Centrifugal compressor for turbocharger with pressure equalization TRIM adjustable mechanism

Abstract

A centrifugal compressor for a turbocharger includes an inlet adjustment mechanism operable to move between an open position and a closed position. The inlet adjustment mechanism includes a plurality of vanes disposed about the compressor air inlet and between an upstream wall surface and a downstream wall surface of an annular space within the air inlet wall. The vanes are pivotable about respective pivot points such that, when the vanes are in the closed position, the vanes extend radially inwardly from the annular space into the air inlet to form an orifice of reduced diameter relative to a nominal diameter of the inlet. Aerodynamic pressure equalization across the vanes is achieved by spacing features that space a majority of the upstream surface of each vane from an opposing upstream wall surface.

Description

Technical Field

[0001] The present disclosure relates to centrifugal compressors, such as those used in turbochargers, and more particularly to centrifugal 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 that increases the power output of the engine by compressing air delivered to the air intake of the engine 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 another center housing is 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 to the turbine wheel through the nozzle 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 air intake.

[0003] Turbochargers typically employ a centrifugal (also called "radial") type compressor wheel because centrifugal compressors can achieve relatively high pressure ratios in a compact arrangement. Intake air for the compressor is received at an inlet inducer portion of a centrifugal compressor wheel in a generally axial direction and is discharged at an outlet inducer portion of the wheel in a generally radial direction. Compressed air from the wheel is delivered to a volute, and from the volute the air is supplied to the intake of an 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 a surge line and a choke line on an operating map of the compressor. A compressor map is typically represented as pressure ratio (discharge pressure Pout divided by inlet pressure Pin) on the vertical axis versus corrected mass flow rate on the horizontal axis. The choke line on the compressor map is located at high flow rates and represents the locus of maximum mass flow rate points over a range of pressure ratios; that is, for a given point on the choke line, it is not possible to increase the flow rate while maintaining the same pressure ratio because a choked flow condition occurs in the compressor.

[0005] The surge line is located at low flow rates and represents the locus of the minimum mass flow rate points over a range of pressure ratios at which surge does not occur; that is, for a given point on the surge line, either decreasing the flow rate without changing the pressure ratio or increasing the pressure ratio without changing the flow rate will cause surge to occur. Surge is a flow instability that typically occurs when the compressor blade incidence angle becomes so large that a large amount of flow separation occurs over the compressor blades. During surge, pressure fluctuations and reverse flow can occur.

[0006] In a turbocharger for an internal combustion engine, compressor surge may occur when the engine is operating at high load or torque and low engine speed or when the engine is operating 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 state. Extending the compressor's surge-free operating range to lower flow rates is often a goal pursued in compressor design.

[0007] Applicant's co-pending U.S. Patent Application No. 15 / 446,054, filed on March 1, 2017, which claims the benefit of the filing date of Provisional Application No. 62 / 324,488, filed on April 20, 2016, the entire disclosure of which is hereby incorporated by reference, describes a mechanism and method for a centrifugal compressor that can cause the surge line of the compressor to be selectively moved to the left (i.e., delaying surge to a lower flow rate at a given pressure ratio), and which claims the benefit of the filing date of Provisional Application No. 62 / 324,488, filed on April 20, 2016, the entire disclosure of which is hereby incorporated by reference. One embodiment described in said application includes a turbocharger having the following features:

[0008] a turbine housing, and a turbine wheel mounted in the turbine housing and connected to the rotatable shaft for rotation therewith, the turbine housing receiving the exhaust gas and supplying the exhaust gas to the turbine wheel;

[0009] a centrifugal compressor assembly including a compressor housing, and a compressor wheel mounted in the compressor housing and connected to a rotatable shaft for rotation therewith, the compressor wheel having blades and defining an inlet inducer portion, the compressor housing having an air inlet wall defining an air inlet for directing air generally axially into the compressor wheel, the compressor housing further defining a volute for receiving compressed air discharged generally radially outwardly from the compressor wheel; and

[0010] A compressor inlet adjustment mechanism is disposed in the air inlet of the compressor housing and is pivotable radially inward and radially outward between an open position and a closed position, the inlet adjustment mechanism comprising a plurality of vanes disposed around the air inlet and each pivotable about one end of the vane, wherein when the vanes are in the closed position, the vanes are pivoted radially inward through slots in the air inlet wall to form an orifice of reduced diameter relative to a nominal diameter of the inlet.

