Patent Description:
In gas turbine engines, compressors can have one or more sets of blades which rotate around a main axis during operation and compress air along the main gas path of the engine. Vanes are airfoil components which also extend across the gas path, typically adjacent to a set of rotor blades, but which do not rotate around the main axis. Vanes can be used to guide/direct the air onto the rotor blades at an angle of incidence which is chosen in a manner to optimize engine performance and efficiency. Since the optimal angle of incidence can vary as a function of operating conditions, it was known to use variable guide vanes (VGV) to change the angle of incidence to keep the angle of incidence suitable in different operating conditions. Variable guide vanes, like non-variable guide vanes, typically do not rotate around the engine main axis, but can be mounted in a manner to rotate around an axis extending along their length, across the main gas path, in a manner to allow changing the angle of the vane chord relative to the gas path.

While existing variable guide vane systems were satisfactory to a certain degree, there always remains room for improvement. Indeed, each set of vanes includes a plurality of vanes which are circumferentially distributed around the main axis. Depending on the configuration of the main gas path, the vanes can individually extend perfectly radially around the main engine, or slope towards the front or towards the rear to a certain extent. Variable guide vane systems typically aim to change the angle of incidence of all vanes of the set simultaneously and uniformly relative to the gas path, and to this end can require a suitable mechanism with several moving parts. Such mechanisms may need to be designed with a number of elements taken into consideration such as weight, cost, reliability, durability/wear, maintenance costs, etc., and improvement appeared to remain possible at least in some embodiments.

<CIT> discloses a lever connection to a synchronizing ring.

<CIT> discloses stator blade ring assemblies for axial flow compressors.

According to an aspect of the present invention, there is provided a variable vane mechanism in accordance with claim <NUM>.

According to another aspect of the present invention, there is provided a gas turbine engine in accordance with claim <NUM>.

Optionally, and in accordance with any of the above, the slide blocks are retained on the corresponding pins along the orientation of the pin axis by a resilient retaining ring, the retaining ring extending partially into a slot defined around the pin and partially into a slot defined around a central aperture of the slide blocks.

Optionally, and in accordance with any of the above, the pins are riveted to the actuator ring.

Optionally, and in accordance with any of the above, the slide blocks each have two removal grooves extending parallel to the pin on opposite removal faces, the removal faces extending between corresponding edges of the slide block faces.

Optionally, and in accordance with any of the above, the pins protrude from the annular body and the pin axes extend away from the main axis, the guide slots defined along the length of corresponding ones of the vane arms.

Optionally, and in accordance with any of the above, an angle between the main axis and the vane axes is at least <NUM> degrees.

Optionally, and in accordance with the above, an angle between the main axis and the vane and pin axes is at least <NUM> degrees.

Optionally, and in accordance with any of the above, the two slide block faces of each slide block and the two guide slot faces of each guide slot are planar, flat and parallel.

According to another aspect of the present invention, there is provided a method of operating a variable vane mechanism in accordance with claim <NUM>.

<FIG> illustrates an example of a turbine engine. In this example, the turbine engine <NUM> is a turboprop engine generally comprising in serial flow communication along a main gas path <NUM>, a multistage compressor <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases around the main axis <NUM>, and a turbine section <NUM> for extracting energy from the combustion gases. The turbine engine terminates in an exhaust section <NUM>. The main gas path <NUM> can be delimited mainly by corresponding walls of a casing <NUM>.

In the embodiment shown in <FIG>, the turboprop engine <NUM> has two stages, including a high pressure stage associated to a high pressure shaft, and a low pressure stage associated to a low pressure shaft. High pressure turbine stage is associated to the high pressure shaft, and a low pressure turbine stage is associated to the low pressure shaft. The low pressure shaft is used as a power source to drive a propeller <NUM> in this embodiment. The compressor section can have a rotor associated to the high pressure shaft, for instance, as is the case in this embodiment.

