Patent Application
20160298633
This application relates to a support for a vane stem of a compressor variable vane.
Gas turbine engines are known and, typically, include a fan delivering air into a compressor section. The air is compressed and delivered into a combustor section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate.
In a standard compressor section, there are rotating rotors carrying stages of blades. Between the stages of rotating blades there are often static vanes. One type of vane has an angle of incidence that may be varied to direct the air flow to a downstream blade in a desired condition. An actuator for the variable vane can change the angle depending on flight conditions. It is known to have the actuator driving an airfoil on the vane through a vane stem. The vane stem is supported in a housing boss with a bushing.
In the prior art, the support for the vane stem is complicated by the possibility that a pressure drop, from outside of the compressor section compared to inside the compressor section, could cause the vane to be drawn inwardly and away from its support.
In a featured embodiment, a variable vane assembly comprises an upstream vane stage including an airfoil coupled with an upstream vane stem and an upstream vane arm, and configured to drive the upstream vane stem to rotate. The upstream vane stem is supported in an upstream housing boss. A downstream vane stage includes an airfoil coupled with a downstream vane stem and a downstream vane arm, and configured to drive the downstream vane stem to rotate. The downstream vane stem is supported in a downstream housing boss. A first clearance is defined between a radially inner end of the upstream vane arm and a radially outer end of the upstream housing boss. A second clearance is defined between a radially inner end of the downstream vane arm and a radially outer end of the downstream housing boss. A clearance ratio of the second clearance to the first clearance is greater than or equal to 10.
In another embodiment according to the previous embodiment, the clearance ratio is greater than 35.
In another embodiment according to any of the previous embodiments, a top hat bushing is inserted in the upstream housing boss. The top hat bushing defines the radially outer end of the upstream housing boss.
In another embodiment according to any of the previous embodiments, a downstream bushing supports the downstream vane stem in the downstream housing boss. The downstream bushing has an outer diameter and extends for a length. An upstream bushing ratio of the length to the outer diameter is greater than or equal to 2.5 and less than or equal to 3.0.
In another embodiment according to any of the previous embodiments, the downstream vane stem has an outer periphery supported within the downstream bushing that has at least one greater diameter portion and a lesser diameter portion.
In another embodiment according to any of the previous embodiments, there are a pair of greater diameter portions on opposed sides of the lesser diameter portion.
In another embodiment according to any of the previous embodiments, the downstream bushing includes graphite.
In another embodiment according to any of the previous embodiments, the upstream vane stage has an upstream bushing positioned within a bore of the upstream housing boss. The upstream bushing extends for a length and has an outer diameter. An upstream bushing ratio of the length to the outer diameter is greater than 3.0.
In another embodiment according to any of the previous embodiments, the upstream vane stage has an upstream bushing positioned within a bore of the upstream housing boss. The upstream bushing extends for a length and having an outer diameter and an upstream bushing ratio of the length to the outer diameter being greater than 3.0.
In another embodiment according to any of the previous embodiments, the downstream bushing includes graphite.
In another featured embodiment, a compressor section comprises a plurality of rotor blade stages. A variable vane assembly has an upstream vane stage including an airfoil coupled with an upstream vane stem and an upstream vane arm configured to drive the upstream vane stem to rotate. The upstream vane stem is supported in an upstream housing boss. A downstream vane stage includes an airfoil coupled with a downstream vane stem and a downstream vane arm and is configured to drive the downstream vane stem to rotate. The downstream vane stem is supported in a downstream housing boss. A first clearance is defined between a radially inner end of the upstream vane arm and a radially outer end of the upstream housing boss. A second clearance is defined between a radially inner end of the downstream vane arm and a radially outer end of the downstream housing boss. A ratio of the second clearance to the first clearance is greater than or equal to 10.
In another embodiment according to the previous embodiment, the clearance ratio is greater than 35.
In another embodiment according to any of the previous embodiments, a top hat bushing is inserted in the upstream housing boss, and defines the radially outer end of the upstream housing boss.
In another embodiment according to any of the previous embodiments, a downstream bushing supports the downstream vane stem in the downstream housing boss. the downstream bushing having an outer diameter and extending for a length, and an upstream bushing ratio of the length to the outer diameter being greater than or equal to 2.5 and less than or equal to 3.0.
In another embodiment according to any of the previous embodiments, the downstream vane stem has an outer periphery supported within the downstream bushing that has at least one greater diameter portion and a lesser diameter portion.
In another embodiment according to any of the previous embodiments, there are a pair of greater diameter portions on opposed sides of the lesser diameter portion.
In another embodiment according to any of the previous embodiments, the downstream bushing includes graphite.
In another embodiment according to any of the previous embodiments, the upstream vane stage has an upstream bushing positioned within a bore of the upstream housing boss, and the upstream bushing extends for a length and has an outer diameter. An upstream bushing ratio of the length to the outer diameter is greater than 3.0.
