JP7517263B2 - Turbocharger - Google Patents

Description

The present invention relates to a turbocharger.

A turbocharger uses the energy of exhaust gas from an internal combustion engine to supercharge the internal combustion engine. The turbocharger has a turbine wheel and a turbine scroll section arranged on the outer periphery of the turbine wheel. The turbocharger also has multiple nozzle vanes in the turbine scroll section. The multiple nozzle vanes are arranged on the outer periphery of the turbine wheel at equal intervals in the circumferential direction of the turbine wheel. The space between adjacent nozzle vanes in the circumferential direction is a gas flow path through which exhaust gas flows. The nozzle vanes regulate the flow of exhaust gas from the turbine scroll section toward the turbine wheel and adjust the flow speed.

The nozzle vane disclosed in Patent Document 1 is a so-called variable nozzle vane. In a turbocharger equipped with a variable nozzle vane, when the flow rate of exhaust gas is low, the variable nozzle vane closes the gas flow path. This speeds up the flow of exhaust gas toward the turbine wheel. In this way, a turbocharger equipped with a variable nozzle vane increases the efficiency of exhaust gas flow into the turbine wheel.

In turbochargers with fixed nozzle vanes, the nozzle vanes are fixed at a predetermined inclination angle that is set during the design stage. The predetermined inclination angle is the angle at which the desired exhaust gas inflow efficiency is obtained in the target exhaust gas flow rate range. In this way, turbochargers with fixed nozzle vanes increase the efficiency of exhaust gas inflow into the turbine wheel.

JP 2013-137017 A

However, in turbochargers, there is always a demand to improve the efficiency of exhaust gas flow into the turbine wheel.

A turbocharger for solving the above problems has a turbine wheel, a turbine scroll section arranged on the outer periphery of the turbine wheel, a gas inlet passage that guides exhaust gas from an internal combustion engine to the turbine scroll section, a plurality of nozzle vanes arranged inside the turbine scroll section and spaced apart in the circumferential direction of the turbine scroll section, and a gas flow passage defined between adjacent nozzle vanes in the flow direction of the exhaust gas in the turbine scroll section, and is a turbocharger that supercharges using the energy of the exhaust gas, and the nozzle vanes are an inlet of the exhaust gas to the gas flow passage. The nozzle vane has an inlet leading edge including a front end located on the exhaust gas outlet side of the gas flow path, and an outlet trailing edge including a rear end located on the exhaust gas outlet side of the gas flow path, and the length of the nozzle vane along the blade centerline connecting the front end and the rear end is taken as the total length, and the inlet leading edge is an arc-shaped portion provided in an area that is 10 to 40% of the total length from the front end, and the radius of curvature of the arc of the inlet leading edge is 10% or more of the total length, or the inlet leading edge is a shape that includes multiple arcs provided in an area that is 10 to 40% of the total length from the front end, and the radius of curvature of the smallest arc of the multiple arcs is 10% or more of the total length.

The comparative example is an inlet leading edge having, as a single arc or as one of multiple arcs, an arc with a radius of curvature that is less than 10% of the overall length. Compared to this comparative example, the length of the arc of the inlet leading edge can be made longer, so the length of the arc along the inlet leading edge to the gas flow path can be made longer. As a result, the area that functions as a nozzle between the inlet leading edge and the outlet trailing edge of adjacent nozzle vanes in the flow direction of exhaust gas can be made longer than in the comparative example. As a result, the nozzle function between adjacent nozzle vanes can increase the flow rate of exhaust gas compared to the comparative example, making it easier for exhaust gas to flow from the inlet leading edge to the gas flow path. Therefore, in a turbocharger, the efficiency of exhaust gas flow into the turbine wheel can be improved.

A turbocharger for solving the above problems includes a turbine wheel, a turbine scroll section arranged on the outer periphery of the turbine wheel, a gas inlet passage that guides exhaust gas from an internal combustion engine to the turbine scroll section, a plurality of movable nozzle vanes arranged inside the turbine scroll section and spaced apart in the circumferential direction of the turbine scroll section, and a gas flow passage defined between adjacent nozzle vanes in the flow direction of the exhaust gas in the turbine scroll section, the turbine scroll section includes two flow passages that branch into two at the outlet of the gas inlet passage, and the flow direction of the exhaust gas that flows into one of the branched flow passages and the flow direction of the exhaust gas that flows into the other flow passage are opposite to each other in the circumferential direction of the turbine scroll section. The turbocharger uses the energy of the exhaust gas to supercharge and adjusts the flow of the exhaust gas flowing through the gas flow passage with the nozzle vane, and the nozzle vane has an inlet leading edge portion including a front end located on the inlet side of the exhaust gas into the gas flow passage, an outlet trailing edge portion including a rear end located on the outlet side of the exhaust gas in the gas flow passage, and an outer surface and an inner surface connecting the front end and the rear end, and the rate of change in the plate thickness of the nozzle vane from the front end to the rear end is defined as a rate of change, and the inlet leading edge portion is a large rate of change portion where the rate of change is larger than the rate of change at a portion including the outlet trailing edge portion, and the outlet trailing edge portion includes a small rate of change portion where the rate of change is smaller than the large rate of change portion, and the large rate of change portion is an arc shape including the front end.

