RU2792983C2 - Method and tool for recovery of damaged threads - Google Patents

Abstract

FIELD: repair work.

SUBSTANCE: invention can be used, for example, to restore damaged threads of connecting assemblies of a transmission casing of an aircraft with a vertical take-off and landing path. The tool contains the first bracket in form of a plate with a protrusion and has a threaded through hole, at least two second brackets pivotally connected to the first bracket and having support surfaces for holding with the corresponding connecting elements, a centring pin. At the same time, it is equipped with two bushings with corresponding threads. A method for restoring a damaged thread using the mentioned tool is also described.

EFFECT: reduction of time and production costs for restoration of a damaged thread due to the possibility of performing work without dismantling the transmission from the aircraft.

2 cl, 17 dwg

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority over European Patent Application No. 18201060.3, filed 10/17/2018, the entire contents of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

The present invention relates to a tool for repairing damaged threads.

The present invention also relates to a method for repairing damaged threads.

In particular, a damaged thread to be repaired is inside the main transmission housing of a vertical takeoff and landing aircraft such as a helicopter or tiltrotor.

BACKGROUND OF THE INVENTION

Helicopters are known that contain one or more turbines, a main rotor and a main transmission that transmits movement from the turbines to the main rotor.

The main transmission is housed within a housing that rotatably supports one or more rotating elements, such as a main rotor drive shaft.

The casing is connected to the shell fixed at an angle to prevent rotation of the casing as a result of transmission operation.

As an example, the shroud may be made of an aluminum or magnesium alloy and the shroud contains a fan power take-off for cooling the transmission oil, a hydraulic pump, a compressor, or any other ancillary equipment.

EP-B-2975306, addressed to the same Applicant, describes the use of threaded studs to releasably connect a shell and shell.

In particular, threaded studs essentially comprise:

- the first thread, which is screwed to the first casing nut;

- a second thread, which is fastened with a screw connection to a fixing element, for example, a nut; And

- a section without a thread, which is located between the first and second threads and passes through the shell body with a certain gap.

In particular, a tightening torque is applied to the nut in order to connect the casing and the sheath. Similarly, a loosening torque is applied to the nut if it is required to remove the connection between the shell and the shell.

Due to the friction between the thread of the nut and the second thread, such screwing and unscrewing torques can determine, in addition to the rotation of the nut, an undesired rotation of the threaded rod relative to the casing.

It is known to use a toothed washer made of cadmium steel to avoid this undesirable rotation of the threaded rod.

More precisely, the toothed washer is placed inside the casing body and contains the first radially inner surface and the second radially outer surface, which are mutually opposite and have teeth. The first radially inner surface of the washer engages with the teeth of the threaded stud. The second radially outer surface of the washer creates serrations on the inner surface of the case body due to the fact that the toothed washer is made of steel, a material harder than the aluminum or magnesium that makes up the case.

Thus, rotation of the threaded stud relative to the housing is prevented by friction generated between the second surface of the washer and the bearing surface of the housing and between the first surface of the washer and the teeth of the threaded stud.

Each threaded stud can be removed with a special tool that removes the washer, allowing the threaded stud to be removed.

Removing the threaded studs may damage the threads on the casing nut.

In these circumstances, it is required:

- remove the entire transmission from the helicopter;

- send it to an authorized repair center for thread restoration;

- completely disassemble the transmission in order to remove gears, bearings, shafts, etc. from the casing with damaged threads;

- install a casing with a damaged thread on a special machine available in the repair center;

- repair threads, reassemble transmission with gears, bearings, shafts, etc. and send it to the location of the helicopter; And

- install the transmission with the repaired thread on the helicopter.

This procedure is associated with significant costs, both because of the need to transport the transmission to the repair center, and because the operation of the helicopter is suspended for a long time.

Therefore, there is a need in the art to reduce as much as possible the cost and time required to repair damaged casing threads.

US 3,148,562 discloses a method and tool for repairing damaged threads according to the preamble of claims 1 and 9, respectively.

DE-U-9101752 discloses a universal centering device comprising three mutually movable elements fixed with a countersunk screw.

