Patent Application
20210222582
The present disclosure relates to vane and shroud arrangement for positioning at a gas inlet of a turbo-machine such as a turbo-charger.
Turbochargers are well-known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to the inlet manifold of the engine, thereby increasing engine power. The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housing.
In known turbochargers, the turbine stage comprises a turbine chamber within which the turbine wheel is mounted; an annular inlet passageway defined between facing radial walls arranged around the turbine chamber; an inlet arranged around the inlet passageway; and an outlet passageway extending axially from the turbine chamber. The passageways and chambers communicate such that pressurised exhaust gas admitted to the inlet chamber flows through the inlet passageway to the outlet passageway via the turbine and rotates the turbine wheel.
It is known to improve turbine performance by providing vanes, referred to as nozzle vanes, in the inlet passageway so as to deflect gas flowing through the inlet passageway towards the direction of rotation of the turbine wheel. Each vane is generally laminar, and is positioned with one radially outer surface arranged to oppose the motion of the exhaust gas within the inlet passageway, i.e. the radially inward component of the motion of the exhaust gas in the inlet passageway is such as to direct the exhaust gas against the outer surface of the vane, and it is then redirected into a circumferential motion.
Turbines may be of a fixed or variable geometry type. Variable geometry type turbines differ from fixed geometry turbines in that the geometry of the inlet passageway can be varied to optimise gas flow velocities over a range of mass flow rates so that the power output of the turbine can be varied to suit varying engine demands.
In one form of a variable geometry turbocharger, a nozzle ring carries a plurality of axially extending vanes, which extend into the air inlet, and through respective apertures (“slots”) in a shroud which forms a radially-extending wall of the air inlet. The nozzle ring is axially movable by an actuator to control the width of the air passage. Movement of the nozzle ring also controls the degree to which the vanes project through the respective slots.
An example of such a variable geometry turbocharger is shown in
Gas flowing from the inlet chamber 2 to the outlet passageway 3 passes over a turbine wheel 9 and as a result torque is applied to a turbocharger shaft 10 supported by a bearing assembly 14 that drives a compressor wheel 11. Rotation of the compressor wheel 11 about rotational axis 100 pressurizes ambient air present in an air inlet 12 and delivers the pressurized air to an air outlet 13 from which it is fed to an internal combustion engine (not shown). The speed of the turbine wheel 9 is dependent upon the velocity of the gas passing through the annular inlet passageway 4. For a fixed rate of mass of gas flowing into the inlet passageway, the gas velocity is a function of the width of the inlet passageway 4, the width being adjustable by controlling the axial position of the nozzle ring 5. As the width of the inlet passageway 4 is reduced, the velocity of the gas passing through it increases.
The nozzle ring 5 supports an array of circumferentially and equally spaced vanes 7, each of which extends across the inlet passageway 4. The vanes 7 are orientated to deflect gas flowing through the inlet passageway 4 towards the direction of rotation of the turbine wheel 9. When the nozzle ring 5 is proximate to the annular shroud 6 and to the facing wall, the vanes 7 project through suitably configured slots in the shroud 6 and into the recess 8. Each vane has an “inner” major surface which is closer to the rotational axis 100, and an “outer” major surface which is further away. Both the nozzle ring 5 and the shroud 6 are at a fixed angular position about the axis 100. The vanes 7 are illustrated in
A pneumatically or hydraulically operated actuator 16 is operable to control the axial position of the nozzle ring 5 within an annular cavity 19 defined by a portion 26 of the turbine housing via an actuator output shaft (not shown), which is linked to a stirrup member (not shown). The stirrup member in turn engages axially extending guide rods (not shown) that support the nozzle ring 5. Accordingly, by appropriate control of the actuator 16 the axial position of the guide rods and thus of the nozzle ring 5 can be controlled. It will be appreciated that electrically operated actuators could be used in place of a pneumatically or hydraulically operated actuator 16.
