Note: Descriptions are shown in the official language in which they were submitted.
1~546~
-- Thi.~ invcntion relates generally to a brake system and~
more particuLa]-ly, to arl improvcd opcrat:ion of such brake
systcm when a pressure responsi~e -valve of the type disclosed
herein is included in such system.
The invention is particularly applicable to a valve for
use in dual circuit pneumatic brake systems applicable to
trucks, truck-tractors, buses and the like which employ dual-
~- diaphragm, spring-ac~uated, air-released brake actuators and
will be described wi~h particular reference thereto. However,
it will be appreciated by those skilled in the art that the
invention may have broader applications and may be employed
.. I. :,.;
in vacuum or other fluid actuated brake systems.
Sa~ety regulations have resulted in the Gommonplace use of
brake actuators of the dual-diaphragm, spring-applied, air
` released type in pneumatic vehicle braking systems. Such
, ~ .;~ actuators comprise tandem front and rear brake chambers. The
rear chamber houses a compression spring which is maintained
i precompressed when the vehicle is in its normal operating mode
by air at~pri~ary, or system or supply or emergency pressures
; 20 (hereinafter termed supply pressure). A forward air chamber
is supplied with supply air modulated to secondary or control
r service or signal pressure (hereinafter termed service pres-
sure) to actuate the vehicle's brakes in a conventional manner.
In the event of a failure in the air system or when the vehicle
is to be parked, the rearward chamber is vented of its air to
release t4e spring which then sets the vehicle's brakes. Ob-
viouslyj if an air failure occurred while t~e vehicle was driven
~' and the rear chamber was automatically vented, the sudden and
- . .
, .. . . .
... :. . .... . . . .
;: , ., . , ~ ~ . , .
3546~iilD
ull appli(~ion o~ thi vihicle's brakcs woiuld present se~ious
colltLol probl~ms to tl~c ope~ or of ~ e vehicle.
To prevent such problems, a valve, generally known as an
inversion valve, has been employed in such systems. The func-
tion of this valve is to maintain the spring in the brake
actuator compressed even though a system failure be sensed and
to vent the air from the rear chamber of the brake actua~or in
an inverse ratio to the air at service pressure supplied to the
service brake chamber by the opera~or through the conventional
treadle valve. In this manner, the brake actuator springs would
be released to exert a braking pressure which would be in "sync"
with the degree of treadle valve actuation.
, ~
Heretofore, prior art inversion valves basically comprised
spxing loaded piston or diaphragm arrangements as illustrated
;` in U.S. Pat. Nos. 3,826,283 and 3~863,992. To provide a fast
spring brake response time to insure equal application of the
brakes, the spring precompression of the valve is established
at a force which modulates system air pressure to a value which
is just su~icient to maintain-the springs compressed in the
actuators during normal operating conditions. While such valve
.; .
arrangement is thus sufficient to provide quick response for
. . ~
actuation of the brakesj there are two significant drawbacks
~ to such an arrangement. First, spring rates in the brake
; actuators vary from one ac~uator to the other and the air pres-
sure ported to the spring brake chambers may be sufficient to
maintain one of the brake actuator's springs compressed while
" permitting the spring of another brake actuator to slightly
. . ~
expand until equilibrlum occurs. In this event, ~he latter
~2~
::. ' , . . ': : ,: .;' .
,
'':' ' ' '' ' ' , ' '
5~66~
spring actuator would slightly app:Ly the brakes of the
vehicle which it controls and thus generate heat and wRar
on such brakes significantly reducing the like thereof. Second,
such inversion valves by regulating supply air pressure to a
lower value do not meet certain safety standard criteria which
require that full system air pressure be applied to the emergency
line of a trailer. Accordingly, the use of prior art inversion ;
valves has been limited to certain vehicle applications.
. .
Specifically, they could not be used to modulate trailer
emergency line pressure (emergency brakes) from the towing
tractor. On the other hand, if the prior art inversion valves
` employed spring rates sufficiently high to insure supply pressure
, . .
in the spring brake chambers, the response time of the spring
brakes would be adversely affected with uneven brake application
,.,
, occurring.
Copending Canadian Patent Application Serial No. 258,073,
.. . . . .
fiIed on July 29, 1~76 assigned to t:he present assignee and of
which this is a division, describes and claims a novel inversion -
valve which overcomes the drawbacks of prior inversion valves.
X 20 The present invention relates to a modification to a
- ~conventional truck-trailer brake system which meets safety
criteria by supplying air at supply pressures to the emergency
chambers of the tractor brake actuators and to the supply line
of the trailer while incorporating the~inversion valve of the
subject invention to sense and control the trailer emergency
brakes as well as the towing vehicle brakes when a brake failure
occurs in the trailer system or towin~ vehicle rear service
brake system.
~, .
