PASSIVE COMPENSATION FOR TURBINE SHAFT ELONGATION

Abstract

PASSIVE COMPENSATION FOR THE ELONGATION OF A TURBINE SHAFT One aspect of the invention relates to a turbomachine (1, 1') comprising a rotor (3) and a stator (4) with an X axis, the rotor (3) being fitted onto a shaft (2) and comprising blades (30) having an orientation defining an angle α relative to the X' axis parallel to the X axis, it is characterized in that the rotor (3) is connected to the shaft (2) by a guide connection defining a helical-shaped displacement path. The rotation of the rotor produces an aerodynamic force which will cause the rotor to move on the drive shaft along the displacement path, in this way the relative displacement of the rotor relative to the stator due to the thermal and mechanical conditions of the turbomachine is compensated. Figure to be published with the abstract: Figure 4

Description

Title of the invention: PASSIVE COMPENSATION FOR THE ELONGATION OF A TURBINE SHAFT TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of turbomachines and in particular turbojets for civil and military aircraft and in particular turbojets having rotating members of the compressor or turbine type attached to a rotor shaft. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] In operation, turbomachines cause variations in temperature and axial forces applied to the elements of the stator and rotor. The differences in thermal conditions, materials and mechanical constraints induce significant relative displacements between these different elements. These relative displacements are a constraint to be taken into account for the dimensioning of rotating members, particularly for compressors and turbines. These displacements result in a loss of thermodynamic efficiency or premature wear of the blades. In addition, the greater the distance from the member to the ball bearing connecting the rotor and the stator, the greater the differential displacement.

[0003] Currently, attempts are being made to limit the axial displacement of the rotor shaft by various means so that the rotating members remain in place relative to the stator. Thus, compensation for axial thrust and therefore axial displacements of a rotor is generally carried out by controlling aerodynamic pressures exerted axially on walls integral with the rotor.

[0004] In particular, patent FR 2 708 044 discloses a device for measuring the axial thrust exerted by a rotor on a stator. It comprises a force sensor consisting of deformable bars inserted into an approximately cylindrical or frustoconical intermediate wall of a bearing support, one or more strain gauges connected to an electronic measuring circuit being arranged on the deformable bars. This measuring device makes it possible to modulate an active device for compensating the axial thrust of the rotor.

[0005] However, this device is bulky and requires sensors, which increases the manufacturing cost and the weight of the turbomachine. Summary of the invention

[0006] The invention offers a solution to the problems mentioned above, by decoupling the shaft from the rotor of the turbomachine (turbine or compressor) with a coupling connection adapted so as to immobilize or greatly limit the axial displacement of the rotor.

[0007] The turbomachine according to the invention comprises a rotor and a stator of axis X, the rotor being fitted on a shaft and comprising blades defining a chord making an angle a with respect to an axis X' parallel to the axis X, it is characterized in that the rotor is connected to the shaft by a guide connection defining a sliding path of helical shape. The rotation of the rotor produces an aerodynamic force which will cause a displacement of the rotor on the drive shaft on the displacement path, in this way the relative displacement of the rotor with respect to the stator due to the thermal and mechanical conditions of the turbomachine is compensated. The drive shaft can be a transmission shaft. The orientation of the angle a defines the nature of the turbomachine, a turbine with blades of angle a generates an aerodynamic force opposite to that generated by a compressor with blades of angle - a.

[0008] Advantageously, the helical-shaped displacement path defines a pitch of angle [3 along the X axis of the same orientation as the angle α of the blades such that 0 < [3 < 90° and 0 < a < 90°. The pitch of the groove has an angle [3 is of the same orientation as the angle α of the blades, making it possible to move the rotor back from upstream to downstream or forward from downstream to upstream on the shaft depending on the aerodynamic force.

[0009] Advantageously, the displacement path has a helical shape with an increasing radius of curvature. This allows an equilibrium position between the resultant of the aerodynamic forces and the torque with the normal to the profile of the displacement path at the equilibrium point considered, the displacement of the rotor relative to the shaft is thus stabilized.

[0010] According to a first embodiment, the guide connection consists of at least one pin and a groove. The pin slides in the groove to allow the rotor to move on the shaft.

[0011] According to a second embodiment, the guide connection consists of at least one ball and a raceway. The ball will roll in the raceway and thus allow the rotor to move on the shaft.

[0012] According to a first variant, the groove or the raceway is arranged on the shaft and the pin or the ball on the rotor. The groove is arranged on the surface of the shaft and the pin is fixed on the inner surface of the rotor opposite the shaft. The groove can be obtained by machining. The raceway is on the surface of the shaft while the ball is placed in a recess provided for this purpose inside the rotor.

[0013] According to a second variant, the groove or the raceway is arranged on the rotor, and the pin or the ball is arranged on the shaft. The groove is arranged on the inner surface of the rotor opposite the shaft and the pin on the surface of the shaft. The raceway is placed on the inner surface of the rotor opposite the shaft and the ball is placed in a recess on the surface of the shaft.

