GB2551982A

GB2551982A - Electric supercharger with a seal

Info

Publication number: GB2551982A
Application number: GB1611473.8A
Authority: GB
Inventors: Lee Don; Hillyard William
Original assignee: Valeo Air Management UK Ltd
Current assignee: Valeo Air Management UK Ltd
Priority date: 2016-06-30
Filing date: 2016-06-30
Publication date: 2018-01-10
Also published as: GB201611473D0; WO2018002267A1

Abstract

An electric supercharger 115 comprises an electric motor 121, a drive shaft 107 and a compressor element (wheel) 103. The electric supercharger further comprises a sealing member 109 for preventing leakage flow around the drive shaft, movable between a closed configuration in which the sealing member forms a seal around the drive shaft and an open configuration in which the sealing member is separated from the drive shaft such that the seal is broken. Preferably a biasing member is arranged to exert force on the seal into its open configuration. There may be a threshold to which when a pressure force acts upon the sealing member exceeds the threshold the seal if forced to a closed configuration. This may be in relation to boost and idle modes of the compressor element. The drive shaft may have a tapered region to facilitate the open and closed configurations (D1, D2, figure 2). A seal assembly and a kit of parts are also claimed.

Description

(54) Title of the Invention: Electric supercharger with a seal Abstract Title: Electric supercharger with a seal (57) An electric supercharger 115 comprises an electric motor 121, a drive shaft 107 and a compressor element (wheel) 103. The electric supercharger further comprises a sealing member 109 for preventing leakage flow around the drive shaft, movable between a closed configuration in which the sealing member forms a seal around the drive shaft and an open configuration in which the sealing member is separated from the drive shaft such that the seal is broken. Preferably a biasing member is arranged to exert force on the seal into its open configuration. There may be a threshold to which when a pressure force acts upon the sealing member exceeds the threshold the seal if forced to a closed configuration. This may be in relation to boost and idle modes of the compressor element. The drive shaft may have a tapered region to facilitate the open and closed configurations (D1, D2, figure 2). Aseal assembly and a kit of parts are also claimed.

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Electric supercharger with a seal

Field of the Invention

The present invention concerns an electric supercharger. More particularly, but not exclusively, this invention concerns an electric supercharger having a seal for preventing leakage flow around the drive shaft.

Background of the Invention

Electric superchargers are known in the art.

Electric superchargers typically provide a compressed air charge to an internal combustion engine by means of a compressor wheel on a drive shaft driven by an electric motor. It is important to protect the bearings and electric components of a supercharger from the contaminants in incoming air flow (i.e. the oil-air mix, particulates and/or exhaust gas recirculation (EGR) gases) .

In a previously suggested arrangement, a ring-seal such as a piston ring, is located around the drive shaft to prevent leakage flow into the bearings and/or motor. However a disadvantage with use of a ring-seal is degradation over time, due to prolonged contact with the moving drive shaft.

The present invention seeks to mitigate the abovementioned problems. Alternatively or additionally, the present invention seeks to provide an improved seal for an electric supercharger.

Summary of the Invention

According to a first aspect of the invention there is provided an electric supercharger comprising an electric motor, a drive shaft and a compressor element, the motor being arranged to effect rotation of the compressor element via the drive shaft, wherein the electric supercharger further comprises a sealing member for preventing leakage flow around the drive shaft, the sealing member being movable between a closed configuration in which the sealing member forms a seal around the drive shaft and an open configuration in which the sealing member is separated from the drive shaft such that the seal is broken.

Providing a sealing member which can move between an open and a closed configuration, enables the sealing member to be moved away from the drive shaft when the seal is not required and/or when excessive levels of wear may be experienced. The sealing member tends to therefore be subjected to relatively little wear (compared to an arrangement in which it is constantly in contact with the shaft). This may enable the working life of the sealing member to be prolonged.

A biasing member may be arranged to exert a force to bias the sealing member into its position in the open configuration. The biasing member may comprise a spring. The biasing member may be coupled to the sealing member.