:; :
1 - 3 -
., " :
., ls/J~
, " , , ,, , , , , .: . ! .,: '
',: ' , .. ' ''. : , '',~' ". , . '' :
~: " . ' ' ~ ,: ' ' :
54~
Thus, the present invention is broadly defined as
; a trac-tor-trailer brake system comprising a first brake
circuit associated with the tractor, a second brake circuit
associated with the trailer, a plurality of brake actuators
~ in each circuit, means for generating in each circuit fluid
i at supply and service pressures, tractor protection valve
means on the tractor providing fluid communication between ~ ;
the trac~or and the trailer when fluid at supply pressure is
ported thereto and interrupting fluid communication between the
tra~tor and the trailer in an off position when fluid at
supply pressure drops below a predetermined pressure, trailer .
valve means on the trailer operable to actuate the trailer
brake actuato.rs when the tractor protection valve means is
in an off position, first valve means on the tractor biased
:~ .
~ by a source of fluid at signal pressure co provide fluid :~
`j communication between the higher source at supply pressure
. in each circuit with the tractor protection valve means and
'~ effective to modulate the higher source of supply pressure
in accordance with the pressure developed by the signal source
of fluid; and inversion valve means providing the source of
: ~ signal fluid and normally operable to generate the signal
~i ~ source of fluid-at supply pressure and operable in a brake ; :
. ~ .
. . .
. failure mode to decrease the pressure of the signal source `
of fluid at a rate proportional to the source of fluid at service
. pressurewhen a decrease in the source of fluid at supply
.' pressure in the second circuit occurs.
~: The invention may take physical form in certain parts ::
:~ and arrangement of parts, a preferred embodiment of which will :
:-.; be described in detail herein and illustrated in the accompanying
~ 4 -
;,; :
.,
' ls~l~
~ 6~0
dra~ings whic11 ~orm a part ll~r~of and w11~rein:
IIGUI~E 1 is a scl1em.l~ic v:iew of a typica1. pneumati.c b~ak-
ing system employing the inversion valve of the subject inven-
. tion;
~IGURE 2 is a sectional view of the inversion valve with
~he parts thereof orientated as they would appear without
pressure in the vehicle air system;
` FIGURE 3 is an exploded sectional view of several com-
ponents of the inversion valve;
;~ 10 FIGURE 4 is a longitudinally sectioned vîew of the valve,
similar to FIGURE l, but with the component parts orientated
as they would appear in a lapped position of the valve; and
,.......................................................................... .
' FIGURE S is a tractor-trailer brake system including the ~
! .
`~ inversion valve as one of its component parts.
~i ,
., .
:;i Referring now to the drawings wherein the showings are ~
., ,
` or the purpose of illustrating a preferred embodiment of the
invention only and not for the purpose of limiting same, there
is: shown in EIGURE 1 a pneumatic brake system lO for use OD a
~ .
vehicle which incorporates an inversion valve 12 of the subject
inventlon hàving a first inlet port 30, a second inlet port 31,
,,: : :
; a third inlet port 32, a delivery port 33 and a vent port 34
tshown in FIGURE 2).
Standard brake components shown in brake system 10 include
` ~ a compressor 13 charging reservoir "A" l~ and reservoir "B" lS
"~
~ with air at supply pressure which in turn is applied through l:
.' brake lines 17, 18 to the inlet side of a dual circuit brake.
' valve l9. The designation "dual circuit brake valve" is defined
,, .
~ ~5~ ~ ~
' . , ,, . 1 , : , , . . ' , ~ .: , ; ' ' , . : , ' : ' , ,
,-: , , , : . . ., ~ : .. . . .
~ ~ 5 466 ~ ~
,. :
hercin ~o inclu(le brake valv~s not only of the treadle ~ype but
also o~ ~he su~perlcled p~dal type and, in particular, refers to
such valves wh;ch u~ilize separate valving mechanisrn to port
air to the front and rear brakes of the vehicle. In the sche- ~ -
matic illustrated, reservoir "A" air at supply pressure enters
the lower portion of dual circuit brake valve 19 and is ported
or modulated to service pressure at the outlet of valve 19 into
brake line 20. Brake line 20 in turn communicates air at ser-
. '
vice pressure to front brake actuators 21 (shown to be of the
single diaphragm, air-applied, spring-released type) and also
communicates air at service pressure to second inlet port 31
of inversion valve 12. Similarly, air at supply pressure
.
from reservoir "B" in line 18 enters the upper portion of
dual circuit brake valve 19 where it is ported or modulated
to service pressure, leaving the outlet side of the valve
through a brake line 23 in turn in fluid communication with
the rear brake actuators 24. -~
. , .
