets each including a shaft surface configured to engage a turbine shaft or an inner core of the electric turbocharger! a sleeve surface configured to abut a rotor sleeve that prevents the magnets from radial outward movement away from the turbine shaft! one or more compliant features located between axially adjacent magnets or on a radial side of a magnet adjacent an end of the turbine shaft or the inner core.

Description

ELECTRIC TURBOCHARGER MAGNET DECOUPLING

TECHNICAL FIELD

The present application relates to electric turbochargers and, more particularly, to magnets used in electric turbochargers.

BACKGROUND

Internal combustion engines (ICE) have benefitted from the forced induction of air into the intake manifolds in an effort to increase engine power per consumption of fuel. Forced induction can be provided by a turbine directly driven from rotational output provided by the vehicle (often referred to as a supercharger or supercharging) or a combination of a compression turbine that is mechanically linked to an exhaust turbine via a shaft. As exhaust gas flow increases, so too does the angular velocity of the exhaust turbine thereby increasing the angular velocity of the compression turbine and compressing intake air entering the intake manifold. This latter example of forced induction can be carried out by a turbocharger or referred to as turbocharging. However, newer forms of forced induction incorporate electric motors that provide some or all of the rotational energy that drives a turbine through a turbine shaft.

The turbine shafts in electrical turbochargers can be coupled with a rotor assembly that is inserted within a stator. During operation, electrical current can be applied to windings on the stator causing the turbine shaft to rotate quickly at a high number of revolutions per minute (RPMs) turning the compressor turbine and forcing compressed air into the intake of an ICE. Traditional turbochargers, without electrical power, use turbine shafts that are carefully balanced to minimize vibrations that may result from high RPM operation. However, electric turbochargers use turbine shafts that are coupled with a rotor including magnets. The combination of rotors and magnets with a turbine shaft can introduce imbalances to the assembly, which may translate to vibration during electric turbocharger operation. It would be helpful to reduce vibration and/or change the natural frequencies of those vibrations resulting from any turbine shaft/rotor imbalances.

SUMMARY

In one implementation, a magnet assembly used with an electric turbocharger has a plurality of magnets each including a shaft surface configured to engage a turbine shaft or an inner core of the electric turbocharger! a sleeve surface configured to abut a rotor sleeve that prevents the magnets from radial outward movement away from the turbine shaft! one or more compliant features located between axially adjacent magnets or on a radial side of a magnet adjacent an end of the turbine shaft or the inner core.

In another implementation, a magnet assembly used with an electric turbocharger has a plurality of axiallyspaced magnets each including a shaft surface configured to engage a turbine shaft or an inner core of the electric turbocharger; a sleeve surface configured to abut a rotor sleeve! a rotor sleeve, engaging the sleeve surface of the plurality of axiallyspaced magnets! one or more compliant features located between axiallyspaced magnets or on a radial side of a magnet adjacent an end of the turbine shaft or the inner core! and one or more apertures extending from an outer surface of the rotor sleeve to an inner surface of the rotor sleeve and positioned along a rotor.

In yet another implementation, a magnet assembly used with an electric turbocharger has a plurality of axiallyspaced magnets each including a shaft surface configured to engage a turbine shaft or inner core of the electric turbocharger; a sleeve surface configured to abut a rotor sleeve! a rotor sleeve engaging the sleeve surface and preventing radially outward movement of the magnets from the turbine shaft, wherein the plurality of magnets are configured to be axiallyspaced along the turbine shaft and received by one or more ribs each having a first radially-extending side, a second radially-extending side, and an annular outer wall connecting the first radially-extending side and the second radially-extending side. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-sectional view depicting an implementation of an electric turbocharger!

Figure 2 is a cross-sectional view depicting an implementation of a rotor assembly and compliant features! and

Figure 3 is a cross-sectional view depicting another implementation of a rotor assembly and compliant features!

Figure 4 is a cross-sectional view depicting a portion of an implementation of compliant features!

Figure 5 is a cross-sectional view depicting a portion of another implementation of compliant features! and

Figure 6 is a cross-sectional view depicting a portion of another implementation of compliant features.

