Patent Application
20100322781
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1. Field of the Invention
The present invention relates to an impeller and a turbocharger.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
An industrial turbocharger compressor impeller is typically made from aluminum. This material is relatively cheap, is easy to machine and is light enough so that turbo lag is not a major problem. Current turbocharger impellers for medium speed diesel engines tend not to have a through bore since this minimizes the stress in the impeller material and reduces the likelihood of the impeller failing due to fatigue during a typical 50,000 hour life.
The life of such an impeller tends to be governed by creep of the impeller material, so that maximum operating pressure ratios are limited to around 5:1 for typical industrial duties. Impeller creep failure is associated with areas of high stress and high temperature. The area of highest temperature, and consequently the area which determines the creep life, is on the back of the impeller near the outer diameter. This is an area where typically a labyrinth seal is located to reduce the leakage of compressed air towards the bearings. The high temperature is associated with windage heating in that area.
The impeller life must typically achieve 50,000 hours. This is achieved traditionally by limiting the operating speed of the turbocharger in line with calculations of the creep life. At lower operating speeds the impeller stresses are lower, the compressed air at the downstream side of the impeller is cooler, and the windage heating is less than at higher operating speed.
More recently cooled air at high pressure has been fed into the area at the back of the impeller to keep the impeller material cool.
In U.S. Pat. No. 5,297,928 and U.S. Pat. No. 6,190,123 B1 methods for direct cooling the rear wall of a compressor impeller are disclosed, wherein a gaseous cooling medium is directed onto the rear wall.
In U.S. Pat. No. 6,257,834 B1 a method for indirect cooling of the flow in radial gaps formed between rotors and stators of turbo machines is provided. The method includes the step of using water as a cooling fluid for stator part adjacent to the radial gap.
In WO 01/29425 A1 a combination of direct and indirect cooling of the flow in radial gaps formed between rotors and stators of turbine-type machines is disclosed, wherein a first cooling fluid, preferably water, is used for indirect cooling and a second gaseous cooling fluid, preferably air, is used for direct cooling.
The cooled air is typically taken from the diesel engine air manifold, after the compressed air has been cooled by the charge air cooler. The introduction of this cooled air is a parasitic loss on the turbocharger efficiency, since the turbocharger has to compress the coolant air but the air is not used in the diesel engine. Also this cooled air leaks into the main stream of the compressor flow between impeller and diffuser and will cause a disturbance to the flow which reduces the compressor efficiency. Nevertheless, by cooling the impeller the compressor is allowed to operate at higher speed while still achieving the required 50,000 hours life. Typically, by cooling the impeller by 200 C, an additional 0.2 bar of boost pressure can be achieved with this system and this typically allows the engine rate power to increase by around 5%.
As well as the parasitic loss in adding this high pressure coolant air, the pressure behind the impeller increases and the thrust load, and consequently parasitic thrust bearing losses, increase.
It is a first objective of the present invention to provide an advantageous impeller, a second objective to provide an advantageous compressor and a third objective to provide an advantageous turbocharger.
The first objective may be solved by an impeller as claimed in claim 1. The second objective may be solved by a compressor as claimed in claim 11. The third objective may be solved by a turbocharger as claimed in claim 12. The depending claims define further developments of the invention.
An inventive impeller comprises a rotation axis, a radial direction, a backplate and a number of vanes which are connected to the backplate at a line of connection. Each vane comprises an upstream side, a downstream side and an outer side. The downstream side of each vane comprises an edge portion which is located near the outer side. The vanes project radially over the backplate and the downstream side further comprises a connecting portion connecting the edge portion to the line of connection between the respective vane and the backplate and including an angle with the radial direction. This means, that part of the inventive impeller's downstream side is removed compared to a conventional impeller's downstream side. The removed area is at high diameter so that stresses are reduced in that area. Also this is the hottest area of the impeller so that the temperature of the impeller is also reduced. However, the radial projection of the vanes means that radially outer parts of the vanes are preserved, which helps to maintain the ability of the impeller to pressurise the flow.
