Turbocharger compressor with adjustable adjustment mechanism and noise damper

Abstract

The present invention relates to a turbocharger compressor having an adjustable adjustment mechanism and a noise attenuator. A compressor for a turbocharger includes an inlet adjustment mechanism in an air inlet of the compressor, the inlet adjustment mechanism being operable to move between an open position and a closed position. The inlet adjustment mechanism includes a plurality of vanes arranged around the air inlet, the vanes being movable radially inwardly from an annular space of an air inlet wall into the air inlet to form an orifice having a reduced diameter relative to a nominal diameter of the inlet. The noise attenuator is arranged in the annular space downstream of the inlet adjustment mechanism for attenuating aerodynamic noise caused by the inlet adjustment mechanism when the inlet adjustment mechanism is closed.

Description

Technical Field

[0001] The present disclosure relates to compressors, such as those used in turbochargers, and more particularly to compressors whose effective inlet area or diameter can be adjusted for different operating conditions. Background Art

[0002] An exhaust-driven turbocharger is a device used in conjunction with an internal combustion engine for increasing the power output of the engine by compressing air delivered to the engine's intake to mix with fuel and burn in the engine. A turbocharger includes a compressor wheel mounted on one end of a shaft in a compressor housing and a turbine wheel mounted on the other end of the shaft in a turbine housing. Typically, the turbine housing is formed separately from the compressor housing, and there is another center housing connected between the turbine housing and the compressor housing for accommodating the bearings of the shaft. The turbine housing defines a generally annular chamber that surrounds the turbine wheel and receives exhaust gas from the engine. The turbine assembly includes a nozzle leading from the chamber to the turbine wheel. Exhaust gas flows from the chamber through the nozzle to the turbine wheel, and the turbine wheel is driven by the exhaust gas. Thus, the turbine extracts power from the exhaust gas and drives the compressor. The compressor receives ambient air through the inlet of the compressor housing, and the air is compressed by the compressor wheel and then discharged from the housing to the engine intake.

[0003] Turbochargers typically employ a centrifugal (also called "radial") type compressor impeller because centrifugal compressors can achieve relatively high pressure ratios in a compact arrangement. Intake air for the compressor is received in a generally axial direction at the inducer portion of the centrifugal compressor impeller and is discharged in a generally radial direction at the outlet inducer portion of the impeller. The compressed air from the impeller is delivered to a volute, and air is supplied from the volute to the intake of the internal combustion engine.

[0004] The operating range of the compressor is an important aspect of the overall performance of the turbocharger. The operating range is typically defined by the surge line and the choke line on the compressor's operating map. The compressor map is typically represented as the pressure ratio (discharge pressure Pout divided by inlet pressure Pin) on the vertical axis versus the corrected mass flow on the horizontal axis. The choke line on the compressor map is located at high flows and represents the locus of the maximum mass flow points over the pressure ratio range; that is, for a given point on the choke line, it is not possible to increase the flow while maintaining the same pressure ratio due to the occurrence of a choke condition in the compressor.

[0005] The surge line is located at low flow and represents the location of the minimum mass flow point without surge over the range of pressure ratios; that is, for a given point on the surge line, decreasing the flow without changing the pressure ratio or increasing the pressure ratio without changing the flow will cause surge to occur. Surge is a flow instability that typically occurs when the compressor blade incidence angle becomes so large that significant flow separation occurs on the compressor blades. Pressure fluctuations and flow reversals may occur during surge.

[0006] In turbochargers for internal combustion engines, compressor surge can occur when the engine is running at high load or torque and low engine speed, or when the engine is running at low speed and there is a high level of exhaust gas recirculation (EGR). Surge can also occur when the engine is suddenly decelerated from a high speed. Extending the compressor's surge-free operating range for lower flows is a goal often sought in compressor design.