[0011] Applicant is also the owner of additional applications related to other inlet adjustment mechanisms employing moving vanes, including U.S. Application No. 15 / 446,090 filed on March 1, 2017, the entire disclosure of which is incorporated herein by reference.

[0012] The present disclosure relates to inlet adjustment mechanisms generally of the type described in the aforementioned '054, '488 and '090 applications, and in particular to the modification or redesign of such mechanisms with the goal of improving certain aspects of the mechanisms. Summary of the invention

[0013] One such aspect of the aforementioned inlet adjustment mechanism that seeks improvement relates to rendering the actuation mechanism unable to actuate the vanes under certain operating conditions. It has been found that at operating conditions approaching the compressor surge line, under which the inlet adjustment mechanism normally closes to reduce the size of the orifice defined by the mechanism, the actuation mechanism sometimes fails to open the vanes, or the vanes open more slowly than desired. This may occur, for example, when the engine is required to accelerate suddenly from a low speed condition approaching surge.

[0014] Applicants have attributed the cause of this opening failure or delay to high aerodynamic loads on the blades in the axial direction. Specifically, the static pressure on the downstream side of the blades is relatively high compared to the pressure on the upstream side. Therefore, the net aerodynamic load on the blades in the upstream axial direction is relatively high. Applicants have found that this high aerodynamic load is a source of difficulty in opening the inlet adjustment mechanism because the load creates a friction force on the blades that is higher than the blade's actuation mechanism can overcome. Therefore, applicants have attempted to mitigate or eliminate this problem.

[0015] According to one embodiment disclosed herein, a turbocharger having the following features is described:

[0016] a turbine housing, and a turbine wheel mounted in the turbine housing and connected to the rotatable shaft for rotation therewith, the turbine housing receiving the exhaust gas and supplying the exhaust gas to the turbine wheel;

[0017] a centrifugal compressor assembly including a compressor housing, and a compressor wheel mounted in the compressor housing and connected to a rotatable shaft for rotation therewith, the compressor wheel having blades and defining an inlet inducer portion, the compressor housing having an air inlet wall defining an air inlet for directing air generally axially into the compressor wheel, the compressor housing further defining a volute for receiving compressed air discharged generally radially outwardly from the compressor wheel, the air inlet wall defining an annulus surrounding the air inlet and opening into the air inlet at a radially inner end of the annulus; and

[0018] a compressor inlet adjustment mechanism disposed in an annular space of the air inlet wall and movable between an open position and a closed position, the inlet adjustment mechanism comprising a plurality of vanes disposed in the annular space between an upstream wall surface and a downstream wall surface, the vanes collectively surrounding the orifice, the upstream surface of each vane opposing the upstream wall surface and the downstream surface of each vane opposing the downstream wall surface, each vane being pivotable about a pivot point fixed in the compressor housing, the vanes pivoting radially inwardly from the annular space into the air inlet when the vanes are in the closed position so as to cause the orifice to have a reduced diameter relative to a nominal diameter of the inlet;

[0019] Wherein at least one of the upstream wall surface and the upstream surface of each vane includes a spacing feature that spaces a majority of the upstream surface of each vane apart from the upstream wall surface, thereby enabling pressure communication between the upstream and downstream surfaces of the vane.