The edge portion may be orientated perpendicular to the radial direction. The connecting portion may have a convex rounded portion which is located near the connection line. For example, in some embodiments such a convex rounded portion can extend from the edge portion to the line of connection between the respective vane and the backplate. In other embodiments, such a convex rounded portion can be part of an S-shape portion which may extend from the edge portion to the line of connection between the respective vane and the backplate.
Preferably, each vane is backswept on moving in an airflow direction from its upstream side to its downstream side. Backsweeping the vanes can introduce an extra tangential component into the flow leaving the impeller, which can improve flow stability and efficiency. Backsweep can also increase bending stresses in the vanes, but advantageously these stresses can be reduced by employing a connecting portion which has a convex rounded portion located near the connection line.
A further advantage of employing a connecting portion which has a convex rounded portion located near the connection line is that the high centrifugal stresses which can be generated in the region where the vane and the backplate meet can be reduced. Particularly advantageous in this respect is a connecting portion which has an S-shape portion.
Moreover, the backplate can comprise a radially outer peripheral surface and the connecting portion can be adjacent to the radially outer peripheral surface of the backplate. The radially outer peripheral surface of the backplate may be located in a plane with a normal being locally parallel to the radial direction. This means that the radially outer surface may run parallel to the rotation axis. Alternatively, the radially outer peripheral surface of the backplate can be located in a plane with a normal which includes an angle between 0° and 45° with the radial direction. Preferably, the angle may have a value between 15° and 25°. This further reduces stress and temperature on the surface of the backplate.
The radially outer surface of the inventive impeller may especially be located at a radial position closer to the rotation axis than the radially outer surface of a conventional impeller. In other words, the distance between the radially outer surface and the rotation axis of an inventive impeller is smaller than the distance between the radially outer surface and the rotation axis of a conventional impeller. By removing some of the backplate of the impeller, the aerodynamic performance of the impeller could be reduced. This reduction is associated with leakage around the base of the vanes, which would otherwise be prevented by the presence of the backplate, and a reduction in the diameter of the impeller vanes. Moreover, a removal of part of the backplate could also increase local stresses in the impeller vanes since they will no longer be entirely supported along their entire length.
To reduce the potential aerodynamic losses and local vane stress, the shape of the vane at the impeller tip is preferably carefully chosen: An angle between a tangent located at the connecting portion adjacent to the connection line and the radial direction may have a value between 10° and 45°, preferably between 15° and 25°. This reduces vane leakage losses. Moreover, the edge portion of the downstream side can have a length in the direction of the rotation axis of more than 50% of the length of the downstream side in the direction of the rotation axis. This means, that only the part of the vane closest to the backplate is removed, so that the part of the vane that is working most efficiently on the working fluid remains.
The vane shape can be modified in the area of the downstream side so that the design conforms closely to the so-called “radial element” design. This ensures that the vane stresses are kept to an acceptable low level.
Typically, the impeller has radially spaced and axially extended ribs projecting from the backplate on the other side of the backplate from the lines of connection with the vanes. Labyrinth seals may then be provided on a casing of the impeller, the seals facing the backplate so as to mesh with the ribs.
Additionally or alternatively, the impeller may have a casing with a sealing portion which forms a seal with the radially outer peripheral surface of the backplate.
The inventive compressor comprises an inventive impeller, as previously described and an inventive turbocharger comprises an inventive compressor. The inventive compressor and the inventive turbocharger have the same advantages as the inventive impeller has.
The inventive impeller can have an increased impeller creep life compared to a conventional impeller. Moreover, the necessity for coolant flow can be kept to a minimum.
Further features, properties, and advantages of the present invention will become clear from the following description of an embodiment in conjunction with the accompanying drawings. Each features or a combination of features can be advantageous.
In the following a first embodiment of the inventive impeller and the inventive turbocharger will be described with reference to
The turbine 11 includes a rotor 4 which is located inside a turbine casing 3. The turbine casing 3 has an exhaust inlet 5 which leads to the rotor 4 so that the exhaust entering the exhaust inlet 5 activates the rotor 4. Further, the turbine casing 3 has an exhaust outlet 6 through which the exhaust coming from the rotor 4 leaves the turbine casing 3. The arrows 18 indicate the exhaust stream entering the turbine casing 3 through the exhaust inlet 5, activating the rotor 4 and leaving the turbine casing 3 through the exhaust outlet 6.
