assembly

Technical Field

The present invention relates to electric superchargers having a radial flow compressor assembly. The present invention also relates to an engine assembly comprising an electric supercharger having a radial flow compressor assembly. The present invention also relates to a method of allocating the area of a support structure of an electric supercharger .

Background of the Invention

A known electric supercharger comprises a compressor wheel rotatable about a rotation axis on a drive shaft driven by an electric motor. An outlet housing comprises a volute section that has a scroll shape and defines a volute passage arranged to receive air compressed by the compressor wheel and to pass the compressed air to an outlet.

The outlet housing has an annular flange that extends radially outwardly from the scroll volute section to a circular radially outer periphery that is concentric with the rotation axis of the compressor wheel.

The annular flange provides an annular surface on which to mount components of the supercharger, such as electrical components that control, and/or connect a power source to, the electric motor.

However, the mounting of the components on the annular flange results in an undesirable increase in the overall size of supercharger. The present invention seeks to address or mitigate at least some of the above mentioned problems. Alternatively, or additionally, the present invention seeks to provide an improved electric supercharger. Alternatively, or additionally, the present invention seeks to provide an improved engine assembly comprising an electric supercharger.

Alternatively, or additionally, the present invention seeks to provide an improved method of allocating the area of a support structure of a supercharger.

Summary of the Invention

According to a first aspect of the invention there is provided an electric supercharger comprising an electric motor and a radial flow compressor assembly, the radial flow compressor assembly comprising:

a compressor wheel rotatable, about a rotation axis, on a drive shaft arranged to be driven by the electric motor; an inlet passage for passing air to the compressor wheel;

an outlet housing comprising a volute that curves about the rotation axis and, at least partially, defines a volute passage arranged to receive air compressed by the compressor wheel and to pass the compressed air to an outlet;

the outlet housing further comprising a support structure that extends radially outwardly from the volute to a periphery, the periphery having a substantially constant radius ;

wherein the centre of curvature of the periphery is offset from the rotation axis of the compressor wheel such that the distance between a radially outer periphery of the volute and the periphery of the support structure varies with circumferential position around the support structure.

The offset of the centre of curvature of the periphery of the support structure from the rotation axis of the compressor wheel may increase the flexibility in the design of the supercharger and allow for the overall size of the supercharger to be reduced.

In this regard, it may allow for the footprints of components of the supercharger to be better matched to the footprints of regions of the support structure that they are mounted on.

Furthermore, it may increase the amount by which components can be mounted within the footprint of the support structure, i.e. to reduce, or eliminate, the distance they protrude radially beyond the periphery of the support structure.

The offset can be selected, in dependence on the sizes and configurations of the components, so that the components can be mounted on the support structure in a relatively space efficient way.

By way of example, the present invention may enable relatively large components to be located within relatively large areas of the support structure (i.e. where distance between a radially outer periphery of the volute and the periphery of the support structure is largest) . Equally, relatively small components may be located within relatively small areas of the support structure (i.e. where distance between a radially outer periphery of the volute and the periphery of the support structure is smallest) .

In addition, certain components of an electric supercharger, such as an electric motor and a cooling system, may typically be mounted coaxially with the rotation axis of the compressor wheel. The offset may be selected to alter the space available between these components and the periphery of the support structure, to allow other components to be mounted in this space in a space efficient way .

The periphery of the support structure may extend only partly around its centre of rotation, but preferably extends entirely around its centre of rotation.

The periphery of the support structure may extend only partly around the rotation axis, but preferably extends entirely around the rotation axis.

Optionally the periphery of the support structure is substantially circular. It will be appreciated that, in this case, the periphery of the support structure forms a substantially circular circumference. This may allow for a circular seal to seal a surface of the support structure against a facing adjacent surface of the supercharger.

A circular seal may provide a relatively strong and durable seal. Accordingly, the substantially circular periphery of the support structure may allow the radial flow compressor assembly to be relatively well sealed.

