Note: Descriptions are shown in the official language in which they were submitted.
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SPRING BR~KE ACTUATOR HAVING TWO-PLY
PRESSURE PLATE ASSEMBLY
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a spring brake ~ctll~tor and, more particularly,
to a spring brake ~r*l~tor having a two-ply pleS:iuiC plate ~ccçmhly
Description of the Related Art
An air brake system for a vehicle such as a bus, truck or the like,
typically includes a brake shoe and drum assembly which is ~ctll~te~l by means
of an ~ct~l~tor assembly operated by the selective application of a fluid such as
co.ll~ressed air. Collvenlional air brake ~ tors have both a service brake
~rtnS~tor for ~ ting the brakes under normal driving conditions by the
application of colllplessed air and an emergency or spring brake ~ctll~tor whichcauses ~ctll~tion of the brakes when air ~les~ule has been released. The
emergency brake ~ct~l~tor inrllltl.os a strong colll~lession spring which forcesapplication of the brake when air is released. This is often referred to as the
spring brake. Typically, the spring brake ~ct~l~tor is disposed in tandem with
the service brake ~ct~l~tor.
When full air ples~ule is applied to the spring brake ~ctllz~tor, air
~les~ule acting against a diaphragm and a ~les~ule plate colll~resses the spring.
A spring brake ~çtn~tQr rod is either integral with the ~res~ure plate and held in
a retracted position by the air pres~ulc or retracted by a return spring.
Depressing the brake pedal during normal driving operation introduces
colll~ressed air into the service brake ~ctll~tor which, acting ~g~in.ct a
diaphragm, causes a service brake pressure plate and ~tt~rhed push rod to be
extended and the brakes to be applied with an application force proportional to
the air pressure in the service brake ~ tor. In the event of a loss of air
ples~ule or an intentiQnal e,~l~auslion of air from the spring brake ~ctll~tor, the
brake will be mer-h~nicz3l1y activated by the force of a strong colll~ression spring
acting on the spring brake ~tll~tor rod which, in turn, acts upon the service
brake push rod to apply the brakes. Examples of known dual chamber spring
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brake assemblies inchlde U.S. Patent No. 5,105,727 to Bowyer, issued April 21,
1992, U.S. Patent No. 3,439,585 to Herrera, issued April 22, 1969; and U.S.
Patent No. 3,842,716 to Swander, Jr., issued October 22, 1974.
A typical serv-ice brake pressure plate assembly comprises a circular, flat
5 plate having the ~ tc r rod welded to the center of one s -rf~ce of the plate.The rod is welded to the plate by a collvc~ ion~l weld bead which çYte-n-lc
around the perimeter of the base of the rod. FIG. 6 depicts an example of a
known ~cS~ulc plate assembly. This ~ccemhly 200 comprises a circular l,res~ule
plate 202 and an ~ tor rod 204 welded to one surface of the pressure plate
10 202 by a circular weld bead 206. The ~ctll~tor rod 204 is welded to the pressure
plate 202 such that the longitll~lin~l aYis of the rod 204 is aligned with the
central aYis of the circular pressure plate 202. Structurally, the largest loadsexperienced by the circular ~les~ule plate 202 are experienced adjacent the
mounting point of the actuator rod 204. Less structural ~llcll~Lll is required
15 near the perimeter of the circular ples~ulc plate 202. Current ~JlCS~UlC plates
are formed of Y4-inch-thick steel and s~ticf~ctQrily meet the structural
requirements near the center of the plate. However, such plates far exceed the
loads encountered ~cljz~cçnt the perimeter of each plate during n~
operation. Consequently, the thickness of the plate at the perimeter col~LiLuLes20 excess weight.
It is desirable to reduce the weight of the pressure plate while at the
same time m~ i..g the structural integrity of the plate under higher stresses
at the center thereof.
SUMMARY OF THE INVENTION
The spring brake ~ctll~tor accoldillg to the invention uvercollles the
problems of the prior art by incorporating a 2-ply pressure plate which resist the
shear forces and creates an integral bond between the ~hl~tor rod and pressure
plate.
A brake ~tll~ting me~h~nicm accolding to the invention comprises a
housing having first and second end walls defining a housing interior with an
opening centrally disposed in the second end wall. An elastomeric diaphragm is
suspended within the housing and divides the housing into a first chamber and a
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second ~ h~llbcr. A ~res~urc plate ~ccemhly is received in the second chamber.
