GB2552367A

GB2552367A - Stator windings in a switched reluctance motor of an electric supercharger

Info

Publication number: GB2552367A
Application number: GB1612676.5A
Authority: GB
Inventors: Peacey Matthew; Lee Don
Original assignee: Valeo Air Management UK Ltd
Current assignee: Valeo Air Management UK Ltd
Priority date: 2016-07-21
Filing date: 2016-07-21
Publication date: 2018-01-24
Also published as: GB201612676D0

Abstract

An electric supercharger 9 comprises a compressor element 14 and a switched reluctance motor (SRM) configured to drive rotation of the compressor element. The SRM comprises a rotor rotatable about an axis of rotation, and a plurality of pairs of stator segments 3 each pair of stator segments comprises segments that are on opposite sides of the axis of rotation. Each segment comprising a stator wire 8 wound around a stator core 27 having a cross sectional shape that is substantially rectilinear. The cross sectional shape of the stator wires preferably is quadrilateral, square or rectangular shaped. Each stator segment may comprise a housing element connecting with adjacent stator segments to form circular cylindrical housing. The SRM preferably has three pairs of stator segments. A method of forming a segment in a SRM is also claimed.

Description

(54) Title of the Invention: Stator windings in a switched reluctance motor of an electric supercharger Abstract Title: Stator windings in a switched reluctance motor of an electric supercharger (57) An electric supercharger 9 comprises a compressor element 14 and a switched reluctance motor (SRM) configured to drive rotation of the compressor element. The SRM comprises a rotor rotatable about an axis of rotation, and a plurality of pairs of stator segments 3 each pair of stator segments comprises segments that are on opposite sides of the axis of rotation. Each segment comprising a stator wire 8 wound around a stator core 27 having a cross sectional shape that is substantially rectilinear. The cross sectional shape of the stator wires preferably is quadrilateral, square or rectangular shaped. Each stator segment may comprise a housing element connecting with adjacent stator segments to form circular cylindrical housing. The SRM preferably has three pairs of stator segments. A method of forming a segment in a SRM is also claimed.

Figure 6

11a

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114

Figure 1 (Prior Art)

2/8

101

103

Figure 2a (Prior Art)

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Figure 2b (Prior Art)

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127

108

103C

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129

103

Figure 3 (Prior Art)

108

6/8

Figure 5

7/8

11a

Figure 6

8/8

Figure 7

Stator windings in a Switched Reluctance Motor of an Electric Supercharger

Field of the Invention

The present invention relates to electric superchargers, and more specifically to electric superchargers having a switched reluctance motor with stator windings.

Background of the Invention

Electric superchargers, driven by switched reluctance motors, are attractive for use with vehicle engines. There is a desire to maximise the power output of the switched reluctance motor (SRM) in the supercharger. An accepted way of increasing the power and efficiency of a motor is to increase the number of windings (i.e. loops of wire) in each stator segment. However, introducing extra windings in the stator segments of an SRM increases the volume of each stator segment, and necessitates an increase in the diameter of the SRM. The demand for space in the engine bay of a vehicle, makes it difficult to package the electric superchargers within a given envelope. The diameter of the SRM is a key design parameter that influences the size of the supercharger and its packing efficiency within the engine bay. Thus it tends to be undesirable to make any changes (such as increasing the number of windings) that would result in an increase of the SRM diameter.

There have therefore been difficulties increasing the power of an SRM-driven electric supercharger, whilst still achieving an acceptable packing efficiency. Given the constraints on the diameter of an SRM, one solution has been to consider replacing the SRM with a different type of electric motor. Alternatively, it may be possible to adjust the topology of the motor (i.e. the number of rotor/stator poles) by adding extra pairs of stator segments, thereby increasing the number of stator poles. This may facilitate a greater torque output from the SRM but it tends to reduce the maximum achievable output speed.

