Patent Description:
The individual mobility sector is experiencing a disruptive change. Especially, the increasing number of electric vehicles entering the market demands higher efficiencies from traditional internal combustion engine (ICE) vehicles. Therefore, more and more vehicles are equipped with efficiency increasing measures, such as charging apparatuses and emission reduction devices. Well known are, for instance, charging apparatuses wherein a compressor may be driven by an e-motor (e-charger) and/or an exhaust gas powered turbine (turbocharger). Generally, an exhaust gas turbocharger has a turbine with a turbine wheel, which is driven by the exhaust gas flow of the combustion engine. A compressor with a compressor wheel arranged on a common shaft with the turbine wheel compresses the fresh air drawn in for the engine. This increases the amount of air or oxygen available to the engine for combustion. This in turn increases the performance of the combustion engine.

Upon reaching a certain charging pressure a part of the exhaust gas can be bypassed around the turbine wheel in order to prevent the turbine wheel exceeding its maximum rotational speed. The amount of exhaust gas which is bypassed is commonly controlled by a bypass valve or wastegate valve which opens and closes a bypass opening connecting a bypass channel with a turbine inlet channel, in particular a volute. The wastegate valve is usually actuated by an actuator assembly which connects the wastegate valve inside the turbine housing with an actuating lever outside the turbine housing.

In the state of the art, various actuator assemblies for bypass valves (wastegate valves) which comprise an actuator shaft being rotatably supported in a bushing are known. In this regard, <CIT> discloses a wastegate valve assembly with a shaft being supported in a first bushing and having a seal ring between the first bushing and a second bushing. One of the main challenges of these actuator assemblies is to reduce exhaust gas leakage from inside the turbine housing to the outside.

Accordingly, the objective of the present invention is to provide an actuator assembly with reduced leakage.

The present invention relates to an actuator assembly for a charging apparatus according to claim <NUM>. Furthermore, the invention relates to a turbine and a charging apparatus having such an actuator assembly according to claims <NUM> and <NUM>, respectively.

The inventive actuator assembly for a charging apparatus comprises an actuator shaft, a bushing and a sealing arrangement. The actuator shaft is arranged inside the bushing and comprises a shaft step and a reduced diameter portion. The sealing arrangement comprises an insert sleeve and a seal ring. The the insert sleeve is arranged on the reduced diameter portion and has a sleeve step between a larger diameter sleeve portion and a smaller diameter sleeve portion. The seal ring is arranged in a cavity formed radially between the bushing and the smaller diameter sleeve portion and axially between the sleeve step and the shaft step. A radial sealing region and an axial sealing region are defined by the sealing arrangement. The radial sealing region is formed between the bushing and the seal ring, and the axial sealing region is formed between the seal ring and the insert sleeve. The seal ring is thereby configured and arranged to be driven into contact with the insert sleeve by exhaust gas pressure. These features advantageously lead to a self-actuated sealing which is enabled by exhaust gas pushing the seal ring in an axial direction against the insert sleeve. On the other hand, there is no or at least a reduced friction wear radially outward (and also radially inward) of the seal ring as the seal ring is slidable or drivable on the bushing in order to come into contact with the insert sleeve. That means also that there is no preload acting on the actuator shaft or the bushing and consequently there is not only less wear on the seal ring but also on the actuator shaft and the bushing. As the seal ring can slide in an axial direction inside the bushing bore, i.e. radially inside the bushing, the actuator shaft (and an outer lever connected thereto) are not restricted in axial and/or rotational movement by seal ring. Thereby thermally or mechanically conditioned displacements or geometry changes of the actuator assembly or parts of it may be possible or compensable without resulting in damages. Furthermore, by having the self-actuated sealing arrangement, there is no need for piston - or o-rings which are clamped at a fixed spot and have a gap in a circumferential direction and, thus mostly result in a leakage at the gap and friction wear due to the clamping. The inventive seal ring, however, leads to close to zero leakage and reduced wear.

In another aspect of the actuator assembly, the sealing arrangement may further comprise an exhaust gas pressure chamber. Additionally, the exhaust gas pressure chamber may be configured to build up exhaust gas pressure to move the seal ring into axial sealing contact with the insert sleeve in order to establish the axial sealing region. Alternatively or additionally, the exhaust gas pressure chamber may be formed radially between the bushing and the insert sleeve and axially between the actuator shaft and the seal ring. By providing an exhaust gas pressure chamber exhaust gas can accumulate inside the chamber in order to provide pressure force which enacts on the seal ring to urge it against the insert sleeve.