As is the case in other types of gas turbine engines, such as turbofan engines and turboshaft engines, the compressor <NUM> can have one or more rotor, having one or more sets of blades <NUM>. One or more of the sets of blades <NUM> can be axial, meaning that the blades of the set are provided in the form of elongated airfoil sections circumferentially distributed around the main axis <NUM> and extending across the annular gas path <NUM>, and which can collectively be rotated for each blade to move circumferentially around the gas path <NUM> and work the fluid medium.

Although the gas path <NUM> is typically annular, the shape it takes along the length of the engine main axis <NUM> can vary from one embodiment to another. Indeed, it can extend relatively straight, or along curved portions. Accordingly, to extend suitably across the gas path, typically roughly transversal to the gas path, and depending on the position of a given set of blades <NUM> along the length of the gas path <NUM>, it can be suitable for the blades to extend radially relative the main axis <NUM> (e.g. across a straight, axially-oriented section of the gas path <NUM>), or to slope towards the front or towards the rear (e.g. across an oppositely sloping section of the gas path <NUM>. The compressor <NUM> can also have a centrifugal compressor section <NUM>, which typically involve a relatively complex swirling blade geometry defining an axial inlet and a radial outlet. In the specific embodiment presented in <FIG>, the main gas path <NUM> extends in a reverse orientation, from the rear to the front, and a single rotor includes three axial compressor blade sets <NUM> followed by a centrifugal compressor section <NUM>. Other configurations are possible in alternate embodiments.

Depending on the specific embodiment, one or more sets of vanes <NUM> can be used in relation with one or more corresponding sets of blades <NUM>. Vanes are airfoil components which also extend across the gas path <NUM>, but which do not rotate around the main axis <NUM>. Each set of vanes <NUM> includes a plurality of vanes which are circumferentially distributed around the main axis <NUM>. Vanes of one set of vanes <NUM> can be used to direct the air onto the blades of the corresponding set of blades <NUM> at an angle of incidence (e.g. swirl angle) which is designed to optimize engine performance and efficiency. With this purpose in mind, each set of vanes <NUM> can be positioned adjacent a corresponding set of blades <NUM> along the length of the gas path <NUM>. Since the optimal angle of incidence can vary as a function of operating conditions, one or more of the set(s) of vanes <NUM> can be a set of variable guide vanes (VGV). The vanes of a set of variable guide vanes can be configured in a manner to allow changing the angle of incidence as a function of varying operating conditions, and allow to keep the angle of incidence suitable or optimal in different operating conditions. Variable guide vanes, like non-variable guide vanes, typically do not rotate around the main axis. However, variable guide vanes, by contradistinction with non-variable guide vanes, can be mounted in a manner to rotate around a vane axis extending along their length, across the main gas path, in a manner to allow changing the angle of the vane chord relative to the gas path. As for blades, depending on the shape of the main gas path <NUM> and their position along it, the vanes can individually extend perfectly radially around the main engine, or slope towards the front or towards the rear to a certain extent.

In the illustrated embodiment three sets of vanes <NUM> are associated to corresponding ones of the three sets of blades <NUM>. Variable guide vanes are typically part of a variable guide vane system which includes a mechanism operable to change the angle of incidence of all vanes of the set simultaneously and uniformly. Such mechanisms may need to be designed with a number of elements taken into consideration such as weight, cost, reliability, durability/wear, maintenance costs, etc., and improvement appeared to remain possible at least in some embodiments.

One type of mechanism, which can be used to simultaneously and uniformly change the angle of incidence of all vanes of a set is schematized in <FIG>. In this embodiment, and as best seen in <FIG>, each vane <NUM> is rotationally mounted to casing components <NUM> at both ends, in a manner to be rotatable around a vane axis <NUM>. The vane axes <NUM> are non-parallel to the main axis <NUM>. In the embodiment illustrated, the vane axes <NUM> extend in a radial orientation relative the main axis <NUM>, and are thus disposed in a common virtual plane which is normal to the main axis. In alternate embodiments, the vane axes <NUM> can extend obliquely relative the main axis <NUM> and thus be disposed in a common virtual conical surface (i.e. it may slope to the front or to the rear to accommodate curvature and/or inclination of the local portion of the gas path). The vane axes <NUM> are non-parallel to the main axis <NUM>. All vanes of a given set can be identical, or, in some embodiments, some vanes of a given set can be different from others. The ends of the vanes <NUM> can be referred to as a (radially) inner end <NUM> and a (radially) outer end <NUM> relative to the main axis <NUM>, independently of whether the vane axis <NUM> is oblique or perfectly radial.

