Field of the Invention
The invention relates to mechanical engineering field and specifically to
assembly of gas turbine engines.
3 Background of the Invention
The current practice of torque tightening of axial slotted nut [060] on HP ball
bearing shaft [040] of an aero engine is by arresting the‘ rotor system [010]
at the other end [011] through locking feature.
This method calls for lifting of complete assembly (rotor system [010] &
casings [020]) from assembly platform [030] by crane, engaging locking
device to the rear end [011] of the rotor system [010] and positioning back
the assembly [010 & 020] on assembly platform [030] - which is not
ergonomic because of size, weight, accessibility & safety and it requires
involvement of multiple operators‘t'o perform the said activities.
The process also leads to tilting of the rotor system [010] with respect tocasings
[020] while applying torque, thus may cause damage to pans (eg.
rotors, seals, etc‘) due to subsequent rubbing.
These problems are addressed by introducing a torque tightening tool set
for aero engine assembly.
'3.1 Prior Art
Prevailing method of applying torque on a nut, assembled over a shaft, is
by holding the shaft on a rigid fixture at one end and apply torque on nut
with a calibrated torque wrench at other end.
Patent USOO788663582 has been considered as a prior art, wherein a bolt
or nut tightening device has been described — consisting of an outer and an
inner shaft coupled to a planetary gear mechanism, the outer shaft having a reaction receiver, the inner shaft being provided with an engaging portion
engageable with a bolt or nut to be tightened.
The device can be used for applying tightening torque on bolt or nut with a
monitored torque value, but in an aero engine assembly scenario. where
the shaft is already fitted into an assemn with bearings (shaft / rotor system
is free to rotate), complete assembly needs to be lifted to attach a rigid
fixture to the other end of rotating parts to hold the shaft stationary against
applied torque.
Once torque is applied, the assembly to be lifted again_t6 remove the fixture.
Multiple operators and supervisors are engaged to carry out the required
activities
Further, the process may also lead to damage of parts while applying torque
because of large distance between location of holding and location of
applying torque.
4 Brief Summary of the Invention
The methodology introduced, comprises of the following features:
The technology involves holding the rotor system [010] from front through
bevel gear [050] (same side where axial slotted nut [060] to be assembled)
while applying torque thus avoiding twist in the complete rotor system [0.10].
This also eliminates the requirement of lifting the assembly [010 & 020] to
engage locking tool to the other end [011] of the rotor system [010].
The technology demands for a change in design of bevel gear [050] by
introducing eight slots of 'T' shape [051] with differential depths [052 & 053]
so as to enable arresting tool pair to be assembled sideway and be locked
in desired position while applying torque
5 Detail Description of the Drawings
The invention can be better understood by reading the detail description of
the disclosed embodiment followed by the accompanied drawings in which,
Figure 1: depicts the schematic of the assembled rotor system [010] and
casings [020] of aero engine. It also includes exploded view of HP ball
bearing shaft [040], bevel gear [050] and axial slotted nut [060] need to be
assembled on existing assembly of rotor system [010] and casings [020].
Figure 2: shows the final assembled view of HP ball bearing shaft [040],
bevel gear [050] and axial slotted nut [060] on rotor system [010] with
casings [020].
Figure 3: details the design of 'T‘ shaped slots [051] on bevel gear [050] with
differential depths [052 & 053}
Figure 4: describes the sideway movement of arresting tool pair [070] on
bevel gear [050] when assembled onto rotor system [010] (casings [020]
are not shown for view clarity) along with HP ball bearing shaft [040] and
axial slotted nut [060].
Figure 5, 6 & 7: explain the design requirement of 'T' shaped slots [051] on
bevel gear [050] with differential depths [052 & 053] to accommodate
arresting tool pair [070].
Figure 8: shows the exploded view of tool set required for applying torque
_on axial slotted nut [060].
Figure 9: shows all of claimed tool set assembled on the rotor system [010]
(casings [020] are not shown for view clarity).
6 Detail Description of the Invention
The following specification particularly describes the invention and the
manner in which it is to be performed
Referring to Figure 1 & 2, HP ball bearing shaft [040] is assembled on the
rotor system [010] (with engine casings [020]) along with bevel gear [050]
and axial slotted nut [060] is tightened to lock the bevel gear [050].
Referring to Figure 3, bevel gear [050] is having 8 slots [051] of ‘T’ shape
with differential depths - depth of head of the 'T' shape (horizontal portion)
[052] of the slots [051] is less than that of bottom (vertical portion) [053] of
slots [051].
Referring to Figure 4-7, each of arresting tools [070] moves sideway
(inward) to match the lugs [071] of the arresting tools [070] with the head of
the 'T' shape (horizontal portion) [052] of the slots [051] on bevel gear [050].
Once all the lugs [071] are engaged into the eight slots [051] of bevel gear
[050], the arresting tool pair [070] to be moved down so that the lugs [O71]
enter into the bottom (vertical portion) [053] of 'T' shape slots [051] on bevel
gear [050].
