KR20070085560A - Variable nozzle turbocharger - Google Patents

Abstract

There is provided a turbocharger with a variable nozzle assembly having a plurality of cambered vanes positioned annularly around a turbine wheel, each vane (20) being pivotable around a pivot point (Pp) and being configured to have a leading edge (Ple) and a trailing edge (Pte) connected by an outer airfoil surface (2) and an inner airfoil surface (4), said outer airfoil surface (2) being substantially convex and said inner airfoil surface (4) having a convex section at the leading edge (Ple) which has a local extreme (Pex) of curvature and transitions into a concave section towards the trailing edge (Pte). The positions of the pivot point (Pp) and the local extreme (Pex) are set such that, even when the vanes are placed in a closed position, the exhaust gas stream exercises a positive torque on the vanes which tends to open the nozzle.

Description

Variable nozzle turbocharger {VARIABLE NOZZLE TURBOCHARGER}

The present invention relates generally to variable nozzle turbochargers and, more particularly, to improved vane design for a plurality of pivoting vanes in a turbine housing of a variable nozzle turbocharger.

Variable nozzle turbochargers generally comprise a central housing attached to one end having a turbine housing and a compressor housing attached to the other end. The shaft is rotatably disposed in a bearing assembly housed within the central housing. A turbine or turbine wheel is attached to one end of the shaft and mounted in the turbo housing, and a compressor impeller is attached to the other end of the shaft and mounted in the compressor housing.

1 shows a portion of a known variable nozzle turbocharger 10 including a turbine housing 12 and a center housing 32. The turbine housing 12 has an exhaust inlet (not shown) for receiving the exhaust gas stream and an exhaust outlet 16 for directing the exhaust gas to the engine exhaust system. A volute 14 connects the exhaust inlet with a nozzle formed between the insert 18 and the nozzle ring 28. The insert portion 19 forms a nozzle outer wall and is attached to the central housing 32 and included in the turbine housing 12 adjacent the volute 14. The nozzle ring 28 acts as a nozzle inner wall and is fitted to the insert portion 18. The turbine wheel 30 is mounted in the exhaust outlet 16 of the turbine housing 12. Exhaust gas or other high energy gas supplied to the turbocharger 10 enters the turbine wheel 30 through the exhaust inlet and through a cylindrical nozzle formed by the insert portion 18 and the nozzle ring 28. It is distributed through the volute 14 in the turbine housing 12 to enter the turbine wheel 30 substantially radially.

A plurality of vanes 20 are mounted to the nozzle 28 using a vane pin 22 protruding vertically outward from the vanes 20. Each vane pin 22 is attached to a vane arm 24, which vane arm 24 is received in a rotatably mounted Unison ring 28. An actuator assembly is connected to the unison ring 26 and externally or internally with respect to the axis of rotation of the turbine wheel 30 to increase or decrease the pressure differential and to modify the flow of exhaust gas through the turbine wheel 30. Rotating the unison ring 26 in one direction or the other direction necessary to move the vane 20 radially. As the unison ring 26 fires, the vane arm 24 moves, and the movement of the vane arm 24 causes the vane 20 to pivot through rotation of the vane pin 24. The throat area of the nozzle is opened or closed according to the rotation direction of the unison ring 26.

An example of a known turbocharger employing such a variable nozzle assembly is disclosed in WO 2004/022926 A.