DISCLOSURE OF THE INVENTION

The objective of the present invention is to provide a method for repairing damaged threads of the transmission casing of an aircraft with a vertical takeoff and landing according to paragraph 1 of the claims.

The present invention also relates to a tool for repairing a damaged transmission thread of a VTOL aircraft according to claim 9.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, the preferred embodiment is described below as a non-limiting example and with reference to the accompanying drawings, in which:

- in Fig. 1 is a perspective view of a transmission housing and a VTOL aircraft for which a tool in accordance with the present invention can be used;

- in Fig. 2 and 3 show a greatly enlarged housing of the transmission unit shown in FIG. 1, with damaged threads, respectively connected and disconnected from the stud;

- In FIG. 4 is a perspective view of a tool for repairing damaged transmission case threads of a VTOL aircraft manufactured in accordance with the requirements of the present invention;

- in Fig. 5 is a plan view of the recovery tool shown in FIG. 4, while attaching the tool to the thread to be repaired;

- in Fig. 6 is a sectional view at a greatly enlarged scale of the repair tool shown in FIG. 4 and 5, at the stage of attachment to the thread to be repaired;

- in Fig. 7 shows a greatly enlarged centering step according to the recovery method according to the present invention;

- in Fig. 8 shows, on a greatly enlarged scale, the step of removing a damaged thread according to the restoration method according to the present invention;

- in Fig. 9-12 show, on a greatly enlarged scale, the corresponding successive steps in the manufacture of a new thread of larger diameter, according to the recovery method in accordance with the present invention;

- in Fig. 13-15 show, on a greatly enlarged scale, the respective successive steps in the application of the threaded insert according to the recovery method of the present invention;

- in Fig. 16 shows, at a greatly enlarged scale, a repaired thread made according to the repair process of the present invention; And

- in Fig. 17 is a further enlarged view of some of the details of FIG. 16.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, numeral 1 denotes the main transmission of an aircraft with a vertical take-off and landing (not shown), in particular a helicopter or tiltrotor.

Transmission 1 in the case shown is suitable for connecting one or more turbines and a main rotor drive shaft (not shown).

Transmission 1 is shown in Fig. 1 only by means of a casing 2 which supports a drive shaft rotatably about axis A.

In FIG. 1 position 3 additionally indicates the power take-off shaft for cooling the lubricating fluid, in particular oil, for cooling the transmission 1.

The power take-off shaft 3 shown in FIG. 1 is bounded by a shell 4 which is fixed in the angular direction with respect to the axis A.

The casing 2 and the shell 4 are connected by means of a plurality of connecting nodes 5 located between the superimposed peripheral edges 13, 14 of the casing 2 and the shell 4.

It should be noted that the shell 4 does not support the transmission 1 in any way. In other words, as shown in FIG. 1, even after the shell 4 is removed, the transmission 1 is fully supported by the shell 2 and is placed on the shell 2.

In the case shown, the casing 2 is made of aluminum or magnesium.

The casing 2 and the shell 4 are connected by means of a plurality of connecting nodes 5, equidistant in the angular direction relative to the axis A.

The following description refers to a single connector 5, since all connectors 5 are identical.

More specifically, the connecting assembly 5 essentially comprises threaded studs 6a, 6b extending along axis B, a nut 7 and a retaining ring (not shown).

Hairpin 6a, 6b essentially contains (Fig. 1-4):

- thread 9, which is screwed to the thread 8, in particular to the nut formed by the hole 23a, 23b, made in the casing 2;

- thread 10 (shown only schematically), on which the nut 7 is screwed with a given tightening torque; And

- a section 11 without thread, located in the axial direction between the threads 9, 10 and engaged with a radial clearance with the support surface 12 formed by the shell 4, and located coaxially with the corresponding hole 23a, 23b of the casing 2.

The stud 6a, 6b additionally contains not shown teeth located between the thread 10 and section 11.

In FIG. 2 and 3, reference numeral 15 indicates the damaged area of thread 8 to be repaired, defined by hole 23a.

