Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The invention relates to a brake disc assembly particularly for large
industrial brake discs having air cooling passages.
Large industrial brake discs, that is brake discs that exceed 0.5 metres in
diameter and are capable of absorbing large amounts of power, are
commonly provided with air cooling passages. The air cooling passages
extend radially from an inlet generally adiacent the centre of the disc to an
10 outlet adjacent a periphery of the disc. The passages pass between surfaces
of the disc that are to be swept by brake shoes. As the disc rotates, air is
sucked into the inlet, and discharged from the periphery somewhat in the
manner of a centrifugal pump. Air passing through the passages between
the surfaces removes heat generated during braking. Temperature
15 variations across the disc produce inequal expansion and contraction, which
can cause serious distortion of the disc and consequent erratic braking.
Commonly, discs of this size are manufactured by sand casting as a single
piece, using expendable cores to produce the air cooling passages within the
20 disc. Difficulties can be encountered when casting large discs, particularly
to produce a sound casting without "cold-shuts" or "mis-runs" ir~ relatively
thin internal webs or walls between the air cooling passages. Large discs of
this type can also be difficult to cast and concurrently maintain material
integrity, in which the material is free of mold inclusions and oxide
25 inclusions, which is necessary for discs which rotate at high speeds and
absorb large amounts of horsepower. The rough-cast disc is machined to
produce smooth annular braking surfaces on each side of the disc. The cost
of manufacturing such discs can be quite high due to the high scrap rates,
and salvaging costs of poorly cast discs~ If a portion of the one-pisce cast
30 disc cannot be salvaged9 the whole disc is rejected, thus increasing
manufacturing costs.
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SUMMARY OF THE INYENTION
The invention reduces the difficulties and dlsadvantages of the prior art by
proYiding a brake disc assembly whlch uses a combinatlon of a main steel
disc produced by a high quality controlled process, eg., from a rolling mlll,
and a plurality of relatively small, preferably dle-cast, components which
are secured to the steel disc. Because the steel disc is produced under
controlled cnnditions, it has high material integrity when compared with a
sand-cast dis~. The small die-cast components have a higher material
integrity than large sand-cast components, and, due to close tolerances that
can be obtained when die-casting, require less machining than equivalent
sand-cast parts. The die cast components are sufficiently small to permit
production in a conventional die casting machine. The smaller cast
components can expand and contract individually relative to each othsr,
thus reducing thermal stresses and distortion when compared with a one-
piece disc. Furthermore, if a few of the small cast components are
- 15 damaged during operation of the disc, the few damaged cornponents can be
replaced with servicable components, without requiring a major salvage or
complete scrapping of the disc.
A brake disc assembly according to the invention has a main disc member
and a plurality of disc segments. The main disc member is adapted for
rotstion about a disc axis and has first and second rnain surfaces disposed
normally to the disc axis. ~he disc segments are secured to the main disc
member, and each disc segment has inner and outer surfaces, inner and
outer edges which define inner and outer margins of the inner and outer
edges, and first and second interconnecting edges which interconnect the
inner and outer edges. The outer surface of each segment is flat and
disposed parallel to the main surfaces of thP disc, and the inner surface has a
plurality of ridges and at least one groove. The ridges are spaced apart by
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the groove, and at least two of the ridges contact one of the main surfaces
of the main disc member so that the groove cooperates with the main
surface to form at least one passage between the disc segment and the disc
member. Each interconnecting edge of one disc segment cooperates with
an adjacent interconnecting edge of an adjacent disc segment so that the
outer surfaces of the disc segments secured to a particular main face of the
disc member are co-planar with each other and form a generally flat braking
surface disposed normally to the disc axis and are adapted to be swept by a
brake pad.
In one embodiment, an external fan element is provided adjacent a portion
of each disc segment closest to the disc axis, so that the fan element is
adapted to cooperate with similar fan elements to provide an external fan
means to direct a flow of air acros~ the outer surfaces of the disc segments
as the disc rotates, thus augmenting cooling.