The support structure may extend along at least part of the circumferential length of the radially outer periphery of the volute. The support structure may extend along substantially the entire circumferential length of the radially outer periphery of the volute.

Optionally the volute comprises a wall that, at least partially, defines the volute passage, wherein the support structure extends radially outwardly from the wall. In embodiments of the invention the volute defines the entire volute passage. In embodiments of the invention the rotation axis of the compressor wheel is located within the periphery of the support structure.

Optionally a substantially circular seal is arranged to provide a seal between a surface of the support structure and a facing surface of the supercharger to prevent compressed air passing out of the volute passage.

Optionally the circular seal is arranged to be retained in position by a circular retaining formation. The circular retaining formation may be provided on at least one of the support structure and the facing surface of the supercharger .

It will be appreciated that the retaining formation extends around the centre of curvature of the radially outer periphery of the support structure with a substantially constant radius.

The retaining formation may, for example, be a groove, channel or protrusion in or on said surface of the support structure and/or said facing surface of the supercharger.

Optionally the outlet housing comprises a front part and a rear part, the front part comprising the volute and the support structure and the rear part comprising a cover that, together with the volute, defines the volute passage.

Optionally the front and rear parts are formed separately to each other and are fixed to each other. The front and rear parts may be fixed to each other by one or more fasteners, for example.

Optionally the seal is arranged to provide a seal between a surface of the support structure and a surface of the rear part. In embodiments of the invention the seal is in contact with said surfaces.

Optionally the rear part further comprises a mounting structure that extends radially outwardly from the cover to a periphery and is mounted on the support structure, wherein the periphery of the mounting structure is substantially concentric with the centre of curvature of the periphery of the support structure. Optionally the mounting structure follows the periphery of the support structure.

Optionally one of the front and rear parts is received by the other and the seal is provided between opposed surfaces of the front and rear parts.

Optionally the supercharger comprises an annular diffuser that fluidly connects the compressor wheel to the volute. Optionally the diffuser is substantially concentric with the rotation axis. Optionally the diffuser is located radially between the compressor wheel and the volute.

Optionally the supercharger comprises a control module for controlling the electric motor. The volute may be located on a front side of the support structure and the control module may be located on a rear side of the support structure .

Optionally the control module is located axially inboard of a rear end of the supercharger.

This may allow for a reduction in the diameter of the supercharger between the support structure and the rear end of the supercharger.

Optionally the diameter of the supercharger decreases between the support structure and the rear end of the supercharger. Optionally the rear end of the supercharger has a diameter that is less than that of the support structure .

Optionally the control module is located axially between the compressor wheel and the electric motor.

Optionally the control module is supported by the support structure. Optionally the control module is mounted on the support structure, preferably on a rear side of the support structure.

In embodiments of the invention the support structure is arranged to support at least one component of the supercharger. The at least one component may be mounted directly or indirectly (i.e. with an intermediary member between the at least one component and the support structure) on the support structure. Optionally at least one component of the supercharger is mounted on the support structure, preferably on a rear side of the support structure .

Optionally at least one component of the supercharger is mounted on the support structure, radially outwardly of the electric motor. Optionally the electric motor rotates about a rotation axis that is co-axial with the rotation axis of the compressor wheel.

Optionally the electric motor is housed in a housing that has a longitudinal axis that is substantially co-axial with the rotation axis of the compressor wheel and the at least one component is mounted on the support structure, radially outwardly of the housing. Optionally the housing is cylindrical. Optionally the housing has a diameter that is less than that of the support structure. Optionally the housing also contains a cooling conduit arranged to cool the electric motor.

Optionally the at least one component is mounted on the same axial side of the support structure as the motor. Optionally the motor and the at least one component are mounted on a rear side of the support structure.

Optionally at least one component of the supercharger is mounted radially between the electric motor and the periphery of the support structure. The at least one component may be at least one electrical component of the control module. The electrical component may be a capacitor, connector, resistor, EMC filter or direct bonded copper module, for example.