In the following description, the thread 8 to be repaired is referred to as the damaged thread 8.

In particular, below in the present description, the stud 6a is associated with a hole 23a with a corresponding damaged thread 8, and the studs 23b are associated with holes 23b located on the respective opposite parts of the hole 23a and directly adjacent to the hole 23a.

In FIG. 4-16, the tool for repairing damaged threads 8 is indicated by the number 20.

Tool 20 contains (FIGS. 4 and 5):

- a bracket 21 located in the hole 23a of the casing 2, containing a hole 24 (Fig. 6-16), which receives a drill 25 and a male element 26 adapted to engage with a damaged thread 8 and suitable for centering on the hole 23a; And

- two brackets 22 pivotally connected to the bracket 21 and having respective bearing surfaces 19 held by respective pins 6a, 6b entering the respective holes 23b of the casing 2.

In the example shown, hole 24 extends along axis C. Holes 23b are also located on opposite sides of hole 23a and directly adjacent to hole 23a.

In more detail, the tool 20 is applied to the hole 23a of the housing 2 having a damaged thread 8 to be repaired in the configuration shown in FIG. 1, namely after unscrewing the nuts 7 and removing the shell 4 from the casing 2, while the transmission 1 is supported and placed inside the casing 2.

Bracket 21 contains (Fig. 4 and 5):

- a plate 27 forming a surface 28 adapted to fit against the peripheral edge 13 of the casing 2 at the opening 23a; And

- an annular protrusion 29 protruding from the plate 27 on the opposite side of the surface 28.

The protrusion 29 protrudes coaxially with the axis C. The axis C coincides with the axis B of the hole 23a when the tool 20 is installed in the hole 23a (FIGS. 4-16).

Hole 24 includes in particular:

a nut 30 located axially on the side of the hole 23a when the tool 20 is installed in the hole 23a; And

- section 39, which has no thread and is located in the axial direction opposite the nut 30.

The protrusion 29 additionally has an annular shoulder 31, limiting the section 39 and having an annular support surface 32.

The bearing surface 32 defines the axial end of the protrusion 29 located on the opposite side of the plate 27.

Tool 20 additionally includes:

- a centering pin 33 (FIG. 7) used in the step of centering the axis C of the protrusion 29 on the axis B of the hole 23a;

- a sleeve 40 (FIG. 8) having an opening 41 into which a drill bit 25 adapted to remove a damaged thread 8 can enter; And

- a sleeve 50 (FIGS. 9-12) having a hollow hole 51 into which a male element 26 can enter to create a new thread 16 with a diameter greater than the diameter of the damaged thread 8.

In more detail, pin 33 has a corresponding E axis.

Axis E coincides with axes B, C when tool 20 is centered in hole 23a and pin 33 is connected to bracket 21.

Pin 33 contains along the axis E:

- a cover 34 adapted to abut the support surface 32 during the centering step of the tool 20;

- section 42 without thread, adapted to enter the section 39 of the hole 24 at the stage of centering the tool 20;

a portion 35 having a screw 37 to be screwed onto a nut 30 in the step of centering the tool 20;

- connecting section 36, which in this case has the shape of a truncated cone; And

- a cylindrical section 38 without thread, adapted to fit into the hole 23a.

As shown in FIG. 8, the sleeve 40 is tubular along the axis F and contains a thread 44 that can be screwed onto the nut 30 of the bracket 21.

The F axis coincides with the B, C axes when the tool 20 is installed in the hole 23a and the sleeve 40 is connected to the bracket 21.

The inner diameter of the hole 41 is greater than the diameter of the drill 25, which allows the latter to be inserted into the hole 41 radially.

As shown in FIG. 9-12, sleeve 50 is tubular and bore 51 is G-axis.

The G axis coincides with the B, C axes when the tool 20 is centered in the hole 23a and the sleeve 50 is connected to the bracket 21.

Sleeve 50 additionally contains:

- screw 53, which can be screwed onto the nut 30 of the bracket 21; And

- a nut 54 onto which the thread 55 of the male element 26 can be screwed.

