FIELD

A stator mechanism is provided that may be used, for example, in a gas turbine, turbocharger, geothermal turbine, turbomachine or similar applications.

BACKGROUND

A turbine is a turbomachine, where energy is trans ^¬ ferred between a flowing medium and a rotating rotor. The rotor usually comprises an impeller where blades are attached around the impeller and the impeller is attached to a common shaft or a drum. The moving medium acts on the blades so that they move and impart rota ^¬ tional energy to the rotor. A stator mechanism determines how much medium is guided to the rotor.

Turbomachines may be arranged into two groups; devices that consume power such as compressors or devices that create power such as turbines. Turbines are usually connected to a generator. There are machines, which have both a turbine and a compressor, such as a gas turbine and a turbocharger. To the gas turbine and the turbocharger it may be possible combine an electric ma ^¬ chine, which functions as a motor or a generator. A turbocharger is a turbine-driven device which increases an engine's efficiency and power by forcing extra air into cylinders of an internal combustion engine. Better efficiency is achieved by lower fuel consumption. At the same time also harmful emissions of the exhaust are reduced .

Geothermal energy utilizes underground heat. Cold water is conducted in the ground via holes that are drilled deep into the ground. The ground temperature heats the water and the water is pumped back to the surface. High temperature makes the water evaporate creating steam and the steam is used to run a geothermal turbine to generate electric power.

There are various types of stator mechanisms in turbine applications. Similar for many of these devices may be that there is an arrangement that determines an intake capability of a device where the stator mechanism is mounted. The intake capability means how much medium such as gas or steam the stator mechanism will pass through to the rotor. The intake capability is deter ^¬ mined by arranging vanes in a certain position in the stator mechanism so that gaps are formed in the stator mechanism. The vanes and the gaps between each vane may limit the amount of medium that passes through from the stator mechanism to the rotor.

The vanes may be adjusted to a certain position or they may be fixed in-place. The shape of the vane varies but the vane usually comprises a curved surface. Different kinds of mechanisms may be used to manipulate the posi ^¬ tion of the vane. Typically in a large turbocharger a shaft power varies and it may be from around 500 kW up to around 5000 kW. Gas turbines' shaft power may be from around 500 kW up to around 100 000 kW. Temperature inside the turbine may be in some applications over 1000 degrees of Celsi- us, which causes challenges for the structure of the stator mechanism and the vanes.

A common problem in these devices is that stator mecha ^¬ nism and vanes in the stator mechanism get contaminated during operation. Usually a hot medium such as gas or steam consists of contaminating particles such as oily soot. This causes formation of a sticky solid in the stator mechanism. The sticky solid is contamination that may cover the surfaces inside the stator mecha ^¬ nism. The formation of the sticky solid, such as carbon formation, may block the vane and the parts that may be connected to the vane. This is not desired because the formation of the sticky solid changes functional prop ^¬ erties of the turbine.

The formation of the sticky solid may also decrease the power and efficiency of the turbine and create malfunc ^¬ tion. Because of the formation of the sticky solid formation the stator mechanism may require regular maintenance. A problem with the traditional stator mechanism structures has been that they are not easy to maintain. The maintenance of a traditional stator requires a lot of manual work around and inside the turbine. The tur ^¬ bine has to be switched off and detached from the ap ^¬ plication where it is used during maintenance and in some situations a spare turbine has to be installed in place. This increases manual work and requires longer shutdown and longer time for a start-up, which increas ^¬ es costs for maintenance.

SUMMARY

According to a first aspect, there is provided a stator mechanism for a turbine. The stator mechanism comprises a cylindrical housing which has a longitudinal center axis, wherein the cylindrical housing comprises a plu ^¬ rality of holes in an outer periphery of the cylindri- cal housing. The stator mechanism further comprises a plurality of vane units, wherein at least one vane unit is configured to be installed through each hole. The vane unit further comprises a vane element comprising a vane shaft and a vane, wherein a first end of the vane shaft extends through the hole inside the stator mecha ^¬ nism towards the longitudinal center axis, and wherein the vane has been arranged at the first end of the vane shaft. The vane unit further comprises an attaching member configured to detachably attach the vane element to the outer periphery of the cylindrical housing. The vane has a maximum transverse dimension, wherein the maximum transverse dimension is larger than a distance between two center points of rotation of two neighboring vane shafts. Thus it is possible to extract the vane element and further, when the stator mechanism is arranged in a turbine, it is possible to have optimal fluid dynamic performance in the stator mechanism and in the turbine because the structure enable optimal vane density, which improves the efficiency and perfor ^¬ mance of the turbine.

According to a second aspect, there is provided a sta ^¬ tor mechanism for a turbine. The stator mechanism comprises a cylindrical housing which has a longitudinal center axis, wherein the cylindrical housing comprises a plurality of holes in an outer periphery of the cy ^¬ lindrical housing. The stator mechanism further comprises a plurality of vane units, wherein at least one vane unit is configured to be installed through each hole. The vane unit further comprises a vane element comprising a vane shaft and a vane, wherein a first end of the vane shaft extends through the hole inside the stator mechanism towards the longitudinal center axis, and wherein the vane has been arranged at the first end of the vane shaft. The vane unit further comprises an attaching member configured to detachably attach the vane element to the outer periphery of the cylindrical housing. Thus it is possible to extract the vane ele ^¬ ment . According to a third aspect, there is provided a stator mechanism for a turbine. The stator mechanism comprises a cylindrical housing which has a longitudinal center axis, wherein the cylindrical housing comprises a plu ^¬ rality of holes in an outer periphery of the cylindrical housing. The stator mechanism further comprises a plurality of vane units, wherein at least one vane unit is configured to be installed through each hole. The vane unit further comprises a vane element comprising a vane shaft and a vane, wherein a first end of the vane shaft extends through the hole inside the stator mecha ^¬ nism towards the longitudinal center axis, and wherein the vane has been arranged at the first end of the vane shaft. The vane unit further comprises an attaching member configured to detachably attach the vane element to the outer periphery of the cylindrical housing which enables an individual extracting of the vane element out of the hole with the attaching member.

