IL46975A

IL46975A - Stator vane actuating mechanism

Info

Publication number: IL46975A
Application number: IL46975A
Authority: IL
Original assignee: United Aircraft Corp
Priority date: 1974-04-10
Filing date: 1975-03-31
Publication date: 1977-03-31
Also published as: IT1034694B; SE7503921L; FR2267454B1; SE393838B; JPS50138208A; CA1015277A; GB1493151A; FR2267454A1; IL46975A0; DE2512292A1; US3873230A; JPS581241B2; DE2512292C2

Description

STATOR VANE ACTUATING MECHANISM i BQD min n^PDn"? τιααιο This invention relates to actuation systems for adjustable vanes in gas turbine engines.

- It is well known to provide axial flow compressors or gas turbine engines with adjustable stages of stator vanes to improve engine performance at various engine operating, conditions « Mechanism for actuating these adjustable vanes are mounted on the engine casing in a manner resulting in large actuation reaction forces being transmitted directly into the engine casing; this often requires strengthening of the casing or actuating mechanism supporting members to reduce system -deflection -^nd -hysteresis,-thereby-adding weight to the engine which is undesirable. Also, since the mounting structure is usually rigidly secured to the engine casing at several locations the structure is subject to stresses imposed by case deflection and case thermal growth, necessitating heavier and stronger components. Unison rings are usually all actuated in the same, direction and their reaction loads are therefore additive and are transmitted into the casing.

It is one object of the- present invention to minimize the reaction forces transmitted into the engine casing through a stator vane actuation system.

A further object of the present invention is to reduce the stresses imposed upon an actuation system support structure due to engine case growth and engine case distortion.

Accordingly, in the present invention a vane ..actuation support structure is isolated, in so far as is possible, from the engine casing. Vane actuation means is connected to bell-crank means and both are entirely supported by this, support structure. Pairs of unison rings are connected to and actuated by the bell-crank means in opposite directions whereby the reaction forces transmitted into the ..support structure are balanced and reduced to a minimum. By having the actuation means as well as the bell-crank "means mounted entirely on the support structure the actuator reaction loads are not transmitted into the engine casing.

•The prior art makes no effort to balance reaction forces off against each other before they are transmitted into the engine casing. It is often as if each bell-crank is directly secured to the engine casing. Also, it is usually the case that the unison rings rotate in the same direction and. the actuation means is secured directly to the casing. Thus, virtually all the forces that are -required to actuate each of the various unison rings are additive and have a direct load path into the engine casing. The present invention provides a common loop for these loads which permits various reaction loads to counteract each other such that the engine casing sees a reduced load. In U. S. Patent 2,999,630 to Warren et al th 1e two forward unison rings are actuated in opposite directions however, this serves no useful purpose from the point of view of reducing engine casing loads since the first bell- crank is pivoted directly from the engine casing .

The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of a preferred embodiment thereof as illustrated in the accompanying drawing.

The single figure is an external perspective view of apportion" of"the ^compressor" section of a~ gas-urb ne engine showing one embodiment of the invention.

Referring to the drawing, the numeral 10 designates the annular casing for the compressor section of an axial flow gas turbine engine. Only a portion of the casing is shown; the forward end of the casing or the inlet end of the engine is to the left in the drawing. In this embodiment the engine includes five stages of adjustable compressor stator vanes, the number not being critical- to the "invention . - The vanes themselves cannot be seen in the drawing but stems of several of the vanes of each stage can be seen extending radially outwardly through openings in the casing 10. The vane stems of the forward most stage are designated by the numeral 12, and the vane steras^ of the next succeeding stages are designated 14, 16, 18 and 20, respectively . Each of the stages has a unison ring associated therewith. The unison ring of the forward most stage is designated by the numeral 22; and the uniso rings of the next succeeding stages are designated 24, 26, 28 and 30,' respectively. The unison rings are of the type which is well known in the prior art. The vanes of each stage are connected to their respective unison rings by means of actuating arms 32 in a manner well known to persons having ordinary skill in the art. . __ The unison ring 22 is connected to a bell-crank 34; the unison rings 24, 26 are connected to a bell-crank 36; ""the "unison "ring 28 is connected to a bell-crank 38 and the unison ring 30 is connected to a bell-crank 40. The connecting means between the unison rings and the bell- •cranks are links 42 secured to brackets 44 which are fixed to the unison rings . The bell-cranks are all pivot- ally mounted on a support structure generally represented by the numeral 46.

