CN110005479B

CN110005479B - Aeroengine and fusing load reduction structure for supporting low-voltage rotor bearing thereof

Info

Publication number: CN110005479B
Application number: CN201810010266.2A
Authority: CN
Inventors: 唐振南; 赵芝梅; 宋会英; 柴象海
Original assignee: AECC Commercial Aircraft Engine Co Ltd
Current assignee: AECC Commercial Aircraft Engine Co Ltd
Priority date: 2018-01-05
Filing date: 2018-01-05
Publication date: 2021-06-29
Anticipated expiration: 2038-01-05
Also published as: CN110005479A

Abstract

The invention aims to provide a fusing load reduction structure for supporting a low-pressure rotor bearing, which can improve the safety performance of an engine, and an aero-engine comprising the fusing load reduction structure. According to the invention, the fusing load reduction structure for supporting the low-voltage rotor bearing comprises a conical wall for mounting the bearing and an intermediate casing for supporting the conical wall, wherein an annular wall body is arranged at the large end of the conical wall, an inner spherical surface is provided on the annular wall body, an outer spherical surface is provided on the intermediate casing corresponding to the inner spherical surface, the inner spherical surface is in surface contact fit with the outer spherical surface, the annular wall body is further connected with the intermediate casing through a fusing structure, and the centers of the inner spherical surface and the outer spherical surface are positioned on the central axis of an engine.

Description

Aeroengine and fusing load reduction structure for supporting low-voltage rotor bearing thereof

Technical Field

The invention relates to a low-pressure rotor supporting structure of an aircraft engine, in particular to a fusing load reduction structure of the low-pressure rotor supporting structure.

Background

The low pressure spool of a typical turbofan engine generally includes a fan, a boost stage, a low pressure turbine, a shaft supported by a plurality of bearings that transmit forces and moments generated by the turbine to the boost stage and the fan, and the like. Under normal conditions, the straight line of the gravity centers of the fan, the booster stage, the low-pressure turbine and other parts is superposed with the rotating shaft. To ensure a margin for critical rotational speed, the low pressure rotor system is typically supported by three bearings, with the # 1 and # 2 bearings located near the fan rotor, referred to as fan bearings. The fan bearing connects the fan rotor to the stator intermediate casing through the supporting structure, so that the fan bearing and the supporting structure thereof are the force transmission components between the fan and the stator structures such as the intermediate casing during normal operation.

During the operation of the aeroengine, the fan blades are broken or fall off due to foreign object suction or fatigue and other factors, namely FBO (Fan Blade off). After an FBO event occurs, the center of gravity of the fan may be offset from the centerline of the low pressure spool. However, due to the limitations of the bearings, the fan still rotates about the centerline of the low pressure rotor. Rotation of the fan about an axis offset from its center of gravity excites the low pressure rotor system to produce one or more modes of oscillation, thereby producing unbalanced loads. For the large bypass ratio turbofan engine commonly used on the current commercial aircraft, the radius of a fan blade is long, the mass is large, and the FBO event can cause the gravity center line of the fan to be not aligned with the center line of the engine, so that huge unbalanced load is caused. Since the bearings radially constrain the fan shaft, FBO imbalance loads are primarily transferred through the bearings and their support structure to the intermediate case and further to the mounting joints and even the aircraft.

Because the FBO event is difficult to avoid, the traditional design method is to ensure that the FBO unbalanced load can be borne by improving the structural strength of related parts on a force transmission path so as to meet the safety requirement. However, this approach can result in increased engine mass and cost, increased fuel consumption, and reduced operating efficiency. Another effective way to cope with FBO events is to perform a fabric fail/fuse design. The concept of the structural failure/fusing design is to make certain components in the engine fail under the FBO load by purposefully designing the components as sacrificial units, on one hand, the unbalanced energy generated by the FBO event is reduced and consumed, on the other hand, the transmission path is changed, the FBO load is redistributed, the unbalanced load transmitted to the key components is reduced, and the safety of the engine is protected. Unbalanced loads generated by FBO events are mainly carried by fan bearings (1# bearing and 2# bearing), bearing support structures, and intervening casings, among others. The fan bearing on the transmission path and the supporting structure of the fan bearing are subjected to failure design, so that the fan bearing has a smaller strength safety coefficient, fails under the FBO unbalanced load, can reduce the FBO unbalanced load born by key parts such as an intermediate casing, a mounting joint and a low-pressure rotating shaft, and ensures the safety of an engine.