Due to their independence from rare earth magnets such as Permanent Magnets (PMs), there is also a growing expectation that electric superchargers with an SRM should be capable of being exposed to high operating temperatures without degradation in performance. This introduces the risk of the supercharger overheating and damage being caused, especially to the electronics controlling the switching of current for the stator coils of the SRM. This risk of overheating increases particularly when the SRM is being operated at a high power for extended duration. Thus there is a demand for SRM-driven electric superchargers with better heat transfer (thermal management) properties to avoid damage to the internal components of the supercharger.

The present invention seeks to mitigate at least some of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved electric supercharger.

Summary of the Invention

The present invention provides, according to a first aspect, an electric supercharger comprising a compressor element and a switched reluctance motor configured to drive rotation of the compressor element; wherein the switched reluctance motor comprises a rotor rotatable about an axis of rotation, and a plurality of pairs of stator segments. Each pair of stator segments may comprise segments that are on opposite sides of the axis of rotation. Each segment comprises stator windings (i.e. loops of wire) wound around a stator core (a 'stator core' may also be known in the art as a 'stator stack'). The cross sectional shape of the wire in the stator windings is rectilinear. By using rectilinear wiring in the stator windings of the switch reluctance motor, the space in the winding volume of the stator windings may be more efficiently used. This may enable more windings of wire to be used in each stator segment (i.e. more loops of wire around the stator core), which may enable the supercharger to produce a higher power and/or torgue output without increasing the diameter and/or complexity of the switch reluctance motor.

Although the use of rectangular wires in motors per se is known, there has been an accepted understanding in the field of SRM-driven superchargers, that motor power can only be increased in other ways (if at all) - see 'Background to the invention' above. The surprising benefits of using rectilinear wires in an SRM-driven supercharger have therefore not been recognised.

It may be that the cross-sectional shape of the wires is quadrilateral. It may be that the crosssectional shape of the wires is square. It may be that the cross-sectional shape of the wires is rectangular.

It will be appreciated that the cross-sectional shape of the wire is typically the shape as viewed in a cut-plane that is perpendicular to the local longitudinal axis of the wire.

Each segment is typically formed by a multiplicity of windings of the stator wire around the core. It may be that each winding of the stator wire directly abuts a neighbouring winding along a substantially planar interface. For example the neighbouring windings may directly abut substantially along the mutual contact area between a face of the rectilinear wire. In embodiments having this feature, as well as the benefits in spacesaving, the increased contact area of the wires (compared to wires having a circular cross-section) increases the efficiency of heat transfer away from the stator, which may reduce the risk of damage to internal and electronic components of the electric supercharger.

It may be that each stator segment comprises a housing element located radially outward of the stator core. The housing elements of adjacent stator segments may connect with one another to form a circular cylindrical housing enclosing the stator segments. The housing elements may be connected by being integral with one another to form the circular cylindrical housing enclosing the stator cores. In some embodiments, the housing elements of adjacent stator segments may interlock with one another to form the circular cylindrical housing enclosing the stator cores. The housing elements may be attached to the respective stator cores, and in some embodiments, the housing elements may be integral with the cores. The term radially outward should be understood to mean radially outward from the axis of rotation of the motor.

The supercharger may comprise a control unit for controlling the switched reluctance motor. The control unit may control current to the motor. For example, the control unit may selectively energise coils of the motor in order to rotate a rotor of the motor.

According to a second aspect of the invention there is provided an internal combustion engine in combination with an electric supercharger according to the first aspect of the invention. The engine is preferably a relatively small capacity engine. The engine is preferably 4 litres or less, more preferably 3 litres or less, and yet more preferably 2 litres or less). The engine is for an automobile. The automobile may be less than 3.5 tonnes (gross), and more preferably less than 2 tonnes .

According to a third aspect of the invention there is provided a vehicle comprising an electric supercharger according to the first aspect of the invention.