The at least one component may be an electrical connector, for connecting the electric motor to an electric power supply.

Optionally the control module comprises a printed circuit board that is supported by the support structure and curves around the rotation axis. Optionally the circuit board is annular. Optionally the circuit board has a radially inner periphery that is curved with a centre of curvature on the rotational axis. Optionally the circuit board has a radially outer periphery that, at least part way along its length, follows the radially outer periphery of the support structure.

Optionally the printed circuit board is located axially inboard of a rear end of the supercharger. Optionally the printed circuit board is located axially between the compressor wheel and the electric motor.

The at least one component may be at least one component of a cooling system arranged to cool the electric motor .

Optionally the electric supercharger comprises a cooling system arranged to cool the electric motor, wherein the cooling system comprises an annular cooling conduit that curves around the rotation axis. Optionally the cooling conduit is supported by the support structure.

Optionally the radially outer periphery of the cooling conduit is substantially contained within the periphery of the support structure. Optionally the footprint of the cooling conduit is substantially contained within the combined footprint of the support structure, volute and diffuser.

Optionally at least one component of the supercharger is mounted on the support structure, radially outwardly of the cooling conduit. Optionally the at least one component is mounted on the same axial side of the support structure as the cooling conduit. Optionally the cooling conduit and the at least one conduit is mounted on the rear side of the support structure.

Optionally at least one component of the supercharger is mounted radially outwardly of the conduit. Optionally at least one component of the supercharger is mounted radially between the conduit and the periphery of the support structure.

Optionally at least 60% of the footprint of the at least one component is contained within the footprint of the support structure. Optionally at least 80% of the footprint of the at least one component is contained within the footprint of the support structure. Optionally substantially the entire footprint of the at least one component is contained within the footprint of the support structure .

Optionally at least 60% of the footprint of the at least one component is contained within the combined footprint of the support structure and the volute. Optionally at least 80% of the footprint of the at least one component is contained within the combined footprint of the support structure and the volute. Optionally substantially the entire footprint of the at least one component is contained within the combined footprint of the support structure and the volute. Optionally the at least one component is a plurality of said components.

Optionally the components are arranged to match their footprints to the footprints of regions of the support structure that they are mounted on.

In this regard, optionally components with larger footprints are mounted on regions of the support structure that have larger footprints and components with smaller footprints are mounted on regions of the support structure that have smaller footprints.

Optionally the components are oriented and positioned, relative to the support structure and to each other, to provide the footprint matching.

According to a second aspect of the invention there is provided an engine assembly comprising an engine and an electric supercharger according to the first aspect of the invention, arranged to supply compressed air to the engine.

The engine is preferably an internal combustion engine. 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 preferably for an automobile. The automobile may be less than 3.5 tonnes, and more preferably less than 2 tonnes .

According to a third aspect of the invention there is provided a vehicle comprising an engine assembly according to the second aspect of the invention.

According to a fourth aspect of the invention there is provided a radial flow compressor assembly for an electric supercharger, the radial flow compressor assembly comprising :

an inlet passage for passing air to a compressor wheel, the inlet passage having a longitudinal axis; an outlet housing comprising a volute that curves about the longitudinal axis of the inlet passage and, at least partially, defines a volute passage arranged to receive air compressed by a compressor wheel and to pass the compressed air to an outlet;

the outlet housing further comprising a support structure that extends radially outwardly from the volute to a periphery, the periphery having a substantially constant radius ;

wherein the centre of curvature of the periphery is offset from the longitudinal axis of the inlet passage such that the distance between a radially outer periphery of the volute and the periphery of the support structure varies with circumferential position around the support structure.

Optionally the radial flow compressor assembly comprises a compressor wheel rotatable, about a rotation axis, wherein the longitudinal axis of the inlet passage is substantially co-axial with the rotation axis of the compressor wheel.