A detailed disclosure following, related to drawings, describes preferred
embodiments of the invention, which is capable of expression in structure
other than that particularly described and illustrated.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a simplifiPd front elevation of a brake disc assembly
according to the invention, as viewed along an axis of a
brake shaft,
Figure 2 is a simplified, partly-sectioned, side elevation Df the
brake disc assembly, as seen from line 2-2 of Figure 1,
Figure 3 is a simplified front elevation of a disc segment shown
secured to a portion of a main disc member, portions of
adjacent disc segments being shown on each side of the
disc segment,
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Figure 4 is a simplified fragmented section as seen on arcuate line
4-4 of Figure 3, looking inwardly towards the axis,
Figure 5 is a simplified front elevation of an alternative brake disc
assembly according to the invention fitted with external
fan means,
Figure 6 is a simplified, partially-sectioned, side elevation oF the
brake disc assembly of Figure 5,
Figure 7 is a simplified front elevation of a disc segment of the
assernbly of Figure 5, portions of adjacent disc segments
being shown on each side of the disc segment,
Figurc ~ is a simplified fragmented section on line 8-8 of Figure 7,
showing a portion of external fan means,
Figure 9 is a simplified, fragmented section on an arcuate line 9-9
of Figure 7, looking inwardly towards the disc centre,
some dimensions being distorted.
DETAILED DIS~OSURE
Figures 1 and 2
P. brake disc assembly 10 according to the invention is mounted on a shaft 12
for rotation about a disc axis 14. The brake disc ~ssembly includes a main
disc member 16 adapted for rotation about the disc axis 14, and having first
and second parallel main surfaces 17 and 18. The shaft 12 is secured, for
30 example by a flange 19, to the disc 16 which thus carries braking torque.
The disc member 16 can be a rolled steel disc of high material integrity and
strength, in contrast to prior art sand-cast brake discs.
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The disc assembly also includes a plurality of disc segments severally 20,
which are secured to the main disc member. The disc segments are
disposed as first and second sets 21 and 22 respectively which are secured to
the first and second main surfaces 17 and 18 of the disc member so that the
main disc member is sandwiched between the two sets of disc segments. A
specific disc segment 25 of the plurality 20 has arcuate inner and outer
edges 28 and 29, and radially disposed, first and second interconnecting
edges 31 and 32 which interconnect the inner and ou~er edges. It is seen
that the term "segment" as used herein is not to be construed in the strict
geometrical sense, but instead the segment 20 is seen to resemble a
truncated sector of a circle. The segments are essentially similar to each
other, and thus when a set of segments is assembled and secured to the main
surface of the main disc member, the set forms circular, concentric inner
and outer edyes 34 and 35 of the sets of disc segments.
Figures 3 snd 4
The disc segment 25 has outer and inner surfaces 41 and 42, the outer
surface being flat and disposed parallel to the main surfaces 17 and 1~ of the
disc, as best seen in ~ Figure 4.
Preferably, shallow grooves 37 extend across the outer surface 4~ and are
inclined at an angle 38 to a central radius 43 of the segment. The angle 38
is not a right angle in order that the grooves 37 are not inclined tangentially
to the segment to avoid producing complementary ridges in the brake pads.
The grooves assist in minimizing distorsion due to thermal gradients across
the segment.
The inner surface has a plurality of ridges 45 and grooves 47, the ridges
being spaced apart by the grooves. The ridges 45 include elongated first
and second ridges 49 and 50 which are generally adjacent and extend the full
length of the first and second interconnecting edges 31 and 32 respectively.
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The ridges 49 and 50 have out~r~edge portions 53 and 54 which contact the
main surface 17, the ridges being of equal depth so that the edge portions 53
and 54 ~re disposed within a plane parallel to the outer surface 41 and
parallel to the main surfaces 17 and 18 of the disc. Preferably, similar
outer portions of the remaining ridges 45 also contact the main surface 17,
so that the grooves 47 cooperate with the main surface 17 to form s plurality
of air cooling passages 46 between the disc ~egment and the disc rnember.
The first and second ridges 49 and 50 are designated as outer ridges~ and the
remaining ridges 45 can be designated as inner ridges which are positioned
between ehe first and second outer ridgss and extend gener~lly radislly to
define the open-ended radially extending cooling passages 46 within the disc
as~embly. The inner ridges include an elongated central inner ridge 48
extending along the central radius of the sagment, two intermediate inner
ridges 51, and four shorter inner ridges 52.
