Note: Descriptions are shown in the official language in which they were submitted.
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
76
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~,
