| Title of Invention | "CASING COVER IN A JET ENGINE" |
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| Abstract | Casing cover (10) in a jet engine, comprising two coaxial shells (36, 38) arranged one inaide uhe other and joiiied fixedly by radial envelopes (40) incdde which extend radial arma (2€) of the casing, the cover being faatened at its downstream end to an element of the casing and bearing axially at its upstream end on another element of the casing, and the cover having, in the free state, an axial dimension (D) of less than the axial distance (L) between the points where its downstream end is fastened to the casing and the points where its upstream end bears axially on the casing, ana beiny Leusiujiifcid ajtially when it is mounted on and "fastcncd to the oacing. |
| Full Text | Casing covsr in a jet engine .i-'- '• Background of the invention and descriptibn of tlie prior art The present invenţiei* relatee to a casing cover such as an fixhaiist crasing cover in a jet engine , this cover comprisincf two coaxial shells arranged one inside the other and joined fixedly by radial envelopes inside which extend radial arms of the caeing, This type of cover ia mounted around a jet engine bearing support and thermally protects the exhaust casing from the stream of hoţ gas whiuh ux j,yin However, thes thermal expansion of the cover, which ia 25 greater than that of the casing, precludes the upstream end of the cover from bearing on the casing, at least during the transient phases between the idling mode and the full-power operation of the jet engine. The cover i s thus mounted in cantilever fashion on the bearing support via its downstream end, and is subjected to considerable vibration stresses which may result in the appearance of £issures or cracks, One eolution to this probiotn would consist in mndifying the geometry of the cover and/or in reinforcing it by nieans of stiffeners. However, this solution is not satisfactory since it is costly and leads to an increase in the mass of the cover, this being a disadvantage in the aeronautical industry. Suiranary of the invention The object of the invention is in particular to provide a simple, effective and economic solution to theee probleme. To this end, the invention provides a casing cover in a jet engine, coraprising two coaxial ehells arranged one insids the other and joined fixedly by radial envelopes inside which extend radial arms of the casing, the cover being faetened at its downstream end to an element of. the caeing and bearing axially at its upstream end on another element of the caying, wherein the cover- h^g, in the free state/ an axial dimeneion of less than tho axial distante between t>iR jirtinl-.s whftrc* •dts downstream end is fastened to the casinq and the points where iţa upstream end bears axially on the casing, and ie tensioned axially when i t ia mounted on and fastened to the casing. The axial tensioning of the cover when ic is mounted on the casing makes it possible to corapeiisaLe JTux- Liiy deviation between its axial thermal cxpansion and t ha 25 axial thermal expansion o£ the c?aeing in order- to kw^n its upstream end bearing axially on the casing during the operation of the jet engine, thereby preventing the cover f rom being subjected to consideratale vibration stresses. According to a feature of the invention, the difference between the axial dimeasion of the cover, in the free state, and the axial distante bfttween the poinfca where iţe downetream end is fastened and the pointg where its upstream end beara axially is substantîally equal to the maximum value of the deviation between the axial thermal expansion of the cover and the axial thermal expansion of the casing during the operation of the jet engine. Thus, the upstream end of the cover alwaya remains bearing axially or radially on the casing whatever the operating mode of the jet engine, this being sufficisnt to prevent the ' appearance of 'vibrat ion stresses in the cover. Thie difference ie, for example, approximately l to 1.2 in r>n part-, i rai la r The cover is, for example, fastened at its downstream end to a flange of a bearing eupport by means of bolta and comprises, at its upstream end, an outwardly oriented radial lip, this radial lip being situated to the inside and' upstream of a radial lip formed at the upstream end of a cylindrical element ui ih« uawing, the radial lip of the upstK-eain end of the covcr bearing axially on the radial lip of the easing element wben ••the cover ±s mounted on the casing. The radial lip of the cover is advantageously formâd on an outer shell of the cover which, as a result of thermal expansion, can bear radially on the casing element during the operation of the jet engine, thereby mafcing it possible to keep the upstream end of the co-ver beating axially and/or radially on the caaing. When the cover has reached its maximum axial thermal expansion in relation to that of the casing, the radial lip of the cover is flush with the radial lip of the casing and the shell of the cover bears radially on the casing element. The upstream end of the cover thue always remains bearing on the casing whâtever the operating mode of the jet engine. The invention also relates to a jet engine which