FR3071313A1 - REMOVABLE NECKLACE FOR IDENTIFYING A ROTARY SHAFT'S UNBALANCE - Google Patents

Abstract

The invention relates to a detachable balancing collar (3) for gripping a balancing cord of a rotary shaft to identify an imbalance of said shaft for locally machining the balancing cord to cancel this unbalance. , this collar (3) comprising two half-collars (4, 6) clamping to each other by their ends (7, 9, 8, 11). These two half-collars (4, 6) have internal faces (20, 22) provided with support portions (21, 23, 24) which are distinct and arranged to ensure an isostatic support of the collar (3) on the cord balancing (2).

Description

REMOVABLE COLLAR FOR IDENTIFYING A ROTATING SHAFT BALOURD DESCRIPTION

TECHNICAL AREA

The invention relates to balancing a rotary shaft of a turbomachine of an aircraft engine such as a turbojet.

PRIOR STATE OF THE ART

A turbojet engine has an inlet sleeve into which air is admitted to be sucked in by a blower before being divided into a central primary flow and a secondary flow surrounding the primary flow. The primary flow then passes through a compressor located after the blower, while the secondary flow is propelled backwards to directly generate a thrust.

The primary flow then passes through a high pressure compressor, then a combustion chamber before being expanded in a high pressure turbine and in a low pressure turbine, in order to drive the compressor and the blower, and before being expelled to the back to generate thrust.

A central shaft or rotor of the engine carries the blade elements of the blower, of the compressor and of the turbine, which form along the rotor unbalances which have to be balanced in order to reduce the deflection and the vibrations of the shaft in service.

In this context, the shaft comprises one or more balancing cords, that is to say annular thickeners, intended to be machined locally to create a corrective unbalance making it possible to reduce the unbalance of the tree.

The identification of an unbalance consists in putting the rotor in rotation on a test bench which makes it possible to identify the existence of an unbalance and to estimate its angular position around the shaft, at the level of the considered cord. .

A balancing collar is then mounted around this cord, this collar comprising two half-collars provided at their ends with means for securing and clamping from one to the other. One or more weights are then attached to this collar at the positions estimated with the test bench.

The shaft is then again rotated to determine if an unbalance is still present, in which case the positions and weights of the weights are modified, until the bench no longer detects an unbalance. This process may require a large number of iterations.

When the unbalance has been completely identified, that is to say when its angular position and its mass are determined, the balancing collar is removed, and the cord is machined at one hundred and eighty degrees from the angular position of this unbalance to remove a mass corresponding to that of the flyweight.

In practice, the cord has a diameter which can vary within its manufacturing tolerances, while a very good concentricity of the collar with the cord is sought, so as not to introduce additional unbalance which distorts the operation.

This implies providing several collars with close diameters, in order to choose for each cord the collar with the appropriate diameter. This avoids injuring the external face of the cord, but significantly increases the complexity and the time required to identify the unbalance.

The object of the invention is to provide a solution which makes it possible to remedy this drawback.

STATEMENT OF THE INVENTION

To this end, the invention relates to a removable balancing collar intended to enclose a rotating shaft to identify and / or correct an imbalance in this shaft, this collar comprising two half-collars tightening to each other by their ends, these two half-collars having internal faces provided with support portions which are distinct and arranged to ensure isostatic support of the collar on the shaft or on a balancing cord of this shaft.

With this arrangement, the collar can be tightened without risk of damaging the surface of the cord which it surrounds, while being usable on several diameters of close cords.

The invention also relates to a collar thus defined, comprising three distinct bearing portions carried by the internal faces.

The invention also relates to a collar thus defined, in which the three bearing portions are distributed two by two about an axis of revolution or of symmetry of the collar while being spaced apart from one another by angles less than one hundred and fifty degrees.

The invention also relates to a collar thus defined, comprising a bearing portion carried by one of the half-collars, and two bearing portions carried by the other half-collar.

The invention also relates to a collar thus defined, comprising bearing portions having planar contact faces.

The invention also relates to a collar thus defined, comprising bearing portions having contact faces curved according to a diameter greater than the external diameter of the shaft.

The invention also relates to a collar thus defined, at least the bearing portions of which are made of a material having a Brinnell hardness less than the Brinnell hardness of the shaft.

The invention also relates to a collar thus defined, comprising tapped holes of radial orientation with respect to an axis of revolution or of symmetry of the collar, each tapped hole opening into an external face of the half-collar in which it is formed, for each receive a balancing weight.

