Engine mounting arrangement

An engine mounting apparatus having a yoke carrier block and a main mount block, the yoke carrier block being connectable to the main mount block, the main mount block being connected to the engine by at least one engine attachment link for transferring loads from an engine in a normal load path during normal operation of the engine mounting arrangement, characterized in that the yoke carrier block is connected to a further engine attachment link independently of the main mount block, the further engine attachment link being unloaded during normal operation of the engine mounting arrangement and arranged to transfer loads from the engine in the event of a failure of one or more components in the normal load path.

CROSS REFERENCE TO RELATED APPLICATION

This application is entitled to the benefit of British Patent Application No. GB 0810589.2, filed on Jun. 11, 2008.

FIELD OF THE INVENTION

The present invention relates to an engine mounting arrangement and is particularly concerned with a mounting arrangement for attaching an aircraft engine to an aircraft pylon.

BACKGROUND OF THE INVENTION

A gas turbine engine210is shown in schematic section inFIG. 1and comprises a main rotational axis208, an air intake212and a propulsive fan214that generates two airflows A and B. The gas turbine engine210comprises, in axial flow A, an intermediate pressure compressor216, a high pressure compressor218, a combustor220, a high pressure turbine222, an intermediate pressure turbine224, a low pressure turbine226and an exhaust nozzle228. A nacelle230surrounds the gas turbine engine210and defines, in axial flow B, a bypass duct232between the air intake212and an exhaust nozzle234. A rear engine mounting arrangement22(rear in the sense of airflows A and B) is shown in the vicinity of the turbines222,224,226. Thrust struts26connect the rear engine mounting arrangement22with a forward section of the engine210. The rear engine mounting arrangement22is connectable to an aircraft pylon206and is located at a radially outer extent of the engine210, Preferably, at top dead centre. For the purposes of the following description, this will be taken to be vertically above the engine although it should be understood that the engine210may be hung at an angle to the vertical.

An engine210is conventionally mounted on an aircraft, whether under a wing or against a fuselage by each of a front and a rear mounting arrangement. Where the engine is a gas turbine engine210, the front mounting is generally provided in the vicinity of the fan214or compressors216,218and the rear mounting is generally provided in the vicinity of the turbines222,224,226. However, other arrangements are possible. The rear mounting arrangement22comprises means for connection of thrust struts26to transfer the thrust generated by the engine210through the mounting arrangement22and the pylon206to the aircraft. The rear engine mounting arrangement22also comprises means to transfer vertical and side loads from the engine210through the pylon206to the aircraft. Typically a forward engine mounting arrangement (not shown) is also provided. Preferably, in the vicinity of the compressors of a gas turbine engine210to transfer engine side and vertical loads but not thrust loads.

A conventional rear engine mounting arrangement22is shown inFIG. 2in highly schematic form. The arrangement comprises a mount block10that includes means to attach it to the aircraft pylon206and two engine attachment links24for connection to the engine210. It further comprises an integral clevis arrangement12protruding forward from the main body of the mount block10. The clevis arrangement12has a main thrust connection14, which is connectable to a thrust yoke16by a pivot pin or similar, and a pair of catcher devises20located on either side of the main thrust connection14that define a clearance around their respective pins. The yoke16is connected to the thrust struts26(FIG. 1) at connection points18by pin and clevis arrangements. Thus the propulsive thrust loads are transferred from the engine210through the thrust struts26, yoke16, main thrust connection14and mount block10and from there into the pylon206of the aircraft. In the event of a failure of the main thrust connection14, the clearance in the catcher devises20is taken up and the thrust load transferred through these instead.

Conventionally, the two integral engine attachment legs24are provided at the lateral ends of the mount block10. An integral catcher leg may also be provided intermediate the engine attachment legs24which transfers engine loads in the event of failure of one or both of the engine attachment legs24. One disadvantage of this engine mounting arrangement is that a failure crack emanating from either of the engine attachment legs24, or the mount block10itself, can propagate through the mount block10to fail the adjacent catcher link without detection. Whilst this can be certified by crack growth and propagation analysis, this is an unsatisfactory solution since it requires heavier and stronger materials to ensure the minimal crack growth properties required. This is the case even with more complex arrangements of engine attachment legs24and catcher links described in the prior art.

