U.S. patent application number 14/785117 was filed with the patent office on 2016-03-24 for dynamic bearing.
The applicant listed for this patent is Messier-Dowty Limited. Invention is credited to Ian Robert BENNETT.
Application Number | 20160084307 14/785117 |
Document ID | / |
Family ID | 48537334 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160084307 |
Kind Code |
A1 |
BENNETT; Ian Robert |
March 24, 2016 |
DYNAMIC BEARING
Abstract
A dynamic bearing for an aircraft landing gear. The bearing
includes a lug; a shaft having a first material; and a bearing
surface having a second material that is softer than the first
material. The bearing surface defines a bore and is arranged to
support the shaft when the shaft is movably housed within the bore
in use. The bearing surface is defined by the lug or a coating
applied to the lug.
Inventors: |
BENNETT; Ian Robert;
(Cheltenham, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Messier-Dowty Limited |
Gloucester, Gloucestershire |
|
GB |
|
|
Family ID: |
48537334 |
Appl. No.: |
14/785117 |
Filed: |
April 3, 2014 |
PCT Filed: |
April 3, 2014 |
PCT NO: |
PCT/GB2014/051041 |
371 Date: |
October 16, 2015 |
Current U.S.
Class: |
384/115 ;
384/114 |
Current CPC
Class: |
F16C 33/1095 20130101;
F16C 2326/43 20130101; F16C 33/125 20130101; F16C 33/102 20130101;
F16C 33/1065 20130101; F16C 2204/12 20130101; F16C 33/121 20130101;
B64D 45/02 20130101; F16C 17/02 20130101; B64C 25/001 20130101 |
International
Class: |
F16C 33/12 20060101
F16C033/12; F16C 17/02 20060101 F16C017/02; F16C 33/10 20060101
F16C033/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2013 |
GB |
1306909.1 |
Claims
1. A dynamic bearing for an aircraft landing gear, the dynamic
bearing comprising: a lug; a shaft comprising a first material; a
bearing surface comprising a second material that is softer than
the first material, the bearing surface defining a bore and being
arranged to support the shaft when the shaft is movably housed
within the bore in use, wherein the bearing surface is defined by
the lug or by a coating applied to the lug.
2. A dynamic bearing according to claim 1, wherein the shaft
includes one or more first ducts which open onto a major surface
thereof and are arranged for the passage of lubricant.
3. A dynamic bearing according to claim 2, wherein one or more of
the first ducts are arranged to extend so as to be generally
parallel with respect to the dominant stress in the shaft.
4. A dynamic bearing according to claim 2, wherein one or more of
the first ducts are arranged to extend lengthwise at an angle of up
to 45.degree. with respect to a longitudinal axis of the shaft.
5. A dynamic bearing according to claim 2, wherein the first ducts
are disposed in a generally parallel arrangement around the
peripheral surface of the shaft.
6. A dynamic bearing according to claim 2, wherein the shaft in use
has a loaded surface portion carrying tension stress substantially
parallel to a longitudinal axis of the shaft, and an unloaded
surface portion carrying compression stress substantially parallel
to the longitudinal axis of the shaft, and the first ducts are
provided in side portions between the centres of the loaded and
unloaded surface portions.
7. A dynamic bearing according to claim 1, wherein the bearing
surface includes one or more second ducts for the passage of
lubricant.
8. A dynamic bearing according to claim 8, wherein one or more of
the second ducts are arranged to extend so as to be generally
parallel with respect to the dominant stress in the lug.
9. A dynamic bearing according to claim 7, wherein one or more of
the second ducts extend lengthwise in a non-parallel direction with
respect to an axis of the bore defined by the bearing surface.
10. A dynamic bearing according to claim 7, wherein one or more of
the second ducts extend depth-wise into the lug through the
coating.
11. A dynamic bearing according to claim 2, wherein the first ducts
are open topped ducts.
12. A dynamic bearing according to claim 1, wherein the coating has
a thickness of at least 0.05 mm.
13. A dynamic bearing according to claim 1, wherein portions of the
lug and/or coating defining extremities of the bore are tapered to
spread edge loading.
14. A dynamic bearing according to claim 1, wherein the second
material comprises a self lubricating material.
15. A dynamic bearing according to claim 1, wherein the first
and/or second material comprises metal.
16. A dynamic bearing according to claim 2, wherein the ducts are
lubricant ducts for the distribution of lubricant.
