System for mechanically stressing a blower cell

Abstract

The invention relates to a system for inspecting a cell (12) of a turbojet engine disk, this cell (12) having a transverse contour arranged to receive a root (33) of a blade in order to carry this blade, this system comprising: – an extensible support (23) comprising a first end (26) and a second end (27) movable in translation relative to each other in a main direction (D); – means for exerting a predetermined force tending to separate the first end (26) from the second end (27); – a template (31) comprising a blade root (33) engaging in the cell (12) and an external portion (34) projecting from the cell (12); – a first member (29) for securing the first end (26) to the blade template (31); – a second securing member (32) of the second end (27) to the disc; – means for measuring the position and / or the orientation of the external portion (34) of the template (31).Figure for abstract: Figure 4.

Description

Title of the invention: System for mechanically stressing a fan cell Technical field

[0001] The invention relates to the verification of the mechanical conformity of the cells of a fan disc, which receive the blades of this fan. STATE OF PRIOR ART

[0002] A turbojet engine with a double flow comprises an inlet sleeve into which air is admitted and is sucked in by the blades of a fan before being divided into a central primary flow and a secondary flow which surrounds the primary flow.

[0003] The primary air flow then passes through a first compressor located after the blower while the secondary flow is propelled backwards to generate additional thrust by being blown around the primary flow.

[0004] The primary flow then passes through a second compression stage, before reaching a combustion chamber, after which it is expanded in a high pressure turbine and then in a low pressure turbine to rotate the compression stages and the fan, before being expelled rearward to generate thrust.

[0005] Each turbine comprises a succession of stages each comprising a series of blades oriented radially and regularly spaced around a central axis of the engine and carried by a disc of a central rotor of this engine.

[0006] The fan blades are carried by a disc of this central rotor and which comprises at its periphery a series of cells regularly distributed around this rotor and which extend parallel to each other in the direction of the axis of rotation or forming a certain angle with respect to this axis.

[0007] Each cell is a groove whose cross-sectional shape is similar to a dovetail contour with rounded tops. Each cell delimits over its entire length a rectangular opening opening radially towards the outside of the disc, and it ends in the front and rear faces of this disc where it opens in the form of dovetail openings with rounded tops.

[0008] The assembly of a blade consists of engaging the root of this blade in the cell by a face of the disc in which it opens by axially moving this root in the cell to engage it there.

[0009] The outline of each cell seen in cross-section, that is to say in a plane normal to its generatrices, is very rounded instead of having acute angles as in the case of a dovetail shape. As for all the parts of the engine, the different characteristics of these discs are controlled.

[0010] A manufacturing defect in these cells, particularly in terms of geometric conformity, results in defects in the orientation of the blades they receive. A metrological control of these cells is thus carried out during manufacture to determine whether they are compliant or not, so as to carry out, if necessary, rework, or even possibly scrap the disc if defects that cannot be corrected are identified.

[0011] This verification is ensured by measuring the shape of the cell contour in a transverse plane to determine whether or not it conforms to predetermined geometric criteria, as described in particular in French patent FR3032270.

[0012] However, direct metrological control of a cell requires a small metrological sensor to allow its engagement in the cell, and an analysis of the measurements which proves to be complex due to the particular shape of the contour to be measured, and its possible deformation in service.

[0013] It follows that the control of the alveoli as it is currently carried out is not entirely satisfactory.

[0014] The aim of the invention is to propose a solution making it possible to overcome this drawback. Statement of the invention

[0015] To this end, the invention relates to a system for inspecting a cell of a turbojet engine disk, this cell having a transverse contour arranged to receive a root of a blade in order to carry this blade, the system comprising:

[0016] - an extendable support comprising a first end and a second end mobile in translation relative to each other in a main direction;

[0017] - means for exerting a predetermined force tending to move the first end of the second end;

[0018] - a template comprising a blade root engaging in the cell and a portion external protruding from the alveolus;

[0019] - a first member for securing the first end of the support to the template of dawn;

[0020] - a second member for securing the second end of the support to the disc;

[0021] - metrological means for measuring the position and / or orientation of the external portion of the template.

[0022] This system thus makes it possible to carry out reliable control of the cells since it is not necessary to make assumptions about their deformations in service, since the control can be carried out under a mechanical load corresponding to the operating conditions of the blade with regard to centrifugal forces.

