CA1120976A - Brake pressure control valve including failure warning mechanism - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A pressure control valve for use in vehicle hydraulic diagonal split brake systems. The valve includes two valve pistons which operate to limit the fluid pressure delivered to the rear wheel brakes relative to that delivered to the front wheel brakes.
The valve also includes a failure warning mechanism having a switch actuating piston. In the event of a failure in one branch of the diagonal split brake system, the switch actuating piston operates to simul-taneously preclude the two valve pistons from limiting the rear wheel brake pressure so that the rear wheel brake in the unfailed branch of the brake system can develop the maximum braking effort for vehicle emergency braking.

Description

BRA~E P~ESSURE CONTROL VALV~
INCLIJDING FAI~URE WARNING ~Cl~NISM

Vehicle hydraulic dual brake systems ha~e i~cluded pressure control vaLves for reducing the potential ~or prema~ure rear wheel lock during brakingO These pressuxe control valves generally ~imit the rear wheel brake pressure relative to the ront wheel brake pressure in order ~o reduce the rear wheel bra~e torque and ~hus preven~ premature rear wheel lock. A drawback of the type of pressure control valve which is used ~n a dlagonal split brake ~ystem is that, in the event o failure in one br~nch o the brake system, the pres~ure control val~e continues to limit the rear wheel brak~ pres-su~e iR the unfa~led branch c the brake system thereby reducing the available remaining rear wheel brake torque that is then needed for emergency braking. Theref~re~ it ~s an object of this invention ;20 to provide a pressure control valve for dlagonal ~plit brake systems which lim~ts the rear wheel brake pressure relatlve to the front wheel brake . pressure during normal braking but which precludes the limiting o the rear wheel brake pressure in the event of partial bra~e system failure so that the rear wheel brake whlch is disposed in the unfa;led branch of the brake system ean develop ~he maximum brake to~que for emergency braking.
SUMYARY OF THE_INVENTION
The control valve of the present invention ( ~
9~

is designed for use ~n vehicle hydraulic dual brake systems of ~he ~ype which include a tandem master cylinder having irst and second separatled portions supp~ying fluid pressure to first and second separated wheel brakes, respectively~ through first an~ second separated fluid branches 9 respectively . . The control alve includes first and second inlets for cannection to the first and second tandem master cylinder separated - p~rtions, respectively, and first and secorld outlets for connection to the f irst and second separated wheel brakes, respectivelyO The control valve also includes ' fir~st valve means which will be disposed in the first ~luid branch of the dual brake system to transmit f luid pressure at the first ~nle~ to the first outlet and to limit the fhid pxessure transrn;~ted to the first outlet relat~ve to the fluid pressure at the ~Eirst ~.nl.e~ when the fluid pressure at the first lnlet is above a prede term~ned level. The control valve further inchldes ~econd valve means which will be disposed in the second iEluid branch of the dual brake system to transmit fluid pressuxe at the s.csnd inle~ to ~he second outlet and to limit the fluid prPssure traIlsmitted ~o the second ou~le~
relative to the f luid pressure at the second inlet when the fluid pressure at the sec:ond inlet is above the pre-determined level. The con~rol valve also includes inhibitirlg means which simultaneously precludes the ~irst and second ~alve means from l~miting the flu~d pressure transmitted fr~m the irst and second inle~s to 'che firs~ and ~econd outlets9 respect~vely, when a ailure occurs in one of the first and second fluid ;~ _ branches of the dual brake systemO
BR~ DESCRIPTION OF THE DRAWINGS
F~Go 1 is a schematic view of a portion o a dual brake system incorporating a control valve ~hioh embodies the present invention shown m ertical section;
~IG. la is a view of one of the parts o the contxol valve of FIG" l;
FIGo lb is a view of a portion o~ the control valve of FIG, 1;
FIG. 2 is a side elevation view o~ the c:ontrol valve of E~IGo l;
FIG~ 3 is an enlarged view, partly in section and partly in elevation~ of one o the parts of the control valve o~ F~G~ 1;
- FIG~ 4 i9 an end view of th~ part illustxated in FIG. 3, - ~IGI. 5 is a sectional view of the part illustrated in FIGo 3 taken along lines 5-5 thexeof, and FIG. 6 is a sec~ional view of a portion of the part illustrated in FIGO 3 tak~ along l~es 6-6 thereofO