[0014] Advantageously, there are several grooves or raceways and sliding pins or balls and at least as many sliding pins or balls as there are grooves or raceways. The use of several grooves in each of which a pin slides allows for a better distribution of forces. In the same way, the use of several raceways each coupled to one or more balls allows for a better distribution of forces.

[0015] Advantageously, a stop is arranged in the groove or the raceway. This stop makes it possible to limit the movement of the rotor relative to the shaft. This stop is particularly useful when the groove or the raceway has a constant radius of curvature.

[0016] Advantageously, the rotor is a compressor rotor or a turbine rotor. The turbine and the compressor have blades of opposite orientations.

[0017] Advantageously, the grooves cover only part of the periphery of the shaft or rotor. Since the displacement of the shaft relative to the rotor is small, the groove does not need to cover the entire periphery of the shaft or rotor. The length of the groove is defined as a function of the desired maximum displacement.

[0018] Advantageously, at least a first pin and a first groove are arranged symmetrically with respect to the X axis to a second pin and a second groove. This symmetrical arrangement of a second pin and a second groove to the first pin and the first groove, or of a second row of pins and grooves to a first row of pins and grooves, on the shaft and the rotor makes it possible to balance the radial forces between them.

[0019] Advantageously, the rotor comprises several rows of blades. All of the blades are thus moved together by the same distance and at the same time.

[0020] Other advantages may also become apparent to those skilled in the art upon reading the examples below, illustrated by the appended figures, given for illustrative purposes. BRIEF DESCRIPTION OF THE FIGURES

[0021] The figures are presented for information purposes only and in no way limit the invention.

[0022] [Fig. 1] is a view along the axis of rotation of the rotor of a turbine showing the forces exerted on the shaft and the rotor;

[0023] [Fig.2] is a view along the axis of rotation of the rotor of a compressor showing the forces exerted on the shaft and the rotor;

[0024] [Fig.3] is an axial view of a turbine according to the invention in the rest position;

[0025] [Fig.4] is an axial view of a turbine of [Fig.3] in equilibrium during its rotation;

[0026] [Fig.5] is an axial view of a compressor according to the invention in the rest position;

[0027] [Fig.6] is an axial view of a compressor of [Fig.5] in the equilibrium position during of its rotation;

[0028] [Fig.7] is a perspective view of a variant of a shaft according to the invention. DETAILED DESCRIPTION

[0029] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0030] Throughout the description, the part arranged forward in the direction of air flow will be called "upstream" and the part arranged behind will be called "downstream". The direction of air flow is represented by arrow A.

[0031] The example described corresponds to the first embodiment, but also applies to the second embodiment by replacing the groove with a rolling track and the pin with a ball.

[0032] A turbomachine 1 or 1' with axis X comprises a rotor 3 equipped with blades 30 distributed over one or more rows and connected to a shaft 2, rotating in a stator 4. The shaft is held by bearings 21 at at least one end.

[0033] A turbomachine 1 or 1' rotating clockwise according to the arrow R, as illustrated in the figures, creates aerodynamic forces Fa which are oriented differently depending on whether it is a turbine 1 ([Fig.l]) or a compressor 1' ([Fig.2]).

[0034] These aerodynamic forces Fa combined with the increase in temperature when the turbomachine is in motion, induce an expansion of the shaft and its elongation under the tensile force due to the aerodynamic forces Fa, which causes an axial displacement of the rotor relative to the stator, hence a risk of loss of efficiency or premature wear of the blades.

[0035] To compensate for this axial displacement, the invention comprises a connection between the shaft 2 and the rotor 3 which allows a displacement da by elongation of the shaft 2 and a displacement dr of the rotor 3 on the shaft.

[0036] This connection is for example illustrated in figures 3 and 4 for a turbine 1. The shaft 2 comprises splines 20 of helical shape, here four, the curvature of which is oriented in the opposite direction to the aerodynamic forces Fa. The rotor 3 comprises on the internal face opposite the shaft 2 pins 31 each arranged in a spline 20. The blade 30 has a chord 300 which is inclined at an angle α relative to an axis X' parallel to the axis X. The splines 20 are oriented at an angle β of the same orientation as the angle α.

[0037] When the turbine 1 is in operation and the aerodynamic force Fa exerts a force on the shaft 2, the pins 31 of the rotor will slide in the grooves 20 causing the rotor to move backwards upstream, as seen in [Fig.4].

[0038] When the groove 20 has a helical shape with an increasing radius of curvature, as in figures 3 and 4, the pin 31 will stop when the force fp exerted by the pin 31, due to the torque C exerted by the shaft on the rotor, on the wall of the groove 20 will balance with the component fd normal to the groove profile at the point of contact with a pin of the force exerted by the displacement of the shaft 2. In this case, the rotor has moved a relative distance e on the shaft compared to its original position.