According to a fourth aspect of the invention there is provided an apparatus for supplying an internal combustion engine with a compressed air charge, the apparatus comprising a turbocharger and an electric supercharger according to the first aspect of the invention, the electric supercharger being downstream of the turbocharger. In such an apparatus, the supercharger tends to be subjected to high-temperatures (for example due to hot intake gases and/or due to heat transfer from adjacent heat sources within the engine bay). There is therefore a particular importance in effective heat transfer away from the stator segments, compared to arrangements in which only a supercharger is used in isolation. The use of rectilinear wires in the switch reluctance motor has been found to be particularly advantageous in terms of heat transfer. The relatively large contact area presented between the planar faces allows more efficient heat transfer away from the segments. This has been found to be especially advantageous in the above-mentioned fourth aspect of the invention, where high temperature can often be a limiting design factor.

According to a fifth aspect of the invention there is provided a method of forming a stator segment in a switched reluctance motor (SRM) of an electric supercharger, the SRM comprising a plurality of stator segments, each stator segment comprising a stator core, with a stator wire forming windings (i.e. loops of wire) wound around that core, wherein the cross sectional shape of the stator wire is substantially rectilinear, the method comprising the step of winding loops of the stator wire to form windings around the stator core, such that each winding of the stator wire directly abuts a neighbouring winding along a substantially planar interface. The planar interface is preferably a contact interface between opposing faces of the rectilinear wires .

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

Figures 2b and 2c are perspective views showing how the individual stator segments of Figure 2a are constructed;

Figure 3 is an axial cross-sectional view of a stator segment along line A-A of Figure 2a;

Figure 4 is a schematic showing part of the crosssection of Figure 3;

Figure 5 is a schematic showing the cross-section of a stator segment in a supercharger according to a first embodiment of the invention;

Figure 6 is a schematic showing a perspective sectional view of the supercharger incorporating the stator segments of Figure 5; and

Figure 7 is a schematic showing an engine incorporating the supercharger of Figure 6.

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 an electric drive assembly having a motor 101 (comprising a stator assembly 111 with stator segments 103 (described in more detail below with reference to Figures 2a-2c), 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. DC Power to the electric motor 101 and control unit 112 is supplied by a lead/acid

- 8 battery (not shown) charged by an alternator (not shown) associated with an engine. In another embodiment (not shown) alternative power sources may be used such as a Lithium battery, or an Ultra/Super capacitor. The drive assembly is arranged to drive the compressor element 114, in the form of a compressor wheel, via the shaft 113.

The shaft 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 an outlet (not shown in Figure 1).

Figure 2a 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 2a (and 2b-2c) is disclosed in GB2510382.

The stator assembly 111 comprises six segments 103 arranged in a circle. Each segment is formed by windings of wire 108 (only the ends of which tend to be visible in Figures 2a-2c) 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, the segment for forming one pole is indicated by the light-coloured wire of the respective windings, and the segment for forming the opposing pole is indicated by the dark-coloured wires of the respective windings .

Figures 2b and 2c show perspective views showing a part of the stator assembly 111 of Figure 2a in different stages of construction. Figure 2b shows two adjacent segments (a first segment from pair 103A, and a second segment from pair 103C). Each segment is formed by the coil of wire 108 (i.e. windings) wrapped around a metallic core 127. A support structure 129 is attached to the radially outer surface of the core 127. For the sake of clarity, the core 127 and support structure 129 are only labelled for one of the segments in Figure 2b.

The support structures 129 attached to the cores 127 around which the respective windings of wire are wrapped, are connected together using a tongue and groove arrangement 123. Figure 2b shows the two segments 103A/C separated, and Figure 2c shows them assembled.

To form the stator assembly 111, two additional sets of segments are connected together in a similar fashion and then arranged to form a circle of six segments (see Figure 2a). The segments diametrically opposite one another each define a pair of segments 103A-C, and are often known as pairs of stator poles.

Figure 3 shows an axial cross-sectional of one of the stator segments 103, viewed along A-A of Figure 2a. The spaces between the support element 129 and the core 127 of one segment, and the support element and core of the neighbouring segment defines a set of circumferentially-spaced, approximately pentagonal, pockets 125. The windings of stator wire 108 are located within the volume of these pockets 125. It will be appreciated that one side of the windings on neighbouring segments 103A/103C occupies half the volume of each pocket 125.