~639~
ESC~IPTTON OF THE P~EFEP~P~D FMBODIM~NT
Reerring to FIG. 1, a portion of a diagonal ~plit brake system is generally illustrated at 10 and includes standaxd components such as a tandem master cylinder 11 operated by a ~rake pedal 12. The brake sys~em portion 10 also includes fron~ wheel brakes 14, 15 - and sear wheel brakes 16~ 17~ A control valve, indicated generally at 18" is interposed between the master cylinder }1 and the fron~ and rear wheel bxakes 14-170 -Brake ~0 ~luid is delivered from the master cylinder 11 to the control valve 18 via ~he conduits 19, 20. Brake 1u;d is then delivered to ~he front wheel brakes 14, 15 ~rom the control valve 18 via the conduits 21, 220 Likewise, brake fluid is delivered to the rear wheel brakes 16, 17 lS ~rom the control valve 18 via the conduits 23, 240 The control va~ve 1~ include~ a hous~g 26~ pre~
ferably ormed of a suitable me~al, having i~let openin~,s - 27, 28 for receiving the conduits 19, 20 respectively.
The housing 26 ~cludes identical a~ially aligned ca~itieS
:~0 3~,. Passages 31, 32 corlalect the inlet openings 27J 28 w~th the cavlties 300 The hous-ing 26 ~ncludes a bore 33, - ~ntersecting ~he passage 32, and a coun~erbore 340 A
shoulder 35 is ~ormed between ~he bore 33 and the count~r-bore 34. Axially aligned bores 37~ which intersect ~he bo~e 33, and r.o~nterbores 38 connect the cavities 30 with the bore 33., Each couqlterbore 38 deflnes ar~ular shoulders 39, 40, The housing 26 also includes a cross bore 42 which intersects the bore 33 a~c ~he same loeatio~ on its axis as the bore 37~, A passage 43 ex~ends from ~he closed 3û end of the bore 42 through the side of the housing 26.

' ~ 4 ~

I ( .
~ 0 97 6 Fittings 44 are threadedly received in the ou~er.
ends of the cavities 30, respectively. ~ring seals 4~
ar~ disposed between the housing 26 and the fittings 440 The ittings 44 include outlet openings 47 for receiving the conduits 23, 240 Each fitting 44 also includes a ce~tral bore 48 which defines a peripheral wall ha~ g an annular end surface 490 Each ~tting 44 further includes a fluid passage 50 cormecting the central boxe 48 and the outlet opening 470 A fitting 52 is thxeadedly received in lQ the outer end o the eounterbore 340 An 0-rirlg seal 53 is disposed between the housing 26 and the fitting 52. :
The 1tting 52 i~cludes an outlet opening 54 ~or receiving the conduit ~1, and the housing 26 lncludes an outlet opening 55 ~or receiving the conduit 22. The fitting 52 ~ncludes a central bore 57 de~ning a pexipheral wall wl~h ~luid passages 58 extending therethroughO The flt~ing 52 also includes a fluid passage 59 connecting the central - bore 57 ~nd the outlet ope~ing 54~ A fluid passage 61 connects o~e cavity 30 and the rounterbore 34~ and a 1u~d passage 6? con~ects the othe cav~ty 30 and the outlet opening 550 ~eferring also to FIGo la, a movabl~ valve member such as a valve piston 63 is disposed in each of the cavities 300 Each va~ve piston 63 has its end portions 64, 65 slidably disposed in the respective f;tting bore 48 and housing bore 370 An ~-ring seal 67 is provided ~n each housing counterbore 38 con~acti~g the respective annular shoulder 40 and valve piston end port~on 65 to prevent fluid flow fro~ the cavitles 30 into the bore 33.
Each valve piston 63 includes a radially extending - 5 ~