17. A dynamic bearing according to claim 1, wherein the lug is
formed in a first landing gear component and the shaft operatively
connects the first landing gear component to a second landing gear
component.
18. (canceled)
19. A dynamic bearing according to claim 7, wherein the second
ducts are open topped ducts.
20. A dynamic bearing according to claim 2, wherein the bearing
surface includes one or more second ducts for the passage of
lubricant.
21. A dynamic bearing according to claim 16, wherein the lubricant
ducts are coupled to a source of lubricant.
22. A dynamic bearing according to claim 7, wherein the ducts are
lubricant ducts for the distribution of lubricant.
23. A dynamic bearing according to claim 22, wherein the lubricant
ducts are coupled to a source of lubricant.
24. An aircraft having a landing gear comprising a dynamic bearing
comprising: a lug; a shaft comprising a first material; a bearing
surface comprising a second material that is softer than the first
material, the bearing surface defining a bore and being arranged to
support the shaft when the shaft is movably housed within the bore
in use, wherein the bearing surface is defined by a coating applied
to the lug.
Description
BACKGROUND
[0001] A dynamic bearing enables constrained relative movement
between two parts. Dynamic bearings can be found in many
assemblies, such as aircraft landing gear, which require a bearing
surface on a dynamic joint.
[0002] Generally, a dynamic bearing includes a lug which defines a
lug bore. A bush is disposed within the lug bore, the bush defining
a bush bore which has a narrower diameter than the lug bore and is
arranged to receive a shaft. The bush is arranged to support the
shaft in use. The bush may be retained in position due to an
interference fit with the lug or may be mechanically fixed to the
lug by a bolt or the like. The bush is formed of a softer material
than the shaft so as to be relatively sacrificial with respect to
the shaft. Once worn, the bush can be replaced without requiring
replacement of the lug or shaft.
[0003] The present inventor has realised that known dynamic
bearings may be improved in one or more of the following ways:
[0004] increased robustness; [0005] reduced weight; [0006] improved
corrosion resistance; [0007] improved fretting resistance; and
[0008] improved lightning protection.
SUMMARY
[0009] According to a first aspect of the invention, there is
provided a dynamic bearing suitable for an aircraft landing gear,
the dynamic bearing comprising:
[0010] a lug;
[0011] a shaft comprising a first material;
[0012] a bearing surface comprising a second material that is
softer than the first material, the bearing surface defining a bore
and being arranged to support the shaft when the shaft is movably
housed within the bore in use,
[0013] wherein the bearing surface is defined by the lug or by a
coating applied to the lug.
[0014] Thus, the bearing surface is either defined by the lug
itself, or by a coating that is applied to the lug. As such, the
dynamic bearing according to the first aspect does not require a
bush to be provided between the shaft and the lug. The inventor has
found that the interface between the coating and the lug is less
likely to result in rotation or migration of the bearing surface in
comparison to the interface between a lug and bush. The dynamic
bearing according to the first aspect may therefore provide for a
more robust dynamic bearing that may be lighter than prior art
bearings due to it not including a bush. Moreover, the corrosion
resistance of the bearing may be improved due to the removal of the
lug-bush interface, which is a primary location for corrosion and
fretting of the lug. Moreover, the dynamic bearing according to the
first aspect may have improved electrical conductivity across the
bearing relative to prior art bearings including a lug-bush
interface, which is advantageous for lightning protection.
[0015] The outer surface of the shaft may include one or more first
ducts for the passage of lubricant. This may reduce friction
between the bearing surface and the shaft.
[0016] The first ducts may be disposed in parallel around the
peripheral surface of the shaft.
[0017] In some embodiments the shaft may in use have a loaded
surface portion carrying tension stress substantially parallel the
shaft axis, and an unloaded surface portion carrying compression
stress substantially parallel to the shaft axis, and the first
ducts may be provided in side portions between the centres of the
loaded and unloaded surface portions, where axial stress is
reduced. The surface portions may be elongate.
[0018] One or more of the first ducts may be arranged to extend so
as to be generally parallel with respect to the dominant stress in
the shaft.
[0019] In embodiments where the dynamic bearing is arranged such
that the dominant load experienced by the shaft is a bending
moment, the dominant stress angle in the shaft will be generally
parallel with respect to the longitudinal axis L of the shaft.
Thus, in some embodiments, one or more of the first ducts may
extend lengthwise generally parallel with respect to the
longitudinal axis L of the shaft such that the first ducts are
generally aligned with the dominant stress in the shaft, which may
reduce the likelihood of the first ducts presenting a stress raiser
problem.