According to a fifth aspect of the invention there is provided a method of allocating the area of a support structure of an electric supercharger comprising providing an electric supercharger comprising: an electric motor and a radial flow compressor assembly, the radial flow compressor assembly comprising: a compressor wheel rotatable, about a rotation axis, on a drive shaft arranged to be driven by the electric motor; an inlet passage for passing air to the compressor wheel ;

an outlet housing comprising a volute that curves about the rotation axis and, at least partially, defines a volute passage arranged to receive air compressed by the compressor wheel and to pass the compressed air to an outlet;

the outlet housing further comprising a support structure that extends radially outwardly from the volute to a periphery, the periphery having a substantially constant radius ;

wherein the method comprises offsetting the centre of curvature of the periphery from the rotation axis of the compressor wheel such that the distance between a radially outer periphery of the volute and the periphery of the support structure varies with circumferential position around the support structure.

Optionally the method comprises offsetting the centre of curvature of the periphery of the support structure from the rotation axis of the compressor wheel so as to match the footprints of regions of the support structure to footprints of components to be mounted on the support structure.

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 allocating the area of a support structure may incorporate any of the features described with reference to the electric supercharger and vice versa.

Other preferred and advantageous features of the invention will be apparent from the following description.

Description of the Drawings

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a perspective view of an electric supercharger according to an embodiment of the invention;

Figure 2 is a front view of the electric supercharger shown in Figure 1 ;

Figure 3 is a side view of the electric supercharger shown in Figure 1 ;

Figure 4 is a rear view of the electric supercharger shown in Figure 1, but where the rear housing 40 is shown as transparent for illustrative purposes;

Figure 5 is a cross-sectional view taken along the line

A-A in Figure 3;

Figure 6 is a rear view of a front part of an outlet housing of the electric supercharger;

Figure 7 shows a rear perspective view of the front part of the outlet housing shown in Figure 6;

Figure 8 shows a front view of the front part of the outlet housing shown in Figure 6;

Figure 9 shows a rear view of the electric supercharger, and

Figure 10 shows a schematic view of a vehicle having an engine assembly comprising the supercharger shown in Figures 1 to 9.

Detailed Description

Referring to Figures 1 to 5 there is shown an electric supercharger 1 according to a first embodiment of the invention .

The electric supercharger 1 is for supplying compressed air to an internal combustion engine. The supercharger 1 comprises an electric motor assembly 2 (see Figure 4) and a radial flow compressor assembly 3. The electric motor assembly 2 comprises an electric motor 4 mounted within an electric motor housing 50.

The radial flow compressor assembly 3 comprises a compressor wheel 5 (see Figure 2) rotatable, about a rotation axis X on a drive shaft 6 arranged to be driven by the electric motor 4.

The electric motor 4 is mounted concentrically with the rotation axis X. In this regard, the rotor of the electric motor is arranged to rotate about the rotation axis X. The electric motor housing 50 has the general shape of a hollow cylinder that is co-axial with the rotation axis X, with the electric motor 4 mounted radially inwardly of the housing 50.

The radial flow compressor assembly 3 further comprises an inlet housing 7 that comprises a cylindrical inlet pipe 8, provided at a front end of the supercharger 1. The inlet pipe 8 defines an inlet passage 9 for passing air to the compressor wheel 5. The inlet passage 9 is cylindrical and has a central longitudinal axis Y that is co-axial with the rotation axis X of the compressor wheel 5.

The radial flow compressor assembly 3 further comprises an outlet housing 12. The outlet housing 12 comprises a front part 21 and a rear part 22 (see Figure 3) .

The front and rear parts 21, 22 are formed separately from each other and are attached by a plurality of fasteners 23 received in bores in flanges distributed in the circumferential direction.

The front part 21 comprises a diffuser 15, a volute 13 and a support structure 14. These features are described in more detail below.