As shown in FIG. 13-15, tool 20 further comprises:

- elongated installation device 60; And

- a metal insert 61 having the claimed thread 62, also known as Heli-coil.

In more detail, the setting tool 60 is in the form of a rod having a bent end 63 that engages with the insert 61.

Insert 61 is in the form of a helical spring.

In step 8 of repairing the damaged thread, the setting tool 60 and the insert 61 are inserted coaxially with axes B, C mutually coinciding inside the hole 24 so that the insert 61 is screwed into the new thread 16.

Then (FIG. 15) the setting tool 60 is removed and the inner diameter of the insert 61 defines the restored thread 8'.

The operation of tool 20 is described below.

In case of damage to the thread 8 formed by the hole 23a, the nuts 7 of the studs 6a, 6b are unscrewed and the shell 4 is removed from the casing 2, while the transmission 1 is supported and placed inside the casing 2 (figure 1).

Below tool 20 is applied to casing 2.

In particular, the bracket 21 is located in the hole 23a having a damaged thread 8, and the brackets 22 are located in the respective holes 23b immediately adjacent to the hole 23a.

The brackets 22 are arranged so that the respective bearing surfaces 19 engage with the pins 6 screwed into the respective holes 23b.

Restoration of damaged thread 8 of transmission 1 involves the following steps:

- centering the tool 20 in the hole 23a (Fig. 7);

- insertion of drill 25 inside tool 20 and removal of damaged thread 8 with drill 25 (Fig. 8);

- insertion of the male element 26 inside the tool 20 and the creation of a new thread 16 inside the hole 23a, having a diameter greater than the diameter of the mentioned damaged thread 8 (Fig. 9-12); And

- insertion of the insert 61 inside the tool 20 in such a way that said insert 61 engages with the hole 23a without damaged thread 8, screwing into the new thread 16 and making up the restored thread 8';

- keeping the specified transmission 1 in the installed state on the helicopter 1 during the above steps.

In more detail, as shown in FIG. 7, the pin 33 is inserted into the hole 23a of the bracket 21 so that the axis C of the hole 24 of the bracket 21 is aligned with the axis B of the hole 23a of the casing 2. Thus, the bracket 21 is "centered" in the hole 23a with the damaged thread 8.

The screw 37 is screwed onto the nut 30 of the bracket 21 so as to insert the section 38 inside the hole 23a and so that the cover 34 abuts against the surface 32.

At the end of this operation, the axis C of the hole 24 of the arm 21 coincides with the axis B of the hole 23a, i.e. the tool 20 is in a "centered" position on the hole 23a.

The nuts 7 are then screwed onto the portions 11 of the aforementioned studs 6b adjacent to the hole 23a, so as to fix the tool 20 in a "centered" position on the hole 23a.

Now (FIG. 8) the sleeve 40 is inserted into the hole 24. In particular, the thread 44 of the sleeve 40 is screwed onto the nut 30 of the bracket 21. At the end of this operation, the axis F of the sleeve 40 coincides with the axes C, B of the respective holes 24, 23a.

Then the drill 25 is inserted into the hole 41 of the sleeve 40 until the corresponding tip 70 enters the hole 23a of the casing 2 and is on the damaged area 15 of the damaged thread 8.

Actuation of the drill 25 removes the damaged thread 8 by rotating the tip 71 of the drill 25 as shown in FIG. 9 and 10.

The drill 25 is now withdrawn from the hole 41, the sleeve 40 is unscrewed and removed from the bracket 21, and compressed air is introduced into the hole 24 to thoroughly clean the hole 23a.

Then (FIG. 9) the sleeve 50 is inserted into the hole 24. In particular, the screw 53 of the sleeve 50 is screwed onto the nut 30 of the bracket 21. At the end of this operation, the axis G of the sleeve 50 coincides with the axes C, B of the respective holes 24, 23a.

The male member 26 is then inserted into the hole 51 of the sleeve 50 (FIG. 10) and screwed onto the nut 54 of the sleeve 50 until the corresponding tip 71 creates a new thread 16 in the hole 23a. The diameter of this new thread 16 is greater than the diameter of the damaged thread 8 (FIG. 11).