The di3c segment 25 has a plurality of parallel clearance openings 5a which
are disposed along the first and second interconnscting edges 31 and 32, and
similar openings 59 disposed along the central inner ridge 48. The fir~t and
second ridges 49 and 50 havs relatively short bos~es 60 containing the
openings 58, the bosses being generally integral with the respective ridges
49 and 50 adjacent the outer surface 41 as shown. The inner ridge 48 has
integral bosses 61 containing the clearance openings 59, the bosses being full
depth to extend between inner and outer surfacea of the 3egrnent. The
openings SB and 59 are counterbored adjacent the outer surface. ln effec~,
the disc segment ha~ a plurslity of parallel openings passing between the
inner and outer surfaces of the disc segment. The main disc mamber 16 ha~
a plurality of internally threaded openings 62 spaced along radii of the disc,
the openings 5B and 59 of the disc ~egment baing adapted to regi~ter with the
openings 62 of the disc. A plurality o~ sorews 63 and 64 p83S through the
openings 58 and 59 respectively in the disc segments which are clearance
openings, and sre threaded into openings 62 in the disc member which are in
registration with each other, so as to ~ecure the disc segments to the main
disc member. The screws 63 in the openings 58 can be smaller than the
7 13~'~5Z4
screws 64 in the openings 59, as shown, thus reducing obstruction of the
outer cooling passages through the disc. The openings 58 and 59 arP in a
particular hole pattern spaced adjacent the interconnecting edges and along
a radial centre line of the segment so as to eliminate essentially any
warpage of the disc segment due to thermal stresses.
The inner and outer edges 28 and 29 are concave and convex respectively,
both edges being concentric with the disc axis 14 of Figures 1 and 2 as
previously stated. The first and second interconnecting edges are inclined
to each other at a sector angle 4b, which is subtended at the axis 14 by the
outer edge 29 of the disc segment. Thus, when the disc segment is secured
to the main disc member, the first and second interconnecting edges are
aligned with radii of the disc, and inwardly inclined radial extensions of the
first and second interconnecting edges intersect at the disc axis. In Figure
3, the radii and radial extensions of the edges 31 and 32 coincide and are
designated 39 and 40 respectively.
The first interconnecting edge 31 has a plurality of recesses 65 and
projections 66 extending therealong and alternating with each other from
adjacent the inner edge 28 to the outer edge 29. Similarly, the second
interconnecting edge ~2 has si nilar recesses 67 and projections 68 extending
therealong. Adjacent the inner edge 28 and on the interconnecting edge 31
there is a half recess 70, and correspondingly on the interconnecting edge 32
there is a half projection 71. The half recess and half projection ensure
that the recess and projections of the first interconnecting edge are
staggered radially relative to the recesses and projections of the second
interconnecting edge. This radial staggering ensures that opposite
interconnecting edges of a disc segment are complemcntary to each other,
and is necessary to permit adjacent segments to fit together as follows. An
3~ adjacent disc segment 73, shown fragmented in broken outline, has a second
interconnecting edge 74, which is essentially indentica~ to the edge 32 and
thus is also complementary to the edge 31. This permits the projections
and recesses of the first interconnecting edge 31 of the first disc segment 25
3 3~ 4
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to be engaged by the recesses and projections of the second interconnecting
eclge 74 of the second disc segment 73. Similarly, a third disc segment 75,
shown fragmented in broken outline on an opposite side of the disc segment
25, has a first interconnecting edge 76 which is complementary to the
second interconnecting edge 32 of the first disc segment.
To reduce weakening effects of the openings 62 in the main disc member 16,
the threaded openings 62 for the segments on one side of the disc are spaced
some distance from similar threaded openings for the segments on the other
side oF the disc. To ensure adequate thread engagement depth, for a
relatively thin disc member 16, ths screws of one set do not engage a disc
opening 62 used by screws of the other set. As seen in Figure 4, the edges
31 and 32 of the disc segment 25 of the first set 21 are staggered
circumferentially by a spacing ~0 relative to an ed~e 78 of a disc 79. The
spacing Bû is equal to one half oF the chord width of a segment at that
particular radial location. Note that openings for the screws 63 along an
interconnecting edge of a segment of one set do not coincide with the
openings for the screws 59 along the central radius of the other set.