The diffuser 15 is annular, extends around the rotation axis X of the compressor wheel 5 and is substantially concentric with the rotation axis X. The diffuser 15 is located radially between the compressor wheel 5 and the volute 13 and fluidly connects the compressor wheel 5 to the volute 13. A rear surface of the diffuser 15, together with an opposed front surface of the rear part 22 of the outlet housing 12, defines a diffuser passage that increases in cross-sectional area with increasing radial distance from the compressor wheel 5, so as to increase the pressure of the air leaving the compressor wheel 5.

The volute 13 is located radially between the diffuser 15 and the support structure 14. The volute 13 has the shape of a scroll. In this regard, the volute 13 comprises an elongate wall 18 that has a generally U-shaped cross-section and extends along a longitudinal direction that spirals about the rotation axis X.

As shown in Figures 6 to 8, which show the front part 21 of the outlet housing 12 on its own, a rear, internal, surface 19 of the wall 18 faces an opposed front surface (not shown) of a cover section of the the rear part 22 of the outlet housing 12 (described in more detail below) . The internal surface of the wall 18 and the opposed surface of the cover section together define a volute passage 17 (best shown in Figure 6) .

The volute passage 17 spirals around the rotation axis X of the compressor wheel 5 and fluidly connects the compressor wheel 5, via the diffuser 15, to an outlet 16 located at an end of the volute passage 17 distal the compressor wheel 5.

The cross-sectional area of the volute passage 17 increases with increasing distance from the compressor wheel 5, towards the outlet 16, so as to increase the pressure of the air leaving the compressor wheel 5.

Referring back to Figure 2, the support structure 14 is an annular wall that extends radially outwardly from the radially outer periphery 24 of the volute wall 18 to a radially outer periphery 25 that extends entirely around the rotation axis X.

The periphery 25 is substantially circular. In this regard, the periphery 25 extends entirely around a centre 26 to form a circumference and has a substantially constant radius (relative to its centre 26) . The support structure 14 forms a circular rim 51 at the periphery 25 (see Figures 6 and 7) .

The support structure 14 has a central axis Z that passes through the centre 26 and is substantially parallel to, but offset from, the rotation axis X.

As shown in Figure 2, the centre 26 (and therefore the central axis Z) of the support structure periphery 25 is offset from the rotation axis X by a distance ^λ Α' . The offset ^λ Α' , and the spiral shape of the volute 13, is such that the distance ^λ Β' (see Figure 2) between the radially outer periphery 24 of the wall 18 of the volute 13 and the periphery 25 of the support structure 14 varies with circumferential position around the support structure 14.

In Figure 1, the distance ^λ Β' is the distance in the radial direction, relative to the centre 26 of the support structure 14. However, it will be appreciated that any suitable measure of distance may be used, as long as it is used consistently at each circumferential position around the support structure 14. For example, the distance ^λ Β' could be the distance in the radial direction, relative to the rotation axis X (instead of the support structure axis Z) .

The offset ^λ Α' is not so great that the rotation axis X is located on the periphery 25 of the support structure 14. In this regard, the rotation axis X is located within the periphery 25 of the support structure 14, i.e. radially inwardly (relative to the centre 26 of the support structure 14) of the periphery 25. The support structure 14 is integrally formed with the volute wall 18. In this regard, the support structure 14 and the wall 18 are formed as a single piece of material.

Referring to Figure 3, the rear part 22 of the outlet housing 12 comprises an annular wall 31 that extends around the central axis Z, has a thickness in the radial direction (relative to the central axis Z) and a length in the axial direction Z.

The annular wall 31 has a substantially circular radially outer periphery 45 that is co-axial with the support structure 14, i.e. it is centred on the central axis Z. A front end of the rear part 22 is received in a rear end of the front part 21. The outer periphery 45 follows the radially inner surface 52 of the rim 51 and forms a close-fit with the surface 52.