The plate assembly coll~ylises a push rod ~Yt~n~1in~ out of the housing through a
centrally disposed opening and adapted to conn~-ct to a brake. The pressure
plate assembly is reciprocally movable, res~onsive, in part, to the intro~lurtion
5 and eYh~1-ct of pres~uli~ed fluid to the first chamber. Accordi~g to one
embo~limPnt of the invention, the ~ies~ure plate ~ccçmhly comprises a first plate
and a second plate. The second plate abuts the first plate in face-to-face
relationship with adjoining central portions. The push rod extends norm~11y
from the first and second plates. The push rod has an end welded to the first
10 and second plates.
In another embodiment of the invention, the push rod is mounted to one
of the central portion of the first plate and the first and second plates are
secured to each other by at least one interconnçction located intermediate the
central portions and the peripheral edges thereof to resist shear forces acting
15 between the first and second plates.
Preferably, the interconnection intermediate the central portions of the
two plates comprises at least one emboccment formed in the first and second
plates to mechanically connect the two plates together. Alternatively, the
intermediate interconnection of the first and second plates is at least one spot20 weld.
The invention relates to a method of m~king a pressure plate ~csemhly
for a brake actuator comprising the steps of placing a conductive metallic
central portion of a first plate member in face to face relationship with a
conductive metallic central portion of a second plate member. Flux material is
25 deposited in a recess in a conductive metallic proximal end of a push rod. The
proximal end of the push rod is positioned on the central portion of the second
plate and ~u~loul~ded with an incn1~ting collar. The first and second plates andthe push rod are placed in compression and a large pulse of electric ~;UllClll iS
applied to the first and second plates and the push rod to create a fusion zone
30 between the central portions of the plates and the push rod to weld the same
together.
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BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with refere,lce to the drawings in
which:
FIG. 1 is a cross sectional view of an air-operated brake ~rt~ ting
S ~emhly having a two-ply pres~u,e plate accor-li"g to the invention;
FIG. 2 is a partial section~l view of a first embo~lim-o-nt of the two-ply
~,es~ure plate accordi,lg to the invention for use in the air-operated brake
~ct~l~ting assembly of FIG. 1.
FIG. 3 is a bottom plan view of the two-ply pressure plate;
FIG. 4 is a cross secti~n~ detailed view of the ~rt~-~tor rod and pressure
plates prior to welding of the rod to the pressure plate;
FIG. 5 is sectional view of a second embodiment of the two-ply ~les~ule
plate accoldi.lg to the invention; and
FIG. 6 is a side elevational view of a prior art l"es~u,~ plate assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings and to FIG. 1, in particular, a cross sectional
view of an air-operated brake ~rtll~ting unit 10 having a general confi~-ration
well known in the art is shown. The ~rt--~ting unit 10 comprises a service brakeportion 12 mounted in t~nclem to a spring brake or emergency brake portion 14.
20 A service brake push rod 18 çxtçn(lc from the service brake 12 for reciprocating
motion and is provided with a clevis 20 which is adapted to connected to a
collvell~ional brake (not shown) in a standard fashion. Reciprocating motion of
the push rod 18 by the ~ct~ting unit 10 will cause the brake to be alternately
applied and released.
The service brake portion 12 col"~,ises a pair of facing cup-shaped
housing sections 21, 22, each having an oulw~Lrdly directed flanged edge 25, 26,respectively. The housing sections 21, 22 are clamped together at their fl~ng~
edges by a clamp 27 to form a serv-ice brake inner chamber 30. The peripheral
edge of an elastomeric diaphragm 32 is ca~lu~ed between the opposed edges 25,
26, of the housing 21, 22 and suspended within the inner chamber 30. The
service brake push rod 18 extends through a central aperture 34 in housing
section 21 into the service brake chamber 30 where it termin~tes at a two-ply
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S
yres~ure plate 36. A colllyress on spring 40 eYtentlc between the two-ply
yres~ure plate 36 and the interior s~lrf~ce of the housing section 21. A spring
seat 48 is disposed around the central opening 34 to receive the end of the
c~Luylession spring 40 and retain it in position around the opening 34. The
5 spring 40 urges the yres~ule plate 36 and the service brake push rod 18 to a
fully retracted position as seen in FIG. 1. MounLi.lg studs 46 are provided to
the housing section 21 to mount the brake ~ tinp unit 10 onto an ayy,oyliate
bracket (not shown).