Thus, it is desirable to have an engine mounting arrangement that has a failure load path that does not rely on crack growth and propagation analysis. The present invention seeks to provide a novel rear engine mounting arrangement that seeks to address the aforementioned problems.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an engine mounting arrangement having a yoke carrier block and a main mount block, the yoke carrier block being connectable to the main mount block, the main mount block being connectable to an engine by at least one engine attachment link for transferring loads from the engine in a normal load path during normal operation of the engine mounting arrangement, characterised in that the yoke carrier block is connectable to a further engine attachment link independently of the main mount block, the further engine attachment link being unloaded during normal operation of the engine mounting arrangement and arranged to transfer loads from the engine in the event of a failure of one or more components in the normal load path.

Preferably, the yoke carrier block and main mount block are secured together.

Preferably, the yoke carrier block comprises a catcher lug connectable to the further engine attachment link. More preferably, the catcher lug is coplanar with the at least one engine attachment link. This means the engine loads are transferred in a single plane, except the thrust loads, and thus reduces the likelihood of generating a torque force to put a twisting strain on connection means.

Preferably, the catcher lug extends through the main mount block. This enables it to be central thereto. More preferably, the main mount block defines a clearance with respect to the catcher lug so that no load passes therebetween during normal operation of the engine mounting arrangement.

Preferably, the further engine attachment link is connected to the main mount block. This provides an additional failure load path.

The connections may comprise clevis and pin arrangements.

Alternatively, other connection arrangements may be used.

Preferably, at least one thrust strut is connectable to the yoke carrier block to transfer loads from the engine during normal operation of the engine mounting arrangement. More preferably, the at least one thrust strut is connectable to the main mount block, the connection being arranged to be unloaded during normal operation of the engine mounting arrangement and to transfer loads from the engine in the event of failure of one or more components in the normal load path.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 3, an exemplary embodiment of the rear engine mounting apparatus22of the present invention is shown. The apparatus22includes a yoke carrier block30and a main mount block32secured together. There are three engine attachment links,34,36,38, which connect between corresponding attachment points on the engine210to one or both of the yoke carrier and main mount blocks30,32as elaborated later. Preferably, the engine attachment links34,36,38are connected to points on the engine210by a clevis and pin arrangement. For example, the port side attachment link38is generally planar and elongate, and includes an aperture40containing a spherical bearing. The port side attachment link38sits within a complementary clevis fixed at a suitable location on a casing of the engine210and is secured by a pin41inserted through the aperture40(as shown by interrupted lines) and a complementary aperture in the clevis to connect them together. A similar arrangement is provided to connect the engine210to each of the starboard side34and central36attachment links. The connection arrangement of the engine attachment links34,36,38to the yoke carrier and main mount blocks30,32will be described below.

An advantage of providing a clevis and pin arrangement between the engine210and the engine attachment links34,36,38of the rear engine mounting arrangement22is that differential thermal expansion does not place undue stress or strain on any of the components as some relative movement is permitted in at least an axial plane. However, other arrangements of connecting the engine attachment links34,36,38to the engine210are considered to fall within the scope of the present invention.

The yoke carrier block30of the rear mounting arrangement22of the present invention is now described with reference toFIG. 3(showing both the yoke carrier and main mount blocks30,32) andFIGS. 4 and 5(showing just the yoke carrier block30from above and below respectively). The yoke carrier block30presents a substantially rectangular profile and comprises a main portion44with a tongue42protruding forwardly therefrom. At each corner of the main portion44of the yoke carrier block30are feet45through which are defined apertures46that receive, in use, attachment bolts50. Only one of the attachment bolts50is shown (FIG. 3) for clarity. The attachment bolts connect the yoke carrier block30to the main mount block32. The underside of the feet45are substantially planar and abut the main mount block32whilst the underside of the main portion44of the yoke carrier block30is spaced apart from the main mount block32.

The main portion44further defines at least one shear pin aperture48; two are shown inFIG. 4. In use, a corresponding number of shear pins extend from the aircraft pylon206and locate within the shear pin apertures48to transfer engine loads to the pylon206. Alternatively, one shear pin may transfer the loads in normal operation and a second shear pin may be located within a shear pin aperture48with a clearance defined around it so that no loads are transferred under normal operating conditions. In the event of a failure of the main shear pin arrangement, the clearance is taken up and the loads are transferred through the second, or catcher, shear pin. The main portion44of the yoke carrier block30may be profiled so as to reduce the component weight without compromising the strength and stiffness characteristics, for example by providing concave edges.