In another aspect, which is combinable with any one of the previous aspects, the radial sealing region may be configured as slide fit. That means, the seal ring may slide closely inside the bushing. In particular, the seal ring can slide on an inner surface of the bushing. Thereby, less force is exerted on the seal ring but also on the bushing. This leads to a negligible wear or at least less wear in comparison to, for instance, a piston ring. The slide fit further ensures an axial movability of the seal ring to compensate for an axial displacement of the actuator shaft and/or the insert sleeve (and/or an outer lever which may be connected to the actuator shaft).

In another aspect, which is combinable with any one of the previous aspects, the radial sealing region may be formed between an outer diameter of the seal ring and an inner diameter of the bushing. In other words, the radial sealing region may be formed between a bushing bore of the bushing (i.e. a radially inner surface of the bushing) and a radially outer surface of the seal ring.

In another aspect, which is combinable with any one of the previous aspects, the axial sealing region may be formed between a first axial end face of the seal ring and a sleeve step face of the insert sleeve. The first axial end face may be formed as an annular face, in particular as an annular face without interruptions. Alternatively or additionally, the sleeve step face may be formed as an annular face, in particular as an annular face without interruptions. Alternatively or additionally, the first axial end face may be formed conical or curved to establish a line contact in the axial sealing region. Alternatively or additionally, the sleeve step face may be formed conical or curved to establish a line contact in the axial sealing region. This feature leads advantageously to the effect, that the sealing arrangement can compensate for tilting of the actuator assembly, in particular tilting of the actuator shaft.

In another aspect, which is combinable with any one of the previous aspects, the insert sleeve may comprise a first sleeve portion with a first outer diameter and a second sleeve portion with a second outer diameter. Additionally, the second outer diameter may be larger than the first outer diameter such that a sleeve step is formed. In particular, the sleeve step may have a sleeve step face. Additionally, the sleeve step may be formed between the first sleeve portion and the second sleeve portion. That means the first sleeve portion and the second sleeve portion may be axially adjacent. Therefore, the first sleeve portion may also be referred to as first axial sleeve portion and the second sleeve portion may also be referred to as second axial sleeve portion. The second sleeve portion may be arranged further to the outside of the actuator assembly, in particular further to the outside of a turbine housing when the actuator assembly is mounted in a turbine. Additionally, an inner diameter of the seal ring may be smaller than the second outer diameter of the second sleeve portion. This latter feature ensures that the seal ring and the insert sleeve are overlapping in a radial direction. Thereby the axial sealing region can be established. Furthermore, the seal ring can be axially secured or restricted by the insert sleeve when exhaust gas pressure urges the seal ring in an axial direction towards the second sleeve portion.

Additionally to the previous aspect, the seal ring may be arranged between, in particular radially between the first sleeve portion and the bushing and between, in particular axially between the second sleeve portion and the actuator shaft. In other words, the seal ring may be arranged in a cavity formed by the bushing, the insert sleeve and the actuator shaft. More specific the cavity may be formed axially between a shaft step face of the actuator shaft and the sleeve step face, and radially between and a radially outer surface of the first sleeve portion of the insert sleeve and a radially inner surface of the bushing.

Alternatively or additionally to the previous aspect and when the sealing arrangement further comprises an exhaust gas pressure chamber, the exhaust gas pressure chamber may be formed between, in particular radially between the first sleeve portion and the bushing and between, in particular axially between the second sleeve portion and the actuator shaft. That means both the exhaust gas pressure chamber and the seal ring are located inside the cavity. In other words, the exhaust gas pressure chamber may equal the space of the cavity minus the space occupied by the seal ring.

In another aspect, which is combinable with any one of the previous aspects, the actuator shaft may comprise a reduced diameter portion at an axial outer end region of the actuator shaft such that a shaft step with a shaft step face is formed. Additionally, the sealing arrangement may be located radially outwardly of the reduced diameter portion. That means the sealing arrangement may be located radially between the bushing and the reduced diameter portion. In other words, the sealing arrangement is located at the axial outer end region. Alternatively or additionally, the seal ring and the insert sleeve may be accommodated between the bushing, the shaft step and the reduced diameter portion. Alternatively or additionally, the insert sleeve may be arranged on the reduced diameter portion such that a sleeve step face of the insert sleeve opposes the shaft step face. Additionally, the seal ring may be arranged between, in particular radially between, the sleeve step face and the shaft step face. Alternatively or additionally, an inner diameter of the insert sleeve may be larger than an outer diameter of the reduced diameter portion such that a radial clearance fit is established between the actuator shaft and the insert sleeve. Alternatively or additionally, the actuator shaft may comprise an undercut which extends circumferentially between the reduced diameter portion and the shaft step. This latter feature ensures an axial abutment of the insert sleeve and the shaft step face.