[0020] Due to the axial clearance of the blade designed into the inlet adjustment mechanism, the net aerodynamic load on the blade acts in the upstream axial direction to automatically space the downstream surface of the blade from the downstream wall surface. The spacing feature at the upstream side of the blade ensures that there is also an air space between the blade and the upstream wall surface, thereby achieving pressure communication between the upstream and downstream surfaces of the blade. Therefore, the pressure on those surfaces is more evenly balanced. Therefore, the net aerodynamic load on the blade in the axial direction is greatly reduced relative to a similar design lacking the spacing feature. The spacing feature also greatly reduces the total surface area of ​​the blade in contact with the upstream wall surface. The reduction in aerodynamic load and the reduction in contact surface area together result in substantially lower friction forces that hinder the pivoting of the blade.

[0021] In one embodiment, the spacing feature is defined by the blade and may include a raised protrusion or rib or ridge that constitutes a small portion of the total surface area of ​​the blade. In another embodiment, the upstream spacing feature is defined in the upstream wall surface. Variations are within the scope of the invention described and claimed.

[0022] In one embodiment, each vane comprises a radially inner edge having an arc shape, the vanes being configured such that the radially inner edges collectively form the aperture as being substantially circular in a selected position of the inlet adjustment mechanism.

[0023] In some embodiments of the invention, the selected position in which the radially inner edge of the vane forms the aperture into a substantially circular shape may be a closed position.

[0024] In one embodiment, the inlet adjustment mechanism includes a pair of (i.e., upstream and downstream) axially spaced annular end plates and the blades are arranged between the end plates so that the inlet adjustment mechanism forms a "cartridge" that can be installed in the compressor. The upstream end plate defines an upstream wall surface, and the downstream end plate defines a downstream wall surface. The inlet adjustment mechanism or cartridge is arranged in an annular space defined by the air inlet wall. The annular space can be defined between the main part of the compressor housing and a separate inlet duct member, which forms a large part of the air inlet to the compressor. The duct member is received in a receiving portion, which is defined in the main part of the compressor housing.

[0025] The end plates may be spaced apart by a plurality of pins which pass through holes in the blades and about which the blades may pivot.

[0026] Alternatively, the pins may be fixed in the compressor housing, thereby eliminating the need for a separate end plate (i.e., the inlet adjustment mechanism is not a separate cassette). For example, the function of one end plate may be performed by an integral part of the compressor housing, and the function of the other end plate may be performed by an integral part of the inlet duct member.

[0027] According to one embodiment, the inlet adjustment mechanism further comprises a unison ring surrounding the vanes, the unison ring being rotatable about the axis of rotation of the turbocharger, wherein each vane is engaged with the unison ring such that rotation of the unison ring causes the vane to pivot about the pin. Each vane comprises an end portion that engages a slot defined in an inner perimeter of the unison ring.

[0028] The inlet adjustment mechanism may also include a plurality of guides for guiding rotation of the unison ring.The guides may be fixed to at least one of the end plates (or in the case of a non-cassette version of the inlet adjustment mechanism, to the compressor housing and / or inlet duct member). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Having therefore generally described the invention, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

[0030] Figure 1is an end view of a turbocharger according to one embodiment of the present invention, looking axially from the compressor end to the turbine end of the turbocharger;

[0031] Figure 2 The turbocharger Figure 1 A cross-sectional view taken along line 2-2;

[0032] Figure 3 yes Figure 1 a partially exploded view of a compressor portion of a turbocharger;

[0033] Figure 4 yes Figure 3 an isometric view of the compressor portion of the compressor with the compressor cover (inlet duct member) exploded to make the inlet adjustment mechanism visible;

[0034] Figure 5 is an isometric view of a partial assembly of the inlet adjustment mechanism and thus the actuator, wherein the inlet adjustment mechanism is in an open position;

[0035] Figure 6 is with Figure 5 a similar view with the inlet regulating mechanism in the closed position;

[0036] Figure 7 is an isometric view of a vane of an inlet adjustment mechanism showing an upstream surface of the vane having a spacing feature;

[0037] Figure 8 is an isometric view of the blade showing the downstream surface of the blade; and

[0038] Fig. 9 is through Figure 1 A cross-sectional view of the compressor housing assembly and inlet adjustment mechanism of a turbocharger. DETAILED DESCRIPTION

[0039] 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 embodied 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 represent like elements throughout.

