Note: Descriptions are shown in the official language in which they were submitted.
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TAMPER-RESISTANT BRAKE ACI'UATOR
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to diaphragm spring brake ~ctll~tors of the
S type used with air brake systems on vehicles such as trucks. In one of itc
aspects, the invention relates to a spring brake ~ctn~tQr having a tamper-
e~:c~ spring chanber.
State of the Prior Art
Spring brake ~ tors are in comm~n use with air brake systems
10 used on trucks, buses, and towed v~hicles. Such ~ctlJ~tors are typically provided
with a service chamber for normally applying and rele~cing the brakes in
res~ollse to delivery and c~ of co~ ,ressed air, and a spring chamber
disposed in t~n~ieln with the service chamber for providing parking or
emergency brake ftm~ tionC A spring brake ~ tor uses spring force to
15 operate a service brake ~ tor and apply brakes when l,les~ul~ed air in the
spring chamber is reduced below some predetermined level. Air pre~u~e may
be reduced in the spring chamber to apply the brakes under the control of the
operator or automatically as a result of failure of the yles~ul~ed air system.
The service chamber and spring chamber are separated by an adapter or flange
20 casing which forms a wall between the two chambers.
In a typical spring brake ~ tor, a barrel-shaped power spring is
used to store energy and to exert the large force required for braking in the
event of air ~,res~ule failure. Air pressure acting on a diaphragm or a piston is
employed to COlllpiCSS the spring and m~int~in it in its brake release position.25 When the air is eyh~llcte~l the spring acts on the diaphragm, typically an
el~ctomeric diaphragm or a piston, and through an ~ ting rod exerts the
spring force on the service push rod to apply the brakes in the event of a failure
of the system air ~res~ule.
The spring brake ~ tor operates within the spring chamber,
30 which is typically formed by clamping an elastomeric diaphragm between a head
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(Sometim~s also known as a spring housing or spring chamber) ~nd the adapter.
The power spring is typically co~ lessed within the spring chamber between the
head and the diaphragm. The spring has a high spring CO.I-CI~ and typically
weighc 3 polln~C or more, being co,lli)r~ssed to a linear length of less than 3
5 inches from an original ~ ol~-~ssed length in an eYt~nde~i cnn~lition of from 9
to 12 inches. With a high spring co ~ , the spring has a s~lbst~nti~l ~mollnt
of potential energy, exerting a force on the head of from 2,000 to 3,000 pounds.In previous diaphragm style brake ~ctu~tors, the brake ~ tor
head is secured to the adapter by means of a band, generally U-shaped in cross
10 sectif n~ to clamp mating flanges on the head and adapter with the diaphragm
cl~mped Lher~cl-.ecn. Typically the band is formed of sectionc bolted togethef
for co-l~,ement flic~cce~nhly. ReC~lce the power spring is under great plcs~u,e,means must be provided to restrain or "cage" the power spring before the spring
,h~ ,,bcr can be safely dic~csçmhled. Failure to ~,lopclly cage the power spring15 prior to ~lic~ccernhly and the reslllti~ slldden release of potential energy in the
spring can cause the head and adapter to fly apart.
To deter ~1ic~ccemhly of the spring charnber, the clamp band has
been formed from a CQ.~ OUS ring, deformed over the flanges to form what is
co~ llollly termed a sealed brake. Safety is an advantage of a sealed brake.
20 Rec~llce it must be defol~cd to be removed, a sealed brake clamp band or
deformed nange deters dic~ce~ ly of the spring chamber.
The same feature which makes sealed brakes safer also deters
future repair, bec~nce tlic~ccçm~ly iS ~liMclllt without ~m~ing the brake. If
the diaphragm should fail for example, the entire brake actu~tQr may need to be
25 replaced. In any event, reCQn~litioni~ of a sealed brake is a very difficult
procedure.