nompr-i fifts ah l ea st one casing cover, in particular an exhaust casinq cover, as described above. Brief description of the drawings The invention will be better understood and other details, features and advantages of the presant invention will become apparent on reading the description given below by way of nonlimiting example and with rafsrence to the appendcd drawings, in which; figure l is a sahamatio ha.l£-view in axial section. of an exhaust casing cover according to the invention-;' figure 2 ia a view on an enlarged scale of the means for faster.ing the cover shown in figure 1; figure 3 is a view on an enlarged scale of the rneans for the axial bearing of the cover shown in figure l . D e B cript iora o£ Ulie p£ti£eirzrţ!d. Figure l shows a cover 10 of an exhanat-. «ssing 1 2 nf a •jet engine, which is mounted around a bearinq support 14 and which makes it possible to thermally protect the casing 12 front a stream of hoţ gas 16 originating f rom the combustion chamber (not shown) and f rom the turbine (not shown) of the jet engine. The bearing support 14 comprisee a BubwL.ttuLici.lly frustoconical wall 10 extendiug down.atrcam toward the axis 20 of the jet engine and bearing an outer race 9.1 of a bearing (not shown) for centering and guiding a shaft of the jet engine. The wall 18 of the bearing support comprises, at its downstrsam end, a flange 22 for fastening to bearing lubrication means 23 and is connected, at iţa upstream end, to an upstream end of a substantially cylindrical wall 24. The exha.ua t gaaing 12 corapi-iscs nine radial arma 2S which are fastened at their internai ends to the cylindrical wall 24 af the bearing support by means of radial boit s 25 and at their externai ends to a cylindrical element 28 of the casing by means of radial bolts 27. Each radial arm 26 comprises an internai cavity 30 for the circulation of cooling air originating frorn a supply enclosure 32, radially 'externai to "trie casing element 28, and diacharged partly into au euulvwujffcj 34 which is radially internai to the wall 24 of thc bearing eupport and which is deiimited by this wall 24 and the fruetoconical wall 18 of the bearing eupport.-. " The cover 10 is in one piece and comprises two coaxial shells 36 and 38 which-extend one inside the other and which are connected by nine radial envelopee 40 inside which extend the radial arms 26. The internai shell 36 extends outside and at a distance f rom the wall 24 o£ Llie beciL'iny auppui'L uud Lhe eAL«iiieil shell 38 extends insidc and at a diatancc from thc aacing element 28. •Each envelope 40 has an axially profiled shape and the radial arm 26 extends inside an upstream portion of the envelope and a.t a diatance therefrom. The radial arm 26 compriaes, upstream, holes 42 which open out toward the upsfcream end portion of the envelope 40, which itself compi'isea, duwusLrecmi, holes 44 which are oricntcd in thc downatjroatn direction and which open out into the flow pat.h of hh«* gas stream. The air which circulates in the internai cavity 30 of the radial arm 26 is partly discharged through the holes 42 and projected onto the upstream end portion of the envelope so that it can be cooled. This air then flowa around the radial arm 26 in the envelope 40 and is injected into the gas streara 16 via the hoies 44. During the operation of the jet enginc, thc cover 10 in exposed to high tempera ture a which may r^ar:h approximately 700 to 8006C, and the air which circulates in the cavities 30 of the radial arms 26 has a nemperature of approximately 300 to 40QOC, thus resulting in considerable differential thermal expansions between the cover and the casing. The downstream end of the cover 10 îs fastened to the bearing support 14 and its upstream end bears on the casing element y 8 so that the cover maintains a freedotn of axial expaiision during operat ion. In the exainpl & represerited, ths Internai shell 36 --of the cover comprises at its downstream end a radially internai annular flange 50 whicii îs clamped by means of bolts 55 between an" annular flange 52, situated upstream, of the wall 24 of the bearing support and the flanges 51, situated downstream, of an annular covering 53 and 54 of an exhaust cone 56 (figure 2), the exhaust cone extendlng in the downstream direct ion cu«3 beiny aligned wibh the internai shell DC of the covcr . •The upstream end of the internai shell 36 is fastened by riveting to elastically deformable means 58 which are borne by the bearing support 14 and allow differential thermal expansions between the cover and the bearing support. The externai shell 3 a of the cover comprîses, in the vicinity of its upstream end, a radially annular lip 60 which haa iţe downetream face axially on the upatream face of an externai annular lip 62 formed at the upatream end of the casing element 28 (figure 3) , The radial dimension of the lip 60 is greater than the radial distance between the externai shell 38 and the cylindrical element 28. The downstreara end of the casing element 28 comprlses elsiBli applied to the flange 52 of the bearing support, which is egual to the axial distance L between the downstream face of the flange 52 to which the flange bu'~'is applied aiid Llie upsLxecim bectiiag IctctJ uC Lhe radial