[0040] In this disclosure, the term "orifice" means "opening" regardless of the shape of the opening. Thus, an "orifice" may be circular or non-circular. In addition, when the vanes of the inlet adjustment mechanism are described as pivoting "radially" inwardly or outwardly, the term "radial" does not exclude some non-radial component of movement of the vanes (e.g., the vanes may occupy a plane that is slightly angled relative to the axis of rotation of the compressor, so that when the vanes pivot radially inwardly and outwardly, they also move with a small axial component of motion).

[0041] Figure 1 A turbocharger 10 according to one embodiment of the invention is shown in an axial end view, and Figure 2 An axial cross-sectional view of a turbocharger is shown in FIG. A turbocharger includes a compressor and a turbine. The compressor includes a compressor wheel or impeller 14 mounted on one end of a rotatable shaft 18 in a compressor housing 16. The compressor housing includes a wall defining an air inlet 17 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 is rotated by a turbine wheel 22 mounted on the other end of the shaft spaced 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 outwardly from the compressor wheel into a volute 21 for receiving the compressed air. From the volute 21, the air is directed to the intake of an internal combustion engine (not shown) for improving the performance of the engine.

[0042] The turbine wheel 22 is disposed within a turbine housing 24 which defines an annular chamber 26 for receiving exhaust gas from an internal combustion engine (not shown). The turbine housing further defines a nozzle 28 for directing the exhaust gas from the chamber 26 generally radially inwardly to the turbine wheel 22. 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.

[0043] Reference Figures 1 to 4 In the illustrated embodiment, the wall defining the air inlet 17 is formed in part by the compressor housing 16 and in part by a separate cover or inlet duct member 16d which is received in a cylindrical receiving portion defined by the compressor housing. The portion of the air inlet 17 proximate the compressor wheel 14 defines a generally cylindrical inner surface 17i having a diameter generally matching the diameter of the inlet inducer portion 14i of the compressor wheel.

[0044] 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.

[0045] According to the present invention, the compressor of the turbocharger includes an inlet adjustment mechanism 100 disposed in the air inlet 17 of the compressor housing. The inlet adjustment mechanism includes an annular assembly and is disposed in an annular space defined between the compressor housing 16 and a separate inlet duct member 16d. The annular space is confined between an upstream wall surface 105 and a downstream wall surface 107. The inlet adjustment mechanism is operable to adjust the effective diameter of the air inlet into the compressor wheel. In this way, the inlet adjustment mechanism can be moved between an open position and a closed position, and can be configured to be adjusted to various points between the positions.

[0046] Now refer to Figure 3 , Figure 5 and Figure 6 , the inlet adjustment mechanism includes a plurality of vanes 102 disposed about a central axis of the air inlet and each pivotable about a pivot pin located at or near one end of the vane. In the illustrated embodiment, the pivot pin for the vane is secured in a downstream wall surface 107 of the compressor housing. The vanes are disposed between the upstream wall surface 105 and the downstream wall surface 107 with a small amount of axial clearance or play for the vanes between those wall surfaces so that the vanes can pivot freely without binding.

[0047] The inlet adjustment mechanism also includes a unison ring 106 for applying pivotal movement to the vanes. The unison ring surrounds the assembly of vanes 102 and is substantially coplanar with the vanes and is rotatable about an axis that coincides with the axis of rotation of the compressor wheel. The unison ring includes a plurality of recesses 108 in its radially inner periphery, and each vane includes an end portion 102e engaged in a respective one of the recesses 108. Thus, rotation of the unison ring in one direction causes the vanes 102 to pivot radially inwardly, and rotation of the unison ring in the other direction causes the vanes to pivot radially outwardly. The assembly of the vanes 102 and the unison ring 106 is captively held between the upstream wall surface 105 and the downstream wall surface 107.

