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Патент USA US2407097

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Sept- 3, 1946-
tcai. E. PORT'ER
’
BRAKE MECHANISM
' 2,407,097
-
Fil'ed Feb. 10, 1943
26
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GILBERT E; PURTER
Patented Sept. 3, 1946
2,407,091
UNITED ‘STATES, PATENT‘ OFFICE
BRAKE MECHANISM
Gilbert E. Porter, Los Angeles, Calif., assignor to
Leonard J. Rosa, Detroit, Mich.
,
.
Application February 10, 1943, Serial No. 475,336
10 Claims.
(01. 188—152)
1
2
The present invention‘ relates to hydraulic
devices operated by the controlled'application' of
hydraulic ?uid and more particularly to hy
draulic brake systems.
One of the primary objects of hydraulic brake CR
design is to provide controls which'result in the
ing the same to control said ports to admit pres
sure fluid to a pressure chamber between. one end
of said tubular piston and one end of said inner
piston to actuate said inner piston to provide
braking action.
uniform application of the brakes and the avoid~
ing of such undesirable characteristics as grab»
These and other objects residing in the ar
rangement, combination and construction of the
parts will be apparent from the following spec
hing and slow release. One particular type of
brake system which might be highly satisfactory
except for the fact that the parts must ‘be closely
i?catio‘n“ ‘when taken with the accompanying
drawing, in which
?tted thereby being subject to sticky valve action
employs valves such as by-pass valves and 11m
brake system according to the present invention,
Fig. 1 is a diagrammatic representation of a
and
Fig. 2 is a vertical section of the master con
trol valve shown as a part of the structure of
loading valves to disperse the fluid pressure when
the brakes are not in use.
If the parts are not
closely ?tted there is a danger of leakage. Ac
cording to the present invention, the disadvan
1.
u
Referring particularly to the drawing, the
tages of the prior art are-eliminated by provid- ‘
reference character I indicates a master control
ing the system wherein there is no fluid pressure
valve having an inlet conduit connection 2 with
except at the time of brake operation. The pres 20 a pump cylinder 3 and a discharge conduit con
sure fluid is controlled by amaster valve, under
nection It with a‘reservoir 5 for the pump cylinder
the control of the foot pedal. The arrangement
3. The master control valve I is under the con
is such that the only metering is done by the
trol of a foot pedal or brake lever l5 pivoted at ‘I
master contro1 valve and this metering is of pres
and having an end thereof pivoted to an actu
sure fluid at its maximum pressure.‘ In other
ator 8.
'
words there is no metering of a vacuum.
‘
An object of the present inventionis ‘to pro-_
vide a hydraulic brake system of the character
_
Pressure for forcing hydraulic ?uid‘from the‘
cylinder 3 through the ‘conduit 2 ‘to the master
control valve I is generated by‘ a vacuum motor
9 in the form of a bellows pivoted by a connec
loading valves for dispersing ?uid pressure is 30 tion It] to a ?xed part I i. The end of the bellows
eliminated.
9 opposite the connection Ill is provided with an
Another object of the invention is to provide
actuating arm I2 which is pivoted to one end of
a brake system of the character described where
the lever IS. The other end of the lever I3 is
in vacuum is employed to develop ?uid pressure
pivoted to a ?xed point ill. Intermediate the
and the only metering for controlling the oper
ends of the lever I3, a piston rod I5 is connected.
ation of the brakes is of pressure fluid at- its
The piston rod at the opposite end thereof is ?xed
maximum pressure.
to a piston I6 within the pump cylinder 3.
Still another object of the invention is to pro
Vacuum for actuating the bellows 3 is con
vide in combination with a master control valve,
ducted through a conduit 29 from a suitable
mechanism for substantially instantaneously sup
source and is controlled by a vacuum valve il be
plying pressure fluid thereto at a predetermined
tween the bellows 3 and the conduit 28. The
maximum pressure.
I
'
vacuum valve H is electrically operated in some
A further object of the invention is to provide
suitable manner not disclosed. The circuit for
a master control valve having an outer tubular
operating the vacuum valve 2i comprises a con
piston, a second piston telescoped within’ said 45 ductor 22, a source of power such as a battery 23,
outer tubular piston,‘ and ports associated there
an ignition switch 23, a conductor 25, a brake
with for metering pressure fluid so as to cause
pedal switch
and a conductor 2i. The igni
said second piston to actuate a brake ?uid pump
tion switch 25 may be the conventional ignition
‘piston and said outer piston to ‘react against the
switch of the vehicle with which the brake system
foot of the operator.