Other means are used for se~lnng the brake ~ tor head to the
adapter in a tamper-lca;~ brake. For example, U.S. Patent No. 5,315,918 to
Pierce, issued May 31, 1994, discloses a bayonet mount for securing the brake
30 actl~tQr head to the adapter. The brake ~ tor head and the adapter have
complçmPnt~ry axially-eyten~lin~ lips. One of the }ips has a series of openings
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-3-
formed therein and in which is received a plug weld to secure the 9~l. tor head
to the adapter.
U.S. Patent No. 5,285,716 to Thompson, issued February 15, 1994,
dic~AlQsec the welding of a brake ~ct~ tor head to an adapter in such a manner
S so that the weld securing the brake ~ Ator head to the adapter is a sl~ffiripnt
~lict~n-~e from the diaphragm so as not to burn the diaphragm. Spe- ifiA~lly, the
brake nctl~AtQr head has an aYially-eYt~Pn~ing flange that ovell~s an aYially-
eYtPnding flange of the adapter and eYtP-n~s a suffilcient flict~nce from the
diaphragm co~ ,rcsscd between the act~<ltQr bead and the adapter so that the
10 heat from the weld formed at the end of the aYially-eYtending flange of the
Ac~l9tor head will not burn the diaphragm.
SUMMARY OF THE rNVENTlON
Accor.l~lg to the invention, a fluid-operated brake ~ctll~Ator of the
type which has a generally cylindrical head and a flange case with an
el~ctomeric diaphragm between the two has a welded connection ~ dj~cent to the
peripheral portion of the diaphragm. The flange case and the head have
radially eyten(ling flanges which are shaped to co~ ress the peripheral edge of
the diaphragm so that the diaphragm s~lbst~nti~lly fills an ~nnlll~r recess formed
between radially eYtendin~ flanges on the flange case and the ~ylindrical head.
In one embo~liment~ the head and the flange case both have
aY~ially eytenrling rims on the outer edges of the fl~ngec The rims overlap and
the weld is made between the rims.
Rec~llce the el~ctomeric gasket s~lbst~nti~lly completely fills the
~nnl~l~r spaces formed between the radially eYtending _anges between the head
and the flange case and closed by ~nmll~r rims on the flanges, the welds can be
placed radially ~dj~ce-nt to the el~ctomeric diaphragm without deleteriously
burning the diaphragm. Thus, the seal rel,la",s intact between the head and the
flange case. Yet, the connection can be welded to avoid lm~l-thQrized
tampering. Thus, material cQ.~te~L can be decreased, there~y decreasing the
cost and weight of the spAng brake ~ct~-~tor.
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BRIEF DESCRIPIlON OF THE DRAWINGS
The invention will now be described with reference to the
;I~comr~nying d-awi,l~ in which:
FIG. 1 shows an elevational view of a fluid-operated combination
5 diaphragm spring brake ~ tor accordillg to the invention; and
FIG. 2 is a partial sectiQn~l view of the fluid-operated comhin~tion
diaphragm spring brake ~ tor of FIG. 1.
DETAILED DESCRIPI~ON OF THE DRAWINGS
Refe.,mg now to FIGS. 1 and 2, there is shown a fluid-operated
10 brake ~ tor 10 in accordance with the invention. The particular embo~limPnt
shown is a fluid-operated co...l. n~t;on diaphragm spring brake actll~tQr havingboth a service chamber 12 and a spring chamber 14. The brake ~ch1~tor is
adapted to mount to a mollntine bracket (not shown) of a vehicle aYle and is
further adapted to operate a brake (not shown) through a service push rod 16
15 which ~ c~lly PYtP~iS to and cQnn~Pcts with a slack adjuster and the braking
system of t_e vehicle.