3L~ 76 annular flange 68 hav~ng an ~nular shoulder 69 on one side and an annular shoulder 70 on the oSher side therPof~, Each valve piston 63 further includes an enlarged portion 72 extending radially outwardly and havi.ng a rounded S amlular shoulder 73 which forms a valve headO The outside diameter of the enlarged port~ ons 72 is sligh~ly less than the diameter o the bores 48 o the f ittings 44 so as to allow 1uid flow around the enlargPd p~rtions 72.
. Eaeh valve piston 63 also includes a redueed diameter cylindrical portion 74 between the annular shoulders 70, 73~ Each valve piston 63 further includes a cylindrical end portion 76 having a noteh 77 extending transversely therethrough to allow fluid flowO
Referring also to FIGS., 3-6, a stationary valve I5 member such as an e~astomeric valve element 78 is disposed in each of the cav~ties 30 and surrounds the reduced cylindrical portion 74 of the associated valve piston 6~o When the valve elements 78 are in the position shown in FIGo 1~ they engage the walls of the cavities 30 and the 2Q amlular end surf~ces 4~ of the iE~ ttings 44 ~, As seen in FIGS,, 3 and 4" each valve element 78 has a l~p 79 whi~h extends outwardly when the valve element 78 is in its free stateO ~her~ the valve elem~nts 7~ are ins~allecl in the cavities 30~ the lips 79 are forced inwardly and, consequently, form seals aga~nst the walls of ~h~ cavi~ies 30 to prevent fluid flow around ~he lips 79 from the cavities 30 to the outLet openings 47O
Each valve element 78 includes a pluraLity o angularly spaced ribs 81 which extend radially ~rom the outer peripheral surface 82 thereof. ~ I,' Each valve element 78 fur~her includes a plurality o~ semispheric.al bosses 83 which extend from the side 84 therev for engagement with the annular shoulder 70 of the associated valve plston 630 The spaçes between the bosses 83 of the valve ele-m2nts 78 deine fluid passages for fluid flow rom the inlet openings 27, 28 ~o the ou~let openings 47. Each valve element ~8 also includes a plurality of angularly . spaced ribs 86 which extend from the side 87 therec) for contacting the annular end surace 49 of the associated fitting 440 As seen în F'IGo 4~ the xibs 86 of the valve elements 78 are angularly aligned wlth the ribs 81 thereof to all~w fluid flow around ~he lips 79 from the outlet open~ngs 47 to the cavities 30. As also seen in l?IG~ ~9 each valve element 78 urther ~includes a rou~ded port~Lon 88 adjacent the end of its lnner peripheral s~ face 8~ -for e~aging th~ annular shoulder 73 or valve head of t~.2 associated valve piston 630 The rounded portions 88 orm va~ve seatsO
2t~ When the control val-7e 18 is assembl~d as shown I.DI FIGo 19 it wil~ be seen that~e diameter o the reduced portions 74 of the valve pis~ons 63 is less tha~ the :
diameter of the iYmer per~pheral surfaces 89 of the valve elements 78 so as to define annular ~luid passages th~ re-25 - lbetweenO Also9 the outer diameter of the flanges 68 o~
the valve pistons 63 is less than the inside diame~er of the l~ps 79 o~ the valve elemen~cs 78 thereby defining annular fluid passages therebe~ween~ Thes~ flslid passages coQIbined with ~he previously ment;oned fluid passages between the bosses 33 of ~che valve elements 78 define '7~ `