,
50 is associated. The brake pedal switch 26 is pro~
A still further object of the invention is to pro
vided with a projecting arm 28 in the path of
vide a master control valve having an outer tu
movement of the portion 29 of the brake lever 6.
bular piston, a second piston telescoped within
Thus when the brake lever 6 is depressed, the
described wherein the use of by-pass and un
said tubular piston, ports in said piston, and an
actuator for said outer tubular piston for mov
switch 25 is closed to close the operating circuit
55 for the vacuum valve 2| to connect vacuum from
2,407,097
3
It
the conduit 29 to the bellows 9. This connection
results in the lever |3 moving in a counterclock
wise direction, as shown in Fig. l, to drive the
pump piston Hi to the right to force hydraulic
?uid in the cylinder 5 through the conduit 2 to
the master control valve I.
44. The port 60 has the portion thereof in the
surface of the piston 44 in the path of movement
draulic brakes or other mechanism to be actu~
ahead of the tubular piston 4| so as to cause the
ated by hydraulic ?uid under pressure.
Movement of the piston 4| to the left as viewed
in Fig. 2 is limited by stops 54 on the actuator
8 abutting against the left end of the cylinder 49.
Movement of the piston 44 to the left, as viewed
in Fig. 2, is restricted by stops 55 projecting
through openings 56 in the head 42 and abutting
against the inside of the left end of the cylin
der 4!]. The openings 56 further serve to pro
vide free passage of hydraulic ?uid to both sides
end of the port 60 in the surface of the piston
44 to move out of registry with the port 59 and
thus shut off the supply of hydraulic ?uid to the
pressure receiving chamber 46. The positioning
of the port 59 through the piston 4 i . The piston
44 is also provided with a port 6|, providing com
munication between the pressure receiving cham~
ber 46 and a discharge port 62 through the wall
of the cylinder 49, connected to the discharge
The pump cylinder 3 is provided with a usual
conduit 4. It will be observed that the right end
reservoir 35 on the top thereof and a port 36 is
of the tubular piston 4| is adjacent the end of
provided providing communication between the
reservoir 35 and the cylinder 3. The port 36 is 10 the port'?l communicating with the surface of
the piston 44.
so located as to be covered up by the piston I6
Each of the sliding surfaces between the ac
immediately after the piston l6 starts to move
tuator 8 and the sleeve 43, the cylinder
and
to the right. Discharged hydraulic ?uid from
and the piston 4|, and the piston 44 and the pis
the master control valve | passes through the
ton 4|, are in ?uid tight contact. These sur
conduit 4 to the reservoir 35. It will be clear that
faces are further provided with sealing rings 65
at the completion of an operating cycle of the
for insuring against leakage. A similar sealing
bellows 9 when the piston I6 is at the left of its
ring 65 is provided in the outer periphery of the
path of movement, hydraulic ?uid from the
pump piston 41. The pump piston 41 is arranged
reservoir 35 will flow by gravity through the port
adjacent the port 50 so as to close the port 59 upon
35 into the cylinder 3 to replenish the supply oi
the start of the travel of the pump piston 41.
hydraulic ?uid therein.
The operation of the entire system is as fol
The master control valve | is shown in detail
lows: When pressure is applied by the foot to
in Fig. 2. The valve I comprises an outer cyl
the brake lever 6, the switch 26 is closed to close
inder 49 having disposed therein an outer tubular
the vacuum valve 2| to cause the bellows 9 to
piston 4|. The piston 4| is closed at one end by
actuate the pump piston IE to force hydraulic
a head 42 and has projecting therefrom through
?uid under full pressure through the conduit 2
the sleeve 43 of the cylinder 49, the actuator 8
to the port 51. Continued downward movement
disclosed generally in Fig. 1.
