GB2516060A

GB2516060A - An electric supercharger having a protected bearing assembly

Info

Publication number: GB2516060A
Application number: GB1312334.4A
Authority: GB
Inventors: Stephen Michael Knight
Original assignee: Valeo Air Management UK Ltd
Current assignee: Valeo Air Management UK Ltd
Priority date: 2013-07-09
Filing date: 2013-07-09
Publication date: 2015-01-14
Anticipated expiration: 2033-07-09
Also published as: GB201312334D0; GB2516060B

Abstract

An apparatus (3, fig.1) for supplying an IC engine (1, fig.1) with a compressed air charge, comprising a turbocharger (5, fig.1) and an electric supercharger (9, fig.1) downstream of the turbocharger. The supercharger 9 comprises, a compressor element 14, a drive shaft 13, an electric drive assembly (10, fig.2) for driving the compressor element 14, and a seal 29a and 29b around the drive shaft 13. A bearing assembly 16 is located downstream of the seal and the apparatus comprises a venting conduit (31, fig.2) arranged to convey leakage flow which leaks through the seal away from the bearing assembly 16 of the supercharger 9 to a region which, when in use, is at a lower pressure than the inlet such that the leakage flow is drawn along the venting conduit by the pressure gradient between the inlet and outlet of the venting conduit.

Description

An electric supercharger having a protected bearing asserrdñy

Technical Field

The present invention relates to electric superchargers, and more specifically to an apparatus comprising an electric supercharger downstream of a turbocharger, and to an electric supercharger suitable for use in such an apparatus.

Background of the Invention

As a result of the desire to reduce carbon dioxide emissions from internal combustion (IC) engines, there is a tendency towards smaller (i.e. reduced capacity) engines. In order to maintain acceptable levels of power output, it has been suggested that a turbocharger be fitted to these smaller engines. r.Jhilst the turbocharger may increase the maximum power output of the engine, it has been found to cause unacceptable levels of turbo-lag, often making the engine impractical in automotive applications. Installing a supercharger upstream, or downstream of the turbocharger (i.e. between the turbocharger and the engine), has been suggested as a way of reducing this problem of excessive turbo lag.

Electric superchargers are attractive for use with low-emission IC engines because they tend to generate less carbon dioxide and a lower fuel consumption compared to conventional (direct engine-driven) superchargers.

The drive assembly in some known superchargers is vented (for example using a breather hole) to ensure the pressure in the drive assembly matches that of the compressor outlet gas; this is necessary to avoid the compressor outlet gas forcing lubricant out of the bearing assembly. Electric superchargers having such a breather hole have not been considered for use downstream of a turbocharger because the drive assembly would be exposed to the corrosive effect of the oil-air mix and particulates that are typically output from the turbocharger, and the exhaust gas recirculation (EGR) gas that can also be present. There has therefore been a tendency to consider only conventional (direct engine-driven) superchargers for this application, or to use electric superchargers upstream of the turbocharger.

Providing a seal to protect the drive assembly from the compressed charge has been suggested as a way of enabling an electric supercharger tc be used downstream of the turbocharger. However, forming a seal that excludes all of the contaminants in the compressed charge (e.g. the oil-air mix, particulates and/or exhaust gas recirculation (EGR) gases) has been found to be difficult. This is especially the case in electric superchargers which can operate at much higher speeds than engine-driven superchargers because the speed at which the electric supercharger can operate is independent of the speed of the engine speed.

In a number of seal designs, a small amount of these contaminants has been found to leak through. For example, a seal in the form of a piston ring is attractive because it is simple and relatively inexpensive; however, piston rings have been found to give rise to moderate amounts of leakage under the extreme environment in a supercharger. Leakage gases passing through the seal have been found to be particularly damaging to the bearing assembly (which tends to be located downstream (i.e. behind) the seal) . Furthermore, even if the rate of leakage is small, it can guiokiy accumulate in the relatively small volume inside the supercharger (e.g. the chamber in which the drive assembly is located), and the concentration of contaminants etc. can reach damaging levels for the drive assembly.