In another aspect, which is combinable with any one of the previous aspects, the actuator shaft may comprise a first shaft bearing land and a second shaft bearing land. The second shaft bearing land may be axially spaced apart from the first shaft bearing land such that an exhaust gas passage is formed therebetween. By providing the shaft bearing lands friction wear between the actuator shaft and the bushing can be reduced. Furthermore, the stability of the actuator shaft can be improved. By providing the exhaust gas passage exhaust gas flow towards the exhaust gas pressure chamber along the actuator shaft can be facilitated. The first shaft bearing land may be arranged at a first axial end region of the bushing. The second shaft bearing land may be arranged adjacent a second axial end region of the bushing. Additionally, the second shaft bearing land may be arranged directly adjacent the shaft step. Additionally, the second shaft bearing land may form an outer diameter of the shaft step.

In another aspect, which is combinable with the previous aspect, an outer diameter of the first shaft bearing land may be smaller than an inner diameter of the bushing such that exhaust gas can flow axially through a gap formed radially between the first shaft bearing land and the bushing. Alternatively or additionally, an outer diameter of the second shaft bearing land may be smaller than an inner diameter of the bushing such that exhaust gas can flow axially through a gap formed radially between the second shaft bearing land and the bushing. Alternatively or additionally, an outer diameter of the first shaft bearing land may be smaller than outer diameter of the seal ring. Alternatively or additionally, an outer diameter of the second shaft bearing land may be smaller than outer diameter of the seal ring. In other words, an outer diameter of the seal ring may be larger than an outer diameter of the first shaft bearing land and smaller than an inner diameter of the bushing. Alternatively or additionally, an outer diameter of the seal ring may be larger than an outer diameter of the second shaft bearing land and smaller than an inner diameter of the bushing.

In another aspect, which is combinable with any one of the previous aspects, the seal ring may be arranged axially between a shaft step of the actuator shaft and a sleeve step of the insert sleeve.

In another aspect, which is combinable with any one of the previous aspects, the actuator assembly may further comprise an outer lever. The outer lever may be attached to an axial outer end region of the actuator shaft such that the insert sleeve is axially press-fit between a shaft step of the actuator shaft and the outer lever.

In another aspect, which is combinable with any one of the previous aspects, the seal ring may be configured as a closed ring. Alternatively or additionally, the seal ring may be configured as a solid ring. In other words, the seal ring may be configured as a solid ring. Alternatively or additionally, the seal ring may be made from metallic material. In other words, the seal ring is shaped to have no interruption in circumferential direction.

The present invention further relates to a turbine for a charging apparatus. The turbine comprises a turbine housing, a turbine wheel rotatably arranged in the turbine housing and a bypass valve. The turbine housing defines a volute and a bypass channel which is fluidically coupled to the volute via a bypass opening. The bypass valve is configured to open and close the bypass opening. The turbine further comprises an actuator assembly according to any one of the previous aspects. Thereby, the actuator assembly is coupled to the bypass valve.

In another aspect of the turbine, the actuator assembly may extend through a bore in the turbine housing from outside the turbine housing into the bypass channel. The sealing arrangement may be located at an outer end region of the bore which is opposite to the bypass channel. In other words, the actuator assembly may be arranged inside the bore of the turbine housing.

In another aspect of the turbine, which is combinable with any one of the previous aspects, the actuator shaft may extend into the bypass channel and may be configured such that exhaust gas residing in the bypass channel can stream from an axial inner end region of the actuator shaft along the actuator shaft to an exhaust gas pressure chamber of the sealing arrangement. Alternatively or additionally, the bushing may extend into the bypass channel and may be configured such that exhaust gas residing in the the bypass channel can stream from an axial inner end region of the actuator shaft along the actuator shaft to an exhaust gas pressure chamber of the sealing arrangement.

The present invention further relates to a charging apparatus. The charging apparatus comprises a compressor with an impeller, a shaft and a turbine according to any one of the previous aspects. The impeller is rotatably coupled to the turbine wheel by the shaft.

The present disclosure further relates to a method for mounting an actuator assembly into a turbine housing. The method comprises:.