direct fluid paths ~or ~luid flow between the valve pis-tons 63 and ~he valve elements 78.
Each valve lpiston 63 is nonnally ur~ed outwardly in FIG. 1 toward the a~socia~ed ou~let opening 47 by a coil spxing 91 so that the end surface of its cyli~drical poxtion 76 engages the end o the bore 48 of the associated fitt~ng 440 Since each valve piston 63 is noxmally ll~ge~
outwardly, a ~luid passage is normally oxmed between each ass~ciated valve head 73 and valve seat 880 One end of each coil spring 91 engages the annular shoulder 69 on ~he flange 68 of the associated valve piston 63~ The other end of each coil spring 91 engages a re~ainlng ring 92. The retaining rings 92 rest against the annular shoulders 39 o~ the cavitles 30 and surro~nd the end lS por~ons 65 of the val~e pistons 63~ l~e retaining rings 92 maintain the 0-ring seals 67 in the housing counter-bn~es 380 With the valve pistons 63 in the positions shown in FIG~ 1~ the ~lu~d pressure at the outlet openings 47 will be equal to the fluld pressure at the ~nlet ope~ings 27, 28 or i~ the master cylinder 11. T~e operation of the valve pistons 63 and the valve elements 78 to provide res~ricted fluid passages to the outlet openings 47 will be explained hexeafterO However~ will be noted that the coil springs 91 determ~ne at what fluid pressure level the valve pistons 63 and the valve elements 78 w~ll begin to restrict the fluld passages to the outlet open m gs 47.
This fluid pressure level is hereaf~er referrPd ~o as $he spli~ poin~ pressure and the coil springs 91 are hereafter 3~ xeferred to as the split point springs 91, Referring also ~o ~IGS. lb and 2, the control valve 1~ also mcludes a ~Eailuxe warning mechanism~ pre ferably of a well-knowrl type which is s-imilar to that disclosed in U., S0 Pa~ent No~, 3,700"286~
. The failure warning mechanism includes an electrical switch 93; a centering pis~con g4, c~d a switch actuating piston 95. The electr.ical switch 93 is received in the counterbore 42 and includes an operating member 97 which extends into the bore 330 The centering piston 94 is slidably dispos ed in the rouIlterbore 34. Ari O-ring seal 98 is also slidably disposed in the counter-bore 34 and engages one end o~ the centering pi5ton 94.
The switch actuating piston 95 is slidably received in the bore 33 and includes opposed cam sur~aces 9~3 7 10(1 for engaging the operatlng me~iber 97 of the elec~rical switch 930 The ~w~ tch ~ctl~ating piston 95 also includes cylin-drical portions 102~ 1030 ~ 0ring seal I04 is carried by the switch actuating piston 95 in ~ealing engagemen~
with the bore 330 With the O~ring seals 67, 98 and 104 in posil:ion, it should be noted that the space where the l:~ores 33, 37 and 42 :~ntersect will be kept free of brake fluid and will be maintained a atmospheric pressureO However, it is possible that a small anount o ~luid could leak into that space if, for example, one or more of the ~rlIlg seals 67, ~89 104 become wo~nO Therefore, a well~knowrl type of weep valve 105 may be installed in the passage 43 to exhaust any leaked f 1 uid to the atmosphere ,, OPEE~ATXC)N
Upon actuation of the tandem mas~er cylindex 11 0" 9 O.

by depressing the brake pedal 1~, substantially equal flu~d pressure is delivered to the inlet openings 27, 2~
of the control valve 18i l`hese substantially equal inlet pressures act on the effective areas o~ ~he switch actuatlng and centering pistons 949 95 in a m~nner similar to that described in the aforementioned U. Sr Patent No.
39700,286 in order to noxmally maintain the swi~ch ac~uat-ing piston 95 in the centered position sh~n in FIG. lo During braking, the ~luid pressure at the ou~let openings 54, 55 o~ the control valve 18 will increase at the same rate as ~he fluid pressure at the inlet openings 27, 28 thereof. Thus, the pressure. delivered to the fr~nt wheel brakes 14~ 15 will be equal to the pressure ~n the master c~linder 11 for the full range of the master ~5 cylinder pressure~
Th~ control valve 18 provldes op~ flu~d paths ~or the direct transmission o~ ~luld pressure r~m ~.he ~nlet openings 27, 28 ~o the outlet openings 47 when ~he va~ve pistons 63 are in the positions sh~wn in FIGe 1 a~
already described~ During a braking application, these 1uid paths remaln open with ~he pressure a~ ~he outlet open;ngs 47 increasing at the same rate as the press~Lre at the inlet openin~s 27, 28 until the predetermined split po~nt pressure ~s reached at the i~le~ openings 27~ 28.
~25 When the fluid pressure delivered to the inlet openings 279 28 is then increased due to the continued braking application and att ins the prede~ermined spli~ point value 9 the valve pistons 63 move ;nward against the force of the split point springs 91 ~o posi~iDns where ~he valve heads 73 thereof contact the valve sea~s 88 of the valve members 7~ and thus close the fluid pathsO P2 hereinafter refers ~o the pressure at each o:E the ou~let openings 47. Pl hereinafter refers to ~he pressure at each of the inlet openings ~79 28 or the pressure ~ the master cylinder llo The pxedetermined level of split po~nt pressure is dependent upon the force o the spli~ point springs 91 c:ompared to the efective area o~ the valve pistons 63 acted llpon by fluid pre9sure in a directîon opposing the J:,0 force o ~che split po~n~ springs 91o This effective axea ~s equal ~o the cross-sectional area o the valve piston end portions 65 since the ends of those portions are ~ealed off from the ~nlet 1uid pressure (Pl) by the 0-ring seals 67 while f~uid pressure acts a~airlst all of the remaining portions o~ the valve pistons 63. During the lower xanges o maste~ cylinder pressure (Pl), the flllld pressu:re actlng on the effective area of each valve pis~on 63 produces a ~orce thereon which is insuf:Eicientbo over-c~me the force o~ the associated split point spring 91~, ~Assuming that Pl equals the fluid pressure at each o~ the ~nlet openings 27, 28, A equals the cross-sectional area of each ~Talve piston end portion 659 and S equals the force of each split point sprîng 91, then the valve pistons 63 will cl~;e the fLuîd paths ~that iS7 valve heads 73 will ~5 ~ve into engagement with v~lve element seats 88) when -Pl ~imes A is greater than 50 After the valv~ head~ 73 close against~e val~le element seats 88 and ~he 1uid pressure a~ the inle~ ope~
ings 27, 28 ~s further increased by thP master cylinder 11, the increased level of fluid pressur~ wilL act against .