Figure 4 shows a section through one of the pockets 125 in simplified form. For the sake of clarity only one half of one segment, and one half of the pocket (i.e.

relating to a single segment) is shown. The segment 103 is made by winding cylindrical wire 108 (i.e. wire with a common-place circular cross-sectional shape) around the core 127. As a result of the cylindrical shape of the wire 108, air gaps 131 are present in between the windingsl08.

It is desirable to be able to increase the power of a switched reluctance motor in a supercharger. An accepted way of increasing the power of a motor per se, is to increase the number of windings (i.e. loops of wire) in each stator segment, or to use larger diameter wires. However, introducing extra windings of stator wire in the stator of an SRM (or introducing larger diameter wires) increases the volume of each stator coil, and necessitates an increase in the diameter of the SRM. The diameter of the SRM is a key design parameter that influences the size of the supercharger and its packing efficiency within the engine bay, and that diameter is often defined by the locking together of the support structures 129 that link together and define the outer diameter of the stator assembly 111 (see Figures 1-4). Thus it tends to be undesirable to make any changes (such as increasing the number of windings of wire) that would result in an increase of the SRM diameter.

Figure 5 shows a winding configuration of a stator assembly in a supercharger according to a first embodiment of the invention, and Figure 6 shows the whole supercharger 9 of the first embodiment, in cross-section. The supercharger 9 is substantially identical to the known supercharger described above with reference to Figures 1-4, except for the wiring and winding configuration described below. Thus, unless described otherwise, it can be assumed that the supercharger of the first embodiment has those features. Features in the first embodiment of the invention that correspond to similar features in the prior art described above, are shown with the same reference numerals as in the first embodiment, but without the prefix '1' (or '10' where appropriate).

In the first embodiment of the invention, the wiring8 that forms the windings of the stator segment 3 has a rectilinear, and more specifically a square, crosssection. The perimeter of the wire 8 thus comprises four faces 8a-8d (for clarity, these are only labelled for a single winding in Figure 5, but it will be appreciated that the wire in each winding has these same corresponding faces). The windings of wire 8 are wound around the core 27 such that each winding directly abuts a neighbouring winding along one or more of the faces 8a8d. As a result, there are no significant air gaps in between the segments 3, and the volume of the pocket 25 is more efficiently used. This, in turn, means that that additional windings 8 can be added within the available space. For example, when comparing the prior art arrangement in Figure 4 with the invention in Figure 5, it will be seen that the invention has fifteen windings 8, whereas the prior art has only thirteen windings 108 in approximately the same volume 25/125.In some other embodiments of the invention, the total number of windings per segment may remain the same, but due to the improved packing density of the wire, the volume they occupy in the segment is smaller, which facilitates a smaller stator diameter.

By including extra windings of wire 8 in each stator segment 3 greater output power may be obtained by the SRM, but crucially the diameter of the SRM (i.e. the outer radius of the support structures 29) need not be increased. The ability to maintain a fixed diameter, yet increase the power output is especially beneficial in the context of SRM-driven superchargers as there are severe space constraints in the engine bay.

Although the use of rectangular wires in motors per se is known (for example in Permanent Magnet Motors), the particular advantages in the field of SRM-driven superchargers have not been recognised.

Yet further, the use of rectilinear wires in embodiments of the present invention has been found to also be advantageous in terms of heat transfer. The relatively large contact area presented between the planar faces 8a-8b, and the relatively large contact area between the some of the planar faces 8a-8b contacting the support structure 29 and/or core 27 allows more efficient heat transfer away from the windings. This is especially advantageous in an SRM-driven superchargers where high temperature can often be a limiting design factor. For example, in an embodiment of the invention, the supercharger having rectilinear wiring is used in conjunction with an IC engine, wherein the supercharger is downstream of the turbocharger. This is shown in Figure 7, to which reference in now made.

