BEARING ASSEMBLY FOR A GAS TURBINE

TECHNICAL FIELD

The present invention relates to a bearing assembly for a gas turbine .

BACKGROUND ART

A known type of gas turbine comprises a rotor, provided with a shaft extending along a longitudinal axis, a cylindrical case, commonly referred to as bearing stand, which extends about the shaft, and at least one bearing assembly, which is arranged between the case and the shaft and is supported by the case .

The bearing assembly of the gas turbine is arranged into an annular groove of the rotor shaft, defined by an annular surface and two facing annular shoulders.

In small-sized gas turbines, the dimensions of the annular groove for accommodating the bearing assembly are obviously smaller than the dimensions of the annular grooves of the larger-sized gas turbines. Specifically, in small-sized gas turbines, the annular surface and the shoulders have a shorter axial length and a shorter radial length, respectively, than those of the larger- sized gas turbines. However, current bearing assemblies are relatively cumbersome and it is often not possible to accommodate such bearing assemblies into the annular grooves of the small-sized gas turbines. This results in considerable difficulties in making bearing assemblies

which simultaneously are effective and small-sized. Indeed, most of the latest bearing assemblies may not be adapted to the dimensions of the grooves of small-sized turbines .

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a bearing assembly which is free from the drawbacks of the known art highlighted herein; specifically, it is an object of the invention to provide a bearing assembly for a small-sized gas turbine which is effective at the same time .

In accordance with such objects, the present invention relates to a bearing assembly for a gas turbine comprising a shaft, which extends along a longitudinal axis and is provided with at least one annular groove delimited by a cylindrical surface, a first annular shoulder and a second annular shoulder facing the first shoulder; the bearing assembly being accommodated into the annular groove and comprising a sliding bearing and a cylindrical supporting body arranged about the sliding bearing; the bearing assembly being characterized in that the sliding bearing axially protrudes with respect to the supporting body in the contact area between the supporting body and the sliding bearing .

In accordance with such objects, the present invention further relates to a gas turbine comprising a

rotor, which is provided with a shaft extending along a longitudinal axis and having an annular groove, a substantially cylindrical case arranged about the shaft, and a bearing assembly accommodated into the groove and supported by the case; the gas turbine being characterized in that the bearing assembly is of the type claimed in any one of the claims from 1 to 17.

BRIEF DESCRIPTION OF THE DRAWINGS Further features and advantages of the present invention will be apparent from the following description of a non-limitative embodiment thereof, with reference to the figures in the accompanying drawings, in which: - figure 1 is a perspective section view, with parts removed for clarity, of a portion on a gas turbine according to the present invention;

- figure 2 is a perspective view, with parts in section and parts removed for clarity, of a first detail of the bearing assembly made according to the present invention; figure 3 is a perspective section view, on enlarged scale, with parts removed for clarity, of a first detail of the gas turbine in figure 1; - figure 4 is a perspective section view, on enlarged scale, with parts removed for clarity, of a second detail of the gas turbine in figure 1;

- figure 5 is a schematic side view, with parts

removed for clarity, of a second detail of the bearing assembly made according to the present invention; and

- figure 6 is a schematic side view, with parts removed for clarity, of a third detail of the bearing assembly made according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In figure 1, numeral 1 indicates as a whole a gas turbine, a portion of which is shown, comprising a rotor 2, provided with a shaft 3, and a case 4.

The shaft 3 extends along a substantially horizontal, longitudinal axis A and rotates about the longitudinal axis A. The case 4 is substantially cylinder-shaped and extends about the shaft 3. The shaft 3 is provided with at least one annular groove 5 delimited by a cylindrical surface 6, one annular shoulder 7 and annular shoulder 8 facing the shoulder 7. Specifically, the groove 5 is arranged close to the inlet of a compressor (not shown in the accompanying figures) of the gas turbine 1.

The gas turbine 1 further comprises at least one bearing assembly 10 adapted to be accommodated into the annular groove 5.

The bearing assembly 10 comprises a sliding bearing 11 arranged about the shaft 3, a supporting body 12 arranged in contact about the sliding bearing 11, a main thrust block 13 , a secondary thrust block 14 , two main thrust half rings 15, and two secondary thrust half

rings 16.

With reference to figures from 1 to 4 , the sliding bearing 11 axially protrudes with respect to the supporting body 12 in the contact area between the supporting body 12 and the sliding bearing 11.

Specifically, the sliding bearing 11 has first and second sides 17 and 18, facing shoulder 7 and shoulder

8, respectively, and axially protrudes with respect to the supporting body 12 at the first and second sides 17 and 18.

With reference to figures from 2 to 4 , the sliding bearing 11 comprises a cylinder 19 and a lining 20 of the cylinder 19.

The cylinder 19 is fixed to the supporting body 13 by connecting means, preferably connecting pins, not shown in the accompanying figures.

The lining 20 is made of low friction coefficient material, e.g. white metal.