According to a fourth aspect, there is provided a sta ^¬ tor mechanism for a turbine. The stator mechanism comprises a cylindrical housing which has a longitudinal center axis, wherein the cylindrical housing comprises a plurality of holes in an outer periphery of the cy ^¬ lindrical housing. The stator mechanism further comprises a plurality of vane units, wherein at least one vane unit is configured to be installed through each hole. The vane unit further comprises a vane element comprising a vane shaft and a vane, wherein a first end of the vane shaft extends through the hole inside the stator mechanism towards the longitudinal center axis, and wherein the vane has a maximum transverse dimen- sion, wherein the maximum transverse dimension is larger than a distance between two center points of rota ^¬ tion of two vane shafts. The vane unit further compris ^¬ es an attaching member for each vane element which detachably attaches the vane element to the outer periph- ery of the cylindrical housing. According to a fifth aspect, there is provided a stator mechanism for a turbine. The stator mechanism comprises a cylindrical housing which has a longitudinal center axis, wherein the cylindrical housing comprises a plu- rality of holes in an outer periphery of the cylindrical housing. The stator mechanism further comprises a plurality of vane units, wherein at least one vane unit is configured to be installed through each hole. The vane unit further comprises a vane element comprising a vane shaft and a vane, wherein a first end of the vane shaft extends through the hole inside the stator mecha ^¬ nism towards the longitudinal center axis, and wherein the vane has been arranged at the first end of the vane shaft. The vane unit further comprises an attaching member configured to detachably attach the vane element to the outer periphery of the cylindrical housing. The stator mechanism further comprises an adjusting mechanism to adjust an angle of rotation of the vane ele ^¬ ment, wherein the vane element is pivotally connected to the attaching member at a second end of the vane shaft extending outside the cylindrical housing for pivoting the vane element with the adjusting mechanism.

In one embodiment, the plurality of holes are spaced at a distance from each other in the outer periphery of the cylindrical housing. In one embodiment, the vane has a maximum transverse dimension, wherein the maximum transverse dimension is larger than a distance between two center points of rotation of two vane shafts.

In one embodiment, the stator mechanism comprises a stator passage, wherefrom a hot medium inflow is configured to lead to the stator mechanism; and a pressurized chamber for supplying air or steam inside the vane unit, wherein the air or steam is pressurized with a higher pressure than a pressure of the hot medium in ^¬ flow in proximity to vanes, wherein the air or steam, which is substantially clean, is configured to be con ^¬ ducted from the pressurized chamber to the vane unit.

In one embodiment, the attaching member of the vane unit further comprises at least one inlet to conduct the air or steam inside the vane unit, and a clearance, which is arranged between the attaching member and the vane shaft, whereto the air or steam is conducted from the inlet.

In one embodiment, the attaching member further comprises a hollow shaft arranged at least partially around the vane shaft, wherein the hollow shaft com ^¬ prises a support element, wherein the stator mechanism comprises a plurality of lead-through holes one for each vane unit, wherein each lead-through hole has the same shape as the support element which enables to keep the attaching member firmly in-place and which prevents excessive leakage of air or steam from the pressurized chamber to the stator passage.

In one embodiment, the stator mechanism further comprises a counter ring, towards which the vane is sealed .

In one embodiment, the cross section of the support el ^¬ ement is configured to be substantially elliptic.

In one embodiment, the vane element is arranged in a fixed position and fixedly arranged to the attaching member .

In one embodiment, the vane unit is detachably attached to an outer periphery of the cylindrical housing for extracting the vane unit inside the housing from the outside of the housing without an essential need to dismantle any other part in the turbine. In one embodi- ment, the vane unit is constructed as a cartridge-like structure, which enables pulling the vane unit outwards from the stator mechanism by detaching only that part of the vane unit which is attached outside of the hous- ing. In one embodiment, the vane unit is constructed as a cartridge-like structure, which enables keeping the rest of the parts in the turbine in-place while detach ^¬ ing the vane unit. In one embodiment, the stator mechanism further comprises an adjusting mechanism to adjust an angle of ro ^¬ tation of the vane element, wherein the vane element is pivotally connected to the attaching member at a second end of the vane shaft extending outside the cylindrical housing for pivoting the vane element with the adjust ^¬ ing mechanism.

In one embodiment, the stator mechanism further comprises a stator passage for conducting gas to the sta- tor mechanism and the attaching member further comprises at least one inlet and the vane unit comprises at least one clearance, wherein the at least one clearance is arranged between the attaching member and the vane shaft, where pressurized air or steam, having higher pressure than the gas in the stator passage in proximi ^¬ ty to vanes, is conducted from the inlet.

In one embodiment, the attaching member further comprises at least one inlet to conduct pressurized air or steam inside the vane unit. In one embodiment, the sta ^¬ tor mechanism further comprises a stator passage for conducting gas to the stator mechanism and the vane unit comprises at least one of a clearance, which is arranged between the attaching member and the vane shaft, and a channel in the vane shaft, where pressur ^¬ ized air or steam, having higher pressure than the gas in the stator passage in proximity to vanes is conduct- ed. In one embodiment, the proximity to vanes means a location of the gas being at a distance maximum 50 mm from the vanes towards the flow direction. In one embodiment, the vane unit comprises a clearance between the attaching member and the vane shaft, where pressur ^¬ ized air or steam, having higher pressure than the gas expanding in a stator passage, is conducted. In one em ^¬ bodiment, the air or steam is substantially clean and cool, which enables to prevent or reduce the formation of a sticky solid in the vane unit by preventing hot and contaminated medium entering inside the vane ele ^¬ ment. In one embodiment, the air or steam is substan ^¬ tially clean and cool, which enables to prevent or re ^¬ duce the formation of a sticky solid in the vane unit by preventing hot and contaminated gas or steam enter ^¬ ing inside the vane element.

In one embodiment, the stator mechanism further comprises a connection piece which comprises a first end and a second end, wherein the connection piece connects the vane element to the adjusting mechanism for pivot ^¬ ing the vane element with respect to the attaching mem ^¬ ber with the adjusting mechanism via the connection piece. In one embodiment, the first end of the connec- tion piece is detachably and non-rotatably connected to the second end of the vane shaft. In one embodiment, the adjusting mechanism comprises a control ring, wherein the second end of the connection piece is at ^¬ tached to the control ring. In one embodiment, the ad- justing mechanism comprises a pivoting device, which pivots the control ring and adjusts the angle of rota ^¬ tion of the vane element via the connection piece.

In one embodiment, the attaching member comprises a sleeve extending in the hole and having a maximum outer diameter that is larger than a maximum transverse dimension of the vane. In one embodiment, the attaching member comprises a hollow shaft extending from the sleeve inside the cylindrical housing, wherein the hol ^¬ low shaft has another maximum outer diameter that is smaller than the maximum outer diameter of the sleeve. In one embodiment, the hollow shaft further comprises at least one inlet for supplying air or steam inside the vane unit.