lip 62 of the eaaing element 28. During o£>eration, the cover expands axially .and radially and the radial lip 60 of iţe externai shell moves axially in the upstream direction in relation to its position in the free state, and thus no longer bears axially on the radial lip 62 of the caeing element, a situation which may căuşe considerable vibration stresses in the cover and result in damage thereto. The invention makes It possihle to solve this problem •by virtue of a cover whose aforementioned axial dimension D is less than the axial distance L, thereby requiring the cover to be placed under axial tension so that it can be mounted on the bearing support. The ditterence between the axial dimension u and the eutid.1 diaLcLiiuw L ly yub»Lc*uL4.iy.lly equal to the maximum deviation botwcon bhc axial thermal expaneiora of the rtciveT 3nd tbe s-sc-isl hheTmsl rtxpansi on of the casing during the operat ion of the jet engine. When the axial thermal expansion of the cover becomes equal to this difference, the bearing face of the radial lip 60 is flush with the radial lip 62 of the casing element, but the radial thermal expaneion of the cover i3 then such that it bears radially on the casing element 28, thi-s beiiiy Butlicienl: Lo preverit the appeax-tm(,:« of -vibratioii strcaoca in the cover. The difference between the dimension D and the distance L is approximately l to 1.2 millimătars in one exemplary embodiment. The radial distance R between the externai shell 38 and the casing element 28 îs advantageously equal to or slightly less than the maximum radial thermal"expansion of the cover so that the cover is kept bearing axially and/or radially on the casing element during operation (figura 3). The cover 10 can be mounted on the exhaust casing 12 in the following way, for example with a vertical arrangement of the componente: with the casing being placed to bear on a aupport, tooling is placed to bear on the upstream portion of the bearir.g support and a torce is applied thereto along the axis of the casing ssu aa to shilt the downstreata pusiLluii of Lhe downatiream flange 50 of the cover ovcr a diotancc o£ l to 1.2 mm. While maintaininrj the position, tbe sc-.rewg •25 and 27 for fastening hhe arms t o the outer casing shell and to the bearing support are tightened. CLAIMS 1. A casing cover in a jet'engine, comprising two coaxial shells arranged one inside the other and joined fixedly by radial envelopes inside which extend radial arms of the casing, the cover being fastened at its downstream end to an element of the casing and bearihg axially at its upstream end on another element of the casing, wherein ths cover has, in the free state, an axial dimension of less than the axial distance between the points where îts downstream end is fastened to the casing and the points where its upstream end bears axially on the caaing, and is tensioned axially when it ia uiwuiiLfcsd yii aud fasLeiiyu Iv llie casiiig. 2. Thp nsR-irig p.ff\r&-r flR ni a-ifiiftH in rslaim l, wherein •the difference between the axial dimension of the cover, in the free state, and the axial distance between the points where its downstream end is fastened and the points where its upstream end bears axially is substantially egual to the maximum deviation between the axial thermal expansion of the cover and the axial thermal expansion ol the casing duriuy L-he operation of the jet engine. 3. The caaing cover as claimed in claim 2, wherein the difference is approximately l to 1,2 millimeters. 4 . The casing cover as claimed in one of the preceding claims, wherein the cover is fastened at its downstream end to a flange of a bearing support by means of bolts and connprises, at its upstream end, tui outwardly oriented radial lip, thie radial lip bcing situated to the inside and upstreatn of a radial lip formed at the upstream end of an element of the casing, the radial lip of the upstream end of the cover bearing axially on the radial lip of the casing ehell whân the cover is mounted on the casing. 5. The caaing cover as claimed in claim 4, whereiri the radial lip of the upstream end of the cover is formed on an outer shell of 'the cover wifich, as a result of thermal expansion, can bear radially on the casing element during the operation of the jet eagine. 6. A jet: engine which comprises at least on'e cas-ihg cover, in particular an exhaust casing cover, as claimed in one of the preeeding claims. |
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| Patent Number | 269968 | |||||||||||||||
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| Indian Patent Application Number | 558/DEL/2007 | |||||||||||||||
| PG Journal Number | 48/2015 | |||||||||||||||
| Publication Date | 27-Nov-2015 | |||||||||||||||
| Grant Date | 20-Nov-2015 | |||||||||||||||
| Date of Filing | 15-Mar-2007 | |||||||||||||||
| Name of Patentee | SNECMA | |||||||||||||||
| Applicant Address | 2 BOULEVARD DU GENERAL MARTIAL VALIN, 75015 PARIS, FRANCE | |||||||||||||||
Inventors:
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| PCT International Classification Number | F01D11/02; F01D5/14; F01D11/12 | |||||||||||||||
| PCT International Application Number | N/A | |||||||||||||||
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