In another embodiment according to any of the previous embodiments, the upstream vane stage has an upstream bushing positioned within a bore of the upstream housing boss. The upstream bushing extends for a length and has an outer diameter. An upstream bushing ratio of the length to the outer diameter is greater than 3.0.
In another embodiment according to any of the previous embodiments, the downstream bushing includes graphite.
These and other features may be best understood from the following drawings and specification.
The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.
The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.
The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.
The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.
A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second.
A compressor section 100 is illustrated in
A plurality of rotor blades 97, 101 and 102 are shown and are driven to rotate as the engine operates. Intermediate to the blades are variable vanes, such as variable vanes 104, 105 and 128. Variable vanes 104 and 105 could be said to be the first and second stage variable vanes, respectively. While the variable vane stages 104 and 105 include structural differences, their components will be identified by common reference numbers for purposes of this application. In general, the differences between the two stages 104 and 105 are relatively small compared to the differences with a downstream stage 128.
A vane stem 130 secures an airfoil of the vanes 104 and 105 and extends outwardly of a boss 108. A vane arm 106 is secured to the vane stem 130 outwardly of the boss 108. Bushings 110 are positioned within the boss 108. The bushings 110 must extend for a relatively great length and, typically, must extend to support radially thicker portions 150 of the vane stem which are spaced on opposed sides of a thinner portion 151 of the vane stem 130. The thicker and thinner portions are best understood from
The vane arm 106 is secured to the vane stem 130, which is supported in the boss 108 by bushing 110, adjacent an outer end of the boss 108. This is because a pressure drop across the variable vanes 104 and 105 could cause the vane to be drawn inwardly. The vane arm 106 is designed to contact a top hat bushing 99, which protects the boss 108 and the vane arm 106 from wear, when the vane drops due to pressure differences.
The third stage variable vane 128, which conditions air flow to approach a compressor blade stage 170, does not have as challenging of a pressure drop. Thus, as shown, the boss 126 supporting the vane stem 124 need not extend as far outwardly as the more upstream stages. A bushing 120 supports the vane stem 124. A vane arm 122 is secured to the outer end of the vane stem 124. The pressure does not cause the vane to drop at this stage so the vane arm 122 will not contact the boss 126. Since no wear is expected, no top hat bushing is required. In addition, the outer diameter height of the boss 126 may be reduced.
The vane stem 124 must still extend radially outwardly beyond the radially outer end of the boss 126, as the vane arm 122 needs to avoid the compressor housing split flange (not illustrated).
The bushing 120, or the combination of the bushings 110 and 99, form a trunnion for the variable vane stems, 124 and 130, respectively.
As shown in
In embodiments, C1 may be on the order of 0.016 inch (0.040 centimeters) or 0.018 inch (0.045 centimeters), depending on which of the two stages 104 and 105 is measured. On the other hand, C2 may be 0.751 inch (1.90 centimeters). In embodiments, a ratio of C2 to C1 may be greater than or equal to 10. More narrowly, the ratio of C2 to C1 may be greater than or equal to 20. Even more narrowly, the ratio of C2 to C1 may be greater than or equal to 35.
As can be appreciated, the vane stems each have an end extending from the airfoils, and another end which is secured by the vane arm. The bosses, such as bosses 108, form part of a housing, and include a bore that receives the bushings 110, or 120.
As shown in
The radial thickness of the thicker portions 150, and a radially thinner portion 151 measured relative to the rotational axis X of the variable vane stems.
The bushing 120 extends for a length L between an inner end 121 and an outer end 123, and has an outer diameter D. In one embodiment, L was about 1.12 inches (2.85 centimeters) while D was about 0.398 inches (1.01 centimeters). A ratio of L to D was thus about 2.81 inches (7.14 centimeters). In various embodiments, the ratio is greater than or equal to about 2.5 and less than or equal to about 3.0.
The bushing 120 may be a graphite bearing available under the trade name POCO. The POCO bearings may be available from Poco Graphite, Inc. under their trade name Jet-2. These may be simple cylinders press fit into a reamed hole in the boss.
Of course, other bearing types such as a metal lined bushing, would also benefit from the teachings of this application.
In at least one existing variable vane system, the ratio of L to D was on the order of 4.68. Such longer bushings were also used at variable vane stages which did not have the concern with pressure drop, and added unnecessary weight. Further, the assembly of the relatively long bushing into a bore in the housing is challenging and can result in breakage, particularly when using graphite containing bushings. Thus, the reduction of the length provides assembly benefits.
As can be appreciated, the shorter bushing 120 is utilized in at least one embodiment with a downstream variable vane stage 128, while the longer bushings 110 are utilized with more upstream rotor stages. As mentioned, those longer bushings have a ratio of a length to an outer diameter which is outside the range of 2.5 to 3.0.
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
This application claims priority to U.S. Provisional Patent Application No. 61/916,358, filed 16 Dec. 2013.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/064486 | 11/7/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61916358 | Dec 2013 | US |