As a result, the flow of the exhaust gas slows down as it flows along the two bifurcated flow paths. In addition, when the inlet leading edge of the nozzle vane is formed as a small change rate section, the exhaust gas is likely to separate from the inlet leading edge. However, by making the inlet leading edge a large change rate section and making the arc longer than the small change rate section, the exhaust gas flows along the arc of the inlet leading edge and is less likely to separate from the inlet leading edge. As a result, the exhaust gas can be efficiently made to flow near the inner surface of the nozzle vane. This prevents the pressure near the inner surface of the nozzle vane from becoming negative compared to the exhaust gas. As a result, the nozzle vane can be prevented from rotating in a direction that closes the gas flow path due to the exhaust gas pressure being applied to the inlet leading edge side of the nozzle vane. Therefore, in the turbocharger, the efficiency of the exhaust gas flowing into the turbine wheel can be improved.

For a turbocharger, the nozzle vane has a blade centerline connecting the front end and the rear end, and when the length of the nozzle vane along the blade centerline is the total length, the large change rate portion is an arc located in an area from the front end that is 10 to 40% of the total length, and the radius of curvature of the arc of the large change rate portion is 10% or more of the total length, or the large change rate portion is a shape including multiple arcs located in an area from the front end that is 10 to 40% of the total length, and the radius of curvature of the smallest arc of the multiple arcs is 10% or more of the total length.

This ensures a long arc at the portion where the rate of change is large, and when the gas flow passage is opened by the nozzle vane, the exhaust gas is even less likely to separate from the inlet leading edge.
For a turbocharger, the nozzle vane may have a straight blade centerline, or the blade centerline may extend straight from the rear end to the front end, and then the outer surface may be curved so as to approach the turbine scroll section toward the front end.

The nozzle vane of the reference example is as follows. In the nozzle vane of the reference example, the blade centerline extends in a straight line from the rear end to the front end, and then the inner surface is curved so that it bulges near the inlet leading edge. Compared to this reference example, exhaust gas flows along the arc of the inlet leading edge, making it less likely to separate from the inlet leading edge.

For a turbocharger, the blade centerline may extend linearly from the rear end to the front end, and the outer surface may be curved to approach the turbine scroll portion as it approaches the front end.

Compared to the reference example, this allows the exhaust gas to flow along the arc of the inlet leading edge, making it less likely to separate from the inlet leading edge.

The present invention improves the efficiency of exhaust gas flow into the turbine wheel.

1 is a schematic diagram showing a turbocharger according to an embodiment; 1 is a cross-sectional view showing a turbocharger according to an embodiment; FIG. 2 is a diagram showing a unison ring, a connecting arm, and a nozzle vane. FIG. 4 is a plan view showing a nozzle vane according to the embodiment. FIG. 4 is a plan view showing a nozzle vane of a comparative example. FIG. 4 is an enlarged view showing a state in which the flow passage cross-sectional area of the gas flow passage is at a minimum. 4 is a graph showing the relationship between a turbine inlet gas flow rate and a turbo overall efficiency. FIG. 4 is a plan view showing a nozzle vane according to another embodiment. FIG. 4 is a plan view showing a nozzle vane according to another embodiment.

Hereinafter, one embodiment of a turbocharger will be described with reference to FIGS.
<Overall composition>
1 and 2, the turbocharger 10 has a compressor 11 and a turbine 12. The turbocharger 10 supercharges by using the energy of exhaust gas from an internal combustion engine (not shown).

<Compressor 11>
The compressor 11 has a compressor wheel (not shown) that rotates together with the turbine wheel 13 of the turbine 12, an intake air inlet 18, and an intake air outlet (not shown).

<Turbine 12>
The turbine 12 has a turbine wheel 13, a turbine scroll section 14, a first gas inlet passage 15a and a second gas inlet passage 15b, a first gas inlet 16a and a second gas inlet 16b, a gas discharge port 17, and a plurality of movable nozzle vanes 30.

The turbine wheel 13 rotates around the rotation axis L. The turbine scroll section 14 is disposed on the outer periphery of the turbine wheel 13. The turbine scroll section 14 is formed for only one continuous revolution in the circumferential direction of the outer periphery of the turbine wheel 13. The turbine scroll section 14 branches into two from the outlet of the first gas introduction passage 15a and the outlet of the second gas introduction passage 15b and surrounds the turbine wheel 13.