In one embodiment, the vane shaft comprises a first shaft portion and a second shaft portion, wherein the first shaft portion is arranged partially inside the hollow shaft and the second shaft portion is arranged partially inside the sleeve and partially outside the sleeve, wherein the second shaft portion extends par- tially outside the cylindrical housing. In one embodi ^¬ ment, the connection piece comprises a fork-like struc ^¬ ture, which is detachably and non-rotatably connected to the second shaft portion. In one embodiment, the second shaft portion comprises a first fixing hole for attaching the fork-like structure to the second shaft portion. In one embodiment, the vane unit comprises a fixing pin for attaching the fork-like structure to the second shaft portion through the first fixing hole. In one embodiment, the vane unit comprises at least one of a clearance, which is arranged between the attaching member and the first shaft portion, and a channel in the first shaft portion, where air or steam, having higher pressure than the gas expanding in the turbine stator passage, is conducted.

In one embodiment, the adjusting of an angle of rota ^¬ tion of the vane element with the adjusting mechanism enables the adjusting of the intake capability of the turbine. In one embodiment, the attaching member comprises a sleeve extending in the hole and having a maximum outer diameter that is larger than a maximum transverse dimension of the vane. In one embodiment, the sleeve is arranged to be sealed in the hole. In one embodiment, the attaching member comprises a fixing flange for attaching the attaching member to the outer periphery of the cylindrical housing. In one embodiment, the vane unit comprises an inlet, which supplies air or steam in at least one of the following locations: inside the vane unit and to the vane.

In one embodiment, the vane unit is arranged with at least one fixing element for fixing the fixing flange to the outer periphery of the cylindrical housing. In one embodiment, the fixing flange comprises a second fixing hole for the fixing element. In one embodiment, the vane unit is equipped with at least one spring be ^¬ tween the fixing flange and the fixing element to press the vane element essentially towards the longitudinal center axis for enabling a sealing effect of the vane.

In one embodiment, the vane further comprises at least one fixing element. In one embodiment, the vane unit further comprises at least one spring between the fix ^¬ ing flange and the fixing element for enabling the vane element to press essentially towards the longitudinal center axis. In one embodiment, the vane unit further comprises at least one spring between the fixing flange and the fixing element for enabling the vane element to press essentially towards the longitudinal center axis and for enabling a sealing effect of the vane.

In one embodiment, the fixing element comprises a screw head, wherein the screw head is arranged at a distance above the fixing flange enabling movement of the at ^¬ taching member axially in the fixing hole along the fixing element. In one embodiment, the fixing element comprises a screw head, wherein the screw head is ar ^¬ ranged at a distance above the fixing flange enabling an axial movement of the attaching member along the fixing element as an effect of thermal expansion.

In one embodiment, the stator mechanism further comprises a counter ring, towards which the vane is sealed. In one embodiment, the stator mechanism further comprises a lead-through ring, which is arranged to lead through the attaching member. In one embodiment, the attachment member comprises a support element con ^¬ figured to be substantially elliptic. In one embodi ^¬ ment, the lead-through ring is arranged to support the attaching member from the support element.

In one embodiment of a turbine comprising the stator mechanism according to the first aspect and further comprising a hollow shaft arranged at least partially around the vane shaft, wherein the hollow shaft com ^¬ prises a support element, wherein the stator mechanism comprises a plurality of lead-through holes one for each vane unit, wherein each lead-through hole has the same shape as the support element which enables to keep the attaching member firmly in-place and which prevents excessive leakage of air or steam from the pressurized chamber to the stator passage, wherein the stator mechanism is configured to bleed the air or steam between the support element and the lead-through hole keeping the vane unit detachable.

According to a sixth aspect, there is provided a method of maintenance of a stator mechanism of a turbine, the stator mechanism comprising a cylindrical housing com- prising a plurality of holes at in an outer periphery of the cylindrical housing. The maintenance of the sta ^¬ tor mechanism comprising a plurality of vane units which are arranged to the holes, is made by detaching at least one vane unit out from at least one hole from the outer periphery of the cylindrical housing. In one embodiment of the method, each vane unit can be indi- vidually detached. This enables at least one of repair ^¬ ing each vane unit and checking the contamination of the stator mechanism from at least one detached vane unit . According to a seventh aspect, there is provided a method of maintenance of a stator mechanism according to the first aspect, wherein the detaching of the vane is possible in both extreme positions, vanes shut and vanes open.

The stator mechanism described here has many significant advantages. When a turbine is connected to a motor the intake capability of the turbine can be adjusted. By adjusting the angle of rotation of each vane the ar- ea for the medium to pass through the stator mechanism between each vane changes, which determines an intake capability of the turbine.

Further, when the stator mechanism is arranged in a turbine, with at least one of the features disclosed above it may be possible to improve the performance and efficiency of the turbine.

In one embodiment it is possible to equip the stator mechanism with an adjusting mechanism enabling a simultaneous adjusting of the vanes.

Hot medium inflow, which may be contaminating, may in course of time jam the mechanism controlling the ad- justment of the vanes and may also block the vanes in a way that the vanes may not move. The stator mechanism may be blocked in a way that it does not sufficiently or at all pass through the medium to the rotor. In the traditional structure the rotor, which is mounted around the same longitudinal axis to a common shaft in flow direction after the stator mechanism, has to be disassembled in order to be able to reach the vanes. In the traditional structure in some turbines the vanes have to be dismantled by operating inside and outside the turbine in order to get out the vanes inside the stator mechanism. This is a problem because the stator mechanism is behind the rotor and the parts may not be reached without disassembling the rotor. The structure disclosed enables that the turbine does not have to be dismantled totally from a larger process where it is used, for example, a power plant steam circuit, in or- der to detach the vane units. This provides cost sav ^¬ ings as there is no need to mount a spare turbine while cleaning the vane units and the vanes. This also means shorter shutdown of the larger process where the turbine is used.

The vane units, which comprise the vanes, may be de ^¬ tached externally from the outside of the turbine. Each vane unit in the stator may be individually detached from the stator mechanism and removed from the housing without disassembling other parts of the turbine. This is advantageous because the maintenance of the stator can be done in a short period of time. Also the replac ^¬ ing and repairing of the vane element or the whole vane unit is simple. This feature is useful, for example, in applications where the vanes are made of a ceramic ma ^¬ terial. The ceramic material in course of time may break or wear and it has to be replaced by a new part.