The support structure 46 comprises a bell-crank . carrier member 48 which is herein shown as being tubular . in form and which extends in a direction substantiall -parallel to "the engine axis . --The- support 46 also includes casing connecting means for securing the bell-crank carrier member to the casing. In this exemplary embodiment the casing connecting means includes forward and rearward support · members or brackets 50, 52, respectively, which are secured by suitable means such as bolts to flanges on the casing 10 such as for example at 54 and at 56. The forward bracket 50 is flexible in the axial direction to accommodate axial casing growth and deflections so as to reduce stresses imposed on the carrier 48. Thus the carrier 48 is isolated from casing growth and deflection. To further the purpose of isolating the carrier member from the casing it is preferable that no more than two spaced apart support members are used to attach the member to the casing.

An actuator .58 is—also -mounted on- he bell-crank carrier 48 by suitable means such as the pin and clevis joint at 60. The actuator 58 is connected to the bell-cranks 34, 36, 38 and 40 by a connecting rod 62 which may be one piece or several interconnected pieces as shown in this embodiment.

In a manner well known to one with ordinary skill in the art, when the connecting rod 62 is moved forwardly or rearwardly by the actuator 58 the bell-cranks 34, 36, 38 and 40 pivot about their respective axes thereby rotating the unison rings_22,.24, _26, -28 _and 30 which in turn rotate the vanes of their associated stage through actuating arms 32.

In accordance with one aspect of the present invent!^ the adjustable vane stages are divided into what shall hereinafter be referred to as "pairs of balanced stages". The two stages' of vanes associated with the unison rings ,24 and 26 are an example of one such pair. In the present invention the unison ring and actuating arms of one stage of a pair are positioned rearwardly of the vanes of their associated stage, while the unison ring and actuating arms of the other stage of such pair are positioned forwardly of the vanes of their associated stage. Thus, the unison ring 24 is positioned rearwardly of the vane stems 14 and the unison ring 26 is positioned forwardly of the vane stems 16. Also in accordance with this invention, each -pair" of "balanced stages has associated therewith a pair of bell-crank arms such as the arms 64 and 66 of the bell- crank 36. , One of the pair of arras extends forwardly of its pivot point, such as the arm 64, and the other of the arms extends rearwardly of its pivot point, such as the arm 66. In this particular instance both arms are part of a single bell-crank 36 and therefore pivot about a common axis 68. Each of the pair of arms 64, 66 is connected to one of" the unison rings 24, 26 by means of links 42.

——I "operation,~ when the actuator 58 moves the connecting rod 62 the bell-crank 36 rotates about the axis 68 and, through links 42. rotate the unison rings 24, 26 in opposite directions. Since the unison rings are positioned on opposite sides of their respective vane stages, vanes of -both-stages- will -rotate—in the same direction. - The · important feature of this arrangement is that the reaction loads at the connection between the bell-crank 36 and the bell-crank carrier 48 (i.e. along the axis 68) are substantially canceled out in view of the substantially equal and opposite loads exerted on the arms 64, 66 during actuation of the unison rings 24, 26 in opposite directions. Only the difference between the reaction forces from the unison rings 24, 26 is felt by the bell-crank carrier 48 and is passed into the casing 10 through the brackets 50,52.

Another pair of balanced stages is also shown in Fig. 1. These are the stages associated with the unison rings 28 and 30. Note once again that the pair of unison rings associated with the pair of balanced stages are positioned on opposite sides of the vanes of their respective stages. The unison ring 28 is positioned forwardly of the vanes of its stage and the unison ring 30 is positioned rearwardly of the vanes of its stage. Note, however, that this pair of balanced stages is actuated through individual bell-cranks 38, 40 rather than a common bell-crank such as the bell-crank 36 which operates two unison rings. As with the previous pair of balanced stages, this pair of balanced- stages also has associated therewith a pair of bell-crank arms 70, 72. The bell-crank arm 70 extends rearwardly of its pivot point and the bell-crank 72 extends forwardly of its pivot point. Thus, once again, when the connecting rod moves the bell-cranks 38, 40 in the same direction the unison rings 28, 30 are rotated in opposite directions and all the vanes of the pair of balanced stages are rotated in the same direction. Since the bell-crank carrier 48 is common to the bell-cranks 38, 40 the substantially equal and opposite reaction forces at the pivots of the bell-cranks 38 and 40 will once again counteract each other. The brackets 50 and 52 and the casing 10 will feel only the difference, which is usually very small.