11~097~

each valve pis~on 63 over an effec~ive circular area having a diametex equal to the main sealing dlameter of the valve head 73 thereof (hereinater referred to as B) less the axea A. ~h;s produces a force on each valve piston 63 assisting the associated spli~ point spring 91, thereby tending to xeopen the valve piston 63 to deliver at least a portion of this increased ~luid pressure to the associated outlet opening 470 However, any of this increased fluid pressure delivered to the outlet opening 47 creates an opposing force on the valve piston 63 a~ing over the area B~ This, of course, tends to reclose the valve pistons 63 against the valve ele~ents 780 These opposing foxces on the valve pistons 63 tend to keep the valve heads 73 closely adjacent to the valve seats 88 for the restricted ~low of fluid from the inle~
openings 27~ 28 to the outlet openin~s 47 ~o create a prsssure at the outlet openin~ 47 which incxeases at a lower rate than the pressure at the ~nlet openings 27, .
280 The ratlo of tke pressures ~Pl/P2~ is de~ermined by ~0 the relationship of the ~fective areas (A and B~ pre-~io~sly mentionedO After the control valve 18 irst closes (i~eO valve heads 73 initially engage valve ~e-ment seats ~8), the increase in pressure at each of the ~nlet openings 27, 28 (hereina~ter referred to as ~ Pl) 25 - will produce an increase in pressure at each of the outlet openings 47 (hereinafter reerred to as ~ P2) in accordance with the following formulaO ~ Pl B = f~ P2 Similarly, assum-lng P2 is ~he pressure at each of the outlet openings 47, ~hen P2~B~ = Pl(B~A) ~ S after the valve pistons 63 become operative (i.e. after the - 12 ~