The tongue42is preferably, provided in the form of a clevis having upper52and lower54lugs, which define apertures56therethrough, the apertures56are aligned to receive a pivot pin (not shown) through the plane of the lugs52,54. A thrust strut balance yoke58(FIG. 3) is located symmetrically within the clevis of the tongue42and comprises an aperture60therethrough that aligns with the apertures56through the tongue42. The pivot pin therefore connects the thrust strut balance yoke58within the tongue42. A clearance is provided between the thrust strut balance yoke58and the rear of the clevis formed by the tongue42, in the plane of the thrust strut balance yoke58and the tongue42, to enable the thrust strut balance yoke58to pivot around the pivot pin through apertures56,60to balance the loads from the thrust struts26. Preferably, the pivot pin is located in a spherical bearing to allow the thrust strut balance yoke58to self-align with the load paths to reduce internal stresses.

Two thrust struts26are provided, one being connected to the each of the lateral ends62of the thrust strut balance yoke58, or more preferably, to forwardly extending protrusions thereof, by pins retained within spherical bearings or any other suitable means. Preferably, the connection is by means of a clevis arrangement to allow the thrust struts26and the balance yoke58to pivot relative to each other to compensate for variations in the thrust transmitted by each of the thrust struts26. For each thrust strut26, the clevis arrangement comprises a pair of lugs on one of the thrust strut26and the yoke58, and a single lug on the other that sits between the pair of lugs. A pivot pin is inserted through aligned apertures, with a spherical bearing therein, to secure the thrust strut26and yoke58pivotably together.

The yoke carrier block30further comprises a catcher lug64, the proximal end of which is attached to and extends from the underside of the block30at a substantially central position. The catcher lug64is planar and elongate, but could be cuboid, with an arcuate distal end65. It is sized to take the loads imparted through it and, as illustrated, is substantially the same width as the main portion44of the yoke carrier block30. The catcher lug64may comprise a chamfered join to the underside of the block30to relieve stresses. The distal end65defines an aperture67to receive an attachment pin therethrough as will be described more fully below. The attachment pin is, preferably, substantially aligned with the tongue42, and therefore is generally aligned parallel to the main axis208of the engine210. The catcher lug64is in the same axial plane as the engine attachment links34,36,38.

FIG. 6shows the yoke carrier block30and the central engine attachment link36mounted together, without the other components of the rear engine mounting arrangement22. The central link36has the form of three lobes66,68,70in generally triangular relation and so arranged, in use, that a first of the lobes66extends towards the engine210for attachment thereto. This first lobe66defines an aperture72. The first lobe66is received in a clevis arrangement on the engine casing and an attachment pin is inserted through aperture72in the lobe66and axially aligned apertures in the clevis to mount the central link36to the engine210. The second lobe68extends to one side of the first lobe66and also defines an aperture74for receiving an attachment pin in use. The second lobe68is received in a clevis defined in the main mount block32as will be described hereinafter. The third lobe70is arranged to be substantially radially outwardly of the first lobe66and to engage with the catcher lug64. It takes the form of a clevis having front and back lugs76,78, rather than the single lug of the first and second lobes66,68, the lugs76,78defining apertures80therethrough. The clevis spacing is so arranged that the distal end65of the catcher lug64can be received between the front and back lugs76,78of the third lobe70. Preferably, the interior of the clevis is profiled to complement the shape of the distal end65of the catcher lug64to seat it more securely. The apertures80align with the aperture67in the catcher lug64so that an attachment pin (not shown) can be received therethrough and connect the central engine attachment link36to the catcher lug64. During normal operation at least one of the apertures80,67is oversized to define a clearance around the attachment pin so that no load is transferred during normal operation. However, in the event of a failure of the attachment pins, first66or second lobes68in the normal load path the clearance in the third lobe70is taken up and engine loads are transferred through the catcher lug64instead.

The main mount block32can be seen more clearly inFIG. 7, and comprises a substantially rectangular block with a profiled rear edge33such that the axial length is greater at the lateral edges than in the centre of the block32, which reduces weight without compromising strength. The upper surface82of the main mount block32is substantially planar and arranged to abut the underside (radially inner surface) of the yoke carrier block30. Recessed portions84are provided which correspond to, and in use receive, the feet45of the yoke carrier block30. Attachment bolts50are received through the apertures46in the feet45and extend into corresponding apertures86in the recessed portions84to secure the yoke carrier block30to the main mount block32. The underside of the yoke carrier block30may abut the upper surface82of the main mount block32, providing additional rigidity. The yoke carrier block30provides a secondary bridging reinforcement across the centre of the main mount block32to prevent propagation of vertical cracks so as to prevent the main mount block32splitting in two.