To operate the service brake, colll~lessed air is introduced through an air
10 service port 38 formed in the housing section 22 to force the diaphragm 32 and
the two-ply pressure plate 36 ~g~inct the force of the con~ression of the spring40 to ~ te the push rod 18. Ev~cn~tion openings 44 are provided in the
housing section 21 to allow for the rapid eV~ tion of air from the inner
chamber 30 as the yles~uli~ed air is introduced through the air service port 38.The spring brake 14 colllylises a pair of facing cup-shaped housing
sections 51, 52 joined at their edges to define an inner chamber 53. Housing
section 51 is provided with an oulw~Lrdly directed cilculllrcl~ntial flanged edge
54 which is received inside of a rolled peripheral edge 56 formed on the housingsection 52. An elastomeric diaphragm 58 is suspended within the spring brake
20 chamber 53 and is ca~luled at its peripheral edge between the edges 54, 56 ofthe opposed hDusing sections 51, 52. The portion of the chamber 53 between
the diaphragm 58 and the housing section 51 forms an air chamber which is
filled with co.ll~ressed air supplied through an air service port 59 in the housing
section 51 when the emergency brake is in its norrnal, released position. An
25 ~ct~tor rod 60, aligned with push rod 18, has one end extending through a
central aperture 64 formed in the end wall of the housing section 51. This end
of the ~ct~-~tor rod 60 termin~tes in a reaction plate 62 which is received in acentral aperture 63 of the end wall of the housing section ~ of the service
brake portion 12. The central aperture 64 is provided with a bearing 66 having
30 :-nml1~r recesses to accomrnodate a pair of O-rings 68. The bearing 66 forms a
bearing surface and an air tight seal for the ~ct~tor rod 60.
The other end of the ~t~tor rod 60 extends through a centrally
disposed aperture 81 in the diaphragm 58 and terrnin~tes in a spring brake
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es~ule plate 70 which eng~gt--s the spring brake colll~ression springs 72. The
spring brake plcs~ule plate 70 co~ lises a subst~nti~lly flat portion 73 en~gingone end of the spring 72 and a tubular portion 74 extending generally aYially
along the aYis of the spring 72. The tubular portion 74 iS press-fit onto an end5 portion of the ~c~l~tor rod 60 such that the spring brake pressure plate 70 and
the rod 60 form an integral unit. The spring brake l~rcs~ule plate 70 may be
formed of cast ~1-..";""...
During normal operation of the brake 10, the ~ch~tQr rod 60 will be in
the fully withdrawn po.cition, as seen in FIG. 1, by means of colll~ressed air
10 which is ...~ ;..ed in the portion of the chamber 53 defined by the diaphragm58 and the housing section 51. When the colll~>ressed air is eYh~lsted~ the
com~les~ion spring 72, one end of which eng~ges the outer end wall of t_e
housing 52, forces the spring brake pressure plate 70 and integrally attached rod
60 in the direction of the brake push rod 18 of the service brake 12. The
15 housing section 22 of the service brake 12 and housing section 51 of the spring
brake 14 are preferably steel shells ~tt~he~l to each other by means of a
~culllrerentially eYten-ling weld bead 76 or other suitable ~tt~çhment me~nc or
can be an integral ~ casting. The force of the spring 72 causes the
~ct~l~tQr rod 60 to be eYtentle~l through the central opening 64 and causes the
reaction plate 62 to apply a force to the diaphragm 32 and two-ply pressure
plate 36 of the service brake. This action causes the service brake push rod 18
to be ~ct~l~te~l and the brake to be applied. When the brake is to be released,
co~ lessed air is once again introduced in the space between the housing
section 51 and diaphragm 58. The force of the colll~lessed air ~g~in~t the
diaphragm 58 overcollles the co~ rc~ion force of the spring 72 and relulns the
pres~ule plate 70 and rod 60 to the position seen in FIG. 1.
The ~chl~tor rod 60iS a hollow tube or rod provided with a central bore
61 to accommodate a brake release or caging bolt 78. The bolt 78 iS adapted to
engage an end edge 80 of the tubular portion 74 of the spring brake l,ies~uie
30 plate 70 to m~int~in the spring 72 in a colll~ressed position whenever so
desired. The bolt 78 may be used to m~nn~lly release the spring brake or to
insure that the colll~les~ion spring 72 will remain fully compressed when
maintenance functions are performed on the brake assembly. The bolt 78 iS
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threaded and çng~ges a fixed, threaded opening or nut 77 affixed by welding or
st~hn~ to the end wall of the housing section 52. A second nut or head 79 is
fixedly attached to the threaded bolt such that the bolt may be rotated in the
nut 77 by a commnn wrench or the like.