The biasing member may be arranged such that when a force acting upon the sealing member exceeds a first threshold, the biasing force is overcome thereby moving the seal to the closed configuration. The force may be a pressure force resulting from the local air pressure acting on the sealing member. Such an arrangement is beneficial because it tends to ensure the sealing member is separated from the shaft (under the action of the biasing force) when the local air pressure is sufficiently low that a sealing function is not necessary. However, when the pressure increases to a level that increases the risk of leakage flow around the shaft, the sealing member may move to form the seal. In embodiments in which this movement is effected by the pressure force, it will be appreciated that the movement of the sealing member between the open and closed is 'passive' (i.e. it does not require a separate actuator). Providing a sealing member which moves passively between an open and a closed configuration tends to be beneficial because such movement may be energy efficient and/or may negate the need for external actuation of the seal which would tend to increase the complexity of the supercharger .

The electric supercharger may have a boost speed at which the compressor element rotates to create a compressed charge, and an idle speed at which the compressor element rotates between boosts. The first threshold may be exceeded when the electric supercharger is at the idle speed, such that the seal is in the closed configuration when the electric supercharger is at the idle speed. The pressure on the sealing member may be below the first threshold when the electric supercharger is at the boost speed, such that during boosting, the seal is in the open configuration. Such an arrangement has been found to beneficial because it tends to protect the sealing member from friction caused by high speed rotation of the drive shaft during boosting, and takes advantage of the fact that the local pressure around the seal tends to be lower during boost than during idling (this is because the speed of the compressor wheel during boost tends to be such that the air is primarily forced out in a radial direction such that the pressure behind the compressor wheel and around the shaft may be relatively low, whereas during the (slower) idling there tends to be less pressure build up in the radial direction and a relatively higher pressure behind the compressor wheel.

The drive shaft may be substantially cylindrical.

The drive shaft may be circular cylindrical. The drive shaft may have a first axial location having a first diameter and second axial location having a second diameter, the first diameter being greater than the second diameter.

Preferably, in the closed configuration the sealing member forms a seal with the drive shaft at the first axial location and in the open configuration, the sealing member moves to the second axial location such that there is a gap between the sealing member and the drive shaft.

The drive shaft may have a tapered region between the first and second axial locations at which the diameter of the drive shaft transitions between the first and second diameters. The taper may be a constant taper. Having a taper tends to be beneficial because it enables the contact pressure between the sealing member and the shaft to be gradually released as the sealing member moves from the open to the closed configurations.

During movement between the open and closed configurations, the sealing member may move relative to the drive shaft, in a direction parallel to the longitudinal axis of the drive shaft. Providing such an arrangement, in combination with a tapered drive shaft, enables a tight seal to be formed because the sealing member is urged along the axial direction towards the increasing radius of drive shaft. Thus, as the pressure increases, the seal may be formed more tightly.

The sealing member may be annular. The sealing member may be concentric with the drive shaft. The sealing member may be formed from a resilient material.

The sealing member may be located downstream of the compressor element. The sealing member may be located upstream of the motor. The sealing member is preferably located behind the compressor element such that the local air pressure behind the compressor element acts on the sealing member.

The electric motor may be a Switched Reluctance Motor. The electric motor may be a Permanent Magnet Motor. The supercharger may comprise a control unit for controlling the 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 a seal assembly comprising a sealing member and biasing member, the seal assembly being suitable for use in an electric supercharger of the above-described first aspect of the invention. The sealing member may be movable between a closed configuration in which the sealing member would form a seal around the drive shaft and an open configuration in which the sealing member would be separated from the drive shaft such that the seal is broken.

According to a third aspect of the invention there is provided a kit of parts for forming an electric supercharger according to the first aspect of the invention. The kit may comprise:

an electric motor;

a drive shaft;

a compressor element; a sealing member;

wherein the sealing member is configurable to be movable between a closed configuration in which the sealing member would form a seal around the drive shaft and an open configuration in which the sealing member would be separated from the drive shaft such that the seal is broken.

According to yet another aspect of the invention, there is provided an engine comprising the supercharger according to the first aspect of the invention. 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 for an automobile. The automobile may be less than 3.5 tonnes, and more preferably less than 2 tonnes.

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 and vice versa.

Description of the Drawings

An embodiment 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 view of the front part of an electric supercharger according to a first embodiment of the invention;

Figure 2 is a close-up view of the sealing member in Figure 1, with the sealing member in the closed configuration; and

Figure 3 is a close up view of the sealing member of Figure 1 but with the sealing member in an open configuration.