of the lever 6 will cause the actuator 8 to move
There is provided telescopically disposed within
the tubular piston 4| a second piston 44. The in 30 the piston 4 |' to cause the port 59 to register with
the end of the port 60 at the surface of the pis
ner end 45 of the second piston 44 is spaced in
ton 44. This registry will conduct pressure ?uid
the relative position of the parts shown in Fig. 2
from the conduit 2 into the pressure receiving
from the inner end of the head 42 of the tubular
chamber 46. At the same time the piston'4l has
piston 4| to provide a pressure receiving chamber
closed the end of the discharge port 6| in the
46. The opposite end of the piston 44 is pro
surface of the piston 44 to prevent the escape of
vided with a pump piston 41. The pump piston
pressure ?uid from the pressure receiving cham
41 is slidably disposed in a pump cylinder 48, the
ber 46. The pressure ?uid in the pressure re
cylinder 48 being at the opposite end of the cyl~
ceiving chamber 46 causes the piston 44 to move
inder 46 from the sleeve 43 thereof. Associated
with the pump cylinder 48 is a reservoir 49 of a 40 to the right to move the pump piston 41 to the
right which in turn forces hydraulic ?uid from
conventional nature. Arranged in the wall of
the pump cylinder 48 into the hydraulic ?uid
the cylinder 48 adjacent the reservoir 49 is a port
conduit 5| to brake or other mechanism to be
50 for permitting the gravity ?ow of hydraulic
actuated by the controlled hydraulic ?uid.
fluid from the reservoir 49 into the pump cylin
With the operation as stated, should the brake
der 48. The pump cylinder 46 is also provided
pedal be held stationary after a predetermined
with an outlet 5| for conducting hydraulic ?uid
downward movement, the second piston 44 moves
under pressure developed by the piston 41 to hy
of the ports 59, 60 and 6|, together with the posi
tion of the outer end of the piston 4| with respect
to the position of the port 6| in the surface of
the piston 44, is such that the piston 44 does
not start to uncover the port 6| until after the
port 59 has moved substantially out of registry
with the port 60. In this manner the hydraulic
of the head 42 so as to permit the free move
ment of the tubular piston 4| under the action - 60 ?uid under pressure within the pressure receiv
of the actuator 8.
Hydraulic ?uid under pressure from the pump
3 is conducted to the control valve I through the
conduit 2 to a port 51 in the wall of the cylinder
40. Opposite the port 51 in the outer surface of
the tubular piston 4| there is provided a relieved
portion or shallow groove 58. The groove 58 is
ing chamber 46 is trapped within the pressure
reeciving chamber 46, thereby holding the pres
annular, extending completely around the piston
pressure ?uid from the pressure receiving cham
4| so as to balance pressure thereon. The groove
58 also provides communication between the port
51 and a port 59 extending from the groove 58
through one wall of the piston 4|.
Arranged in the piston 44 is a port 66 providing
communication between the pressure receiving
chamber 46 and the outer surface of the piston
sure generated in the pump cylinder 48 at its
maximum value until the brake lever 6 is eased
up to cause the actuator 8 to move to the left to
further move the tubular piston 4| to the left to
uncover the port 6| to permit the discharge of
ber 46 through the ports 6| and 62 to the dis
charge conduit 4.
In the operation of the brake system accord
ing to the present invention, should there be a
failure of pressure ?uid through the conduit 2,
movement of the actuator 8 to the right under
~ 75 the action of the brake lever 6 will cause the
2,407,091
5
head 42- of! the outer tubular piston. 41“ to. abut
against the end 45 of the second piston 44‘, and
bodily move the‘ secondE piston 4'4 to» the right,
as viewed in Fig. 2, to move the pump piston 47
in the pump cylinder 48* to force hydraulic ?uid
6
?uid ‘ from
said. ?uid. transmitting
chamber
through said outlet port, and means for controlled
delivery of ?uid under pressure into said ?uid
pressure receiving chamber, said‘ means having a
valve connecting a source of ?uid under pressure
to said ?uid pressure receiving chamber, said
through the conduit 5|. In such a case theop‘era
tion of the brake or other mechanism operated
valve comprising an outer piston having said ?rst
by the hydraulic ?uid passing through the con
named piston telescoped therein, said pistons
duit 5| would be manual without the bene?t of the
having coactin'g‘ ports arranged so that when in
power actuation. The pump“ cylinder d8 may 10 conducting. alignment ?uid flows into said pres
be of such a diameter‘ with respect to the diameter
sure receiving chamber and when not in conduct
of the piston 44 as to serve as‘ a debooster in a
ing‘ alignment ?uid cannot ?ow into said pressure
desired“ ratio. In this way the pressure of the
receiving chamber, said‘ outer piston. beinor con?
hydraulic ?uid“ in the conduit 5‘! may be provided
nected to said. actuating means for movement
at any degree independently‘of the pressure of the 15 thereby and. said first‘ named piston moving in
pressure ?uid passing through the conduit 2.
response to pressure in‘ said pressure receiving
chamber.