[0023] The invention also relates to a system thus defined, in which the first securing member comprises a first pivot connection with an axis normal to the main direction.

[0024] The invention also relates to a system thus defined, in which the second securing member comprises a second pivot connection with an axis parallel to that of the first pivot connection.

[0025] The invention also relates to a system thus defined, in which the axis of the first pivot connection passes through a point of the blade template corresponding to the center of gravity of the blade to be carried by the cell.

[0026] The invention also relates to a system thus defined, in which the second securing member is arranged so that the axis of the second pivot connection coincides with the axis of rotation of the disc.

[0027] The invention also relates to a system thus defined, in which the means for exerting a force tending to separate the ends are carried by the support.

[0028] The invention also relates to a system thus defined, in which the support comprises a deformable parallelogram, the first end and the second end corresponding to two opposite vertices of this deformable parallelogram, with a spring tending to bring the two other vertices of the deformable parallelogram closer together.

[0029] The invention also relates to a system thus defined, in which the external portion of the template comprises calibrated surfaces. Brief description of the drawings

[0030] [Fig.l] is a schematic view of a dual-flow turbojet engine in longitudinal section;

[0031] [Fig.2] is a schematic view of a jet engine fan disk shown alone in perspective;

[0032] [Fig.3] is a schematic representation showing the outline of a cell in cross section;

[0033] [Fig.4] is a schematic representation of the tool according to the invention installed on a disc;

[0034] [Fig.5] is a partial view showing the blade template installed in a cell to be checked.

[0035] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0036] In the turbojet 1 shown in [Fig.l], the outside air is admitted into an inlet sleeve 2 then passes through a fan 3 comprising a series of rotating blades before splitting into a central primary flow and a secondary flow surrounding the primary flow.

[0037] The primary flow is then compressed in a first and second compression stage 4 and 6 before arriving in a combustion chamber 7, after which it expands by passing through a set of turbines 8 before being evacuated towards the rear, generating thrust. The secondary flow is propelled directly towards the rear by the fan to generate additional thrust.

[0038] This engine comprises a rotor rotating around its axis of rotation AX, and including several discs each carrying at its external periphery a series of blades or vanes, these discs corresponding to the fan, the compressors and the turbines.

[0039] As visible in [Fig.2], a fan disk 11 has a general shape of revolution comprising at its outer periphery a series of cells 12 regularly distributed around its axis of rotation AX and parallel to each other. These cells 12 which are manufactured for example by broaching are each intended to receive a fan blade, the blades extending radially relative to the axis AX when they are mounted.

[0040] As visible in [Fig. 3], the contour C of a cell 12 in a plane normal to a generatrix of this cell, that is to say in cross section, has a shape which corresponds overall to the contour of a dovetail shape whose angles are strongly rounded. This shape thus corresponds to that of a letter U having a base of width greater than the distance separating the ends of its branches.

[0041] This contour C comprises a bottom 13, corresponding to the base of the letter U, of orthoradial orientation relative to the axis of rotation AX, and which is extended by two bearing surfaces 14, 16 inclined to converge towards each other and which correspond to the branches of the letter U. These bearing surfaces 14, 16 jointly form the root of the cell 12, their ends corresponding to the lips or edges 17, 18 of the opening 19 of this cell in the radial direction.

[0042] The connecting portions of the bottom 13 with each bearing surface 14, 16 are rounded sections marked 21 and 22, and the shape of the contour C has an axis of symmetry located midway between the two lips 17 and 18 and passing through the center of the bottom 13.

[0043] The invention is based on the observation that the geometry of the cells changes when the engine is in operation due to the centrifugal forces to which the blades carried by these cells are subjected. It follows that a geometric control of the blades during manufacture is ultimately not representative of the functional conformity of these cells.

[0044] The idea behind the invention is to place a cell to be inspected under mechanical stress corresponding to the centrifugal forces it undergoes when the engine is in service in order to carry out a check of its conformity, so as to make such a check meaningful and consistent.

[0045] According to the invention, a template comprising a blade root is engaged in the cell at control, and this template is carried by a support exerting on it a radial force corresponding to the centrifugal force undergone by a blade when the engine is in operation. The control of the cell can then be carried out according to a situation corresponding to the operating conditions in terms of mechanical constraints applied to the cell.