A vane arm <NUM> can extend from one end of the vanes <NUM>, such as the outer end <NUM> for instance. The vane arm <NUM> can have a length, which will be referred to herein as the vane arm length, extending transversally or obliquely relative the vane axis <NUM> in a manner to pivot around the vane axis <NUM> when the vane <NUM> rotates around the vane axis <NUM>, and vice-versa, a movement best seen in comparing <FIG>. The vane arm <NUM> can be said to extend away from the vane axis <NUM>. The pivoting of the vane arms <NUM> can be controlled in a manner to control the rotation of the vanes <NUM> and their angle of incidence relative the gas path <NUM>. To this end, a component which can be referred to as the actuator ring <NUM> can be used.

The actuator ring <NUM> can extend circumferentially around the main axis <NUM> and be configured in a manner to be rotatable around the main axis <NUM>, relative the casing <NUM>. A plurality of solid-of-revolution elements which can be referred to herein as pins <NUM> for simplicity can protrude from the actuator ring <NUM> and be circumferentially distributed around the actuator ring <NUM>. The pins <NUM> are defined along axes which will be referred to herein as the pin axes <NUM>. The number of pins <NUM> and their circumferential distribution can correspond with the number of vanes <NUM> and the circumferential distribution of the vanes <NUM>, and therefore with the number of vane arms <NUM>. The pin axes <NUM> are circumferentially distributed around the main axis <NUM> and extend non-parallel to the main axis <NUM>. Depending on the embodiment, the pin axes <NUM> can extend radially relative the main axis <NUM>, and thereby all be aligned in a common virtual plane, or, as in the embodiment presented in <FIG>, extend somewhat obliquely relative the main axis <NUM>, and thereby all extend along a common virtual conical surface. The vane arms <NUM> can each be provided with a guide slot <NUM>, best seen in <FIG>, configured to receive a corresponding pin <NUM> in sliding engagement. The guide slot <NUM> can extend along the length of the vane arm <NUM>, and thus transversally relative the vane axis <NUM>. Accordingly, the guide slots <NUM> can extend away from the vane axis <NUM>.

The mechanism can operate as follows : the actuator ring <NUM> can be rotated around the main axis <NUM> by a suitable actuator such as a pneumatic or hydraulic actuator. The rotation of the actuator ring <NUM> entrains the rotation of the pins <NUM> which are engaged with corresponding guide slots <NUM>. The pins <NUM> are configured for sliding-ability in the guide slots <NUM>, and can thus pivot the vane arms <NUM> as they are circumferentially moved with the actuator ring <NUM>, sliding along the length of the guide slots <NUM> as they do so. In alternate embodiments, the guide slots <NUM> can form part of the actuator ring <NUM> and the pins <NUM> can form part of the vane arms <NUM> to provide a very similar functionality, as will be understood by persons having ordinary skill in the art.

It will be understood that since the vane axis <NUM> around which the vane <NUM> rotates and the vane arm <NUM> pivots, and the main axis <NUM> around which the actuator ring <NUM> rotates, are non-parallel, the mechanism involves a three-dimensional configuration which is more complex to visualize than if the vane axis <NUM> was oriented parallel to the main axis <NUM>. The three dimensional configuration increases complexity of the mechanism and also raises a number of potential hurdles.

The vane arms <NUM>, pins <NUM>, guide slots <NUM>, and actuator ring <NUM> can be said to form part of the variable vane mechanism <NUM>.

