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Патент USA US2109168

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Feb. 22, 1938.
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'
R. E. MILLER
2,109,168
BRAKE CONTROL MEANS
Filed April 6, 1956
mW E N T O R
RAYMEIND E.MILLER
~
BY
2%“. %
ATTORNEY f’
2,109,163“
Patented Feb. 22, 1938
UNITED STATES PATE NT" orriice
2,109,168
BRAKE CONTROL MEANS
Raymond E. Miller, Wilkinsburg, Pa., assignor to
The Westinghouse Air Brake Company, Wil
merding, Pa., a corporation of Pennsylvania
Application April 6, 1936, Serial No. 72,889
17 Claims.
My invention relates to brake systems for ve
hicles and more particularly to means for re
ducing the degree of application of the brakes
upon the sliding of the wheels on the rails.
It is well known that for a given braking pres
sure friction type brakes are less effective in re
tarding the motion of a vehicle at high speed
than at low speed because the coe?icient of fric
tion between the rubbing parts is lower at high
10 speed than at low speed, In order to bring the
vehicle to a stop quickly it has been the usual
practice for an operator to apply the brakes with
a high degree of braking pressure at the high
speed and as the speed of the vehicle decreases
to so operate the brakes as to cause the braking
pressure to decrease in such manner, that the
vehicle is brought to a stop quickly and smooth
ly without sliding of the wheels.
When railway trains and traction vehicles are
20 operated at very high speeds a correspondingly
which is connected to the lowerendof the hanger
bar 4 by a brake rod l3.‘v Abackicylinder lever
I9 is provided,..the upper end of which is pivoted
to the pressure end of the brake cylinder 1 and
the lower endrof whichis connected by a brake‘
rod IE’ to the lower. end of the hanger bar 3.;
The two cylinder levers l4 and I2 are connected
together. at points intermediate their ends. by
the cylinder lever rod ll.
_
To apply the. brakes fluid under pressure is 10
supplied to thebrake cylinderv 7‘ through a con
trol‘ pipe [6, a brake control valve device I‘! and
brake cylinder pipe l8 as supplied, for example,
by a relay valve device, not shown, in a known
manner. A magnet valve device is provided inv
the upper portion of the brake control valve-de
vice l1 and is controlled by a tuned relay IBIand
a pressure responsive switch 22 in a manner to be
later described.
The brake control valve I‘! comprisesa casing;
high braking force must be employed to bring
providing a piston chamber 23 containing a piston '
the train or vehicle to a stop in a reasonable
24i'having .a piston stem 25; for engaging a slide
valve 26‘contained within a slide valve chamber.
2‘! also‘ provided within a bushing ,28 and which
extends upwardly from a shoulder 29 against
which the piston 24 is adapted toiengage. A screw
plug 31 is provided in the upper end‘ of the bush
length of time.
When a braking force is applied corresponding
25 to a full service or emergency application of the
brakes at high vehicle speeds the braking pres
sure may exceed the pressure required to slidn
the wheels as the car speed reduces. The prob
’lem of properly reducing the braking force by
manual operation as the vehicle slows down be
comes a di?icult one and there is considerable
danger of wheels sliding on the rails. It is, there
fore, desirable to provide, as a part of the brak
ing equipment on high speed trains and vehicles,
ing 28 to form » a partition betweenv the valve
chamber 27 andva chamber 33'connected'by a
port 32 through the plug 31. A spring 34 is pro 3.0
vided within the piston chamber 23 for normally
urging the piston. 24 against the shoulder 29.
An exhaust chamber 3?lis also provided within
the casing of the brake control valve device l'l
' some means for automatically relieving wheel
that is in constant open communication with the
sliding when it occurs.
It is an object of this invention to provide
means responsive to the sliding of the wheels on
atmosphere through an exhaustport 35 and which
the rails for reducing brake cylinder pressure to
a predetermined low value, and thus prevent the
continuance of the sliding of the wheels.
Other advantages and objects will appear from
the following description of my invention taken
in connection with the accompanying drawing in
45 which the single ?gure is a diagrammatic View
of one preferred embodiment of the invention.