The nozzle ring 5 has axially extending inner and outer annular flanges 17 and 18 respectively that extend into the annular cavity 19, which is separated by a wall 27 from a chamber 15. Inner and outer sealing rings 20 and 21, respectively, are provided to seal the nozzle ring 5 with respect to inner and outer annular surfaces of the annular cavity 19, while allowing the nozzle ring 5 to slide within the annular cavity 19. The inner sealing ring 20 is supported within an annular groove 22 formed in the inner surface of the cavity 19 and bears against the inner annular flange 17 of the nozzle ring 5, whereas the outer sealing ring 21 is supported within an annular groove 23 provided within the annular flange 18 of the nozzle ring 5 and bears against the radially outermost internal surface of the cavity 19. It will be appreciated that the inner sealing ring 20 could be mounted in an annular groove in the flange 17 rather than as shown, and/or that the outer sealing ring 21 could be mounted within an annular groove provided within the outer surface of the cavity rather than as shown. A first set of pressure balance apertures 25 is provided in the nozzle ring 5 within the vane passage defined between adjacent apertures, while a second set of pressure balance apertures 24 are provided in the nozzle ring 5 outside the radius of the nozzle vane passage.
Note that in other known turbomachines, the nozzle ring is axially fixed and an actuator is instead provided for translating the shroud in a direction parallel to the rotational axis. This is known as a “moving shroud” arrangement.
In known variable geometry turbo-machines which employ vanes projecting through slots in a shroud, a clearance is provided between the vanes and the edges of the slots to permit thermal expansion of the vanes as the turbocharger becomes hotter. As viewed in the axial direction, the vanes and the slots have the same shape, but the vanes are smaller than the slots. In a typical arrangement, the vanes are positioned with an axial centre line of each vane in a centre of the corresponding slot, such that in all directions away from the centre line transverse to the axis of the turbine, the distance from the centre line to the surface of the vane is the same proportion of the distance from the centre line to the edge of the corresponding slot. The clearance between the vanes and the slots is generally arranged to be at least about 0.5% of the distance of a centre of the vanes from the rotational axis (the “nozzle radius”) at room temperature (which is here defined as 20 degrees Celsius) around the entire periphery of the vane (for example, for a nozzle radius of 46.5 mm the clearance may be 0.23 mm, or 0.5% of the nozzle radius). This means that, if each of the vanes gradually thermally expands perpendicular to the axial direction, all points around the periphery of the vane would touch a corresponding point on the slot at the same moment. At all lower temperatures, there is a clearance between the entire periphery of the vane and the edge of the corresponding slot.
The present disclosure aims to provide new and useful vane and shroud assemblies for use in a turbo-machine, as well as new and useful turbo-machines (especially turbo-chargers) incorporating the vane assemblies.
In an earlier patent application (GB 1619347.6, which was unpublished at the priority date of the present application), the present applicant proposed that in the turbine of a turbomachine of the kind in which, at a gas inlet between a nozzle ring and a shroud, vanes project from the nozzle through slots in the shroud, one “conformal” portion of a lateral (i.e. transverse to the rotational axis) surface of each vane substantially conforms to the shape of a corresponding “conformal” portion of a lateral surface of the corresponding slot, so as to enable the respective conformal portions of the surfaces to be placed relative to each other with only a small clearance between them. An advantage of this is that gas flow between the respective conformal portions of the surfaces of the vane and the slot can be substantially reduced. This reduces leakage of gas into or out of a recess on the other side of the shroud from the nozzle ring. Such leakage reduces the circumferential redirection of the gas caused by the vanes, and has been found to cause significant losses in efficiency.
Although this proposal represents a significant technical improvement to turbine technology, the present inventors have discovered that in practice its advantages may not be entirely realised. Firstly, the formation of the vanes and slots is subject to tolerances, so that exact conformity between the vane and slot may not be possible. Secondly, after the turbocharger has been in use for some time, the vanes are subject to foreign object damage (FOD) due to debris in the exhaust gas, which reduces the quality of the conformity between the shapes of the vanes and the slots.
In general terms, the present disclosure proposes that the vanes and slots are formed and arranged such that there is contact between them at a leading surface portion of the vane. Away from the leading surface portion, towards the trailing edge of the vane, the vane and slot include respective trailing portions which are spaced apart, such as by a substantially constant amount, and arranged to conform in shape with each other.