— —In -view of the -fact that the axes or pivot points of the arms 70, 72 are spaced apart and the loads act in opposite directions, the bell-crank carrier 48 will be subjected to a local" bending moment . For that reason a pair of bell-crank arms acting about a common axis, such as the arras 64, 66 is preferred for actuating a pair of balanced stages. Generally, space considerations around the engine casing and the spacing between adjustable vane sta'ges will determine whether or not a single or two separate bell-cranks are used to actuate a pair of balanced __stages. If -it is necessary to use -the two separate bell- cranks then it is preferable to have their pivot points as close together as possible to minimize the bending moment generated by the reaction forces. It is thus preferable, although not mandatory, that the pairs of balanced stages be adjacent stages such as they are in the exemplary embodiment of Fig. 1. Also, within a multi-stage compressor the force required to rotate the vanes ,in a given stage will likely be different from the force required to rotate the vanes in another stage, and similarly the angle of rotation desired may vary from stage to stage. Within these constraints, linkage geometry and the arrangement of pairs of balanced stages are selected such that the summation of reaction forces and moments acting on the bell-crank carrier member 48 is_as near. zero as possible thus minimizing the loads on brackets 50 and 52 and the engine casing 10. I should be noted in this embodiment that there is an odd number of stages and therefore it may not be possible to balance all the reaction loads going into the support structure 46. In this embodiment the forward most stage is the odd stage. Preferably there should never be more than one unpaired stage. Note that in this embodiment it may also be stated that the rearward most stage is the odd stage and that the forward and next to last stages are. the pair of balanced stages.

A further important feature of the present invention which is in keeping with the purpose of minimizing the loads transmitted to the casing 10 is that the actuator is mounted entirely on the support structure 46 so that the reaction forces associated therewith are confined to the load path loops formed by the support structure 46, the connecting rod 62, the bell-cranks 34, 36, 38, 40 and the actuating cylinder 58. The reaction forces thereby balance each other and are not transmitted into the casing 10.

Claims

WHAT WE CLAIM IS :

1. lh <*n axial flow gas turbine engine a stator -vane actuation -system -comprising: an annular casing, a plurality of stages of rotatably mounted stator vanes disposed within said casing, including at least one pax .r of' .ba,lan■ ced, s_tages;P il, i H^/tf 11, a plurality of first actuating arms connected to the vanes of a fiz-st stage of each of said pairs and extending rearwardly therefrom; a plurality of second actuating arms connected to the vanes of a second stage of each of said pairs and extending forwardly therefrom; a first unison rin Mg fo.r each of said pairs surrounding said casing and disposed rearwardly of the vanes of said first stage of each of said pairs, said first actuating arms being connected thereto; a second unison ring for each of said pairs surrounding said casing and disposed forwardly of the vanes of said second stage of each of said pairs, said second actuating arms being connected thereto; a bell-crank support assembly including sub- stantially axially extending bell-crank carrier means, said support assembly also including casing connecting means secured to said carrier means and to said casing, and adapted to substantially isolate said carrier means from deflection and axial growth of said casing; - "bell-crank-means including -a- pair- of-bell-crank arms for each of said pairs of stages, said arms being pivotally connected to said carrier means, one of said pair of bell-crank arms extending forwardly of its pivot point and the other of said pair of bell-crank arms extend ing rearwardly of its pivot point, one of said pair of bell-crank arms being connected to said first unison ring and the other of said pair of bell-crank arms being connected to said second unison ring; and actuation means mounted entirely on said bell-crank support assembly and connected to said bell-crank means^and adapted to simultaneously rotate said pairs of bell-crank arms in the same direction thereby rotating said first and second unison rings of each of said pairs of stages in opposite" directions to balance the reaction forces transmitted into said carrier means through each of said pairs of bell-crank arms and to effectuate rotation in the same direction of the vanes of each of said pairs of stages.

2. The stator vane actuation system according to claim 1 wherein the stages .of each of said pairs of stages aire adjacent stages.

3. The stator vane actuation system according to claim 1 wherei at least one pair of bell-crank arms is pivotally connected to said carrier means about a common axis. i i- ■

4. The stator vane actuation system according to claim 1 wherein not more than one of said stages of rotatably mounted stator vanes is an unpaired stage.

5. The stator vane actuation system according to claim 4 wherein said casing connecting means includes forward support means and rearward support means one of said support means being substantially rigid and the other permitting relative movement between said casing and said carrier means thereby substantially isolating said carrier means from said casing, said forward and rearward support means being the only load paths from said carrier means into said casing.

6. A stator vane actuation system substantially as hereinbefore described with reference to and as illustrated the accompanying drawings. ADVOCATE, PATENT ATTORNEY P. O. B. 39251 TEL-AVIV, I SRAEL