` Rear brake actuators 24 are of the known dual diaphragm
; ~ type and include a forward or service brake chamber 25 and
,; . ~
a tandem rearward or emergency brake chamber 26. Service
brake chamber 25 normally brakes the rear wheels of the
`i vehicle since it receives air at service pressure through
line 23 which displaces a diaphragm therein against a cen-
i .,~
trally supported output shaft 27 which in turn rotates a con-
ventional slack adjuster mechanism 28 to apply the rear brakes ;~
of the vehicle. During normal highway operation of the
., . i
. ....................................................................... .
vehicle, emergency brake chamber 26 is supplied air at sup-
ply pressure via brake line 36 in fluid communication with '-
:" .
~6-
., . , . .: . . . . . . : ., , ., , . . ,: ~ . ..
. . : . - ,. . . . : ., , ,., . . - ~ .
~ q~546~D
delivt-~ry port 33 of invt~rsion va:lve 12 to mainta;n a spring 29
, .,
prtctmpJ^tssccl by ~ d;apllragm therein. When a failure occ~lrs
in that por~i.on of ~he brake system associated with reservoir
:: "B" or when the vehicle is parked, the air at supply pressllre
i.n emergency brake chamber 26 is vented to allow compression
` spring 29 t:o expand against output shaft 27. The manner in
which compression spring 29 is allowed to expand is dependent
upon inversion valve 12 o the subject invention.
: Completing the brake schematic is a brake line 37 "T'd''
to reservoir "B" brake line 18 and connected to first inlet
I port 30 of inversion valve 12 which, as explained hereafter,
:i ~
will f~lction as a sensor means to reguIate inversion valve ,-~.
12. The ~hird inlet port 32 of inversion valve 12 is connected
.:. to brake line 38 in turn connected to a conventional park con-
., - ,i;
trol valve 39 which always senses supply pressure by means of
a conventional two way check valve 40 in fluid communica~ion
~, :
` with either reservoir "A" or "B" depending upon which one is
;"'`~ ' , 1:
at higher pressure.
~ : Referring now to FIGURES 2.and 3,.inversion valve 12 is
- ` 20 s~own to include~a valve body 42 having a stepped cylindrical
- bore 43 extending therein. First inle~ port 30 is in fluid
. communication with bore 43 at one end thereo and bore 43 is
closed at its opposite end by a vent cover 45 threadably fas~
.,; I ,~
~, . , l
',3 ~ ~ened as at 46 to valve body 42. Ribs 47 in vent cover 45 en- ~
, .
~.` gage the valve body's end portion opposite first inlet port 30
., 1
to define a plurality`of vent passages or vent ports 34 in
~ fluid communication with bore 43. In betwee~ vent port 34
: and first inle~ port 30 are second inlet port 31, third inlet
~ _7_
- . . . .
, . . . , . . .-
.. . . . . . . -
-: .
~54~6~
por~ 32 allcl clc.l.ivery l~ort 33, all i.l~ fluid communlcation
with bore 43. Dis~ose~ itllin bore 43 acljacen~ vent port 34
is a ~irst hollowed, cylindri~cally s~epped tuhular piston 50.
Fi.rst piston 50 has a main body portion 51, an end portion 52
stepped radially outwardly from main body portion 51 and gen-
erally adjacent vent port 34. ~t the opposite end of main
body portion 51, first pis~on 50 extends radially inwardly to
define an annular shoulder seat surface 55 terminating in a
longitudinally extending llollow stem portion 53 ~hich in turn
terminates in a flanged conical valve seat 54. The exterior
of hollow stem portion 53 is stepped radially outwardly as at
56 and stem portion 53 extends in~o the interior of main
body portion 51 to define a boss 57 for r~taining a spacer-
washer 59 serving as a seat for a pair of compression springs
60 functioning as biasing means to exert a bias to first
piston 50 towards first inlet port 30. First piston 50 is ~.
retained within bore 4~ by sealing means in the form of O-
rings 63, 62 disposed within grooves located in main body ~.
portion 51 and end portion 52 respectively o~ first piston 50.
,~
;: 20 The area between first piston 50 and bore 43 enclosed by O-
:rings 62, 63 defines~a first pressure responsive area of the
: . valve, hereindefined as "A-l". The area circumscribed by
first valve seat 5~, borè 43, first piston 50 and O-ring 63
. ~ is defined as the second pressure responsive area of valve
3 , .'
12, hereindefined as "A-2". . ;
Dis~posed in bore 43 adjacent first inlet port 30 is a
~i second piston or piston means 65 defined as comprising a pis- : .
ton member 66, an end cap member 67 and a valve cage member 68.
: -8- ;
,, :. . .... .. . . . ....... ... . . . .......... . . ........... .
.,';. . : ,'', .; , ' : ,: ~
... . .
~ 5 4~
ris~on ~ncmher 66 has a cylindrical ~ase portion 70 at
one end and a f]anged end portion 71 at its opposite end. Cap-
ping the end of flange~ end por~:;on 71 is an annular seal 74
made of resilient material and having its outer periphery
U-shaped as at 75 for sealing engagement with piston member
annular shoulder 73. Seal 74 is grasped about its outer
periphery by a metal cup-shaped annular retainer 76.