In another aspect of the method, the bore may be provided from outside the turbine housing into a bypass channel of the turbine housing. Alternatively or additionally, the bushing may be pressed into the bore from outside of the turbine housing. Alternatively or additionally, the actuator shaft may be inserted the with the reduced diameter portion in front from the bypass channel into the bushing. Alternatively or additionally, the seal ring may be inserted into the space from outside the turbine housing. Alternatively or additionally, the insert sleeve may be inserted into the space from outside the turbine housing. Alternatively or additionally, the insert sleeve may be press-fit axially between the shaft step and the outer lever.

In another aspect of the method which is combinable with the previous aspect, the method steps are performed in the order in which they are listed.

In the context of this invention, the expressions axially, axial or axial direction is a direction parallel of or along a rotation axis of the actuator shaft or the bushing or the seal ring or the insert sleeve. Thus, with reference to the figures, see, especially <FIG>, <FIG>, an axial dimension is described with reference sign <NUM>, a radial dimension extending "radially" away from the axial dimension <NUM> is described with reference sign <NUM>. Furthermore, a circumferential dimension around the axial dimension <NUM> is described with reference sign <NUM>. In the context of this invention the expression "outside" or "outer" should be referred to a location relative to a turbine housing into which the actuator assembly may be mounted. That means, "outside" means outside the turbine housing, and "outer" means relative closer to the outside than another portion which is closer to the inside of the turbine housing. With respect to the actuator assembly alone, "outer" can be interpreted as a driving side of the actuator assembly and "inner" as driven side of the actuator assembly.

<FIG> illustrates an exemplary embodiment of the actuator assembly <NUM> for a charging apparatus <NUM> according to the present invention. The inventive actuator assembly <NUM> comprises an actuator shaft <NUM>, a bushing <NUM> and a sealing arrangement <NUM>. For illustrative purposes the actuator assembly <NUM> is depicted in <FIG> being arranged in a housing, in particular a turbine housing <NUM> which, however, will be explained further below. The sealing arrangement <NUM> comprises an insert sleeve <NUM> and a seal ring <NUM>. A radial sealing region <NUM> and an axial sealing region <NUM> are defined by the sealing arrangement <NUM>. The radial sealing region <NUM> is formed between the bushing <NUM> and the seal ring <NUM>. The axial sealing region <NUM> is formed between the seal ring <NUM> and the insert sleeve <NUM>. This can also be seen in greater detail in <FIG> which shows the actuator assembly of <FIG> in greater detail. The seal ring <NUM> is thereby configured and arranged to be driven into contact with the insert sleeve <NUM> by exhaust gas pressure. More specifically, the seal ring <NUM> is configured and arranged to be axially driven into contact with the insert sleeve <NUM> by exhaust gas pressure. These features advantageously lead to a self-actuated sealing which is enabled by exhaust gas pushing the seal ring <NUM> in an axial direction <NUM> against the insert sleeve <NUM>. On the other hand, there is no or at least a reduced friction wear radially outward (and also radially inward) of the seal ring <NUM> as the seal ring <NUM> is slidable or drivable on the bushing <NUM> in order to come into contact with the insert sleeve <NUM>. That means also that there is no preload acting on the actuator shaft <NUM> or the bushing <NUM>. Consequently, there is not only less friction wear on the seal ring <NUM> but also on the actuator shaft <NUM> and the bushing <NUM>. As the seal ring <NUM> can slide in an axial direction <NUM> inside a bore of the bushing <NUM> (the bore being radially inside the bushing <NUM>), the actuator shaft <NUM> (and an outer lever <NUM> connected thereto which will be explained further below in more detail) are not restricted in axial and/or rotational movement by the seal ring <NUM>. Thereby thermally or mechanically conditioned displacements or geometry changes of the actuator assembly <NUM> or parts of it, in particular the actuator shaft <NUM> may be possible or compensable without resulting in damages. Furthermore, by having the self-actuated sealing arrangement <NUM>, there is no need for piston - or o-rings which are clamped at a fixed spot and have a gap in a circumferential direction <NUM> and, thus mostly result in a leakage at the gap and friction wear due to the clamping. The inventive seal ring <NUM>, however, leads to close to zero leakage and reduced wear. The expressions radial sealing region <NUM> and axial sealing region <NUM> are to be understood as sealing regions which seal in a radial direction <NUM> (radial sealing region <NUM>) and in an axial direction <NUM> (axial sealing region <NUM>).