There are apertures88(only some are indicated for clarity) provided through the main mount block32in a spaced row parallel to each lateral edge of the main mount block32. These apertures88are arranged to receive attachment bolts to secure the main mount block32to the pylon. Additional shear pin apertures90may be provided laterally inwardly of the apertures88to receive shear pins extending from the pylon to transfer loads from the engine210, through the main mount block32and thence to the pylon of the aircraft. These shear pin arrangements may be in additional to the shear pin apertures48provided in the yoke carrier block30for transferring normal engine loads. Alternatively, they may define a clearance around the corresponding shear pins so that they act as catcher shear pins (meaning no load is transferred in normal operation of the rear engine mounting arrangement22but an alternative load path is provided in the case of a failure of one or more of the shear pins in the normal load path).

The main mount block32includes a cutaway section92in its forward edge to accommodate, in use, the tongue42of the yoke carrier block30. On either lateral side of this cutaway section92there are catcher devises94comprising a pair of lugs as is well known in clevis design. Each catcher clevis94comprises an aperture96through its lugs. The catcher devises94are arranged to receive, in use, the balance yoke58between their lugs. There are apertures provided in the balance yoke58to align with the apertures96in the catcher devises94. A pivot pin (not shown) is inserted through each aperture arrangement to hold the components in pivotable relation. The apertures96through the catcher devises94are provided with a clearance gap around their pivot pins so that no load is transferred through them during normal operation of the rear engine mounting arrangement22.

In the event of a failure of the tongue42of the yoke carrier block30, the clearance around the pivot pins through the catcher devises94is taken up and engine loads are transferred from the balance yoke58, through the catcher devises94and thence to the aircraft pylon in the alternative load path.

A clevis98is defined between forward and rear walls100,102extending from the underside of the main mount block32towards the engine210(not shown). The forward and rear walls100,102define four apertures104,106,108,110symmetrically distributed across their lateral width, as can be seen more clearly in the exploded component view ofFIG. 8. These apertures104,106,108,110are arranged to receive a pivot pin (not shown) through each. A cutaway section112is located between the middle two apertures106,108. The cutaway section112is profiled to complement the central engine attachment link36, particularly the third lobe70thereof. The spacing of the forward and rear walls100,102is substantially the same as the front and back lugs76,78of the third lobe70of the central link36so that when correctly seated together, the front lug76and forward wall100, and the back lug78and rear wall102, are planar and present substantially continuous surfaces. The second lobe68of the central link36is arranged to seat within the clevis98formed by the forward and rear walls100,102so that the aperture74through the second lobe68aligns with axially extending apertures108through the walls100,102.

The port side engine attachment link38is elongate and comprises a pair of lobes, one at each end. The axial aperture40is defined through the lobe at the distal end of the link38, which is arranged to seat within a clevis arrangement on the engine casing and be secured thereto by a pin41as previously described. At the proximal end of the link38is another axial aperture114defined through the other lobe. The link38seats, in use, within the clevis98formed by the forward and rear walls100,102so that the axial aperture114through its proximal end aligns with the apertures110through the walls100,102. An attachment pin is inserted through the aligned apertures114,110to secure the port side engine attachment link38to the main mount block32.

The starboard side engine attachment link34is substantially L-shaped and oriented so that a first leg of the link34extends towards the engine210and the second leg of the link34extends parallel to the underside of the main mount block32and is located within the clevis98formed by the forward and rear walls100,102. At the distal end of the first leg of the link34is an axial aperture116, which engages with a clevis on the engine casing in similar manner to the distal end of the port side engine attachment link38. The starboard link34defines two further axial apertures118,120, one at the intersection of the first and second legs and the other at the distal end of the second leg. These apertures118,120align, respectively, with the apertures104,106through the forward and rear walls100,102. Preferably, at least one of the apertures in the aperture set106,120define a clearance around their attachment pin so that it transfers no loads during normal operation of the rear engine mounting arrangement22. Thus the normal load path from the engine210through the starboard link34and into the main mount block32is aligned through the centres of aperture116and aperture set104,118. In the case of a failure of the attachment pin through aperture set104,118the clearance is taken up through the apertures80,67in the third lobe70of the central engine attachment link36and the load transferred through the alternative load path comprising the central and port engine attachment links36,38.