Referring to the drawing a car wheel I is illusv~
trated that is mounted to be carried by the usual
truck frame 2 from which are supported hanger
bars 3 and 4 for supporting brake shoes 5 and 6
on opposite sides of the car wheel. A brake cyl
inder ‘l is provided, supported on the car frame
8, and from which a piston stem 9 extends through
the low pressure end and is pivotally connected
to a front cylinder lever l2, the lower end oi‘
contains a valve 36 having a stem extending
through a bore in a partition between the cham
ber 34 ‘and the chamber. 33. and adapted to en
gage the stem 38 ‘ofra valve 31 contained within
the chamber 33. . The lower end .of the stem138
extends into a bore in ‘the plug 3|. A spring 39 is
provided within'the- chamber. 33, the lower end
of which engages theplug 3i and the upper end
of which engages a collar 4| carried by the stem
38' for urging. the valve- 31 upwardly to its seat
and the valve 36 upwardly from its seat. A mag
net 42 is provided in the upper end. of the eas
ing which, when. energized, forces the valve 36
downwardly to its seat and the valve 31 down
wardly from its seat.
The pressure operated-switch device 22 com-'
prises a casing providing a‘, piston.’ chamber 44
that is in constant open communication with the
control‘ pipe is and. which contains a piston 45
2
2,109,168
that is connected by a stem to a movable switch
contact member 46 that is adapted to engage ?xed
switch contact members 41 and 48 to connect one
terminal of a battery 49 to a conductor 52. A
spring 5| within the casing of the switch device
22 biases the piston 45 and the contact member
46 to their lower or illustrated position. A circuit
is completed from the conductor 52 through the
primary winding 54 of a transformer 53, con
10 ductor 55 and brush 56 of a circuit interrupting
device having conducting segments 51 and 58 sep
arated by insulating segments 59 and 62 that are
adapted to engage the brush 56 to intermittently
interrupt the circuit through the transformer
15 primary winding at a rate depending upon the
vehicle speed.
The tuned relay l9 comprises a winding 63 and
‘20
an armature 64 that is normally held in its up
per or illustrated position by a spring 65 and is
adapted when the winding 63 is energized to com
plete a circuit from the conductor 52 through
a conductor 66, the winding of the magnet 42
to ground at 61 and to the grounded terminal
68 of the battery 49; The winding 63 of the
tuned relay I9 is energized from the secondary
winding 12 of the transformer 53. The induc
tance of the winding '12, the resistance‘ .of the
winding 63, and the capacitance of the condenser
13 are so adjusted as to provide a tuned circuit
30 such that the relay l9 will remain energized
so long as the frequency in the secondary wind
ing of the transformer 53 is above a predeter
mined value, and will become deenergized when
45
55
'05
70
75
If the degree of application. of the brakes be
comes su?icient to cause the wheel I to slow U!
down below a speed such’ that the frequency of
interruptions in the circuit of the primary wind
ing 54 results in a frequency of alternating cur
rent in the secondary winding 12 of the trans
former below the value necessary to maintain the
relay I S energized, the relay armature 64 will
be urged upwardly by the spring 65, thus inter
rupting the above traced circuit through the
windings of the magnet 42,
Upon interruption’ cf‘ this circuit the spring
39 forces the valve 31 upwardly to its seat, clos
ing communication between the chamber 33 and
the piston chamber 23, and forcing the valve 36
upwardly from its seat to effect communication
from the piston chamber 23 to the atmosphere 20
through the exhaust port 35. Upon the venting
of fluid under pressure from the piston chamber
23 the force of the spring 34 is insufficient to
overcome the pressure in the slide valve cham
ber 21 on the upper side of the piston 24 and the 25
piston is forced downwardly thus moving the
‘slide valve 26 to a position such that a cavity
13 therein effects‘ communication between the
brake cylinder passage I8 and a passage 14 lead
ing to the atmosphere-through a safety valve
75 that is adjusted to permit the release of fluid
under pressure when above some predetermined
pressure. rl‘he pressure in the brake cylinder 1
is thus automatically reduced to the value de
termined by the setting of the safety valve de 35
The operation of the equipment described is vice l5.