The turbine scroll section 14 includes a first flow path 14a and a second flow path 14b that are bifurcated at the outlet of the first gas introduction path 15a and the outlet of the second gas introduction path 15b. Exhaust gas flows into the first flow path 14a from the first gas introduction path 15a. Exhaust gas flows into the second flow path 14b from the second gas introduction path 15b. In a plan view of the turbine scroll section 14 along the rotation axis L, the exhaust gas that flows into the first flow path 14a flows in a clockwise direction as one direction, and the exhaust gas that flows into the second flow path 14b flows in a counterclockwise direction as the other direction. Therefore, the flow direction of the exhaust gas that flows into the first flow path 14a, which is one flow path, and the flow direction of the exhaust gas that flows into the second flow path 14b, which is the other flow path, are opposite to each other in the circumferential direction of the turbine scroll section 14.

Therefore, the turbocharger 10 of this embodiment employs a method in which exhaust gas flowing into the turbine 12 is branched into two flow paths and flows into the turbine scroll section 14. In this type of turbocharger 10, the flow path cross-sectional area of the first flow path 14a and the flow path cross-sectional area of the second flow path 14b are the same or approximately the same at any position in the circumferential direction of the turbine scroll section 14. Therefore, the amount of change in the flow path cross-sectional area of the first flow path 14a along the circumferential direction of the turbine scroll section 14 is zero or small. Similarly, the amount of change in the flow path cross-sectional area of the second flow path 14b along the circumferential direction of the turbine scroll section 14 is zero or small. Note that the flow path cross-sectional area of the first flow path 14a and the flow path cross-sectional area of the second flow path 14b are the same or approximately the same.

The first gas introduction passage 15a and the second gas introduction passage 15b are connected to an exhaust pipe (not shown). The first gas introduction passage 15a and the second gas introduction passage 15b guide exhaust gas from an internal combustion engine (not shown) to the turbine scroll section 14.

The first gas inlet 16a is disposed on the inlet side of the first gas introduction passage 15a. The second gas inlet 16b is disposed on the inlet side of the second gas introduction passage 15b. The first gas inlet 16a and the second gas inlet 16b are divided by a partition wall 27a so that their opening areas are approximately the same. The partition wall 27a is provided in the first gas introduction passage 15a at a position from the first gas inlet 16a to the nozzle vane 30, and in the second gas introduction passage 15b at a position from the second gas inlet 16b to the nozzle vane 30.

A flow passage end partition 27b is arranged around the position opposite to the first gas introduction passage 15a and the second gas introduction passage 15b in the turbine scroll section 14. The flow passage end partition 27b is provided so as to extend from the inner peripheral surface of the turbine scroll section 14 to the nozzle vane 30. The flow passage end partition 27b divides the turbine scroll section 14 into a first flow passage 14a that swirls the exhaust gas in a clockwise direction and a second flow passage 14b that swirls the exhaust gas in a counterclockwise direction. The flow passage end partition 27b prevents the exhaust gas swirling in the clockwise direction along the first flow passage 14a and the exhaust gas swirling in the counterclockwise direction along the second flow passage 14b from colliding and interfering with each other.

The nozzle vanes 30 are arranged inside the turbine scroll section 14. The nozzle vanes 30 are arranged on the outer periphery of the turbine wheel 13 in the turbine scroll section 14. Each nozzle vane 30 is supported by the nozzle plate 24. Each nozzle vane 30 regulates the flow of exhaust gas blown onto the turbine wheel 13. The nozzle vanes 30 are arranged at equal intervals along the circumferential direction of the turbine wheel 13. A gas flow passage 39 is defined between adjacent nozzle vanes 30 in the flow direction of the exhaust gas in the turbine scroll section 14. The flow passage cross-sectional area of the gas flow passage 39 is changed by adjusting the opening degree of the nozzle vane 30. Therefore, each nozzle vane 30 regulates the flow of exhaust gas flowing through the gas flow passage 39.

Each nozzle vane 30 has a pin 29 integrally formed therewith, which protrudes from the nozzle vane 30. Each nozzle vane 30 rotates about the central axis of the pin 29. The pin 29 passes through the nozzle plate 24.

As shown in FIG. 3, the pin 29 that passes through the nozzle plate 24 is attached to the first end 50a of the connecting arm 50. The second end 50b of the connecting arm 50 is connected to the unison ring 25. The unison ring 25 has the same number of connecting grooves 26 as the nozzle vanes 30. The unison ring 25 is placed on top of the nozzle plate 24 so that the central axis of the unison ring 25 coincides with the rotational axis L of the turbine wheel 13.

The second end 50b of the connecting arm 50 is connected to each of the connecting grooves 26 of the unison ring 25. Note that there is a slight gap in the circumferential direction of the unison ring 25 between the inner surface of the connecting groove 26 and the second end 50b of the connecting arm 50.

As shown in Figures 1 and 2, the turbocharger 10 has a nozzle vane drive unit 21, a nozzle vane opening detection unit 22 such as an encoder, and an arm 23 and a link member 28 that transmit power from the nozzle vane drive unit 21 to a unison ring 25. A first end of the link member 28 is swingably connected to the tip of the arm 23. A shaft (not shown) is rotatably supported at a second end of the link member 28. A first end of a drive arm 49 is swingably connected to the shaft (not shown). The second end of the drive arm 49 is connected to the unison ring 25.

