BACKGROUND OF THE INVENTION
This invention relates to a multi-disc aircraft brake system and
more particularly to a new and improved protective heat shield installation for
an aircraft multi-disc friction braking system.
During the braking of an aircraft, the alternately splined stator
and rotor discs of each of the multi-disc brakes are brought into sliding contact
with another, generating considerable heat energy that must be dissipated to eliminate
the highly deteriorative effects on the wheel and tire structure which, in certain
instances such as an aborted or rejected take-off, can result in sufficiently high
temperature to result in tire ruptures or fires.
The heat energy generated within the braking elements of the stators
and rotors (hereinafter also referred to as the heat sink), of each multi-disc
brake is dissipated via conduction, radiation and convection to the adjacent braking
components, such as the wheel assembly, bearings, pistons and other adjacent structures
as well as the associated tire. It is important to limit the heat transfer into
the adjacent structures and tire as much as possible to protect these structures
from excessive temperatures while dissipating the heat energy from the heat sink
to the atmosphere as quickly as possible. In certain braking systems, the heat
sink is of greater axial dimension than the wheel rim member into which the heat
sink extends. In such a braking system, it is important to protect the tire from
excessive radiant heat and the heat sink from contaminants such as water, especially
water containing de-icing chemicals, and other debris that may be kicked up from
the runway. One manner of protecting these is to provide a heat shield between
the heat generating elements of the (stators and rotors) heat sink and the wheel
assembly, with its adjacent components and bearings.
SUMMARY OF THE INVENTION
The present invention is directed to a tire supporting wheel and
brake assembly including a protective heat shield. The wheel has a rim member
having an inner surface that surrounds a heat sink composed of a plurality of stator
and rotor brake discs. The stators are slidably connected to a torque tube that
is connected to the stationary portion of the wheel supporting structures while
the rotors are slidably mounted to circumferentially spaced torque bars that are
connected to the rotatable wheel. A generally cylindrical louvered protective
heat shield extends axially beyond and is secured to the rim member to overlie
a portion of the interior wheel heat shield to protect such interior wheel heat
shield and protect the tire, wheel and brake discs while enhancing convection
cooling of the brake discs. A separate interior wheel heat shield is located in
the clearance space between the inner surface of the rim member and the circumferentially
spaced torque bars and secured thereto.
The protective heat shield of the present invention is a generally
cylindrical structure having a series of spaced louvers along and about its circumference
that is fastened to the wheel. The heat shield may be a single piece cylindrical
structure or formed of arcuate segments which when assembled form a cylindrical
structure. The heat shield serves to protect the tire and wheel rim flange from
excessive brake heat during high energy stop conditions by blocking the radiation
path while enhancing convection cooling of the heat sink due to the presence of
the louvers. In addition to the above described advantage, the louvered heat shield
protects the braking elements by impeding the ingress of rain or other liquids
and foreign objects as the vehicle is moving because the ingression path is blocked
and any matter which may contact the shield is deflected away due to its rotation
with the wheel. The louvers are constructed to retain any liquid on the circumferentially
external surface of the shield by provision of a raised lip at the bottom of each
louver opening. Also liquid sprayed on the circumferentially external surface of
the shield such as that created by the action of the tires rolling on the runway
will not easily enter the louvered opening because of its overlapping construction.
The heat shield also serves to protect the interior wheel heat shield, which may
be vulnerable to damage during maintenance operations, from handling damage and
is easily replaceable.
BRIEF DESCRIPTION OF THE DRAWINGS
- Figure 1 is a fragmentary cross-sectional view of a wheel and brake assembly
with heat shields according to the invention installed thereon;
- Figure 2 is a front elevational view partly in section of a portion of an interior
wheel heat shield fastened to a torque bar spacer and rim member;
- Figure 3 is a front elevational view partly in section of a portion of a protective
heat shield according to the invention mounted on the inboard end of the rim member;
- Figure 4 is a fragmentary plan view of the protective heat shield shown in
- Figure 5 is a fragmentary perspective view of a segmented cylindrical protective
heat shield according to the invention;
- Figure 6 is a fragmentary exploded view of the joint of Figure 5;
- Figure 7 is a fragmentary elevational view of another embodiment of a protective
heat shield according to the invention having an alternate arrangement of louvers
useful in the invention;
- Figure 8 is a cross-sectional view of a further embodiment of a protective
heat shield according to the invention;
- Figures 9A through 9C are schematic sectional views showing the manner of formation
of a louver according to the invention.