It is desirable to provide an electric supercharger for use downstream of a turbocharger that mitigates at least some of the above-mentioned drawbacks.

Summary of the Invention

J&ccording to a first aspeot 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, the electric supercharger being downstream of the turbocharger to receive the output of the turbocharger, and wherein the electric supercharger comprises; a compressor element for oompressing the output of the turbocharger into the compressed air charge; a drive shaft; an electric drive assembly for driving the compressor element via the drive shaft; a seal around the drive shaft, the seal being arranged to at least partially seal the drive assembly from the compressed oharge; and a bearing assembly through which the drive shaft extends, the bearing assembly being located downstream of the seal and charaoterised in that the apparatus comprises a venting conduit, the venting conduit being arranged to convey leakage flow which leaks through the seal away from the bearing assembly of the supercharger.

By providing a venting conduit, the leakage flow may be conveyed away from the bearing assembly thereby reducing the potential damage to the bearing assembly caused by the leakage flow. This also enables such an electric supercharger to be used downstream of a turbocharger.

The venting conduit preferably provides a lower resistance path for the leakage flow than the path for leakage flow into the bearing assembly. This minimises the amount of leakage flow that will force itself into the bearing assembly.

The venting conduit preferably defines a fluid pathway along which the leakage flow may travel.

The supercharger may comprise a casing wall separating the compressor element from the drive assembly. The drive shaft may extend through an opening in the casing wall. The seal may be arranged to seal said opening. At least part of the venting conduit may be within the casing wall. At least part of the venting conduit may be defined by the casing wall. For example, at least part of the conduit may be in the form of a bore in the casing wall.

The supercharger may comprise a first length of the venting conduit, but need not necessarily comprise the whole length of the venting conduit. Other parts of the apparatus may comprise a second length of the venting conduit. The second length of the venting conduit may be coupled to said first length. For example, the supercharger may comprise a connector for connecting the first length of the conduit to the second length of the conduit.

The inlet of the venting conduit is preferably downstream of the seal. The inlet may be adjacent to the seal, but downstream thereof. The inlet of the venting conduit is preferably upstream of the bearing assembly. The inlet of the venting conduit is preferably between the seal and the bearing assembly.

The venting conduit is for conveying leakage flow away from the bearing assembly. In principle, the outlet of the venting conduit may vent into a chamber surrounding the drive assembly, but more preferably the venting conduit conveys the leakage flow to a location remote from the supercharger. Such an arrangement avoids exposure of sensitive parts of the supercharger (e.g. bearing assembly or drive assembly) to the leakage flow. The venting conduit is preferably arranged to convey the leakage flow to a location remote from the supercharger; the outlet of the venting conduit may be remote from the supercharger.

The outlet may be in fluid communication with a region which, during use of the apparatus, is at lower pressure than the inlet, such that the leakage flow is drawn through the venting oonduit by the pressure gradient between inlet and outlet. Such an arrangement is especially beneficial as it provides a simple way of ensuring the leakage flow is conveyed away from the seal.

The outlet of the venting conduit may be arranged such that the leakage flow discharges back into the apparatus, and preferably such that the leakage flow is re-circulated back into the apparatus. Such an arrangement is especially beneficial because it can avoid exhausting the contaminants etc in the leakage flow, into the atmosphere. Re-circulating the leakage flow has been found to have negligible impact on the composition flowing around the apparatus because the volume of leakage flow tends to be negligible compared to the flow circulating in the apparatus for supplying the compressed charge.

The turbocharger may comprise an air-intake for drawing in air to be compressed. The outlet of the venting conduit may be connected to said air-intake. The pressure at the air-intake of the turbocharger has been found to be relatively steady during use. Connecting the outlet of the venting conduit to this location is thus beneficial as it may provide a relatively steady pressure gradient in order to draw the leakage flow through the venting conduit.