Since the unbalanced load is first transferred to the intermediate case through the # 1 bearing, many of the solutions herein have been designed for fusing, also referred to as primary fusing. For example, patent document FR2752024B1 discloses the use of a necked bolt at the mounting edge of the bearing cone wall of the 1# bearing, patent document US 6428269B 1 discloses the use of a compression bolt at the bearing cone wall of the 1# bearing, patent document US6447248B1 discloses the use of a thinned section at the bearing cone wall, and patent document US7097413B2 discloses the use of three sections of cone walls with a weakened area left behind, when a blade fall-off causes a large imbalance, the fusing structure fails, cuts off the force transmission path at the bearing of the 1# bearing, releasing the constraint of the low-pressure rotating shaft at the bearing of the 1# bearing, and the rotor can rotate about the new center of gravity, reducing the imbalance load. However, the bolts fall off after failure, the structure of the junction is subjected to impact damage, and after the cone wall is fused, the free front section of the cone wall collides and rubs with the fan shaft in the mode of arranging the weak section, so that the fan shaft is damaged. According to the scheme, after the primary fusing structure fails, the fan rotor swings greatly, and a lubricating system of the 1# bearing is easily damaged, so that dry grinding, overheating and blocking of the bearing are caused, and the engine cannot normally rotate. Too much swing of the fan rotor can also cause severe dry rubbing between the fan blades and the rigid containing casing, resulting in more blade loss and increased risk of fire. When the rotating speed is reduced, the combined action of unbalance and resonance of the rotor is experienced, no support is arranged at the 1# bearing, the fan rotor is in a cantilever state, the vibration amplitude of the rotor is increased, and the damage to the bearing and the main structure is caused.

In view of the above problem, patent document US5974782A discloses the use of a double conical wall, which fails after FBO has occurred, reduces the supporting stiffness of the conical wall, allows a small portion of the imbalance forces to be transmitted through the conical wall to the intermediate casing, and limits the large swing of the fan shaft. The cone wall which is not completely failed forms a moment arm, and bending moment is generated while unbalanced radial force is transmitted, so that the stress state of the key structure of the intermediate casing is more severe. The patent document US6494032B2 discloses the use of a conical structure and a spherical connection on one side which can be deactivated, allowing the rotor to rotate about the sphere at this point, preventing the transfer of bending moments at this point, but this structure is used on three-rotor engines and is not suitable for two-rotor engines. In some patents of secondary fusing, a ball joint structure is adopted at the 2# bearing, such as those disclosed in patent documents US6491497B1 and US6783319B2, which aim to relieve stress concentration of the fan shaft after the primary fusing occurs, but the primary fusing is not performed and the secondary fusing is not performed substantially.

Disclosure of Invention

The invention aims to provide a fusing load reduction structure for supporting a low-pressure rotor bearing, which can improve the safety performance of an engine, and an aero-engine comprising the fusing load reduction structure.

According to the invention, the fusing load reduction structure for supporting the low-voltage rotor bearing comprises a conical wall for mounting the bearing and an intermediate casing for supporting the conical wall, wherein an annular wall body is arranged at the large end of the conical wall, an inner spherical surface is provided on the annular wall body, an outer spherical surface is provided on the intermediate casing corresponding to the inner spherical surface, the inner spherical surface is in surface contact fit with the outer spherical surface, the annular wall body is further connected with the intermediate casing through a fusing structure, and the centers of the inner spherical surface and the outer spherical surface are positioned on the central axis of an engine.

In one embodiment, the fusing structure is formed by welding the inner spherical surface and the outer spherical surface.

In one embodiment, the fusing structure is formed by connecting the annular wall body and the intermediate casing through a dead bolt.

In one embodiment, the fuse structure includes a retaining ring including a first ring portion connected to the intermediate casing by a fastener and a second ring portion engaged with a groove in the annular wall body by a breakable rib.