Referring to the drawings, wherein like reference numerals designate
like or corresponding parts throughout the several views, there is shown in Figure
1 a friction brake mechanism 10 for use with a cylindrical wheel 11, having matching
inboard wheel section 12 and outboard wheel section 13. Each of the wheel sections
12, 13 has a corresponding respective rim member 14, 15, web member 16, 17, and
hub member 18, 19. The wheel sections 12 and 13 are fastened together by suitable
bolts (not illustrated) disposed in aligned bores (not illustrated) within web
members 16 and 17 to form an integral unit. Friction brake mechanism 10 is generally
symmetrical about its central axis of rotation 33.
The hub members 18 and 19 are rotatably supported by bearings 22
mounted on a nonrotatable axle member 23. A stationary carrier or boss 24 provided
with a circumferentially-extending flange 25 is suitably mounted on stationary
axle 23. Flange 25 has a plurality of circumferentially spaced bores 21 to receive
bolts 26 for securing such flange to one end of a cylindrical torque tube 27. The
other (outboard) end of torque tube 27 has an annular and radially outwardly extending
reaction member 28. The reaction member 28 may be made integrally with the torque
tube 27 as illustrated in Figure 1 or may be made as a separate annular piece
and suitably connected to the torque tube 27.
Torque tube 27 has on its exterior a plurality of circumferentially
spaced, axially extending splines 30. Inboard wheel section 12 has a plurality
of circumferentially spaced torque-transmitting bars 35 each connected to the
rim flange portion 85 of wheel section 12 at their inboard ends by respective spacer
means 62 to be described and at their outboard ends to the radially outward portion
of web member 16 by seating in respective annular recesses 43 in such web member.
The torque bars 35 may be varied in design from those shown and secured to the
wheel section 12 by other suitable means such as is described in U.S. Patent 5,024,297
to Russell to provide an integral connection therebetween.
Splines 30 support an axially non-rotatable piston end disc or stator
disc 38 and inner discs 39, 40 and 41. All of such non-rotatable discs 38, 39,
40 and 41 have slotted openings at circumferentially spaced locations on their
respective inner peripheries for captive engagement by the splines 30, as is old
and well-known in the art. A non-rotatable annular disc or annular braking element
42 is suitably connected to the torque plate or reaction member 28 and acts in
concert with the stator discs 38, 39, 40 and 41 which discs (38, 39, 40, 41 and
42) constitute the stators for the friction brake 10. A suitable manner of connection
of disc 42 to reaction member 28 is described in U.S. Patent 4,878,563 to Baden
Each of a plurality of axially-spaced discs (rotor discs) 44, 45,
46 and 47 interleaved between the stator discs 38 through 42, has a plurality of
circumferentially spaced openings along its respective outer periphery for engagement
by the corresponding wheel torque bar 35, as is old and well known in the art,
thereby forming the rotor discs for the friction brake 10. All of the non-rotatable
discs (38, 39, 40, 41 and 42) and rotatable discs (44, 45, 46 and 47) may be made
from a suitable brake material such as steel or other metal or other wear-resistant
material such as carbon for withstanding high temperatures and providing a heat
sink. The number and size of discs may be varied as necessary for the application
involved. Those stator discs and rotor discs that have circumferentially spaced
openings on their repective inner and outer peripheries may accommodate reinforcing
inserts to provide reinforcement to the walls of such slotted openings and to
enhance the life of such slots, as is old and well-known in the art.
The actuating mechanism or power means for the brake includes a plurality
of circumferentially spaced cylinders 50 suitably mounted on or connected to the
flange 25. Within each of the cylinders 50 is a hydraulic piston, which is operative
to move the stator discs 38 through 41 axially into and out of engagement with
their respective associated rotatable discs 44 through 47, which in turn causes
the facing radial surfaces of all of the brake discs to frictionally engage their
radial surfaces as they are forced toward but are resisted by the end stationary
annular disc 42 and the reaction member 28 on torque tube 27. During this period
of brake disc engagement, the friction forces among all the rotatable and non-rotatable
discs generate considerable heat energy within the discs. It is the frictional
engagement of these stator and rotor discs which produces the braking action for
the aircraft wheel.
An interior wheel heat shield 60 as shown in Figures 1 and 2 is cylindrically
shaped and is located between the inner surface 20 of wheel section 12 and the
torque-transmitting bars 35. Interior wheel heat shield 60 may be formed as a
single cylindrical piece or by joining together a plurality of arcuate pieces.
As described above, each torque bar 35 at its outboard (wheel web) end is connected
to the web member 16 by seating in an annular recess 43. The inboard (piston)
end of each torque bar 35 and the adjacent portion of the heat shield 60 is secured
to inboard rim member 14 of inboard wheel section 12 by a spacer 62 (Figure 2).