In general, vanes having an airfoil shape configured to provide an auxiliary fit to adjacent vanes when placed in the closed position and to provide the turbine wheel with a path of exhaust gas within the turbine housing when placed in the open position are designed. do. This vane has a substantially smaller second radius of curvature connected by a leading edge or nose having a first radius of curvature, and an airfoil inner surface on the outside of the vane and an airfoil outer surface on the outside of the vane. It has a trailing edge or tail with a tail. In this vane design, the outer surface of the airfoil is convex, the inner surface of the airfoil is convex at the bow edge and concave in the trailing edge direction. The inner and outer surfaces of the airfoil that complement each other are formed in a substantially continuous curve. As used herein, the vane surface has a "concave" or "convex" characteristic with respect to the interior (not outside) of the vane. This asymmetric shape of the vanes creates a curved centerline, which is also referred to as the camberline of the vanes. The camber line is a line passing through the center points between the vane's airfoil inner and outer surfaces between the bow and tail edges of the vane. This meaning is easily understood by those skilled in the art. Since this vane has a curved camber line, it is a "cambered" vane.

The use of such camber vanes in variable nozzle turbochargers provides some improvement in aerodynamic effects within the turbine housing. Some particularly useful designs of vanes are disclosed in US Pat. No. 6,709,232 B1. This vane design reduces unwanted aerodynamic effects in the turbine housing by keeping the exhaust gas constant as it passes upwards, contributing to losses in operating efficiency of the turbocharger and turbocharged engine. Reduce unwanted back pressure in the known turbine housing.

Although the use of camber vanes brings some improvement in efficiency, it has been found that there is a risk of inversion of aerodynamic torque acting on the vane surface. In particular, it was observed that negative torque usually occurs when the nozzle throat area is small, and positive torque occurs when the nozzle throat area is large. The torque is defined as positive when the flow of exhaust gas has sufficient force to bring the vane into the open position. Reversal of aerodynamic torque affects the actuator assembly and the union ring's ability to pivot the vanes. With regard to controllability, it is desirable that the torque acting on the vanes always have the same orientation regardless of the position of the vanes. It is more preferable that the torque is positive and that the nozzle is easy to open (ie, increase the throat area of the nozzle).

Accordingly, it is desirable to provide a variable nozzle turbocharger with improved vane controllability when compared to conventional turbo rudders.

The inventors have done extensive research to determine the cause of the torque reversal in a turbocharger having a variable nozzle assembly with a plurality of camber vanes arranged annularly around a turbine wheel. They found that the dominant factors were: (a) the position of the vane pivot point, (b) the position of the local extreme of curvature in the convex region of the inside of the airfoil relative to the pivot point, (c) the shape of the convex zone on the inner surface of the airfoil, and (d) the angle of incidence of the flow of exhaust gas on the vane surface.

Regarding factor (a), in the coordinate system where the origin is the bow edge of the vane and the x-axis goes to the trailing edge of the vane, the y-axis is perpendicular to the x-axis and outward of the vane, the pivot point is It has been found that it is desirable to be placed in a position that satisfies the expression:

0.25 <Xp / C <0.45, preferably 0.30 <Xp / C <0.40;

And

−0.10 ≦ Yp / C ≦ 0.05, preferably −0.10 ≦ Yp / C ≦ 0, most preferably −0.10 ≦ Yp / C ≦ −0.05

Where Xp is the distance between the pivot point and the bow edge on the x-axis, C is the distance between the bow edge and the trailing edge, and Yp is the pivot point and the vane on the y-axis. Is the distance between the camber lines of and a negative value of Yp represents the pivot point located further inside of the vane. The pivot point is preferably disposed between the outer surface of the airfoil and the inner surface of the airfoil.

Regarding factor (b), it has been found that the local pole of the curved part in the convex region of the inner surface of the airfoil has a strong influence on the aerodynamic torque acting on the vane, especially when the local pole is at its maximum. In the above coordinate system, the local pole is preferably placed at a position satisfying the following expression:

0.3 <(Xp-Xex) / Xp <0.8, preferably 0.4 <(Xp-Xex) / Xp <0.7, most preferably 0.49 <(Xp-Xex) Xp <0.60

Xp is the distance between the pivot point Pp and the bow edge Ple on the x-axis, and Xex is between the local pole Pex and the bow edge Ple on the x-axis. Is the distance.