Indeed, as shown by comparison between <FIG>, in which the movement has been exaggerated for clarity, as the actuator ring <NUM> rotates around the main axis <NUM>, the pin <NUM> moves circumferentially with it, and the vane arm <NUM> pivots around the vane axis <NUM>, at which point a circumferential separation s can occur between the circumferential position of the pin <NUM> and the circumferential position of the vane axis <NUM>, which can create an increasing gap s between the actuator ring <NUM> and the vane arm <NUM>, essentially "pulling" the pin <NUM> downwardly (radially) relative to the guide slot <NUM> in addition to sliding it along the length of the guide slot <NUM>. The pin <NUM> can be designed in a manner to accommodate such a downward sliding movement in addition to accommodating the sliding movement along the length of the guide slot <NUM>. Moreover, the pin <NUM> may pivot p relative to the guide slot <NUM>. Such downward sliding movement and pivoting movement p of the pin <NUM> can be greater when the circumference of the actuator ring <NUM> is lower and lower when the circumference of the actuator ring <NUM> is greater.

Such relative movements must typically be taken into account in the design of practical embodiments. Indeed, in a typical practical embodiment in a gas turbine engine, the amount of play between the pin <NUM> and the guide slot <NUM> is typically minimized because the presence of lateral gaps can reduce the angular accuracy of the angle of incidence of the vane and can also entrain delays or minor shocks in vane angular response to actuator ring movement. Accordingly, while play can allow to accommodate relative movements in theory, it is typically not found suitable in practical embodiments.

The effects of relative pivoting p between the pin <NUM> and the vane arm <NUM> are minimized by designing the mechanism <NUM> in a manner for the axis <NUM> of the pins to intersect the vane axis <NUM> at a point along the main axis <NUM>, such as is the case in the embodiment presented in <FIG>.

In some embodiments, notwithstanding the care taken to design components in a manner to optimize their relative motions, using a simple pin <NUM> to slide directly in the guide slot <NUM>, in such complex three dimensional motions, can represent a source of wear which it may be desired to further attenuate. Indeed, wear of the pin along its contact line with the guide slot can cause loss of material, eventually causing a gap to form between the pin and the guide slot, which can result in slop in the system. Slop can introduce minor delays in VGV responsiveness and accelerate the degradation of the guide slot and pin. Wear rate can then further be increased as a result of the minute impacts between the guide slot and pin which may occur at each pitch change.

<FIG> presents another embodiment. In this latter embodiment, a component referred to as a slide block <NUM> is introduced and can reduce the effects of wear in some embodiments. The slide blocks <NUM> can be mounted to corresponding pins <NUM> in a manner to be rotatable around the corresponding pin axes <NUM>. The slide block <NUM> can be designed in a manner have two slide block faces <NUM>, <NUM>, which can face transversally opposite sides relative the pin axis <NUM>, and which are configured to offer a smoother and larger sliding surfaces against the corresponding faces <NUM>, <NUM> of the of the guide slot <NUM> than a cylindrical pin would have (see <FIG>). Moreover, since the slide block <NUM> rotates around the pin axis <NUM>, it can accommodate the change of angular orientation between the length of the guide slot <NUM> and the pin <NUM> as the actuator ring <NUM> rotates (the movement perhaps best illustrated by comparing <FIG>). As can be seen in <FIG>, the two slide block faces <NUM>, <NUM> can be planar, flat, and parallel to one another. Moreover, the two guide slot faces <NUM>, <NUM> can also be planar, flat and parallel to one another. The slide block <NUM> can form a broader, rotating intermediary between the pin <NUM> and the guide slot <NUM>, and which may be designed to maintain surface contact throughout the entire actuator stroke.

