DEVICE FOR SEALING AN OPENING OF AN ENCLOSURE WALL FOR ACCESS TO A ROTARY SHAFT

The invention relates to a device for sealing an opening of an enclosure wall for access to a rotary shaft. The device is capable of being sealingly inserted in said opening and of being secured against the wall by securing elements. The device includes two cylindrical parts assembled slidably relative to one another, coaxially relative to the opening: a first part capable of being statically inserted in the opening, and a second part capable of being secured to the wall by the securing elements and subjected to the action of a resilient means provided between the parts and tending to axially separate the second part from the wall.

The present invention relates to a device for sealing an opening provided in a wall of an enclosure and permitting access, for inspection purposes, to a rotary shaft housed therein. It relates, in a particular though not exclusive application, to an enclosure of a gearbox of the type intended for driving accessory equipment in a turboshaft engine, such as a turbojet engine, the box comprising a shaft for the manual driving of the gears permitting rotation of the rotor during maintenance operations on the engine. The shaft being accessible from outside the box, a removable sealing device closes off the passage during operation when maintenance is not underway.

It is known that an aeronautic turboshaft engine, turbojet engine or turboprop engine comprises accessory or auxiliary equipment: pumps, alternators and the like, which are generally driven mechanically by drive shafts, in particular by the shaft of the HP rotor. According to a conventional use, the accessories are mounted on an equipment support. The support, which is commonly referred to by its English abbreviation AGB, standing for “accessory gear box”, comprises a box incorporating a mechanism formed of pinions with parallel axes, said pinions meshing with one another. The pinions are driven by an input shaft, which is itself connected by a kinematic chain to a shaft of the turboshaft engine. The accessories are thus mounted in parallel on the support while being coupled mechanically to the pinions by which they are driven. Lubrication of the pinions is provided by a circulation of oil inside the gearbox.

One of the pinions is not used for driving any accessory equipment; it serves mainly for the manual rotation of the rotor during inspection and servicing of the turboshaft engine. The AGB thus comprises an opening or passage giving access to a shaft carrying this pinion from the outside by a drive member. This opening is closed off, sealingly, by a sealing device when the engine is not being serviced.

The device generally comprises a single-piece cylindrical body provided, at its periphery, with O-ring seals engaging with the internal surface or periphery delimiting the opening in the wall. At the external exit of the opening, the body extends radially through a transverse collar forming the cover and which rests against the wall in order to be secured thereto by securing elements such as screws.

This device is removed when inspection of the engine requires access to this pinion and therefore to the shaft, with removal of the screws and axial extraction of the sealing device. After inspection of the shaft (with rotation thereof by the drive member of the crank type or the like), the sealing device is replaced by introducing the body with the sealing joints into the opening and then bolting the cover on the wall of the box, before the engine is started.

To ensure the safety of aeronautic machines, it is, however, essential to take into account the eventuality of the cover not being correctly reassembled or simply being forgotten. If this were to occur, during operation, the oil lubricating the mechanical members of the box would escape through the opening with the inevitable consequence of the engine coming to a stop.

In addition, in the case that concerns us, an internal oil pipe opens into the periphery of the opening in an external recess in the body, delimited by O-ring seals.

Thus, if inadvertently the sealing device is not installed, as soon as the engine is started, a low-pressure alarm in the oil circuit is triggered and then a large amount of the oil escapes to the outside through the pipe and then to the open air, which makes it possible to quickly identify the problem and to stop the engine before this results in disastrous consequences for the aircraft.

However, the cover of the sealing device may be installed in the opening without the screws, that is to say with the body and sealing joints engaged in the opening and the cover pressed against the wall. Thus the device may be held in place in the opening by friction forces between the O-ring seals and the internal periphery of the opening.

In this case, when the engine is operating on the ground at slow speed, it is improbable that the sealing device would be ejected, so that the low-pressure alarm does not detect anything. However, the risk of not detecting incorrect assembly, without the screws, is patent, and in particular before the takeoff or cruising phases with an engine under full load, and therefore an oil circuit pressurised to the maximum, undoubtedly causing ejection of the sealing device. Such a situation would cause the engine to stop at an inopportune moment and must therefore be absolutely avoided.

The case can also be envisaged where the screws are indeed mounted but insufficiently tightened, so that a clearance may appear between the cover of the body of the device and the wall of the enclosure, with oil quickly being lost when the engine is in operation.

The object of the present invention is to remedy these drawbacks by eliminating the problems related in particular to the absence of the securing elements after reassembly of the sealing device.