‘
A feature of the invention which is considered
to be of importance is'the fact that the pressure
2’. A device‘ of the character described compris
?uid in the pressure chamber 46' provides a net
ing‘ a cylinder‘, a tubular: piston disposed in said
cylinder, a second piston telescoped in said tubular
reaction on the actuator 8 in‘ a direction against
the operating movement of the brake‘ lever B,
piston, an: actuator connected to said tubular pis
ton and extending through. one end wall of said
or in other words towards the left, as viewed in
cylinder, a pump‘ cylinder at the other end of
Fig. 2. This reaction provides a “feel’fto- the
operator to indicate to him the extent of braking
said cylinder, a pump piston connected to one
pressure being applied. This “feel” will be in
direct proportion to the amount of‘pressure in
thecond'uit 5 I.
'
_
.
During certain phases of the operation‘ of the
master control valve I, an annular space ‘ill exists
between the‘ end of the tubular piston M and the
pump piston 41. At other phases of the opera"
end’ of said second piston adjacent said pump
cylinder and operative therein, a ?uid discharge
from said pump cylindena pressure ?uid receiving
chamber within said tubular piston and adjacent
the other end of said second piston. pressure ?uid
in said‘ pressure ?uid receiving chamber moving
said second piston to move said pump piston, a
source of pressure ?uid, and pressure ?uid inlet
and: discharge ports‘ under the control of said
tubular piston: for conducting pressure ?uid to
said pressure fluid chamber from said source and
from said fluid pressure chamber for actuating
said second. piston to move said pump piston.
3.) In a. fluid operated device of the character
described, for applying ?uid under pressure to an
tion, the space 70 is partly or substantially closed.
In order to permit the escape of discharge pres
sure ?uid from said space, the tubular‘ piston 4!
provided adjacent the port 62 with an undercut
ll extending from the outer end of the tubular
piston M inwardly a su?icient distance to pro".
vide discharge communication between the space
‘is and the port 62 communicating with the dis
charge conduit 4. Also the pump cylinder‘ 48, has Ill) expansible unit, and adapted to be controlled'by
provided therein a spring 13 maintained under
actuating means, the combination of a ?uid pres
sure receiving chamber‘ having a wall movable by
compression so as to urge the piston M continu
?uid pressure in said chamber‘, a ?uid pressure
ously to the left. The spring 73 serves to return
the pump piston 41 and the piston M to their
transmitting chamber having a movable wall and
- anv outlet port whereby movement of said wall
starting position when foot pressure on the brake
will discharge fluid from said ?uid transmitting
lever 6 is released. Suitable structure, not shown.
chamber, a ?oating piston connecting said walls
may be employed to maintain the cylinder M3;
whereby the: movement of said ?rst named wall
the piston 4|, and the piston M against relative
by‘ ?uid pressure in said ?uid pressure receiving
rotation so as to maintain the desired alignment
between the respective ports therein.
last named wall so as to
50 chamber will move
discharge ?uid from said ?uid transmitting cham
While it is desirable to operate
suction valve
ber through said outlet port, a source of vacuum,
2!, disclosed in Fig‘. l, by an‘ electrical actuator, it
is to be understood that this valve may be‘ actu»
ated by mechanical means ‘operated. by the brake
lever 53. Also, instead of employing the bellows
5! for developing pressure for the pressure ?uid,
a suitable rotary pump or other device of conven
tional' nature might be employed to develop the
necessary pressure. Accordingly, I do not wish i;
be limited,’ except by the scope of the following
claims.
I claim:
1. In a ?uid operated device of the character
described, for applying ?uid under pressure to an
a vacuum motor, a pump, adapted to be actuated
‘ by said motor, constituting a source of ?uid under
pressure when actuated by said motor, an elec~
trically" controlled valve to control the connection
of said source of vacuum to said motor, an elec
tric circuit to control said valve, means for con
trolling said circuit by said actuating means, and
means for controlled delivery of ?uid under pres—
sure‘ into said ?uid pressure receiving'chamher,
said last named means having a valve connecting
said source of ?uid under‘ pressure to said ?uid
pressure receiving chamber, said valve compris
expansible unit, and adapted to be controlled by 65 ing an outer piston having said ?rst named piston
actuating means, the combination of a ?uid pres
telescoped therein, said pistons having coacting
sure receiving chamber having a wall movable by
ports arranged so that when in conducting align
ment ?uid flows into said pressure receiving
chamber and when not in connecting alignment
?uid cannot ?ow into said pressure receiving
chamber, said outer piston being connected to
said actuating means for movement thereby and
said ?rst named piston moving in response to pres
sure in said pressure receiving chamber, whereby
will move said last named wall so as to discharge 75 operative movement of said actuating means pro
?uid pressure in said chamber, a ?uid pressure
transmitting chamber having a movable wall and
an outlet port whereby movement of said wall will
d'mcharge ?uid from said ?uid transmitting cham
ber, a ?oating piston connecting said walls where.