In one embodiment, the inner and outer side surfaces of the annular wall body are respectively spherical surfaces with a common spherical center, the inner side surface of the annular wall body provides the inner spherical surface, the groove is arranged on the outer side surface of the annular wall body, and the second annular part is sleeved on the outer side of the annular wall body, and the inner side surface of the second annular part is also spherical surface and is in surface contact fit with the outer side surface of the annular wall body.

In one embodiment, the outer spherical surface extends beyond an end surface of the annular wall body to provide a space for the annular wall body to slide after the fusing structure is fused.

In one embodiment, the outer spherical surface is provided with a damping ring opposite to an end surface of the ring wall body to buffer sliding of the ring wall body after the fusing structure is fused.

In one embodiment, the outer spherical surface extends beyond an end face of the annular wall body, and a damping ring is arranged on the outer spherical surface opposite to the end face of the annular wall body, with a gap therebetween.

In one embodiment, the low pressure rotor comprises a fan disc, a fan shaft, the position of the fan shaft close to the fan disc is installed on the small end of the conical wall through a first bearing, and the other end of the fan shaft is installed on the intermediate casing through a second bearing; and the distance between the spherical center and the mass center of the fan disc of the low-pressure rotor is larger than the distance between the center of the second bearing and the mass center of the fan disc by taking the vertical projection of the central axis of the engine as a reference.

According to another aspect of the invention, an aircraft engine comprises a fan, a booster stage, a low pressure turbine, and a shaft for transmitting forces and torques generated by the turbine to the booster stage and the fan, wherein the shaft comprises a fan shaft for rotatably supporting the fan and the booster stage on an intermediate casing, and further comprises any one of the fuse load-reducing structures for low pressure rotor bearing support.

The inner spherical surface and the outer spherical surface are in surface contact fit, the annular wall body is further connected with the intermediate casing through a fusing structure, the spherical centers of the inner spherical surface and the outer spherical surface are located on the central axis of the engine, the inner spherical surface and the outer spherical surface form a spherical joint structure, the spherical joint structure has the function of decoupling bending moment, the degree of collision and abrasion of fan blades and the fan casing is limited, the critical rotating speed of the rotor can be reduced after fusing, the rotor is in a supercritical state and has a self-centering effect, unbalance is reduced, and therefore even if large unbalance is generated after FBO, the safety of the main structure of the engine is guaranteed.

Drawings

The above and other features, properties and advantages of the present invention will become more apparent from the following description of the embodiments with reference to the accompanying drawings, in which:

FIG. 1 is a partial schematic view of an aircraft engine;

FIG. 2 is a schematic view of a fuse load reduction structure for low voltage rotor bearing support;

FIG. 3 is a schematic view of another embodiment of a fuse load relief structure for low pressure rotor bearing support;

FIG. 4 is a schematic view of the low voltage spool position before and after a fuse structure failure.

Detailed Description

The present invention is further described in the following description with reference to specific embodiments and the accompanying drawings, wherein the details are set forth in order to provide a thorough understanding of the present invention, but it is apparent that the present invention can be embodied in many other forms different from those described herein, and it will be readily appreciated by those skilled in the art that the present invention can be implemented in many different forms without departing from the spirit and scope of the invention.

It is to be noted that the drawings are designed solely as examples and are not to scale and should not be construed as limiting the scope of the invention as it may be practiced otherwise than as specifically claimed.

As an embodiment of the present invention, the aircraft engine is a turbofan engine, which includes a fan, a low pressure compressor (booster stage), a high pressure compressor, a combustor, a high pressure turbine driving the compressor, a low pressure turbine driving the fan, an exhaust system, and the like. The high-pressure compressor, the combustion chamber and the high-pressure turbine are collectively called a core machine, part of the available energy in the gas discharged by the core machine is transmitted to the low-pressure turbine to drive the fan, and the rest part of the available energy is used for accelerating the discharged gas in the spray pipe. The fan rotor is a compressor with 1 or several stages of long blades, and after air flows through the fan, the air is divided into two paths: one path is a contained air flow, air is compressed by the air compressor continuously, the air and fuel oil are mixed and combusted in the combustion chamber, the fuel gas is expanded by the turbine and the spray pipe, the fuel gas is discharged from the tail nozzle at high speed to generate thrust, and the flow path is that the fuel gas is discharged from the spray pipe through the low-pressure air compressor, the high-pressure air compressor, the combustion chamber, the high-pressure turbine and the low-pressure turbine; the other path is bypass airflow, and air behind the fan is directly discharged into the atmosphere through the bypass or is discharged together with the bypass fuel gas in a spray pipe. The similar parts of the prior aircraft engine are not described in detail later, and mainly illustrate the fusing load reduction structure for supporting the low-pressure rotor bearing.

