Title: Gearbox Lubrication
Description of Invention
This invention relates to a gearbox for a vehicle, and in particular, but not exclusively,
to a tail rotor gearbox for a helicopter.
The invention has innovative concepts that can be utilised in other technological
fields, for example, automotive gearboxes, in a manner that will be appreciated.
In application to a tail rotor gearbox, more particularly, the invention relates to the
lubrication of such a gearbox and specifically to the lubrication of a bearing assembly
in such a gearbox by which a pitch control shaft is moved axially within a hollow
output shaft of the gearbox through the action of an actuating member. The output
shaft carries the tail rotor of the helicopter, and the pitch control shaft is connected to
the tail rotor in such a way as to vary, collectively, the pitch of its blades as the pitch
control shaft is moved axially relative to the output shaft. Although movable axially
therein, the pitch control shaft rotates with the output shaft, and the actuating
member, which does not rotate but which is movable in the direction in which the pitch
control shaft moves within the output shaft, has to be connected to the pitch control
shaft by way of a thrust bearing assembly which is able to transmit axial forces in both
directions between the rotating pitch control shaft and the (non-rotating) actuating
member.
In a conventional helicopter, the tail rotor gearbox transmits power between a drive
shaft assembly which extends longitudinally of the helicopter, from the engine(s) and
transmission in the vicinity of the main rotor of the helicopter, to the tail rotor. The
output shaft of the gearbox, on which the tail rotor is mounted, extends transversely of
the helicopter. The gearbox includes gearing, e.g. a crown wheel and pinion
arrangement which provides for power transmission between the output shaft and an
input member whose axis of rotation is at least substantially at right angles to the axis
of rotation of the output shaft, the input member of the gearbox being connected to
the longitudinal drive shaft assembly of the helicopter. The gearbox provides a
reduction gearing transmission ratio between the driveshaft and output shaft.
In a tail rotor gearbox utilised by the present applicant in some of its helicopters, the
thrust bearing assembly, by which movement of the actuating member in the direction
axially of the output shaft is transmitted to the pitch control shaft, is disposed within an
end part of the pitch control shaft within the output shaft. One potential problem
associated with such disposition of the bearing assembly is that of lubrication thereof,
since any oil in the vicinity of the axis of rotation of the output shaft is centrifuged
outwardly from such axis as the output shaft rotates. Without adequate lubrication,
the service life of the bearing assembly may be curtailed.
The present invention addresses the problem of lubrication of such a bearing
assembly.
According to a first aspect of the present invention, we provide a helicopter tail rotor
gearbox including:
a housing;
an output shaft for connection to a tail rotor rotatably supported in the housing and
having an open end therein;
an input member rotatably supported in the housing;
gearing providing a power transmitting connection between the input member and
output shaft;
a pitch control shaft for effecting a change in the pitch of the tail rotor, the pitch control
shaft being disposed at least partially within the output shaft, rotatable therewith, and
movable relative thereto along the rotational axis of the output shaft;
an actuating member for effecting axial movement of the pitch control shaft, the
actuating member being movable axially of the output shaft but held against rotation
therewith; and
a bearing assembly positioned in between the pitch control shaft and the actuating
member for permitting relative rotation therebetween;
wherein the gearbox includes at least one formation for diverting oil, dispersed within
the housing in use, towards the open end of the output shaft.
According to a second aspect of the invention, we provide a helicopter including a
gearbox according to the first aspect of the invention.
According to a third aspect of the invention, we provide a helicopter tail rotor system
including a gearbox according to the first aspect of the invention.
The gearbox may have an oil feed member held for co-operation with the output shaft
at or adjacent the open end thereof and/or with the pitch control shaft, and adapted on
relative rotation between the oil feed member and output shaft to cause oil to be fed
axially to the vicinity of the bearing assembly.
The oil feed member may have at least one helical formation for causing oil to be fed
axially on relative rotation between the oil feed member and a surface co-operating
therewith.
The oil feed member may have an external peripheral surface which lies in close
proximity to an internal surface of the output shaft, the peripheral surface of the oil
feed member being provided with the helical formation(s) to cause oil to be fed axially
of the output shaft on relative rotation between the output shaft and oil feed member.
The oil feed member may be held against rotation by being supported on the
actuating member.
The at least one formation for diverting oil to the open end of the output shaft may
include a deflecting member for deflecting oil from an upper part of the housing
interior towards a region adjacent to the open end of the output shaft.
The output shaft may have a formation for retaining oil within the interior of the output
shaft and preferably the oil feed member fluidly communicates with the oil retaining
formation.