[0048] A plurality of guides 103 are also fixed in the downstream wall surface 105, or alternatively, may be fixed in the upstream wall surface 107 instead, or may be fixed to both wall surfaces. The guides are positioned so as to engage with the circular inner periphery of the unison ring 106. The guides 103 serve to guide the unison ring when rotating about its central axis so that the unison ring remains substantially concentric with respect to the compressor wheel. The guides 103 may include rollers or fixed guide pins.

[0049] It is advantageous to include some kind of mechanical stop to limit the radially outward pivoting of the vanes 102 in the fully open position of the inlet adjustment mechanism. The stop may be provided in a variety of ways in the practice of the present invention. As an example, in Figure 5 , the radially inner perimeter of the unison ring 106 acts as a stop. Alternatively, a machined feature at the inner diameter of the compressor housing 16 may serve as a stop. Still another alternative is to configure the guide 103 to serve dual purpose as a unison ring guide and a mechanical stop for the vanes. Other variations are also contemplated within the scope of the invention.

[0050] The radially inner edges of the blades 102 include portions that are preferably generally arcuate in shape, and these edges collectively surround and define a generally circular opening or aperture (although the degree of roundness may vary depending on the location of the blade, as will be further described below).

[0051] The range of pivotal movement of the blades is sufficient so that the blades can be pivoted radially outwards (by rotation of the unison ring in one direction, Figure 5 (clockwise in the middle) to the open position, such as Figure 5 In the open position, the vanes are completely on the inner surface 17i ( Figure 2 ). Thus, in the open position of the vanes, the inlet adjustment mechanism does not modify the nominal inlet diameter defined by the inlet surface 17i. As noted, in this particular embodiment, the vanes pivot out against a stop formed by the radially inner perimeter of the unison ring.

[0052] The blades can also be pivoted radially inwards (by rotation of the unison ring in the opposite direction, Figure 5 counterclockwise) to the closed position, such as Figure 6 . In the closed position, the arcuate edges along the radially inner side of the blades collectively form an orifice. In the illustrated embodiment, in the closed position, the orifice is substantially circular, having a diameter that is less than the diameter of the inlet surface 17i. ("Substantially circular" in this disclosure means that the arcuate edges are all located on the same circle and collectively occupy at least 80% of the circumference of the circle.) As a result, the effective diameter of the inlet is reduced relative to the nominal inlet diameter. Moreover, in an embodiment not illustrated, the blades can be pivoted an additional amount to a super-closed position in which there is a degree of overlap between adjacent blades, which is achieved by forming the corresponding overlapping edge portions of the adjacent blades into complementary or convex-concave shapes. When the blades are in the super-closed position, the arcuate edges of the blades collectively define an opening or orifice that is not a perfect circle, but is more Figure 6The opening of the closed position is smaller and still effective. Therefore, the inlet adjustment mechanism further reduces the effective diameter of the inlet relative to the closed position. In this way, the inlet adjustment mechanism can adjust the effective diameter of the air inlet close to the compressor wheel.

[0053] However, it should be noted that it is not necessary for the orifice defined by the inlet adjustment mechanism to be circular in the closed position. Alternatively, the orifice may be non-circular. The present invention is not limited to any particular shape of orifice.

[0054] As previously described, the vanes 102 are actuated to pivot between their open and closed positions (and, optionally, over-closed positions) by a unison ring 106 rotatable about the central axis of the air inlet. Figures 4 to 6 , a rotational movement is applied to the unison ring by an actuator 116 which is received in a receiving portion 116a defined in the compressor housing. The actuator comprises an actuator rod 117 which extends through a space defined in the compressor housing and is attached at its distal end to a groove 109 ( Figure 3 ) engages pin 118. The actuator is operable to linearly extend and retract rod 117 along its length to rotate unison ring 106 and thereby actuate vanes 102. Extending the rod pivots the vanes toward the closed position, and retracting the rod pivots the vanes toward the open position.

