CA1054660A - Inversion brake valve and system therefor - Google Patents
Inversion brake valve and system thereforInfo
- Publication number
- CA1054660A CA1054660A CA308260A CA308260A CA1054660A CA 1054660 A CA1054660 A CA 1054660A CA 308260 A CA308260 A CA 308260A CA 308260 A CA308260 A CA 308260A CA 1054660 A CA1054660 A CA 1054660A
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- CA
- Canada
- Prior art keywords
- fluid
- brake
- valve
- pressure
- inlet
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Valves And Accessory Devices For Braking Systems (AREA)
Abstract
Abstract A pneumatic brake system employing dual-diaphragm, spring-actuated, air-released brake actuators is provided with an inversion valve which, in the event of a brake system failure, prevents the brakes from being automatically applied while permitting controlled brake application by releasing compressed air from each actuator's spring chamber in an in-verse ratio to that normally supplied from the system by the operator applied brake valve thus permitting a controlled spring brake application. The valve employs first and second pressure responsive pistons with associated valve seats to maintain the actuator springs compressed with air at supply pressure when the vehicle is normally operated. The air at supply pressure in each actuator's spring chamber is automati-cally ported to a lower pressure through the valve when a system failure occurs and prior to brake application to insure fast response time of the spring actuated brake.
Description
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-- 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 - . .
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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.
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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~
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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.
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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.
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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 ; :
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. 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 -;,; :
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~ 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 ~
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`~ inversion valve as one of its component parts.
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:;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
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~ 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 ,, .
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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. -~
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` 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 '-:" .
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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~
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~, . , l ',3 ~ ~ened as at 46 to valve body 42. Ribs 47 in vent cover 45 en- ~
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~.` 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_ - . . . .
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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.
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;: 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.
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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 .
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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 .
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~ and the vehicle in a parked position with a depressurized air ~ -1 0 - .
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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 : : `
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.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- ` '~
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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 ,.. , ..... ; . , .. .. . .. ,..... . . . , . ; , . , . : .
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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 .; .
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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 :... . . .. - . . . . - - - -: , , - , ~, .
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"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 ., . . .
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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.
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Trailer brake actuators 343 are shown to be of the single : ' ' :" ' , ' :
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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 ,.
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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 ;
':., .'' .. ' ' .' .. ' ~ . '' , . . .
:,, , .
- 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 .. . . ~
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.. . .
~ ~ 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 ., ,................... ~ ', . ~ : , . . ' ', , . ~ , .. . ..
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 .":. . ' ' . ' ' ~ , 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.
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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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-- 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 - . .
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... :. . .... . . . .
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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~
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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.
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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 -;,; :
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~ 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 ,, .
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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 '-:" .
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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~
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~, . , 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.
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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 .
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~ and the vehicle in a parked position with a depressurized air ~ -1 0 - .
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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- ` '~
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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 ,.. , ..... ; . , .. .. . .. ,..... . . . , . ; , . , . : .
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.,,.. . , , . - . . . ..
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 .; .
: : .. , . .. : :
., : .. . :
, : - ::
,: . - . .-:
~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 :... . . .. - . . . . - - - -: , , - , ~, .
.~ - . : . , . . . i .
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- - .
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, . . :.
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"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 ., . . .
:. ,, :
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 : ' ' :" ' , ' :
~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 ,.
: .. , , . . .,: .. . ~
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~ L~S~
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 ;
':., .'' .. ' ' .' .. ' ~ . '' , . . .
:,, , .
- 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 ., ,................... ~ ', . ~ : , . . ' ', , . ~ , .. . ..
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 .":. . ' ' . ' ' ~ , 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-~ , , ~ , , , . .
., , :` ' ` '~ ; ' ~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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Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A tractor-trailer brake system comprising a first brake circuit associated with said tractor, a second brake circuit associated with said trailer, a plurality of brake actuators in each circuit, means for generating in each circuit fluid at supply and service pressures, tractor protection valve means on said tractor providing fluid communication between said tractor and said trailer when fluid at supply pressure is ported thereto and interrupting fluid communication between said tractor and said trailer in an off position when fluid at supply pressure drops below a predetermined pressure, trailer valve means on said trailer operable to actuate said trailer brake actuators when said tractor protection valve means is in an off position, first valve means on said tractor biased by a source of fluid at signal pressure to provide fluid communication between the higher source at supply pressure in each circuit with said tractor protection valve means and effective to modulate said higher source of supply pressure in accordance with the:
pressure developed by said signal source of fluid; and inversion valve means providing said source of signal fluid and normally operable to generate said signal source of fluid at supply pressure and operable in a brake failure mode to decrease the pressure of said signal source of fluid at a rate proportional to said source of fluid at service pressure when a decrease in said source of fluid at supply pressure in said second circuit occurs.
pressure developed by said signal source of fluid; and inversion valve means providing said source of signal fluid and normally operable to generate said signal source of fluid at supply pressure and operable in a brake failure mode to decrease the pressure of said signal source of fluid at a rate proportional to said source of fluid at service pressure when a decrease in said source of fluid at supply pressure in said second circuit occurs.
