Patent Application
20050220616
Subject matter disclosed herein relates generally to turbomachinery for internal combustion engines and, in particular, vanes for variable geometry turbines.
Conventional vanes used in variable geometry turbochargers or variable nozzle turbochargers typically have a two-dimensional cross-section or profile that remains constant in shape along the axis of rotation of a turbine. As discussed herein, exemplary vanes have a two-dimensional cross-section that may vary, for example, in a direction parallel to the axis of rotation of a turbine. Such exemplary vanes can provide enhanced performance when compared to conventional vanes.
A more complete understanding of the various methods, devices, systems, arrangements, etc., described herein, and equivalents thereof, may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:
Various exemplary methods, devices, systems, arrangements, etc., disclosed herein address issues related to technology associated with turbochargers. Turbochargers are frequently utilized to increase the output of an internal combustion engine. Referring to
The exemplary turbocharger 120 acts to extract energy from the exhaust and to provide energy to intake air, which may be combined with fuel to form combustion gas. As shown in
Adjustable vanes positioned at an inlet to a turbine typically operate to control flow of exhaust to the turbine. For example, GARRETT® VNT™ turbochargers adjust the exhaust flow at the inlet of a turbine in order to optimize turbine power with the required load. Movement of vanes towards a closed position typically increases the pressure gradient across the turbine and directs exhaust flow more tangentially to the turbine, which, in turn, imparts more energy to the turbine and, consequently, increases compressor boost. Conversely, movement of vanes towards an open position typically decreases the pressure gradient and directs exhaust flow in more radially to the turbine, which, in turn, reduces energy to the turbine and, consequently, decreases compressor boost. Thus, at low engine speed and small exhaust gas flow, a VGT turbocharger may increase turbine power and boost pressure; whereas, at full engine speed/load and high gas flow, a VGT turbocharger may help avoid turbocharger overspeed and help maintain a suitable or a required boost pressure.
A variety of control schemes exist for controlling geometry, for example, an actuator tied to compressor pressure may control geometry and/or an engine management system may control geometry using a vacuum actuator.
Overall, a VGT may allow for boost pressure regulation which may effectively optimize power output, fuel efficiency, emissions, response, wear, etc. Of course, an exemplary turbocharger may employ wastegate technology as an alternative or in addition to aforementioned variable geometry technologies.
In this example, the vanes 220 are positioned on posts 230, which are set in a vane base 240, which may be part of a variable geometry mechanism. In the system of
Each vane also has an inner surface and an outer surface. The inner surface faces the turbine wheel while the outer surfaces faces away from the turbine wheel. The inner surface and the outer surface of each vane meet at the leading edge 226 and at the trailing edge 224.
In general, the outer surface experiences a higher pressure than the inner surface; thus, at times, the outer surface may be referred to as a “pressure” surface.
During operation, exhaust flows from the leading edge 226 to the trailing edge 224 of a vane. An inner surface of a vane and an outer surface of an adjacent vane form a throat. Thus, an adjustment to the vanes typically adjusts throat shape. In general, the number of throats equals the number of vanes.
Point C is typically located at even greater radial distance from point A and at a lesser height along the z-axis. Point D is the lowest point of the blade outer edge 208 along the z-axis. The edge from C to D is the leading edge of the turbine blade 206. In some instances, vanes may be defined with respect to the leading edge of a turbine blade. For example, an axial dimension “b” may correspond to the axial length of the leading edge of a turbine blade and be used to define a dimensionless blade parameter. A vane may also have an axial dimension “b”, which corresponds to the axial length of a trailing edge of a vane. This dimension may be used to define a dimensionless vane parameter.
Various plots described herein use the axial length of a trailing edge of a vane “b” to define a dimensionless vane parameter.