With reference to figure 2, the cylinder 19 and the lining 20 respectively have two outlet holes 21 for the lifting oil of the shaft 3 which are substantially arranged at a substantially vertical, middle plane including the axis A of the shaft 3, and two arrays of holes 22 (only one of which is shown in figure 2) for the lubrication oil outlet, which are arranged on opposite sides of the axis A with respect to the middle plane and preferably comprise three holes 23, e.g. aligned. The lubrication oil is required for the

operation of the bearing assembly 10 because it is used to create an oil film which supports the shaft under hydrodynamic lubrication conditions. The sliding bearing 11 thus made may be advantageously replaced when it shows damages caused by wear; specifically, the sliding bearing 11 may be simply pulled out when required.

With reference to figures from 2 to 4, the supporting body 12 is substantially cylindrically shaped and has a main side 24, substantially facing the shoulder 7, and a secondary side 25, substantially facing the shoulder 8.

The supporting body 12 is provided with a main annular edge 27, which extends from the main side 24 in the axial direction, and a secondary annular edge 28, which extends from the secondary side 25 in the axial direction. The main edge 27 and the secondary edge 28 define a preferably cylindrical, main annular seat 30 for accommodating the main thrust block 13, and a preferably cylindrical, secondary annular seat 31 for accommodating the secondary thrust block 14, respectively .

With reference to figures 2 and 3, on the main side 24, at the main annular seat 30, the supporting body 12 is provided with two substantially semi-circular, main grooves 32a (only one of which is shown in figures 2 and 3) for accommodating the main thrust half rings 15.

At the main grooves 32a, the supporting body 12 is further provided with a plurality of cylindrical main

seats 33 adapted to be engaged by respective main pistons 34 (figure 3) being substantially cylindrically shaped and provided with main thrust surfaces of center

Bl. With reference to figure 5, the primitive obtained by joining the centers Bl of each main piston 34 is substantially a circumference of radius Rl.

With reference to figure 4, on the secondary side

25, at the secondary annular seat 31, the supporting body 12 is provided with two substantially semicircular, secondary grooves 32b for accommodating the secondary thrust half rings 16.

At the secondary grooves 32b, the supporting body

12 is further provided with a plurality of cylindrical secondary seats 35 adapted to be engaged by respective secondary pistons 36 being substantially cylindrically shaped and provided with secondary thrust surfaces of center B2.

With reference to figure 6, the primitive obtained by joining the centers B2 of each secondary piston 36 is substantially a circumference of radius R2.

In the non-limitative example shown and described herein, there are sixteen cylindrical main seats 33, and therefore sixteen respective main pistons 34, while there are fourteen cylindrical secondary seats 35, and therefore fourteen respective secondary pistons 36.

With reference to figures 3 and 4, each cylindrical main seat 33 and each cylindrical secondary seat 35 is

connected by means of respective main holes 38 (figure 3) and secondary holes 39 (figure 4) to a hydraulic circuit 40, provided inside the main body 12. A pressurized fluid, generally oil, which moves the main pistons 34 and the secondary pistons 36 in the axial direction to compensate for the dimensional variations of the shaft 3 due to temperature variations, flows into the hydraulic circuit 40.

With reference to figure 2, the supporting body 12 is connected to the case 4 by cylindrical coupling means. Specifically, the cylindrical coupling means comprise two cylinders 42 of the supporting body 12, which extend in a direction orthogonal to axis A and are arranged on opposite sides of the axis A with respect to the middle plane, and two rings of the case 4 (not shown in the accompanying figures) , which are engaged by the respective cylinders 42. This type of cylindrical coupling allows the bearing assembly 10 to easily comply with the movements of the shaft 3 during the operation of the turbine 1. In such a manner, possible offsets between the shaft 3 and the main and secondary thrust blocks 13 and 14, which may cause overloads on the same main and secondary thrust blocks 13 and 14, are avoided.

With reference to figures from 1 to 4, the supporting body 12 further comprises a circuit 44 for feeding lubricant oil to the sliding bearing 11, a circuit 45 for feeding shaft-lifting oil, a circuit 46 for feeding lubricant oil to the main thrust block 13

and a circuit 47 for feeding lubricant oil to the secondary thrust block 14.

Specifically, the circuit 44 for feeding lubricant oil to the sliding bearing 11 comprises a manifold (not shown in the accompanying figures) , which communicates with a feeding pipe 49 (figure 1) through a hole 50

(figures 1 and 2) , and a plurality of pipes 51 (figures

2, 3 and 4), preferably three, connected to the holes 23

(figure 2) of the sliding bearing 11. With reference to figure 1, the circuit 45 for feeding shaft- lifting oil comprises a pipe 53, which receives the oil through a hole 54 from a feeding pipe

(not shown in the accompanying figures) , and two branches 55 which communicate with the interior of the sliding bearing 11 by means of the holes 21 (figure 2) . The circuit 45 for feeding shaft-lifting oil mainly intervenes during the steps of starting the gas turbine 1 in which the shaft 3 is either static or is at low revolutions . The circuit 46 for feeding lubricant oil to the main thrust block 13 and the circuit 47 for feeding lubricant oil to the secondary thrust block 14 comprise a lubrication pipe 56 (figures 3 and 4) of the main thrust block 13 and a lubrication pipe 57 (figures 3 and 4) of the secondary thrust block 14, respectively, and are fed by the same feeding pipe (not shown in the accompanying figures) through the hole 58 (figure 2) .

