Variable vane actuating system

A variable guide vane (VGV) apparatus has a variable guide vane (VGV) rotatable about a vane rotation axis. An actuating arm is mounted to the VGV. The actuating arm has a fork defining a slot for receiving a drive pin. The slot is profiled to accommodate angular misalignment between the pin and the fork throughout a range of motion of the associated pin along the slot.

TECHNICAL FIELD

The application relates generally to an apparatus for actuating a variable guide vane in a compressor or a turbine.

BACKGROUND OF THE ART

Gas turbine engines sometimes have variable guide vanes (VGVs) disposed in an inlet section of an airflow duct of a compressor or turbine section. The guide vanes are adjustable in an angular orientation in order to control the airflow being directed through the airflow duct. An actuator positioned outside the airflow duct is conventionally used to actuate adjustment of the angular orientation of the VGVs. Various torque transfer arrangements have been created for connection between the actuator and the VGVs.

For VGV actuating systems with radial VGV (vanes oriented generally radially relative to the engine centerline), the VGV system is typically designed with a rotary actuator and vane actuating links. The contact between the rotary actuator and the actuating links has to be reduced in order to cater for greater VGV angle range. This results in increased wear at the link-actuator interface which leads to system inaccuracy.

SUMMARY

In accordance with a general aspect, there is provided a variable guide vane apparatus for a compressor or a turbine, comprising: a unison ring rotatable about a central axis thereof, the unison ring having an array of circumferentially spaced-apart drive pins; a set of variable guide vanes (VGV) circumferentially distributed around the central axis and mounted for rotation about respective spanwise axes of the vanes, the spanwise axes extending non-parallel to the central axis of the unison ring; and a plurality of actuating arms operatively connected to respective variable guide vanes for rotation therewith, the actuating arms each including a fork having a pair of spaced apart fingers with inwardly facing surfaces defining a slot therebetween, a corresponding one of said drive pins slidably received in the slot; wherein in a plane normal to a longitudinal axis of the slot, the inwardly facing surfaces have opposed end portions flaring outwardly from an intermediate throat in a direction away from the slot.

In accordance with another general aspect, there is provided a gas turbine engine comprising: a casing circumferentially extending around a central axis, vanes circumferentially distributed around the central axis, the vanes rotatably mounted to the casing for rotation about respective spanwise axes of the vanes, the spanwise axes of the vanes being transversal to the central axis, a unison ring mounted for rotation about the central axis; drive pins mounted to the unison ring; actuating arms operatively connected to respective vanes for rotation therewith, each actuating arm including a fork having a pair of fingers with inwardly facing surfaces defining a slot, an associated pin of the drive pins slidably engaged in the slot, the inwardly facing surfaces of the slot being profiled with top and bottom outwardly flaring sections to accommodate angular misalignment between the associated pin and the fork throughout a range of motion of the associated pin along the slot.

DETAILED DESCRIPTION

FIG. 1illustrates an example of a gas turbine engine. In this example, the turbine engine10is a turbofan engine generally comprising in serial flow communication a fan12, a compressor section14for pressurizing air, a combustor16in which the pressurized air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases.

It should be noted that the terms “axial”, “radial” and “circumferential” are used with respect to the centerline or central axis11of the engine10.

In this example, the compressor section14defines an annular airflow duct25having an axial inlet section (not numbered) to direct an airflow axially inwardly into the annular airflow duct25of the compressor section14, as indicated by the flow arrows. A variable guide vane (VGV) apparatus26is mounted to the compressor section14and has a plurality of variable inlet guide vanes28(VIGVs) positioned and rotatably supported within the inlet section of the airflow duct25. The VIGVs28are rotatable about respective spanwise axes30thereof, which are angled to the central axis11of the engine (i.e. non-parallel to the engine axis11). The angular orientation of the VIGVs28about the respective spanwise axes30is adjustable such that the airflow entering the inlet section of the airflow duct25is controlled by the VIGVs28. The VIGVs are configured to orient the flow before entering the first stage of compressor blades of the compressor section14. The VGV apparatus is configured to vary an angle of attack of its vanes depending of the operating conditions of the gas turbine engine. However, it is understood that VGVs may be used at other locations within the engine10.