[0055] As noted, the inlet adjustment mechanism 100 enables adjustment of the effective size or diameter of the inlet into the compressor wheel 14. Figure 2 As shown in , when the inlet adjustment mechanism is in the closed position, the effective diameter of the inlet into the compressor wheel is determined by the inside diameter defined by the vanes 102. To achieve this effect, the axial separation distance between the vanes and the compressor wheel must be as small as practical so that there is insufficient distance downstream of the vanes for the air to expand to the full diameter of the inlet inducer portion of the compressor wheel 14 when it encounters it. Thus, the inlet diameter is effectively reduced to a value that is dependent on the vanes.

[0056] At low flow rates (e.g., low engine speeds), the inlet adjustment mechanism 100 may be placed Figure 2 and Figure 6 The compressor wheel is then moved to a closed position in the compressor. This may have the effect of reducing the effective inlet diameter and therefore increasing the flow velocity to the compressor wheel. The result will be a reduction in the compressor blade incidence angle, effectively stabilizing the flow (i.e., making blade stall and compressor surge less likely). In other words, the compressor surge line will be shifted to a lower flow rate (to the left of the compressor pressure ratio versus flow rate graph).

[0057] In the case of medium and high flow rates, the inlet regulating mechanism 100 may be partially opened or fully opened, such as Figure 5 This may have the effect of increasing the effective inlet diameter so that the compressor regains its high flow performance and choke flow essentially as if the inlet adjustment mechanism was not present and as if the compressor had a conventional inlet matching the wheel diameter at the inlet inducer portion of the wheel.

[0058] According to the present invention, by providing a spacing feature that spaces a majority of the upstream surface 102u of each blade from the adjacent upstream wall surface 105, the friction forces that hinder the pivotal movement of the blade 102 are significantly reduced. Figures 5 to 9 In one embodiment, the spacing features R include raised areas (e.g., but not limited to, ribs, ridges, dimples, etc.) that contact the upstream wall surface 105. The spacing features R collectively constitute a small portion of the total upstream surface 102u of each blade, thereby separating a majority of the upstream surface area of ​​each blade from the upstream wall surface 105. (The phrase "upstream surface area of ​​each blade" refers to the surface area of ​​the blade that could have frictionally contacted the upstream wall surface 105 but cannot due to the provision of the spacing features.) Alternatively, the spacing features may be defined in or by the upstream wall surface 105.

[0059] Reference Fig. 9 As previously described, due to the axial clearance of the blades designed into the inlet adjustment mechanism, the net aerodynamic load on the blades 102 acts in the upstream axial direction ( Fig. 9 The spacing feature R at the upstream side of the blade ensures that there is also an air space between the blade and the upstream wall surface 105, thereby achieving pressure communication between the upstream and downstream surfaces of the blade. Therefore, the pressure on those surfaces is more evenly balanced. As a result, the net aerodynamic load on the blade in the axial direction is greatly reduced relative to a similar design lacking the spacing feature. The spacing feature R also greatly reduces the total surface area of ​​the blade 102 in contact with the upstream wall surface 105. The reduction in aerodynamic load and the reduction in contact surface area together result in substantially lower friction forces that hinder the pivoting of the blade. Therefore, the present invention greatly alleviates or eliminates any tendency of the blade to fail to move outward or move too slowly when starting from the closed position of the inlet adjustment mechanism during operating conditions close to surge (low engine speed and high compression ratio).