The compressor 10 includes an impeller 12 which is located inside a compressor casing 1. Moreover, the compressor 10 has an air inlet 7 which air leads to the impeller 12 and an air outlet 8 through which the air coming from the impeller 12 leaves the compressor casing 1. The arrows 19 indicate the air stream entering the compressor casing 1 through the air inlet 7, being compressed by the impeller 12 and leaving the compressor casing 1 through the air outlet 8.
The impeller 12 comprises a backplate 2 and vanes 9. The backplate 2 is connected to the shaft 20. Further, the backplate 2 is generally conical in shape and a plurality of circumferentially spaced arcuate vanes 9 are formed about its periphery. Typically the vanes are backswept. The back surface 16 of the impeller 12 has radially spaced and axially extended ribs 17. Labyrinth seals 13 are mounted to the compressor casing 1 opposite to the back surface 16 of the impeller 12 so as to mesh with the ribs 17. The labyrinth seals 13 engage the annular ribs 17 to reduce the leakage of compressed air towards the bearings along the back surface 16 of the impeller 12.
Moreover, the backplate 2 comprises a radially outer peripheral surface 25. A sealing portion 50 of the casing forms a seal with a radially outer peripheral surface 25 of the backplate to further reduce the leakage of compressed air.
The rotor 4 of the turbine 11 is connected to the shaft 20 so that the activated rotor 4 activates the shaft 20. The shaft 20 is further connected to the impeller 12 inside the compressor 10. Hence, the rotor 4 activates the impeller 12 by means of the shaft 20. The rotation axis is indicated by reference numeral 21.
In the turbine 11, the exhaust stream 18 entering the exhaust inlet 5 activates the rotor 4 and leaves the turbine through the exhaust outlet 6. The arrows 18 indicate the direction of the exhaust stream. Meanwhile, the impeller 12 in the compressor 10 driven by the rotor 4 sucks atmospherically fresh air into the air inlet 7 and compresses it to pre-compressed fresh air, which enters the air outlet 8. The compressed air is then used for example in a reciprocating engine like e.g. a diesel engine. The arrows 19 indicate the air stream direction.
The air which is sucked into the air inlet 7 arrives at the upstream side 14 of the vane 9, passes the vane 9 along the direction 19 and leaves it at the downstream side 15 towards the air outlet 8.
Opposite to the line of connection 22 an outer side 23 is located. The outer side 23 has a concave shape. The upstream side 14 runs, perpendicular to the rotation axis 21. However, an angle may be present between the upstream side 14 and the rotation axis 21 may have a value between 0° and ±100. The downstream side 15 is orientated perpendicular to a radial direction which is defined by the rotation axis 21. The radially outer peripheral surface 25 is located in a plane with a normal being locally parallel to the radial direction. The distance between the radially outer peripheral surface 25 and the rotation axis 21 is indicated by reference numeral 30.
The downstream side 15 of the inventive impeller 112 comprises an edge portion 27 which is located near the outer side 23 and a connecting portion 24 which is located near the line of connection 22 and connects the line of connection 22 to the edge portion 27. The connecting portion 24 in
The edge portion 27 which is located near the outer side 23 is further orientated perpendicular to a radial direction which is defined by the rotation axis 21. Furthermore, the edge portion 27 which is located near the outer side 23 may run parallel to the rotation axis 21. This is the case for the vane 9, which is shown in
The edge portion 27 which is located near the outer side 23 adjoins to the connecting portion 24 which is located near the line of connection 22. At the line of connection 22 the connecting portion 24 adjoins to the radially outer peripheral surface 25, which has the same properties as the corresponding radially outer peripheral surface 25 in
The improved configuration of the inventive impeller 112, 212 reduces vane leakage losses and keeps vane stresses to an acceptable low level. This increases the impeller creep life and minimizes the necessity for coolant flow.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08002766.7 | Feb 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB08/04190 | 12/18/2008 | WO | 00 | 8/16/2010 |