The general geometry of the vane axes <NUM>, pin axes <NUM>, main axis <NUM>, vane arms <NUM>, guide slots <NUM>, and actuator ring <NUM> are generally as described above with reference to <FIG>, with some exceptions. As perhaps best seen in <FIG>, in this embodiment, the vane axis <NUM> extends obliquely rather than radially relative the main axis. As can be seen, in this embodiment, the variable vanes <NUM> are used in a curving portion of the main gas path <NUM> and to operate efficiently, its angle relative to the main axis <NUM> is selected accordingly. However, it will be noted that here as well, the pin axis <NUM>, around which the slide block <NUM> is rotatably mounted here, is even further sloping relative the main axis <NUM>. Notwithstanding these angles, the pin axis <NUM> remains configured to intersect the vane axis <NUM> roughly around the main axis <NUM>, to facilitate the accommodation of the relative displacements between the vane arm <NUM> and the pin <NUM>, similarly to how the pin axis <NUM> and vane axis <NUM> intersected along the main axis in <FIG>. The angles can vary strongly from one embodiment to another. In some embodiments, the vane axes <NUM> can have more than <NUM> degrees relative the main axis <NUM>, and in some embodiments, both the vane axes <NUM> and the pin axes <NUM> can have at least <NUM> degrees relative the main axis <NUM>.

Accordingly, it will be understood that the movement of the slide block <NUM> in the guide slot <NUM> may not be purely along the length of the guide slot <NUM> when the vane arm <NUM> pivots, but may be oblique and include a somewhat radially oriented component due to the presence of an increasing spacing s (see <FIG>). Such movement may tend to pull or push the slide block <NUM> along the pin axis <NUM> over time. To avoid separation of the slide block <NUM> from the pin <NUM>, a snapping feature may be introduced. For instance, as shown in <FIG>, in the illustrated embodiment, the pin <NUM> is generally cylindrical around the pin axis <NUM> except for a pin slot <NUM> formed annularly around its outer circumference at a given axial position. Similarly, the slide block <NUM> has a pin aperture delimited by an internal wall which is generally cylindrical except for a block slot <NUM> formed annularly around its inner circumference at a given axial position. A resilient retaining ring <NUM> can be engaged with a first one of the block slot <NUM> and pin slot <NUM> and elastically deformed in a manner to accommodate the engagement of the pin <NUM> inside the pin aperture until the block slot <NUM> becomes axially aligned with the pin slot <NUM>, at which point the elastic energy stored in the elastically deformed resilient retaining ring <NUM> can be released to snap the retaining ring <NUM> further into the other one of the pin slot <NUM> and block slot <NUM>, bridging the two, at which point the retaining ring <NUM> may retain the slide block <NUM> axially relative the pin <NUM> in the orientation of the pin axis <NUM>. If the retaining ring <NUM> is first engaged into the pin slot <NUM>, it can be compressed to accommodate the cylindrical portion of the pin aperture and expand into the block slot <NUM> upon axial alignment, whereas if the retaining ring is first engaged into the block slot <NUM>, it can be stretched to accommodate the cylindrical portion of the pin <NUM> and contract upon axial alignment. The engaging end of the pin <NUM>, of the pin aperture, or of both the pin <NUM> and the pin aperture can be beveled in a manner to assist or drive the elastic deformation of the resilient retaining ring <NUM> prior to its release.

In such an arrangement, it may be required to break the slide block <NUM> in order to remove it from the pin <NUM> when maintenance is eventually performed. The slide block <NUM> can be designed for being split into two pieces by an appropriate splitting tool to this end. For instance, and as exemplified in <FIG>, the slide block <NUM> can be provided with removal grooves <NUM>, <NUM> to accommodate opposed splitting members of a compressive splitting tool. The removal grooves <NUM>, <NUM> can be defined parallel to the pin axis <NUM>, and can be provided on opposite removal faces of the slide block <NUM>. The removal faces can extend between corresponding edges of the slide block faces <NUM>, <NUM> which are designed for maintaining a surface contact with the corresponding guide slot faces <NUM>, <NUM>.

In the illustrated embodiment, the pins <NUM> are designed in the form of initially separate components which are riveted to the annular body of the actuator ring <NUM> in this embodiment, as best seen in <FIG>. Other configurations are possible in alternate embodiments. Once assembled, the pins protrude from the annular body and the pin axes extend away from the main axis. The guide slots can be defined along the length of corresponding ones of the vane arms.