Spacer 62 is a rectangular shaped member that is recessed on its upper and lower
surfaces to present an upper flat surface 63 with a pair of spaced abutments or
shoulders that receive the sides of torque bar 35 and present a lower surface
66 with a lower pair of abutments or shoulders. Extending outboardly toward the
wheel web member 16 (as viewed in Figure 2) from the rectangular shaped member
of spacer 62 is a flanged portion 70 of substantially less thickness than the main
body portion of spacer 62. The flanged portion 70 has a bore 71 to facilitate
the securing of the spacer 62 to the interior wheel heat shield 60 by fasteners
or a rivet 72.
The interior wheel heat shield 60 has a plurality of circumferentially
spaced rectangular apertures 80 adjacent its inboard end to receive the main rectangular
shaped body portion of spacer 62 to secure the heat shield axially and radially
in position. As seen in Figure 2, the torque bar 35 has a bore 81 in alignment
with a bore 82 (in the spacer 62) and bore 83 in a flanged portion 85 of inboard
rim member 14 to receive a bolt 89 which interconnects and secures these members
(torque bar 35, spacer 62, heat shield 60 and rim member 14). With the interior
wheel heat shield 60 firmly in place, the protective heat shield 90 effectively
protects the wheel and its supporting structure from the transfer of heat energy
from the heat sink.
The interior wheel heat shield may be formed by laminating a layer
of ceramic fibrous material between two layers of stainless steel in a manner well
known in the art.
A protective heat shield 90 of cylindrical configuration has a plurality
of circumferentially spaced apertures 91 adjacent one side (outboard) edge and
a plurality of circumferentially spaced recesses or cut-out portions 92 along the
same (outboard) side edge alternating with the apertures 91. Preferably, each of
apertures 91 is located within one of a plurality of tabs 88 that are circumferentially
spaced from one another along the outboard edge of heat shield 90. Tabs 88 are
provided to reduce the stresses in the shield 90, wheel flange portions 93 and
the fasteners 95 that might otherwise occur due to thermal gradient induced differences
in thermal expansion, or deviation in shape or dimensions of the shield 90 or flange
portions 93. The heat shield 90 is mounted on a plurality of flange portions 93
that extend axially inboardly from rim member 14, at circumferentially spaced apart
locations with a plurality of fasteners 95 extending through a plurality of corresponding
bores 96 in flange portions 93 and apertures 91 in heat shield 90. Flange portions
93 lie substantially along the same arc as flange 85 of rim member 14. The respective
circumferentially spaced cut-outs or recesses 92 in heat shield 90 register with
the fasteners 89 of the spacers 62. As seen in Figure 3, the protective heat shield
90 is of a larger diameter than interior wheel heat shield 60 to protect the interior
heat shield 60 from the ingress of foreign objects thereinto and for the deflection
of foreign materials such as water, deicing chemicals, and other debris which
contact the radially exterior surface of protective heat shield 90.
The other (inboard) side edge of the cylindrically shaped heat shield
90 (Figures 1, 3, 4 and 4) and 90' (Figure 5) has a reinforcing edge such as edge
103. Adjacent the inboard side edge the protective heat shield 90 has a plurality
of circumferentially spaced series of louvers 98. The louvers in all the series
are alike and only one louver will be described. Each louver has a curvilinear
radially outer portion or cap 99 that overlies a circumferentially extending aperture
100 with the overlying edge portion 101 of cap 99 being effective to deflect liquid
or foreign objects from entering the aperture 100. When viewed in cross section
defined by a plane that includes the central axis of rotation 33 as shown in Figures
1 and 3, the generally cylindrical radially outer surface of heat shield 90 appears
as generally flat surface 106 and edge 101 overlies the aperture 100 such that
a plane perpendicular to the generally flat surface 106 of the heat shield 90
and extending radially outward from the edge 104 of aperture 100 would fall inwardly
of the edge 101 onto the curvilinear portion 99. The base 102 of each respective
louver 98 that joins the main body of the cylindrical heat shield 90 includes an
edge 104 having a curvature to allow flow of liquid circumferentially therealong
thereby inhibiting the flow of liquid into the aperture 100 from radially external
In Figures 5 and 6 there is illustrated a portion of a modified protective
heat shield 90'. Heat shield 90' differs from the previously described embodiment
shown in Figures 1, 3 and 4 in that it is formed of a plurality of arcuate segments
110 and its circumferentially adjacent sets of louvers 99 are axially offset relative
to one another. Each of the arcuate segments 110 is preferably alike as shown.