9'7~; ( valve heads 73 engage valve seats 88)o Accordingly, the fluid pressure delivered to the ront wheel brakes 14, 15 will be greatex than the fluid p~essure delivered ~o ~he rear wheel brakes 16, 17 when the master cylinder pressure S Pl exceeds the split point pressureO There:Eore~ the brak-ing effort developed by the rear wheel brakes 16, 17 will be reduced,thereby prevent;ng premature rear wheel lock~
Dw:ing that portion o:E a brake application ill which the applied pedal ef~ort is reduced subsequent to a pedal effort of sufficient in~ensity to have moved the valve pistons 63 to their restricted flow positions, P~
acting on the area B-A o~E each valve piston 63 is xeduced.
Thus9 the ~orces tending to move ~he valve pistons 63 outwardly toward the outlet openings ~7 are reduced, and each valve pist~n 63 moves inwardly under the in1uence of the pres5ure at the assc~ciated outlet opening 47 (P2) act~ng on the area B thereofO As the valve pistons 63 -move inward, their valve heads 73 slide within the inner periphexal suraces 89 of the valve elements 78, thereby ~() increasillg th~ available volume for the fluid at the ~ear wheel brakes 16, 17 aIld thereby accomplishing a reduction in P2. The valve pistons 63 will cont;inue their inward movement in an effort to reduce P~ to satis:fy the previously mentioned formula: P2(B) ~ Pl(B-A) ~ SO
~5 However, the valYe pistons 63 may not completely achieve lthis result because of their limited possible inward travel. During the descent in brake pressure, the pressure at the outlet openings 47 can never be greater than the pressure at the inlet openings 27, 28. This ~s because the 1uid at the outlet op~nings 47 is able to o - ~3 - -3~ 6 ~low axound the valve elements 78 between the lips 79 and the walls o~ the cavities 30 if the flu;d pressure in the eavities 30 is at a lower levelO The lips 79 of the valve elements 78 accordingly function as relie valves ~o prevent rear brake pressure (P2 at outlet openings ~7) from ever being greater than front brake pressure (Pl at master cylinder 11 or inlet openings 27, 28)o When the pressure at th~ inlet openings 27, 28 is reduced beneath the level at which ~he con~rol valve 18 oxiginally closed the fluid paths to the outlet open-ings 47, the valve pistons 63 will be urged ou~wardly ~y the split point springs 91 to xeopen ~he fluld passages between the valve heads 73 and valve seats 88.
- The fo7 lowing description is concerned with the }S operatlon of the con~rol valve 18 when a failure occuxs in one of the b~anches of the brake system port:lon ll)o In the event o a ail~lre ~eOg. a pressure leakj ln the branch o:E the brake system portion 10 which in-cludes the conduits 19, 21, ~35, the front wheel brake 15 and the rear wheel brake 17, the pressure at the ~nlet open~ng 27 o~ the control valve 18 due ~o a braking application will be elimina$ed or signl~icantly reduced relative to the pressure at the inlet opening 28 therea~.
Then, the greater pressure at the ~nlet opening 28 acting on the swltch actuating piston 9S will cause righ~ward anovement thexeof in FIGo 1 ~cO a translated position where ~ts-cylindrical portion 102 engages the valve piSton end port;ons 65 thus maintaining the valve pistons 63 ~n the positions shown in ~IG. lo This provides open ~luid paths through the cantrol valve lB from the inlet openings 27 - 14 ~

( ~Z~g'76 (-28 to the outlet openings 470 Thus, the pressure subse-quently delivered to the other rear wheel brake 16 ~hrough the conduit 24 in the int:act bra:nch of t:he brake system portion 10 will be equal to the pressure in the master cylinder 11 for the ull range of master cy~inder pressuxe.
The rear wheel brak~ 1~ is th~efore ~apable o~ developing the maximum braking efort for vehicle emergency brakingO
T~e rightward movement of the switch actuating piston 95 moves the operating member 97 of the elec~rical swltch 93 rightward in FIG~ 2 to its circuit making positîon to complete the dri~er warning circuit and light a driver warning lamp ~not shown)O
Conversel~, in the event of a faiLure (eOg~ a pressure leak) in the branch of the brake system portion 10 which includes the conduits 20, 22, 24~ the fron~ wheeL
brake 14, and the rear wheel brake 16, ~he pressuxe at the inlet opening 28 of the control valve ~8 due to a - 1.
braking application will be eliminated o~ significantly .
reduced relative to the pressu~e at the inlet opening 27 thereof. Then, the greater pxessure at ~he ~nlet opening 27 acting on the switch actuating pisto~ 95 will cause letward mQvement thereof in FIG~ 1 to a translated posi-tion where its cylindrical portion 103 engages the val~e piston end por~i~ns 65 thus maintaining the valve pistons 25 ~ 63 in the positions shown in FIGo lo This provides open fluid paths through ~he control valve 18 from the inle~
upenings 27, 28 to the outlet openings 47. Thus~ the pressure subsequently delivered to the other rear wheel brake 17 through the conduit 23 in ~he intact branch of the brake system portion 10 will be e~qual to the pxessure O
- 15 - `