The invention also relates to a collar thus defined, in which the tapped holes are blind holes.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an overview of a tree having a balancing cord;

Figure 2 is an overview of a shaft having a balancing cord enclosed by a collar according to the invention;

Figure 3 is an overall view of a first half-collar of the collar according to the invention;

Figure 4 is an overview of a second half-collar of the collar according to the invention;

Figure 5 is an overview showing the two half-collars joined to form the collar according to the invention;

Figure 6 is a cross-sectional view showing flat support portions of the collar according to the invention enclosing a balancing cord;

Figure 7 is a cross-sectional view showing curved support portions of the collar according to the invention enclosing a balancing cord;

Figure 8 is a cross-sectional view of the collar according to the invention enclosing a balancing cord of a rotary shaft;

FIG. 9 is a transverse view of the collar according to the invention enclosing a balancing cord of a rotary shaft.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

In FIG. 1, a portion of hollow shaft 1 extending in a direction AX is provided with a balancing cord 2, being in the form of a localized annular allowance, and which is intended to receive the collar d balancing according to the invention 3 as shown in FIG. 2.

This balancing collar 3 comprises a first half-collar 4 and a second half-collar 6, which are fixed and tightened to one another by their ends. As visible in FIG. 3, the first half-collar 4 has the shape of an arm in an arc of a circle comprising a simple articulation end 7 and a tightening end 8. In a similar manner, and as visible in FIG. 4, the second half-collar 6 has an arcuate shape extending between a hinge end 9 which here has a yoke shape, and a clamping end 11.

The two half-collars 4 and 6 are secured to each other by their articulation ends 7 and 9, the end 7 comprising a bore 12 being engaged between the wings of the yoke forming the end 9 each comprising a bore 13, 14. The assembly receives a pin 16 passing through the holes 12-14 to secure the ends to each other while allowing them to pivot relative to each other, in order to form a hinge joining the half-collars.

When the two half-collars assembled by the axis 16 are folded towards one another, as in FIG. 5, their clamping ends 8 and 11 which are provided with holes marked respectively by 17, 18 in FIGS. 3 and 4 are located opposite one another, so that they are both crossed by a tightening bolt 19. In this situation, the two half-collars 4, 6 jointly delimit a circular shape extending around an axis of revolution AX. The axis 16 extends parallel to the axis AX, while the bolt 19 which passes through holes 17, 18 is oriented perpendicular to this axis AX.

The first half-collar 4 has a semi-cylindrical internal face 20 which is provided with a support portion 21 situated at its central part, that is to say halfway between its ends 7 and 8. The second half -collar 6 also has a semi-cylindrical internal face 22 provided with two support portions 23, 24 spaced from one another along this surface 22. The first half-collar 4 and the second half-collar 6 also each includes a semi-cylindrical external face, these external faces being identified by 24 and 26 respectively in FIG. 5.

Each support portion 21, 23, 24 may have a planar contact face as is the case in FIG. 6, which makes it possible to exert support on the balancing cord 2 without risk of injuring its surface. The contact faces of the bearing portions 21, 23, 24 can also be provided curved, according to a diameter of curvature greater than that of the balancing cord 2, as illustrated in FIG. 7. This makes it possible to extend the area of contact to homogenize the stress without risk of injuring the external face of the support cord.

In the example of the figures which corresponds to a preferred embodiment, the support portions are three in number, but it is possible to envisage providing a different number of support portions.

Advantageously, the collar, and in particular its bearing portions, is formed from a material which is less hard than the balancing cord. For example, for a steel shaft, the half-collars are made of aluminum, so that the Brinell hardness of the bearing portions is less than that of the balancing cord.

As shown in Figures 6 to 9, the two support portions 23 and 24 are spaced ninety degrees from each other around the axis AX, and they are each spaced one hundred and thirty -five degrees of the portion 21, which ensures isostatic support of the collar on the external face of the balancing cord when this collar is in place.

In general, the largest of the three angles separating the portions 21, 23 and 24 is chosen to be less than one hundred and fifty degrees, so as to obtain the most homogeneous distribution of the support forces.

The mounting of the balancing collar on a balancing cord thus consists in opening the half-collars 4 and 6 by pivoting them around the axis 16 to close them around the cord to place its ends 8 and 11 opposite. opposite each other. At this stage, the operator engages a tightening screw in the holes 17 and 19, to then screw a nut at the free end of this screw in place, so as to constitute the bolt 19. The operator then proceeds to the tightening of the collar by tightening this bolt 19.