For this purpose, the device for sealing an opening provided in the wall of an enclosure and permitting access to a rotary shaft, said device being capable of being sealingly inserted in said opening and of being secured against the wall by securing elements, is characterised in that it comprises two cylindrical parts assembled slidably with respect to each other, coaxially relative to the opening, a first part capable of being statically inserted in the opening, and a second part capable of being secured to the wall by the securing elements and subjected to the action of a resilient means provided between the assembled parts and tending to axially separate the second part from the wall.

Thus, unlike a sealing device with a single-piece body, if the securing elements are absent, or even incompletely screwed, the second movable part will be pushed towards the outside of the opening in the wall, by the resilient means assisted in addition by the pressure of the oil when the engine is started. In this way, a space is created between the opening and the second part, giving rise to a significant leakage of oil, which will then inevitably be detected by the usual low-pressure alarm.

Consequently, such a sealing device does away with the aforementioned drawbacks and avoids the risk of operating the engine with a sealing device engaged and poorly secured (without the screws or with non-tightened screws).

In a preferred embodiment, the resilient means is a compression spring that rests on corresponding transverse faces of the first secured part and of the second movable part.

To mark the axially secured position of the first cylindrical part, said part is mounted in axial abutment in the opening.

For example, the first part has an external shoulder capable of resting against an internal shoulder forming an axial stop in said opening.

In particular, said first and second cylindrical parts carry around them sealing joints capable of engaging with the opening (the sealing joint on the first secured part engaging with the internal surface of the opening, and the sealing joint on the second movable part engaging with this internal surface or with the transverse face of the wall delimiting the entrance to the opening), said resilient means being provided in a peripheral space or chamber provided between the sealing joints of said parts. The oil-feed channel issuing from the box or from the enclosure opens into this space between the two sealing joints, when the device is mounted, to allow flow of oil and causes the leakage of oil out of the opening when the second movable part is pushed from the opening by the resilient means, as a result of the absence or insufficient screwing of the securing elements.

In a preferred embodiment, the second movable cylindrical part is mounted sealingly in part between the first secured part and the internal surface of the opening, and terminates in a radial collar forming a cover capable of being attached against the wall of the enclosure by the securing elements.

Advantageously, the second part is mounted around the first part and can be moved axially between an external shoulder of the first part and a stop part rigidly connected to the first part. Thus it remains connected to said first part and its axial movement, under the action of the resilient means, is moreover limited and sufficient to cause significant leakage.

For example, the stop part is screwed into a threaded passage in the first secured part and has an external transverse ledge forming an axial stop for the second movable part.

The invention also relates to a gearbox forming an enclosure supporting the accessory machines of a turboshaft engine, comprising an external wall in which there is provided an opening for access to a shaft for the manual driving of a rotor of the turboshaft engine or of an accessory machine, and a device for sealing said access opening.

Advantageously, said sealing device is as described above.

Referring toFIG. 1, a turboshaft engine1can be seen, in this case a twin spool bypass turbojet engine. It commonly comprises a high-pressure rotor2with successively, from upstream to downstream, a high-pressure compressor4, a combustion chamber5and a turbine6; said turbine is connected by a shaft3to the compressor that it drives. The low-pressure rotor7comprises the fan9upstream and the low-pressure compressor10upstream of the high-pressure rotor; the two are connected by a low-pressure shaft8to the turbine11downstream of the high-pressure turbine6.

An equipment support14, forming a box or enclosure, is mounted on the external collar of the fan casing or of the intermediate casing. This support contains the accessory equipment of the engine, such as the fuel and oil pumps and the electrical generators. This equipment is driven by pinions16housed in the box14, to which they are coupled by suitable connections. These pinions16mesh with one another and are themselves moved by a kinematic chain consisting of a plurality of transmission shafts17between the box14and the conical pinions15of an angle gearbox on the shaft3of the high-pressure rotor.

Referring toFIG. 2, this shows the end of a shaft18that is accessible from the outside of the box14through an opening19, which may for example be circular, provided in the wall20of the box, coaxially with the shaft.

The end of the shaft18is shaped so as to allow the engagement of a tool for the manual rotation of the pinions16(one of said pinions, which is not shown, being rigidly connected to the shaft18) of the shafts17and of the kinematic chain during inspections of the high-pressure rotor of the engine.

When said engine is not being maintained, the opening19is closed off by a plugging or sealing device21that is secured removably by securing elements22to the wall of the box.