OPERATION
The main disc membsr 16 is mounted for rotation on the shaft 12 and the
first and second %ets of segments 21 and 22 are secured by screws 6~ and 64
passing through respective openings 58 and 59 in the disc segments alignsd
with the openings 62 in the disc member. The disc assembly is then
machined so as to remove a skim of material from the outer surfaces 41 of
the disc segments, so that outer surfaces of the disc segments secured to a
particular main face of the disc member are coplanar with each other and
form a generally flat braking surface disposed normally to the disc axis.
This is to ensure that minor manufacturing and fitting errors are essentially
removed so that the braking surface can be swept by a brake shoe or pad
r~
without interference between joints between adjacent disc segments.
During operation, air is drawn adjacent the centre of the disc and passes
through the cooling passages to exit through the outer periphery of the disc,
similarly to a normal air cooled brake disc. Heat generated during braking is
conducted from the outer surfaces of the segments to the inner surfaces
thereof, and then to the disc member 16 itself. There is sufficient
clearance between the screws 63 and 64 and the clearance openings 5B and
59 to permit the segments to move slightly relative to each other and the
disc member 16; and to accommodate any deflection of the screws that
lû might occur due to relative movement between the segments and the disc
member. This slight movement and the shallow grooves 37 are sufficient to
avoid excessive distortion of the disc assembly as a whole due to thermal
expansion and contraction. The projections and recesses of the
interconnecting edges similarly permit this slight movement to svoid
excessive distortion.
~LTERNATI VES
The disc segment is shown with the two outer ridges 49 and 50 adjacent the
20 edges 31 and 32 and a plurality of inner ridges disposed between the central
ridge. This provides a plurality of grooves ~7 between the ridges but if only
two ridges were usedJ only one groove between the two ridges would result.
This is adequate for some applications. If each ridge of the plurality of
ridges contacts a respective surface of the disc member, a plurality of
25 passages 46 is formed between the segment and disc member 16. Clearly,
the more ridges there are, the more passages are formed and the greater is
the surface area for cooling. To ensure a sufficient connection between the
disc segment and disc member, a minimum of two ridges should contact the
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disc member, and preferably these should be the ridges adjacent the
interconnecting edges. The inner ridges do not need to contact the disc
member surface but this is preferred for improved thermal conductivity
from the discs outer surface to the disc member and to enhance strength of
the disc assembly.
The brake disc assembly ~0 of Figures 1 and 2 is provided with two sets of air
cooling passages 46 on both sides of the main disc member 16 which removes
heat internally from the disc. For enhanced cooling of the braking
surfaces, an external fan means can be provided which directs jets of air
across the braking surfaces from the centre of the disc outwardly, so as to
increase air flow across the disc and thus enhance cooling from the outer
surface of the disc segment. Figures 5 through 9 show alternative disc
segments including fan elements which can be cast or fabricated as a single
or integral unit with the disc segment, and assembled in the manner as
described previously. Alternatively, a separate annular fan element can be
cast as a single-plece independent pump unit and then secured adjacent the
centre of the disc assembly of the segments 20, but this alternative is not
shown.
Figures 5 and 6
An alternative disc assembly 81 is mounted for rotation on a shaft 82 and has
a main disc member 85, the shaft 82 and disc member 8S being essentially
similar to those of Figures 1 and 2. Alternative disc segments, severally
88, are secured as first and second sets 89 and 90 to opposite first and
second main faces 91 and 92 of the main disc member 86. The first and
second sets 89 and 90 have external fan means 95 and 96 respectively which
surround the shaft 92 and direct jets of air outwardly across outer surfaces
of the sets 89 and 90 respectively of the disc segments. The fan means 95
has annular inlet and discharge openings 97 and 98 which surround the shaft
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82, and similar openings are provided for the fan means 96 of the set 90 on
the opposite side of the assembly.