Base portion 70 of piston member 66 is adapted to be
sealingly received within a centrally located, blind bore
portion 78 of end cap member 67. End cap member 67 has a
cylindrical main body portion 79, a flanged base portion 80
adjacent first inlet 30 at one end of main body portion 79
and a shouldered end 81 extending from the other end of cylin-
drical main body portion 79. Shouldered end 81 functions as
~ i, .
` a spring seat for one end of a conical spring 82 which is
sea~ed at its opposite end underne~th cup-shaped member 76.
Flanged base portion 80 of end cap member 67 is lockingly
engaged within a base portion 84 of valve case member 68 by
; means of a snap ring 85. Valve cage member 68 is of tubular
:;~
shape having a main body portion 86 extending from base por-
tion 84, indented radially inwardly in the area of thîrd inlet
,
port 32 and having a plurality of openings or windows 87 to
permit air passage from third inlet port 32 to its interior.
. ,
Extending from main body portion 86 is a f~rward portion 88
from which extends a plurality of shouldered stops 89 ex-
tending in an annular array from forward portion 88 and -
adapted to contact shouldered seat surface 55 of first piston
50. Extending radially inwardly from the interior o~ forward
', ' ~ ` -
~ ~ 5 4~ ~
por~i.on ~38 :is a ~rus~o-conic~ll second valve seat 90. The dia-
me~e-.r of ~ cond valve s~at 90 is ~o].eranced closely to the
diam~er o~ ~i.rst valve sca~ 54 and, as shown in kIGURE 2, is
closely concentr-ic with stem portion 53. Formed in the in-
terior o valve cage member 68 and extending from second valve
seat 90 towards base portion 84 are a plurality of splines 92
having an interna] diameter sized closely to the e~ternal
diameter of cup-shaped retainer 76 for guiding piston member
66 in its movement. The spaces between splines 92 define
passages for air flow through the val.ve seat from third inlet
port 32 ~o delivery port 33. Sealing means for second piston
:65 are provided in the form of O-rings 95, 94 received within :~:
grooves formed in base and forward portions 84, 88 respective-
. . .
:;. . ly of valve cage member 68. : :
, O-rings 94, 95 function as se:aling means to define a
.~ third pressure respons;ve area "A-3" of valve 12 specifically
~. defined by that portion of bore 43 closed by O-rings 94, 95
`~ and second valve seat 90. Bore 43 and the diameters of pis-
:.~ tons 50, 65 are sized equally along their lands which contain
. ~ 20 O-rings 63, 94, 95~, Pressure responsive areas f'A 27' and;~
.. ; . ,
. "A-3" may be considered to be equivalent to one another and
. : pressure responsive area 1'A-l" is sized greater than pressure .
.. . . . .
responsive areas "A-2", "A-31', preferably at a ratio of l.5 ;:~
3 to l. i . .
OPERATION ,;
The operation of inversion valve J.2 will first be ex~
plained with reference to the brake system s~own in FIGURE l .
" ,~
~ and the vehicle in a parked position with a depressurized air
~ -1 0 - .
:. , , ., . ~,, , . . . . .~ , , . , :
~ ~ 5 ~6~
systcm. In ~lliS l~ode, rescrvoirs "A" and "B" are assulncd tln-
ch~rged, ~i~h scrvice br.llcc l:in~s 20, 23 vented ~o atmosphere
: thus venting sccond i-nlet port 31 of inversion -valve 12. Park
valve 39 is ven~ed ~o atmosphere thus venting brake line 38
- and third inlet port 32 ~o atmosphere. Similarly, reservoir
"B" is no~ pressurized and little or no pressure exists in
brake line 37 and first inlet port 30 of invers;on valve 12.
With the pressures thus established, the component parts of
: înversion brake valve 12 will assume the position shown in
FIGURE 2. With little or no pressure at first inle~ port 30,
~: the force exerted by compression spring 60 is sufficient to .
bias first piston 50 dow~wardly in valve bore 43 sealing first
. valve seat 54 against seal 74 and contacting annular shoulcler
surEaces 55 with shoulder stops 89 orcing first and second
~ pistons 50, 65 to "column up" until base por~ion 84 of cage
`~ member 68 contacts the bottom of valve bore 43. In this posi-
.. ..
tion, first valve seat 54 is sealed and second value seat 90
is opened to permit air ~rom emergency brake chamber 26 of .,
., .:
~ the rear brake actuators 24 to vent to atmosphere via third
~ :
: 20 inlet port 32 by traveling through pressure responsive area
, .
`., "A-3", around second valve seat 90~ through openings in : : `
. .
.i ~ . splines 92, ~he windows 87 in valve cage member 68 and from ~ . .
:j
i thence through third inlet port 32.