The annular wall 31 has a curved radially inner periphery that follows the radially inner periphery of the volute 13. A section of the annular wall 31, that overlies the volute 13, forms a cover section. A front facing radial surface of the cover section, together with a rear facing surface of the volute wall 18, defines the volute passage 17. In this regard, the cover section is the section of the annular wall 31 that has a matching (and aligned) footprint to that of the volute wall 18.

It will be appreciated that a reference to the footprint' of something refers to its planform shape when looking in the axial direction X.

A section of the annular wall 31, that extends radially outwardly from the cover section, to the periphery 45 of the annular wall 31, along substantially the entire periphery of the cover section, forms a mounting structure. In this regard, the mounting structure is the section of the annular wall 31 that has a matching (and aligned) footprint to that of the support structure 14. A front surface of the mounting structure is in contact with a rear surface of the support structure 14.

It will be appreciated that the radial length of the mounting structure (relative to the centre 26 of the support structure) varies with circumferential position around the mounting structure and that this variation matches that of the support structure 14.

An annular seal 100 is mounted in an annular groove 27 (see Figure 7 - in Figure 6 the seal 100 is omitted for illustrative purposes) provided in a radially inner surface 51 of the rim 51 of the front part 21. The seal 100 and annular groove 27 each extend circumferentially around the centre 26 of the periphery 25 of the support structure 14, with a substantially constant radius. Accordingly the seal 100 and groove 27 are circular and are concentric with the centre 26 of the periphery 25. The seal 100 seals against the opposed radially outer surface 45 of the annular wall 31 of the rear part 22.

The circular seal 100 may provide a relatively strong and durable seal. Accordingly, the substantially circular periphery 25 of the support structure 14 may allow the radial flow compressor assembly 3 to be relatively well sealed.

The annular groove 27 provides a retaining formation for retaining the seal 100 in place. It will be appreciated that any other suitable type of retaining formation may be used, for example, a channel or protrusion. The retaining formation may be in or on the radially inner surface 51 of the rim 51 of the front part 21 and/or the opposed surface 45 of the annular wall 31.

Referring to Figures 3 to 5 and 9, the supercharger 1 further comprises an annular rear housing 40, provided on a rear side of the rear part 22 of the outlet housing 12. The rear housing 40 comprises a connecting section 41, that attaches the rear housing 40 to the rear part 22 of the outlet housing 12 and a cylindrical section 42 that extends from the connecting section 41 to a rear end 43 of the housing 40. The cylindrical section 42 houses the electric motor 4 and its housing 50.

The cylindrical section 42 has a generally cylindrical shape and is co-axial with the rotation axis X, i.e. it has a central longitudinal axis that is co-axial with the rotation axis X. The diameter of the cylindrical section 42 is less than that of the support structure 14. As discussed in more detail below, electrical components of the supercharger 1 are mounted on the rear side of the support structure 14, radially outwardly of the cylindrical section 42.

The connecting section 41 is attached to the rear part 22 of the outlet housing 12 by a plurality of fasteners 44 circumferentially distributed around the periphery of the rear part 22 and the rear housing 40.

Referring to Figures 4 and 5, the supercharger 1 comprises a control module 60 that is arranged to control the electric motor 4. The control module 60 is located on the rear side of the support structure 14, axially inboard of the rear end 43 of the rear housing 40. The control module 60 is located axially between the compressor wheel 5 and the electric motor 4.

The connecting section 41 is provided within an internal annular mounting surface 75. The mounting surface 75 extends radially from a radially inner periphery that is circular and concentric with the rotation axis X, to a radially outer periphery that is circular and concentric with the centre 26 of the support structure 14. The radially outer periphery of the connecting section 41 follows the outer periphery of the support structure 14. The footprint of the mounting surface 75 is contained within the combined footprint of the support structure 14 and the volute 13.

The control module 60 comprises an annular printed circuit board 61 mounted on the mounting surface 75. The circuit board 61 is located in the connecting section 41 of the rear housing 40. In this regard, the circuit board 61 is located axially between the compressor wheel 5 and the electric motor 4.