The supercharger, and more preferably the casing wall, may comprise a bearing sleeve arranged to receive the bearing assembly. The opening (through which the drive shaft extends) may be formed in the bearing sleeve. The bearing assembly may be axially constrained by the bearing sleeve. For example the bearing assembly may abut an upper face of the bearing sleeve.

The bearing assembly may be radially constrained by the bearing sleeve. For example the bearing assembly may abut a circumferential face of the bearing sleeve. The bearing assembly may be both axially and radially constrained by the bearing sleeve. Such an arrangement ensures that axial and/or radial loads on the bearing assembly are reacted into the bearing sleeve. The bearing assembly may be held by the bearing sleeve.

Tn some embodiments of the invention the bearing sleeve is a separate component in the casing wall. In other embodiments of the invention, the bearing sleeve may be integral with the casing wall.

The present invention is especially useful in arrangements in which the seal does not necessarily fully seal the drive assembly from the compressed charge, because it is in such arrangements that potentially damaging leakage flow exists.

The seal is around the drive shaft. The seal may form a circumferential seal around the drive shaft. The seal may be a dynamic seal. The seal may comprise, or consist of, a piston ring. Such an arrangement is simple and relatively inexpensive but had previously been dismissed as being unsuitable because it tends to give rise to some leakage flow.

However, it has been recognised that by providing the venting conduit of the present invention, such a sealing arrangement may be used despite the leakage flow.

The seal is preferably arranged to allow a leakage flow of less than 50g/min, and more preferably less than 40g/min (at degrees C and 4 bar pressure) . The seal may be arranged to allow a leakage flow of more than 0.8g/min (at 180 degrees o and 4 bar pressure) The seal may be directional. The seal may be arranged to inhibit ingress of the compressed air charge into the drive assembly, but not necessarily to prevent fluid travelling cut of the drive assembly.

The supercharger may comprise a second seal around the drive shaft. The second seal may be arranged to substantially seal the drive assembly from the leakage flow; thus the seoond seal is preferably downstream of the first seal. The second seal is preferably downstream of the venting conduit. By arranging the second seal downstream of the venting conduit, the second seal tends not to be subjected to high pressures because the venting conduit provides a discharge route for the leakage flow, upstream of the second seal. The second seal can therefore be relatively simple. The second seal may form a circumferential seal around the drive shaft. The second seal may be a dynamic seal. The second seal may comprise, or consist of, a piston ring. The second seal is preferably upstream of the bearing assembly.

The output of the turbocharger may itself be relatively corrosive (for example it may comprise an oil-air mix and/or particulates) . In some embodiments of the invention, the output of the turbocharger may be mixed with EGR gases prior to being received by the supercharger. The compressor element of the supercharger in such embodiments is therefore arranged to compress the output of the turbocharger and the EGR gases into the compressed air charge for the engine.

The compressor element of the supercharger is suitable for compressing the output of the turbocharger into the compressed air charge. A compressor element is typically arranged such that, when driven, it draws in intake air, compresses the intake air and outputs a compressed charge. The compressor element is preferably rotatable. The compressor element may be a compressor wheel. It will be appreciated that the compressor element need not necessarily be a single piece and may comprise a plurality of sub-elements.

The electric drive assembly may comprise an electric motor for rotating the drive shaft. The electric drive assembly may comprise a control unit for controlling the motor.