As each vane unit is individually detachable this ena- bles the monitoring of the condition of the stator mechanism. The stator mechanism may be regularly checked to determine the level of contamination inside the stator mechanism. One vane unit may be detached from the housing and inspected. This is useful because by detaching one vane unit the condition of the whole stator mechanism may be determined. Usually the contam- ination is equally spread among the vane units. The op ^¬ eration of the stator mechanism can be made more reliable by using the method described before as the condi ^¬ tion of the stator mechanism may be monitored during its lifetime. This may also enable preventing unex- pected shutdowns.

By using the structure disclosed before it may be pos ^¬ sible to have a longer service life for the stator mechanism than with the traditional structure. The ad- vantage of the structure of the stator mechanism is that the condition of the stator mechanism can be monitored during a very short shutdown. Further advantage is that the stator mechanism is easy to maintain thus providing also lower overall product service expenses.

The embodiments described herein may be used in any combination with each other. Several or at least two of the embodiments may be combined together to form a fur ^¬ ther embodiment. A method or a device may comprise at least one of the embodiments described hereinbefore.

It is to be understood that any of the above embodi ^¬ ments or modifications can be applied singly or in com ^¬ bination to the respective aspects to which they refer, unless they are explicitly stated as excluding alterna ^¬ tives

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to pro- vide a further understanding and constitute a part of this specification, illustrate various embodiments and together with the description help to explain the principles. In the drawings:

Figures la - Id are simplified example illustration of a stator mechanism;

Figure 2a - 2b is other simplified example illustration of a stator mechanism; Figure 3a is simplified example illustration of a piv ^¬ oting device of a stator mechanism;

Figure 3b is explosion view of a pivoting device of a stator mechanism;

Figure 3c - 3d is simplified example illustration of a pivoting member of a pivoting device;

Figure 4a - 4c is simplified example illustration of a vane unit;

Figure 5a - 5c is other simplified example illustration of a vane unit; Figure 5d is simplified example illustration of a vane unit, wherein the vane unit is illustrated as an explo ^¬ sive view;

Figure 6 is an example illustration of a lead-through ring;

Figure 7 is an example illustration of a lead-through ring and a counter-ring;

Figure 8 is a schematical example illustration of a turbine equipped with a stator mechanism; Figure 9 is other simplified example illustration of a stator mechanism having one vane unit illustrated as an explosive view; and Figure 10 is an illustration of a partial sectional view of a stator mechanism.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodi- ments, examples of which are illustrated in the accom ^¬ panying drawings .

Figure la illustrates one example of a stator mechanism 1 for a turbine (not illustrated in Figure la) . The turbine is disclosed later in Figure 8. The stator mechanism 1 comprises a cylindrical housing 3 which has a longitudinal center axis 30, wherein the cylindrical housing 3 comprises a plurality of holes 24 spaced at a distance from each other in the circumferential direc- tion of an outer periphery 25 of the cylindrical hous ^¬ ing 3. The stator mechanism 1 further comprises a plurality of vane units 5a, wherein at least one vane unit 5a is configured to be installed through each hole 24. The vane unit is disclosed in more detail in Figures 4a to 4c. The vane unit 5a goes through a lead-through ring 35. The lead-through ring 35 is disclosed in more detail in Figures 7 and 8. A vane 18 of the vane unit 5a is directed towards a counter-ring 34. The counter ring is disclosed in more detail in Figure 8. A hot me- dium inflow HMI is lead from a stator passage 64 to the stator mechanism 1. The hot medium inflow HMI may refer to any type of gas or gases.

Each vane unit 5a is individually detachable with an attaching member 6a. The vane units 5a are mounted on the outer periphery 25 of the cylindrical housing 3 close to each other. The shape of the vane 18 may vary but the vane 18 usually comprises a curved surface. Figure la discloses the stator mechanism 1 with non- adjustable vane units 5a equipped with non-adjustable vane elements 7a. Adjustable vane elements 7 are dis- cussed in more detail in Figures 5a to 5d.

The stator mechanism 1 is designed to have as much vane elements 7a as is required for optimal fluid-dynamic performance. The stator mechanism 1 may also be con- structed with adjustable vane elements 7. The stator mechanism 1 may have a similar structure in both embod ^¬ iments (with adjustable vane elements 7 and non- adjustable vane elements 7a) . When the structure of the stator mechanism 1 is wanted to be adjustable, only the non-adjustable vane units need to be changed into ad ^¬ justable vane units and adjusting means need to be add ^¬ ed to the stator mechanism 1.

Figure lb illustrates an enlargement of positions of the holes 24. Figure lb illustrates that the holes 24 are arranged around the cylindrical housing 3. The plu ^¬ rality of holes 24 are spaced at a distance from each other in the outer periphery 25 of the cylindrical housing 3. In Figure lb holes 24 are cylindrical through holes going through the cylindrical housing 3. The holes 24 are spaced at a fixed distance from each other and located symmetrically in the outer periphery 25 of the cylindrical housing 3. The midpoint of each hole 24 is located to a same sectional plane. Other ar- rangements of the holes 24 are also possible. Also the shape of the hole 24 may vary. For example, the shape of the hole 24 may be rectangular, triangular or oval (not illustrated) . In one example, the holes 24 may be arranged very close to each other so that outer periph- eries of the holes 24 tangent each other (not illus ^¬ trated) . There may also be other types of solutions for a hole pattern (not illustrated) available. In one so- lution the holes 24 may be arranged so that the center point of each hole 24 are not all located on a periph ^¬ ery in the same sectional plane (not illustrated) . Figure lc illustrates the stator mechanism 1 as a front view. Two cut out directions are indicated with arrows. For simplicity lc does not have all reference numbers as they are already indicated in Figure la. The vane unit 5a has a vane shaft 27a and a first end of the vane shaft 27a extends through the hole 24 inside the stator mechanism 1 towards the longitudinal center axis 30. The vane 18 has been arranged to the first end of the vane shaft 27a. Figure Id illustrates an enlarged view of one of the cut-outs. Figure Id illustrates that the vane unit 5a is arranged through the hole 24 with the attaching member 6a. The vane unit 5a is sealed to the hole 24 with a first seal 46 of the attaching member 6a.