by the movement of said ?rst named wall by ?uid
pressure in said ?uid pressure receiving chamber
2,407,097
7
transmitting chamber, a ?oating piston connect
ing said walls whereby the movement of said
?rst named wall by ?uid pressure in said ?uid
vides a source of ?uid under pressure and con
trols the application of said last named ?uid under
pressure to said expansible unit.
pressure receiving chamber will move said last
named wall so as to discharge ?uid from said
4. A device of the character described com
prising a cylinder, a tubular piston disposed in
said cylinder, a second piston telescoped in said
tubular piston, an actuator connected to said
?uid transmitting chamber through said outlet
tubular piston and extending through one end
wall of said cylinder, a pump cylinder, a pump
motor for actuating said pump, means responsive
port, a source of vacuum, a pump constituting a
source of pressure ?uid when actuated, a vacuum
piston connected to the end of said second pis 10 to said actuating means for connecting said
source of vacuum to said motor to atcuate said
ton away from said actuator and operative in
pump, and means for controlled delivery of ?uid
said pump cylinder, a ?uid discharge from said
under pressure into said ?uid pressure receiving
pump cylinder for conducting controlled pres
chamber, said last means having a valve con
necting a source of ?uid under pressure to said
sure ?uid, a pressure ?uid receiving chamber
within said tubular piston and adjacent the
other end of said second piston, pressure ?uid in
said pressure ?uid receiving chamber moving
?uid pressure receiving chamber for actuating
said ?rst named pump, said valve comprising
an outer piston having said ?rst named piston
said second piston to move said pump piston, a
telescoped therein, said pistons having coacting
vacuum motor, a source of vacuum adapted to
ports arranged so that when in conducting align
ment ?uid flows into said pressure receiving
chamber and when not in conducting alignment
of actuating pressure ?uid when actuated by
?uid cannot ?ow into said pressure receiving
said motor, an actuating pressure ?uid control
chamber, said outer piston being connected to
ling valve controlled by said tubular piston for
controlling the admission of pressure ?uid to 25 said actuating means for movement thereby and
said ?rst named piston moving in response to
said pressure ?uid chamber, a valve controlled
pressure in said pressure receiving chamber.
by said tubular piston for discharging pressure
7. A device of the character described compris
?uid from said pressure ?uid receiving chamber,
ing a cylinder, a tubular piston disposed in said
a valve to control the connection of said source
vacuum to said motor, and means for controlling 30 cylinder, a second piston telescoped in said tubu
lar piston, an actuator connected to said tubu
said valve by said actuator.
lar piston and extending through one end wall of
5. A device of the character described com
said cylinder, a pump cylinder at the other end
prising a cylinder, a tubular piston disposed in
of said cylinder, a pump piston connected to
said cylinder, a second piston telescoped in said
tubular piston, an actuator connected to said 35 one end of said second piston adjacent said pump
cylinder and operative therein, a ?uid discharge
tubular piston and extending through one end
from said pump cylinder for conducting con
wall of said cylinder, a pump cylinder at the
trolled pressure ?uid, a pressure ?uid receiving
other end of said cylinder, a pump piston con
chamber within said tubular piston and adjacent
nected to one end of said said second piston
the other end of said second piston, pressure
adjacent said pump cylinder and operative
?uid in said pressure ?uid receiving chamber
therein, a ?uid discharge from said pump cylin
moving said second piston to move said pump
der for conducting controlled pressure ?uid, a
piston, a source of pressure ?uid, and pressure
pressure ?uid receiving chamber within said
?uid inlet and discharge ports under the con
tubular piston and adiacent the other end of
trol of said tubular piston for conducting pres
said second piston, pressure ?uid in said pres
sure ?uid to said pressure ?uid chamber from
sure ?uid receiving chamber moving said second
said source, and from said ?uid pressure cham
piston to move said pump piston, a port in said
ber for actuating said second piston to move
second piston providing communication between
said pump piston, a source of vacuum, a pump
said pressure ?uid receiving chamber and a side
be connected to said motor, a pump adapted to
be actuated by said motor constituting a source
surface of said second piston, a port through a. 5 O constituting said source of pressure ?uid when
actuated, a vacuum motor for actuating said
side wall of said tubular piston, a port through
pump, and means responsive to said actuator
a side wall of said cylinder, a source of pressure
for connecting said source of vacuum to said
?uid, a connection between said last named port
motor to actuate said pump.