With further reference to <FIG> the actuator shaft <NUM> comprises an axial inner end region <NUM> and an axial outer end region <NUM> which can also be referred to first axial end region <NUM> and second axial end region <NUM>. Similarly, the bushing <NUM> comprises a first axial end region <NUM> (axial inner end region <NUM>) and a second axial end region <NUM> (axial outer end region <NUM>). The actuator shaft <NUM> is thereby arranged inside the bushing <NUM>. The actuator shaft <NUM> is arranged inside the bushing <NUM> such that the first axial end region <NUM> of the actuator shaft <NUM> is adjacent the first axial end region <NUM> of the bushing <NUM> and that the second axial end region <NUM> of the actuator shaft <NUM> is adjacent the second axial end region <NUM> of the bushing <NUM>. The sealing arrangement <NUM> is thereby located radially between the second axial end regions <NUM>, <NUM>.

The actuator shaft <NUM> comprises a reduced diameter portion <NUM> such that a shaft step <NUM> with a shaft step face <NUM> is formed (see, <FIG> and <FIG>). The shaft step face <NUM> is directed in a substantial axial direction <NUM>. The reduced diameter portion <NUM> is arranged at the axial outer end region <NUM>. The sealing arrangement <NUM> is located radially outwardly of the reduced diameter portion <NUM>. That means the sealing arrangement <NUM> is located radially between the bushing <NUM> and the reduced diameter portion <NUM>. In other words, the sealing arrangement <NUM> is located between the bushing <NUM>, the shaft step face <NUM> and the reduced diameter portion <NUM>. This means also that the seal ring <NUM> and the insert sleeve <NUM> are accommodated between the bushing <NUM>, the shaft step <NUM>, in particular the shaft step face <NUM> and the reduced diameter portion <NUM>.

The insert sleeve <NUM> comprises a first sleeve portion <NUM> with a first outer diameter <NUM> and a second sleeve portion <NUM> with a second outer diameter <NUM>. The first sleeve portion <NUM> and the second sleeve portion <NUM> are arranged axially adjacent. Therefore, the first sleeve portion <NUM> may also be referred to first axial sleeve portion <NUM> and the second sleeve portion <NUM> may also be referred to second axial sleeve portion <NUM>. This can be seen, in particular, in <FIG>, whereby <FIG> depicts an even more detailed view of the sealing arrangement <NUM> of the actuator assembly <NUM> as shown in <FIG>. In detail, <FIG> schematically shows the geometrical relations, in particular the diameter relations of the different parts of the actuator assembly <NUM>. For illustrative purposes the respective diameters and dimensions are schematically depicted in an exaggerated way to better distinguish between the different parts. For instance, between the seal ring <NUM> and the bushing <NUM> a gap is clearly visible. Although shown quite broad, this gap might be smaller such that a slide fit between the seal ring <NUM> and the bushing <NUM> but also a good sealing function is ensured. The second outer diameter <NUM> of the insert sleeve <NUM> (also referred to as outer diameter <NUM> of the second sleeve portion <NUM>) is larger than the first outer diameter <NUM> of the insert sleeve <NUM> (also referred to as outer diameter <NUM> of the first sleeve portion <NUM>) such that a sleeve step <NUM> is formed between the first sleeve portion <NUM> and the second sleeve portion <NUM>. The sleeve step <NUM> has a sleeve step face <NUM> which is directed in a substantial axial direction <NUM>. Thereby, the sleeve step face <NUM> and the shaft step face <NUM> are directed in opposing axial directions <NUM>. The insert sleeve <NUM> is arranged at the reduced diameter portion <NUM> such that the sleeve step face <NUM> opposes the shaft step face <NUM>. That means that the sleeve step face <NUM> and the shaft step face <NUM> face each other.

The first sleeve portion <NUM> is arranged axially between the shaft step <NUM> and the second sleeve portion <NUM> (see, in particular <FIG>). The seal ring <NUM> is thereby arranged radially between the first axial sleeve portion <NUM> and the bushing <NUM> and axially between the second axial sleeve portion <NUM> (more specifically the sleeve step <NUM>) and the shaft step <NUM>. In other words, the seal ring <NUM> is arranged in a cavity <NUM>. The cavity <NUM> is formed radially between the bushing <NUM> and the first sleeve portion <NUM> and axially between the second axial sleeve portion <NUM> (more specifically the sleeve step <NUM>) and shaft step <NUM>. More specifically, the cavity <NUM> is formed axially between the shaft step face <NUM> and the sleeve step face <NUM> and radially between and a radially outer surface of the first sleeve portion <NUM> and a radially inner surface of the bushing <NUM>.