~76 in the master cyl~nder 11 for ~che full range of master cylinder pressure. The rear wheel brake :17 is thereoxe capable of developing the maxlmum braking e~ort for vehicle emergency brakingO The leftward movement of the S swi.tch actuating piston 9S also causes the driver waxning lamp ~not sh~n~ to light ~n the manner as previously describedO
ad~tantage of the present invention is that the . switch actuating p~ston 95 provides a means for precluding the pressure limiting operation of the control valve 18 in ~he event o partial brake sys~em failure without utilizing sealing members to open and close bypass passages betweea~ the inlet openings 27, 28 a:nd ~he ou~le~c openings 470 . 15 :It will be understood that the claims are interlded to cover all modifications and v~ria~ions of the pxe~erred embodiment o~ the invention, herein chosen for the purpose of illustration, without departing from the spi~it and s~ope of the irLvention~,

Claims (5)

I claim:

1. A control valve for a vehicle hydraulic dual brake system of the type including a tandem master cylinder having first and second separated portions for supplying fluid pressure to first and second separated wheel brakes, respectively, through first and second separated fluid branches, respectively, said control valve comprising:
a) first and second inlets for connection to said first and second tandem master cylinder separated por-tions, respectively;
b) first and second outlets for connections to said first and second separated wheel brakes, respectively;
c) first valve means disposed in said first fluid branch for transmitting fluid pressure an said first in-let to said first outlet and for limiting the fluid pres-sure transmitted to said first outlet relative to the fluid pressure at said first inlet when the fluid pressure at said first inlet is above a predetermined level;
d) second valve means disposed in said second fluid branch for transmitting fluid pressure at said second inlet to said second outlet and for limiting the fluid pressure transmitted to said second outlet relative to the fluid pressure at said second inlet when the fluid pressure at said second inlet is above said predetermined level; and e) inhibiting means for simultaneously precluding said first and second valve means from limiting the fluid pressure transmitted from said first and second inlets to said first and second outlets, respectively, upon a failure in one of said first and second fluid branches,

2. The control valve defined in claim 1, wherein:
a) said first valve means includes a first valve member movable between an open position and a closed position for limiting the pressure transmitted to said first outlet relative to the pressure at said first inlet when the pressure at said first m let is above said predetermined level;
b) said second valve means includes a second valve member movable between an open position and a closed position for limiting the pressure transmitted to said second outlet relative to the pressure at said second inlet when the pressure at said second inlet is above said predetermined level; and c) said inhibiting means is positioned for simul-taneously holding said first and second valve members in their open positions upon said failure.

3. The control valve defined in claim 2, wherein said inhibiting means is movable from a normally centered position into one of two opposed translated positions where it is positioned for simultaneously engaging and holding said first and second valve members in their open positions upon said failure.

4. The control valve defined in claim 3, wherein said inhibiting means comprises a piston having first and second ends acted upon by the fluid pressure in said first and second fluid branches, respectively, for effect-ing movement of said piston from said normally centered position into one of said two opposed translated posi-tions upon said failure.

5. A control valve for a vehicle hydraulic dual brake system of the type including a tandem master cylinder hav-ing first and second separated portions for supplying fluid pressure to first and second separated wheel brakes, res-pectively, through first and second separated fluid branches, respectively, said control valve comprising:
a) first and second inlets for connection to said first and second tandem master cylinder separated portions, respectively;
b) first and second outlets for connection to said first and second separated wheel brakes, respectively;
c) first valve means disposed in said first fluid branch for transmitting fluid pressure at said first inlet to said first outlet, said first valve means including a first valve member movable between an open position and a closed position for limiting the pressure transmitted to said first outlet relative to the pressure at said first inlet when the pressure at said first inlet is above a predetermined level;
d) second valve means disposed in said second fluid branch for transmitting fluid pressure at said second inlet to said second outlet, said second valve means including a second valve member movable between an open position and a closed position for limiting the pressure transmitted to said second outlet from said second inlet when the pressure at said second inlet is above said predetermined level; and e) a piston having first and second ends acted upon by the fluid pressure in said first and second fluid branches, respectively, for effecting movement of said piston from a normally centered position into one of two opposed translated positions where it is positioned for simultaneously engaging and holding said first and second valve members in their open positions upon a failure in one of said first and second fluid branches.