The gearbox may include an oil catcher member with a drainage channel formation
for catching oil from the at least one formation for diverting oil. The drainage channel
formation may extend radially from a peripheral surface of the oil catcher member
towards the rotational axis of the output shaft. Preferably the oil catcher member
further includes a further formation in fluid communication with the drainage channel
formation for directing caught oil towards the open end of the output shaft. The further
directing formation may communicate with the formation for retaining oil within the
interior of the shaft and preferably includes a frusto-conical formation.
According to a fourth aspect of the invention, we provide a gearbox including:
a housing;
an input member rotatably supported in the housing;
a rotatable shaft supported in the housing;
gearing providing a power transmitting connection between the input member and the
rotatable shaft; and
an oil feed member held against rotation relative to the housing;
wherein the oil feed member has at least one helical formation for causing oil within
the gearbox to be fed axially of the oil feed member, on rotation of the rotatable shaft.
According to a fifth aspect of the invention, we provide a vehicle including a gearbox
according to the fourth aspect of the invention.
The rotatable shaft may have an open end therein and the oil feed member is
positioned in an interior portion of the rotatable shaft.
In use, the oil feed member may cause oil dispersed within the housing to be fed into
the interior of the rotatable shaft or cause oil within the rotatable shaft to be fed into
an interior of the housing.
The gearbox may include at least one formation for diverting oil towards the oil feed
member. The at least one formation for diverting oil may include a deflecting member
for deflecting oil from a remote part of the housing towards the oil feed member.
The oil feed member may have an external peripheral surface on which the at least
one helical formation is formed, the external peripheral surface lying in close proximity
to an internal surface of the rotating shaft.
The oil feed member may be supported on a member which is held against rotation
relative to the rotatable shaft.
The rotatable shaft may have a formation for retaining oil within the interior of the
rotatable shaft and preferably the oil feed member fluidly communicates with the oil
retaining formation.
The gearbox may further include an oil catcher member with a drainage channel
formation for catching oil from an interior of the housing. The oil catcher drainage
channel formation may catch oil from the at least one formation for diverting oil. The
drainage formation preferably extends radially from a peripheral surface of the oil
catcher member towards the rotational axis of the rotatable shaft. The oil catcher
member may include a further formation in fluid communication with the drainage
channel formation for directing caught oil towards the interior portion of the rotatable
shaft. The further directing formation may communicate with the formation for
retaining oil within the interior of the shaft and preferably comprises a frusto-conical
formation.
These and other features of the invention will now be described by way of example
with reference to the accompanying drawings of which:
Figure 1 is a sectional illustration of a tail rotor gearbox to which the invention has
been applied,
Figure 2 is an enlargement of part of figure 1,
Figure 3 is an exploded perspective view of parts of the gearbox,
Figure 4 is a perspective view of a further part of the gearbox.
Referring to the drawings, the illustrated gearbox is a tail rotor gearbox that comprises
a housing indicated generally at 10. The housing comprises a number of housing
parts secured together by screw-threaded fastenings at joint faces therebetween, the
housing including an elongate, tapering, first part 12, a second part 14, an end cover
part 16 and a side part 18. The side part 18 carries a bearing-supporting structure 20,
which supports, by way of two oppositely-oriented taper roller bearing assemblies
only one of which is indicated at 22, an input member 24 having a pinion gear 26
inside the housing of the gearbox. Outside the housing, the input member 24 carries
a drive flange (not shown) or other element for connection to a tail rotor drive shaft
assembly.
In the interior of the housing 10, the housing part 12 carries a bearing-support
member 30 containing oppositely-oriented taper roller bearings whose outer races are
supported in the member 30. The inner races of the bearings 32, 34 are received on
the exterior surface of a hollow gearbox output shaft 36 which is provided, adjacent its
free end within the gearbox housing 10, with a flange part 38 to which is fastened a
crown wheel gear 40, having teeth which mesh with the teeth of the pinion gear 26 so
as to provide a reduction gear ratio between the input member 24 and output shaft 36
of the gearbox. The output shaft 36 rotates by the gearing connecting the input
member 24 to the output shaft 36. The other end of the output shaft 36 extends
through the casing part 12 and is supported by another bearing or bearings not
shown, the shaft emerging from the gearbox housing 10 and being adapted for
carrying a tail rotor assembly, also not shown.
Within the output shaft 36 there is disposed a pitch control shaft 44. This is movable
relative to the output shaft 36 in the direction of the rotational axis of the output shaft
36, but it rotates with the output shaft 36, having a splined connection with the interior
thereof.