The sealing arrangement <NUM> further comprises an exhaust gas pressure chamber <NUM> (see, in particular <FIG> and <FIG>). The exhaust gas pressure chamber <NUM> is formed radially between the first axial sleeve portion <NUM> and the bushing <NUM> axially between the second axial sleeve portion <NUM> and the shaft step <NUM>. That means both the exhaust gas pressure chamber <NUM> and the seal ring <NUM> are located inside the cavity <NUM>. In other words, the exhaust gas pressure chamber <NUM> represents a portion of the cavity <NUM> minus the space occupied by the seal ring <NUM>. That means the exhaust gas pressure chamber <NUM> is actually formed radially between the bushing <NUM> and the first sleeve portion <NUM> and axially between the shaft step <NUM> and the seal ring <NUM>. Furthermore, the exhaust gas pressure chamber <NUM> comprises a small annular portion which is formed radially between the seal ring <NUM> and the first sleeve portion <NUM>. However, this small annular portion does is functionally negligible for the function of the exhaust gas pressure chamber <NUM> as the pressure forces which enact on the seal ring <NUM> from the small annular portion are equalized by themselves due to the geometry of the small annular portion. The exhaust gas pressure chamber <NUM> is configured to build up exhaust gas pressure to move the seal ring <NUM> into axial sealing contact with the insert sleeve <NUM> in order to establish the axial sealing region <NUM>. By providing the exhaust gas pressure chamber <NUM>, exhaust gas can accumulate inside the exhaust gas chamber <NUM> in order to provide pressure force which enacts on the seal ring <NUM> to urge it against the insert sleeve <NUM>. More specifically, the seal ring <NUM> is urged in an axial direction <NUM> towards the sleeve step face <NUM>. The exhaust gas pressure chamber <NUM> can further ensure that exhaust gas is distributed along the whole circumference of the first sleeve portion <NUM>. Thereby the exhaust gas pressure can equally enact on the sleeve ring <NUM> in an axial direction <NUM>. This can for instance prevent tilting and leads to a more homogenous and smooth movement of the seal ring <NUM>.

With further reference to <FIG>, the shaft <NUM> comprises a first shaft bearing land <NUM> and a second shaft bearing land <NUM>. The second shaft bearing land <NUM> is axially spaced apart from the first shaft bearing land <NUM> such that an exhaust gas passage <NUM> is formed therebetween. The first shaft bearing land <NUM> is arranged close to the first axial end region <NUM> of the actuator shaft <NUM> such that it is adjacent to the first axial end region <NUM> of the bushing <NUM>. The second shaft bearing land <NUM> is arranged in the second axial end region <NUM> of the actuator shaft <NUM> such that it is adjacent to the second axial end region <NUM> of the bushing <NUM>. The second shaft bearing land <NUM> is arranged directly adjacent the shaft step <NUM> or more precisely on the shaft step <NUM>. That means the second shaft bearing land <NUM> may form an outer diameter 234a of the shaft step <NUM>. By providing the shaft bearing lands <NUM>, <NUM> friction wear between the actuator shaft <NUM> and the bushing <NUM> can be reduced. Furthermore, the stability of the actuator shaft <NUM> can be improved. By providing the exhaust gas passage <NUM> exhaust gas flow towards the exhaust gas pressure chamber <NUM> along the actuator shaft <NUM> can be facilitated.

To provide the exhaust gas flow towards the exhaust gas pressure chamber <NUM>, an outer diameter 232a of the first shaft bearing land <NUM> and the outer diameter 234a of the second shaft bearing land <NUM> are smaller than an inner diameter <NUM> of the bushing <NUM> (see, in particular <FIG>). The outer diameters 232a, 234a are adapted such that exhaust gas can flow axially through a gap 232b formed radially between the first shaft bearing land <NUM> and the bushing <NUM> and through a gap 234b formed radially the second shaft bearing land <NUM> and the bushing <NUM> (gap 232b only indicated in <FIG> whilst gap 234b is clearly visible in <FIG>). The outer diameter 232a of the first shaft bearing land <NUM> and the outer diameter 234a of the second shaft bearing land <NUM> are smaller than an outer diameter <NUM> of the seal ring <NUM>. In other words, the outer diameter <NUM> of the seal ring <NUM> is larger than the outer diameter 232a, 232b of the first and second shaft bearing land <NUM>, <NUM> and smaller than the inner diameter <NUM> of the bushing <NUM>.