[0020] In embodiments where the dynamic bearing is arranged such
that the shaft experiences combined bending and torsional moments,
the dominant stress angle in the shaft will be at a non-zero angle
with respect to the longitudinal axis L of the shaft. Thus, in some
embodiments, one or more of the first ducts may extend lengthwise
at an angle of up to 45.degree. with respect to the longitudinal
axis L of the shaft such that the first ducts are generally aligned
with the stress resulting from the combination of bending and
torsional loads on the shaft. In some embodiments one or more of
the first ducts may extend lengthwise at an angle of up to
25.degree., up to 10.degree. and even more preferably up to
5.degree. with respect to the longitudinal axis L of the shaft.
[0021] The bearing surface may include one or more second ducts for
the passage of lubricant. This may reduce friction between the
bearing surface and the shaft. The one or more second ducts may be
arranged to enable the passage of lubricant from a lubrication
point to the first ducts via the bearing interface. Thus, the first
and second ducts together define a lubrication network arranged to
lubricate the bearing surface.
[0022] The first ducts may be arranged to accept lubricant from
second ducts in the lug and distribute grease along the bearing
interface between the shaft and bearing surface.
[0023] One or more of the second ducts may extend lengthwise in a
direction generally orthogonally with respect to the axis B of the
bore defined by the bearing surface. Thus, the second ducts are
generally aligned with the circumferential dominant stress in the
lug and/or coating, which may reduce the likelihood of the second
ducts presenting a stress raiser problem. The second ducts may
extend generally circumferentially around the bore. In some
embodiments one or more of the second ducts may extend lengthwise
at an angle of no greater than Tan.sup.-1=(lug width-3.times.groove
width)/lug bore diameter.
[0024] One or more of the second ducts may extend depth-wise into
the lug through the coating. This enables the second ducts to be
deeper than the coating for improved grease transfer.
[0025] The first and/or second ducts may be open topped ducts; for
example, a major portion of the first and/or second ducts may be
open topped. This may improve fluid communication between the
ducts. The first and/or second ducts may be arranged to generally
retain grease or the like so as to slowly dispense grease to the
interface between the shaft and bearing surface.
[0026] The second ducts may be arranged in fluid communication with
a source of lubricant such as grease.
[0027] The coating may have a thickness of at least 0.05 mm. The
coating may have a thickness between 0.1 mm and 10 mm, preferably
between 0.1 mm and 5 mm, more preferably between 0.1 mm and 3 mm
and even more preferably between 0.1 mm and 1 mm. A thickness of
0.1 mm provides for a reasonable amount of wear, but anything above
0.3 mm is likely to be outside the amount of wear expected in most
embodiments. It may however be advantageous for the coating to be
up to 1 mm to allow for edge wear. The coating thickness may be
generally uniform.
[0028] Portions of the lug defining the extremities of the bore may
be tapered to spread edge loading.
[0029] The first material may comprise any suitable hard material,
such as steel, titanium or an anodised aluminium alloy.
[0030] The second material may comprise any suitable relatively
soft material, such as bronze.
[0031] The second material may comprise a self lubricating
material. This may reduce friction between the bearing surface and
the shaft.
[0032] In some embodiments the shaft may be coated to improve its
hardness; for example, a coating comprising chromium, or a carbide
based coating such as WC--Co--Cr, or nickel or nickel alloy, or
diamond like carbon. In such embodiments, it is preferred that the
shaft coating is not applied to the first ducts due to the
detrimental effect that the plating process may have on the fatigue
resistance of the shaft.
[0033] According to a second aspect of the invention, there is
provided an aircraft landing gear including a dynamic bearing
according to the first aspect. The dynamic bearing according to the
first aspect may for example define at least part of a drag stay, a
retraction actuator, a steering cylinder, a pintle, or landing gear
door linkage.
[0034] According to a third aspect of the invention, there is
provided an aircraft comprising a dynamic bearing according to the
first aspect and/or an aircraft landing gear according to the
second aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Embodiments of the invention will now be described with
reference to the accompanying drawings, in which:
[0036] FIG. 1 is a schematic diagram of a prior art dynamic
bearing;
[0037] FIG. 2 is a schematic diagram of a dynamic bearing according
to an embodiment of the invention;
[0038] FIG. 3 is a schematic diagram of a dynamic bearing according
to a further embodiment of the invention;
[0039] FIG. 4 is a schematic diagram of a dynamic bearing according
to a further embodiment of the invention; and
[0040] FIG. 5 is a schematic diagram of a dynamic bearing according
to a further embodiment of the invention.