If,‘upon the reduction in brake cylinder pres
as follows.
Upon the supply of ?uid under pressure to the . sure thus effected, the speed of the vehicle is such
control pipe Hi to effect an application of the that the wheel I will again rotate above the pre
brakes the piston 45 in the pressure operated determined speed necessary to energize the tuned 40
switch device 22 moves upwardly against the bias relay is, this relay will again operate to com-'
of the spring 5| to close the circuit through the plete the circuit through the winding of the mag~
primary winding 54 of the transformer 53, which net 42 and force the valves 35 and 3‘! down
circuit is intermittently interrupted at the brush wardly to cause the pressure in the piston cham
56 by the insulating’portions 59 and 62, on the ber 23 to equalize with the pressure in the slide 45
collector ring, thus developing a frequency in valve chamber 2“! at a value corresponding to
the secondary winding ‘I2 of the transformer 53 the pressure in the control pipe l6. Upon the
corresponding to the speed of the wheel I. If, equalization of these pressures the spring 34,v
upon the application of the brakes, the vehicle is forces the piston‘ 24 together with its stem 25
traveling at a sufliciently high speed to cause and slide valve 25 upwardly to their illustrated‘
positions, and again permit the flow of fluid un
the tuned circuit including the secondary trans
former .winding 12 to energize the winding 83 der pressure from the pipe “5 to- the brake cylin
der 7 to increase the braking force.
of the tuned relay IS, the armature 64 will be at
it will be noted that, upon the slowing down
tracted into circuit-closing position to complete
a circuit through the winding of the magnet 42 of the wheel‘! resulting from the decrease in 55
speed of the vehicle the brake cylinder pressure
of the brake control valve device I‘L'thus forc
ing the valve 36 downwardly to- its seat to close is automatically decreased through the safety
communication from the piston chamber 23 to valve ‘l5 in the same manner as when the wheel.
the atmosphere through the exhaust port 35 and slips on the rails at a high vehicle speed. In
effecting communication from the chamber 33 to this case, however, the magnet 42 will not be re 60
energized upon the decrease in brake cylinder
the piston chamber 23.
'
As the pressure in the control pipe l6 builds pressure so that the brake cylinder pressure is
up, ?uid under pressure will ?ow through the not again built up but remains at its low value,
passage l?'inthe brake control valve device I‘! which is desirable when the vehicle speed be
comes reduced to a low value.
'
to the slide valve chamber 21 and through pas
It will be apparent to those skilled in the art
sage and pipe l8 to the brake cylinder 1 to force
that many modi?cations in the apparatus and
the upper ends of the cylinder levers l4 and I2
apart and force the brake shoes 5 and 6 against circuits illustrated and described may be made
the wheel I. Fluid under pressure will also flow Without departing from the spirit of my inven
from the slide valve chamber 27 through port tion and I do not wish to be limited otherwise
32 in the plug 3| to the chamber 33, past the than by the scope of the appended claims.
valve 31 that is unseated upon, the energization
Having now described my invention, what I
of the winding of the magnet 42 in a manner to
claim as new and desire to secure by Letters
be presently described, through a passage 10 to Patent, is:
the piston chamber 23 so that the pressure with—
1. ,In a brake equipment for vehicles, in com
the frequency in the transformer secondary
35 winding falls below that predetermined value.
40
in the piston chamber 23 is maintained at a value
sufficient to hold the piston 24 against the shoul
der 29 so long as the magnet 42 is energized.