2. The brake system of Claim 1, further including governor valve means associated with said inversion valve means, said governor valve means operable to place said inversion valve means in its brake failure mode when said source of fluid at supply pressure in said second circuit drops below a predetermined pressure.
3. The brake system of Claim 2, wherein:
said source of fluid at supply pressure in said first circuit includes a first reservoir, said source of fluid at supply pressure in said second circuit includes a second reservoir, said source of fluid in said first and second circuits at service pressure includes dual circuit foot valve means modulating said sources of fluid at supply pressure;
said trailer valve means including a two way check valve having inlets connected to said first and second reservoirs and an outlet, a relay valve having an inlet connected to said check valve outlet, an outlet in fluid communication with said tractor protection valve means, and a signal line inlet for receiving said source of fluid at signal pressure to control porting between said inlet and said outlet of said relay valve; and, said inversion valve means including an inversion valve having a delivery port in fluid communication with said signal line inlet, a first inlet in fluid communication with said governor valve means, a second inlet in fluid communication with said source of fluid at service pressure in said first circuit, a third inlet in fluid communication with said outlet of said two way check valve and piston means within said inversion valve normally effecting fluid communication between said third inlet and said delivery port and upon a brake failure mode interrupting said communication and venting fluid from said delivery port at a rate proportional to that applied to said second inlet.
said source of fluid at supply pressure in said first circuit includes a first reservoir, said source of fluid at supply pressure in said second circuit includes a second reservoir, said source of fluid in said first and second circuits at service pressure includes dual circuit foot valve means modulating said sources of fluid at supply pressure;
said trailer valve means including a two way check valve having inlets connected to said first and second reservoirs and an outlet, a relay valve having an inlet connected to said check valve outlet, an outlet in fluid communication with said tractor protection valve means, and a signal line inlet for receiving said source of fluid at signal pressure to control porting between said inlet and said outlet of said relay valve; and, said inversion valve means including an inversion valve having a delivery port in fluid communication with said signal line inlet, a first inlet in fluid communication with said governor valve means, a second inlet in fluid communication with said source of fluid at service pressure in said first circuit, a third inlet in fluid communication with said outlet of said two way check valve and piston means within said inversion valve normally effecting fluid communication between said third inlet and said delivery port and upon a brake failure mode interrupting said communication and venting fluid from said delivery port at a rate proportional to that applied to said second inlet.
4. The system of Claim 1, said inversion valve means including:
an inversion valve having a first inlet in fluid communication with fluid at supply pressure in said second circuit;
a third inlet in fluid communication with fluid at supply pressure in either said first or second circuits, whichever is greater;
a second inlet in fluid communication with fluid at service pressure in said first circuit;
a delivery outlet in fluid communication with said second chamber; and, a vent outlet;
piston means within said valve (a) providing fluid communication between said third inlet and said delivery outlet when said vehicle is in its normal highway operating mode, (b) sealing said delivery outlet from said third inlet while providing for a limited, predetermined period of time fluid communication between said vent and said delivery outlet when fluid at supply pressure in said second circuit drops in pressure and (c) thereafter providing further fluid communication between said vent outlet and said delivery outlet for a pre-determined period of time while sealing said third inlet when fluid at service pressure is provided to said second inlet whereby fluid pressure in said second brake chamber is reduced in value at a rate proportional to that which is applied to said second inlet.
an inversion valve having a first inlet in fluid communication with fluid at supply pressure in said second circuit;
a third inlet in fluid communication with fluid at supply pressure in either said first or second circuits, whichever is greater;
a second inlet in fluid communication with fluid at service pressure in said first circuit;
a delivery outlet in fluid communication with said second chamber; and, a vent outlet;
piston means within said valve (a) providing fluid communication between said third inlet and said delivery outlet when said vehicle is in its normal highway operating mode, (b) sealing said delivery outlet from said third inlet while providing for a limited, predetermined period of time fluid communication between said vent and said delivery outlet when fluid at supply pressure in said second circuit drops in pressure and (c) thereafter providing further fluid communication between said vent outlet and said delivery outlet for a pre-determined period of time while sealing said third inlet when fluid at service pressure is provided to said second inlet whereby fluid pressure in said second brake chamber is reduced in value at a rate proportional to that which is applied to said second inlet.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/611,648 US4017125A (en) | 1975-09-09 | 1975-09-09 | Inversion brake valve and system therefor |
| CA258,073A CA1053295A (en) | 1975-09-09 | 1976-07-29 | Inversion brake valve and system therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1054660A true CA1054660A (en) | 1979-05-15 |
Family
ID=25668332
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA308260A Expired CA1054660A (en) | 1975-09-09 | 1978-07-27 | Inversion brake valve and system therefor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1054660A (en) |
-
1978
- 1978-07-27 CA CA308260A patent/CA1054660A/en not_active Expired
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