Regarding factor (c), it has been found that preferably the convex zones on the inner surface of the airfoil have a rather long shape. Thus, in the coordinate system described above, the local pole is preferably placed at a position satisfying the following expression:

0.40 <Yex / Xex <0.83

Where Xex is the distance between the local pole and the bow edge on the x-axis, and Yex is the distance between the local pole and the bow edge on the y-axis.

Regarding the factor (d), it was found that when the vane is positioned in the closed position, it is preferable that the flow incident angle of the exhaust gas with respect to the line connecting the bow edge and the pivot point is 5 ° or more.

According to the invention, the turbocharger satisfies at least one of the expressions discussed in relation to factors (a), (b), (c), and (d).

Further, the bow edge of the vane is preferably defined by a circular curve with a radius r that satisfies the following expression:

0.045 <r / Xp <0.08

Where Xp is the distance between the pivot point and the bow edge on the x-axis.

In addition, the convex region of the inner surface of the airfoil is formed of a series of synthetic curves consisting of one selected from a curved line forming the bow edge and transforming into a parabola, and a curve or elliptic curve connecting the parabolic and convex areas It is preferable. In addition, the outer surface of the airfoil is preferably formed of a series of synthetic curves including a curved line that forms the bow edge and shifts into an elliptic curve.

Finally, when the vanes are pivoted between the closed and open positions, the tangential radii of the bow edges Ple of the vanes 20 relative to the tangential radius Rte of the trailing edges Pte ( The ratio of Rle) (Rle / Rte) preferably has a range between 1.03 and 1.5.

The invention will be more clearly understood with reference to the following drawings:

1 is a partial cross-sectional view of a turbocharger employing a variable nozzle assembly;

2 is a side view of a camber vane according to an embodiment of the present invention;

3 shows a cross section of the vane of FIG. 2 in a variable nozzle assembly of a turbocharger;

4 details region A of FIG. 3;

5 shows vanes with different vane contours; And,

FIG. 6 shows a composite effect of varying the pivot point for a given vane contour on the aerodynamic torque and maximum nozzle throat area.

2 shows a camber vane 20 according to a preferred embodiment of the present invention. The camber vanes 20 according to the present embodiment may be used in the variable nozzle turbocharger 10 shown in FIG. 1. In addition, other turbocharger arrangements may be suitable.

As shown in FIG. 2, the camber vanes 20 comprise an airfoil outer surface 2, which is substantially convex in shape and formed into a series of synthetic curves, and convex and concave shaped regions, and also a series of synthetic It comprises an opposite airfoil inner surface 4 formed of curves. Bow edge or nose Ple is disposed at one end of the vane between the inner and outer surfaces of the airfoil, and trailing edge or tail Pte is disposed at the other end of the vane between the inner and outer surfaces of the airfoil. The bow edge Ple is formed of a curve having a first radius of curvature r, not shown, and the trailing edge Pte is preferably formed of a curve having a smaller second radius of curvature.

The vane has a predetermined length defined by the length of the chord C, passing between the bow and trailing edges Ple and Pte of the vane. The vane also has a pivot point Pp that rotates.

The series of synthetic curves forming the airfoil outer surface 2 are constant or reduced over the remainder of the vane length C and the region having an elliptical shape cut for the first 10 or 20% of the vane length C. It includes a region having a radius of curvature. The series of synthetic curves forming the airfoil inner surface 4 are convex regions defined by the second order polynomial for the first 20-30% of the vane length C and almost all of the vane length C. A concave region having a radius of curvature constant or decreasing relative to the rest. The end of the convex zone is indicated by the inflection point. The convex zone resembles a parabola, which gradually transitions into a short curve or elliptic curve connecting the parabolic and the convex zones. The vertex of the parabola is defined as the local pole (Pex) of the curved portion. The midpoint between the inner and outer surfaces 2 and 4 of the airfoil having the above-described shape forms a curved camber line 6. The camber wire is almost flat with respect to the first 15-25% of the vane length C, at which point the camber wire 6 is curved.