Fig. 1 shows a part of a longitudinal section of the engine, which is taken in the axial direction of the engine. As shown in fig. 1, one end of the fan shaft 3 is provided with a fan disc 2, the fan disc 2 is provided with fan blades 1, the fan disc 2 is further connected with a pressure increasing stage 10 (comprising a rotating disc and the blades), and the end of the fan shaft 3 is arranged at one end of the conical wall 6 through a first bearing 4. The other end of the fan shaft 3 is mounted on an intermediate casing 9 via a second bearing 5. In fig. 1, the dashed line 12 is the axis of rotation of the fan shaft 3, and also the engine axis. The first bearing 4 is commonly referred to in the industry as a # 1 bearing and the second bearing 5 is commonly referred to in the industry as a # 2 bearing.

Fig. 2 is a partially enlarged view of a fusing load-reducing structure for supporting a low-voltage rotor bearing corresponding to fig. 1. As shown in fig. 1 and 2, the large end of the conical wall 6 is provided with an annular wall 20, the inner side surface of the annular wall 20 is an inner spherical surface, the intermediate casing 9 is provided with a support portion 21, the support portion 21 is provided with an outer spherical surface, and the inner spherical surface and the outer spherical surface are in contact fit to form a ball joint 7 with the spherical surface 8 as a sliding surface. The fuse load reduction structure for low-voltage rotor bearing support further includes a fuse structure, which in the embodiment shown in fig. 1 and 2 includes a retaining ring including a first ring portion 23 and a second ring portion 24, the first ring portion 23 and the second ring portion 24 being connected together, the first ring portion 23 extending following the contour of the ring wall body 20, and the second ring portion 24 extending following one wall surface of the intermediate casing 9. For example, when the outer surface of the annular wall body 20 is a spherical surface, the inner surface of the first ring portion 23 is also a spherical surface, the inner surface of the first ring portion 23 is in surface contact with the outer surface of the annular wall body 20, a spherical joint having the spherical surface 30 as a sliding surface is formed, and the spherical surface 8 on which the spherical joint 7 is located has the same spherical center 13 as the spherical surface 30. The first ring part 23 is fixedly connected with the intermediate casing 9 through a fastener 24, the inner side surface of the second ring part 24 is provided with a convex rib 22, the convex rib 22 can be a discrete boss or a continuous convex ring, a groove is arranged on the outer side surface of the annular wall body 20 corresponding to the convex rib 22, and the convex rib 22 is embedded into the groove. The rib 22 is a cuttable structure and is a sacrificial unit, and the structure fails or is cut off under the FBO load, so that the unbalanced energy generated by the FBO event is reduced, the force transmission path is changed, the FBO load is redistributed, the unbalanced load transmitted to the key component is reduced, and the safety of the engine is protected.

With continued reference to fig. 2, the outer spherical surface of the support portion 21 extends beyond the right end of the annular wall body 22, and after the fusing structure fails, the annular wall body 22 can slide on the outer spherical surface, that is, a sliding space of the annular wall body 22 after the failure is provided, and a damping ring 27 is further provided on the outer portion of the outer spherical surface, and after the end portion of the annular wall body 22 is in sliding contact with the damping ring 27, the damping ring 27 damps the sliding thereof.

In one embodiment, there may be no gap or a gap between the damping ring 27 and the right end of the annular wall 22.

Referring back to fig. 1, the spherical center 13 of the ball joint 7 is on the engine central axis 12 with reference to the orthographic projection on the engine central axis 12, and the distance L1 from the center of mass of the fan disc 2 is greater than the distance L from the center of the second bearing 5 to the center of mass of the fan disc 2.