Whe~ the operator o~ the vehicle starts the engine, com~
pressor 13 automatically charges reservoirs "A" and "B" with
~- air at supply pressure. Reservoir "B" air at supply pressure
.` is then.ported via lines 18, 37 into first inlet port 30 ~:
causing pistons 50, 65 to move in a column, compressing
', -11- ` '~
.~ ,. . . : , . . .
. :
. , : .
1~ ~ 4~
Sprillg 60, u-n~il end por~ion 52 of first piston 50 contacts
vent cover 45 which acts as a solid stop. First and second
valve seats 54,90 remain in their same rela~ive position as
^ previously described in a depressurized mode. When park con-
- trol valve 39 is actuated, air at supply pressure from either
reservoir "A" or "B" (whichever is higher) is supplied to
~, .
third inlet port 32 and travels through the valve in the path
previously described to delivery port 33, thence through brake
- line 36 into emergency brake chamber 26 to precompress actua-
-~ 10 tor spring 29. In this position~ ~he valve is in its normal
operating highway mode and so long as a brake failure in the
~ rear brake actuator system does not occur, air at supply pres- ;
; sure is ported to emergency brake chamber 26 of the rear brake
~ actuators thus insuring that the brake ac~uator springs 29~ `~
.. ~ ~ . ,
' ~ ~ do not tend to partially apply the rear brakes of the vehicle.
It should also be noted that service air brake applications
to the vehicle with the valve in its normal highway operating
~ : . .....
mode do not affect the ~alve since first piston 50 is posi-
tively stopped from furt'ner travel by contac~ with vent co~er ~-
45,
.; ~ . . .
~ ~ Any brake failure in the rear a~le brake system which ~1
c~ results in a loss in pressure in reservoir "Bl' will trigger ~-
.~
actuation of inversion valve 12 in a manner now to be described.
Reservoir "B" could lose pressure as a result of leakage or
failure in reservoir "B" itself, or failure or rupture in any
`I
of the rear brake lines 18, 23, 37, or ~ailure or leakage in
~, ,~ dual circuit brake valve 19, or failure in rear brake actuators
.' , ~ .
; 24. If failure occurred in any of these components, pressure
-12-
,.. , ..... ; . , .. .. . .. ,..... . . . , . ; , . , . : .
,., . . . ... : - . . . . . , . . ~ . . ~ :
.,,.. . , , . - . . . ..
1~3546;~
i.n {irs~ ].e~ por~ 30 wo~lld (1rop. Since air at s~1pply pres-
sure exis~s at pressure xcs1~ullsive a~ea "A~~", tlle second
piston would be forced downwardly in bore 43 while first pis-
ton 50 would remain biased ~gainst vent cover cap 45. As t1e
pistons separate from their c~olumned-up position which they
assume in a nomlal operating highway mode, second valve seat
90 would move closer in~o a contact engaging position with
seal 74. If reservoir "B" pressure continues to drop7
second valve seat 90 would contact seal 74. Up to this point,
conical spring 82 would maintain first valve seat 54 in seal-
ing engagement with seal 74. Further downward movement of
valve cage member 68 will result in opening first valve seat
54 ~ile maintaining second val.ve seat 90 sealed. During
this movement, air at supply pressure in third inlet port 32
is trapped within valve cage member 68 and is not efective
: to bias second piston 65 in any direction within bore 43
' !
while second valve se.at 90 is sealed. Therefore, when first
valve seat 54 moves away from seal 74, air within emergency
G
brake chamber 26 of spring brake ac~uator 24 will begin to
vent through seat 54, and vent ports 34 to atmosphere. Ac-
~cordingly~ the pressure within pressure responsive area "A-2"
of inversion valve 12 will drop until springs 60 cvercome the
force generated by air pressure acting on area "A-2" and -
. move piston 50 downward. Equilibrium will occur when the
pressure developed in area "A-2" exerts a orce equal to the
bias of compression spring 60. In this condition, the valve
will be in a lapped position such as shown in FI&URE 4 with
both valve seats 54, 90 seated against seal 74. If there has
-13-
.; .
: : .. , . .. : :
., : .. . :
, : - ::
,: . - . .-:
~s~
beerl a coml)l.e~e ~ailllrc in ~he prc~ssure of the reclr brake sys-
tem, firs~ pi-;~on 50 will be at the bottom of bore 43 with
the bias o~ springs G0 exer~in~ a force against area "A-2"
just sufficient to maintain compression spring 29 and brake
actuators 24 slightly compressed and valve 12 is no~J ready to
cycle to an emergency mode for quick brake application. Under
these condîtions, it should be noted that a slight extension
of the brake actuator output shaft, which may necessarily
occur9 is not viewed as a detriment since the condition is
not permanent.