In order to define the position of the pivot point Pp and the local pole Pex, the coordinate system shown in FIG. 2 is used. The origin of this coordinate system is the bow edge Ple. The x-axis defines the vane length and coincides with the demonstration (C) passing between the bow and trailing edges (Ple, Pte) of the singer vanes. The y-axis is perpendicular to the x-axis and faces out of the vane in the direction in which the airfoil outer surface 2 extends. In this coordinate system, the pivot point Pp is the distance Xp between the pivot point Pp on the x-axis and the bow edge Ple and the pivot point Pp on the y-axis. It is arrange | positioned at the position determined by the distance Yp between the camber lines 6 of the said vanes. A negative value of Yp indicates a pivot point Pp closer to the inner side of the airfoil 4 or the vane (see example on the upper right side of the figure). The local pole Pex is the distance Xex between the bow edge Ple and the local pole Pex on the x-axis and the bow edge Ple and the local pole Pex on the y-axis. It is arrange | positioned at the position determined by the distance Yex between ().

More specifically, the vanes of this embodiment have the following specifications:

Xp / C = 0.35;

Yp / C = 0.00;

(Xp-Xex) / Xp = 0.56;

Yex / Xex = 0.50;

r / Xp = 0.05

As shown in FIGS. 3 and 4, a plurality of, for example, eleven vanes 20 are spaced at equal intervals and radially surround the turbine wheel while forming a variable discharge nozzle assembly, the turbine housing of the turbocharger. Disposed within. The pivot point of each vane 20 is located on a radius Rp having a common axis at the radial center O of the variable discharge nozzle assembly. The vanes 20 pivot between a minimum and maximum stagger angle θ. The installation angle θ is defined as the angle between the straight line passing between the radial center O of the variable discharge nozzle assembly and the pivot point Pp of the vane and the demonstration C of the vane. At the maximum installation angle θ, the vanes 20 are in the closed position forming a minimum throat distance d between two adjacent vanes. At the minimum installation angle θ, the vanes 20 are in an open position forming a maximum throat distance d. When the vanes 20 pivot between a maximum and minimum installation angle θ, the bow edge Ple of the vane forms a first radius Rle, and the trailing edge Pte of the vane A second radius Rte smaller than the first radius Rle is formed.

As shown by the arrows in FIG. 4, the vanes 20 are arranged in the turbine housing with the airfoil inner surface 4 facing the exhaust gas stream. As best shown in FIG. 2, the flow incident angle α of the exhaust gas is defined with respect to the straight line passing between the bow edge Ple and the pivot point Pp of the vane. Positive values of α are likely to open the nozzle, while negative values of α are likely to close the nozzle. Therefore, the risk of aerodynamic torque reversal affecting the controllability of the vanes 20 is highest when the installation angle θ is large and the flow incident angle α is small.

In this embodiment, it was confirmed that there is no aerodynamic torque reversal when the maximum installation angle θ of the vane 20 is set such that the flow incident angle α of the exhaust gas is approximately 5 °. In other words, using the vanes 20 of this embodiment can provide a variable nozzle turbocharger with improved vane operation controllability as compared to conventional turbochargers.

The inventors have prepared a large number of vanes with different vane contours and investigated the effects of vane contours on motion controllability and turbocharger operation efficiency using flow analysis and other methods. Aerodynamic torque was measured at two installation angles (θ) close to the minimum and maximum installation angles, and efficiency was measured at the minimum installation angle with the maximum throat distance (d).

