Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2000-05-17
2002-01-15
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S537000, C384S906000, C415S170100
Reexamination Certificate
active
06338578
ABSTRACT:
TECHNICAL FIELD
Described is an arrangement for retaining a bearing, designed in particular to support a high-pressure compressor shaft, without this application be restrictive.
BACKGROUND ART
The construction of turbomachines demands complicated layouts because of the nesting of the high-pressure compressor and turbine stage inside the low-pressure turbine and compressor stage and because of the presence of two concentric runs of shafts each of which connects the compressor of one stage to the corresponding turbine. This complication is encountered above all during machine maintenance, when the machine has to be disassembled then reassembled.
A particular problem arises in the case of the high-pressure compressor. If we examine
FIG. 1
, which depicts an aircraft engine in longitudinal section, a rotor
1
is engaged in the center of a stator
2
and conventionally comprises a fan
3
, a low-pressure compressor
4
, a high-pressure compressor
5
, a high-pressure turbine
6
and a low-pressure turbine
7
which are aligned from front to rear. All of these elements carry blades which alternate with stationary vanes of the stator
2
and, like those, are located in an annular stream
8
through which the gases flow; a combustion chamber
9
is arranged in the annular stream
8
between the high-pressure turbine
6
and compressor
5
, and allows the fuel injected further upstream in the stream
8
to be burnt and thus produce combustion gases which drive the turbines
6
and
7
. There is also a run of high-pressure shafts
10
connecting the high-pressure compressor
5
to the high-pressure turbine
6
and a run of low-pressure shafts
11
extending into a cavity
12
of the previous run of shafts
10
and which connects the low-pressure compressor
4
to the low-pressure turbine
7
.
The high-pressure run of shafts
10
comprises, in particular, a high-pressure compressor stub shaft
13
around which is engaged a bearing
14
which supports it via a rib
15
belonging to the stator
2
. Referring to
FIG. 2
now for a more detailed examination, it can be seen that the bearing
14
is a rolling bearing, the inner ring
16
of which is slipped around the stub shaft
13
and held in place by a stop ring
17
, it too being slipped around the stub shaft
13
from its end face
18
and which presses the inner ring
16
backwards, against an opposed stop ring
19
which touches a step
20
of the stub shaft
13
. The inner ring
16
is kept clamped between the stop rings
17
and
19
by a nut
21
which, on its interior face, has a screw thread
22
engaged in a screw thread
23
made on the stub shaft
13
near the end face
18
: by tightening the nut
21
, the stop ring
17
, the inner ring
16
and the opposite stop ring
19
are pushed back in turn before this stack of components is compressed against the step
20
. The arrangement is supplemented by a locking piece
24
, the purpose of which is to prevent the nut
21
from working loose as a result of vibration; this locking piece
24
is engaged in the cavity
12
and held in place in the stub shaft
13
by a circle of splines
25
engaged in corresponding splines belonging to the stub shaft
13
and by curved-over ends
26
of flexible tabs
27
engaged in a groove
28
in the stub shaft
13
. The first of these connecting means prevents the locking piece
24
from rotating and the second prevents its translational movement, with respect to the stub shaft
13
. The flexible tabs
27
are further supplemented by engagement tongues
29
, adjacent to the curved-over ends
26
. However, the locking piece
24
also comprises a circle of teeth
30
, protruding from the cavity
12
and which engage between complementary teeth
31
, also arranged in a circle and produced on a portion
32
of the nut
21
which extends inwards, in front of the end face
18
of the stub shaft
13
, which it covers. For the sake of preciseness, it is added that the teeth
30
are at the front of the locking piece
24
, the flexible tabs
27
at the rear, and the curved-over ends
26
and the engagement tongues
29
at the rear of the tabs
27
.
To remove the high-pressure compressor
5
to which the stub shaft
13
belongs, this shaft needs to be disengaged from the bearing
14
. A preliminary step consists of removing the low-pressure turbine
7
so that a high-pressure turbine shaft
33
which belongs to the line of low-pressure shafts
11
and occupies most of the cavity
12
can be extracted, by pulling it backwards. An appropriate tool with claws is then inserted around the engagement tongues
29
to press against them and push them all towards the axis of the machine by curving the flexible tabs
27
, whereby the curved-over ends
26
come out of the groove
28
and the locking piece
24
can then be pulled backwards to extract its splines
25
from the splines of the stub shaft
13
and to disengage its teeth
30
from the teeth
31
.
It would then seem possible to unscrew the nut
21
using a tool engaged between the teeth
31
, but such an operation is actually premature because a low-pressure compressor shaft
34
, also belonging to the run of low-pressure shafts
11
, has remained in place and extends just in front of the nut
21
: the axial space denoted I which separates them is smaller than the length, denoted J, by which the nut
21
is engaged on the stub shaft
13
. It is therefore necessary also to remove the low-pressure compressor
4
and its shaft
34
before the high-pressure compressor
5
can be removed, this being an operation which is not necessarily useful. What is more, removing the low-pressure compressor
4
itself may be complicated and need to be preceded by the removal of other parts of the machine, for example a gearbox which has not been depicted in the figures. All of this means that removing the high-pressure compressor
5
is a lengthy and tiresome operation that cannot be made any easier by enlarging the space I, as this would entail reviewing the entire design of the machine and would increase its size.
DISCLOSURE OF THE INVENTION
The object of the invention therefore consists in facilitating the removal of such an arrangement for retaining a bearing comprising a stop, a clamping nut and a locking piece by reducing the preliminary manual interventions intended to free these parts, so that the bearing can be separated from the stub shaft it supports. The advantages of the invention are obvious with an arrangement of runs of shafts such as the one just described because there is no longer the need to remove parts in front of the front end of the stub shaft, and access to just one side of the retaining arrangement, from which the stub shaft will be removed, will suffice. To do this, a novel type of retaining arrangement is proposed. In its most general design, the arrangement, arranged around a stub shaft in which is machined a cavity and which is bounded by an end face, comprises a ring forming a stop for the bearing, a nut for clamping the ring and a piece for locking the nut, the locking piece being held in the cavity of the stub shaft by removable means of attachment and connected to the nut by imbricated teeth arranged in a circle on the nut and on the locking piece, and it is characterized in that the ring comprises an interior portion covering the end face of the stub shaft as far as the cavity and equipped with a screw thread for screwing onto a thread of the nut, and the nut is placed in the cavity and comprises a stop face directed towards the end face and engaged against a stop face standing up from the stub shaft in the cavity.
Further light will be shed on the nature of this new arrangement and on its advantages using the following figures, in addition to
FIGS. 1 and 2
already described and which depict a turbomachine and that portion thereof which bears a conventional retaining arrangement.
REFERENCES:
patent: 4201426 (1980-05-01), Garten et al.
patent: 4531847 (1985-07-01), F'Geppert
patent: 4973221 (1990-11-01), Anderson et al.
patent: 5415478 (1995-05-01), Matthews et al.
patent: 0359659 (
Adde Danielle Christiane Roberte
Bertrand Jean-Louis
Lavigne Gérard Jean
Lefebvre Olivier Richard
Hannon Thomas R.
Societe Nationale d'etude et de Construction de Moteurs d&a
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