As the outer diameter <NUM> of the seal ring <NUM> is smaller than the inner diameter <NUM> of the bushing <NUM>, the seal ring <NUM> can slide with respect to the bushing <NUM> (see, <FIG>). In other words, the radial sealing region <NUM> is configured as slide fit. That means, the seal ring <NUM> can slide closely inside the bushing <NUM> but at the same time prevents or at least reduces leakage. In particular, the seal ring <NUM> can slide on a radially inner surface of the bushing <NUM>. Thereby, less force is exerted on the seal ring <NUM> but also on the bushing <NUM>. This leads to a negligible friction wear or at least less friction wear in comparison to, for instance, a piston ring. The slide fit further ensures an axial movability of the seal ring <NUM> to compensate for an axial displacement of the actuator shaft <NUM> and/or the insert sleeve <NUM> (and/or an outer lever <NUM> which may be connected to the actuator shaft <NUM>). Furthermore, the axial movability ensures that the seal ring <NUM> can be pushed against and in close contact with the insert sleeve <NUM>. Consequently, the radial sealing region <NUM> is formed between an outer diameter <NUM> of the seal ring <NUM> and an inner diameter <NUM> of the bushing <NUM>. In other words, the radial sealing region <NUM> may be formed between the radially inner surface of the bushing <NUM> and a radially outer surface of the seal ring <NUM>. On the radially opposite side of the seal ring <NUM> an inner diameter <NUM> of the seal ring <NUM> is larger than the outer diameter <NUM> of the first sleeve portion <NUM> such that a clearance fit is provided radially between the seal ring <NUM> and the first sleeve portion <NUM>. This ensures free movability of the seal ring <NUM> and prevents friction wear between the first sleeve portion <NUM> and the seal ring <NUM>.

<FIG> shows that the seal ring <NUM> comprises a first axial end face <NUM> and a second axial end face <NUM>. The first and second axial end faces <NUM>, <NUM> are oriented in opposing axial directions <NUM>. The first axial end face <NUM> is directed towards the sleeve step face <NUM> and the second axial end face <NUM> is directed towards the shaft step face <NUM>. The inner diameter <NUM> of the seal ring <NUM> is smaller than the outer diameter <NUM> of the second sleeve portion <NUM>. By this the seal ring <NUM> and the insert sleeve <NUM> are overlapping in a radial direction <NUM>. Thereby the axial sealing region <NUM> can be established. That means, the axial sealing region <NUM> is formed between the first axial end face <NUM> and the sleeve step face <NUM>. Furthermore, the seal ring <NUM> can be axially secured or restricted by the insert sleeve <NUM> when exhaust gas pressure urges the seal ring <NUM> in an axial direction <NUM> towards the second sleeve portion <NUM>. Both axial end faces <NUM>, <NUM> are formed as an annular faces. They do not comprise interruptions and thus form a full <NUM>° ring shape. Similarly, the sleeve step face <NUM> is formed as an annular face, does comprise interruptions and thus form a full <NUM>° ring shape. These features ensure, that there is a full <NUM>° sealing contact possible. Although in <FIG>, <FIG>, <FIG> and <FIG> the first axial end face <NUM> and the sleeve step face <NUM> are depicted substantially flat, in alternative configurations on or both of them could be formed conical or curved to establish a line contact in the axial sealing region <NUM>. This feature leads advantageously to the effect, that the sealing arrangement <NUM> can compensate for tilting of the actuator assembly <NUM>, in particular tilting of the actuator shaft <NUM>. Furthermore, friction wear between the seal ring <NUM> and the insert sleeve <NUM> could be reduced to the reduced contact area.

As already mentioned, the seal ring <NUM> is configured as a closed ring (axial end faces <NUM>, <NUM> form a full <NUM>° ring shape). In other words, the seal ring <NUM> is shaped to have no interruptions in a circumferential direction <NUM>. Furthermore, the seal ring <NUM> is configured as a solid ring, in particular a substantially rigid ring. In particular, the seal ring <NUM> is made from metallic material. In alternative embodiments, the seal ring <NUM> can also be made from any other suitable material, for instance, a heat-resistant thermosetting material.

As illustrated in <FIG>, <FIG>, the actuator assembly <NUM> further comprises an outer lever <NUM>. The outer lever <NUM> is attached to the axial outer end region <NUM> of the shaft <NUM>.