Altho.leh the invention relates to a spring chamber, the service
chamber 12 and spring chamber 14 are illustrated joined together in t~n~em
bec~llse this atla~gelllent is CO.~ in a spring brake ~ tor. The
co,~luction of the service chamber 12 iS well known. Therefore, the service
chamber 12 will only be described generally. The service chanuber 12 iS ~efine~
by a cup-shaped lower serYice housing 18 and a cup-shaped upper service
hollcine 20 joined together by a clarnp 22 to form a hollow interior chamber. A
first el~c(o...~ric diapLr~lll24 (also known as the service brake diaphragm) is
co~ ressed in fluid-tight en~ n ent between the lower service housing 18 and
the upper service housing 20. A service chamber air port 26iS connected to a
source of ples~ure to pre~ul~e the upper service housing 20 and to an eYh~llst
valve (not shown) to reciprocally ~ctu~te the service push rod 16 upon the
additi~n and eYh~uctiQn of air.
The spring chamber 14 is defined by a flange case 34 and a
generally cylindrical head 36, also known as a spring chamber, which is secured
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to the flange case 34. It is the securing of the chamber 36 to the flange case 34
that is the ,pro.~lllent which forms the subject matter of the invention as willbe shown. A second elastomeric diaphragm 38, known as the spring diaphragr4
is clamped in fluid-tight engagement between the flange case 34 and the
5 ch~,-ber 36 to form a pres~ule chamber 46 between the spring diaphragm 38
and flange case 34.
A spring air port 40 ~Yt~ntlc from the flange case to c~mnect the
pre~urc chamber 46 with a source of prec!~ur;i-ed air (not shown). ~essul-2ed
air is directed into the pressure chamber 46 between the diaphragm 38 and the
10 flange c~e 34.
A spring push rod 42 eytentls through the flange case 34 and
upper service housing 20 through a seal 44 so that one end of the spring push
rod 42 is within the spring ~l.~ber 14 and the other end is within the service
er 12. The spring push rod 42 has a re~is)n plate 48 rigidly molmte~l to
15 the end in the service ch~ber 12, and a l,ies~ure plate 50 is mollnted to theother end in the spring chamber 14. The ~rcs~ure plate S0 bears against the
diaphragrn 38. A power spring 52 is position~d between the pres~ule plate 50
and the head 36 to bias the l~res~ule plate 50 and the spring push rod 42 against
the force of the ~resslll~cd air in the pres~ule chamber 46. When pressurized
20 air is forced into the pre;,~ure cl.~ber 46, it o.ercollles the force of the power
spring 52 to retract the spring push rod 42 and release the brake. When the
ples~ul~ed air is eYh~llsteA, the power spring 52 moves the spring push rod 42
to ~ctu~te the bralce.
As illustrated, the service chamber 12 is mounted to the spring
chamber 14 by welding the upper service hollcin~e 20 to the flange case 34.
However, it is co~ on for the upper service housing 20 and flange case 34 to
be made as a single piece, which is often referred to as an adapter honcine~ It
~ is within the scope of the invention for the fluid-operated brake ~C~u~t5~r 10 to
incolllor~te a one-piece adapter housing.
A release tool 56 can be provided within a central opening 61 of
the head 36 for m~ch~nically drawing the ~re~sure plate 50 into a retracted or
"caged" position in the event there is a need to mech~nically release the brake.
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The release tool typically CO~ , ses a threaded rod having an integral head on
the bottom end thereof and a nut swaged on the top thereof. A second nut is
threaded onto the rod and is welded to the head 36. The head on the nut is
selectively engageable with portions of the pressure plate 50 in a m~nner well
S known in the spring brake ac~latQr field to retract the pres~ule plate as the rod
is u~ eaded from the head.
T ~okine now more closely at the connection securing the flange
case 34 to the cylindrical head 36, the cylindrical head hac a ch~u~erential,
radially eyten~line flange 60 from which PYten~lc a circumferential aY~ial flange
10 62. Preferably, the radial flange 60 has a slight upw~rd cant in a radial direction
or, in other words, forms an ulJ..aldly rYten~ling acute angle with resl,c~;l to a
plane that is orthogonal to the lone tu~lin~l axis of the spring push rod. The
a~Yial aange 62 eYt~n~ls axially toward the service chamber 12 and is snb~l;~..l;~lly
parallel to the loneit.~l~lin~l axis of the spring push rod. ~lefe~ably, the radial
15 aange 60 and axial aange 62 are formed by s~,~hlg the head 36. A radius
tr~nCitinln at 64 is formed between the side wall 63 of the head 36 and radial
f~ange 60 and a radius tr~n.cition at 66 is formed between radial flange 60 and
axial flange 62.