If a brake application is now ~ade by the vehicle operator,
service air is delivered to second inlet port 31. The service
air pressure acting against area "A-l" develops a force ini-
tially additive to that developed by emergency brake chamber
air acting against area "A-2" and is effective to move first
` piston 50 towards vent cover cap 4'; opening delivery port 33
to atmosphere via ~irst valve seat 54. 'Fhe pressure of the
aîr in emergency brake chamber 26 is reduced to a lower value
w~ich mul~iplied by area "A~2" develops a force that is addi-
tive to that developed by service air pressure in area "A-l"
to equalize the bias of spring 60 whereat the valve returns
to the lapped position. While areas "A-2" and "A-l" could
be equal, it is desirable, for energy considerations, to have
spring 29 of rear brake actuators 24 expand or travel further
against output shaft 27 to insure a brake application force
at rear brake actuators 24 at least equal to that developed
by the unfailed front brake actuators 21. Thus pressure re- -
sponsive area "A-l" is sized ~o be slightly grea~er than area
-14-
:... . . .. - . . . . - - - -
: , , - , ~, .
.~ - . : . , . . . i .
: : - . . . .:
- - .
:, .
, . . :.
: . : . .
: .. ~ . .. , .. ~ ,
~ s~
"A~2" alld pr~C~rably ].5 ~lnl~s ~s great. ~li.S penlli t-S the
air press~lre wi~ n~rgency brake chamb~r 26 to drop in
pressure at a ra~e 1.5 times as great as that which is applied
by air at service pressure. ~hile i~ is contemplated that
inversion valve 12 of the subject invention could be manu-
~actured with various ratios of areas "A-l" and "A 2", a
ratio higher tha~ 1.5 to 1.0 ma~ not be desired. Generally
speaking, spring brake torque must always remain under the
control of the vehicle operator. Assuming that ~he unfailed
axles of the vehicle are equipped with antiskid devices or
antilock controlled, a ratio higher than 1.5 ~o 1.0 may re-
sult in an overly severe brake reaction from the spring brakes.
In such instance, the spring brakes could lock the wheels
~'
they control while the wheels unfailed under antilock con-
trol would not lock. It has been discovered that an inver-
sion valve ratio of approximately 1.5 to 1.0 provides a good
balanced brake reaction between unfailed and failed brake
actuators although in antilock ins~allations the inversion
valve could adequately function at ratios less than 1.5 to 1Ø
After service brake application has been completedg
second inle~ 31 will be vented to atmosphere by dual circuit
` brake valve 19 venting air from pressure responsive area
'A-l". Springs 60 will force first valve seat 5~ against
seal 74 compressing conical spring 82 to open second valve
seat 90. This will establish fluid communication between
third inlet port 32 and delivery port 33. Pressure will
build in area "A-2" and emergency brake actuator chamber 26
until equilibrium is reached with spring 60 whereat first
-15-
.,
. . .
:. ,, :
S~
pi.S~Oll 50 ~7ill move towards vellt cover c~p 45 to seat second
valve seat 90 against seal 74 establis}ling a lapped position
of the v~lve and readying same to be triggered for the next
brake application.
The features and operating characteristics of inversion
valve 12 of the subject invention, as thus described, make
inversion valve 12 suitable for unique application to a
tractor-trailer brake system. Such application is shown in
FIGURE 5 which illustrates the unique trac~or-trailer brake
system which offers safe~y advan~ages not possible with con-
ventionzl air brake systems. As illustrated, a tractor brake
:
system employing conventional antiskid or antilock system is
shown on the le~t-hand side of FIGURE 5 and a conventional
eme~gency relay type trailer brake sys~em is shown on the
right-hand side of the drawing, although it should be clear
to those skilled in the art that the trailer will function in
~'l the brake system illustrated if equipped with the standard
type of antiskid or antilock brake arrangement. With respect
to the tractor brake system illustrated, dotted lines refer to
brake lines with air at service pressure and solid lines refer
to brake lines with air at supply pressure and l;ke numbers
with reference to FIGURE 1 will designate like parts where
applicable.
~ he conventional trailer system illustrated in FIGURE 5
includes an emergency relay valve 340 which is connected to
service and supply lines 334, 335 respectively, a reservoir
341 and trailer brake actuators 343 through suitable lines 344.
J
Trailer brake actuators 343 are shown to be of the single
-16-
: ' ' :" ' , ' :
~S~
diapllragrll, air applied-sprillg releas~d ~ype a]tllough other brake
ac~uators nlay be applied to ~lle trailer systern if sligh~ changes,
known to those skilled in the art, be made in the fluid com-
munication lines. Independent of the brake actuators em-
ployed, emergency relay valve 340 functions in the usual man-
ner to emi~ reservoir pressure to brake actuators 343 when
dual circuit valve 19 is depressed and vent same when the
dual circuit valve is released. Similarly, in the event of
a predetermined pressure drop in supply line 335, relay valve
10 340 is actuated to supply air at system pressure from reser-
voir 341 to trailer brake actuators 343 to set the brakes.