5 shows some examples of vane contours examined by the inventors. The table below details the specifications. It should be noted that example a) is the same as that shown in FIG. 2.

example Xp / C Yp / C (Xp-Xex) / Xp Yex / Xex a) 0.35 0.00 0.56 0.50 b) 0.34 0.00 0.60 0.51 c) 0.36 0.00 0.44 0.19 d) 0.36 0.00 0.67 0.32 e) 0.37 0.00 0.94 1.04

Of the vane contours shown in FIG. 5, example a) shows both good controllability and good efficiency when mounted on a turbocharger. The controllability of example b) is as good as the controllability of example a), but the efficiency is good but somewhat diminished. Example c) has the best controllability but only shows good efficiency. Example d) has the best efficiency but not enough controllability. Example e) is as controllable as Example d), but the efficiency is similar to Example c). Example a) corresponding to the vanes shown in FIG. 2 is the best compromise for the demand for good controllability and good efficiency. However, examples b) and c) also meet this requirement.

In general, the test shows the best results for vanes with a local pole Pex located approximately midway between the trailing edge Ple and the pivot point Pp. In particular, the local pole Pex has a distance Xex between the local pole Pex and the bow edge Ple on the x-axis of 0.3 <(Xp-Xex) / Xp <0.8, preferably 0.4 <(Xp -Xex) / Xp < 0.7, and most preferably 0.49 < (Xp-Xex) / Xp < 0.60.

It has also been found that local poles Pex are preferably arranged such that the convex section of the airfoil inner surface 2 has a rather long shape, with local poles Pex on the x-axis and on the y-axis, respectively. It is preferable that the distance (Xex, Yex) between the bow edge Ple) and the bow edge Ple are disposed at positions Xex, Yex satisfying the expression 0.40 <Yex / Xex <0.83.

In addition, the inventor prepared a plurality of vanes having the same shape as the vanes 20 shown in FIG. 2 but having pivot points Pp disposed at different positions Xp and Yp. Again, the aerodynamic torque was measured at two installation angles θ1 and θ2 close to the minimum and maximum installation angles, respectively, and the efficiency was measured at the minimum installation angle where the throat distance d was maximum. The results of this test are shown in FIG.

In FIG. 6, the left side of the two vertical lines corresponding to the installation angles θ1 and θ2 forms a positive torque region, and the lower right side of the slope curve forms an increasing maximum nozzle throat region. If the distance Xp between the pivot point Pp and the bow edge Ple on the x-axis and the vane length C satisfy the expression Xp / C <0.45, it is possible to obtain the desired amount of torque. However, the smaller the Xp / C, the smaller the maximum nozzle throat area and hence the operating efficiency of the turbocharged and turbocharged engine. Therefore, it is preferable that Xp / C is 0.25 or more. More preferably, Xp and C satisfy the expression 0.30 <Xp / C <0.40.

In addition, FIG. 6 shows that the distance Yp between the pivot point Pp on the y-axis and the camber line 6 of the vanes 8 has some influence on the aerodynamic torque and efficiency. The closer the pivot point Pp is to the airfoil inner surface 4, the more the maximum nozzle throat area increases. If the pivot point Pp is located below the camber line 6 on the inside of the vane, the risk of aerodynamic torque reversal at a large mounting angle θ is further reduced. Thus, the pivot point Pp is placed at a position that satisfies the expression -0.10 ≤ Yp / C ≤ 0.05, preferably -0.10 ≤ Yp / C ≤ 0, most preferably -0.10 ≤ Yp / C ≤ -0.05 It is preferable to be. That is, the construction requirements may be contrary to the arrangement of the pivot point Pp on the inside and outside of the airfoil 2, 4.

The present inventors also investigated the influence of the flow incident angle α of the exhaust gas in terms of aerodynamic torque. Using the vane 20 shown in FIG. 2, the flow incident angle α of the exhaust gas with respect to the line connecting the bow edge Ple and the pivot point Pp of the vane 20 is the maximum installation angle θ. It has been found that the risk of aerodynamic torque reversal is minimized when set to above 5 °. This is compared with a conventional turbocharger where the flow incident angle α of the exhaust gas is usually between 0 ° and 3 ° at the vane's maximum installation angle θ.