The disclosure is motivated by an observation by the inventors that the FOD damage is typically not present in a leading portion of the radially inner surface of the vane, so it should be possible to realise high quality contact in that area between the vane and the edge of the slot. However, if the trailing portion of the vane is designed to be very close to the edge of the slot, then a small amount of FOD damage there, or imperfections in that portion of the vane or slot, can lead to the leading portion of the vane being disadvantageously spaced from the slot edge. By forming the trailing portion of the vane spaced from the slot edge, this effect can be mitigated.
Forming the trailing portion of the slot and vane surfaces can be regarded as analogous to a relief cut using in mechanical cutting of objects, which reduces the risk of the cutting being impeded due to portions of the object distant from where the cutting is occurring.
Furthermore, arranging for the vane and slot to be spaced apart in their respective trailing portions, can reduce the chance of the vane becoming trapped against the slot due to a thermal transient. This is because differential thermal expansion of the trailing portions of the nozzle and slot is less likely to cause them to impact each other, even if it causes the gap between them to decrease.
A specific expression of the disclosure is a turbine comprising:
This spacing provides an effective trade-off between a low spacing, which would reduce gas leaking between the trailing portions, and a high spacing, which would reduce the tendency of imperfections in the trailing portions of the inner vane inner and slot surface to cause those surfaces to meet.
Preferably, at room temperature, the respective profiles of the trailing surface portion of the vane surface and the trailing surface portion of the slot surface diverge from each other by no more than 30 microns, 20 microns or even 10 microns (for a 48.1 mm nozzle radius these correspond to 0.05%, 0.04%, or even 0.02% of the nozzle radius).
The conformity of the trailing surface portions of the vane surface and slot surface may mean that each point on the trailing surface portion of the vane is spaced from a corresponding respective point on the slot inner surface by a distance which is in the range 0.1%-0.3% of the nozzle radius. For a 48.1 mm nozzle radius, this would be a distance range of about 0.05 mm to 0.15 mm.
In a first case, the leading surface portion of the vane may be short (e.g. no more than 5% of the length of the median line), or even a point contact. This may have the advantage of minimising the risk of the vane becoming trapped against the slot due to a thermal transient, since the size of the region in which they approach each other is small.
In a second case, the leading surface portion of the vane may be longer (e.g. extending along at least 15% of the length of the median line). The length of the leading surface portion may for example differ by less than 10% from 100% minus the percentage of the median line along which the trailing surface portion of the vane inner surface extends. The leading surface portion of the vane may be arranged to conform closely with the shape of the leading surface portion of the corresponding slot. They may designed to have exactly the same shape. In practice, however, due to machining tolerances, the respective profiles of the leading surface portion of the vane surface and the corresponding leading surface portion of the respective slot surface may diverge from each other by an amount in the range 1 micron to 50 microns, or more preferably 1 micron to 25 microns. The divergence is preferably less than the minimum spacing of the trailing portions of the vane inner surface and slot surface.
The leading surface portion of the vane surface may extend along 15-20% of the length of the median line, or 15-25% of the length of the median line.
The leading surface portion of the vane may include a point where the median line intercepts the leading edge of the vane. Indeed, when the leading surface portions of the vane surface and slot surface are in contact, the vane surface and slot surface may further contact each other at at least one point which is on the radially-outer surface of the vane.
The trailing portion of the vane surface may extend for at least 50%, at least 60% or at least 70% of the length of the median line.
In this document, the statement that the trailing surface portions of the vane inner surface and slot surface are spaced apart by a certain distance range means that the respective distance from each point in the trailing surface portion to the respective closest point of the trailing surface portion of the slot surface, is in that range. The statement refers to the portion of the vane inner surface which is in axial register with the slot surface.
In this document the statement that two lines diverge from each other by no more than a certain distance x may be understood to mean that the lines can be placed such that the lines do not cross and such that no point along either one of the lines is further than a distance x from the other of the lines. The statement that the leading surface portion of the vane surface and the corresponding leading surface portion of the slot surface diverge from each other by no more than a certain distance x refers to the parts of the leading surface portion of the vane surface and the leading surface portion of the slot surface which are in axial register with each other, and which appear as respective lines when viewed in the axial direction. In such a view, these lines diverge from each other by no more than the distance x.
Preferably the turbine is of the sort in which the radially inner surfaces of the vane and slot are at a lower pressure than the radially outer ones.