DETAILED DESCRIPTION
[0041] FIG. 1 shows a prior art dynamic bearing 100. A structural
component includes a lug 102 which defines a lug bore. A bush 104
is disposed within the lug bore, the bush 104 defining a bush bore
which has a narrower diameter than the lug bore and is arranged to
receive a shaft 106. The bush 104 is arranged to support the shaft
106 in use. The bush 104 may be retained in position due to an
interference fit with the lug or may be mechanically fixed to the
lug 102 by a cross bolt or the like. The bush 104 is formed of a
softer material than the shaft 106 so as to be relatively
sacrificial with respect to the shaft 106. Once worn, the bush 104
can be replaced without requiring replacement of the lug 102 or
shaft 106.
[0042] The inventor has identified that the interface between the
lug 102 and bush 104, which will be referred to as the "lug-bush
interface", is prone to problems. These problems will now briefly
be explained.
[0043] The bush 104 may rotate within the lug 102, or may migrate
from its intended position. This can affect the normal working of
the dynamic bearing 100.
[0044] The lug-bush interface may lead to corrosion or fretting.
This is due to the fact that the lug 102 and bush 104 are separate
components which are mechanically connected. Corrosion will
typically affect the lug 102 and results from moisture ingress
which enables ion migration between the lug 102 and bush 104.
Fretting is a process of wear that occurs at the lug-bush
interface, which is under load and subject to minute relative
motion by vibration or other forces. Corrosion and fretting can be
particularly problematic because the lug-bush interface is often
difficult to inspect.
[0045] The lug-bush interface may also increase electrical
resistance across the dynamic bearing 100. This can be problematic
when the dynamic bearing 100 is for assemblies such as aircraft
landing gear which may require lightning protection.
[0046] In order to satisfactorily be retained within the lug 102,
the bush 104 has a wall thickness T of 2.5 mm to 4 mm. However, a
relatively small thickness of the bush 104, such as 0.1 mm, is
likely to be eroded due to wear during the life of the bush 104.
The excess bush thickness adds to the weight of the dynamic bearing
100 and increases the bulk of it.
[0047] FIG. 2 shows a dynamic bearing 10 according to an embodiment
of the invention. The dynamic bearing 10 includes a lug 12 which
may be defined by a structural component of an assembly such an
aircraft landing gear. The lug 12 defines a generally cylindrical
lug bore arranged to receive an elongate, generally cylindrical pin
or shaft 16. The inner peripheral wall of the lug 12, which defines
the lug bore, defines a bearing surface or counter face 14 arranged
to support the shaft 16 when the shaft 16 is movably housed within
the bore in use.
[0048] The shaft 16 is formed from a first material, which is
harder than a second material from which the lug 12 is formed.
Thus, the bearing surface 14 of the lug is relatively sacrificial
with respect to the shaft 16.
[0049] Thus, the dynamic bearing 10 according to the illustrated
embodiment of the invention provides a lug 12 which performs the
function of both the lug and bush of a prior art bearing. As such,
there is no lug-bush interface to give rise to the problems
identified above with reference to FIG. 1, especially bush
migration and lug corrosion/fretting. Although the lug 12 may be
heavier than known lugs, due to it being formed from the second
material, the inventor has found that in embodiments of the
invention the advantage of the bearing surface being suitable for
frequent application of high stresses outweighs the associated
weight disadvantage. Such embodiments may be particularly well
suited to joints such as a landing gear door linkage.
[0050] FIG. 3 shows a dynamic bearing 20 according to a further
embodiment of the invention. The dynamic bearing 20 includes a lug
22 which may be defined by a structural component of an assembly
such an aircraft landing gear. The lug 22 defines a lug bore.
[0051] The inner peripheral wall of the lug 22, which defines the
lug bore, is provided with a lug coating or plating 24 which
defines a cylindrical bore arranged to receive an elongate,
generally cylindrical pin or shaft 26 when the shaft 26 is movably
housed within the bore in use. Thus, the bore-defining face of the
coating 24 defines a bearing surface. The coating 24 may be applied
by known techniques such as electroplating or metal spraying.