Various exemplary vanes are disclosed herein. In general, vanes for variable geometry turbines have an airfoil shape that is configured to both provide a complementary fit with adjacent vanes when placed in a closed position, and to provide for the passage of exhaust gas within the turbine housing to the turbine wheel when placed in an open position. An individual vane has a leading edge or nose having a first radius of curvature and a trailing edge or tail having a substantially smaller second radius of curvature connected by an inner airfoil surface on an inner side of the vane and an outer airfoil surface on an outer side of the vane. The outer airfoil surface may be convex in shape, while the inner airfoil surface may be convex in shape near or at the leading edge and optionally concave in shape near the trailing edge. The inner and outer airfoil surfaces are defined by a substantially continuous curve which complement each other. As used herein, the vane surfaces are characterized as “concave” or “convex”. The asymmetric shape of such a vane results in a curved centerline, which is also commonly referred to as the camberline of the vane. The camberline is the line that runs through the midpoints between the vane inner and outer airfoil surfaces between the leading and trailing edges of the vane. Its meaning is well understood by those skilled in the relevant technical field. A vane with a curved camberline, may be referred to as a “cambered” vane.
In
A vane thickness may be defined as the distance between the inner surface and the outer surface of a vane, for example, with respect to a local coordinate system wherein the normal to a plane tangent to a surface of the vane is used to define a direction to measure vane thickness.
Substantially crescent shaped surfaces 223, 225 of the vane 220 are referred to as an upper axial surface or shroud end surface 225 and a lower axial surface or hub end surface 223 (note that while the hub end surface 223 of the vane 220 is not shown in
In general, for the xy-coordinate system shown, an overall minimum PLE is located at a minimum x value. The trailing edge 224 coincides with a trailing edge point (PTE), which in this conventional example is constant with respect to the z-axis. In general, for the xy-coordinate system shown, an overall maximum PTE is located at a maximum x value. The y-axis is normal to the x-axis and runs to the outer side of the vane in the direction in which the outer airfoil surface 227 extends. As described herein, various exemplary vanes include one or more minimum PLEs and one or more maximum PTEs. Further, in such exemplary vanes, the minimum PLE(s) may be located at z-axis position(s) that differ from the maximum PTE(s).
In conventional vanes, the leading edge 226 is typically defined by a circular curve having a first radius of curvature r (not shown), and the trailing edge 224 is defined by a circular curve having a substantially smaller second radius of curvature. As described herein, various exemplary vanes may include a leading edge that is defined by more than one circular curve radii or a trailing edge that is defined by more than one circular curve radii. For example, at the leading edge the curve may be elliptical with the major axis along the direction of the camber line and an aspect ratio in a range from about 2 to about 4 (defined as the ratio of major over minor ellipse axes) may be used.
With respect to vane length, a commonly used measure is the chord length. The chord length is defined as a straight line length along “x” from the leading edge to the trailing edge at a constant z-axis value (i.e., a cross section in the x-y plane normal to the z-axis of the turbine coordinate system). Further, the pivot point (PP) of a vane may be located with respect to x and y coordinates. The chord length from PP to PTE is referred to as XTE while the chord length from PP to PLE is referred to as XLE.
Another point that may be associated with the vane 220 is an inflection point, which demarcates the transition of the inner surface 229 from concave to convex.
The convex section resembles a parabolic curve that potentially transitions into a short circular or elliptic curve connecting the parabolic curve and the concave section. The vertex of the parabolic curve defines a local extreme of curvature. For a vane with such a concave to convex transition, the camberline is represented in
In general, if the camber line is even partially concave (as seen from the inner surface) then the inner surface will transition from convex to concave.
In general, vanes pivot between a minimum and a maximum stagger angle Φ. At the maximum stagger angle Φ, the vanes are in a closed position defining a minimum throat distance or throat width (d) between two adjacent vanes. At the minimum stagger angle Φ, the vanes are in an open position defining a maximum throat distance d. When the vanes pivot between the minimum and maximum stagger angles, the vane leading edges define a first radius RLE and the vane trailing edges define a second radius RTE which is smaller than the first radius RLE.