More specifically, the outer lever <NUM> is attached to the reduced diameter portion <NUM>. The outer lever <NUM> is thereby axially adjacent to the insert sleeve <NUM> such that the insert sleeve <NUM> is axially press-fit between the shaft step <NUM> and the outer lever <NUM>. An inner diameter <NUM> of the insert sleeve <NUM> is larger than an outer diameter <NUM> of the reduced diameter portion <NUM> such that a radial clearance fit is established between the shaft <NUM> and the insert sleeve <NUM>. The shaft <NUM> comprises an undercut <NUM> which extends circumferentially between the reduced diameter portion <NUM> and the shaft step <NUM>. This latter feature ensures an axial abutment of the insert sleeve <NUM> and the shaft step face <NUM>.

<FIG> shows a turbine <NUM> for a charging apparatus <NUM> which is depicted in <FIG>. The turbine <NUM> comprises a turbine housing <NUM>, a turbine wheel <NUM> (only visible in <FIG>) rotatably arranged in the turbine housing <NUM> and a bypass valve <NUM>. The turbine housing <NUM> defines a volute <NUM> and a bypass channel <NUM> which is fluidically coupled to the volute <NUM> via a bypass opening <NUM>. The bypass valve <NUM> is configured to open and close the bypass opening <NUM>. The turbine <NUM> further comprises the actuator assembly <NUM>. Thereby, the actuator assembly <NUM> is coupled to the bypass valve <NUM>. More specifically, the bypass valve <NUM> is coupled to the first axial end region <NUM> of the actuator shaft <NUM>.

The actuator assembly <NUM> extends through a bore <NUM> of the turbine housing <NUM> from outside the turbine housing <NUM> into the bypass channel <NUM> (see, <FIG> and <FIG>). In other words, the actuator assembly <NUM> is arranged inside the bore <NUM> of the turbine housing <NUM>. The sealing arrangement <NUM> is located at an outer end region 713b of the bore <NUM> which is opposite to the bypass channel <NUM>. The actuator shaft <NUM> extends into the bypass channel <NUM> and is configured such that exhaust gas from the bypass channel <NUM> can stream at the axial inner end region <NUM> of the actuator shaft <NUM> along the shaft <NUM> to the exhaust gas pressure chamber <NUM> of the sealing arrangement <NUM>. More specifically, exhaust gas can stream from the bypass channel <NUM> along the gaps 232b, 234b and the exhaust gas passage <NUM> into the exhaust gas pressure chamber <NUM>. The bushing <NUM> extends into the bypass channel <NUM> and is configured such that exhaust gas from the bypass channel <NUM> can stream from the axial inner end region <NUM> of the actuator shaft <NUM> along the shaft <NUM> to the exhaust gas pressure chamber <NUM> of the sealing arrangement <NUM>.

<FIG> illustrates that the charging apparatus <NUM> comprises a compressor <NUM> with an impeller <NUM>, a shaft <NUM> and the turbine <NUM>. The impeller <NUM> is rotatably coupled to the turbine wheel <NUM> by the shaft <NUM>. In alternative embodiments the charging apparatus <NUM> may further comprise an electric motor (not depicted). The electric motor can also be coupled to the impeller <NUM> via the shaft <NUM>.

Claim 1:
An actuator assembly (<NUM>) for a turbine (<NUM>) of a turbocharger comprising:
a bushing (<NUM>),
an actuator shaft (<NUM>) with a shaft step (<NUM>) and a reduced diameter portion (<NUM>), wherein the actuator shaft (<NUM>) is arranged inside the bushing (<NUM>), and
characterized by
a sealing arrangement (<NUM>) comprising an insert sleeve (<NUM>) and a seal ring (<NUM>),
the insert sleeve (<NUM>) having a sleeve step (<NUM>) between a larger diameter sleeve portion (<NUM>) and a smaller diameter sleeve portion (<NUM>), the insert sleeve (<NUM>) being arranged on the reduced diameter portion (<NUM>),
wherein the seal ring (<NUM>) is arranged in a cavity (<NUM>) formed radially between the bushing (<NUM>) and the smaller diameter sleeve portion (<NUM>) and axially between the sleeve step (<NUM>) and the shaft step (<NUM>),
wherein the sealing arrangement (<NUM>) defines a radial sealing region (<NUM>) which is formed between the bushing (<NUM>) and the seal ring (<NUM>), and an axial sealing region (<NUM>) which is formed between the seal ring (<NUM>) and the insert sleeve (<NUM>), and wherein the seal ring (<NUM>) is configured and arranged to be driven into contact with the insert sleeve (<NUM>) by exhaust gas pressure.