DETAILED DESCRIPTION

Electric turbochargers use a rotor assembly that attaches to a turbine shaft. The rotor assembly may include a plurality of magnets and a rotor sleeve and be placed in close proximity to a stator having a plurality of windings. When electrical current flows through the windings it imparts an angular force on the magnets of the rotor assembly thereby translating that angular force into rotational motion of the turbine shaft. The plurality of magnets can press against an outer surface of the turbine shaft and be held in place by a rotor sleeve that slides axially over the turbine shaft to maintain the magnets against the outer surface pressing them radially inwardly toward the turbine shaft. The combination of the rotor assembly with the turbine shaft can yield subtle imbalances that, when the turbine shaft is rotated above a particular RPM level, generate high-frequency vibrations or an unwanted frequency of those vibrations.

The rotor assembly includes compliant features that can be implemented in one or more portions of the assembly, such as the magnets, the rotor sleeve, or both. The compliant features can decouple the magnets of the rotor assembly from the compression applied by a compressor wheel nut to the nose of the compressor turbine. Electric turbochargers can be implemented in a variety of ways. In some implementations, an electric turbocharger includes a turbine shaft coupled to a rotor assembly, a compressor turbine, and an exhaust turbine. In this implementation, the compressor turbine can be driven by the rotor assembly as it is acted on by electrical current passing through windings included with a stator, the exhaust turbine, or both.

Turning to Figure 1, a perspective view of one implementation of an electric turbocharger 10 is shown. The electric turbocharger 10 includes a compressor housing 12, an electric motor housing 14, and an exhaust housing 16 that are assembled to form a structure that receives the components of the turbocharger 10. A turbine shaft 18 extends through the compressor housing 12, the electric motor housing 14, and the exhaust housing 16. At one end, the turbine shaft 18 couples with a compressor turbine 20 located in the compressor housing 12 that spins to compress air, which is ultimately supplied to an intake plenum (not shown) of an internal combustion engine (ICE). Another portion of the turbine shaft 18 that is axially-spaced from the compressor turbine 20 and located in the electric motor housing 14 couples with a rotor assembly 22 of an electric motor 24. The rotor assembly 22 can be positioned concentrically relative to a stator 26 included in the electric motor housing 14. One or more bearings 28 are included in the electric motor housing 14 and axially spaced along the turbine shaft 18 to support and stabilize the turbine shaft 18, the compressor turbine 20, the rotor assembly 22, and an exhaust turbine 30 as these elements rotate within the turbocharger 10 during operation. The exhaust turbine 30 coupled to an end of the turbine shaft 18 distal to the compressor turbine 20 located in the exhaust housing 16.

The compressor housing 12 includes a compressor turbine chamber 32 in which the compressor turbine 20 spins in response to the rotation of the turbine shaft 18 and compresses air that is ultimately supplied to the intake manifold of an internal combustion engine (ICE). The compressor turbine 20 is coupled with the turbine shaft 18 that extends from the compressor housing 12 into the electric motor housing 14 and the exhaust housing 16. The rotor assembly 22 is coupled to the turbine shaft 18 so that the rotor assembly 22 and the turbine shaft 18 are not angularly displaced relative to each other. When combined, the rotor assembly 22 extends axially relative to the shaft 18 in close proximity to the stator 26. The stator 26 can include a plurality of windings that convey electrical current and induce the angular displacement of the rotor assembly 22 and the turbine shaft 18 coupled to the rotor assembly 20. In one implementation, the stator 26 and the rotor assembly 20 can be implemented as a direct current (DC) brushless motor that receives DC voltage from a vehicle battery. The amount of DC voltage applied to the stator 26 may be greater than 40 volts (V), such as can be provided by a modern 48V vehicle electrical system. The compressor turbine chamber 32 is in fluid communication with a compressor intake plenum 36 that draws air from the surrounding atmosphere and supplies it to the compressor turbine 20. As a controller selectively flows current through windings of the stator 26, the rotor assembly 22 is induced to rotate and impart that rotation on the turbine shaft 18 and the compressor turbine 20.