The device21for sealing the opening that is provided in the wall20of the box14, for accessing the rotary shaft18, comprises, as shown inFIG. 2, two cylindrical main parts23and24assembled so as to slide with respect to each other with a resilient means25between them, tending to separate or move them axially away from each other.

In the application of the invention, the first part23is intended to engage with axial abutment in the first bore26of the opening19, being held therein statically, as will be seen subsequently. And the second part24is mounted in part around the first part and is intended to also engage in the opening but in a bore27with a greater diameter than the first bore, opening into the outside of the box, in order to be secured to the wall20by securing elements such as screws22.

In particular, the first cylindrical part23forming a seal comprises a transverse bottom28closing off the opening19and at the periphery29of which a groove30is provided for receiving an0-ring seal31. An external annular shoulder32is also provided at this periphery and is capable of coming into axial abutment against an internal annular shoulder33provided at the change in cross sections of the two bores26,27of the opening.

The transverse bottom28is extended, on the side opposite to the shaft, by an annular lateral wall34that comprises at its periphery a groove35for receiving an O-ring seal36.

Around the lateral wall34of the first part23, the annular lateral wall37of the second part24is mounted. To prevent said second part coming out with respect to the first part, a stop part38is provided. Said stop part is mounted by screwing in a central threaded hole39that is delimited by the lateral wall34of the first part until it rests, by an external transverse ledge40on the part38, against the corresponding transverse face41of the lateral wall34of the first part.

The transverse ledge40projects radially from said first part so that the second annular part24, previously mounted on the lateral wall of the first part, is pushed, under the action of the resilient means, such as a compression spring25, in axial abutment against the transverse ledge40of the part39, against which the external transverse face42of the second part24rests. The second part can thus slide between this stop position and another position, with the spring compressed, in the direction of an external transverse shoulder43on the lateral wall34, following the screwing of the screws, as will be seen below.

Moreover, at the external periphery of the lateral wall37of the second part there is a groove44in which an O-ring seal45is received, said O-ring seal being capable of engaging with the surface of the second bore27.

As for the compression spring25, this surrounds the parts23,24and rests firstly against a transverse face46provided in the periphery29of the bottom and from which there issues the shoulder32of the first part for abutment against the opening, and, secondly against a transverse face47of the annular wall37of the second part.

When the two parts of the sealing device21are assembled, the spring is situated between the joints31,45with the parts which have a tendency to separate spontaneously through the spring25, pushing the second part24against the transverse ledge40on the stop part38, the wall37of the second part engaging with the sealing joint36of the first part.

It is seen moreover that the annular wall37of the second part extends transversely through a collar or base49in which, distributed regularly, holes50are provided for passage of the threaded rods22A of the securing screws22.

The approach of the sealing device21thus assembled, with regard to the opening19in the box14, is shown inFIG. 2.

The wall20of the box comprises, around the opening19, threaded holes51for receiving the rods of the screws22and, conventionally, the oil-feed pipe or channel52firstly in communication with the inside of the box14in which the shaft18is situated and secondly opening into the bore27as shown inFIGS. 2 to 6.

The mounting itself of the device21in the opening19does not raise any difficulties.

As shown inFIG. 3, the first cylindrical part23of the device is engaged in the opening with the O-ring seal31, at the external periphery29of the bottom, in contact with the surface delimiting the first bore26, an engagement that continues until the external shoulder32of the first part comes into contact against the internal shoulder33of the opening.

Then the clamping screws22are mounted for securing the collar49of the second cylindrical part24against the external transverse face54of the wall, the rods22A being screwed into the threaded holes51in the wall until the heads22B of the screws come into contact against the collar, which itself is against the wall.

Simultaneously, as the first part23is in axial abutment against the box, the screwing has caused the second part24to slide towards the first part with compression of the spring25, and the wall37to approach the shoulder43of the first axially secured part. During the sliding, the external sealing joint45on the movable second part24has come into contact with the surface delimiting the second bore27, while the wall37of the second annular part is still in contact with the sealing joint36of the lateral wall34of the first part23. The second part24is thus distant from the transverse ledge40forming the stop for the part38. In a variant embodiment that is not shown, it can be envisaged arranging the sealing joint45between the collar49and the transverse face54of the wall. In this case, the O-ring seal inFIG. 3will be replaced by a flat seal, the sealing being provided by the complete tightening of the screws22.

The internal chamber or space53in which the spring25is situated and which is delimited by the transverse faces46and47of the parts and the surface of the bore27is in communication with the oil pipe52, while being made impervious vis-à-vis the outside by the various sealing joints.