When supply pressure is restored in line 335, relay valve 340
vents the air in trailer brake actuators 343 to re-es~ablish
normal operating mode of the system.
; With respect to the tractor brake system, the additional
components illustrated therefor in FIGURE 5 and not shown in
FIGURE 1 include conventional skid control modulator valve
200 and appropriate brake line plumbing associated therewith,
known to those skilled in the art and thus not described in
- 20 ~detail herein. Component valves shown in FIGURF. 5 which ren-
der inversion valve 12 sui~able for tractor-trailer applica~
tion include a traîler control valve 201, a relay valve 202,
" .
~` ~ a tractor protection valve 203 and a governor valve 204, all
these valves are known to those skilled in the art and thus
are not shown or described in detail herein.
Governor valve 204 is inserted in line 37 and functions
::;
as an on-of~ switch controlling air to first~inlet port 30 o~
inversion valve 12. Governor valve 20~ is typically set at
-17-
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~, , ' ' ~ ' .'.' ' ': ; ' '
. . . . . .
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a~ ro~ at:cly 75-80 psi .~ so long as rear br~lke reservoirs
"B" ~evelol) a pressuxe excee~]i-lg ~his value, reser-voir "B" will
be in fluid communication wi~h ~irst inlet port 30. When
pressure ln reservolr "B'7 drops below 75-80 psi, governor
valve 204 will act to prevent fluid communication between
reservoir "Bl' and first inlet port 30 and will also drop the
pressure at first inlet port 30 to atmosphere through a vent
; - . .
mechanism provided in governor valve 204 thereby rendering
i~version valve 12 ready for complete spring brake application.
The advantage of this will be explained later.
Trailer control valve 201 is similar in operation to park
l control valve 39 and operates, upon application, ~o vent the
i trailer supply line of air. The trailer emergency relay valve
~ responds in a known manner to apply the trailer brakes when
;~ this line is vented. The inlet of trailer control valve 201
is in fluid communica~ion with the outlet of two way check
valve 40 and thus always senses air at supply pressure. The
~' ~ outlet of trailer control valve 201 is in fluid communication
:, . .
; ~ with a brake line 205 in turn in fluid communication with the
( - 20 reservoir port of relay valve 202.
~" :
A brake line 206 in~fluid communication at one end with
delivery port 33 of inversion valve 12 is in fluid communica- ;
tion with the control port of relay valve 202. Brake line 206
. } .
and control port of relay valve 202 may ~e viewed as a line
carrying a source of fluid at a signal pressure. A third
brake line 207 is in fluid communication with the ou~let of re~
lay valve 202. When air at signal pressure exists in brake
line 206, relay valve 202 cycles to provide full fluid
-18-
;
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- COmlnUIl iCa~:iOn l~etW~CI- ~ral<e lines 207 ~lld 205. I~len air pre~-
sure in lin~ 20G ~IOI)S b~low 75-80 ps; (signal pr~ssure), re-
lay valve 202 is .Ictua~ed to produce a similar drop in pressure
between lines 205 and 207. Wllen trailer control valve 201 is
vented in an actuated position, line 205 is vented and relay
valve 202 receives no air at its reservoir port~ therefore
no delivery is possible.
Brake line 207 is in fluid communication with the air
supply line inlet of ~ractor protection valve 203. Tractor
protection valve 203 operates to provide fluid co~nunication
with air at supply and service pressures on the tractor to
that on the trailer so long as air at supply pressure enters
its inlet side. If supply pressure air drops at the inlet
side of tractor protection valve 203, tractor protection valve
203 cycles to prevent fluid communicatlon of air at service
pressure from the tractor side to the trailer side. A typi-
cal tractor protection valve will cycle to its "off" position
when supply line pressure drops to appro~imately 30-40 psi.
In operation and with reference to the previous descrip-
tion of the operation of inversion valve 12, it should beclèar that in the normal highway operating mode, ~ir at
full supply pressure will enter third inlet port 32 and exit
delivery port 33 to maintain springs 29 of the spring actuators
24 fully compressed. Tractor protection valve 203 will be
biased into its open position and the trailer supply line 335
will be pressurized in the normal manner.
A normal service brake application resu~ts in conventional
response from the system. Tractor front service brakes are
. --1 9-- i
.. . . ~
: , ' ~ ' ' . ', :
.. . .
~ ~ 5 ~6 ~
actuat~d by prcssillre in lill~ 20. Rcar service and trailer
~ralccs .Ir~- actu~t~d ~y pr~ssure in ]ine 23. ~t this point
it is important ~o note ~h~t the trailer supply line is
pressurized rom lines 207 and 205 by way of valves 202, 201
and 40. Air from either part of the tractor dual circuit
brake system can fill this supply line. The trailer signal
line receives pressure by way of line 23 from valves 203 and
19 and as such is only able to draw pressure from reservoir
"B". This feature has several advantages during emergency
,
stops when one or more components of the service brake air
system have failed as discussed below.