The electric supercharger is preferably arranged to operate at high speeds. For example, the supercharger may be arranged such that the drive shaft is rotatable at more than 40,000rpm, more preferably more than 50,000 rpm, and yet more preferably more than 60,000rpm. The speed at the interface between the seal member of the seal and the drive shaft may be more than 2cm/s and more preferably more than 30m/s. Rubber lip-seals found on conventional engine-driven superchargers are typically designed to keep oil within the supercharger and tend to only work at muoh lower speeds (around 5-lO,000prm) ccording to a second aspect of the invention there is provided an electric supercharger comprising: a compressor element for generating a compressed air charge; a drive shaft; an electric drive assembly for driving the compressor element via the drive shaft; a seal around the drive shaft, the seal being arranged to at least partially seal the drive assembly from the compressed charge; and a bearing assembly through which the drive shaft extends, the bearing assembly being located downstream of the seal and characterised in that the supercharger comprises at least part of a venting conduit, the venting conduit being arranged to convey leakage flow which leaks through the seal away from the bearing assembly. The seal may be a first seal and the supercharger may further comprises a second seal. The second seal may be around the drive shaft and be located downstream of the first seal, but upstream of the bearing assembly. The inlet of the venting conduit may be between the first and second seals.

J&ccording to yet another aspect of the invention there is provided an internal combustion engine in combination with the apparatus described herein. The engine is preferably for use in an automobile. The engine is preferably a relatively small capacity engines. The engine is preferably 4 litres or less, more preferably 3 litres or less, and yet more preferably 2 litres or less) . The engine may in an automobile. The automobile may be less than 5 tonnes, more preferably less than 3.5 tonnes, and more preferably less than 2 tonnes.

It will be appreciated that any features described with reference to one aspect of the invention are equally applicable to any other aspect of the invention, and vice versa. For example any features described with reference to the first aspect of the invention are equally applicable to the second aspect of the invention.

Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings of which: Figure 1 is a schematic showing an engine incorporating an apparatus according to a first embodiment of the invention; Figures 2 and 3 are sectional views of the supercharger in the first embodiment of the invention; -10 -Figure 4 is a sectional view of part of a supercharger in a second embodiment of the invention; Figure 5 is a perspective view of the bearing sleeve in the second embodiment of the invention.

Detailed Description

Figure 1 shows a three-cylinder internal combustion (IC) engine 1 in combination with an apparatus 3 for supplying compressed intake gases (i.e. a compressed air charge) in accordance with a first embodiment of the invention. The apparatus 3 (marked by a dotted line) comprises a turbocharger 5, an exhaust gas recirculation (EGR) valve 6, a charge air cooler (CAC) 7, a supercharger 9 and a supercharger bypass valve 10.

In accordance with conventional turbochargers, the turbocharger 5 is driven by the exhaust gases from the engine 1 passing through the Variable-Nozzle Turbine (VNT) 5a thereby driving the turbocharger compressor Sb which draws in, and compresses, feed air supplied via an air intake 8. Some of the exhaust gas output of the engine 1 is returned as an input to the engine via the EGR valve 6.

The output of the turbocharger 5 is then fed through the CAC 7 before being supplied to the supercharger 9 (in another embodiment (not shown) the CAC is downstream of the supercharger 9) . The supercharger 9 further compresses the output of the turbocharger and supplies the compressed intake gases (referred to herein as a compressed air charge) to the engine 1. Having a turbocharger 5 and a supercharger 9 in series (sometimes referred to a twincharger) is well known.

This arrangement can be used to reduce turbo-lag because the supercharger tends to be most effective at low speeds whereas the turbocharger tends to be most effective at higher speeds.

-11 -A twincharger arrangement has been found to be especially beneficial on relatively small capacity engines (e.g. less than 3 litres, and preferably less than 2 litres) where having a turbocharger alone may generate sufficient power, but would tend to cause excessive turbo-lag making the engine unusable in automotive applications. This enables relatively small engines to be used (with associated smaller fuel consumption and emissions) without necessarily sacrificing the engine power. It is desirable to increase the efficiency of such an arrangement yet further.