While the foregoing findings are considered the main features for forming the camber vanes of the present invention, there are other features that affect the controllability of the vanes.

Radius r forming the curve of bow edge Ple and distance Xp between pivot point Pp and bow edge Ple on the x-axis are preferably 0.045 < r / Xp < 0.08 It was found that the expression was satisfied. Setting the radius r within this range reduces the vane's sensitivity to changes in incidence of the flow.

Further, the minimum and maximum installation angles θ of the vanes are determined by a ratio (Rle / Rte) of the tangential radii Rle of the bow edges Ple of the vanes to the tangential radii Rte of the trailing edges Pte. It was confirmed that it is preferable to have a range of 1.03 to 1.5. This is in comparison with conventional turbochargers with typical Rle / Rte ranges between 1.05 and 1.7.

Further, the shape of the convex section of the airfoil inner surface 4 is not limited to a curve having a local maximum value between the parabola or bow point Ple and a bending point indicating a transition to the concave area, but having a local minimum value. Quadratic polynomials are also suitable. However, local maximums are preferred.

Claims (12)

In a turbocharger (10) having a variable nozzle assembly having a plurality of camber vanes (20) arranged annularly around a turbine wheel (30), Each vane 20 is pivotable around a pivot point Pp and connected by an airfoil outer surface 2 on the outside of the vane 20 and an airfoil inner surface 4 on the inside of the vane 20. Configured to have a leading edge (Ple) and a trailing edge (Pte), The airfoil outer surface 2 is substantially convex, The airfoil inner surface 4 has a convex section at the bow edge Ple that has a local pole Pex of the curved portion and shifts into a concave zone towards the trailing edge Pte, In the coordinate system where the origin is the bow edge Ple and the x-axis goes to the bow edge Pte and the y-axis is perpendicular to the x-axis and outward of the vane 20, the pivot point Pp is Xp is the distance between the pivot point Pp and the bow edge Ple on the x-axis, C is the distance between the bow edge Ple and the trailing edge pte, and Yp is the y The distance between the pivot point Pp on the axis and the camber line 6 of the vane 20, and a negative value of Yp represents the pivot point Pp further inside of the vane 20. Expression 0.25 <Xp / C <0.45, preferably 0.30 <Xp / C <0.40; And −0.10 ≦ Yp / C ≦ 0.05, preferably −0.10 ≦ Yp / C ≦ 0, most preferably −0.10 ≦ Yp / C ≦ −0.05 Turbocharger, characterized in that arranged in a position to satisfy the. The method of claim 1, Yp is turbocharged (10), characterized in that the pivot point (Pp) is set between the airfoil outer surface (2) and the airfoil inner surface (4). The method according to claim 1 or 2, The local pole (Pex), An expression where Xex is the distance between the local pole Pex and the bow edge Ple on the x-axis 0.3 <(Xp-Xex) / Xp <0.8, preferably 0.4 <(Xp-Xex) / Xp <0.7, most preferably 0.49 <(Xp-Xex) / Xp <0.60 Turbocharger, characterized in that arranged in a position that satisfies. The method according to any one of claims 1 to 3, The local pole (Pex), Xex is the distance between the local pole Pex and the bow edge Ple on the x-axis, and Yex is the distance between the local pole Pex and bow edge Ple on the y-axis. 0.40 <Yex / Xex <0.83 Turbocharger, characterized in that arranged in a position that satisfies. The method according to any one of claims 1 to 4, When the vanes 20 are in the closed position, the turbocharger characterized in that the flow incident angle α of the exhaust gas with respect to the line connecting the bow edge Ple and the pivot point Pp is 5 ° or more. (10). In a turbocharger (10) having a variable nozzle assembly having a plurality of camber vanes (20) arranged annularly around a turbine wheel (30), Each vane 20 is pivotable about a pivot point Pp and is connected by an airfoil outer surface 2 on the outside of the vane 20 and an airfoil inner surface 4 on the inside