Referring concurrently toFIGS. 2-10, the apparatus26may further include a unison ring32having a central axis axially aligned with the central axis11of the engine10. The unison ring32is supported in the engine10, for example, directly on the outer diameter of the casing31forming the annular air duct25. The unison ring32is mounted for rotation over the casing31. As shown inFIG. 2, an actuator27is connected to the unison ring32to rotate the unison ring in a selected direction on the casing31. The actuator27can take various forms. For instance, it can be provided in the form of a linear actuator, such as a piston and cylinder arrangement, configured to apply a tangential force to the ring32so as to rotate the ring32about its central axis on the casing31. As best shown inFIGS. 2 and 4, the unison ring32may have a cantilevered portion carrying an array of circumferentially spaced-apart drive pins34for engagement with respective actuating links35, which are, in turn, operatively connected to respective VIGVs28to transfer a torque from the unison ring32to the VIGVs28and, thus, cause the same to rotate about their respective axes30. As can be appreciated fromFIG. 4, the drive pins34may project generally radially inwardly from an inner diameter of the cantilevered portion of the unison ring32. The drive pins34may be removably mounted in corresponding circumferentially spaced-apart holes define in the cantilevered portion of the unison ring32.

According to one embodiment, the actuating link or arm35has a base38and a fork36having a pair of spaced-apart fingers extending in a parallel relationship from the base38. The base38defines a central opening for receiving a stem48projecting from a radially outer end of each VIGV28. The stem48may be connected to or integrated with each of the VIGVs28, and extending coaxially with respect the axis30of the associated VIGV28. For example, as shown inFIG. 2, the stem48may have a cylindrical section rotatably supported in the engine to thereby define the rotation axis30of the respective VIGVs28. The stem48according to one embodiment may include an end section rigidly connected or keyed to the base38of an associated actuating arm35via any suitable connections, such as bolts and the like. The end section of the stem48and the corresponding central opening in the base38of the actuating arm35may have flat sides (i.e. planar surfaces) to transmit a torque from the actuating arm35to the VIGV28about axis30.

As best shown inFIGS. 5, 7, 89aand10a, the fork36and the base38define a U-shaped profile. The fingers of the fork36in combination define an open ended slot therebetween into which an associated one of the drive pins34may be slidably received. When the unison ring32is circumferentially adjusted (i.e. rotated) about its axis, each of the drive pins34which is affixed on the unison ring32, moves together with the unison ring32in the circumferential direction to drive an associated one of the actuating arms35(which is connected with the stem48) to rotate together with the stem48about the respective rotational axes30of the VIGVs28, resulting in adjustment of the angular orientation of the respective VIGVs28in order to control the airflow entering the inlet section of the air duct25. As shown inFIGS. 7 and 8, the VIGVs28are pivotable about their respective axes30between a fully closed position (FIG. 7) and a fully open position (FIG. 8). The drive pin34is allowed to slide along the slot defined between two fingers of the fork36when the drive pin34drives the actuating arm35in rotation about the vane rotation axis30. In this way, the mounting arrangement of the unison ring32can be simplified as the ring32only has to be movable (i.e. rotatable) in the circumferential direction. The ring32does not have to slide axially to account for the relative axial movement between the pins34and the actuating arms36. This relative movement is rather accommodated by the axially elongated component of the slots defined by the fork36.

Also, as the pivot axes30of the vanes28are not parallel to engine axis11and, thus, to the rotation axis of the unison ring32, but rather oriented at an angle with respect thereto. As a result and as shown inFIGS. 9band 10b, the angle A between the pins34and the fork36changes through the range of motion of the unison ring32. Indeed, for applications where the VGVs are angled with respect the engine centerline11and the unison ring32(e.g. VIGVs perpendicular to the engine axis11) the movement of the unison ring32introduces a twisting motion between the drive pins34and the forks36. As the unison ring32rotates, the pins34slide along the slots and as the pins slide, the relative position of the pins34and the forks36introduces an angular misalignment that needs to be accounted for. This is schematically depicted inFIGS. 5,6, 9band10b.