[0046] In [Fig. 3], a support 23 comprises four bars 24 of the same lengths articulated to each other by their ends to constitute a deformable parallelogram. This deformable parallelogram constitutes a support comprising a first end 26 and a second end 27 corresponding to two of its opposite vertices.

[0047] These two ends are movable relative to each other in translation along a main direction D, and a spring 28 extends between the two other opposite vertices of this parallelogram. The spring 28 works in traction (it continually tends to retract) to bring together the vertices of the parallelogram to which it is secured, in order to continually tend to separate the first end 26 from the second end 27 of the support 23.

[0048] The first end 26 is equipped with a first securing member 29 by which it is secured to the blade template 31. Advantageously, this first securing member 29 comprises, or forms with the template 31, a first pivot connection with an axis normal to the main direction D.

[0049] The second end 27 is equipped with a second securing member 32 allowing it to be secured to a fixed element such as the disc 11 or a frame carrying this disc. Advantageously, this second securing member 32 comprises, or forms with the fixed element, a second pivot connection with an axis parallel to that of the first pivot connection.

[0050] As visible in [Fig. 5], the template 31 comprises a blade root 33 extended by an external portion 34 which protrudes radially outside the disc 11 when this root 33 is engaged in the cell 12. This external portion 34 corresponds substantially to the blade of a blade carried by a root such as the root 33, but its external faces 36 constitute or comprise metrological reference surfaces.

[0051] These reference surfaces are for example six in number to allow the position and orientation of the blade template to be completely identified. These surfaces are oriented and positioned in a known and precise manner relative to the root 33, these surfaces being advantageously flat to be accessible by a metrological means 37 which is here a metrological probe in the example of [Fig. 5]. Thus, a metrological control of these reference surfaces makes it possible to deduce in a simple manner the precise position and / or orientation of the root 33 relative to a radial reference axis AR normal to the axis AX and passing through the cell.

[0052] The orientation of the root (and therefore of the blade to be carried by such a root) includes in particular its angle relative to the radial axis AR measured in a plane normal to the axis AX (“circumferential tilt”), its angle relative to the radial axis AR measured in a plane containing the axis AX (“perpendicularity”), and its inclination relative to the axis AX around the radial axis AR (“inclination”).

[0053] The verification of the cells of the disk 11 thus consists of installing this disk on a control frame. The second end 27 of the support 23 is secured to this frame, at the level of the axis of rotation AX of the disk 11, by means of the second securing member 32, and the foot 33 of the blade template 31 is then engaged in a cell 12, the spring 28 then having for example one of its ends detached from the support. Once the foot 33 is in place in the cell 12, the spring is put under tension, for example by securing again its temporarily released end, to the corresponding top of the support.

[0054] Under these conditions, the foot 33 is supported on the bearing surfaces 14, 16 of the cell while being held in support by the force exerted by the spring 28 which tends to move it away from the axis AX by exerting a force corresponding to the centrifugal force to which a blade is subjected when the engine is in operation.

[0055] At this stage, the blade template 31 is in place in the cell 12 which is subjected to mechanical stresses identical or close to those it undergoes in operation, so that it deforms substantially to adopt the shape it has when the engine is in service.

[0056] A metrological probe can then be approached to the reference surfaces of the external portion 34 of the blade to measure, for example, six values, in order to identify the circumferential balance, the perpendicularity, and the inclination of the blade template. If these three parameters are within ranges of values ​​considered satisfactory, the cell is considered valid, and if not, it is decided that the cell must be rectified before being put into service.

[0057] Once a cell has been checked in this way, the tension of the spring 28 is released to extract the foot 33 from this cell, and to place it in the neighboring cell in order to carry out its check in the same way.

[0058] In the example which has been described, the connection of the first securing member 29 with the template 31 is a pivot connection, and this securing member 29 corresponds here to the mechanical axis connecting the two bars 24 of the deformable parallelogram at its first end 26, to articulate them to each other. This mechanical axis extends to be housed in a corresponding bore formed in the blade template 31, so that the template 31 and the two bars 24 are connected to each other by the same pivot connection materialized by this axis.