The male member 26 is now removed from the hole 51, the sleeve 50 is unscrewed from the bracket 21 and compressed air is introduced into the hole 24 to thoroughly clean the hole 23a.

Then (FIG. 13) the fixture 60 and the metal insert 61 are inserted together into the hole 24 of the bracket 21 until the insert 61 is screwed into the new thread 16 previously formed in the hole 24 (FIG. 14).

The setting tool 60 is removed from the hole 24 (FIGS. 15) and the inside diameter of the insert 61 defines a repaired thread 8' having the same diameter as the damaged thread 8 (FIGS. 16 and 17).

The 8' thread now constitutes a restored 8 thread.

Now the nuts 7 of the studs 6 on the supporting surfaces 19 of the brackets 22 are removed and the tool 20 is removed from the casing 2.

The shell 4 is again installed on the casing 2 and fixed on it by screwing the nuts 7 onto the corresponding studs 6a, 6b.

After studying the characteristics of the tool 20 and the method according to the present invention, its advantages are quite clear.

In particular, the method according to the present invention comprises the following steps:

- centering the tool 20 in the hole 23a;

- introduction of the drill 25 inside the tool 20 in the center of the hole 23a and removal of the damaged thread 8;

- insertion of the male element 26 inside the tool 20 and the creation of a new thread 16 inside the hole 23a, having a diameter greater than the diameter of the specified damaged thread 8; And

- screwing the insert 61 into said new thread 16 in such a way that a restored thread 8' is formed.

The above steps are carried out in the presence of the transmission 1 on the housing 2 and therefore on the helicopter 1.

In contrast to the known solutions described in the introductory part of this description, this invention allows you to restore the damaged thread 8, while leaving the casing 2 on the helicopter 1.

Due to this, the restoration of a damaged thread 8 does not require the removal of the transmission 1 and sending it to a repair center.

Thus it is possible to repair damaged threads 8 in a manner that is much cheaper and requires a much shorter outage of the helicopter than the methods required in known and previously mentioned solutions.

Tool 20 additionally includes:

- a bracket 21 located in the hole 23a and having an opening 24 into which the drill 25, the male element 26 and the insert 61 enter during the restoration of the damaged thread 8; And

- a pair of brackets 22, fixed with nuts 17 of the respective studs 6b, included in the holes 23b adjacent to the holes 23a.

Thus, on the one hand, the bracket 21 allows the correct placement of the drill 25, the male element 26 and the insert 61 by means of the bushings 40, 50 inserted into the hole 24; on the other hand, bracket 21 also makes it possible to fix brackets 22 with nuts 7 of studs 6b and to center axis C of hole 24 on axis B of hole 23b with damaged thread 8.

This results in a high design simplicity and a high final accuracy of the restored 8' thread.

In conclusion, it should be noted that modifications and changes can be made to the tool 20 and the method described and shown here, which do not go beyond the protection scope defined by the attached claims.

In particular, the studs 6a, 6b can be replaced by corresponding bolts with corresponding nuts 7.

In addition, the transmission 1 can be installed not on a helicopter, but on a tiltrotor.

Finally, the shell 4 may contain a working group different from the power take-off shaft 3, provided that the removal of the shell 4 keeps the transmission 1 on the casing 2.

Claims (29)