As shown inFIGS. 6, 9a,9b,10aand10b, the angular movement of the drive pins34in the slots can be accommodated by profiling the forks36. For instance, this can be done by introducing a curvature in the forks36to give freedom for the drive pins34to actually angularly move or tilt with respect to the forks36. According to the illustrated embodiments, the inwardly facing surfaces of the forks36may have a top and a bottom rounded or curved section36a,36band a central flatten section36c. Such a variable profile of the inwardly facing surface of the forks36in a plane normal to the longitudinal axis of the slot is configured to accommodate the angular motion of the pin34relative to the forks36while at the same time maximizing the surface contact area between the pins34and the forks36. The rounded sections36a,36bincluding the top and bottom rounded edges on the opposed facing surfaces of the pairs of fingers of the forks36provide the room required to accommodate the relative angular movement while the flatten profile of the central or intermediate section36cmaximizes the contact area and, thus, minimize wear.

Alternatively, the fork profiled surface could be designed as a single radius from top to bottom of the fork arm or even chamfered top and bottom of the fork with the pin contact interface as a line contact. Nonetheless, combining a flatten area with outwardly flaring top and bottom areas allows to increase contact area to minimize wear rate while providing the required freedom of angular movement between the pin the forks. With such a pin-fork arrangement, the interface can then be optimized to increase the contact surface between the pin and fork.

According to these embodiments, the width of the slot varies along the height (h) of the slot. This can be appreciated fromFIG. 9b. Indeed, the width W3at the bottom of the slot and the width W2at the top of the slot are greater than the width W1at an intermediate or mid region of the slot. This width distribution provide for top and bottom sections flaring outwardly from a central throat region. It defines two outwardly diverging end sections linked by a bridge or throat section. This slot geometry is configured to accommodate the tilting motion of the pin relative to the forks while the pin slides along the slot.

Therefore, according to at least some embodiments, the accuracy and durability at the pin-fork interface may be improved by: 1) introducing variable profile to the fork surface to allow for drive pin angle change over full range of motion of the vanes.

Furthermore, as shown inFIGS. 10aand 10binstead of having longitudinally straight forks (FIGS. 9a, 9b), the forks36′ may be designed to offer a non-rectilinear longitudinally extending cam surface for the pins34. For instance, as shown inFIG. 10a, the forks36may be curved in the longitudinal direction to provide for a non-rectilinear slot. More particularly, according to the illustrated embodiment, the distal end portion 36d′ of the forks have a curved contour to act as a vane angle schedule adjustment. The forks36′ thus define a curved or bent slot allowing the forks36′ to act as a “cam” to actually change the vane angle schedule. By so introducing a profile change along at least a portion of the length of the forks36′, the vane angle schedule can be changed/adjusted for a given unison ring stroke. That is with the bent slot design shown inFIGS. 10a, 10b, it is possible to use the fork itself to change the vane angle schedule of the vanes while keeping a simple common actuating system. In other words, with the same movement of the actuator, different vane angle responses can be obtained by simply changing the longitudinal shape of the forks36′. In the illustrated example, the curved distal end portion 36d′ of the forks includes two serially interconnected longitudinal segments 36d′1, 36d′2defining a different degree of curvature. It is understood that the curved or bent can be composed of any desired number of differently oriented segments.

As shown inFIGS. 2 and 4, the unison ring32can ride directly on the radially outer surface of casing31. The unison ring32and the casing31are designed so that the inner diameter surface of the ring32matches the outer diameter surface of the casing31, thereby allowing the ring32to circumferentially slide on the casing31. The union ring32can, for instance, be made of a wear resistant composite material similar to materials used for sliding bumper pads to avoid metal to metal rubbing between the unison ring and casing. This eliminates the need for any intermediate slider bushing pads, bearings or tracks between the casing and the unison ring. The casing31can be made out of metal or any other suitable material. Such an arrangement allows to simplify and to improve the system durability between the unison ring and casing interface.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, it is understood that the various features of the VGV actuating system are not limited to turbofan applications. Indeed, they could be applied to any engines, including turboshaft, turboprop, APU engines as well as non-gas turbine engines. Also, it is understood that the VGVs are not limited to VIGVs as exemplified herein above. Any variable guide vane apparatus having VGVs with pivotal axes angled to the engine centerline could benefit from the various aspects of the present invention. For instance, VGVs apparatus in the turbine section of the engine could integrate at least some of the various features described herein above. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.