PASSIVE COMPENSATION FOR TURBINE SHAFT ELONGATION

Abstract

PASSIVE COMPENSATION FOR TURBINE SHAFT EXTENDED One aspect of the invention relates to a turbomachine (1, 1') comprising a rotor (3) and a stator (4) with axis X, the rotor (3) being fitted onto a shaft (2) and comprising blades (30) having an orientation defining an angle α with respect to the axis X' parallel to the axis X. It is characterized in that the rotor (3) is connected to the shaft (2) by a guide link defining a helical path of movement. The rotation of the rotor produces an aerodynamic force which causes a displacement of the rotor on the drive shaft along the path of movement. 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. Figure to be published with the abbreviation: 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 turbomachinery, and in particular turbojet engines for civil and military aircraft, and especially turbojet engines having rotating components of the compressor or turbine type attached to a rotor shaft. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] During operation, turbomachinery generates variations in temperature and axial forces acting on the stator and rotor components. Differences in thermal conditions, materials, and mechanical stresses induce significant relative displacements between these components. These relative displacements are a constraint that must be considered when sizing rotating parts, particularly compressors and turbines. These displacements result in a loss of thermodynamic efficiency or premature wear of the blades. Furthermore, the greater the distance of the component from the ball bearing connecting the rotor and stator, the greater the differential displacement.

[0003] Currently, efforts are being made to limit the axial displacement of the rotor shaft by various means so that the rotating components remain in place relative to the stator. Thus, the compensation of axial thrust, and therefore of axial displacements of a rotor, is generally achieved by controlling aerodynamic pressures acting axially on walls attached to the rotor.

[0004] A device for measuring the axial thrust exerted by a rotor on a stator is known from French patent FR 2 708 044. 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 are arranged on the deformable bars. This measuring device allows for the modulation of an active compensation device for 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 rotor shaft of the turbomachine (turbine or compressor) with a suitable coupling link 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 with axis X, the rotor being mounted on a shaft and comprising blades defining a chord making an angle α with respect to an axis X' parallel to the X axis. It is characterized in that the rotor is connected to the shaft by a guide joint defining a helical sliding path. The rotation of the rotor produces an aerodynamic force that causes a displacement of the rotor on the drive shaft along 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 α defines the nature of the turbomachine; a turbine with blades of angle α generates an aerodynamic force opposite to that generated by a compressor with blades of angle -α.

[0008] Advantageously, the helical displacement path defines a pitch of angle [3] along the X-axis with the same orientation as the angle α of the blades such that 0 < [3] < 90° and 0 < α < 90°. The pitch of the spline with an angle [3] and the same orientation as the angle α of the blades allows the rotor to move backward from upstream to downstream or forward from downstream to upstream on the shaft according to 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 considered equilibrium point, thus stabilizing the displacement of the rotor relative to the shaft.

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

[0011] According to a second embodiment, the guide joint consists of at least one ball and a raceway. The ball rolls in the raceway, thus enabling the rotor to move along the shaft.

[0012] According to a first embodiment, the spline or raceway is disposed on the shaft and the pin or ball on the rotor. The spline is disposed on the surface of the shaft and the pin is fixed to the inner surface of the rotor opposite the shaft. The spline may be machined. 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 embodiment, the spline or raceway is disposed on the rotor, and the pin or ball is disposed on the shaft. The spline is disposed 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 tree and the ball is placed in a recess on the surface of the tree.

[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. Similarly, the use of several raceways, each coupled to one or more balls, allows for a better distribution of forces.

[0015] Advantageously, a stop is provided in the spline or raceway. This stop limits the rotor's displacement relative to the shaft. This stop is particularly useful when the spline or 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 with opposite orientations.

[0017] Advantageously, the splines cover only a portion of the periphery of the shaft or rotor. Since the displacement of the shaft relative to the rotor is small, the spline does not need to cover the entire periphery of the shaft or rotor. The length of the spline is defined according to the desired maximum displacement.

[0018] Advantageously, at least one first pin and one first spline are arranged symmetrically with respect to the X-axis to a second pin and a second spline. This symmetrical arrangement of a second pin and a second spline to the first pin and the first spline, or of a second row of pins and splines to a first row of pins and splines, 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 the blades are thus moved together by the same distance and at the same time.

[0020] Other advantages may become apparent to a person skilled in the art upon reading the examples below, illustrated by the accompanying figures, which are given for illustrative purposes. BRIEF DESCRIPTION OF THE FIGURES

[0021] The figures are presented for illustrative purposes only and are in no way limiting of 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 a rest position;

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

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

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

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

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

[0030] Throughout this description, the part positioned at the front in the direction of airflow will be referred to as "upstream" and the part positioned at the rear as "downstream". The direction of airflow 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' of X axis 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 along 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.1]) or a compressor 1' ([Fig.2]).

[0034] These aerodynamic forces Fa combined with the increase in temperature when the turbomachine is in motion, induce a dilation 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 includes a link between the shaft 2 and the rotor 3 which allows a displacement da by lengthening of the shaft 2 and a displacement dr of the rotor 3 on the shaft.

[0036] This connection is illustrated for example in Figures 3 and 4 for a turbine 1. The shaft 2 includes helical splines 20, here four, whose curvature is oriented in the opposite direction to the aerodynamic forces Fa. The rotor 3 includes on the inner 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 with respect to an axis X' parallel to the axis X. The splines 20 are oriented at an angle 3 with 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 splines 20 causing the rotor to recoil 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 come to rest 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 spline 20 will balance with the component fd normal to the spline profile at the point of contact with a pin of the force exerted by displacement of the shaft 2. In this case, the rotor has moved a relative distance e on the shaft with respect to its original position.

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

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

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

[0042] The sliding connection between the shaft 2 and the rotor 3 can be achieved either by means of a lubricated spline and a pin, or by means of a helical bearing. In the latter case, the connection between the shaft and the rotor is ensured by a first ball bearing race and a second helical bearing race, or alternatively by a first and a second helical bearing race and balls. This arrangement can limit the maximum transmissible forces to guarantee the integrity of the balls.

[0043] Flexible elements acting as springs can be used to force the return to the initial position after the turbomachine has stopped. Slowing down the rotational speed of the turbomachine, combined with the cooling of the parts, and in particular the shaft, allows the rotor to return to its original position.

[0044] In the case of a compressor 1', the aerodynamic force is reversed, therefore 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 with respect to an axis X' parallel to the axis X. The grooves 20 are oriented at an angle [3] of the same orientation as the angle α. Thus in this case, in motion, 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 splines 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 a relative distance e on the shaft relative to its original position.

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

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

Claims

Demands

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 with respect to an axis X' parallel to the axis X, characterized in that the rotor (3) is connected to the shaft (2) by a guide link defining a helical path of displacement.

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

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

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

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

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

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

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

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

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

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