Adjacent the end of pitch control shaft 44 within the gearbox housing 10, a thrust
bearing assembly indicated generally at 46 in figure 1, and visible in greater detail in
figure 2 of the drawings, is provided. The thrust bearing assembly 46 is a double row
bearing assembly with barrel shaped rollers arranged in two oppositely inclined rows.
The outer race 48 of the thrust bearing assembly 46 is held in a seating 50 of the
shaft 44, while the inner race 52 of the thrust bearing assembly 46 receives, and is
held on, a shaft portion 54 extending axially from an actuating member 56 (figure 3).
The remainder of the actuating member 56 comprises a body 58 with a splined bore
60 extending into the body from its free end. The external surface of the body 58,
outside the splined bore 60 (the splines in the bore 60 not being shown in figure 3) is
provided with a number of circumferentially spaced axially-extending grooves 62. The
actuating member 56 is held against rotation relative to the housing 10.
An oil feed member 63 is carried by the body 58 of the actuating member 56. This is
an annular component, having a cylindrical central bore 64 which fits on the external
cylindrical surface of the body 58. The visible end face 66 of the oil feed member 63
is provided with a number of circumferentially spaced axially and radially extending
recesses 68, some of which are engaged by radially outwardly extending tabs 70 on a
locking washer 72, the locking washer also having one or more inwardly extending
tabs 74 engageable in a respective one or more of the grooves 62 on the actuating
member 56. Hence the oil feed member 63 is held against rotation relative to the
actuating member 56 and the housing 10. The oil feed member 63 is stationary
during operation of the gearbox. A retaining ring, e.g. a "Spirolox" ™ retaining ring,
76, is engaged in an annular undercut groove 78 adjacent the end face 66 of the oil
feed member 63, retaining the locking washer 72 in the interior of the oil feed
member 63.
The external surface 80 on a peripheral portion of the oil feed member 63 lies in close
proximity to the interior cylindrical surface of the output shaft 36 surrounding it. The
surface 80 of the oil feed member 63 is provided with at least one helical groove 82 of
such width, depth, and hand as to cause oil in the vicinity thereof, when the output
shaft 36 is rotating in use but the oil feed member 63 not rotating, to be fed axially to
the right hand side of the oil feed member 62, having regard to the orientation in
which it is shown in the drawings. In other words, such feed of oil is towards the
thrust bearing assembly 46.
If more than one helical groove 82 is provided in the surface 80, the grooves may be
arranged in the manner of a multi-start screw thread.
Adjacent the free end of the output shaft 36, beyond the oil feed member 63, an
undercut annular recess within the output shaft 36 accommodates a member 86
having an annular radially inwardly extending wall formation. The effect of the
member 86 is to retain a small quantity of oil in the interior of the output shaft 36, as a
pool at its lowermost part when the output shaft 36 is not rotating, or as a film around
its inner surface under centrifugal action when the output shaft 36 is rotating. Such oil
contacts the oil feed member 63, to be fed towards the thrust bearing assembly 46 by
the action of the helical formation on the peripheral surface of the oil feed member 63.
To aid retention of oil in the interior of the output shaft 36, so that the oil can be
moved towards the thrust bearing assembly 46 as aforesaid, an oil catcher member
90, shown in figure 4 of the drawings, is held within the housing of the gearbox, inside
the end cover part 16 and facing the open end of the output shaft 36.
An external flange 92 of the oil catcher member 90 is held between joint faces of the
respective housing parts 14, 16. The oil catcher member 90 has a central aperture 94
through which the output member (not shown) of an actuator assembly (not shown),
but disposed outside the housing part 16, extends, such an output member having a
splined end portion which engages the splined bore 60 of the actuating member 56.
This prevents the actuating member 56 and components carried thereby from
rotating. The output member of the actuator assembly causes displacement of the
pitch control shaft 44, moved through the intermediary of the actuating member 56
and thrust bearing assembly 46, axially relative to the gearbox output shaft 36,
thereby effecting collective control of the pitch of the tail rotor blades.
The oil catcher member 90 has an oil-catching drainage channel formation 98
extending at an inclination downwardly, from its peripheral region facing the crown
wheel 40, towards the central aperture 94. The channel 98 leads into a somewhat
frusto-conical directing formation 100, discharging oil from an end portion 102 of the
formation 100, which end portion lies within the end of the output shaft 36 beyond the
member 86. An oil deflecting member 104 is provided within the housing part 14 at a
remote part of the housing, adjacent the upper part of the housing and generally
above part of the periphery of the crown wheel 40, so as to deflect oil thrown
centrifugally around the interior of the housing towards the channel 98 of the oil
catcher member 90.