Figure le illustrates an enlarged view of another cut out. To have a substantially large amount of vane ele ^¬ ments 7a in the stator mechanism 1, in these examples 45 pes, the vane element 7, 7a and the vane 18 has to be constructed in a special way. It may be preferred that the vane 18 would be arranged symmetrically in the middle of the first end of the vane shaft 27, 27a. The vane 18 has a maximum transverse dimension 12, wherein for optimal fluid-dynamic performance the maximum transverse dimension 12 is larger than a distance be ^¬ tween two center points of rotation 29 of two vane shafts 27, 27a. The shape of the cross section of the vane 18 resembles to a cross section of for example an aeroplane wing. The maximum transverse dimension 12 is a dimension from a leading edge 39 of the vane 18 to a trailing end 40 of the vane 18, which is indicated with a dash-dot line in Figure le. In another embodiment of Figure le, it is also possible to use adjustable vane elements 7 having pivoting vane shafts 27 which both are discussed in more detail in Figure 5a to 5d. The purpose of the stator vanes in a turbine is to turn the flow at a specific angle and to accelerate the flow rate. This angle may be rather steep. When the flow moves in the axial direction, the angle is zero. When the flow then moves to the stator vanes and comes out, the flow angle can be for example approximately 70 de ^¬ grees, whereupon it takes a steep turn with the flow velocity increasing radically at the same time. A prob ^¬ lem has been that the vanes are too far from each other, whereby it is not possible to provide the above- described turn in the direction of the flow. When the vanes are too far from each other, the surface of the vane may become subject to a pressure load that is too heavy, the flow tends to lose its contact with the vane, and the turning angle will be smaller than what is desirable. There will also be losses, i.e. so-called non-contacting flow, in the turbine if the turning angle of the flow is smaller than intended and losses oc ^¬ cur reducing the turbine performance and efficiency. The optimum vane density may be provided when the maxi- mum transverse dimension (12) is larger than a distance between two center points of rotation (29) of two neighboring vane shafts (27) . The vanes are designed in such a way that they provide just the right turn in the flow without the flow losing its contact. It is benefi- cial to keep the flow in contact with the vanes so that there will be no wake from the flow that has lost con ^¬ tact. With this feature the turning of the flow may be optimal in a way that the flow is not detached. It is preferable to keep the flow in contact to the vanes in order to have the above mentioned optimal fluid dynamic performance . Figure 2a illustrates a stator mechanism 1 with adjust ^¬ able vane units 5 equipped with adjustable vane ele ^¬ ments 7. The stator mechanism 1 in Figure 2a is otherwise similar to the one in Figure la. The only differ- ence is that the non-adjustable vane unit 5a is re ^¬ placed by the adjustable vane unit 5 and that an ad ^¬ justing mechanism 4 is also used. The adjusting of an angle of rotation of the vane element 7 with the ad ^¬ justing mechanism 4 enables the adjusting of the intake capability of the turbine 2. The adjusting mechanism 4 is arranged to adjust an angle of rotation of the vane element 7, wherein the vane element 7 is pivotally con ^¬ nected to the attaching member 6 at a second end of a vane shaft 27 extending outside the cylindrical housing 3 for pivoting the vane element 7 with the adjusting mechanism 4. The vane unit 5 is illustrated later in detail in Figures 5a to 5d.

For example, in one embodiment the features above ena- ble the adjusting of the intake-capability in a turbine 2. The intake capability of the turbine 2 can be ad ^¬ justed by adjusting directly the area of the openings where the flow leaves the stator vanes and enters the rotor blades of the turbine 2.

The stator mechanism 1 further comprises a connection piece 8 which comprises a first end and a second end, wherein the connection piece 8 connects the vane ele ^¬ ment 7 to the adjusting mechanism 4 for pivoting the vane element 7 with respect to the attaching member 6 with the adjusting mechanism 4 via the connection piece 8. The connection piece 8 is detachably and non- rotatably connected at the second end of the vane shaft 27 at the first end of the connection piece 8. The ad- justing mechanism 4 comprises a control ring 22, where ^¬ in the second end of the connection piece 8 is attached to the control ring 22. The control ring 22 has a plu- rality of through holes 41 spaced at a distance from each other in the circumferential direction of the control ring 22. The connection pieces 8 are connected to the through holes 41 by joints (not illustrated), wherein the connection piece 8 function as a crank. The joints may be sleeve bearings, which are locked to the through holes 41 with a retaining ring or similar type of device. The connection piece 8 and the joint are fitted together in such a way that connection piece 8 may be moved axially in the through hole 41. The stator mechanism 1 is arranged e.g. with three bearings 42 ar ^¬ ranged to an inner periphery 45 of the control ring 22, wherein the bearings 42 functions as support wheels, which enables the rotation of the control ring 22. Each bearing 42 is equipped with a pair of sliding elements 44 to keep the inner periphery 45 of the control ring 22 on an outer surface 11 of the bearing 42. Each bearing 42 is axially fixed to the cylindrical housing 3. Figure 2b illustrates an enlargement of the position of the holes 24. Figure 2b illustrates that the holes 24 are arranged around the cylindrical housing 3.

Figure 3a is an example illustration of a pivoting de- vice 23. For simplicity some reference numbers are left out from Figure 3a as they are already described be ^¬ fore. The adjusting mechanism 4 comprises the pivoting device 23, which pivots the control ring 22 and adjusts the angle of rotation of the vane element 7 via the connection piece 8. The pivoting of the control ring 22 is provided by the pivoting device 23, which is equipped with a pivoting member 43. By turning a hexagon head 53 in the pivoting member 43 the turning of the control ring 22 is enabled. This leads to turning of the vane element 7 and the vane 18 via the connec ^¬ tion piece 8. The first end of the connection piece 8 is connected to the vane shaft 27 and the second end is pivoted to the control ring 22. The hexagon head 53 is arranged to an indicating plate 58. By turning the hex ^¬ agon head 53 also the indicating plate 58 turns. By reading the indicating plate 58 the angle of rotation of the vane 18 may be determined. The indicating plate 58 has a first stamping 59, which indicates the posi ^¬ tion of the vane 18.

The pivoting of the parts in the pivoting device 23 is indicated with arrows. For example, if the vane element 7 in the vane unit 5 is needed to be pivoted anti ^¬ clockwise in Figure 3a the function is following:

- The hexagon head 53 is turned clockwise,

- Same time the control ring 22 pivots clockwise in the direction indicated with a dash-dot arrow,

- This pivots the connection piece 8 into same di ^¬ rection and simultaneously pivoting the vane ele ^¬ ment 7 anti-clockwise.

The clockwise pivoting of the vane element 7 in the vane unit 5 is opposite to the operation what is ex ^¬ plained above.