Referring again to
Exemplary vanes described herein can be formed from the same types of materials, and in various instances in the same manner, as that used to form traditional vanes (e.g., the vane 220). Exemplary vanes may have a substantially solid design or may alternatively have a cored out design.
A cored out design may provide better formability, a higher stiffness to weight ratio, be more cost effective to produce, and have a reduced mass when compared to solid vanes.
As described herein, an exemplary vane may have a modified stagger angle ΦM that varies with respect to axial position (e.g., position parallel to the z-axis). In
In this example, the particular shape acts to increase efficiency and reduce fatigue when implemented in a variable geometry turbocharger. More specifically, such a throat shape acts to improve steady-state and high cycle fatigue performance.
While a dimension “b” may refer to an edge height of a vane, as previously described, it may alternatively refer to another constant, such as the maximum vane height. In such an example, dimensionless vane height values would not exceed unity. However, where a dimension “b” is less than the maximum vane height, dimensionless vane height values may exceed unity. Various exemplary vanes optionally have more than one vane height, for example, a vane height that varies from the leading edge to the trailing edge.
In these examples, stagger angle Φ decreases by about 10% between the hub end and shroud end. The change in stagger angle Φ with respect to vane height, as described above, may be due solely to the trailing edge, i.e., a change in the modified stagger angle ΦM. For the vane 1212, the minimum stagger angle Φ is at the midpoint of the trailing edge, for the vane 1214, the minimum stagger angle Φ is closer to the hub end and, for the vane 1216, the minimum stagger angle Φ is closer to the shroud end. Of course, a minimum may exist at an end (e.g., shroud end or hub end), depending on particular purpose of the vane (e.g., efficiency, fatigue, etc.). Again, adjacent vanes will typically have a wider throat at the minimum modified stagger angle ΦM.
Various exemplary vanes may create a throat that is widest at the shroud end or widest at the hub end.
Various exemplary vanes may have a constant overall chord length (XTotal), yet differ in shape along the z-axis. For example, referring to
As already mentioned, the stagger angle Φ may vary due to variations in the trailing edge (i.e., due to variations in the modified stagger angle ΦM). As shown, the exemplary vanes have a stagger angle Φ with a minimum between a hub end (e.g., z/b=0) and a shroud end (e.g., z/b=1). In these examples, stagger angle Φ decreases by about 10% from a maximum stagger angle Φ For the vane 1222, the minimum stagger angle Φ is near the midpoint of the trailing edge, for the vane 1224, the minimum stagger angle Φ is closer to the hub end and, for the vane 1226, the minimum stagger angle Φ is closer to the hub end yet the angle at the hub end is about the same as the minimum stagger angle Φ.
Of course, a minimum may exist at an end (e.g., shroud end or hub end), depending on particular purpose of the vane (e.g., efficiency, fatigue, etc.). As described herein, adjacent vanes will typically have a wider throat at the minimum modified stagger angle ΦM.
As described above, various exemplary vanes include a hub end and a shroud end that define vane height, a leading edge and a trailing edge that define vane length along a camberline and an inner surface and an outer surface that extend from the hub end to the shroud end and meet at the leading edge and the trailing edge and that define vane thickness. Various exemplary vanes include, for at least a portion of the vane, a vane length that varies with respect to vane height. Various exemplary vanes include, for at least a portion of the vane, a vane thickness that varies with respect to vane height. Of course, some exemplary vanes may include, for at least a portion of the vane, a vane length and a vane thickness that vary with respect to vane height. Various exemplary vanes include three-dimensional shapes that form advantageous throat shapes when positioned along a common radius (e.g., a pivot radius).