of the vane 20. Configured to have a leading edge (Ple) and a tailing edge (Pte), The airfoil outer surface 2 is substantially convex, The airfoil inner surface 4 has a convex section at the bow edge Ple that has a local pole Pex of the curved portion and shifts into a concave zone towards the trailing edge Pte, In the coordinate system where the origin is the bow edge Ple and the x-axis goes to the bow edge Pte and the y-axis is perpendicular to the x-axis and outwards of the vane 20, the local pole Pex is Xp is the distance between the pivot point Pp and the bow edge Ple on the x-axis, and Xex is the distance between the local pole Pex and the bow edge Ple on the x-axis. Expression 0.3 <(Xp-Xex) / Xp <0.8, preferably 0.4 <(Xp-Xex) / Xp <0.7, most preferably 0.49 <(Xp-Xex) / Xp <0.60 Turbocharger, characterized in that arranged in a position that satisfies. In a turbocharger (10) having a variable nozzle assembly having a plurality of camber vanes (20) arranged annularly around a turbine wheel (30), Each vane 20 is pivotable around a pivot point Pp and connected by an airfoil outer surface 2 on the outside of the vane 20 and an airfoil inner surface 4 on the inside of the vane 20. Configured to have a leading edge (Ple) and a trailing edge (Pte), The airfoil outer surface 2 is substantially convex, The airfoil inner surface 4 has a convex section at the bow edge Ple that has a local pole Pex of the curved portion and shifts into a concave zone towards the trailing edge Pte, In the coordinate system where the origin is the bow edge Ple and the x-axis goes to the bow edge Pte and the y-axis is perpendicular to the x-axis and outwards of the vane 20, the local pole Pex is Xex is the distance between the local pole Pex and the bow edge Ple on the x-axis, and Yex is the distance between the local pole Pex and bow edge Ple on the y-axis. 0.40 <Yex / Xex <0.83 Turbocharger, characterized in that arranged in a position that satisfies. In the turbocharger (10) having a variable nozzle assembly having a plurality of camber vanes (20) arranged annularly around a turbine wheel (30), Each vane 20 is pivotable around a pivot point Pp and connected by an airfoil outer surface 2 on the outside of the vane 20 and an airfoil inner surface 4 on the inside of the vane 20. Configured to have a leading edge (Ple) and a trailing edge (Pte), The airfoil outer surface 2 is substantially convex, The airfoil inner surface 4 has a convex section at the bow edge Ple that transitions into a concave section towards the trailing edge Pte, When the vanes 20 are in the closed position, the turbocharger characterized in that the flow incident angle α of the exhaust gas with respect to the line connecting the bow edge Ple and the pivot point Pp is 5 ° or more. (10). The method according to any one of claims 1 to 8, The bow edge Ple is, Xp is an expression representing the distance between the pivot point Pp and the bow edge Ple on the x-axis. 0.045 <r / Xp <0.08 Turbocharger (10), characterized in that formed as a curve having a radius (r) satisfying the. The method according to any one of claims 1 to 9, The convex section of the airfoil inner surface 4 comprises a series of curves which form the bow edge Ple and transitions into a parabola, and one selected from a curve or an elliptic curve connecting the parabola and the concave section. Turbocharger (10), characterized in that formed by a synthetic curve of. The method according to any one of claims 1 to 10, The turbocharger (10), characterized in that the airfoil outer surface (2) is formed of a series of synthetic curves comprising a curved line which forms the bow edge (Ple) and shifts into an elliptic curve. The method according to any one of claims 1 to 11, When the vanes 20 pivot between a closed position and an open position, the tangent of the bow edges Ple of the vanes 20 with respect to the tangential radius Rte of the trailing edges Pte. Turbocharger (10), characterized in that the ratio (Rle / Rte) of the radius (Rle) ranges from 1.03 to 1.5.

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