The main mount block32further comprises a slot-shaped aperture122, as shown inFIG. 7, which extends radially through the centre of the block32. The slot-shaped aperture122is positioned and sized to receive the catcher lug64therethrough when the yoke carrier block30is secured to the main mount block32. Thus the catcher lug64passes through the slot-shaped aperture122, between the forward and rear walls100,102of the main mount block32and into the clevis formed by the front and rear lugs76,78of the third lobe70of the central engine attachment link36. There is thus a redundant, alternative load path from the engine210, through the central engine attachment link36and the catcher lug64directly into the yoke carrier block30and from thence, via the shear pins, into the aircraft pylon. Thus a crack propagating into the main mount block32does not affect the redundant load path since this transfers loads directly to the yoke carrier block30and thence to the pylon and bypasses the main mount block32.

The engine attachment links34,36,38can take any suitable form as known in the art that provides the required redundancy. This is particularly the case for the port and starboard side engine attachment links34,38. The connection arrangement also provides a quick and simple method of detecting a failure case without requiring removal of the rear engine mounting arrangement22. If the pivot pins located through the aperture pairs106,120;80,67are able to rotate freely (unloaded) there is no failure. If one or both of these pivot pins is loaded, and therefore unable to rotate freely, there has been a failure and the rear engine mounting arrangement22should be removed, dismantled and repaired or replaced.

During normal aircraft and engine operation the engine to airframe loads take a normal load path comprising the following components: main mount block32; starboard attachment link34via pins through the apertures116,104,118; central attachment link36via pins through apertures72,74in the first and second lobes66,68; and port attachment link38via pin41and the pin through apertures110,114.

There are three potential failure paths, dependent on which component fails. The first failure load path occurs when the central attachment link36fails. Thus the load path therethrough is replaced by loading of the pin through apertures106,120.

The second failure path occurs when the port attachment link38fails and therefore the load path through that is replaced by loading of the third lobe70of the central attachment link36and consequent loading of the catcher lug64and yoke carrier block30.

The third failure path occurs when the starboard attachment link34fails and therefore replaces loading of this component by loading of the central attachment link36, catcher lug64and yoke carrier block30as for the second failure path.

The various connections have primarily been described as clevis arrangements comprising a pair of lugs on one component and a single lug forming part of the other component to seat between the pair of lugs. However, the connections could equally be formed by providing the pair of lugs on the other component, or by providing a pair of lugs on each component forming an interleaving connection. Alternatively a single lug could be provided on each component. This reduces the weight of the components but removes some redundancy from the system. For example, the third lobe70of the central attachment link36could comprise a single lug and the catcher lug64could comprise a pair of lugs forming a clevis. In another example, the catcher devises94could comprise single lugs to be secured via pivot pins to the balance yoke58or the tongue42could comprise a single lug to be secured to the balance yoke58.

In another alternative arrangement, a different system of connection could be substituted for any of the clevis arrangements hereinbefore described. Although the engine mounting arrangement of the present invention has been described as a rear mounting arrangement, it could alternatively be a front engine mounting arrangement.

Although the connection means have been described as attachment pins, pivot pins or attachment bolts, any suitable form of connection means may be substituted with equal felicity in the present invention. Preferably, such means are reusable in the sense that they can be removed and reapplied to enable dismantling and rebuilding of the engine mounting arrangement22for maintenance etc. However, other alternatives such as riveting or adhesive bonding may be appropriate in other situations.

Preferably, two catcher devises94are provided to transfer the thrust loads from the engine210via the balance yoke58in the event of a failure of a component in the normal load path. This provides the advantage that any crack in the normal thrust load path that propagates to fail the tongue42or upper and lower lugs52,54cannot propagate to cause failure of the catcher devises94. However, other arrangements comprising a single, or more than two, catcher devises94are contemplated within the scope of the present invention.

Although the engine attachment links34,36,38have been described in one configuration, the links may be mirrored with equal felicity, such that the port engine attachment link38is substantially L-shaped and the starboard engine attachment link34is substantially elongate. Other arrangements may also be possible without deviating from the inventive concept herein described.