According to the foregoing embodiment, the ball joint 7 includes the gap 26 and the damping ring 27, as shown in fig. 2, the sizes of the gap 26 and the damping ring 27 may affect the rotation distance of the ball joint, and may be reasonably selected to control the swing angle a of the blown fan rotor and the distance E between the fan blade tip and the casing, as shown in fig. 4. In fig. 4, a solid line part is a position of the fan rotor after the fuse structure fails, and a dotted line part is a position of the fan rotor in a normal state before the fuse structure fails. Referring to fig. 1 and 4, the distance D between the blade tip and the casing is greater than the distance E after failure.

Other embodiments of the fuse structure are also possible, such as a welded structure 22 formed by various processes to connect the conical wall 6 and the intermediate case 9, as shown in fig. 3, or any other form, such as a bolt connecting the conical wall 6 and the intermediate case 9, which can be disabled.

As shown in fig. 1 and 4, when the unbalanced load is greater than a predetermined value, the fusing structure corresponding to the ball joint 7 fails, the fan rotor (including the fan disc 2, the fan blades 1, the booster stage 10, the fan shaft 3, and the like) can rotate around the spherical center 13 on the spherical surface 8, the rotation radius of the fan rotor is L1 and is greater than the distance L, the swing angle a of the fan shaft 3 is reduced, and the bending stress of the fan shaft 3 can be reduced. After the fusing structure corresponding to the ball joint 7 is fused, the swing radius of the fan shaft 3 is increased, the collision and abrasion between the fan blades 1 and the easily-abraded layer/filling layer on the fan casing 11 are increased, the reduction of the rotating speed of the fan rotor is accelerated, and the unbalanced load value is reduced. After fusing, the first bearing 4 weakens the constraint on the fan rotor, and the fan rotor can rotate along the rotating shaft closer to the new mass center, so that the unbalanced load value is further reduced.

After the fusing structure fails, the gap 26 and the damping ring 27 can limit the swing of the fan rotor within a certain range, prevent the fan blade and the rigid casing from dry abrasion for a long time, reduce the risk of secondary damage and ignition of the blade, and prevent dangerous consequences such as abrasion of the high-pressure rotor and the low-pressure rotor caused by excessive bending of the rotor.

After the fusing structure fails, the supporting rigidity of the fan rotor is changed, the critical rotating speed of the fan rotor is reduced, the fan rotor can pass through the resonant rotating speed at a lower rotating speed, the damping ring 23 can reduce the vibration peak value, and the vibration load transmitted to the main structure of the engine/airplane is reduced.

After the fusing structure fails, the ball joint 7 still has a certain radial supporting function on the conical wall 6, and under the combined action of unbalance and resonance, the rotor is prevented from swinging without limit, and the damage to the main structure is reduced.

After failure of the fused structure, a small portion of the unbalanced radial load can still be transmitted to the intermediate casing 9 through the tapered wall 6, slowing down the degree of loading of the second bearing 5 and its supporting structure.

The foregoing embodiment has the following advantageous effects:

1. in the case of FBO, the conical wall 6 supporting the first bearing 4 and the ball joint 7 on the mounting edge of the intermediate casing 9 fail, and the fan shaft 3 can rotate around the spherical center of the ball joint 7, so that the degree of constraint of the first bearing 4 on the rotor is reduced, the rotation center of the rotor is closer to the new center of mass, the unbalance radius is reduced, and the unbalance amount is reduced.

2. After the ball joint which can be failed is fused, the radial constraint of the first bearing 4 on the fan casing 11 is weakened, the constraint in the bending direction is released, the swing radius of the fan shaft 3 is increased, the collision and abrasion among the fan blades 1, the easily-abraded layer and the containing layer are increased, the reduction of the rotating speed is accelerated, and the unbalance is reduced.

3. The damping ring 27 at the ball joint 7 can partially absorb the impact energy at FBO and reduce the subsequent vibration peak.

4. The damping ring 27 limits the rotation distance of the ball joint 7, so that the swing of the fan rotor is limited within a certain range, the long-time dry abrasion between the fan blade and the rigid casing is prevented, and the secondary damage and the fire risk of the fan blade are reduced.

5. After the ball joint 7 is fused, the supporting rigidity of the rotor is changed, the critical rotating speed of the rotor is reduced, the rotor can pass through the resonant rotating speed at a lower rotating speed, and the vibration load transmitted to the main structure of the engine/airplane is reduced.