In the first embodiment of the invention, the supercharger 9 is an electric supercharger. Electric superchargers have been found to reduce the fuel consumption and emissions of an engine in comparison to conventional (direct engine-driven) superchargers. They are therefore attractive in applications in which the fuel consumption and/or the carbon dioxide output of the engine are looking to be improved. However, electric superchargers have previously been dismissed for use downstream of a turbocharger because the electric supercharger would suffer from the corrosive effect of the partioulates and oil-air mix that are typically output from the turbocharger as well as the EGR gas. There has therefore been a tendency to consider only conventional (direct engine-driven) superchargers for this application, or to instead use a twinoharger arrangement having the electric supercharger upstream of the turbocharger.

Providing a seal to seal the drive assembly from the compressed charge has been suggested as a way of enabling an electric supercharger to be used downstream of the turbocharger. However, forming a seal that successfully excludes all of the contaminants in the compressed charge (e.g. the oil-air mix, particulates and/or exhaust gas recirculation (EGR) gases) has been found to be difficult. In -12 -a number of seal designs, a small amount of these contaminants has been found to leak through. Leakage gases passing through the seal have been found to be particularly damaging to the bearing assembly, which tends to be located behind the seal.

Figure 2 is a sectional view part of the electric supercharger 9 in the first embodiment of the invention, and Figure 3 is another sectional view focusing on the region surrounding the front bearing assembly 16. In Figure 2, the supercharger is shown in a vertical orientation for clarity purposes only. Referring to Figures 2 and 3, the electric supercharger 9 includes an electric drive assembly 10. The electric drive assembly is not shown in detail in Figures 2 or 3, and is instead denoted by the hat-shaped box in Figure 2.

The drive assembly 10 has a motor and a control unit in the form of a Printed circuit Board (PCB) located to the rear of the motor) . Power to the electric motor and control unit is supplied by a lead/acid battery (not shown) charged by an alternator (not shown) associated with the engine 1. The drive assembly is arranged to drive the compressor element 14, in the form of a compressor wheel, via the shaft 13. The shaft is supported by a front bearing assembly 16 and a rear bearing assembly (not shown) In common with known superchargers, the supercharger 9 receives air through an inlet 12. The compressor element 14 then compresses the inlet air and expels it into a radial chamber and through an outlet 11. A casing wall 17 is located between the compressor element 14 and the drive assembly, thereby separating the drive assembly 10 from the compressed charge.

The casing wall 17 has an integral bearing sleeve in which the front bearing assembly 16 is received. The drive shaft 13 of the supercharger extends through the bearing assembly 16 and continues through an opening 27 in the casing -13 - 17, above which the shaft 13 connects to the compressor element 14.

The opening 27 in the casing wall 17 through which the drive shaft 13 extends contains two dynamic seals in the form of two, axially-spaced, piston rings 29a, 29b. The first piston ring 29a (i.e. upstream of the second piston ring 29b) is largely effective in sealing the compressed charge from the drive assembly, but has been found to suffer from some leakage. For example, at 180 degrees C and 4 bar absolute pressure the seal has a leakage rate of 0.85 g/min when seated, and a worst-case (i.e. unseated) leakage rate of 30.6 g/min.

At the unseated leakage rates, and even at the leakage rates when the piston ring 29a is seated, the leakage flow through the first seal 29a could damage a bearing assembly 16.

In particular, a bearing assembly 16 has been found to suffer when exposed to the contaminants in the compressed charge (e.g. the oil-air mix, particulates and/or exhaust gas recirculation (EGR) gases) . The provision of the second seal 29b in itself has been found to be ineffective at stopping the leakage flow (it tends to reduce the total leakage flow only by around 25%) . To tackle this problem, the first embodiment of the invention comprises a venting conduit 31 as will be described in more detail below.