Cne particular failure worth considering is a broken or
disconnected trailer service line. This has serious conse-
quences with conventional systems. The service line îs un-
, ., . . ~
~j pressurized unless a brake application is made. The open
;~ line goes unnoticed by a driver sïnce no air escapes, but
.`~.`!
l when a brake application is required, a massive leak occurs.
-;! This leakage rapidly drains a conventional tractor air brake
~ ~ .
s~s~em diminishing the tractor brake effectiveness, and
`~ 20 since the trailer service line is open, the trailer brakes
~emain inoperative. Even the newer dual air brake systems
do not correct this def;ciency. With the proposed system,
the vehicle driver retains control of the tractor and trailer
brakes and brake effectiveness is not greatly impaired. The
brake application would initially result in massive leakage
.. . . .
- from the open hose as before, except this leakage would only
affect reservoir "B". Pressure in reservoir "B" would rapid~
ly fall to 75-80 psi at which time governor 204 would function
.,
-20-
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, . ~ , .. . ..
s
' ' ' . : ,
:L~95~i60
,- to exhau~t port 30 of the inv~rsion valve. This causes ~l~e
inversion valve to func~;on .as describcd above. The delivery
pressure fro~ the valve au~ornatically drops to i~s preset
emergency level or if the brake application is still being
held, the inversion valve delivery will be further reduced
by l.5 times the amount of the service application. During
this time, the tractor front brakes have been fully active
- and the rear brakes ac~ive to the extent allowed by reser-
voir pressure at "B". The trailer brakes had been inopera-
tive to this point. The reduction of delivery pressure from
`; the inversion valve changes this situation~ Reduced pressure
in line 206 is sensed by relay valve 202 and as a result pres-
sure in line 207 drops quickly to the same level. Two events
occur due to the pressure drop in line 207. First, the
tractor protection valve 203 cycles in a known manner to
close off the passage between line 23 and the open trailer
signal line. This stops the air leak from the tractor and
~i retains 75-80 psi in reservoir "B'~. The second reaction is
by the ~railer emergency relay valve. This valve functions
in a Icnown manner upon reduction of pressure in line 207 to
;~ automatically apply the trailer emergency brakes. This series
of events occurs rapidly and automatically so that the brak-
ing performance of the vehicle is not greatly different from
that experienced w~en the trailer signal hose is connected.~ ;~
~ Once the stop has been made and the brake treadle released,
y. the inversion valve delivery pressure goes up to the preset
- emergency level. This pressurizes line 2~ thus cycling ~-
relay valve 202 to permit supply pressure communication between
-21-
.":. . ' ' . ' ' ~ ,
59~66~)
lines 205 and 2~7 tl-lereby o~ning the tractor protection va]ve
connec~ion b~ween the tractor and trailer to pressurize the
trailer supply line for r~leasing the trailer emergency brakes.
The system response to the open trailer signal hose failure is
. made possible by the full pressure delivery characteristic of
.~
the inversion valve which allows this valve to be interposed
in the trailer supply line. In general, a valve that de-
livers a regulated pressure lower than the supply pressure
should not be used in the towed vehicle supply line. Thus ~
~` 10 other known inversion control valves should not be used in `
:.~
`~ this application.
The above description illustrates the unctional inter-
~` relationships of the various valves in system shown by
3 FIGURE 5. Persons familiar with vehicle air brake systems
will recognize that this system is capable o stopping the
vehicle under all manner of situations regardless of failures
that may occur in one or more components and is, therefore,
::. : . , 1: .
safer than conventional systems.
The invention has thus been described with re~erence
20~ ~to a preferred`embodiment. Obviously, modifications and al~ h7
terations will occur to others upon reading and understanding
the specification. For example, fasteners securing the vent
cover to the vaIve body could be modified to be adjustable
so that the compression spring force could be adjustable. !;~
The valve parts couId be inverted. The piston shapes changed
~?
x ~ and the valve seal could be attached to the first piston. It
is my intention to include all such modifications insofar as
they come within the scope of the invention.
,...... ~ .
~ -22-
~ , , ~ , , ,
. .
., ,
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~546GO
~:
I~ is thus ~l~e essence of the in~ention to provide i~l a
1uid actuated, vellicular brake system employing dual diaphragm
brake actuators on at least one axle of the vehicle, an inver-
sion valve which is nol~ally effective to maintain the springs
in the brake ac~ua~ors com?ressed at supply air pressure and
,~.
.', which is capable of rapidly applying the spring brakes of the
brake actua.ors upon a system failure in a predetermined
~ ratio to the ~raking ~orce generated by other brake actuators
,~ employed on the vehicle. f
This is a division of copending Canadian Patent Applicallon
~` Serial No. 258l073 which was filed on July 29, 1976.
,! ~ .
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