The turbine may include a rotational mechanism for generating a rotational torque for urging the nozzle ring to rotate with respect to the shroud, in a sense which urges the respective leading surface portions of the vanes and slots together. In some arrangements, this rotational mechanism is simply the force exerted by the exhaust gas on the vanes.
Embodiments of the disclosure will now be described for the sake of example only, with reference to the following drawings in which:
Referring to
The axis of the shaft about which the turbine wheel 9 (not shown in
Viewed in this axial direction, the substantially-planar annular nozzle ring 5 encircles the axis 100. From the nozzle ring 5, vanes 7 project in the axial direction. Defining a circle 70 centred on the axis 100 and passing through the centroids of the profiles of the vanes 7, we can define the nozzle radius 71 as the radius of the circle 70. Gas moves radially inwardly in the gap between the nozzle ring 5 and the shroud 6.
The nozzle ring 5 is moved axially by an actuator 16 (not shown in
The actuator exerts a force on the nozzle ring 5 via two axially-extending guide rods. In
The location, as viewed in the axial direction, at which a second of the guide rods is connected to the nozzle ring 5 is shown as 31. The connection between the nozzle ring 5 and the second guide rod is due to a second bracket (not visible in
Holes 24, 25 are balance holes provided in the nozzle ring 5 for pressure equalisation. They are provided to achieve a desirable axial load (or force) on the nozzle ring 5.
Facing the nozzle ring 5, is the shroud 6 illustrated in
Specifically, the vane 7 has a vane inner surface 41 which is closer to the wheel. The vane inner surface 41 is typically generally concave as viewed in the axial direction, but may alternatively be planar. The vane 7 also has a vane outer surface 42 which is closer to the exhaust gas inlet of the turbine. Each of the vane inner and outer surfaces 41, 42 is a major surface of the vane. The vane outer surface 42 is typically convex as viewed in the axial direction, but may also be planar. The major surfaces 41, 42 of the vane 7 face in generally opposite directions, and are connected by two axially-extending end surfaces 43, 44 which, as viewed in the axial direction, each have smaller radii of curvature than either of the surfaces 41, 42. The end surfaces 43, 44 are referred to respectively as the leading edge surface 43 and the trailing edge surface 44.
In most arrangements, the vane outer surface 42 is arranged to oppose the motion of the exhaust gas the inlet passageway, i.e. the motion of the exhaust gas in the inlet passageway is such as to direct the exhaust gas against the vane outer surface. Thus, the vane outer surface 42 is typically at a higher pressure than the vane inner surface 41, and is referred to as the “high pressure” (or simply “pressure”) surface, while the vane inner surface 41 is referred to as the “low pressure” (or “suction”) surface. These oppose corresponding portions of the inwardly-facing surface which define the edge of the slot 30, and which are given the same respective names.
As viewed in the axial direction, each vane 7 has a median line 51 which extends from one end of the vane to the other (half way between the vane inner and outer surfaces 41, 42 when viewed in the axial direction), and this median line has both a radial and a circumferential component. We refer to the surface of the slot which the vane inner surface 41 faces as the slot inner surface 46, and the surface of the slot which the vane outer surface 42 faces as the slot outer surface 47. As shown in
In contrast to the known vanes of
To further this effect, the vane surface and slot surface are formed with a conformal portion 145 which extends along at least about 80% of the length of the median line 151. As illustrated in
If there is differential thermal expansion between the vanes 107 and the shroud (for example, because they are formed from different materials and/or experience different temperatures), the conformal portion of the vane 107 may be forced against the against the slot inner surface 146. Fictional force between them may then prevent axial motion of the vane relative to the shroud. However, there is a certain free play in the system (for example, due to the coupling of the nozzle ring 5 to the rods illustrated in
In the case of a nozzle ring of nozzle radius 48.1 mm, and with each of the vanes having a length of 23 mm (i.e. the length of the median line), the undamaged portion of the vane inner surface 141 has been found to extend for at least the first 4 mm of the length of the median line from the end of the median line at the leading edge 167 (i.e. 17% of the length of the vane). Between 4 mm and 5 mm there are some small impact craters and minor pitting. At all points further than 5 mm from the leading edge 167 of the vane 107a, the surface has the same condition. This effect is observed to be equal on all the vanes of the turbine. (Note that a computer simulation suggested at all FOD would be at least 5.5262 mm from the leading end 167, but this was found to be an over-estimate.)