In the turbocharger 10, a control device (not shown) calculates a target opening of the nozzle vanes 30 based on the operating state of the internal combustion engine (not shown). The control device controls the nozzle vane drive unit 21 so that the opening of the nozzle vanes 30 detected using the nozzle vane opening detection unit 22 approaches the target opening. When the arm 23 is driven by the nozzle vane drive unit 21, the link member 28 swings and the shaft (not shown) rotates. This causes the drive arm 49 to swing and the unison ring 25 to rotate. As the unison ring 25 rotates, the nozzle vanes 30 move in the direction in which the unison ring 25 rotates.

When the nozzle vanes 30 are moved to adjust the opening of the nozzle vanes 30, the distance between adjacent nozzle vanes 30 is adjusted. This adjusts the flow passage cross-sectional area of the gas flow passage 39, and also adjusts the flow direction and flow speed of the exhaust gas flowing from the turbine scroll section 14 to the turbine wheel 13.

<Details of the nozzle vane 30>
Next, the nozzle vanes 30 will be described in detail.
The nozzle vane 30 is viewed in the axial direction of the pin 29 in a plan view.

As shown in Figures 2 and 4, the nozzle vane 30 has an inlet leading edge 31, an outlet trailing edge 32, and a connecting portion 33. The inlet leading edge 31 is located on the inlet side in the direction in which exhaust gas flows from the turbine scroll portion 14 toward the turbine wheel 13. The outlet trailing edge 32 is located on the outlet side in the direction in which exhaust gas flows from the turbine scroll portion 14 toward the turbine wheel 13. The connecting portion 33 connects the inlet leading edge 31 and the outlet trailing edge 32.

The composite curve connecting the inlet leading edge 31 and the outlet trailing edge 32 of the nozzle vane 30 is the blade centerline 35. The nozzle vane 30 has a leading end 30a at the position where the inlet leading edge 31 and the blade centerline 35 intersect, and a trailing end 30b near the position where the outlet trailing edge 32 and the blade centerline 35 intersect. Thus, the nozzle vane 30 has an inlet leading edge 31 including the leading end 30a located on the inlet side of the exhaust gas to the gas flow path 39, and an outlet trailing edge 32 including the trailing end 30b located on the outlet side of the exhaust gas in the gas flow path 39.

The nozzle vane 30 has an inner surface 41 and an outer surface 42 that connect the front end 30a and the rear end 30b in a plan view. The outer surface 42 is closer to the turbine scroll section 14 than the inner surface 41. If the dimension between the inner surface 41 and the outer surface 42 is the plate thickness of the nozzle vane 30 in a plan view, the outer surface 42 is the surface opposite the inner surface 41 in the plate thickness direction. The blade centerline 35 passes through the center of the nozzle vane 30 in the plate thickness direction in a plan view.

The inlet leading edge 31 is defined by an arc with a first radius of curvature R1. That is, the inlet leading edge 31 is defined by a single arc. In plan view, the inlet leading edge 31 is a smoothly curved arc. The outlet trailing edge 32 is defined by an arc with a second radius of curvature R2 that is much smaller than the first radius of curvature R1.

The nozzle vane 30 has a front inflection point Pf at the boundary between the inlet leading edge 31 and the connection 33 in a plan view. The nozzle vane 30 also has a rear inflection point Pb at the boundary between the outlet trailing edge 32 and the connection 33 in a plan view.

The inner surface 41 at the connection portion 33 is a compound curve in plan view. The inner surface 41 at the connection portion 33 extends between the front inflection point Pf and the rear inflection point Pb. The inner surface 41 at the inlet leading edge portion 31 extends in an arc shape from the front inflection point Pf to the leading end 30a.

The outer surface 42 at the connection portion 33 extends in a compound curve in plan view. The outer surface 42 at the connection portion 33 curves to gently bulge from the rear inflection point Pb to the vicinity of the pin 29, then curves to gently concave toward the inner surface 41 near the pin 29 to reach the front inflection point Pf. The outer surface 42 at the inlet leading edge portion 31 extends in an arc from the front inflection point Pf to the leading end 30a. The entire inlet leading edge portion 31 is arc-shaped with a constant radius of curvature.

Therefore, in plan view, the nozzle vane 30 has a blade centerline 35 that extends in a compound curve from the rear end 30b to the front end 30a, and then curves toward the turbine scroll section 14 near the pin 29, i.e., near the inlet leading edge 31, toward the front end 30a. Therefore, in plan view, the inlet leading edge 31 has a shape in which the outer surface 42 bulges toward the turbine scroll section 14. In other words, the inlet leading edge 31 does not bulge toward the turbine wheel 13 on the inner surface 41 side.