[0052] The shaft 26 is formed from a first material, which is
harder than a second material from which the coating 24 is formed.
Thus, the coating 24 is relatively sacrificial with respect to the
shaft 26. The lug 22 may be formed from a conventional lug material
such as steel or titanium.
[0053] Thus, the dynamic bearing 20 according to the illustrated
embodiment of the invention provides a lug coating 24 which
performs the function of the bush of a prior art bearing. The lug
coating 24 is applied to the lug 22 and may in embodiments of the
invention be applied by techniques such as those described below
which result in a high bond strength between the lug coating 24 and
lug 22. This reduces the likelihood of migration or rotation of the
bearing surface in comparison to prior art dynamic bearings. Also,
the bond at the lug-coating interface is less likely to permit
moisture ingress in comparison to the lug-bush interface of prior
art dynamic bearings.
[0054] FIG. 4 shows a dynamic bearing 30 according to a further
embodiment of the invention. The dynamic bearing 30 includes a lug
32 which may be defined by a structural component of an assembly
such an aircraft landing gear. The lug 32 defines a lug bore
arranged to receive a shaft 36. The inner peripheral wall of the
lug 32, which defines the lug bore, provides a bearing surface 34
arranged to support the shaft 36 when the shaft 36 is movably
housed within the bore in use.
[0055] The shaft 36 is formed from a first material, which is
harder than a second material from which the lug 32 is formed.
Thus, the bearing surface 34 of the lug is relatively sacrificial
with respect to the shaft 36.
[0056] The dynamic bearing 30 also includes grease grooves or ducts
38, 39 arranged to enable lubricant to be distributed around and/or
across the bearing surface 34. This may reduce friction between the
bearing surface 34 and the shaft 36.
[0057] The outer surface of the shaft 36 includes a plurality of
first ducts 39. The first ducts 39 extend lengthwise generally
parallel with respect to the longitudinal axis L of the shaft 36.
The dominant stress in a shaft 36 when used in a landing gear joint
is generally a bending stress due to a bending moment. Thus, the
first ducts 39 are generally aligned with the dominant stress in
the shaft 36, which reduces the likelihood of the first ducts 39
presenting a stress raiser problem.
[0058] The first ducts 39 are disposed in parallel around the
peripheral surface of the shaft 36. However in some embodiments,
the shaft 36 may in use have a loaded surface portion carrying
tension stress substantially parallel to the shaft axis, and an
unloaded surface portion carrying compression stress substantially
parallel to the shaft axis, and the first ducts 39 may be provided
in side portions between the centres of the loaded and unloaded
surface portions, where axial stress is reduced. This may be
particularly advantageous in embodiments where the shaft 36 is
arranged to be static relative to the load, with the lug 32 moving
around it such as an application on a joint on a stay, where the
shaft is static relative to one link of the stay, or on a torque
link assembly if the shaft is fixed in rotation relative to the
torque link.
[0059] The lug 32 includes a second duct 38. The second duct 38 is
circumferential and extends lengthwise in a direction generally
orthogonally with respect to the axis B of the bore defined by the
bearing surface 34. The dominant stress in a lug is generally
circumferential due to applied radial load placing the lug 32 in
tension. Thus, the second duct 38 is generally aligned with the
dominant stress in the lug 32, which reduces the likelihood of the
second duct 38 presenting a stress concentration or stress raiser
problem.
[0060] It is advantageous to provide the first ducts 39 in the
shaft 36 rather than the lug 32 because, if corresponding first
ducts 39 were provided in the lug 32, the first ducts 39 would
extend so as to be generally orthogonal with respect to the
dominant stress in the lug 32, meaning that the first ducts 39
would provide a stress raiser problem in the lug 32.
[0061] A lubricant such as grease is supplied to the ducts 38, 39
through a hole 37 in the lug 32 in a conventional manner, such as a
grease nipple connected to the duct 38 through a passageway. The
ducts 38, 39 are arranged to function as temporary reservoirs
between lubrication intervals. In some embodiments the lubricant
may be applied to one or more of the first ducts 39 and in use at
least some of the lubricant will migrate to the second duct or
ducts via the lubrication network defined by the ducts 38, 39. The
ducts 38, 39 are preferably open topped to enable grease or the
like to be exchanged between the ducts 38, 39.
[0062] FIG. 5 shows a dynamic bearing 40 according to a further
embodiment of the invention. The dynamic bearing 40 includes a lug
42 which may be defined by a structural component of an assembly
such an aircraft landing gear. The lug 42 defines a lug bore.