The two-ply ple~ule plate 36 acco~ g to the invention provides an
equally strong mounting between the push rod 18 and the plate 36 than
heletofole realized while enabling red~lce~l weight. As seen in FIGS. 3-5, a first
embodiment of the ples~ule plate ~ccembly 36 coll-l~lises a diaphragm plate 92,
a support plate 98 mounted to the diaphragm plate 92 and the service brake
push rod 18 which is mounted to both the diaphragm plate 92 and support plate
98. The diaphragm plate 92 comprises a front surface 94, a rear surface 96 and
an arcuate or rolled outer peripheral edge 97. The support plate 98 comprises a
front surface 100, a rear snrf~ce 102 and a peripheral edge 103. It can be seen
that the support plate 98 has a diameter s-lbst~nti~lly less than the diaphragm
plate 92.
Preferably, the diaphragm plate 92 and support plate 98 are mounted
adjacent to one another with the front surface 100 face to face with the rear
surface 96, and secured to each other at multiple locations. The two plates are
interconnected through a plurality of emboccment.c 106 which are formed in
both plates intermediate the peripheral edge 103 of the support plate 98 and therod 18. The embo.ccment.c can be formed by cooperating male and female dies
which deform the diaphragm plate 92 and support plate 98 such that a
projection 108 extends rearwardly from the rear surface 102 of the support plate98 and a colle~onding recess 110 is formed on the front surface 94 of the
diaphragm plate 92. The two plates have been deformed such that a projection
111 formed on the rear surface 96 of the diaphragm plate 92 is received in a
complementary recess 112 formed on the front surface of the support plate 98.
- In the plefelled embodiment of the llles~ule plate ~ccemhly 36, the embossment
106 is flimencioned such that the depth of the recess 110 and the height of the
30 projection 108 is a~ .xi~tely one-half of the thickness of the diaphragm
plate 92.
As seen in FIG. 3, the emboccmentc 106 are preferably arcuate and, if
connected, would define a circle cnn~çntric with the perimeter of the diaphragm
-
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plate 92. The emboccm~-ntc 106 serve to ~rcvel,t the two plates from .chiftin~
with respect to one another by resicting shear forces acting between the two
plates. In ~ lition, the emboccmentc 106 are spaced radially uuLwdrdly from the
push rod 18 to distribute the load throughout the entire body of the ~u~po,l
5 plate 98. The interc~ ection of the emboccm~-ntc 106 of the plates 92, 98 resist
the shear forces caused by warping or deflecting of the outer portions of the
diaphragm plate 92 relative to the support plate 98. In order for the outer
portion of the diaphragm plate to shear or deflect relative to the ~ul"~o,l plate
98, the rear surface 96 of the diaphragm plate 92 would have to slide across the10 front surface 100 of the support plate 98. The interconnection between the
front and rear sllrf~ces reslllting from the emboscmentc 106 l~rGve"~ this sliding,
shear movement. Therefore, the assembly will have the strength of the two
plates where it is most needed, adjacent the mounting point of the push rod 18.
F~efe,dbly, the interconnections between the two plates are formed adjacent the
perimeter of the smaller plate, in this case, the support plate 98. However, therelative position of the interconn~cti~ nc will depend largely upon the shear
forces which are expected to be exerted on the pressure plate ~ccemhly. By
interconnecting the two plates to one another ~dj~çnt the perimeter of the
smaller plate, the .. ~xi... resict~nce to shear forces is achieved as a result of
the greater shear area being available at the farthest interconnection point from
the push rod 18.
The emboscmentc 106 also can act as a locator on the rear surface 102 of
the su~l o,l plate 98 for the co",~lession spring 40 of the serv-ice brake 12. It is
h~l~o~ldnt to keep the spring 40 centered around the longitll-lin~l axis of the
push rod. The embossments 106 retain the co-.l~lession spring 40 in a
particular orientation with respect to the push rod 18 as a result of abutting
contact between the embossments 106 and the spring 40.
An alternative to the upsets described above would be an upset
commercially known as the Tog-I~LockTY which is commercially available.
30 Similarly to the upset described above, the Tog-L-LockTY upset results in
deform~tion of a portion of one of the plates into the other plate, thereby
mechanically interconnecting these two plates.
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The two plates 92, 98 are also connected to one another at the push rod
18. As seen in FIG. 2, the push rod 18, diaphragm plate 92 and support plate
98 are integrally welded to one another at a fusion zone 114 compAsing
m~tçri~l from each of the separate elem-ontc The fusion zone 114 results from
e 5 the integral welding, or bon-ling, of portions of the push rod 18, diaphragm plate
92 and ~ul~oll plate 98. The ~refelled welding method is a resistance welding
operation wherein an end 116 of the push rod 18 along with portions of the
support plate 98 and diaphragm plate 92 are welded to one another creating
integral, metallurgical bonding between these three elem~n~c.