Here, the rate of change in thickness from the front end 30a to the rear end 30b of the nozzle vane 30 is defined as the rate of change. In plan view, the inlet leading edge 31 has an arc with a first radius of curvature R1. Therefore, the thickness of the nozzle vane 30 increases at a constant rate of change from the front end 30a to the front inflection point Pf at the inlet leading edge 31. Furthermore, the thickness of the nozzle vane 30 decreases at a smaller rate of change near the pin 29 from the front inflection point Pf to the rear end 30b than at the inlet leading edge 31. The thickness of the nozzle vane 30 gradually decreases from the vicinity of the pin 29 to the rear end 30b at a smaller rate of change than at the inlet leading edge 31.

In other words, the rate of change in the thickness of the nozzle vane 30 increases rapidly from the front end 30a toward the front inflection point Pf, and then decreases rapidly once the front inflection point Pf is exceeded. The outer surface 42 of the inlet leading edge portion 31 bulges rapidly toward the turbine scroll portion 14 on the rear end 30b side of the front inflection point Pf.

For the nozzle vane 30, the inlet leading edge 31 is the large change rate portion 51. In contrast, the portion from the rear end 30b of the nozzle vane 30 to the pin 29 has a smaller change rate than the inlet leading edge 31. Therefore, the portion from the rear end 30b of the nozzle vane 30 to the pin 29 is the small change rate portion 52. Therefore, the nozzle vane 30 has the large change rate portion 51 in the portion including the front end 30a, and the small change rate portion 52 in the portion including the rear end 30b, which has a smaller change rate than the large change rate portion 51. Therefore, it can be said that the inlet leading edge 31 is the large change rate portion 51, whose rate of change is larger than the rate of change in the portion including the outlet trailing edge 32.

The blade centerline 35 passes through the center of the plate thickness of the nozzle vane 30. Therefore, in this embodiment, the shape of the blade centerline 35 can be said to indicate the rate of change of the plate thickness. The blade centerline 35 is inclined at a greater angle on the leading end 30a side than the pin 29. Therefore, the nozzle vane 30 can be said to have a large rate of change portion 51 at the inlet leading edge portion 31 located on the leading end 30a side than the pin 29.

The length of the nozzle vane 30 along the blade centerline 35 connecting the front end 30a and the rear end 30b is defined as the total length M. The large change rate portion 51, i.e., the inlet leading edge portion 31, is provided in a region having a length of 10 to 40% of the total length M from the front end 30a along the blade centerline 35. The first curvature radius R1 of the large change rate portion 51, i.e., the inlet leading edge portion 31, is 10% or more of the total length M. In this embodiment, the first curvature radius R1 is set to 15% of the total length M of the blade centerline 35. By setting the first curvature radius R1 in this manner, even in the nozzle vane 30 having the small change rate portion 52 including the outlet trailing edge portion 32, the outer surface 42 side of the inlet leading edge portion 31 is suddenly bulged toward the turbine scroll portion 14.

In the nozzle vane 30, the vicinity of the forward inflection point Pf on the inner surface 41 side is configured as a throat portion 44 that constitutes a throat portion where the flow cross-sectional area of the gas flow passage 39 is minimum between the adjacent nozzle vane 30 on the upstream side in the flow direction of the exhaust gas.

In each nozzle vane 30, the surface located on the front end 30a side of the throat portion 44 is the nozzle forming surface 34, which is arcuate in plan view. The nozzle forming surface 34 functions as a nozzle that narrows the gas flow path 39 between the outer surface 42 of the adjacent nozzle vane 30 on the upstream side.

<Action>
Next, the operation of the turbocharger 10 will be described.
First, the nozzle vane 70 of the comparative example will be described.

As shown in FIG. 5, the nozzle vane 70 of the comparative example is viewed in a plan view along the axial direction of the pin 80. The nozzle vane 70 has an inlet leading edge 71 on the side where exhaust gas flows from the turbine scroll section 14 toward the turbine wheel 13. The nozzle vane 70 has an outlet trailing edge 72 at the edge close to the turbine wheel 13. The nozzle vane 70 also has a connecting portion 73 that connects the inlet leading edge 71 and the outlet trailing edge 72.

The straight line connecting the inlet leading edge 71 and the outlet trailing edge 72 of the nozzle vane 70 is the blade centerline 75. The blade centerline 75 passes through the center of the nozzle vane 70 in the plate thickness direction. In a plan view of the nozzle vane 70, the nozzle vane 70 has a leading end 70a at the position where the inlet leading edge 71 and the blade centerline 75 intersect. In a plan view of the nozzle vane 70, the nozzle vane 70 has a trailing end 70b near the position where the outlet trailing edge 72 and the blade centerline 75 intersect.