The venting conduit 31 comprises a first part 31a and a second part 31b. The supercharger 9 comprises the first part 31a of the venting conduit. This first part 31a is in the form of three drillings into the casing 17 (most clearly shown in Figure 3) . The drillings together form a conduit linking an inlet 37 (that is located adjacent to, but downstream of, the first seal 29a and upstream of the bearing assembly) to a connector 35 on the housing of the supercharger 9. The conduit 31a is formed by drilling into the casing 17 and to -14 -ensure a single route for the ieakage flow, two of the drillings are subsequently closed off with stoppers 32. The first part 31a of the conduit terminates at the connector 35 attached one the side of the supercharger. The connector 35 receives a second part of the conduit 31b (not shown in Figures 2 and 3, but denoted by a line in Figure 1) in the form of a flexible hcse which connects at one end to the connector 35, and at the other end to an outlet 39 discharging into the air intake 8 of the turbocharger (see Figure 1) The venting conduit 31 thus forms a fluid pathway for conveying the leakage flow through the first seal 29a away from the bearing assembly 16. More specifically, by connecting the venting conduit 31 to the air intake 8 of the turbocharger, there will be (during use) a pressure gradient between the inlet 37 and outlet 39 of the conduit that ensures the leakage flow is drawn along the conduit and away from the bearing assembly 16. Any leakage flow that is not drawn away in this manner can, in any case, be prevented from reaching the bearing assembly 16 by the second seal 29b, which need only cope with relatively small pressures due to the pressure relief ensured by the venting conduit.

Having the venting conduit 31 thus enables an electric supercharger 9 to be used downstream of the turbocharger 5, even if the seal is imperfect. Using an electric supercharger may facilitate an engine 1 with not only low turbo-lag but also particularly low fuel consumption and/or low emissions engine.

Figures 4 and 5 show an alternative embodiment of the invention in which the supercharger again comprises a venting conduit for conveying the leakage flow away from the bearing assembly. However, in this second embodiment of the invention, the leakage flow is discharged behind the bearing assembly. Although this can expose some parts of the drive -15 -assembly to the leakage flow, it has been found to avoid contamination of the bearing assembly.

Features in the second embodiment of the invention that correspond to similar features in the first embodiment of the invention, are shown with the same reference numerals as in the first embodiment, but with the addition of the prefix 1' (or 10' where appropriate) . Referring now to Figures 4 and 5, the general layout of the supercharger 109 is similar to that in the first embodiment, namely it comprises a compressor wheel 114 mounted on a shaft 113. The shaft 113 is supported on a bearing assembly 116 with two piston rings 129a, 129b forming seals upstream of bearing assembly 116.

The bearing assembly is held in a bearing sleeve 119.

The bearing sleeve 119 comprises a channel 131 (shown in section in Figure 4 along A-A (Figure 5)) . The channel extends radially outward in opposing directions from the opening 127. When the bearing assembly 116 is received in the bearing sleeve 119, the channel and the bearing assembly together define the boundaries of a venting conduit 131. The venting conduit 131 extends either side of the opening 127 in two sections. Each section has an inlet 137 adjoining the shaft 113 below the two seals 129a,b, and an outlet 139 below the bearing assembly 116.

The bearing sleeve 119 is shown in a perspective view (from below) in Figure 5. In the second embodiment of the invention the bearing sleeve 119 is a separable component forming part of the casing wall 117. Tn other embodiments of the invention (not shown) the bearing sleeve 119 may be integral with the remainder of the casing wall 117. Referring to Figure 5, the bearing sleeve 119 comprises a disc-shaped upper face 121 from which a circumferential axially-extending skirt 123 extends to define a disc-shaped recess in which the bearing assembly (not shown in Figure 5) is received. The -16 -bearing assembly 116 is radially constrained by virtue of it abutting the inner circumference of the skirt, and the bearing assembly 116a is axially constrained by virtue of it abutting the underside of the upper face 121.

During operation of the supercharger, leakage flow leaks through the piston ring seal 129a, and then through the second piston ring seal 129b. Once through the seals 129a,b, this leakage flow adopts a path of least resistance. The leakage flow therefore travels through the venting conduit 131 rather than force its way through the bearing assembly 116. This reduces the exposure of the bearing assembly 116 to the leakage flow and therefore reduces damage caused by contaminants in that flow.