With reference to figure 3, the main thrust block

13 is substantially ring-shaped and comprises a frame 60 and an array of main slides 61.

The frame 60 is substantially ring-shaped and substantially arranged in abutment with the main edge 27 of the supporting body 12 close to the main side 24 of the supporting body 12 and with the main thrust half rings 15.

The main slide array 61 is annular and comprises a plurality of main slides 63, specifically nineteen, each of which has a surface 64 substantially in contact with the main shoulder 7 and is coupled to respective main leverages 65 of kinematic load transmission of known type (diagrammatically shown in figure 3 by a section block) . The main leverages 65 are in contact with the main thrust half rings 15 at contact points Cl. Such contact points Cl coincide with the load transmission points between the main thrust half rings 15 and the main leverages 65, which, in turn, exchange them with the respective main slides 63.

With reference to figure 5, the primitive obtained by joining the contact points Cl of the main thrust half ring 15 is substantially a circumference of radius R3.

With reference to figure 4, the secondary thrust block 14 is substantially ring-shaped and comprises a frame 66 and an array of secondary slides 67.

The frame 66 is substantially ring-shaped and substantially arranged in abutment with the secondary

edge 28 of the supporting body 12 close to the secondary side 25 of the supporting body 12 and with the secondary thrust half rings 16.

The secondary slide array 67 is annular and comprises a plurality of secondary slides 69, specifically thirty, each of which has a surface 70 substantially in contact with the secondary shoulder 8 and is coupled to respective secondary leverages 71 of kinematic load transmission of known type (diagrammatically shown in figure 3 by a section block) . The secondary leverages 71 are in contact with the secondary thrust half rings 15 at contact points C2. Such contact points C2 coincide with the load transmission points between the secondary thrust half rings 16 and the secondary leverages 71, which, in turn, exchange them with the respective secondary slides 69.

With reference to figure 5, the primitive obtained by joining the contact points C2 of the secondary thrust half ring 16 is substantially a circumference of radius R4.

With reference to figure 3, the two main thrust half rings 15 are adapted to be accommodated into the respective main grooves 32a between the supporting body

12 and the main thrust block 13 and have a given axial length Al.

Specifically, the main thrust half rings 15 have one face in contact with the main pistons 34 of center Bl and one face in contact with the main leverages 65 at

the points Cl .

With reference to figure 5, the centers Bl and the contact points Cl are radially and circumferentially misaligned due to design constraints. The radial misalignment may generate a non-uniform distribution of the thrusts generated by the main pistons 34 in the main thrust half rings 15.

Specifically, the radial misalignment is equal to the difference between the radius Rl of the primitive of centers Bl of the main pistons 34 and the radius R3 of the primitive of contact points Cl between the main leverages 65 and the main thrust half rings 15.

The effects of the radial misalignment are strongly mitigated by using main thrust half rings 15 having an axial length Al equal to at least the radial misalignment .

On the other hand, the circumferential misalignment may cause damages to the main leverages 65. The effects of the circumferential misalignment are considerably mitigated by an adequate distribution of the main pistons 34 with respect to the main thrust half rings 15 so as to minimize the circumferential misalignment between the centers Bl and the contact points Cl .

With reference to figure 4, the two secondary thrust half rings 16 are adapted to be accommodated into the respective secondary grooves 32a between the supporting body 12 and the secondary thrust block 14 and have a given axial length A2.

Specifically, the secondary thrust half rings 16 have one face in contact with the secondary pistons 36 of center B2 and one face in contact with the secondary leverages 71 at the points C2. With reference to figure 6, the centers B2 and the contact points C2 are radially and circumferentially misaligned due to design constraints.

The radial misalignment may generate a non-uniform distribution of the thrusts generated by the secondary pistons 34 in the secondary thrust half rings 16.

Specifically, the radial misalignment is equal to the difference between the radius R2 of the primitive of centers B2 of the secondary pistons 36 and the radius R4 of the primitive of contact points C2 between the secondary leverages 71 and the secondary thrust half rings 16.

The effects of the radial misalignment are strongly mitigated by using secondary thrust half rings 16 having an axial length A2 equal to at least the radial misalignment.

On the other hand, the circumferential misalignment may cause damages to the secondary leverages 71. The effects of the circumferential misalignment are considerably mitigated by an adequate distribution of the secondary pistons 36 with respect to the secondary thrust half rings 16 so as to minimize the circumferential misalignment between the centers B2 and the contact points C2.

It is finally apparent that changes and variations may be made to the bearing assembly and gas turbine described herein, without departing from the scope of the appended claims.