Figures 7 through 9
A typical alternative disc segment 101 of the segments 88 has outer and
inner surfaces 103 and 104, and inner and outer edges ln7 and lD8 whic
define inner and outer margins respectively of the surfaces of the disc. The
disc element also has first and second interconnecting edges 109 and 110
which interconnect the inner and outer edges to define the shape of the disc
segment. In contrast with the segment 20 of Figures 1 through 4 the edges
109 and 110 are not provided with recesses and projections, but inst~ad are
straight, so that all interconnecting edges are similar to each otherO The
outer surface 103 is flat and dlsposed parallel to the main surfaces of the
disc member, and the inner surface 104 has a plurality of ridges and grooves
112 and 113 respectively to form air cooling passages 114 which are
generally similar to those previously described with reference to Figures 3
and 4, with main di fferences as described below.
The segment 101 has a plurality of spaced parallel clearance openings 105
extending along and generally adjacent the interconnecting edges 109 and
110, and a plurality of spaced paralle~ clearance openings 106 extending
along a central radius of the segment. The openings 105 and lU6 pass
through respective relatively short bosses 102 and 111 respectively, and
receive screws 116 and 119 respectively to secure the segment to the disc
member. The relatively short bosses minimally obstruct air flow through
the passages 114. In contrast with the segment 20 of Figures 1 through 4,
some of the ridges are intersected by the screws which pass clearly through
clearance gaps in the ridges, and the full depth bosses 61 of Figures 3 and 4
containing the screws are eliminated. A central inner ridge 121 i8 divided
intn five aligned ridge portions 127 by four screws 119. Similarly a typical
- 12 -
outer ridge 128 adjacent the edge 110 is divided into a plurality of aligned
ridge portions by five screws 116. Shanks of the screws 116 and 119 are
aligned with the ridge portions to reduce air obstruction, and spaces on
opposite sides of the shanks separate the screws from the ridge portions,
thus permitting movement of the segments relative to the screws and
accommodating any deflection of the screws.
An external fan element 115 is provided adjacent a portion of the disc
segment closest to the disc axis, not shown, and is adapted to cooperate
with similar fan elements of the plurality of disc segments to provide the
external fan means 95 as described previously. The fan element includes
first and second fan side walls 117 and 118 which are circumferentially
spaced apart and radially extending as inward extensions of the
interconnecting edges 109 and 110. The side walls 117 and 118 also extend
outwardly axially from the main disc member to a position spaced outwardly
axially from the outer surface 103 of the disc segment. The fan element
also includes a fan interconnecting wall 120 which extends between the two
spaced fan side walls and is spaced axially distances 122 and 123 from the
outer surface 103 of the brake segment and the main surface 91
respectively. It can be seen that the interconnecting wall 120, the two fan
side walls 117 and 118 and a portion of the outer surface 103 of the brake
segment define an elemental discharge opening 124, which is a portion of the
annular discharge opening 98. The discharge opening is adapted to direct a
Jet of air, shown as arrow 125, across the outer surface 103 of the brake
segment as the assembly rotates. The fan interconnecting wall 120 has an
outwardly flared portion 126 which diverges axially outwardly from the main
surface of the main disc member, as best seen in Figure 8. Preferably, the
outwardly flared portion is generally concentric with the shaft axis, so thst
when the plurality of disc segments are secured to the main disc member,
the generally annular inlet opening 97 is generated, as shown partially in
Figures 5,6 and 7. It can be seen that the assembly of external fan
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- 13 -
elernents functions as a centrifugal pump so that air entering the opening 97
passes between the walls 117, llB and 120 and the surface 103 to discharge
partially through the discharge opening 124 as the arrow 125, and partially
to pass along the generally radial air cooling passages 114 within the disc
segment as an arrow 130. The external ~an element is particularly
advantageous in large brake discs adapted to absorb large amounts of
horsepower, so as to improve cooling from both surfaces of the disc
segments.
Iû While the alternative segment lûl is shown with alternative straight
interconnecting edges and alternative ridges intersected by screws at
clearance gaps between aligned ridge portions, the segment 20 could be
provided with similar alternative straight interconnecting edges and aligned
ridge portions. Similarly, the segment 101 could have interconnecting
edges provided with recesses and proiections and continuous ridges
containing full depth bosses to receive the screws.