Figure 7 shows an internal combustion (IC) engine 33 in combination with an apparatus 35 for supplying compressed intake gases (i.e. a compressed air charge). The apparatus 35 (marked by a dotted line) comprises a turbocharger 37, an exhaust gas recirculation (EGR) valve 39, a charge air cooler (CAC) 41, the supercharger 9 (of Figure 6) and a supercharger bypass valve 43.

In accordance with conventional turbochargers, the turbocharger 37 is driven by the exhaust gases from the engine 33 passing through the Variable-Nozzle Turbine (VNT) 37a thereby driving the turbocharger compressor 37b. Some of the exhaust gas output of the engine 33 is returned as an input to the engine via the EGR valve 39.

The output of the turbocharger 37 is then fed through the CAC 41 before being supplied to the engine 33 or the supercharger 9, depending on the status of the bypass valve 43.

Such an arrangement, where the supercharger 9 is located downstream of the turbocharger 37, can be attractive. However, it often results in the supercharger being subjected to high temperatures (either as a result of the hot gases leaving the turbocharger 37, and/or as a result of the supercharger 9 necessarily being located in proximity to heat sources when it is packaged into the engine bay. It is therefore of particular importance that there is effective heat transfer away from the stator segments 3. The supercharger 9 of the first embodiment of the invention has been found to be especially beneficial in this arrangement because the rectilinear shape of the wire in the windings has been found to facilitate effective thermal management.

Whilst the present invention has been described and illustrated with reference to a particular embodiment, 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.

For example, while in the first embodiment wiring with a square cross-section is used, in other embodiments any other wiring with any rectilinear cross-section is used, such as rectangular. By way of another example, in the first embodiment, the SRM is a six-pole stator and four pole rotor but other numbers of poles may be possible. The first embodiment of the invention seeks to improve power of the SRM whilst maintaining a fixed size. In some embodiments, the power may be kept constant, but the invention may facilitate a smaller SRM to achieve that power.

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 a compressor element and a switched reluctance motor configured to drive rotation of the compressor element;

wherein the switched reluctance motor comprises a rotor rotatable about an axis of rotation, and a plurality of pairs of stator segments each pair of stator segments comprising segments that are on opposite sides of the axis of rotation, and each segment comprising a stator wire wound around a stator core; and characterised in that the cross sectional shape of the stator wire is substantially rectilinear.

2. An electric supercharger according to claim 1, wherein each stator segment comprises a housing element located radially outward of the stator core, the housing elements of adjacent stator segments connecting with one another to form a circular cylindrical housing enclosing the stator segments.

3. An electric supercharger according to claim 1 or 2, wherein the cross sectional shape of the stator wire is substantially quadrilateral-shaped.

4. An electric supercharger according to claim 3, wherein the cross section of the stator wire is substantially square-shaped or rectangular-shaped.

5. An electric supercharger according to any preceding claim, wherein each segment is formed by a multiplicity of windings of the stator wire around the core, and each winding of the stator wire directly abuts a neighbouring winding along a substantially planar interface.

6. An electric supercharger according to any preceding claim, wherein the switched reluctance motor comprises three pairs of stator segments.

7. An internal combustion engine in combination with an electric supercharger according to any preceding claim.

8. An apparatus for supplying an internal combustion engine with a compressed air charge, the apparatus comprising the electric supercharger according to any of claims 1 to 6, and a turbocharger, the electric supercharger being downstream of the turbocharger .

9. A vehicle comprising an electric supercharger according to any of claims 1 to 6.

10. A method of forming a segment in a switched reluctance motor (SRM) of an electric supercharger, the SRM comprising a plurality of segments, each segment comprising a stator core, with a stator wire forming windings wound around that core, wherein the cross sectional shape of the stator wire is substantially rectilinear, the method comprising the step of winding loops of the stator wire to form windings around the stator core, such that each winding of the stator wire directly abuts a neighbouring winding along a substantially planar interface .

11. An electric supercharger substantially as herein 5 described with reference Figures 5 and 6 of the accompanying drawings .

Intellectual

Property

Office

Application No: GB1612676.5 Examiner: Mr Mat Smith