[0063] The inner peripheral wall of the lug 42, which defines the
lug bore, is provided with a lug coating or plating 44 which
defines a cylindrical bore arranged to receive an elongate,
generally cylindrical pin or shaft 46 when the shaft 46 is movably
housed within the bore in use. Thus, the bore-defining face of the
coating 44 defines a bearing surface. The lug coating 44 may be
applied by known techniques such as electroplating or metal
spraying.
[0064] The shaft 46 is formed from a first material, which is
harder than a second material from which the lug coating 44 is
formed. Thus, the coating 44 is relatively sacrificial with respect
to the shaft 46. The lug 42 may be formed from a conventional lug
material such as steel or titanium.
[0065] Thus, the dynamic bearing 40 according to the illustrated
embodiment of the invention provides a lug coating 44 which
performs the function of the bush of a prior art bearing. The
coating that is applied to the lug 42 results in a high bond
strength between the lug coating 44 and lug 42. This reduces the
likelihood of migration or rotation of the bearing surface in
comparison to prior art dynamic bearings. Also, the bond at the
lug-coating interface is less likely to permit moisture ingress in
comparison to the lug-bush interface of prior art dynamic
bearings.
[0066] The dynamic bearing 40 also includes grease grooves or ducts
48, 49 arranged to enable lubricant to be distributed around and/or
across the bearing surface 44. This may reduce friction between the
bearing surface of the lug coating 44 and the shaft 46.
[0067] The outer surface of the shaft 46 includes a plurality of
first ducts 49. The first ducts 49 extend lengthwise generally
parallel with respect to the longitudinal axis L of the shaft 46.
The dominant stress in a shaft 46 is generally a bending stress.
Thus, the first ducts 49 are generally aligned with the dominant
stresses in the shaft 46, which reduces the likelihood of the first
ducts 49 presenting a stress raiser problem.
[0068] The lug 42 includes a second duct 48. The second duct 48 is
circumferential and extends lengthwise in a direction generally
orthogonally with respect to the axis B of the bore defined by the
bearing surface 44. The dominant stress in a lug is generally
circumferential due to applied radial load placing the lug 42 in
tension. Thus, the second duct 48 is generally aligned with the
dominant stress in the lug 42, which reduces the likelihood of the
second duct 48 presenting a stress concentration or stress raiser
problem. The second duct 48 extends depth-wise into the lug through
the lug coating 44. This enables the second ducts to be deeper than
the coating, which may improve grease transfer.
[0069] It is advantageous to provide the first ducts in the shaft
46 rather than the lug 42 because, if corresponding ducts 49 were
provided in the lug 42, the first ducts 49 would extend so as to be
generally orthogonal with respect to the dominant stress in the lug
42, meaning that the first ducts 49 would provide a stress raiser
problem in the lug 42.
[0070] A lubricant such as grease is supplied to the ducts 48, 49
through a hole 47 in the lug 42 in a conventional manner. The ducts
48, 49 are open topped to enable grease to be exchanged between the
first duct 48 and the plurality of second ducts 49.
[0071] In embodiments of the invention the lug coating may have a
thickness of at least 0.05 mm. The lug coating may have a thickness
between 0.1 mm and 10 mm, preferably between 0.1 mm and 5 mm, more
preferably between 0.1 mm and 3 mm and even more preferably between
0.1 mm and 1 mm. A thickness of 0.1 mm provides for a reasonable
amount of wear, but anything above 0.3 mm is likely to be outside
the amount of wear expected in most embodiments. It may however be
advantageous for the lug coating to be up to 1 mm to allow for edge
wear.
[0072] In embodiments of the invention a coating such as the lug
coating may be applied by any suitable technique, such as
electroplating, or metal spraying or thermal spraying such as
plasma or high velocity oxygen fuel (HVOF) thermal spraying.
[0073] In embodiments of the invention the ducts may have any
suitable configuration which enables grease transfer without
adversely affecting the strength of the lug and shaft; the ducts
may be of conventional size, such as semicircular cross section of
1.5 mm radius, or generally rectangular cross section 2 to 5 mm
wide and 0.5 to 1 mm deep, and may be formed by any suitable
conventional technique, such as machining. Some detail shaping,
such as semi-hemispherical ends, or other tapering shapes may be
provided to reduce any local stress raiser effects at the groove
ends.