A few additional details about one example embodiment are also exemplified in <FIG>. An actuator <NUM>, which can be of any suitable type such as pneumatic, hydraulic or electric, can be used to drive the rotation of the actuator ring <NUM> around the main axis <NUM>. In one example, the actuator <NUM> can have a cylinder which extends a shaft mounted to a piston received in the cylinder. Such a shaft can be pivotally mounted to the actuator ring at the distal end, such as exemplified in <FIG>. Depending on the embodiment, the vane arm can be manufactured integrally with the vane, such as by casting, additive manufacturing or machining, or provided initially as a separate component configured to be assembled to the vane. In the example embodiment of <FIG>, the latter avenue was retained and fasteners are used to secure the vane arms to a protruding end of the vanes. In the example embodiment illustrated, the vane arms have a generally rectangular slide with rounded corners. The rounded corners can help reduce stress concentration. Moreover, reinforcing ribs are present on both circumferentially opposite sides of the vane arms which can be useful from a structural point of view in some embodiments. The actuator ring can have a plurality of apertures formed therethrough, as shown, in a manner to optimize the structural characteristics while also factoring in minimization of weight and material costs. Many variations are possible in alternate embodiments.

In accordance with one potential mode of operation presented in <FIG>, the method can include rotating <NUM> the actuator ring around a main axis, the rotation of the actuator ring pivoting the vane arms and thereby rotating the corresponding vanes around the vane axes, via sliding of the slide blocks in the guide slots and rotation of the slide blocks around the guide pins, the sliding of the slide blocks in the guide slots occurring obliquely relative the length of the guide slots.

Prior to rotating the actuator ring, the method includes assembling <NUM> the slide blocks to corresponding ones of the pins, said assembling including engaging a resilient retaining ring into a pin annular slot defined around each pin, around the pin axis, compressing the resilient retaining ring into the pin annular slot, sliding an inner wall of the corresponding slide block over the compressed resilient ring until a block annular slot defined in the inner wall comes into alignment with the retaining ring, at which point the compressed retaining ring expands into the block annular slot and retains the slide block along the pin axis.

Claim 1:
A variable vane mechanism (<NUM>) comprising :
a casing (<NUM>);
an actuator ring (<NUM>) having an annular body defined around a main axis (<NUM>), the actuator ring (<NUM>) being rotationally mounted to the casing (<NUM>) for rotation around the main axis (<NUM>);
a set of vanes (<NUM>) including a plurality of vanes (<NUM>) circumferentially distributed around the main axis (<NUM>), each vane (<NUM>) of the set of vanes (<NUM>) having a vane axis (<NUM>) extending from an inner end (<NUM>) to an outer end (<NUM>), the inner end (<NUM>) and the outer end (<NUM>) being rotationally mounted to the casing (<NUM>) to allow rotation of the corresponding vane (<NUM>) around the vane axis (<NUM>), the vane axes (<NUM>) extending non-parallel to the main axis (<NUM>), each vane (<NUM>) having a vane arm (<NUM>) with a vane arm length extending transversally to the vane axis (<NUM>);
a first one of the actuator ring (<NUM>) and the vane arms (<NUM>) having a plurality of pins (<NUM>) circumferentially distributed around the main axis (<NUM>), each pin (<NUM>) extending along a pin axis (<NUM>);
a plurality of slide blocks (<NUM>), each slide block (<NUM>) rotationally mounted to a corresponding one of said pins (<NUM>) for rotation around the pin axis (<NUM>), each slide block (<NUM>) having two slide block faces (<NUM>, <NUM>) facing transversally opposite sides relative the pin axis (<NUM>); and
a second one of the actuator ring (<NUM>) and the vane arms (<NUM>) having a plurality of guide slots (<NUM>), each guide slot (<NUM>) having a length extending away from a corresponding vane axis (<NUM>), each guide slot (<NUM>) slidingly receiving a corresponding one of the slide blocks (<NUM>) with each one of the two slide block faces (<NUM>, <NUM>) slidingly received by a corresponding guide slot face (<NUM>, <NUM>) of the corresponding guide slot (<NUM>),
characterised in that:
the pin axes (<NUM>) intersect the vane axes (<NUM>) along the main axis (<NUM>).