[0007] The applicant is the owner of several patent applications describing various inlet adjustment mechanisms for delaying the onset of surge to lower flows (i.e., moving the surge line to the left on the compressor map) at a given compressor pressure ratio, including but not limited to: Application Nos. 14 / 642,825, filed March 10, 2015; 14 / 551,218, filed November 24, 2014; 14 / 615,428, filed February 6, 2016; 15 / 446,054, filed March 1, 2017; and 15 / 446,055, filed March 1, 2017. 15 / 446,090, filed March 10, 2017; 15 / 456,403, filed March 10, 2017; 15 / 836,781, filed December 8, 2017; 15 / 806,267, filed November 7, 2017; 15 / 822,093, filed November 24, 2017; 15 / 907,420, filed February 28, 2018; 15 / 904,493, filed February 26, 2018; and 15 / 909,899, filed March 1, 2018; the entire disclosures of all of the aforementioned applications are incorporated herein by reference. The inlet adjustment mechanism according to the aforementioned applications generally includes a plurality of blades or vanes that together define an orifice whose effective diameter can be adjusted by radially inward or outward movement of the blades or vanes. By adjusting the effective compressor inlet diameter to a reduced value under operating conditions where surge may be imminent, the surge line on the compressor map is moved toward lower flows, thereby preventing surge from occurring under said operating conditions. Summary of the invention

[0008] The present application relates to a turbocharger, the compressor of which comprises an inlet regulating mechanism of the above-mentioned type. The applicant has found that when the inlet regulating mechanism is closed to effectively reduce the diameter of the compressor inlet, the mechanism generates aerodynamically induced noise at certain frequencies. The purpose of the present application is to solve this problem and reduce this noise.

[0009] In one embodiment described herein, a turbocharger includes a turbine including a turbine housing and a compressor assembly including a compressor housing and a compressor impeller mounted in the compressor housing and connected to a rotatable shaft for rotation therewith. The compressor impeller has blades and defines an inducer portion, the compressor housing has an air inlet wall defining an air inlet for introducing air generally axially into the compressor impeller, the air inlet wall defining an annular space therein upstream of the compressor impeller, the radially innermost end of the annular space opening into the air inlet.

[0010] The inlet adjustment mechanism is arranged in the air inlet and is adjustable between an open position and a closed position. The inlet adjustment mechanism includes a plurality of vanes arranged around the air inlet and collectively defining an orifice, the vanes being movable radially inwardly into the air inlet when the vanes are in the closed position so that the orifice has a reduced diameter relative to a nominal diameter of the inlet.

[0011] The turbocharger further comprises a noise attenuator arranged in an annular space downstream of the inlet regulating mechanism, the noise attenuator being constructed and arranged to define an axially continuous first annular cavity and a second annular cavity, each of which leads to the air inlet. The first annular cavity has a radial height h1, and the second annular cavity has a radial height h2. According to this embodiment of the invention, h1 and h2 are not equal.

[0012] In one embodiment, the first annular cavity is located upstream of the second annular cavity, and h1 is greater than h2. In another embodiment, the heights of the two cavities are equal.

[0013] In one embodiment described herein, a noise attenuator includes an annular first plate and an annular second plate axially adjacent to the first plate. The first plate defines a flange at its radial outer periphery, the flange protruding axially upstream from an upstream surface of the first plate.

[0014] According to one embodiment, the inlet adjustment mechanism comprises a rotatable unison ring for actuating the movement of the vanes, and the unison ring abuts against a flange of the first plate, the flange forming a bearing surface for the unison ring when the unison ring is rotated.

[0015] The vanes of the inlet adjustment mechanism may be mounted to the first plate by pivot pins, the vanes engaging the unison ring such that rotation of the unison ring in one direction or the opposite direction causes the vanes to pivot radially inwardly or radially outwardly, thereby adjusting the size of the orifice.

[0016] According to another embodiment of the invention, the noise attenuator cooperates with the annular space in the air inlet wall to define an annular cavity, and the noise attenuator includes a plurality of elongated fingers adjacent to its radial inner end, the fingers spanning from the upstream side to the downstream side of the annular cavity. The fingers are circumferentially unevenly spaced around the entire circumference of the air inlet.