Figure 3b is an explosion view of the pivoting device 23. For simplicity some reference numbers are left out from Figure 3b as they are already described before. The pivoting device 23 comprises a bracket 54. The bracket 54 is non-rotatably fixed into the turbine 2. The bracket 54 comprises a cylindrical hole 55. The pivoting member 43 is equipped with a second bearing 21, which is fixed inside the cylindrical hole 55. The bracket 54 comprises a second stamping 61, from which the angle of rotation of the vane 18 may be determined. The indicating plate 58 comprises a cut-out groove 60, which enables to show the first stamping 59 from the bracket 54 through the indicating plate 58. The first stamping 59 functions as a pointer pointing towards the second stamping 61 and indicating how much the vane 18 is pivoted and whether the vanes 18 are open or shut .

Figures 3c and 3d provide an example illustration of the pivoting member 43. The pivoting member 43 comprises a cylinder 57, which is extends from the indicator plate 58 and is concentric with the hexagon head 53. The second bearing 21 is fixed around the cylinder 57. The pivoting member 43 comprises a pivoting pin 56, whose first end is eccentrically arranged with the cyl ^¬ inder 57.

The control ring 22 comprises a second groove 62 on the side of the control ring 22, where to a second end of the pivoting pin 56 is arranged. By turning the hexagon head 53 the pivoting pin 56 pivots as it is connected to the second bearing 21. As the pivoting pin 56 is connected to the second groove 62 the pivoting of the control ring 22 is enabled.

There may be also other ways to construct the mechanism for the pivoting device 23. Other arrangements for piv ^¬ oting member 43 are also possible. One example is to arrange the inner periphery 45 of the control ring 22 with a gearing. The control member may be a gear, which is connected to the gearing. By pivoting a shaft of the gear the control ring may be pivoted. The turning of ring 22 may, naturally, be arranged also with different kind of motorized devices having an electric feedback of the vane position.

Figure 4a to 4c and 5a to 5c illustrate two examples of vane units 5a, 5. The vane unit 5a as illustrated in Figure 4a to 4c is the non-adjustable vane unit 5a. The vane unit 5 as illustrated in Figure 5a to 5c is the adjustable vane unit 5. The vane unit 5, 5a further comprises the vane element 7, 7a comprising a vane shaft 27, 27a and the vane 18, wherein a first end of the vane shaft 27, 27a extends through the hole 24 in ^¬ side the stator mechanism 1 towards the longitudinal center axis 30, and wherein the vane 18 has been ar- ranged at the first end of the vane shaft 27, 27a. The vane unit 5, 5a further comprises the attaching member

6, 6a configured to detachably attach the vane element

7, 7a to the outer periphery 25 of the cylindrical housing 3. This enables extracting of the vane element 7, 7a out of the hole 24 with the attaching member 6, 6a. The vane element 7a illustrated in Figures 4a to 4c is arranged in a fixed position and fixedly arranged to the attaching member 6a. The vane element 7 illustrated in Figures 5a to 5c is pivotally arranged with the at- taching member 6.

The attaching member 6a further comprises at least one inlet 9 to conduct air inside the vane unit 5a. The vane unit 5a comprises a channel 31 in the vane shaft 27a, where to the air or steam is conducted from the inlet 9. The air or steam is conducted through the vane shaft 27a to the vane 18 via the channel 31. The air or steam is substantially clean and cool, which enables to prevent or reduce formation of a sticky solid, such as carbon, on the surfaces of the vane 18 by preventing a hot and contaminated gas being in contact with the vane unit 5a and the vane 18. The air or steam has a higher pressure than the gas in the stator passage 64 in prox ^¬ imity to vanes 18. In the proximity to vanes 18 means a location of the gas being at a distance maximum 50 mm from the vanes 18 towards the flow direction.

In the example of the vane unit 5a in Figures 4a to 4c the vane shaft 27a and the vane 18 do not pivot. In this example the vane shaft 27a, attachment member 6a, vane element 7a and the vane 18 are all integrated to ^¬ gether as a single part. The position of the vane 18 may be fixed to a certain fixed angle for example by fixing the vane unit 5a to the cylindrical housing 3 to the certain fixed angle. The attaching member 6 comprises a sleeve 10 extending in the hole 24 and having a maximum outer diameter 13 that is larger than a maximum transverse dimension 12 of the vane 18. The sleeve 10 is arranged to be in cylindrical housing 3 inside the hole 24. This is enabled by the first seal 46. The attaching member 6a comprises a fixing flange 32 for attaching the attaching member 6 to the outer periphery 25 of the cylindrical housing 3.

The vane unit 5 illustrated in Figure 5a to 5c is an adjustable vane unit 5, wherein the vane element 7 is pivoted inside the attaching member 6. The attaching member 6 further comprises at least one inlet 9 to con ^¬ duct air or steam inside the vane unit 5. The vane unit 5 comprises a clearance 19, which is arranged between the attaching member 6 and the vane shaft 27, where to the air or steam is conducted from the inlet 9. The air or steam is substantially clean and cool, which enables to prevent or reduce formation of sticky solid, such as carbon formation, in the vane unit 5 by preventing a hot and contaminated gas or steam entering inside the vane element 7. The air or steam is in a higher pres ^¬ sure than the pressure of the gas in the stator passage 64 in the proximity to vanes 18. In the proximity to vanes 18 means a location of the gas being at a dis ^¬ tance maximum 50 mm from the vanes 18 towards the flow direction.

The vane element 7 pivots inside the attaching member 6. The attaching member 6 comprises a sleeve 10 extend ^¬ ing in the hole 24 and having a maximum outer diameter 13 that is larger than a maximum transverse dimension 12 of the vane 18. The sleeve 10 is arranged to be sealed towards the cylindrical housing 3. This is ena- bled by the first seal 46. The attaching member 6 com ^¬ prises a fixing flange 32 for attaching the attaching member 6 to the outer periphery 25 of the cylindrical housing 3.

The attaching member 6 comprises a hollow shaft 14 extending from the sleeve 10 inside the cylindrical hous ^¬ ing 3, wherein the hollow shaft 14 has another maximum outer diameter 15 that is smaller than the maximum out- er diameter 13 of the sleeve 10. The hollow shaft 14 further comprises at least one inlet 9 for supplying air or steam inside the vane unit 5. The vane shaft 27 comprises a first shaft portion 16 and a second shaft portion 17, wherein the first shaft portion 16 is ar- ranged partially inside the hollow shaft 14 and the second shaft portion 17 is arranged partially inside the sleeve 10 and partially outside the sleeve 10, wherein the second shaft portion 17 extends partially outside the cylindrical housing 3. The clearance 19 is arranged between the attaching member 6 and the first shaft portion 16, where to the air or steam is conduct ^¬ ed from the inlet 9.