The inlet leading edge 71 is defined as a multi-arc shape including curves having a third radius of curvature R3, a fourth radius of curvature R4, and a fifth radius of curvature R5. The fourth radius of curvature R4 is smaller than the third radius of curvature R3, and the fifth radius of curvature R5 is larger than the third radius of curvature R3. In a plan view of the nozzle vane 30, the inlet leading edge 71 is a multi-arc shape portion. The third to fifth radii of curvature R3 to R5 are less than 10% of the total length of the blade centerline 75. Therefore, the inlet leading edge 71 is an arc shape with a radius of curvature that is less than 10% of the total length of the blade centerline 75. The outlet trailing edge 72 is defined as an arc shape including a curve having a sixth radius of curvature R6 that is smaller than the third to fifth radii of curvature R3 to R5.

The third to fifth radii of curvature R3 to R5 of the comparative example are smaller than the first radius of curvature R1, and the sixth radius of curvature R6 of the comparative example is approximately the same as the second radius of curvature R2.
The nozzle vane 70 has an inner surface 74 connecting a leading end 70a to an aft end 70b and an outer surface 76. The inner surface 74 and the outer surface 76 extend in a compound curve between an inlet leading edge 71 and an outlet trailing edge 72.

In a plan view of the nozzle vane 70, the dimension between the inner surface 74 and the outer surface 76 is the plate thickness. The plate thickness of the nozzle vane 70 gradually increases from the leading end 70a to the trailing end 70b along the blade centerline 75, and then gradually decreases.

The rate of change in thickness of the nozzle vane 70 increases at a constant rate from the front end 70a at the inlet leading edge 71. The rate of change in thickness then decreases at a nearly constant rate toward the outlet trailing edge 72. Therefore, the nozzle vane 70 can be said to have a small rate of change over the entire area between the leading end 70a and the trailing end 70b.

Next, the effect of the turbocharger 10 will be described. It is assumed that the flow rate of exhaust gas discharged from the internal combustion engine is low, and the opening of the nozzle vanes 30 is adjusted to the closing side to reduce the flow passage cross-sectional area of the gas flow passage 39.

Now, as shown in FIG. 2, the turbine wheel 13 rotates in a counterclockwise direction. The exhaust gas that flows into the first gas introduction passage 15a from the first gas inlet 16a swirls in a clockwise direction in the first passage 14a. The exhaust gas swirling in the clockwise direction is adjusted by the nozzle vane 30 so that it swirls in a counterclockwise direction and flows toward the gas passage 39.

The exhaust gas that flows into the second gas introduction passage 15b from the second gas inlet 16b swirls in a counterclockwise direction in the second passage 14b. The exhaust gas swirling in the counterclockwise direction is adjusted by the nozzle vane 30 so that the flow direction of the exhaust gas continues to flow counterclockwise toward the gas passage 39.

In such a turbocharger 10, the exhaust gas flows through the turbine scroll section 14, splitting into two parts: the exhaust gas that flows into the first flow passage 14a and the exhaust gas that flows into the second flow passage 14b. The flow passage cross-sectional area of each of the first flow passage 14a and the second flow passage 14b has zero or little change in the circumferential direction of the turbine scroll section 14. Therefore, the flow of the exhaust gas that flows into the first flow passage 14a gradually slows down, and the flow of the exhaust gas that flows into the second flow passage 14b gradually slows down. In addition, the exhaust gas that flows into the first flow passage 14a has difficulty flowing in a counterclockwise direction near the nozzle vane 30, and flows in a radial direction relative to the nozzle vane 30. Similarly, the exhaust gas that flows into the second flow passage 14b has difficulty flowing in a counterclockwise direction near the nozzle vane 30, and flows in a radial direction relative to the nozzle vane 30.

Compared to the nozzle vane 70 of the comparative example, the length of the arc of the inlet leading edge 31 can be made longer, so the length of the arc from the front end 30a to the gas flow passage 39 can be made longer. As a result, as shown in FIG. 6, even if the opening of the nozzle vane 30 is adjusted to the closing side, the area that functions as a nozzle between the inlet leading edge 31 and the outlet trailing edge 32 of adjacent nozzle vanes 30 in the exhaust gas flow direction can be secured longer than in the comparative example.

As a result, the nozzle function between adjacent nozzle vanes 30 can increase the flow rate of the exhaust gas, making it easier for the exhaust gas to flow from the inlet leading edge 31 toward the gas flow path 39.

On the other hand, even if the flow rate of exhaust gas discharged from the internal combustion engine increases and the opening of the nozzle vane 30 is adjusted to open the cross-sectional area of the gas flow passage 39, the exhaust gas tends to flow along the arc with the first radius of curvature R1. This prevents the area near the inner surface 41 on the inlet leading edge 31 side of the nozzle vane 30 from becoming negative pressure compared to the exhaust gas. This prevents the nozzle vane 30 from receiving the pressure of the exhaust gas and rotating in the direction of closing the gas flow passage 39. This allows an appropriate rotational torque to be generated near the inlet leading edge 31 of the nozzle vane 30.

Then, the second end 50b of the connecting arm 50 connected to each nozzle vane 30 is pressed against the inner surface of the connecting groove 26 of the unison ring 25. As a result, the gap between the inner surface of the connecting groove 26 and the second end 50b of the connecting arm 50 is absorbed. Therefore, the angle of the nozzle vane 30 is determined to be constant. In other words, the nozzle vane 30 receives the flow of exhaust gas from the turbine scroll section 14 side and rotates in the direction in which it should rotate.