1. A tool (20) for repairing damaged threads (8) of connecting assemblies (5) of a housing (2) of a transmission (1) of an aircraft with a vertical takeoff and landing path, containing: - the first bracket (21) having a through hole (24) with a thread (30) and made with the possibility of placing above the first hole (23a) of the specified casing (2) having the specified damaged thread (8), and with the possibility of centering relative to the specified first hole (23a) by aligning the axis of the through hole (24) with the axis of the first hole (23a), while the hole (24) is configured to accommodate one or more tools (25, 26, 60) suitable for processing said damaged thread (8), - at least two second brackets (22) pivotally connected to the first bracket (21) and having support surfaces (19) configured to be held by the respective connecting elements (6b) located in the second holes (23b) of said casing (2) next to said first hole (23a) containing said damaged thread (8) and - a centering pin (33) which has an end (38) configured to enter said first hole (23a) during said centering operation; characterized in that it is provided the first sleeve (40) with a thread (44) on the outer surface, made with the possibility of placing in the specified through hole (24) with screwing on the specified thread (30) and with the possibility of passing through its axial hole (41) of the first tool (25), adapted to remove said damaged thread (8), and the second bushing (50) with a thread (53) on the outer surface and with an additional thread (54) on the surface of its axial hole (51), while the second bushing (50) can be placed in the specified through hole (24) with screwing on the specified thread (30) and with the possibility of passing through its axial hole (51) with screwing on the additional thread (54) of the second tool (26) to create a new thread (16) inside the specified first hole (23a), having a diameter greater than the diameter of the specified damaged threads (8), while the specified first bracket (21) is made in the form of a plate (27) having a first surface (28) with the possibility of adjoining to the section of the specified casing (2), where the specified first hole (23a) is located, and protrusion (29), which includes the specified through hole (24) and is located on the opposite surface of the plate (27) with the formation of an annular shoulder (31) with a support surface (32) for the first and second bushings (40, 50) when they are placed in said through hole (24), and the specified pin (33) is made with a threaded part (37) in the area (35) with the possibility of being screwed into the specified thread (30) of the hole (24) during the said centering of the first bracket (21) relative to the first hole (23a), wherein said pin (33) has a cover (34) made with the possibility of adjoining to the supporting surface (32) of the said first bracket (21) during said centering, a section (42) without a thread located in the axial direction between the cover (34) and the section (35) with a threaded part (37) and made with the possibility of entering the section (39) without a thread of the specified through hole (24) during the mentioned centering, a connecting section (36) in the form of a truncated cone, located in the axial direction after the specified section (35), and cylindrical section (38) without thread, located in the axial direction after the connecting section (36) and made with the possibility of entering into the specified first hole (23a). 2. A method for restoring damaged threads (8) of connecting assemblies (5) of a casing (2) of a transmission (1) of an aircraft with a vertical takeoff and landing path, including the use of a tool (20) according to claim 1 and the following steps: - placement of the first bracket (21) of the specified tool (20) over the first hole (23a) of the specified casing (2), which has a damaged thread (8), - placing the second brackets (22) of the specified tool (20) over the corresponding second holes (23b) of the specified casing (2), located on both sides of the first hole (23a), - screwing the nuts (7) on the connecting elements (6b) installed in the respective said second holes (23b), ensuring that the said bearing surfaces (19) of the brackets (22) are held, - centering the tool (20) relative to the specified first hole (23a) by inserting the pin (33) through the hole (24) of the tool (20) inside the specified first hole (23a) with the pin (33) screwed onto the thread (30) of the hole (24) until the cover (34) of the pin (33) stops against the support surface (32) of the specified ledge (29) of the tool (20), - removal of the pin (33) from the hole (24) of the tool (20), - placement of the first sleeve (40) in the hole (24) of the tool (20) with screwing onto the thread (30), - introduction of the first tool (25) through the axial hole (41) of the first sleeve (40) into the first hole (23a) of the casing (2) until the working end (70) of the first tool (25) reaches the indicated damaged thread (8), - actuating said first tool (25) and removing said damaged thread (8), - removal of the first bushing (40) from the hole (24) and placement of the second bushing (50) in this hole with its screwing onto the thread (30), - insertion of the second tool (26) through the axial hole (51) of the second sleeve (50) with its screwing on the additional thread (54) until the working end (71) of the second tool (26) enters the specified first hole (23a), - creating with the second tool (26) inside said first hole (23a) a new thread (16) having a diameter greater than the diameter of said damaged thread (8), - removal of the second sleeve (50) from the hole (24), - insertion through the hole (24) of the tool (20) into the specified first hole (23a) with screwing on the new thread (16) of the insert (61) made with the possibility of forming a restored thread (8').

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