One solution is also to make the structure of the at- taching member 6, 6a with more than one vane elements 7, 7a. For example, the attaching member 6, 6a may have two vane elements 7, 7a integrated to the same attach ^¬ ing member. In this case the hole 24 may have to be wider, for example, having an oval or rectangular shape. Also a mounting surface of the attaching member 6, 6a may have to be arranged arched in order to be sealed properly. This is not illustrated as the solu ^¬ tion may be described for example by combining two at ^¬ taching members 6, 6a together.

The connection piece 8 comprises a fork-like structure 49, which is detachably and non-rotatably connected to the second shaft portion 17. The second shaft portion 17 comprises a first fixing hole 36 for attaching the fork-like structure 49 to the second shaft portion 17. The vane unit comprises a fixing pin 37 for attaching the fork-like structure 49 to the second shaft portion 17 through the first fixing hole 36. The attaching member comprises a second seal 63, which seals the vane shaft 27 to the attaching member 6. The second seal 63 is arranged around the second shaft portion 17.

Figures 4a to 4c and 5a to 5c illustrate that the vane unit 5, 5a is provided with two fixing elements 33 for fixing the fixing flange 32 to the outer periphery 25 of the cylindrical housing 3. The fixing flange 32 com- prises two second fixing holes 38 for the fixing ele ^¬ ment 33. The vane unit 5, 5a is equipped with at least one spring 20 between the fixing flange 32 and the fixing element 33 to press the vane element 7, 7a essen ^¬ tially towards the longitudinal center axis 30 for ena- bling a sealing effect of the vane 18.

Figure 5d is a simplified example illustration of the vane unit 5, wherein the vane unit 5 is illustrated as an explosive view. Figure 5d discloses the disassem- bling of the vane unit 5. The vane element 7 may be ex ^¬ tracted from the attaching member 6. The vane unit 5 may be detached from the cylindrical housing 3 by un ^¬ screwing the fixing elements 33 from the second fixing holes 38. The connection piece 8 is detached from the vane shaft 27 by detaching the fixing pin 37 from the first fixing hole 36. The example illustrated in Figure 5d also discloses clearly the different structural parts of the vane element 7 (the vane shaft 27, the first shaft portion 16, the second shaft portion 17 and the vane 18 and their locations) . Figure 6 is an example of a lead-through ring 35. As disclosed in Figures la and 2a the lead-through ring 35 is arranged to lead through the attaching member 6, 6a and the vane 18. To the end of the hollow shaft 14 there is provided a support element 47. The cross sec ^¬ tion of the support element 47 is configured to be sub ^¬ stantially elliptic. The cross section of the support element 47 may not exactly match to a geometrical el ^¬ lipsis. The attaching member 6, 6a is supported towards the lead-through ring 35 from a lead-through hole 48. The lead-through ring 35 comprises a plurality of these lead-through holes 48, one for each vane unit 5, 5a. The lead-through hole 48 has the same shape as the sup ^¬ port element 47 which enables to keep the attaching member 6 firmly in-place and which prevents excessive leakage of air or steam from the pressurized chamber 65.

Figure 7 illustrates the counter-ring 34 inside the lead-through ring 35. On outer periphery of the counter-ring 34 there is provided a plurality of counter elements 50, which enables the sealing of the vane 18. The end of the vane 18 is sealed towards the counter element 50. The counter element 50 comprises a flat face.

Figure 8 is a schematical example illustration of a turbine 2 equipped with a stator mechanism 1. All the parts in the turbine 2 except the stator mechanism 1 are indicated with dash-dot lines. A rotor disc 28 is mounted to a rotating shaft 51. The stator mechanism 1, being stationary, has common axis of symmetry with the shaft 51. The maintenance of the rotor disc 28 may be done by detaching a pipe housing 52 from the turbine 2. But the maintenance of the vane units 5, 5a and the vanes 7, 7a is not possible if the vanes 18 are not de ^¬ tachable from the outside of the cylindrical housing 3. The arrow in Figure 8 represents the hot medium inflow HMI which is leaded to the stator mechanism 1 from the stator passage 64. The vane units 5, 5a and the vanes 18 are arranged into the stator mechanism 1, which is located behind the rotor disc 28. In order to reach to the stator mechanism 1 in the traditional structure the rotor disc 28 must be dismantled from the rotating shaft 51, which means that the whole turbine 2 has to be detached from the application. When the vane units 5, 5a may be reached outside the cylindrical housing 3 the dismantling of the turbine 2 is not necessary.

The vane unit 5 is detachably attached to an outer pe ^¬ riphery 25 of the cylindrical housing 3 for extracting the vane unit 7, 7a inside the housing 3 from the out ^¬ side of the housing 3 without an essential need to dis ^¬ mantle any other part in the turbine 2. The vane unit 5 is constructed as a cartridge-like structure, which en ^¬ ables pulling the vane unit 5, 5a outwards from the stator mechanism 1 by detaching only that part of the vane unit 5, 5a which is attached outside of the hous ^¬ ing 3. The vane unit 5, 5a is constructed as a car ^¬ tridge-like structure, which enables keeping the rest of the parts in the turbine 2 in-place while detaching the vane unit 5, 5a.