In a selection block 1304, selection of various parameters occurs whereby values for such parameters may be adjusted with respect to performance criteria. Another selection block 1308 provides for selection of one or more performance criteria (e.g., efficiency, fatigue, noise, etc.). A determination block 1312 optionally relies on computational software for heat transfer, mass transfer, fluid dynamics, stress, noise, etc., to determine values for one or more of the parameters, wherein at least one of the parameters corresponds to a dimension of a vane that varies with respect to a z-axis (e.g., a pivot axis of the vane, an axis of rotation of a wheel, etc.). A decision block 1316 follows whereby a decision is made as to whether the performance criteria have been met. If the criteria are not met, then the exemplary method 1300 may continue at the selection block 1304 or at the selection block 1308. If the criteria are met, then the exemplary method 1300 may continue at the construction block 1320 wherein construction of an exemplary vane occurs according, substantially, to the one or more parameter values determined by the determination block 1312.
An exemplary method includes selecting one or more vane parameters related to a throat shape where a trailing edge of one vane and an inner surface of an adjacent vane define the throat shape, selecting stress-related performance criteria for a turbine wheel, and determining a value for each the one or more vane parameters, based at least in part on the stress-related performance criteria of the turbine wheel, where the value or values correspond to a throat shape having a maximum width located between a hub end and a shroud end of the vanes. For example, the maximum width may be located as to reduce stress on the turbine wheel.
As discussed herein, variables related to vane shape include, but are not limited to, chord length, chord segments (i.e., as measured from the pivot axis), stagger angle, modified stagger angle, and camberline.
In one example, a chord segment from the pivot axis to the trailing edge may vary due to an arcuate trailing edge (e.g., curved inward generally toward the pivot axis of the vane). In such an example, the camberline may optionally be constant with respect to vane height or vary with respect to vane height.
As discussed herein, variable nozzle geometry turbines are widely used in commercial and passenger vehicles.
Vehicle fuel efficiency and drivability are strongly affected by the efficiency of various turbocharger components. There is therefore constant commercial pressure to improve turbocharger efficiency. The aforementioned technology concerns vane shape modifications that can apply to variable geometry turbines and result in appreciable turbine efficiency improvements. In general, vane shape may be selected to reduce noise, fatigue or address other concerns.
Various exemplary vanes consider shape in three-dimensions where, for example, profile may vary in size, orientation and shape along the axial direction or other directions. Referring again to
Various exemplary vanes may also help improve high cycle fatigue characteristics of a downstream rotor by reduction of shock-wave strength in the middle of the throat.
Such a reduction may result from the lower modified stagger angle and larger flow area near the middle of the throat. Reduction of the shock strength reduces the unsteady forcing function, which reduces the resulting rotor's alternating strains, which is important for the rotor's inducer vibrational mode (typically the most hazardous), where the maximum modal displacement is typically near the midspan of the rotor along its leading edge.
Various exemplary vanes are also of particular importance to the latest generation of radial turbines employing profiled leading edges for high cycle fatigue considerations. For example, leading edge profiling tends to introduce a spanwise variation in the flow incidence on the blades near midspan, which can penalize the steady state performance. As described herein, varying vane shape (e.g., modified stagger, length, profile, etc.) can be used to optimize the flow incidence for such arrangements.
Various exemplary vanes are interchangeable with conventionally used “two-dimensional” vanes (or stacked profile vanes) since the same actuation mechanism may typically be used. An exemplary method of construction optionally includes a casting or other process that differs from that used for conventional vanes.
With respect to conventional vanes, if a conventional vane is intersected at various axial locations by a plane normal to the turbocharger centerline (e.g., z-axis or axis of rotation), the resulting airfoil profiles are identical in shape and orientation in space along the centerline. As described herein, various exemplary vanes have one or more dimensions, features, etc., that vary along the centerline of a turbine or other wheel (and/or along a pivot axis of an exemplary vane). Thus, various exemplary vanes have profiles that vary in shape, size, orientation, etc., in the axial direction to further optimize a turbine stage aero/mechanical performance.
This application claims the benefit of U.S. Provisional Application 60/529,078, entitled “Vane and Throat Shaping”, filed Dec. 12, 2004, to Vogiatzis, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60529078 | Dec 2003 | US |