[0060] The technical personnel of the field to which these inventions belong, who benefit from the teachings set forth in the foregoing description and the related drawings, will think of many modifications and other embodiments of the invention set forth herein. For example, although the illustrated embodiment employs three blades 102, the invention is not limited to any specific number of blades. The invention can be practiced with as few as two blades or as many as 12 or more blades. The more blades there are, the closer the opening surrounded by the blades can be to a circle (although, generally speaking, the opening can be circular in only one position of the blade). Therefore, the number of blades can be selected as desired, taking into account that the complexity will be greater when there are more blades, which may offset the advantages of increased roundness. In addition, in the illustrated embodiment, the blades are configured so that the opening surrounded by the blades is approximately circular when the blades are in the closed position. However, alternatively, the blades can be configured so that the opening is non-circular when the blades are in the closed position. Moreover, although blades with arc-shaped edges have been illustrated and described, the blades do not necessarily have arc-shaped edges. Blades with edges of different shapes (linear, elliptical, etc.) are also included in the scope of the invention. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.Although specific terms are employed herein, these terms are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A turbocharger, comprising: a turbine housing and a turbine wheel mounted in the turbine housing and connected to a rotatable shaft for rotation therewith, the turbine housing receiving exhaust gas and supplying the exhaust gas to the turbine wheel; a centrifugal compressor assembly including a compressor housing and a compressor wheel mounted in the compressor housing and connected to the rotatable shaft for rotation therewith, the compressor wheel having blades and defining an inlet inducer portion, the compressor housing having an air inlet wall defining an air inlet for directing air generally axially into the compressor wheel, the compressor housing further defining a volute for receiving compressed air discharged generally radially outwardly from the compressor wheel, the air inlet wall defining an annulus surrounding the air inlet and opening into the air inlet at a radially inner end of the annulus; as well as a compressor inlet adjustment mechanism disposed in the annular space of the air inlet wall and movable between an open position and a closed position, the inlet adjustment mechanism comprising a plurality of vanes disposed within the annular space between an upstream wall surface and a downstream wall surface, the vanes collectively surrounding an orifice, the upstream surface of each vane opposing the upstream wall surface and the downstream surface of each vane opposing the downstream wall surface, each vane being pivotable about a pivot point fixed in the compressor housing, the vanes pivoting radially inwardly from the annular space into the air inlet when the vanes are in the closed position so as to cause the orifice to have a reduced diameter relative to a nominal diameter of the inlet; Wherein, at least one of the upstream wall surface and the upstream surface of each blade includes a spacing feature, which separates most of the upstream surface of each blade from the upstream wall surface to achieve pressure communication between the upstream and downstream surfaces of the blade.

2. The turbocharger according to claim 1, wherein: The spacing feature is defined by the upstream surface of each blade.

3. The turbocharger according to claim 2, wherein: The spacing feature includes a raised area on the upstream surface of each vane that contacts the upstream wall surface and spaces a majority of the upstream surface of each vane apart from the upstream wall surface.

4. The turbocharger according to claim 1, wherein: Each vane includes a radially inner edge having an arc shape, the vanes being configured such that the radially inner edges collectively form the aperture into a circular shape in a selected position of the inlet adjustment mechanism.

5. The turbocharger according to claim 4, wherein: The selected position where the radially inner edge forms the orifice into a circular shape is the closed position.

6. The turbocharger according to claim 1, wherein: The number of the blades is three.

7. The turbocharger according to claim 1, wherein: The inlet adjustment mechanism further includes a unison ring rotatable about an axis of rotation of the turbocharger, wherein each of the vanes is engaged with the unison ring such that rotation of the unison ring causes the vanes to pivot.

8. The turbocharger according to claim 7, wherein: Each vane includes an end portion that engages a slot defined in an inner perimeter of the unison ring.

9. The turbocharger according to claim 7, wherein: The inlet adjustment mechanism further includes a plurality of guides for guiding the rotation of the unison ring.

10. The turbocharger according to claim 9, wherein: The guide is configured to limit the amount of radially outward pivoting of the vanes to the open position.

Images