The circuit board 61 curves around the rotation axis X. It has a radially inner periphery 71 that is circular and concentric with the rotation axis X and a radially outer periphery 72 that, part way along its length, follows the radially outer periphery of the support structure 14.

In the described embodiment the electric motor 4 is a permanent magnet motor. It will be appreciated that any suitable type of motor may be used, including a switched reluctance motor (SRM) .

The control module comprises control electronics for controlling the motor 4. The control module 60 comprises a plurality of electrical components that are mounted on, and electrically connected to, the circuit board 61. In the currently described embodiment, the electrical components comprise a pair of capacitors 62, a connector 63 and a direct bonded copper module (shown schematically in Figure 5 as dashed rectangle 64) .

The printed circuit board 61 is electrically connected to an electrical power supply by a power cable 66 that is mounted on the circuit board 61.

The electrical components 62-64 and the power cable 66 are mounted on the rear side of the support structure 14, radially outwardly of the cylindrical section 42.

The capacitors 62 and connector 63 are mounted on the circuit board 61 such that 80% of their footprints are contained within the combined footprint of the support structure 14 and the diffuser 13.

The direct bonded copper module 64 is mounted on a rectangular flange 67 that protrudes radially outwardly of the periphery 25 of the support structure 14, such that 60% of the footprint of the direct bonded copper module 64 is contained within the footprint of the support structure 14.

Similarly, the power cable 66 is mounted on a flange 68 that protrudes radially outwardly of the periphery 25 of the support structure 14, such that 75% of the footprint of the power cable 66 is contained within the footprint of the support structure 14.

The electrical components 62-64 and power cable 66 are supported by the support structure 14 by being mounted on the support structure 14. In this regard, the components 62-64 and power cable 66 are indirectly mounted on the support structure 14 by being mounted on the circuit board 61, which is mounted on the mounting surface 75, which is mounted on the support structure 14. The electrical components 62-64 and power cable 66 are arranged, by being oriented and positioned relative to the support structure 14 and to each other, to match their footprints to the footprints of regions of the support structure 14 that they are mounted on.

In this regard, components 62-64, 66 with larger footprints are mounted on regions of the support structure 14 that have larger footprints and components with smaller footprints are mounted on regions of the support structure 14 that have smaller footprints.

Components 62-64, 66 that have a larger radial length are mounted on regions of the support structure 14 that have a larger radial length and components that have a smaller radial length are mounted on regions of the support structure 14 that have a smaller radial length ( Radial' relative to the central axis Z ) .

It will be appreciated that the comparison of footprints and radial length of regions of the support structure 14 is in relation to regions that subtend angles, about the central axis Z, of the same magnitude.

By offsetting the central axis Z of the support structure 14 from the rotation axis X of the compressor wheel 5 and motor, the support structure 14 exposes a relatively large area on one side of the volute 13 and a relatively small area on the opposite side of the volute 13. The present invention recognises that doing this can be advantageous because the components 62-64, 66 can then be located according to the area of support structure available. This minimises lasted area' of the support structure and thereby makes the supercharger more space-efficient.

The feature that the control module 60, and specifically the circuit board, is located axially inboard of the rear end 43 of the supercharger 1 (and more particularly that it is located towards the front of the supercharger between the motor and the compressor wheel), tends to enable the supercharger 1 to be more efficiently packed in the engine bay. This is because the widest (largest diameter) part of the control module is located towards the front of the supercharger, enabling the rear of the supercharger to ^x taper' . For example, as shown in Figure 3, the rear end 43 of the cylindrical section 42 has a diameter that is less than that of the support structure 14. This Capered' shape tends to be relatively easily and efficiently located in an engine bay.

Referring to Figures 4 and 9, the supercharger 1 further comprises a cooling system 77 that comprises a conduit 76 fluidly connected within a cooling circuit (shown schematically as the dashed square ^λ 78') . The cooling circuit is arranged to circulate a working fluid around the conduit 76 so as to remove heat from the electric motor 4. In the currently described embodiment the working fluid is water. However, it will be appreciated that any suitable working fluid may be used.