[0017] In one embodiment, the noise dampener comprises an annular plate with fingers projecting axially downstream from a downstream surface of the plate adjacent a radially inner periphery thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Having generally described the invention, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

[0019] Figure 1 is a side view of a turbocharger according to one embodiment of the present invention, which is partially cut away to show the internal features of the compressor;

[0020] Figure 1A for Figure 1 an enlarged portion of which shows a compressor of a turbocharger;

[0021] Figure 2 for Figure 1 An exploded view of a compressor assembly of a turbocharger;

[0022] Figure 3 is an isometric view of a compressor assembly, which is partially cut away to show internal features of the compressor;

[0023] Figure 4A for Figure 1 Exploded view of the turbocharger noise attenuator;

[0024] Figure 4B is an isometric view of a noise attenuator;

[0025] Figure 5 is an isometric view of a compressor assembly according to another embodiment of the present invention, which is partially cut away to show the internal details of the compressor;

[0026] Figure 6 for Figure 5 An exploded view of the compressor assembly; and

[0027] Figure 7 For use Figure 5Isometric view of a noise attenuator for a compressor assembly. DETAILED DESCRIPTION

[0028] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, these inventions may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout.

[0029] exist Figure 1 A turbocharger 10 according to an embodiment of the present invention is shown in a side view. Figure 2 An axial cross-section of the turbocharger is shown in FIG. The turbocharger includes a compressor 12 and a turbine 22. The compressor includes a compressor wheel or impeller 14 mounted in a compressor housing 16 on one end of a rotating shaft 18. The compressor housing includes an air inlet wall 17 defining an air inlet for directing air generally axially into the compressor wheel 14. The shaft is supported in bearings mounted in a center housing 20 of the turbocharger. The shaft passes through the turbine wheel of the turbine 22 (at Figure 1 The turbine wheel is mounted on the other end of the shaft 18 from the compressor wheel, thereby rotatably driving the compressor wheel, which compresses air drawn in through the compressor inlet and discharges the compressed air generally radially outward from the compressor wheel into a volute 21 for receiving the compressed air. From the volute 21, the air is routed to the intake of an internal combustion engine (not shown) for improving the performance of the engine.

[0030] The turbine wheel is arranged in a turbine housing 24 which defines an annular chamber for receiving exhaust gas from an internal combustion engine (not shown). The turbine housing also defines a nozzle for directing the exhaust gas from the chamber generally radially inwardly to the turbine wheel. The exhaust gas expands as it passes through the turbine wheel and rotatably drives the turbine wheel, which in turn rotatably drives the compressor wheel 14 as already mentioned.

[0031] Reference now Figure 1A In the illustrated embodiment, the air inlet wall 17 is formed in part by the compressor housing 16 and in part by a separate inlet duct member 16d that is received in a cylindrical container defined by the compressor housing. The portion of the air inlet wall 17 proximate the compressor impeller 14 defines a generally cylindrical inner surface having a diameter that generally matches the diameter of the inducer portion 14i of the compressor impeller.

[0032] The compressor housing 16 defines a shroud surface 16s that is immediately adjacent the radially outer tips of the compressor blades. The shroud surface defines a curved profile that is generally parallel to the profile of the compressor wheel.

[0033] According to a first embodiment of the invention, the compressor of a turbocharger includes an inlet adjustment mechanism 100 arranged in an annular space S within the air inlet wall 17. The annular space S is defined between the downstream-facing end surface ES of the inlet duct member 16d, the upstream-facing surface 30 of the compressor housing 16, and the cylindrical radially inward-facing surface 32 of the compressor housing. The inlet adjustment mechanism includes an annular assembly and is operable to adjust the effective diameter of the air inlet entering the compressor impeller. In this way, the inlet adjustment mechanism can be moved between an open position and a closed position, and in some embodiments can be further closed to an over-closed position, and can be configured to adjust to various points between the positions.

[0034] Reference now Figure 2 , the inlet adjustment mechanism includes a plurality of vanes 102 arranged about a central axis of the air inlet, and each vane is pivotable about a pivot pin located at or near one end of the vane. The mechanism also includes a unison ring 106 rotatable about the central axis and engaged with each vane 102, such that rotation of the unison ring in one direction pivots the vanes radially inward, and rotation in the opposite direction pivots the vanes radially outward. Alternatively, the inlet adjustment mechanism may include other types of vane or blade arrangements that actuate the vanes or blades to move inward or outward in a different manner, such as radial translation, or in a combined radial and circumferential motion (i.e., a spiral motion).