[0059] So that the forces exerted by the support 23 on the template 31 correspond to the better to the centrifugal forces undergone by a blade corresponding to this template 31, the first securing member 29 constitutes a first connection with the template 31 whose connection center is located in a central region of the template 31.

[0060] The connection center is more particularly located on a radial axis passing through the barycenter of the blade intended to be carried by the cell, and advantageously at the level of this barycenter.

[0061] This first connection, which is a pivot connection in the example described, can advantageously be a ball joint in order to generate an optimal distribution of forces. Conversely, this first connection could also be a complete connection (embedded connection) in order to simplify the system, in the case where the question of the distribution of forces does not prove to be a relevant characteristic with regard to the control of the cell.

[0062] As regards the second securing member 32, it comprises a second connection with a fixed element of the control frame 38 or possibly with the disc 11 passing through a central part of the cell and containing the axis of rotation AX of the disc 11. Advantageously, this second connection is located at the level of the axis AX, which avoids dismantling and reassembling the device for each cell to be tested.

[0063] As in the case of the first securing member, the second securing member can be materialized by the mechanical axis connecting the bars 24 of the deformable parallelogram at its second end.

[0064] In the example that has been described, the second securing member 32 comprises a connection with the disc 11 or the control frame which is a pivot connection, but this second connection could be of another nature, such as a ball joint connection or a complete connection. The nature of the second connection mainly has an impact on the distribution of the forces exerted on the template, so that the choice of the type of connection is mainly conditioned by the impact of the distribution of the forces on the control.

[0065] As will have been understood, the second securing member 32 ensures, depending on the case, the securing of the support 23 with the disc 11 or with a control frame on which the disc 11 is installed to carry out its inspection.

[0066] In the description which has been given, the support 23 is formed on the basis of a deformable parallelogram equipped with a spring, in order to be able to exert a force tending to separate its two ends from each other. Other arrangements are possible for the support 23, the spring 28 being able to be replaced by a jack, the deformable parallelogram being able to be replaced by a rail carrying the two securing members, one being movable relative to the other along this rail.

[0067] As regards the control frame, allowing the inspection of the cells, it comprises means for receiving the disc by positioning it precisely, for receiving the support, and it is equipped with metrological means such as the probe 37 allowing the position and / or orientation of the external portion of the blade template to be precisely determined.

[0068] Furthermore, the invention has been described in the context of a fan disk cell, but it applies generally to the verification of the geometry of a turbine or compressor disk cell.

Claims

Claims

1. System for inspecting a cell (12) of a disk (11) of a turbojet engine, this cell (12) having a transverse contour (C) arranged to receive a root (33) of a blade in order to carry this blade, the system comprising: - an extensible support (23) comprising a first end (26) and a second end (27) movable in translation relative to each other in a main direction (D); - means for exerting a predetermined force tending to separate the first end (26) from the second end (27); - a template (31) comprising a blade root (33) engaging in the cell (12) and an external portion (34) projecting from the cell (12); - a first member (29) for securing the first end (26) of the support (23) to the blade template (31); - a second member (32) for securing the second end (27) of the support (23) to the disc (11);- metrological means (37) for measuring the position and / or orientation of the external portion (34) of the template (31).;

2. System according to claim 1, in which the first securing member (29) comprises a first pivot connection with an axis normal to the main direction (D).

3. System according to claim 2, in which the second securing member (32) comprises a second pivot connection with an axis parallel to that of the first pivot connection.

4. System according to claim 2, in which the axis of the first pivot connection passes through a point of the blade template (31) corresponding to the center of gravity of the blade to be carried by the cell (12).

5. System according to claim 4, in which the second securing member (32) is arranged so that the axis of the second pivot connection coincides with the axis of rotation (AX) of the disc (11).

6. System according to one of the preceding claims, in which the means for exerting a force tending to separate the ends are carried by the support (23).

7. System according to one of the preceding claims, in which the support (23) comprises a deformable parallelogram, the first end (26) and the second end (27) corresponding to two opposite vertices of this deformable parallelogram, with a spring (28) tending to bring the two other vertices of the deformable parallelogram closer together.

8. System according to one of the preceding claims, in which the external portion (34) of the template (31) comprises calibrated surfaces.

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