In a similar m~nnP.r, the flange cace 34 also has a .h~ elenlial,
20 radially-PYten~ine flange 68 from which eYtçn~lc a circ-l~elc~lial axial flange
70, which te~...in~tes in a terminal edge 71. Preferably, the radial flange 68
formc a dowl-wardly eYten~line acute angle with respect to a plane orthogonal tothe loneit~l~lin~l axis of the spring push rod 42. The radial flange 68 and aYial
flange 70 are also created by bçn-line the flange case 34, forming sholllders 7225 and 74. The radial flange 68 eyte~tlc a radial (lict~n~e less than the radialflange 60 of the head 36. The di~ere~ce in the radial extension of the two
radial flanges 68, 60 is a~ o~;...~tely e~ual to the thir~ne$s of the axial flange
62 to permit the axial flange 70 to nest within the axial flange 62.
During ~ccembly of the brake ~ct~tor 10, the spring diaphragm 38
30 has an ~nnnl~r bead which is disposed between the radial flanges 60 and 68 and
co~ cssed therebetween, preferably by applying a co~l~prcssive force between
the radial flanges 60 and 68. An ~nnlll~r recess 76 is formed by the radial
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flanges 60, 68 and axial flanges 62, 70. The bead on the spring diaphragm 38
has a shape ~ro~ A~ g the ~nn~ r recess 76. The radial flanges 60 and 68
are in ~ligrment and col~ress the spring diaphragm therebetween to assure
ecc~-nti~lly complete filling of the bead of the spring diaphragm 38 into the
S ~nn~ r recess. As the spring diaphragm 38 is col-lplessed between the radial
flanges 60 and 68, a portion of the spring diaphragm 38 is directed into and
completely fills the ~nmll~r recess. The axial flange 70 can be of a
predetermined length so that the terminal edge 71 of the axial flange 70 abuts
the radial flange 60 when the spring diaphragm 38 is fully colllpressed. The
10 axial flange 62 is welded to the axial flange 70 along weld 78. The weld 78 is
~,re~elably a weld wherein the axial flange 62 is fused to the axial flange 70
without the addition of weld material and ,~in~ es the heat affected zone.
~d~ition~lly~ with specific procesces, a heat sink may be nece~ to remove
excess heat.
.Although the spring diaphragm 38 may be singed by the heat, the
s~mg is not sllffir~ent to degrade the pelrollllance of the spring diaphragm as
would occur if the spring diaphragm were bumt during the welding process.
By placing the weld adjacent to the diaphragm, less material is
required to m~nl~f~cture the head 36 and flange case 34. It is not llcce~c~. ~r to
20 extend the edge of the axial flange beyond the diaphragm to pl~ell~ the heat
from the weld at the edge of the flange from burl~ the diaphragm, as in
previous brake a~ Atol~.
In operation, air ~,res~ure is co..~ lly supplied to the spring
chamber 14 through the spring air port 40 to m~int~in the spring diaphragm 38
25 in a position to colllpless the power spring 52. In this positionJ the service push
rod 16 normally will be operated, as described above, by selective pres~uli~dlion
of air into the service chamber 12 through the service air port 26. However, in
the event of a loss of prc~ure, either intçnti(!n~lly, as when the ~arkillg brake is
set, or by failure of the air pres~urc systern, the ~,rcss~lre in the spring chamber
30 14 will be decreased and the power spring 52 will activate the brakes by pushing
the plCSSule plate 50, spring diaphragm 38, and thus the spring push rod 42 to
thereby ~ tç the sennce push rod 16 to apply braking pres~ e to the brakes.
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Re~con~le variation and modification are possible within the
scope of the foregoing ~~ic~losl-re without dep~lhlg from the spirit of the
invention which is clefined in the ~cco~ y,ng claim_.