Turning to
The embodiment is a turbine with a construction equal to that of the known system of
Firstly, in a leading surface portion 260 of the vane 207, the vane inner surface 241 and slot inner surface 246 closely conform to each other. In particular, they may be designed with exactly the same shape, but in practice diverge from each other by 1 micron to 50 microns, or more preferably 1 micron to 25 microns.
Secondly, when the vane inner surface 241 and slot inner surface 246 are in contact with each other in the leading portion 260, at all positions on the vane inner surface 241 which are closer towards the trailing edge 265 than the leading portion 260 (this set of positions is referred to as a “trailing surface portion” 266 of the vane inner surface 241), the vane inner surface 241 is spaced from the slot inner surface 246. The spacing in substantially all of the trailing surface portion 266 may be at least 0.05 mm, which, in the case of a nozzle ring with a nozzle radius of 48.1 mm, corresponds to about 0.1% of the nozzle radius. In practice, tolerances in the manufacture of the vane 207 or slot 230 can cause this spacing to be reduced. Furthermore, in use this spacing is reduced at isolated positions within the trailing surface portion 266 due to crater damage on the vane inner surface 241.
However, even if there is FOD in the trailing surface portion 266 which causes the surface of the vane inner surface 241 to be raised by a height of 0.05, this will not cause the vane inner surface 241 to impact the slot inner surface 246 in the trailing surface portion 266, and therefore will not cause the vane inner surface 241 to be spaced from the slot inner surface 246 in the leading surface portion 260.
Similarly, if, due to tolerances in the manufacture of the vane 207 and/or the slot 230, the inner surface 241 of the vane 207 in the trailing surface portion 266 happens to be deformed by a distance 0.05 mm in the direction toward the slot inner surface 246, this will not cause the vane inner surface 241 to impact the slot inner surface 246 in the trailing surface portion of the vane inner surface 241, so it will not cause the inner surface 241 to be spaced from the slot inner surface 246 in the leading surface portion 260. In practice the manufacturing tolerance of the vane 207 and slot 230 may be as high as 0.1 mm, so a spacing of 0.05 mm merely reduces the chance of the vane inner surface 241 being spaced from the slot inner surface 246 in the leading surface portion 260. For that reason, it may be preferred to provide a larger spacing between the vane inner surface 241 and the slot inner surface 246 in at least the majority of the trailing surface portion 266, such as a spacing of 0.1 mm.
The spacing between the vane inner surface 241 and the slot inner surface 246 in the trailing surface portion 266 has the further advantage of reducing the risk of the vane 207 becoming stuck to the shroud due to a thermal transient.
In
Turning to
From the point 3463 towards the leading edge 367 of the vane 307, the vane's leading edge surface 343 is spaced from the opposed corresponding portion 349 of the inner surface 346 of the slot 330. The distance of the contact point 3463 from the leading edge 367 of the vane may be less than 10% of the length of the median line, or even less than 5%. The contact between the vane 307 and the inner surface of the slot 330 extends along much less than 5% of the median line of the vane between its opposed major surfaces, such as along less than 1% of the length of the median line, or even 0.1% of the length of the median line.
Since the trailing surface portion 3461 of the slot inner surface 346 is spaced from the trailing surface portion 366 of the vane inner surface 341, imperfections on the trailing surface portions due to machining tolerances and/or due to FOD to the vane 307, do not cause the trailing surface portions to touch each other. Thus, there is no force developed between the trailing surface portions which separates the slot inner surface 346 and the vane inner surface 341 in their respective leading surface portions 368, 3462, such that contact at the contact point 3463 is lost.
Since all the contact between the vane 307 and the slot 330 is at the narrow contact point 3463, there is little of no risk of the vane 307 becoming locked against the slot 330, such that sliding motion of the vane 307 in the axial direction is impaired.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1807883.2 | May 2018 | GB | national |
The present application claims priority to PCT Application No. PCT/GB2019/051316, filed May 14, 2019, which claims priority to United Kingdom Patent Application No. 1807883.2, filed on May 15, 2018, the disclosure of which being expressly incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2019/051316 | 5/14/2019 | WO | 00 |