The stator mechanism 1 of a turbine 2 may be contaminated and/or the vanes 18 may wear. In the traditional structure of a stator mechanism the vanes 18 are con- structed in a way that the detaching of the vanes 18 is difficult. For example generally in a gas turbine the turbine-portion of the machine is located between a combustion chamber and an exhaust piping or a recuperator. Generally in a turbocharger the turbine-portion is located between a compressor and exhaust pipe. General ^¬ ly in a geothermal turbine the turbine-portion is lo ^¬ cated between a main steam line and a condensate line. The detaching of the turbine 2 from the application in order to make maintenance procedures is a big and is expensive task, which requires lots of work. Essential parts of the application have to be detached from the turbine 2 in order to make the maintenance. Especially in a ship in a marine application the detaching of the heavy turbine 2 is particularly hard as the ship may sway back and forth. Further, after detaching the turbine 2 the cleaning of the stator mechanism 1 requires usually that the rotor disc 28 is detached. This procedure may require a lot of effort as the rotor disc 28 is usually connected to the rotating shaft 51 with a tight interference fit. Detaching this interference fit may require that the common shaft 51 is cooled with liquid nitrogen and the rotor disc 28 is heated with induction heating. This type of procedure is complicated and expensive. Figure 9 illustrates a partial explosive view of a sta ^¬ tor mechanism 1 where one vane unit 5 is detached from the stator mechanism 1. For simplicity some reference numbers are left out from Figure 9. The maintenance of the stator mechanism 1 may be done by a method of maintenance of a stator mechanism 1 of a turbine 2, the stator mechanism 1 comprising a cylindrical housing 3, comprising a plurality of holes 24 spaced a distance from each other in an outer periphery 25 of the cylindrical housing 3. The maintenance of the stator mecha- nism 1 comprising a plurality of vane units 5, 5a which are arranged to the holes 24, is made by detaching at least one vane unit 5, 5a out from at least one hole 24 from the outer periphery 25 of the cylindrical housing 3. Each vane unit 5, 5a is individually detached ena- bling at least one of repairing of each vane unit 5, 5a and checking the contamination of the stator mechanism 1 from at least one detached vane unit 5, 5a. This ena- bles that the condition of the stator mechanism 1 may be monitored during the life-time of the product.

The structure as described before provides significant cost savings because the structure enables that each vane unit 5, 5a may be individually detached from the turbine 2 for maintenance and inspection in such a way that the detaching of the turbine 2 from the process, where it is intended to operate, is not needed. Also the essential parts of the turbine 2 may not be needed to be dismantled in order to make the maintenance for the vane unit 5, 5a and the vanes 18.

Figure 10 illustrates a partial sectional view of the stator mechanism 1 disclosed in Figure 2a. Figure 10 illustrates the adjustable vane unit 5 inside the sta ^¬ tor mechanism 1 and the sealing locations inside the stator mechanism 1. It also discloses how the vane unit 5 functions in case of thermal expansion of the attach- ing member 6.

There are five places where sealing is enabled in the vane unit 5. A first sealing location A seals a sleeve 10 to a hole 24 with a first seal 46. A second sealing location B is arranged between a support element 47 and a lead-through hole 48. A third sealing location C is arranged between a vane 18 and a hollow shaft 14. A fourth sealing location D is arranged between a flat face of a counter element 50 and the vane 18. A fifth sealing location E seals a gap between a second shaft portion 17 and a fixing flange 32 with a second seal 63.

Springs 20 press an attaching member 6 which presses the vane 18 towards the flat face of the counter ele- ment 50. The springs 20 press the fixing flange 32 downwards and the hollow shaft 14 presses the vane 18 towards the counter-ring 34. This prevents the by-pass of the hot medium inflow HMI . The attaching member 6, being in-contact with a hot medium inflow HMI, expands axially in the hole 24 because of thermal expansion. Also the vane 18 expands because it is in contact with the hot medium inflow HMI. Because of these expansions, the attaching member 6 must be attached to the hole 24 in a way that axially sliding of the attaching member 6 in the hole 24 is possible. This sliding feature is in ^¬ dicated with double sided arrow. This is enabled by the sliding of the sleeve 10 in the hole 24 and the sliding of the support element 47 inside the lead-through hole 48. A fixing element 33 comprises a screw head 26, wherein the screw head 26 is arranged at a distance above the fixing flange 32 enabling an axial movement of the attaching member 6 along the fixing element 33 as an effect of thermal expansion. The distance between a mounting face 66 of the screw head 26 and an outer face 67 of the fixing flange 32 enables this expansion. The spring 20 is mounted between the mounting face 66 and the outer face 67. The fixing element 33 and a fix ^¬ ing hole 38 of the fixing flange 32 functions as a guide, wherein a shaft of the fixing element 33 guides the attaching member 6 along the fixing element 33. The shaft of the fixing element 33 is inside the fixing hole 38. The spring 20 compresses when the attaching member 6 expands .

The springs 20 also create a sealing effect in a way that on the third sealing location C and on the fourth sealing location D the by-pass flow is restricted. The sliding of the attaching member 6 along the fixing elements 33 is advantageous because it prevents the block ^¬ ing of the vane 18 between the hollow shaft 14 and the counter element 50. Without this feature the adjustment of the vane 18 would not be possible in case of thermal expansion . The stator mechanism 1 comprises a pressurized chamber 65 for supplying air or steam inside the vane unit 5 from an inlet 9 and further to a clearance 19. This is represented with an arrow. Air or steam, which is sub- stantially clean, is conducted from the pressurized chamber 65 to the vane unit 5. Substantially clean means that most parts of the air or steam do not con ^¬ tain contaminating particles. The cleanliness level is not defined but normal indoor air or air, which is suitable for pneumatic systems, are possible examples. The first seal 46 and the second seal 63 enables to keep the air or steam inside the pressurized chamber 65. The first seal 46 and the second seal 63 may be, for example O-rings. The clean air or steam is pressur- ized with a higher pressure than a pressure of the hot medium inflow HMI in proximity to vanes 18. The proximity to vanes 18 means a distance below 50 mm from the vanes 18 towards the flow direction. This prevents the hot medium inflow HMI to enter inside the vane unit 5 and prevents it from blocking the vane unit 5. The air or steam is bled out from the second sealing location B and the third sealing location C and further towards the hot medium inflow HMI. The air or steam also bleeds between the support element 47 and the lead-through hole 48 keeping the vane unit 5 detachable. The support element 47 is constructed so that the detaching of the vane unit is possible in both extreme positions; vanes 18 shut and vanes 18 open. The cross section of the support element 47 is so large that the vane 18 is lim- ited inside the cross section in both extreme posi ^¬ tions. This determines the shape of the support element 47. The shape of the support element 47 may be substan ^¬ tially oval or elliptic. It is obvious to a person skilled in the art that with the advancement of technology, the basic idea may be implemented in various ways. The solution and its em- bodiments are thus not limited to the examples de ^¬ scribed above, instead they may vary within the scope of the claims.

The embodiments described herein may be used in any combination with each other. Several or at least two of the embodiments may be combined together to form a fur ^¬ ther embodiment. A method or a device may comprise at least one of the embodiments described hereinbefore.

It is to be understood that any of the above embodi ^¬ ments or modifications can be applied singly or in com ^¬ bination to the respective aspects to which they refer, unless they are explicitly stated as excluding alterna ^¬ tives .