Referring to Figure 8 & 9, Cover-Arresting Tool [080] to be assembled over
the pair of Arresting Tool [070] to hold them together in place‘ Both the legs
[101] of Holding Tool [100] to be engaged into the sockets [072] on Arresting
Tool pair [070], which provides an ergonomic provision for a single person
to hold the Holding Tool [100] comfortably with both hands. The lugs [091]
of Locking Tool [090] is engaged into the slots [061] of axial slotted nut [060]
and a standard calibrated torque wrench (preset with desired torque value)
is engaged into the socket [092] of Locking Tool [0901‘ Torque is applied on
the axial slotted nut [060], while holding the Holding Tool [100] rigidly thus
making the complete rotor system [010] rigid against the torque. This
method requires only two operators to perform the activities- one person to
hold the Holding Tool [100] rigidly, while other to apply the desired torque
with torque wrench.
Referring to Figure 4, pair of Arresting Tool [070] and the bevel gear [050]
both have lugs [071] / slots [051] (respectively) at circumferentially equi
spaced locations, whereas each of the Arresting Tools [070] is moved
radially inward (i.e. sideway) from opposite directions to engage onto bevel
gear [059] slots [051]. It is imperative that if the slots [051} are straight,
instead of 'T' shape, having same width of the lugs [071] (of Arresting Tool
[070]) it is impossible to engage thé Arresting Tool pair [070] onto bevel gear
[050]. The same may be possible if the Arresting Tool pair [070] is engaged
onto bevel gear [050] from bottom (instead of sideway) before the bevel
gear [050] is assembled on HP ball bearing shaft [040], but afterwards it
cannot be disengaged (once the bevel gear [050] is locked on HP ball
bearing shaft [040], each of Arresting Tools [070] has to move sideways
outward- which is not possible).
I
Referring to Figure 5 & 6, head (horizontal portion) [052] of 'T' shape slots
[051] on bevel gear [050] provides extra width for the lugs [071] of Arresting
Tool pair [070] to get engaged into even when it is assembled sideway
(radially inward) and also possible to remove (radially outward).
Referring to Figure 7, bottom of 'T' shape (vertical portion) [053] of the slots
[051] on bevel gear [050] provides constrained space to the lugs [071] of
Arresting‘ Tool pair [070] to withstand the torque while applied.
The. depth of step of slots [051] on bevel gear [050] are different at head
(horizontal portion) [052] and bottom (vertical portion) [053] of 'T' shape: the
depth is more at the bottom (vertical portion) [053]. When the Arresting Tool
pair [070] is held together with Cover-Arresting Tool [080] the lugs [071] of
the Arresting Tool pair [070] can only match with the depth of bottom
(vertical portion) [053] of ‘T‘ shape of the slots [051] on bevel gear [050],
thus restricts the Arresting Tool pair [070] to move up towards head
(horizontal portion) [052] of 'T' shape of the slots [051] on bevel gear [050]-
enabling to have a rigid grip on the bevel gear [050] at the time of applying
torque.
Structural analysis has been carried out for design modification on bevel
gear and all tool set méntioned herein to assess structural integrity during
torque application. Subsequently, detailed drawings of the components (tool
set & modified bevel gear) have been released and the methodology has
5 been implemented. The assembly process (applying tightening torque on
axial slotted nut) has become simpler (lifting of complete'assembly of rotor
system & casing is no more required). Total cost of assembly is reduced
compared to the existing method as time and man-power requirement has
been reduced.
We Claim,
1. A torque tightening tool set to apply tightening torque on akial slotted nut
[060] over HP ball bearing shaft [040] of a turbofan ehgine by holding at
eight slots [051] of a bevel gear [050], comprising:
a pair of arresting tools [070] to arrest the rotation of the rotor system
[010] through bevel gear [050] and HP ball bearing shaft [040];
a cover-arresting tool [080] which holds the pair of arresting tools [070]
in position;
a holding tool [100] which engages onto the pair of arresting tools [070]
to provide holding provision while applying torque; and
a locking tool [090] which engages into axial slotted nut [060] to apply
desired torque while the bevel gear [050] along with HP ball bearing
shaft [040] and rotor system [010] held stationary using the pair of
arresting tools [070], the cover-arresting to'ol [080] and the holding
tool [100].
2. The torque tightening tool set as clairfied in Claim 1, wherein pair of
arresting tools [070] characterized by four lugs [071] 6n each arresting
tool [070] which engage to eight slots [051] of bevel gear [050] and
sockets [072] which engages with the holding tool [100].
3. The torque tightening tool set as claimed in Claim 1, wherein cover
arresting tool [080] characterized by the assembled position where it
holds the pair of arresting tool [070] together, thus restricting the
arresting tools [070] from falling apart at the time of applying torque‘
4‘ The torque tightening tool set as claimed in Claim 1, wherein holding tool
[100] characterized by two legs [101] engaged into the sockets [072] on
the arresting tool pair [070].
5‘ The torque tightening tool set as claimed in Claim 1, wherein locking tool
[090] characterized by lugs [091] engaged into the slots [061] of axial
slotted nut [060] and a socket [092] to insert standard calibrated torque
wrench.
5 6. The bevel gear [050] as claimed in Claim 1, characterized by eight slots
[051] of ‘T’ shape construction with differential depth [052 & 053] enables
sideway entry of the arresting tool [070] pair and locking of the same while applying tightening torque.