The circumferentially leading edge 111 of segment 110 and the circumferentially
trailing edge 121 of adjoining segment 110 are complementarily formed such that
they mechanically interlock. The circumferentially leading 111 edge of segment
110 is split approximately midway of it axial width to form axially outboard tab
112 and axially inboard tab 114. The circumferentially trailing edge 121 of adjoining
segment 110 is also split approximately midway of its axial width to form axially
outboard tab 122 and axially inboard tab 124. When assembled as shown in Figures
5 and 6, tab 112 extends beneath tab 122 and tab 114 extends over tab 124. A portion
of the reinforced axially inboard edge 103 is removed from each segment 110 to
enable full engagement of tabs 112, 122, 114, and 124. Each segment 110 includes
an aperture 91 along its outboard side edge and circumferentially spaced therefrom
a recess or cutout portion 92. Aperture 91 is positioned within tab 88 which is
defined by two circumferentially spaced slots 94 which extend axially from the
axially outboard edge of segment 110. The leading edge 111 and the trailing edge
121 of each segment 110 may be provided with apertures 125 for receipt of mechanical
fasteners after joinder of two segments 110.
Still having reference to Figure 5, if shield 90' is impacted between
louvers 130 and 132 by liquid such as by drop 136 as shield 90' is rotated in the
direction of arrow 138, drop 136 will travel along the external surface of shield
90' until it is deflected radially outwardly by the leading edge ramp or curved
surface 139 of cap 99 of louver 140. The leading edge ramp or curved surface of
each cap serves to sling off liquids which contact the radially external surface
of shield 90' as it rotates.
In Figure 7 there is shown another embodiment of a protective heat
shield 90'' differs from the embodiments shown and described with respect to Figures
1, 3, 4, and 5 in that the louvers 98 are provided in series of spirally extending
rows spaced about the circumfential direction the shield 90''.
A modification of the louvered construction is shown in Figure 8.
Each louver 98' includes a curvilinear cap 99' which overlies the aperture 100'
that is modified compared to cap 99 of previously described embodiment of Figure
3 such that the outermost portion of the cap 99' is nearly straight as shown in
Figure 8 when viewed in in cross-section defined by a plane that includes the
central axis of rotation, and that portion of the base 102' of each louver 98'
is essentially flat when viewed in cross-section as shown in Figure 8 (and cylindrical
when viewed in a perspective view) with a turned radially outwardly lip 104'.
The reinforcing edge 107 is formed of a separate piece of metal 108 that is wrapped
around the inboard edge of the shield. This construction is a variation of the
previously described embodiment of Figures 3 and 4 and the embodiment of Figure
As shown and described above the protective heat shield 90 is a full
circle construction which provides for enhanced thermal protection, structural
integrity and clearance to the wheel while also protecting the interior wheel
heat shield 60 and heat sink from foreign objects. Such louvered heat shield allows
for convection cooling of the heat sink and can be easily replaced if damaged beyond
repair. Where the protective heat shield is formed of segments such as segments
110, any segments that are damaged can be easily replaced if damaged beyond repair.
A manner of formation of louvers like those shown in Figures 1, 3,
4, and 5 to achieve overlap of their respective apertures by their associated caps
is schematically depicted in Figures 9A, 9B and 9C sequentially. A flat sheet
of metal such as sheet 142 shown in Figure 9A is deformed to the shape shown in
Figure 9B by stamping in a press fitted with a set of matched (male/female) dies
corresponding to the desired shape such as that shown in Figure 9B. Stamping causes
the metal of region 144 to be drawn and that of region 145 to be bent at an angle
from base plane 143. The edge of region 145 is then severed slightly above the
base plane 142 thereby forming a lip 104 and region 145 is forced away from base
plane 143, thereby completing formation of a cap 99 (such as cap 99 shown in Figures
1, 3, 4, 5, 7 or 99' as in Figure 8) whose edge 101 overlaps the lip 104.
A suitable protective heat shield may be constructed from stainless
steel (for example, from a sheet of about 0.050 to about 0.060 inch in thickness)
or other material that is resistant to corrosion and to warping at the temperatures
expected in service.
It will be apparent that although a specific embodiment and a certain
modifications of the invention have been described in detail, the invention is
not limited to the specifically illustrated and described constructions since
variations may be made without departing from the principles of the invention.
For example, the number, size, shape and spacing of the louvers may be varied.
The louvers may be provided in spirally extending rows as shown in Figure 7 or
other patterns. The radius and height of the lip such as lip 104 may be varied.
The louvers may be formed at an angle to the circumferential direction of the shield;
however, this is not believed to be the most economical approach because the sense
of the angle must be reversed if the shield is to be installed on a wheel and brake
assembly to be rotated in the reverse direction, as when a pair of wheels are
positioned on opposites sides of the same landing gear. The manner of attachment
of the louvered heat shield to the remainder of rotatable wheel and brake assembly
may be varied from that described and illustrated. If formed of segments, the segments
need not all be identical, although such construction is preferred for economy.
The cylindrical shield may be formed of segments that are welded and/or mechanically
joined, e.g. by rivets or threaded or other fasteners, to form a complete cylindrical
structure prior or subsequent to attachment to the wheel and brake assembly.