The exhaust housing 16 is in fluid communication with exhaust gases generated by the ICE. As the revolutions per minute (RPMs) of the crankshaft of the ICE increase, the volume of the exhaust gas generated by the ICE increases and correspondingly increases the pressure of exhaust gas in the exhaust housing 16. This increase in pressure can also increase the angular velocity of the exhaust turbine 30 that communicates rotational motion to the compression turbine 20 through the turbine shaft 18. In this implementation, the compressor turbine 20 receives rotational force from the exhaust turbine 30 and the electric motor 24. More particularly, when the ICE is operating at a lower RPM, the electric motor 24 can provide rotational force to the compressor turbine 20 even though exhaust gas pressure within the exhaust housing 16 is relatively low. As the ICE increases the RPM of the crankshaft, exhaust gas pressure within the exhaust housing 16 can build and provide the rotational force that drives the compressor turbine 20. However, it should be appreciated that the concepts described herein can be applied to turbochargers that are configured in different ways. For example, the turbocharger can be implemented using a compressor housing and an electric motor housing while omitting the exhaust housing. In this implementation, the turbocharger includes a compressor turbine coupled to the electric motor via a turbine shaft without relying on an exhaust turbine to also be coupled to the turbine shaft. This implementation can sometimes be referred to as an electric supercharger because forced induction in this implementation relies solely on the rotational force provided by an electric motor rather than also using an exhaust turbine that is rotationally driven by exhaust gases.

Turning to Figure 2, an implementation of the rotor assembly 22 that includes compliant features and can be used with the turbocharger 10. The rotor assembly 22 comprises a plurality of magnets 36 that are axially spaced from each other, a rotor sleeve 38, and one or more compliant features 40 positioned between two magnets 36 or at an end of a magnet 36. In the implementation shown in Figure 2, the rotor assembly 22 includes three axially spaced magnets 36 disposed about the turbine shaft 18. The magnets 36 each include an inner surface 42 and an outer surface 44. The inner surface 42 is shaped to closely conform to an outer surface 46 of the turbine shaft 18. For example, the inner surface 42 can be annularly shaped so that it closely matches a cylindrical outer surface 46 of the turbine shaft 18. In some implementations, each magnet 36 is annular so that it is defined by an inner diameter and an outer diameter. During assembly, the annular magnet 36 can be axially slid onto the turbine shaft 18 so that the inner surface 42 of the magnet 36 abuts and engages the outer surface 46 of the turbine shaft 18. However, other implementations can comprise segmented magnets in which each magnet can be formed from a plurality of elements and then joined together when coupled with the turbine shaft 18. For example, each magnet can include two components that span approximately 180 degrees of the outer surface 46 of the turbine shaft 18. When these two components are joined together so that the inner surface 42 of the magnet 36 abuts the outer surface 46 of the turbine shaft 18, one or more fasteners can join the components together. The fasteners can include mechanical fixation in the form of welding or a screw that fits into a mechanical receiver. This could involve compressing the components and the magnet against the turbine shaft 18 to prevent angular displacement of the magnet 36 relative to the turbine shaft 18. The turbine shaft 18 can be an elongated element including a shoulder 48 that abuts one end of the rotor assembly 22 and a rotor fastener 50 that axially compresses the rotor assembly 22 against the shoulder 48.

Compliant features 40 are positioned axially between magnets 36 or between a magnet 36 and another component. In the implementation shown in Figure 2, the compliant features 40 comprise an annular space 52 defined by the radial surfaces 54 of adjacent magnets 36, the outer surface 46 of the turbine shaft 18, and an inner surface 56 of the rotor sleeve 38. This annular space 52 can be filled with a substrate, such as a polymeric material or synthetic rubber, an epoxy filler, a coating, or other similar vibration reducing substrate. In one implementation, the compliant feature 40 can be the application of a plurality of material layers as coatings layered on top of the inner surface 56 that collectively form the substrate. In another implementation, the annular space 52 can be filed with a solid material having a defined surface. In the implementation shown, the compliant features can be filled with elastomeric washers. However, it should be appreciated that the annular space 52 can also be left unfilled. The compliant feature 40, in the form of a solid elastomeric washer including an inner diameter and an outer diameter, can be slid over an end of the turbine shaft 18 and along the shaft 18 until it abuts the shoulder 48. A first magnet 36a can then be slid over the outer surface 46 of the turbine shaft 18 in a similar way until the radial surface 54 of the first magnet 36a abuts a radial surface 58 of the compliant feature 40. A second compliant feature 40 can then be added to the turbine shaft 18 followed by a second magnet 36b, a third compliant feature 40, a third magnet 36c, and a fourth compliant feature 40. The rotor sleeve 38 can then slide axially over the magnets 36a, 36b, 36c so that an inner surface 56 of the rotor sleeve 38 abuts and engages an outer surface 44 of the magnets 36a, 36b, 36c. The rotor sleeve 38 can then prevent the radial movement of the magnets 36a, 36b, 36c relative to the turbine shaft 18. The rotor fastener 50 can then compress the rotor sleeve 38 against the shoulder 48. In one example, a nut can engage a threaded end of the turbine shaft 18 and compress the rotor sleeve 38 against the shoulder 48. As the turbine shaft 18 and the rotor assembly 22 spin during operation, the compliant features 40 can absorb high-frequency vibrations and/or change the naturally-occurring vibration frequency of the turbine shaft 18 and rotor assembly 22. As the turbine shaft 18 rotates about a center axis (x) the compliant features 40 can absorb vibration generated by such movement. The greater the radial outward defection of the turbine shaft 18 relative to the center axis (x), the greater the compression of the compliant features 40, in this implementation, the elastomeric washers.