As seen in FIG. 4, the push rod 18, pAor to welding, has a recess 118
formed in the end 116 thereof. A suitable ilux mateAal 120 is packed into the
recess 118. The flux 120 is col-ve..~inn~l in recict~n~e welding operations. After
the flux 120 has been placed into the recess 118 of the control rod 18, a ceramic
collar 124 is telescopically received on the rod 18 to abut the rear snrf:lce 102 of
15 the ~U~pUll plate 98 and ~ulloulld the base of the rod 18 which also is placed
~g~inct the rear surface 102. The support plate 98 is a~lopliately positioned
zlg~in.ct the diaphragm plate 92, with central portions thereof 126, 128 ~dj~ce.nt
each other and coaxial with the push rod 18. The collar 124 acts as a mold to
m~int~in the desired shape of the rod 18 and plates 92, 98 in the fusion zone
20 114. After all elements are in place, a coLul,lcssion force is applied between the
push rod 18 and diaphragm plate 92 and support plate 98. Preferably, 150
pounds of compression force is applied. After a sufficient col~ lessive force has
been applied, a large pulse of electric ~;ullelll is passed through the diaphragm
plate 92, support plate 98 and control rod 18. As the ~;ullclll passes through the
25 elements, resict~n~e to the CUllellt flow between the several elements m~nifçctc
itself as heat. The combination of the large pulse of ~;ullellt, the pressure
between the several elements and the abutting surfaces of the elements results
- in fusing portions of the diaphragm plate 92, support plate 98 and push rod 18
to one another within the fusion zone 114. After the fusion zone has been
30 sufficiently cooled, the collar 124 is removed from the push rod 18 and the
reslllting product is a twû-ply pressure plate accoldi~lg tû the invention wherein
the surfaces of the two plates are integrally conn~cte~l to one another at points
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spaced from the push rod 18 and the central portions of the two plates are
integrally welded to each other and to the push rod 18.
FIG. 5 shows a second embodiment of the service brake ~res~ule plate
~ccçmhly accoldill~ to the invention. In this emborlim~o-nt the pressure plate
5 :~cc~mhly 130 col~ ises the push rod 18, support plate 98 and diaphragm plate
92 which are centrally welded to one another at a fusion zone 114, preferably bythe previously described resict~nce welding process. Huw~ver, incte~-l Of
m.och~niç~lly interconnecting the surfaces 96, 100 by emboccmentc as illustratedin FIGS. 2 and 3, the surfaces 96, 100 are welded to one another by a
10 collve..l;on~l spot welding process. Preferably, a circle of staggered spot welds
132 ~ulloullding the rod 18 secures the perimeter of the two plates to one
another. The spot welds 132 resist the sliding, shear forces exerted on the two
plates. For all embo~liment.c, it will be appre~te~l that each ply of the pressure
plate can be formed of 10 gauge steel which results in .cignific~nt weight
15 redn~tion from prior art pressure plates.
The two-ply pressure plate ~ccçmhly accor.ling to the invention provides
significant advantages over the conventional plate assemblies. First, the dual
plate assembly provides the structural strength nececc~ry adjacent the push rod
of the assembly while also elimin~ting material adjacent the perimeter of the
20 plate which is not structurally required. Therefore, the overall weight of the
pressure plate assembly is reduced without s~rifi~ing any of the structural
requirements.
Prior testing has shown that the force output curve of a brake can be
r~ved by forming a lip or flange about the perimeter of the pressure plate
25 which bears against the diaphragm. The pres~ule plate assembly accoldhlg to
the invention can be formed from two thinner pieces of steel which replace one
thick piece of steel. A flange or lip can more easily and inexpensively be
formed on the outer perimeter of a thin piece of steel than on a thick piece of
steel. For example, it is extremely .liffi~llt and costly to attempt to form a
30 flange on a piece of ~4-inch steel. However, the same flange can be easily rolled
into a 10-gage steel plate. Therefore, an u~loved force output curve can be
achieved for a brake in~ln~ling a two-ply ~les~ure plate accor.ling to the
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invention through a less expensive and easier m~n-lf~ctllring process than was
previously known in the prior art.
Re~con~hle variation and mo-lifir~tion are possible within the spirit of
the fol~oi-lg specifi~tion and drawings without departing from the scope of the
S invention.