When the collar is mounted on a balancing cord of too large a diameter, owing to the fact that only the portions 21, 23, 24 constitute by their number and their arrangement an isostatic support, the half-collars can be tightened by means of the bolt 19 passing through their ends 8 and 11, without risk of damaging the external face of the cord.

Thanks to the isostatic support offered by the portions 21, 23 and 24, the pressing forces exerted by these three portions on the external face of the cord depends directly and solely on the tightening force exerted by the bolt 19. In other words, calibrate tightening the bolt 19 makes it possible to ensure that the collar is sufficiently tightened to ensure firm support but without risk of deterioration of the external surface of the collar.

Once the collar is mounted and tightened, it can receive one or more weights to identify the position and the mass of the unbalance of the shaft and / or of the rotary assembly carried by this shaft.

To this end, the collar comprises a series of eight tapped holes regularly distributed around its axis of revolution AX and which open in its external face. The first half-collar 4 is provided with four tapped holes 27 spaced from one another by forty-five degrees, the first and the last of these four holes 27 are spaced respectively from the end 7 and the end 8 of an angle corresponding to half of forty-five degrees. Similarly, the second half-collar 6 has four other tapped holes 28 spaced forty-five degrees, the first and the last of these four holes 28 are spaced respectively from the end 9 and the end 11 of a angle corresponding to half of forty-five degrees.

As can be seen more particularly in FIG. 7, each of the tapped holes 27, 28 is a blind tapped hole of radial orientation relative to the axis AX, and which opens into the external face, in order to receive a retaining screw. a flyweight. These holes are provided with blinds to ensure that excessive tightening of a screw carrying a counterweight does not risk degrading the external surface of the cord 2.

Furthermore, as can be seen in FIGS. 5 and 8, each half-collar comprises between each pair of consecutive holes a recess which opens into its external face, and which makes it possible to limit the mass of the collar, while allowing it to have a extended cross section to give it high rigidity.

Thus, during the balancing process, based on an estimated angular position of the imbalance around the axis AX, the operator fixes by simple screwing a counterweight opposite this estimated position, that is to say at one hundred and eighty degrees from it around the axis AX.

By proceeding if necessary in several iterations during which it modifies the mass of the counterweight and possibly its position, the operator ends up precisely identifying the mass of the unbalance of the shaft and its angular position, without disassembly and reassembly of the collar on the tree during the process.

When the identification is complete, the collar can be removed to machine the balancing cord 2 so as to remove a mass corresponding to that of the counterweight, at a position opposite the latter around the axis AX.

In general, the invention makes it possible to improve the centering of the collar on the shaft thanks to the three support portions at one hundred and twenty degrees, to ensure that the balancing collar does not risk adding an unbalance additional disrupting the balancing operation. The invention also makes it possible to make the collar adaptable to several close diameters, and to limit the risk of degrading the external face of the balancing cord when the collar is tightened.

Claims (9)

1. Removable balancing collar (3) intended to enclose a rotary shaft (1) to identify and / or correct an imbalance of this shaft (1), this collar (3) comprising two half-collars (4, 6) is clamping to each other by their ends (7, 9, 8, 11), these two half-collars (4, 6) having internal faces (20, 22) provided with bearing portions (21, 23 , 24) which are distinct and arranged to provide isostatic support for the collar (3) on the shaft or on a balancing cord (2) of this shaft. 2. Collar according to claim 1, comprising three separate bearing portions (21, 23, 24) carried by the internal faces (20, 22). 3. Collar according to claim 2, in which the three bearing portions (21, 23, 24) are distributed two by two around an axis (AX) of revolution or of symmetry of the collar (3) being spaced apart. each other of angles less than one hundred and fifty degrees. 4. Necklace according to claim 3, comprising a support portion (21) carried by one of the half-collars (4), and two support portions (23, 24) carried by the other half-collar ( 6). 5. Necklace according to one of the preceding claims, comprising bearing portions (21, 23, 24) having planar contact faces. 6. Collar according to one of the preceding claims, comprising bearing portions (21, 23, 24) having contact faces curved with a diameter greater than the external diameter of the shaft. 7. Collar according to one of the preceding claims, at least the bearing portions (21, 23, 24) are made of a material having a Brinnell hardness lower than the Brinnell hardness of the cord of the tree. 5 8. Collar according to one of the preceding claims, comprising tapped holes (27, 28) of radial orientation relative to an axis (AX) of revolution or of symmetry of the collar, each tapped hole (27, 28) opening out in an outer face (25, 26) of the half-collar (4, 6) in which it is formed, to each receive a balancing weight. 9. Collar according to claim 8, in which the threaded holes (27, 28) are blind holes.