Figure 3 depicts another implementation of the rotor assembly 22 that includes compliant features 40 and can be used with the turbocharger 10. The rotor assembly 22 shown in Figure 3 is substantially similar to the rotor assembly 22 shown in Figure 2. However, in the implementation shown in Figure 3, the rotor assembly 22 includes three axially spaced magnets 36a, 36b, 36c disposed about an inner core 60. The inner core 60 can be an annular sleeve having an inner surface 62 and an outer surface 64. The inner diameter 62 is sized to closely conform to an outer surface of a turbine shaft. The magnets 36a, 36b, 36c each include an inner surface 42 and an outer surface 44. The inner surface 42 of the magnets 36a, 36b, 36c is shaped to closely conform to the outer surface 64 of the inner core 60. For example, the inner surface 62 can be annularly shaped so that it closely matches a cylindrical outer surface of a turbine shaft 18.

Other implementations of compliant features 40 are possible. Turning to Figure 4, another implementation of compliant features 40 is shown. A cross- section of a portion of the turbine shaft 18 coupled with two axially- adjacent magnets 36 is shown. The compliant feature 40 is formed as part of a first magnet 36a and as part of a second magnet 36b. The first magnet 36a and the second magnet 36b include an inner surface 42 that abuts the turbine shaft 18 and an outer surface 44 that abuts the rotor sleeve 38. The outer surfaces 44 of the magnets 36a, 36b are axially shorter relative to the inner surfaces 42 of the magnets 36a, 36b. A transitionary section 66 on a radial surface 54 of the magnets 36a, 36b connects the inner surface 42 of the magnets 36a, 36b to the outer surface 44 of the magnets 36a, 36b. The transitionary section 66 can be shaped according to a desired amount of damping provided by the compliant feature 40. For example, a radius angle between the inner surface 42 and the outer surface 44 can be selected based on the amount of damping desired from each compliant feature. As the turbine shaft 18 deflects radially outwardly from the center axis (x), the outer surface 44 of the first magnet 36a can move axially closer to the outer surface 44 of the second magnet 36b. The inner surface 56 of the sleeve 38 can resist this movement with a force directed radially inwardly toward the turbine shaft 18. The collective movement of the outer surfaces 44 of the magnets 36a, 36b and the inner surfaces 56 of the rotor sleeve 38 can reduce vibration and/or change the vibration frequency resulting from imbalances in the rotor assembly and/or the turbine shaft.

Figure 5 depicts another implementation of a compliant feature 40. A cross-section of a portion of the turbine shaft 18 coupled with two axially adjacent magnets 36 is shown. The compliant feature 40 includes a rotor sleeve 38 having an aperture 68 positioned radially outwardly from an axial space 70 between magnets 36. The rotor assembly 22 can include a first magnet 36a and a second magnet 36b axially spaced from the first magnet 36a along the turbine shaft 18. The aperture 68 does not fully circumscribe the rotor sleeve 38 and passes from an inner surface 56 of the rotor sleeve 38 to an outer surface 72 of the rotor sleeve 38. For instance, the aperture 68 can extend angularly around the rotor sleeve for a particular angular range.