The conduit 76 is curved around the rotation axis X. The conduit 76 is disposed radially outwardly of, and proximal to, the electric motor 4. The radially inner and outer periphery of the conduit 76 is circular and concentric with the rotation axis X. The radially outer periphery of the cooling conduit 76 is substantially contained within the periphery 25 of the support structure 14. The footprint of the conduit 76 is contained within the combined footprint of the support structure 14 and the volute 13.

Referring to Figure 10, there is schematically shown a vehicle 92 comprising an engine assembly 91 that forms the power-plant of the vehicle 92. The engine assembly 91 comprises the supercharger 1 and an internal combustion engine 90 that drives the vehicle. The supercharger 1 is arranged to supply compressed air, from its outlet 16, to an air intake 93 of the engine 90, so as to boost the power from the engine 90.

The offset of the centre 26 of the periphery 25 of the support structure 14 from the rotation axis X may increase the flexibility in the design of the supercharger 1 and allow for the overall size of the supercharger 1 to be reduced.

In this regard, it may allow for the footprints of components of the supercharger 1 to be better matched to the footprints of regions of the support structure 14 that they are mounted on.

Furthermore, it may increase the amount by which the components can be mounted within the footprint of the support structure 14, i.e. to reduce, or eliminate, the distance they protrude radially beyond the periphery 25 of the support structure 14.

The offset can be selected, in dependence on the sizes and configurations of the components 61-64, 66, 77, so that the components can be mounted on the support structure 14 in a relatively space efficient way.

In addition, the offset may be selected to alter the space available between the electric motor 4, and/or the cooling system 77, and the periphery 25 of the support structure 14, to allow the components 61-64, 66, 77 to be mounted in this space in a space efficient way.

According to a further embodiment of the invention, a method of allocating the area of a support structure of an electric supercharger comprises providing the supercharger of the above described embodiment, offsetting the centre of curvature 26 of the periphery 25 of the support structure 14 from the rotation axis X of the compressor wheel 5 such that the distance between the radially outer periphery 24 of the volute 13 and the periphery 25 of the support structure 14 varies with circumferential position around the support structure 14.

The method comprises offsetting the centre 26 of the periphery 25 of the support structure 14 from the rotation axis X so as to match the footprints of regions of the support structure 14 to footprints of the components 61-64, 66, 77 to be mounted on the support structure.

It will be appreciated that features described in relation to one embodiment of the present invention may be incorporated into other embodiments of the present invention. For example, the method of allocating the area of a support structure of an electric supercharger may incorporate any of the features described with reference to the electric supercharger 1 and vice versa. 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 currently described embodiments the periphery 25 of the support structure 14 extends entirely around its centre 26. Alternatively, the periphery 25 may extend only partly entirely around its centre 26. In this case, the periphery 25 may form an arc of a circle. Similarly, the periphery 25 may extend only partly around the rotation axis X.

In the currently described embodiments the support structure 14 extends along substantially the entire

circumferential length of the radially outer periphery of the volute 13. Alternatively, the support structure 14 may only extend along part of the circumferential length of the

radially outer periphery of the volute 13.

In the currently described embodiments the components are mounted indirectly on the support structure 14. Alternatively, the components may be mounted directly on the support

structure 14.

In the currently described embodiments, the support structure 14 is integrally formed with the volute wall 18. Alternatively, the support structure may be formed separately to the volute wall 18 and attached to the volute wall, by any suitable means (e.g. by welding or by discrete fasteners) .

In the currently described embodiments the front and rear parts 21, 22 of the outlet housing 12 are formed separately from each other and are attached by a plurality of fasteners. Alternatively, the front and rear parts 21, 22 may be

integrally formed with each other. In this regard, the front and rear parts 21, 22 may be formed as a single piece, i.e. to form a one-piece volute.

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.