Detailed Description

Figure 1 shows a sectional view of part of an electric supercharger 115 according to a first embodiment of the invention. For the sake of clarity, some parts of the supercharger (e.g. the inlet, the volute, the outlet and the housing) are not shown. Those aspects of the supercharger are, however, conventional and will be readily understood by the skilled person.

The electric supercharger 115 has an electric motor (shown schematically as unit 121) which may be a switched reluctance motor or a permanent magnet motor. The motor 121 drives rotation of a drive shaft 107 which is fixedly coupled to a compressor wheel 103. The drive shaft 107 is supported by bearings 105.

The rear of the compressor wheel 103 is recessed such that a volume 117 is defined between the rear of the compressor wheel 103 and the surface of a front plate

101. During operation of the supercharger 115 the compressor wheel 103 is accelerated to a boost speed (typically around 70,000 rpm) in order to generate a compressed charge. Between boosts the compressor wheel 103 is rotated at an idle speed (typically around 5,000 rpm). During boosting, the majority of the air is forced radially outwards into a volute (not shown). During boosting, the air pressure in the volume 117 behind the compressor wheel 103 tends to therefore be relatively

- 8 low. In contrast, when the supercharger 115 is idling, the radial airflow is lower and there tends to actually be a relatively higher pressure in the volume 117 behind the compressor wheel 103.

The above-mentioned features and functions of an electric supercharger are known per se. A problem with known superchargers having the above-described features is that the air pressure behind the compressor wheel can be sufficiently high (especially when idling) to cause leakage flow into the bearings and/or electric motor. In known arrangements, it tends to be necessary to provide a ring seal, such as a piston ring, to prevent such leakage flow. However, such seals may be subjected to relatively high wear as they need to be in constant contact with the drive shaft at all rotating speeds.

The first embodiment of the invention seeks to address this problem. Referring back to the first embodiment of the invention in Figure 1, the supercharger 115 comprises a seal assembly formed from a sealing member 119 and spring 111. The seal assembly is located behind the rear of the compressor wheel and the upper surface of the sealing member 109 is exposed to the air in the volume 117. The sealing member 119 is a rubber annulus and is located concentrically with the drive shaft 107 such that it surrounds the circumference of the drive shaft 107. The spring 111 is located between the underside of the sealing member 107 and an adaptor 123 that connects the sealing assembly to the front plate 101. The spring 111 is arranged to bias the sealing member 119 in an axial direction towards an open configuration, but to also allow it to be moved to a closed configuration (discussed in more detail below with reference to Figures 2 and 3).

Reference is now made to Figure 2 which is a closeup view of the seal assembly and drive shaft of Figure 1. As shown most clearly in Figure 2, the drive shaft 107 (which is cylindrical) has a tapering diameter that transitions from a relatively narrow part (Di) upstream of the sealing member 109 to a relatively wide part (D2) downstream of the seal 109.

Figures 1 and 2 show the sealing member 109 in a closed configuration, in which it is positioned to surround a part of the tapered region of the drive shaft 107 having a relatively large diameter. The inner diameter of the annular sealing member 119 is smaller than the diameter of the drive shaft 107 at this location, such that the inner face 119a of the sealing member 119 is compressed against the surface of the drive shaft 107 to form a seal for preventing leakage flow around the drive shaft 107.

The spring 111 exerts a biasing force to urge the sealing member 119 in an axial direction (i.e. parallel to the longitudinal axis of the drive shaft) away from its closed configuration shown in Figures 1 and 2 and towards the compressor wheel. However, the spring 111 is chosen such that when the supercharger is idling, this biasing force is overcome by the opposing pressure force generated by the relatively high local air pressure (acting on the upper surface of the sealing member 119). This pressure force thus urges the sealing member in the opposite axial direction and holds it in the closed configuration. Although not shown in the schematic of Figure 1, it will be appreciated that the underside of the sealing member 119 at which the spring 111 is attached, is isolated from the surrounding air pressure by a housing surrounding the sealing assembly, such that a net pressure force acts on the sealing member.

In the first embodiment of the invention, the sealing member thus passively adopts the closed configuration when the supercharger is idling by virtue of the higher local air pressure acting on the sealing member 119 and urging it against the wide diameter portion of the drive shaft 107. However, when the supercharger 115 is accelerated to boost speed, the local air pressure in volume 117 and the vicinity of the sealing member 107 reduces. The biasing force exerted by the spring is then sufficient to move the sealing member 119 in an axial direction towards the compressor wheel

103. Since the diameter of the drive shaft 107 tapers to a smaller diameter along this axial direction, but the inner diameter of the sealing member remains constant, this movement has the effect of moving the sealing member 119 to an open configuration in which the inner face 119a of the sealing member 119 is separated from the shaft 107 such that the seal is broken. This open configuration is illustrated in Figure 3.