Turning to Figure 6, another implementation of a compliant feature 40 is shown. Figure 6 depicts a cross-section of a portion of the turbine shaft 18, the magnet 36, and the rotor sleeve 38. The rotor sleeve 38 includes compliant features 40 in the form of a plurality of axially- spaced ribs 74 that each receive one of a plurality of magnets 36. Each rib 74 can include a first radially- extending side 76, a second-radiallyextending side 78, and an annular outer wall 80 that links the first radially-extending side 76 with the second radially- extending side 78. The first radially-extending side 76, the second radially- extending side 78, and the outer wall 80 can define a space in which the magnet fits. Adjacent ribs 74 of the rotor sleeve 38 can be linked by shaped sleeve sections 82. The shaped sleeve sections 82 can extend between adjacent radially- extending sides 76, 78. The thickness of the shaped sleeve section 82 and the radius of a transition between a radially-extending side 76, 78 and the shaped sleeve section 82 can each be selected to increase or decrease the damping effect of the compliant features 40.

It is to be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims. For example, the magnets in the embodiments shown and described above are directly attached to the turbine shaft. However, it is possible to attach the magnets to an inner core. The inner core can be an annular sleeve that carries the magnets and the rotor sleeve. The turbine shaft can then axially slide over an outer surface of the turbine shaft and engage with the shaft in a way that prevents the inner core from being angularly displaced relative to the turbine shaft.

As used in this specification and claims, the terms "e.g. "“for example,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open- ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.

Claims

What is claimed is:

1. A magnet assembly used with an electric turbocharger, comprising:

a plurality of magnets each including:

a shaft surface configured to engage a turbine shaft or an inner core of the electric turbocharger!

a sleeve surface configured to abut a rotor sleeve that prevents the magnets from radial outward movement away from the turbine shaft! and

one or more compliant features located between axially adjacent magnets or on a radial side of a magnet adjacent an end of the turbine shaft or the inner core.

2. The magnet assembly recited in claim 1, further comprising the rotor sleeve.

3. The magnet assembly recited in claim 2, wherein the rotor sleeve includes one or more apertures.

4. The magnet assembly recited in claim 1, wherein the compliant feature is included in the rotor sleeve.

5. The magnet assembly recited in claim 1, wherein the compliant feature is partially included with a first magnet and is partially included with a second magnet.

6. The magnet assembly recited in claim 1, further comprising a transitionary section.

7. The magnet assembly recited in claim 1, wherein the transitionary section includes a radius.

8. The magnet assembly recited in claim 1, wherein the compliant feature further comprises a substrate.

9. The magnet assembly recited in claim 8, wherein the substrate further comprises an elastomeric washer.

10. The magnet assembly recited in claim 1, wherein flexibility of the turbine shaft is controlled by selecting the amount of thickness of the magnets measured from the shaft surface to the sleeve surface.

11. A magnet assembly used with an electric turbocharger, comprising:

a plurality of axially- spaced magnets each including:

a sleeve surface configured to abut a rotor sleeve!

a rotor sleeve, engaging the sleeve surface of the plurality of axially- spaced magnets!

one or more compliant features located between axially -spaced magnets or on a radial side of a magnet adjacent an end of the turbine shaft or the inner core! and

one or more apertures extending from an outer surface of the rotor sleeve to an inner surface of the rotor sleeve and positioned along a rotor.

12. The magnet assembly recited in claim 11, wherein the compliant feature further comprises a substrate.

13.. The magnet assembly recited in claim 11, wherein the substrate further comprises an elastomeric washer.

14. The magnet assembly recited in claim 1, wherein flexibility of the turbine shaft is controlled by selecting the amount of thickness of the magnets measured from the shaft surface to the sleeve surface.

15. A magnet assembly used with an electric turbocharger, comprising:

a plurality of axially- spaced magnets each including:

a shaft surface configured to engage a turbine shaft or inner core of the electric turbocharger!

a sleeve surface configured to abut a rotor sleeve! andD a rotor sleeve engaging the sleeve surface and preventing radiallyoutward movement of the magnets from the turbine shaft, wherein the plurality of magnets are configured to be axially-spaced along the turbine shaft and received by one or more ribs each having a first radially-extending side, a second radially-extending side, and an annular outer wall connecting the first radially-extending side and the second radially-extending side.

16. The magnet assembly recited in claim 15, further comprising a shaped sleeve section.

17. The magnet assembly recited in claim 15, wherein the shaped sleeve section includes a radius.