In the representation shown inFIG. 3, the opening19is suitably closed off by the sealing device21by the O-ring seals31,36,45, so that the engine can operate in complete safety. The low-pressure alarm remains inactive since it does not detect any drop in pressure in the box.

The shaft is thus isolated sealingly from the outside.

It is now supposed that, after removal of the sealing device21and inspection of the shaft18and the associated mechanisms, the device is returned to the opening19in the position shown inFIG. 4. The device is certainly engaged in the opening with the sealing joint31of the first part in contact with the internal surface of the bore26, but the second part remains outside the opening as a result of the action of the compression spring.

Such a position occurs when the clamping screws22are not reset place in due to an oversight by the operator.

Advantageously, the design of the device21in two parts that are axially movable through a resilient means makes it possible to hold the second part outside and at a distance from the opening19, creating sufficient space between the wall of the second part24and the entrance to the opening19(bore27). This is because, through the action of the spring25, the second part24is spontaneously pushed against the ledge40of the part38.

In this way, as soon as the engine is started, a massive leakage of oil occurs as a result of the oil emerging from the channel32in order to go into the chamber53and escape out of the box14by way of the opening through the annular space created, as shown by the arrow F.

This total loss of seal results in a drop in pressure in the box, which is immediately detected by the low-pressure alarm.

The second part24is held outwards under the effect of the spring and the internal pressure of the oil escaping through the channel. The device21thus perfectly fulfils its safety role by establishing a quickly detectable significant oil leakage.

In the view inFIG. 5, the mounting of the screws22in the threaded holes51is effective but the complete locking or screwing of said screws is not achieved. A very small space appears between the collar49of the movable part24and the transverse face54of the wall20of the box.

The axial movement of the second part24by the heads22B of the screws has caused the compression of the spring25with the wall37of the part24moving towards the shoulder43of the secured part23, and has allowed the sealing joint45to be placed in the second bore27, so as to ensure a seal vis-à-vis the outside. The oil (arrow F) leaving the channel52cannot leak towards the outside of the opening through the device21because of the presence of the sealing joints36and45.

To avoid an incomplete reassembling of the screws of this type, it is necessary to use screw locking devices55introduced into the bottom of the threaded holes51of the screws so that, once the screws are tightened by hand, that is to say before the threaded rods22A engage with the locking devices55, the sealing joint45of the second movable part24of the device is still at a distance from the entrance to the second bore27. The purpose of these screw locking devices is to prevent the second part approaching and therefore to prevent the impermeability of the sealing joint that is associated with the opening, other than through the use of a specific tightening tool guaranteeing the tightening of the screws in the locking devices and the correct mounting of the sealing device with impermeability.

Thus it is possible to determine or calculate the axial position of the screw locking devices with respect to the length of the screws tightened manually so that said screws provide the correct tightening with sealing of the device only after having been screwed by means of a specific tool. The second part24(collar49) cannot therefore be moved close to the wall20(transverse face54) other than with the use of the specific tool, which provides a guarantee of tightening of the screws.

As shown inFIG. 6, the screw locking devices55are rings housed in the bottom of the threaded holes and produced from a suitable material for engagement of the threaded rods of the screws by a tightening tool.

In this drawing, the screws22have been mounted by hand in the threaded holes51in the wall as far as the level of the rings55(coming into abutment against said rings), where only the use of a tool makes it possible to continue the tightening of the screws to the required torque with fitting of the sealing joint45. If the operator forgets to tighten the screws by means of the tool and leaves the sealing device1in the position shown, the sealing joint45of the movable part24is still axially distant from the entrance to the bore27, with the part subjected to the action of the spring25tending to move it away outwards, in this case against the heads22B of the screws.

Thus, if the engine is started, a significant leakage of oil issuing from the channel52and passing through the chamber53(and therefore the opening) occurs immediately towards the outside of the box in the direction of the arrow F inFIG. 6. This leakage simultaneously causes a drop in pressure in the box, which is detected by the low-pressure alarm. Here, too, the leakage created by the sealing device of the invention means that in the event of the incorrect tightening of the screws having been overlooked, it is inevitable that said incorrect tightening will be detected. Only the final tightening of the screws in the rings with a suitable tool will ensure that the device in the opening is correctly sealed, as shown inFIG. 3.

Unlike the conventional, static, single-piece devices, the device according to the invention has two parts, one of which is made movable with a piston effect (by means of the spring that is assisted by the oil pressure), when the operator forgets to replace the screws or replaces them incompletely, creating a quickly detectable significant leakage.