[0035] The range of pivotal movement of the vanes 102 is sufficient to enable the vanes to be pivoted radially outwardly by rotation of the unison ring in one direction to an open position in which the vanes are completely radially outward of the inner surface of the air inlet wall 17. Thus, in the open position of the vanes, the inlet adjustment mechanism does not change the nominal inlet diameter defined by the inlet surface.

[0036] The vanes can also be pivoted radially inward by rotating the unison ring in a direction opposite to the closed position. In the closed position, the arcuate edges along the radially inner sides of the vanes 102 together form an orifice that is substantially circular with a diameter that is smaller than the diameter of the inner surface of the inlet. As a result, the effective diameter of the inlet is reduced relative to the nominal inlet diameter. In this way, the inlet adjustment mechanism is able to adjust the effective diameter of the air inlet close to the compressor impeller.

[0037] At low flows (e.g., low engine speeds), the inlet adjustment mechanism 100 may be placed in a closed position. This may have the effect of reducing the effective inlet diameter and therefore increasing the flow rate entering the compressor impeller. The result will be to reduce the angle of incidence to the compressor blades, thereby effectively stabilizing the flow (i.e., making blade stall and compressor surge less likely). In other words, the compressor surge line will move to lower flows (to the left on a plot of compressor pressure ratio versus flow).

[0038] At medium and high flows, the inlet adjustment mechanism 100 may be partially or fully opened. This may have the effect of increasing the effective inlet diameter so that the compressor regains its high flow performance and chokes essentially as if there were no inlet adjustment mechanism and as if the compressor had a conventional inlet at the inducer portion of the impeller that matched the impeller diameter.

[0039] As previously mentioned, the applicant has discovered that when the inlet adjustment mechanism is in the closed position, the mechanism tends to generate aerodynamically induced noise at certain frequencies. It is desirable to attenuate this noise as much as possible without compromising the surge delay benefits of the mechanism. According to the present invention, in one embodiment, noise attenuation is achieved by providing a noise attenuator 120 located just downstream of the inlet adjustment mechanism 100, such as Figure 1A , 4A The noise attenuator 120 is arranged in the annular space S of the air inlet wall 17. Figure 1A As shown, the inlet adjustment mechanism 100 is also arranged in the annular space S, adjacent to the end face ES of the inlet duct member 16d. The noise attenuator 120 is arranged downstream of the inlet adjustment mechanism and includes an annular first plate P1 and an annular second plate P2, which are continuously arranged axially so that the first plate P1 faces the inlet adjustment mechanism 100 and the second plate P2 is immediately downstream of the first plate. The noise attenuator is constructed and arranged to define at least two axially continuous annular cavities, each of which leads to the air inlet. In the embodiment shown, the noise attenuator defines two such axially continuous annular cavities C1 and C2. By abutting the first flange F1 from the radial outer periphery of the first plate P1 with the unison ring 106 of the inlet adjustment mechanism, another annular cavity C3 is defined, but this cavity C3 has nothing to do with noise attenuation, on the contrary, it is a space where the inlet adjustment mechanism 100 is located. The first flange extends from the first plate in the upstream direction to abut the unison ring, so that the unison ring is axially spaced from the upstream surface of the first plate P1. The vane 102 of the inlet adjustment mechanism is pivotally mounted (as further described below) to the first plate P1 and is located at least partially within the third annular cavity C3.

[0040] The first annular cavity C1 is defined by a second flange F2 from the second plate P2 abutting the downstream side of the first plate P1, the second flange F2 protruding from the radial periphery of the second plate in the upstream direction. The second annular cavity has a radial height h1. It should be understood that the first cavity can be formed by a second flange protruding downstream from the first plate P1 and abutting the second plate P2 (then the second plate P2 will not have a flange on its upstream side). The present invention is not limited to any particular structure or arrangement for forming the cavity.

[0041] The second annular cavity C2 is defined by the third flange F3 protruding from the radial periphery of the second plate P2 in the downstream direction adjoining the downstream wall 30 of the annular space S defined in the air inlet wall 17. The second annular cavity has a radial height h2. The values ​​of h1 and h2 may be equal or different from each other.