[0074] In embodiments of the invention one or more first ducts may
be provided in the shaft and arranged to extend so as to be
generally parallel with respect to the dominant stress in the
shaft. This may refer to the portion of the shaft disposed within
the lug. When the dynamic bearing is arranged such that the
dominant load experienced by the shaft is a bending moment, the
dominant stress angle in the shaft will be generally parallel with
respect to the longitudinal axis L of the shaft. Thus, in some
embodiments, one or more first ducts may extend lengthwise
generally parallel with respect to the longitudinal axis L of the
shaft such that the first ducts are generally aligned with the
dominant stresses in the shaft, which may reduce the likelihood of
the first ducts presenting a stress raiser problem.
[0075] In embodiments of the invention where the dynamic bearing is
arranged such that the shaft experiences combined bending and
torsional moments, the stress angle in the shaft will be at a
non-zero angle with respect to the longitudinal axis L of the
shaft. Thus, in some embodiments, one or more first ducts may
extend lengthwise at an angle of up to 45.degree. with respect to
the longitudinal axis L of the shaft such that the first ducts are
generally aligned with the dominant stress in the shaft, taking
account of both bending and torsion loading, which may reduce the
likelihood of the first ducts presenting a stress raiser
problem.
[0076] In embodiments where the dynamic bearing is arranged such
that the shaft experiences just torsion, the dominant stress angle
would be 45.degree. with respect to the longitudinal axis L of the
shaft and the first ducts may be arranged accordingly.
[0077] In embodiments of the invention one or more second ducts may
be provided in the lug and arranged to extend so as to be generally
parallel with respect to the dominant stress in the lug and in come
cases the lug coating also. One or more of second ducts may extend
at an angle of up to Tan.sup.-1=(lug width-3.times.groove
width)/lug bore diameter, in some embodiments up to 15.degree., in
some embodiments up to 10.degree. and in some embodiments up to
5.degree. from a plane perpendicular with respect to the bore axis
B.
[0078] In embodiments of the invention the shaft may comprise an
elongate member, such as a bar or hollow pipe. At least the portion
of the shaft arranged to be received by the lug may be generally
cylindrical.
[0079] In embodiments of the invention the shaft may be coated to
improve its hardness; for example, a coating comprising chromium, a
carbide based coating such as WC--Co--Cr, nickel or nickel alloy,
or diamond like carbon. In such embodiments, it is preferred that
the shaft coating is not applied to the first ducts due to the
detrimental effect that the plating process may have on the fatigue
resistance of the shaft.
[0080] In embodiments of the invention the first material may
comprise a relatively hard metal such as steel, titanium or a
nickel chrome alloy. In some embodiments the first material may
comprise a high strength corrodible steel which is plated for
harder coating and corrosion protection as described in the
preceding paragraph. Stainless steel is preferred if the shaft is
not coated.
[0081] In embodiments of the invention the second material may
comprise a relatively soft material; for example, a metal such as
aluminium bronze, aluminium-nickel-bronze, bronze, or other copper
alloys, or `white metal` families of alloys. In some embodiments
the second material may comprise a self lubricating material; for
example a self lubricating material containing PTFE, graphite or
molybdenum sulphide.
[0082] Thus, in embodiments of the invention the bearing surface is
either provided by the lug itself, or by a coating that is applied
to the lug. As such, a dynamic bearing according to embodiments of
the invention does not require a bush to be provided between the
shaft and the lug. The inventor has found that the interface
between a coating and the lug is less likely to result in rotation
or migration of the bearing surface. The dynamic bearing according
to the first aspect may therefore provide for a more robust dynamic
bearing that may be lighter than prior art bearings due to it not
including a bush. Moreover, the corrosion resistance of the bearing
may be improved due to the removal of the lug-bush interface, which
is a primary location for corrosion and fretting of the lug.
Moreover, the dynamic bearing according to the first aspect may
have improved electrical conductivity across the bearing relative
to prior art bearings including a lug-bush interface, which is
advantageous for lightning protection.
[0083] Although the invention has been described above with
reference to one or more preferred embodiments, it will be
appreciated that various changes or modifications may be made
without departing from the scope of the invention as defined in the
appended claims. The word "comprising" can mean "including" or
"consisting of" and therefore does not exclude the presence of
elements or steps other than those listed in any claim or the
specification as a whole. The mere fact that certain measures are
recited in mutually different dependent claims does not indicate
that a combination of these measures cannot be used to
advantage.
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