6. After being fused, the first bearing 4 still has a certain supporting function, and when the rotor undergoes resonant rotation speed, the rotor is prevented from swinging without limit, and the damage to the main structure is reduced.

7. The first bearing 4 can still share a portion of the unbalanced radial load, preventing the unbalanced load from being transmitted from the # 2 bearing and its supporting structure, thereby requiring structural reinforcement and increased structural weight.

8. The ball joint and fusing connection structure are arranged on the mounting edge of the conical wall 6 supporting the first bearing 4 and the intermediary casing 9, so that the structure is simple and the assembly is easy.

Although the present invention has been disclosed in terms of the preferred embodiment, it is not intended to limit the invention, and variations and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention. Therefore, any modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope defined by the claims of the present invention, unless the technical essence of the present invention departs from the content of the present invention.

Claims

1. The fusing load reduction structure for supporting the low-voltage rotor bearing comprises a conical wall for mounting the bearing and an intermediary casing for supporting the conical wall, and is characterized in that the large end of the conical wall is provided with an annular wall body, the annular wall body is provided with an inner spherical surface, the intermediary casing is provided with an outer spherical surface corresponding to the inner spherical surface, the inner spherical surface is in surface contact fit with the outer spherical surface, the annular wall body is further connected with the intermediary casing through a fusing structure, and the centers of the inner spherical surface and the outer spherical surface are located on the central axis of an engine;

the fusing structure comprises a retaining ring, the retaining ring comprises a first ring portion and a second ring portion, the first ring portion is connected with the intermediary casing, the inner side surface and the outer side surface of the ring wall body are spherical surfaces sharing a sphere center respectively, the inner side surface of the ring wall body provides the inner spherical surface, and the second ring portion is sleeved on the outer side of the ring wall body, the inner side surface of the ring wall body is also a spherical surface, and is in surface contact fit with the outer side surface of the ring wall body.

2. The fusing load reduction structure for supporting a low pressure rotor bearing of claim 1, wherein the fusing structure is formed by welding the inner spherical surface and the outer spherical surface.

3. The fuse load-reducing structure for supporting a low-voltage rotor bearing of claim 1, wherein said fuse structure is formed by connecting said annular wall body and said intermediate casing by a dead bolt.

4. The fuse load-reducing structure for supporting a low pressure rotor bearing according to claim 1, wherein said first ring portion is connected to said intermediate casing by a fastening member, and said second ring portion is engaged with a groove of said annular wall body by a breakable rib.

5. The fuse load relief structure for a low pressure rotor bearing support of claim 4 wherein said recess is provided in an outer surface of said annular wall.

6. The fuse load-reducing structure for supporting a low-voltage rotor bearing according to claim 1, wherein said outer spherical surface extends beyond an end surface of said annular wall body to provide a space for said annular wall body to slide after said fuse structure is fused.

7. The fusing load reduction structure for a low-voltage rotor bearing according to claim 1, wherein a damping ring is provided on the outer spherical surface to oppose an end surface of the ring wall body to damp sliding of the ring wall body after the fusing structure is fused.

8. The fusing load reduction structure for supporting a low-pressure rotor bearing according to claim 6, wherein a damping ring is provided on the outer spherical surface so as to oppose an end surface of the ring wall body, and a gap is provided between the damping ring and the end surface.

9. The fuse load-reducing structure for supporting low-voltage rotor bearing according to claim 1, wherein said low-voltage rotor includes a fan disk, a fan shaft, said fan shaft being mounted at a position close to said fan disk by a first bearing at a small end of said conical wall and at another end thereof being mounted at said intermediate casing by a second bearing; and the distance between the spherical center and the mass center of the fan disc of the low-pressure rotor is larger than the distance between the center of the second bearing and the mass center of the fan disc by taking the vertical projection of the central axis of the engine as a reference.

10. An aircraft engine comprising a fan, a pressure stage, a low pressure turbine, and a shaft for transmitting forces and moments generated by the turbine to the pressure stage and the fan, the shaft comprising a fan shaft for rotatably supporting the fan and pressure stage on an intermediate casing, wherein the aircraft engine further comprises a fuse load reduction structure for low pressure rotor bearing support according to any one of claims 1 to 9.