[0042] The axial width of the first annular cavity C1 is tC1, and the axial width of the second annular cavity C2 is tC2. The axial thickness of the second plate P2 is tP2. Advantageously, the values ​​of tC1 and tC2 are not equal to the plate thickness tP2. For example, Figure 1A As shown, cavity widths tC1 and tC2 may be equal to each other and may be greater than the second plate thickness tP2.

[0043] As previously mentioned, the vane 102 of the inlet adjustment mechanism is pivotally mounted to the first plate P1. This is accomplished by a plurality of pins 113 ( Figure 2 ) is achieved by having one such pin per blade, which is fixedly mounted on the downstream wall 30 ( Figure 1A ), the wall 30 delimiting the downstream end of the annular space S. The pins 113 pass through corresponding holes 124 in the second plate P2 and through corresponding holes 123 in the first plate P1 and are received in bearing holes 103 in each blade 102, as in Figure 2 1. The vanes 102 can thus pivot about the pins 113. The ends of the vanes are received in the slots 107 in the inner periphery of the unison ring 106 so that, as described, rotation of the unison ring about the turbocharger axis causes the vanes to pivot. The rotation of the unison ring is guided by a plurality of guide pins 111 fixedly mounted in holes (not shown) in the downstream wall 30. The guide pins pass through corresponding holes 122 in the second plate P2 and through corresponding holes 121 in the first plate P1 and engage with the inner periphery of the unison ring 106 to guide its rotational movement and keep it substantially concentric with the turbocharger axis.

[0044] The two annular cavities C1 and C2 act as quarter-wave resonators for the main fluid flow flowing to the compressor impeller through the air inlet. As will be appreciated by those skilled in the art, the quarter-wave resonator can be tuned to a certain fundamental frequency so as to attenuate the frequency and harmonics of the frequency based on the length of the cavity (in this case, the radial height h1 or h2). Therefore, the two cavities C1 and C2 can be tuned to the same frequency by making their radial heights equal, or can be tuned to different frequencies by making their radial heights different from each other. Both possibilities are included within the scope of the present invention. In addition, the plate P2 between the two cavities serves as a partition wall that helps to reduce the energy of the vortex generated by the blades of the inlet adjustment mechanism 100, and therefore helps to reduce the noise associated with such vortex. Although the illustrated embodiment has two such annular cavities that act as quarter-wave resonators, the present invention is not limited to this aspect, and more than two such cavities may be employed if advantageous in a particular case.

[0045] Reference now Figures 5 to 7 A turbocharger according to a second embodiment of the invention is described. The turbocharger of the second embodiment differs from the turbocharger of the first embodiment in terms of the noise attenuator, but is similar in other respects, and the description of the same or similar features common between the two embodiments will not be repeated. The noise attenuator 220 of the second embodiment includes an annular plate having a flange F extending from the radial periphery of the plate in the upstream direction and abutting a unison ring 106, similar to the first plate of the first embodiment. The vanes 102 of the inlet adjustment mechanism are pivotally mounted to the noise attenuator 220 by pins 113 passing through holes 223 in the plate, and are fixedly mounted in holes in the downstream wall 30 of the annular space of the air inlet wall, also similar to the first embodiment. The guide pin 111 for the unison ring 106 extends through the hole 221 in the plate and is mounted in a hole in the wall 30 (see in particular Figure 5 ).

[0046] However, unlike the first embodiment, the noise attenuator of the second embodiment includes a plurality of fingers 222 extending from the radial inner periphery of the noise attenuator in a downstream direction. The noise attenuator 220 cooperates with the annular space S to define an annular cavity C. The fingers 222 span the cavity C and are circumferentially unevenly spaced around the entire circumference of the air inlet. Each finger 222 causes an abrupt change in impedance to the air approaching the compressor impeller, and because the fingers are unevenly spaced, the impedance changes continuously around the circumference, which helps prevent the propagation of noise.