The horizontal axis of the graph in Figure 7 shows the turbine inlet gas flow rate, and the vertical axis shows the turbo overall efficiency. The turbine inlet gas flow rate is the total amount of exhaust gas that flows into the turbine scroll section 14. The turbo overall efficiency indicates how much of the exhaust gas energy was recovered as rotational energy for the turbine wheel 13. The solid line graph shows the results for the turbocharger 10 using the nozzle vane 30, and the dashed line graph shows the results for the turbocharger using the comparative nozzle vane 70.

Compared to the turbocharger of the comparative example, the turbocharger 10 of the embodiment showed improved turbo overall efficiency in areas with low turbine inlet gas flow rates. This is because the area that functions as a nozzle between the inlet leading edge 31 and the outlet trailing edge 32 of the nozzle vanes 30 adjacent in the exhaust gas flow direction is longer than in the comparative example.

According to the above embodiment, the following effects can be obtained.
(1) The inlet leading edge 31 is provided in a region having a length of 10 to 40% of the total length M from the front end 30a. The arc of the inlet leading edge 31 has a radius of curvature of 10% or more of the total length M. Compared to the nozzle vane 70 of the comparative example, the length of the arc of the inlet leading edge 31 can be made longer, so that the portion that functions as a nozzle between adjacent nozzle vanes 30 can be made longer than in the comparative example. Therefore, even when the nozzle vane 30 is adjusted to the closing side of the gas flow path 39, the flow velocity of the exhaust gas in the gas flow path 39 can be increased, so that the exhaust gas can easily flow from the inlet leading edge 31 toward the gas flow path 39. Therefore, in the turbocharger 10, the inflow efficiency of the exhaust gas into the turbine wheel 13 can be improved.

(2) Even when the nozzle vane 30 is adjusted to the opening side of the gas flow path 39, the exhaust gas flows along the inlet leading edge 31 and is less likely to separate from the inlet leading edge 31. As a result, the exhaust gas is prevented from flowing near the inner surface 41 of the nozzle vane 30 and generating negative pressure near the inner surface 41. This makes it possible to prevent the nozzle vane 30 from rotating in the direction of closing the gas flow path 39 due to the pressure of the exhaust gas.

(3) Because exhaust gas is prevented from flowing near the inner surface 41 of the nozzle vane 30 and generating negative pressure, the nozzle vane 30 receives the pressure of the exhaust gas and generates an appropriate rotational torque, making it easier to determine the angle of the nozzle vane 30 at a constant value. In other words, the nozzle vane 30 receives the flow of exhaust gas from the turbine scroll section 14 side and rotates in the direction it should rotate. This makes it possible to appropriately adjust the flow rate of exhaust gas heading toward the turbine wheel 13.

(4) The arc of the inlet leading edge 31 has a radius of curvature that is at least 10% of the total length M of the blade centerline 35. This ensures a long arc at the inlet leading edge 31, making it even more difficult for exhaust gas to separate from the inlet leading edge 31 when the nozzle vane 30 opens the gas flow path 39.

(5) The blade centerline 35 extends in a compound curve from the rear end 30b to the front end 30a, and then the outer surface 42 bulges toward the turbine scroll section 14 near the pin 29 toward the front end 30a. Compared to a shape in which the inner surface 41 side of the inlet leading edge 31 bulges toward the turbine wheel 13, the flow passage cross-sectional area of the gas flow passage 39 can be made larger. In addition, separation of exhaust gas along the inlet leading edge 31 is easily suppressed.

This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.
8, the blade centerline 35 of the nozzle vane 30 may extend linearly between the leading end 30a and the trailing end 30b. The inlet leading edge 31 of the nozzle vane 30 bulges toward the turbine wheel 13 on the inner surface 41 side, and bulges toward the turbine scroll section 14 on the outer surface 42 side. The inner surface 41 curves so as to bulge gently from the trailing end 30b to the vicinity of the pin 29, and then curves so as to dent gently near the pin 29, until it reaches the front inflection point Pf.

As shown in FIG. 9, the nozzle vane 30 may have a blade centerline 35 that extends in a compound curve from the trailing end 30b to the leading end 30a, and then the inner surface 41 may be curved to bulge near the inlet leading edge 31.

○ The inlet leading edge 31 may be a compound curve made up of multiple arcs. In this case, the radius of curvature of the smallest arc among the multiple arcs that make up the inlet leading edge 31 is 10% or more of the total length M. The arc with the smallest radius of curvature is located in an area that is 10 to 40% of the total length M from the leading end 30a.

The turbocharger 10 does not have to include the partition 27a and the flow passage end partition 27b. The turbocharger 10 may also include either the partition 27a or the flow passage end partition 27b.