In use, by virtue of the operation of the oil feed member 63 and the supply of oil
thereto by the oil deflector member 104 and the oil catcher member 90, is to ensure
that the thrust bearing assembly 46 is effectively lubricated. However, it will be
appreciated that the oil deflector member 104 can be used independently of the oil
catcher member 90 and the oil feed member 63 to deliver oil to the interior of the
output shaft 36 and thereby lubricate the thrust bearing assembly 46. Furthermore,
the oil catch member 90 can be used in conjunction with the oil deflector member 104
to aid in lubrication of the thrust bearing assembly 46. The oil deflector member 104
may be in co-operation with other features well known in the art for channelling oil so
as to deflect oil from a remote part of the housing to an intended region.
It will be appreciated that the concept of using a stationary oil feed member together
with other rotatable surfaces has application in many technological fields, e.g.
aviation gearboxes, automotive gearboxes. In an alternative mode of operation, the
oil feed member may also be utilised to cause oil within the rotatable shaft/output
shaft to be fed into an interior of the housing. In other words, the oil feed member can
be configured to cause oil to flow in either direction by altering the direction of the
rotatable shaft or the configuration of the helical channel on the surface of the oil feed
member.
The oil feed member 63 may conveniently be a moulding of a suitable plastics
material, e.g. PEEK (polyether ether ketone).
When used in this specification and claims, the terms "comprises" and "comprising"
and variations thereof mean that the specified features, steps or integers are
included. The terms are not to be interpreted to exclude the presence of other
features, steps or components.
The features disclosed in the foregoing description, or the following claims, or the
accompanying drawings, expressed in their specific forms or in terms of a means for
performing the disclosed function, or a method or process for attaining the disclosed
result, as appropriate, may, separately, or in any combination of such features, be
utilised for realising the invention in diverse forms thereof.

We Claim:
1. A gearbox including:
a housing;
an input member rotatably supported in the housing;
a rotatable shaft supported in the housing;
gearing providing a power transmitting connection between the input
member and the rotatable shaft; and
an oil feed member held against rotation relative to the housing;
wherein the oil feed member has at least one helical formation for causing oil
within the gearbox to be fed axially of the oil feed member, on rotation of the rotatable
shaft.
2. A gearbox according to claim 1 wherein the rotatable shaft has an open end
15 therein and the oil feed member is positioned in an interior portion of the rotatable
shaft.
3. A gearbox according to claim 1 or 2, wherein, in use, the oil feed member
causes oil dispersed within the housing to be fed into the interior of the rotatable
20 shaft.
4. A gearbox according to claim 1 or 2, wherein, in use, the oil feed member
causes oil within the rotatable shaft to be fed into an interior of the housing.
25 5. A gearbox according to any one of claims 1 to 4 wherein the gearbox includes
at least one formation for diverting oil towards the oil feed member.
6. A gearbox according to claim 5, wherein the at least one formation for
diverting oil includes a deflecting member for deflecting oil from a remote part of the
30 housing towards the oil feed member.
7. A gearbox according to any one of claims 1 to 6 wherein the oil feed member
has an external peripheral surface on which the at least one helical formation is
provided, the external peripheral surface lying in close proximity to an internal surface
of the rotating shaft.
8. A gearbox according to any one of claims 1 to 7 wherein the oil feed member
5 is supported on a member which is held against rotation relative to the rotatable
shaft.
9. A gearbox according to any one of claims 1 to 8 wherein the rotatable shaft
has a formation for retaining oil within the interior of the rotatable shaft.
10
10. A gearbox according to claim 9 wherein the oil feed member fluidly
communicates with the oil retaining formation.
11. A gearbox according to any one of claims 1 to 10, further including an oil
15 catcher member with a drainage channel formation for catching oil from an interior of
the housing.
12. A gearbox according to claim 1 1, when appendent to claim 6, wherein oil
catcher drainage channel formation catches oil from the at least one formation for
20 diverting oil.
13. A gearbox according to claim 12 wherein the drainage formation extends
radially from a peripheral surface of the oil catcher member towards the rotational axis
of the rotatable shaft.
25
14. A gearbox according to any one of claims 11 to 13 wherein the oil catcher
member includes a further formation in fluid communication with the drainage channel
formation for directing caught oil towards the interior portion of the rotatable shaft.
30 15. A gearbox according to claim 14, when appendent to claim 9 or 10 wherein
the further directing formation communicates with the formation for retaining oil within
the interior of the shaft.
16. A gearbox according to claim 14 or 15 wherein the further directing formation
comprises a frusto-conical formation.
17. A vehicle including a gearbox according to any one of claims 1 to 16.