[0047] Many modifications and other embodiments of the inventions set forth herein will come to mind to those skilled in the art having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it should be understood that the invention is not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A turbocharger, comprising: a turbine, the turbine comprising a turbine housing; a compressor assembly including a compressor housing and a compressor impeller mounted in the compressor housing and connected to a rotatable shaft for rotation therewith, the compressor impeller having blades and defining an inducer portion, the compressor housing having an air inlet wall defining an air inlet for introducing air generally axially into the compressor impeller, the air inlet wall defining an annular space therein upstream of the compressor impeller, the annular space opening at a radially innermost end into the air inlet; an inlet adjustment mechanism disposed in the air inlet and adjustable between an open position and a closed position, the inlet adjustment mechanism comprising a plurality of vanes disposed about the air inlet and collectively defining an orifice, the vanes being movable radially inwardly into the air inlet when the vanes are in the closed position to cause the orifice to have a reduced diameter relative to a nominal diameter of the inlet; as well as A noise attenuator is arranged in an annular space downstream of the inlet regulating mechanism, and the noise attenuator is constructed and arranged to define an axially continuous first annular cavity and a second annular cavity, each of the first annular cavity and the second annular cavity radially opens to the air inlet, so that the first annular cavity and the second annular cavity act as a quarter-wavelength resonator for the main fluid flow flowing through the air inlet to the compressor impeller, the first annular cavity has a radial height h1 and the second annular cavity has a radial height h2.

2. The turbocharger according to claim 1, wherein: h1 and h2 are not equal.

3. The turbocharger according to claim 1, wherein: The noise damper includes an annular first plate and an annular second plate axially adjacent to the first plate.

4. The turbocharger according to claim 1, wherein: h1 and h2 are equal.

5. The turbocharger according to claim 3, wherein: The axial width of each of the first and second annular cavities is greater than the axial thickness of the second plate.

6. The turbocharger according to claim 5, wherein: The first plate defines a flange at a radially outer periphery thereof, the flange protruding axially upstream from an upstream surface of the first plate.

7. The turbocharger according to claim 6, wherein: The inlet adjustment mechanism comprises a rotatable unison ring for actuating the movement of the vanes, the unison ring abutting the flange, the flange forming a bearing surface for the unison ring when the unison ring is rotated.

8. The turbocharger according to claim 7, wherein: The vane is pivotally mounted to the first plate, the vane engaging the unison ring such that rotation of the unison ring in one direction or the opposite direction pivots the vane radially inwardly or radially outwardly to adjust the size of the orifice.

9. A turbocharger comprising: a turbine, the turbine comprising a turbine housing; a compressor assembly including a compressor housing and a compressor impeller mounted in the compressor housing and connected to a rotatable shaft for rotation therewith, the compressor impeller having blades and defining an inducer portion, the compressor housing having an air inlet wall defining an air inlet for introducing air generally axially into the compressor impeller, the air inlet wall defining an annular space therein upstream of the compressor impeller, the annular space opening at a radially innermost end into the air inlet; an inlet adjustment mechanism disposed in the air inlet and adjustable between an open position and a closed position, the inlet adjustment mechanism comprising a plurality of vanes disposed about the air inlet and collectively defining an orifice, the vanes being movable radially inwardly into the air inlet when the vanes are in the closed position to cause the orifice to have a reduced diameter relative to a nominal diameter of the inlet; as well as A noise attenuator is arranged in the annular space of the air inlet wall downstream of the inlet regulating mechanism, the noise attenuator cooperates with the annular space to define an annular cavity, and the noise attenuator includes a plurality of elongated fingers adjacent to its radial inner end, the fingers spanning from the upstream side to the downstream side of the annular cavity, the fingers being unevenly spaced circumferentially around the entire circumference of the air inlet.

10. The turbocharger according to claim 9, wherein: The noise damper comprises an annular plate, the fingers projecting axially downstream from a downstream surface of the plate adjacent a radial inner periphery thereof.

11. The turbocharger according to claim 10, wherein: The plate defines a flange at its radial outer periphery, the flange protruding axially upstream from the upstream surface of the plate.

12. The turbocharger according to claim 11, wherein: The inlet adjustment mechanism comprises a rotatable unison ring for actuating the movement of the vanes, the unison ring abutting the flange, the flange forming a bearing surface for the unison ring when the unison ring is rotated.

13. The turbocharger according to claim 12, wherein: The vanes are pivotally mounted to the plate, the vanes engaging the unison ring such that rotation of the unison ring in one direction or the opposite direction pivots the vanes radially inwardly or radially outwardly to adjust the size of the orifice.

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