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. 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.

Claims

-17 -Claims 1. An apparatus for supplying an internal combustion engine with a compressed air charge, the apparatus comprising a turbocharger and an electric supercharger, the eleotrio supercharger being downstream of the turbocharger to receive the output of the turbocharger, and wherein the electric supercharger comprises; a compressor element for compressing the output of the turbocharger into the compressed air charge; a drive shaft; an electric drive assembly for driving the compressor element via the drive shaft; a seal around the drive shaft, the seal being arranged to at least partially seal the drive assembly from the compressed charge; and a bearing assembly through which the drive shaft extends, the bearing assembly being located downstream of the seal and characterised in that the apparatus comprises a venting conduit, the venting conduit being arranged to convey leakage flow which leaks through the seal away from the bearing assembly of the supercharger.
2. An apparatus according to claim 1, wherein the venting conduit is arranged to convey the leakage flow to a location remote from the supercharger.
3. An apparatus according to claim 1 or claim 2, wherein the inlet of the venting conduit is downstream of the seal and the outlet of the venting conduit is in fluid communication with a region which, during use of the apparatus, is at lower pressure than the inlet such that the leakage flow is drawn -18 -through the venting conduit by the pressure gradient between inlet and outlet.
4. An apparatus according to any preceding claim, wherein the venting conduit is arranged to convey the leakage flow such that it discharges back into the apparatus, thereby re-circulating the leakage flow around the apparatus.
5. An apparatus according to claim 4, wherein the turbocharger comprises an air-intake for drawing in air to be compressed, and wherein the venting conduit is arranged to discharge into said air-intake.
6. An apparatus according to any preceding claim, wherein the supercharger comprises a casing wall separating the compressor element from the drive assembly, the drive shaft extending through an opening in the casing wall and the seal being arranged to seal said opening.
7. An apparatus according to claim 6, wherein the at least part of the venting conduit is defined by the casing wall.
8. An apparatus according to claim 7, wherein the supercharger comprises a first length of the venting conduit, and the apparatus comprises a second length of the venting conduit coupled to the first length.
9. An apparatus according to claim 8, wherein the supercharger comprises a connector for connecting the first length of the conduit to the second length of the conduit.
10. An apparatus according to claim 8 or claim 9, wherein the second length of the conduit is connected to a region which, -19 -during use of the apparatus, is at lower pressure than the inlet such that the leakage flow is drawn through the venting conduit by the pressure gradient between inlet and outlet.
11. An apparatus according to any preceding claim wherein the seal is a first seal and the supercharger further comprises a second seal, the second seal being around the drive shaft and being located downstream of the first seal, but upstream of the bearing assembly.
12. An apparatus according to claim 11, wherein the inlet of the venting conduit is between the first and second seals.
13. An apparatus according to claim 11 or claim 12, wherein the first and second seals each comprise a piston ring.
14. An apparatus according to any preceding claim wherein the electric drive assembly comprises an electric motor and a control unit for controlling the motor.
15. An electric supercharger comprising: a compressor element for generating a compressed air charge; a drive shaft; an electric drive assembly for driving the compressor element via the drive shaft; a seal around the drive shaft, the seal being arranged to at least partially seal the drive assembly from the compressed charge; and a bearing assembly through which the drive shaft extends, the bearing assembly being located downstream of the seal and characterised in that the supercharger comprises at least part of a venting conduit, the venting conduit being arranged -20 -to convey leakage flow which leaks through the seal away from the bearing assembly.
16. A supercharger according to claim 15, wherein the supercharger comprises a first part of the venting conduit, and a connector for connecting the first part of the venting conduit to a second part of the venting conduit.
17. An internal combustion engine in combination with the apparatus of any of claims 1 to 14.
18. A supercharger as herein described with reference to the drawings.