and said source, said ports being in the same
8. In a ?uid operated device of the character
longitudinal path whereby a predetermined rela
described, for applying ?uid under pressure to
tive movement between said ports brings them
an expansible unit, and adapted to be controlled
into and out of register to connect said source
by actuating means, the combination of a ?uid
to and to disconnect it from said pressure ?uid
pressure receiving chamber having a wall mov
receiving chamber, and other ports in said sec
able by ?uid pressure in said chamber, a ?uid
ond piston and cylinder controlled by said
tubular piston for discharging pressure ?uid from 60 pressure transmitting chamber having a mov
able Wall and an outlet port whereby movement
said pressure ?uid receiving chamber at prede
of said wall will discharge ?uid from said ?uid
termined relative positions of said pistons and
cylinder whereby movement of said pump piston
is controlled by actuation of said tubular piston
by said actuator.
6. In a ?uid operated device of the character
described, for applying ?uid under pressure to
an expansible unit, and adapted to be controlled
by actuating means, the combination of a ?uid ’
pressure receiving chamber having a wall mov
able by ?uid pressure in said chamber, a ?uid
pressure transmitting chamber having a mov
able wall and an outlet port whereby movement
of said wall will discharge ?uid'from said ?uid
transmitting chamber, a ?oating piston connect
ing said walls whereby the movement of said ?rst
named wall by ?uid pressure in said ?uid pressure
receiving chamber will move said last named wall
so as to discharge ?uid from said ?uid transmit
ting chamber through said outlet port, and means
for controlled delivery of ?uid under pressure
O into said ?uid pressure receiving chamber, said
means having a valve connecting a source of ?uid
under pressure to said ?uid pressure receiv
ing chamber, a source of ?uid pressure connected
to said valve means, means responsive to initial
75 movement of said actuator to supply substantially
I
2,407,097
9
instantaneously pressure ?uid from said source
to said last named means at maximum pressure,
said valve comprising an outer piston having said
?rst named piston telescoped therein, said pis
tons having coacting ports arranged so that when
in conducting alignment ?uid ?ows into said
pressure receiving chamber and when not in con
ducting alignment ?uid cannot ?ow into said
pressure receiving chamber, said outer piston
eluding alignable outlet ports in said valve and
associated structure, said inlet and outlet ports
being axially spaced to trap ?uid under maxi
mum pressure in said last chamber following
movement of said valve by said actuator, where
by movement of said piston is arrested without
the metering or by-passing of ?uid.
10. In a hydraulic brake system, a manual
actuator, a control valve, operatively connected
being connected to said actuating means for 10 to said actuator for axial movement, a piston for
movement thereby and said ?rst named piston
delivering and directing hydraulic pressure to the
moving in response to pressure in said pressure
brakes, a housing in which said piston operates,
receiving chamber.
chambers on opposite sides of said piston, a
source of ?uid pressure, inlet ports in said valve
and piston to connect one of said chambers with
said source on axial relative movement between
said valve and piston to align said inlet ports,
a ?uid return, outlet ports in said piston and
operating connection between said valve and said
valve to connect said last chamber with said re
manual actuator, a piston for developing and di 20 turn in one relative position of said valve and
recting hydraulic pressure to the brakes, cham
piston, said inlet and outlet ports being so lo
bers. on opposite sides of said piston, inlet ports
cated as to seal said last chamber from said
in said valve and associated structure adapted
source and return to arrest movement of said pis
to be brought into alignment to connect said
ton under full operating ?uid pressure without
source in one of said chambers with the maxi 25 the metering or by-passing of the ?uid.
mum pressure of said source, a ?uid return in
‘
GILBERT E. PORTER.
9. In a hydraulic brake system, a manual actu
ator, a control valve, a source of hydraulic pres
sure, means to deliver the maximum pressure of
said source to said control valve during the pe
riod of operation of said manual actuator, an
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