[0039] It is also possible to put stops 22 in order to restrict the movements of pins 31. A single stop 22 is shown in [Fig.4], but it is preferable to provide one per groove.

[0040] When the groove 20 has a helical shape with a constant radius of curvature, it is a stop 22 arranged in the groove which will stop the pin 31. The position of this stop 22 is chosen in order to limit the movement of the rotor 3 on the shaft 2 to a predetermined value.

[0041] As illustrated in [Fig.7], the shaft 2 may comprise splines 200 and 201 partially covering the shaft 2 and arranged symmetrically on either side of a plane passing through the axis X. Preferably the splines 200 and 201 each cover at most only half of the periphery of the shaft.

[0042] The sliding connection between the shaft 2 and the rotor 3 can be made either by means of a lubricated groove and a pin, or by means of a helical bearing. In this second case, the connection between the shaft and the rotor is ensured by a first raceway with balls and a second helical raceway or else a first and a second helical raceway and balls. This assembly can limit the maximum transmissible forces to guarantee the integrity of the balls.

[0043] Flexible elements serving as springs can be used to force the return to the initial position after stopping the turbomachine. The slowing down of the rotation speed of the turbomachine combined with the cooling of the parts and in particular of the shaft, allows a return of the rotor to its original position.

[0044] In the case of a compressor 1', the aerodynamic force is reversed so the helical shape of the groove 20 is also reversed, as can be seen in Figures 5 and 6. The blade 30 has a chord 300 which is inclined at an angle α relative to an axis X' parallel to the axis X. The grooves 20 are oriented at an angle α of the same orientation as the angle α. Thus in this case, in movement, the shaft 2 extends by a length da downstream while the rotor 3 moves relative to the shaft 2 upstream by a distance dr thanks to the sliding of the pins 31 in the grooves 20, five in figures 5 and 6, until the forces stabilize, or the movement is blocked by a stop 22. The rotor 3 will have moved by a relative distance e on the shaft relative to its original position.

[0045] The illustrated examples show splines 20 on the shaft 2 and pins 31 on the inner surface of the rotor 3 opposite the shaft 2, but it is possible to arrange the grooves on the inner surface of the rotor 3 and the pins 31 on the outer surface of the shaft 2 without departing from the scope of the present invention.

[0046] Here the pawns shown are round in shape, but it is also possible to replace them with another type of protruding element of oval, square or rectangular shape.

Claims

Claims

1. Turbomachine (1, 1') comprising a rotor (3) and a stator (4) of axis X, the rotor (3) being fitted onto a shaft (2) and comprising blades (30) defining a chord making an angle α relative to an axis X' parallel to the axis X, characterized in that the rotor (3) is connected to the shaft (2) by a guide connection defining a helical-shaped movement path.

2. Turbomachine (1, 1') according to claim 1 characterized in that the helical-shaped displacement path defines an angle [3 along the X axis of the same orientation as the angle a of the blades (30), such that 0 < [3 < 90° and 0 < a < 90°.

3. Turbomachine (1, 1') according to one of the preceding claims, characterized in that the helical-shaped displacement path has an increasing radius of curvature.

4. Turbomachine (1, 1') according to one of the preceding claims, characterized in that the guide connection consists of at least one pin and one groove.

5. Turbomachine (1, 1') according to one of claims 1 to 3, characterized in that the guide connection consists of at least one ball and a rolling track.

6. Turbomachine (1, 1') according to one of the preceding claims, characterized in that the groove (20) or the bearing race is arranged on the shaft (2), and the sliding pin (31) or the ball is arranged on the rotor (3).

7. Turbomachine (1, 1') according to one of the preceding claims, characterized in that the groove (20) or the raceway is arranged on the rotor (3), and the sliding pin (31) or the ball is arranged on the shaft (2).

8. Turbomachine (1, 1') according to one of the preceding claims, characterized in that there are several grooves (20), or raceways, and sliding pins (31), or balls, and as many sliding pins (31), or balls, as there are grooves (20), or raceways.

9. Turbomachine (1, 1') according to one of the preceding claims, characterized in that a stop (22) is arranged in the groove (20) or in the raceway.

10. Turbomachine (1, 1') according to one of the preceding claims ca- characterized in that the rotor (3) is a compressor rotor (1') or a turbine rotor (1).

11. Turbomachine (1, 1') according to one of claims 3 to 8, characterized in that the grooves (20) cover only part of the periphery of the shaft (2) or the rotor (3).

12. Turbomachine (1, 1') according to one of the preceding claims, characterized in that at least a first pin (31) and a first groove (200) are arranged symmetrically with respect to the X axis to a second pin (31) and a second groove (201).

13. Turbomachine (1, 1') according to one of the preceding claims, characterized in that the rotor (3) comprises several rows of blades (30).

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