The first embodiment thus provides an arrangement in which the sealing member 119 is arranged to prevent leakage flow around the drive shaft 107 (i.e. it is in the closed configuration) when the local pressure is relatively high, but is passively moveable to a configuration in which the sealing member 119 is separated from the drive shaft 107 (i.e. it is in the open configuration) when the local pressure is relatively low. This reduces the wear on the sealing member because it ensures the sealing member is only contacting the drive shaft when its sealing function is necessary, but is not contacting the drive shaft when the sealing function is not required. Furthermore, such an arrangement is especially beneficial in an electric supercharger because this lower pressure occurs when the rotational speeds of the drive shaft are very high (during boosting) and thus when a sealing member would otherwise be subjected to high amounts of frictional wear .

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.

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

Claims

1. An electric supercharger comprising an electric motor, a drive shaft and a compressor element, the motor being arranged to effect rotation of the compressor element via the drive shaft, wherein the electric supercharger further comprises a sealing member for preventing leakage flow around the drive shaft, the sealing member being movable between a closed configuration in which the sealing member forms a seal around the drive shaft and an open configuration in which the sealing member is separated from the drive shaft such that the seal is broken.

2. An electric supercharger according to claim 1 wherein a biasing member is arranged to exert a force to bias the sealing member into its position in the open configuration.

3. An electric supercharger according to claim 2 wherein the biasing member is arranged such that when a pressure force acting upon the sealing member exceeds a first threshold, the biasing force is overcome thereby moving the seal to the closed configuration.

4. An electric supercharger according to claim 3 wherein the electric supercharger has a boost speed at which the compressor element rotates to create a compressed charge, and an idle speed at which the compressor element rotates between boosts, and wherein the first threshold is exceeded when the electric supercharger is at the idle speed, such that the seal is in the closed configuration when the electric supercharger is at the idle speed.

5. An electric supercharger according to claim 4 wherein the pressure on the sealing member is below the first threshold when the electric supercharger is at the boost speed, such that during boosting, the seal is in the open configuration.

6. An electric supercharger according to any preceding claim wherein the drive shaft is substantially cylindrical and has a first axial location having a first diameter and second axial location having a second diameter, the first diameter being greater than the second diameter.

7. An electric supercharger according to claim 6 wherein in the closed configuration the sealing member forms a seal with the drive shaft at the first axial location and in the open configuration, the sealing member moves to the second axial location such that there is a gap between the sealing member and the drive shaft.

8. An electric supercharger according to claim 6 or 7 wherein the drive shaft has a tapered region between the first and second axial locations at which the diameter of the drive shaft transitions between the first and second diameters .

9. An electric supercharger according to any preceding claim wherein the sealing member is annular and is concentric with the drive shaft.

10. An electric supercharger according to any preceding claim wherein the sealing member moves relative to the drive shaft, in a direction parallel to the longitudinal axis of the drive shaft.

11. An electric supercharger according to any preceding claim wherein the seal is located downstream of the compressor element.

12. An electric supercharger according to any preceding claim wherein the electric motor is a Switched Reluctance

Motor .

13. An electric supercharger according to any of claims 1 to llwherein the electric motor is a Permanent Magnet Motor .

14. A seal assembly comprising a sealing member and biasing member, suitable for use in the electric supercharger according to any of claims 1 to 5, wherein the sealing member is movable between a closed configuration in which the sealing member would form a seal around the drive shaft and an open configuration in which the sealing member would be separated from the drive shaft such that the seal is broken.

15. A kit of parts for forming an electric supercharger according to any of claims 1 to 13, the kit comprising:

an electric motor; a drive shaft; a compressor element; a sealing member;

wherein the sealing member is movable between a closed configuration in which the sealing member forms a seal around the drive shaft and an open configuration in which the sealing member is separated from the drive shaft such that the seal is broken.

16. An electric supercharger substantially as herein 5 described with reference to any of Figs. 1 to 3 of the accompanying drawings .

Intellectual

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GB1611473.8

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