○ The turbocharger may be a fixed type in which the opening of the nozzle vanes 30 cannot be adjusted.

L... axis of rotation, M... overall length, 10... turbocharger, 13... turbine wheel, 14... turbine scroll section, 14a... first flow passage, 14b... second flow passage, 15a... first gas inlet passage, 15b... second gas inlet passage, 30... nozzle vane, 30a... front end, 30b... rear end, 31... inlet leading edge, 32... outlet trailing edge, 35... blade centerline, 39... gas flow passage, 41... inner surface, 42... outer surface, 51... large rate of change section, 52... small rate of change section.

Claims (5)

A turbine wheel;
A turbine scroll portion disposed on an outer periphery of the turbine wheel;
A gas introduction passage for introducing exhaust gas from an internal combustion engine into the turbine scroll portion;
a plurality of nozzle vanes disposed inside the turbine scroll portion, spaced apart in a circumferential direction of the turbine scroll portion , and rotating about a central axis of a pin ;
a gas flow passage defined between adjacent nozzle vanes in a flow direction of the exhaust gas in the turbine scroll portion;
A turbocharger that uses the energy of the exhaust gas to supercharge the engine,
the nozzle vane has an inlet leading edge portion including a front end located on an inlet side of the exhaust gas into the gas flow passage, an outlet trailing edge portion including a rear end located on an outlet side of the exhaust gas in the gas flow passage, and a connecting portion connecting the inlet leading edge portion and the outlet trailing edge portion ,
If the length of the nozzle vane along the blade centerline connecting the front end and the rear end is defined as the total length,
The inlet leading edge portion is an arc-shaped portion provided in a region having a length of 10 to 40% of the total length from the front end, and the radius of curvature of the arc of the inlet leading edge portion is 10% or more of the total length.
Alternatively, the inlet leading edge portion has a shape including a plurality of arcs provided in a region having a length of 10 to 40% of the total length from the leading end, and a radius of curvature of the smallest arc among the plurality of arcs is 10% or more of the total length ,
The pin is integrated with the connection portion, and in a plan view of the nozzle vane looking in the axial direction of the pin, a circle with the radius of curvature of the arc at the inlet leading edge portion is located on the front end side of the pin . A turbine wheel;
A turbine scroll portion disposed on an outer periphery of the turbine wheel;
A gas introduction passage for introducing exhaust gas from an internal combustion engine into the turbine scroll portion;
a plurality of movable nozzle vanes disposed inside the turbine scroll portion, spaced apart in a circumferential direction of the turbine scroll portion , and rotating about a central axis of a pin ;
a gas flow passage defined between adjacent nozzle vanes in a flow direction of the exhaust gas in the turbine scroll portion;
The turbine scroll portion includes two flow paths branched into two at an outlet of the gas introduction passage,
a flow direction of the exhaust gas flowing into one of the bifurcated flow paths and a flow direction of the exhaust gas flowing into the other bifurcated flow path are opposite to each other in a circumferential direction of the turbine scroll portion,
A turbocharger that uses energy of the exhaust gas to supercharge and adjusts a flow of the exhaust gas flowing through the gas flow passage by the nozzle vanes,
the nozzle vane has an inlet leading edge portion including a front end located on the inlet side of the exhaust gas into the gas flow passage, an outlet trailing edge portion including a rear end located on the outlet side of the exhaust gas in the gas flow passage, a connection portion connecting the inlet leading edge portion and the outlet trailing edge portion, and an outer surface and an inner surface connecting the front end and the rear end,
If the rate of change in the plate thickness of the nozzle vane from the front end to the rear end is defined as a change rate,
the inlet leading edge portion is a large change rate portion in which the change rate is larger than the change rate at a portion including the outlet trailing edge portion,
the outlet trailing edge portion includes a small change rate portion having a smaller change rate than the large change rate portion,
the large rate of change portion has an arc shape including the front end,
the pin is integrated with the connection portion, and in a plan view of the nozzle vane looking in the axial direction of the pin, a circle with a radius of curvature of the arc at the large change rate portion is located on the front end side of the pin . The nozzle vane has a blade centerline connecting the front end and the rear end, and the length of the nozzle vane along the blade centerline is the total length. The large change rate portion is an arc-shaped portion located in a region from the front end that is 10% to 40% of the total length, and the radius of curvature of the arc of the large change rate portion is 10% or more of the total length. Or, the large change rate portion is a shape including multiple arcs located in a region from the front end that is 10% to 40% of the total length, and the radius of curvature of the smallest arc of the multiple arcs is 10% or more of the total length. The turbocharger according to claim 2. The turbocharger according to claim 3, wherein the nozzle vane has a straight blade centerline, or the blade centerline extends straight from the rear end to the front end, and then the outer surface is curved so as to approach the turbine scroll portion as it approaches the front end. The turbocharger according to claim 4, wherein the blade centerline extends linearly from the rear end to the front end, and the outer surface is curved so as to approach the turbine scroll portion toward the front end.