2,109,168‘
bination, a brake cylinder, a control pipe, means
for supplying ?uid under pressure to said brake
cylinder at control pipe pressure, a valve device
for interrupting communication between said
v, control pipe and said brake cylinder and for
venting ?uid under pressure from said brake cyl
inder to a predetermined‘ low value, said valve
device comprising a valve and a~pistonrfor mov
ing the valve, said piston being constantly sub
ject on one side to the pressure in the control
pipe and normally subject on the other side to
the pressure in the control pipe and also to an
additional biasing force, electrical means respon
sive to the speed of rotation of a vehicle wheel
15 for releasing ?uid under pressure from the sec
bination, a- brake cylinder, a control pipe, means‘
for supplying ?uid under pressure to said brake
cylinder at control pipe pressure, a valve device‘
for interrupting communication between said con
trol pipe and said brake cylinder and for vent
ing ?uid under pressure from said brake cylin
der to a predetermined low value, said valve de
vice comprising a valve and a piston for moving
the valve, said piston being constantly subject on
one side to the pressure in the control pipe and 10
normally subject on the other side to the pressure
in the control pipe and also to an additional
biasing force, electrical means responsive to the
speed of rotation of a car wheel for releasing
?uid under pressure from the second named side
of said, piston for effecting movement of said
ond named side of said piston for e?ecting move—
ment of said valve to eiiect a reduction in brake
valve to a brake releasing position, means for
cylinder pressure.
2. In a brake equipment for vehicles, in combi
means comprising a relay, a transformer for en
20' nation, a brake cylinder, means including a con
trol pipe for supplying ?uid under’ pressure to
said brake cylinder at control pipe pressure, valve
means between said control pipe and said brake
cylinder for‘ e?ecting a reduction in brake cylin
der pressure to a predetermined value, electrical
means for controlling said valve means to reduce
the brake cylinder pressure, means for control
ling the energization of said electrical means
comprising a relay, a transformer for energizing
30 said relay and comprising a secondary winding
connected thereto and a primary winding, a
source of direct current electrical energy for the
primary winding of said transformer and means
responsive to the speed of revolutionoi a vehicle
controlling the energization of said electrical
ergizing said relay and comprising a secondary 207
winding connected thereto and a primary wind
ing, a source of direct current electrical energy
for the primary winding of said transformer and
means responsive to the speed of revolution of a
vehicle wheel for intermittently interrupting said 251
primary winding circuit, said relay circuit be
ing tuned to eifect a substantial energization of
the relay when the energizing circuit is above a
predetermined frequency and to effect the de
energization of said relay when the frequency of 301
said circuit is below said predetermined frequency.
6. In a brake equipment for vehicles, in com
bination, a brake cylinder, a control pipe, means
for supplying fluid underlpressure to said brake
cylinder at control pressure, a valve device for
CG. UK wheel for intermittently interrupting said pri
mary winding circuit, said relay circuit being ‘interrupting communication between said‘ con
tuned to effect a substantial energization of the trol pipe and said brake cylinder and for vent
relay when the frequency of interruptions are
above a predetermined value and to remain de
40 energized when the frequency of interruption of
said circuit is below said predetermined value.
3. In a brake equipment for vehicles, in com
bination, a brake cylinder, a control pipe, means
for supplying fluid under pressure to said brake
cylinder at control pipe pressure, valve means
between said control pipe and said brake cylin
der, electrical means for controlling said valve
means to reduce the brake cylinder pressure to
a predetermined value and including an elec
trical relay, means for supplying alternating cur
rent to said relay at a frequency corresponding
to the speed of the car wheel, said relay being
so tuned as to become energized when supplied
with alternating current above a predetermined
frequency and unenergized when supplied with
alternating current below said predetermined fre
quency.
4i. In a brake equipment for vehicles, in com
bination, a cylinder, a control pipe, means for
(50 supplying ?uid under pressure to said brake cylin
der at control pipe pressure, valve means be
tween said control pipe and said brake cylin
der, electrical means for controlling said valve
means to reduce brake cylinder pressure to a
predetermined value and including an alternat~
ing current relay responsive to alternating cur
rent above a predetermined frequency, means for
controlling the energization of said relay includ
ing a transformer the secondary winding of which
TO is connected to said relay, and the primary wind
ing of which is supplied with direct current, and
means for interrupting the primary winding cir
cuit intermittently at a rate corresponding to
the speed of the car wheel.
5. In a brake equipment for vehicles, in com~
ing ?uid under pressure from said brake cylin
der to a predetermined low value, said valve de
vice comprising a valve and a piston for moving
the valve, said piston being constantly subject
on one side to the pressure in the control pipe
and normally subject on the other side to the
pressure in the control pipe and also to an addi
tional biasing force, electrical means for releas
ing fluid under pressure from the second named
side of said piston for causing movement of
said valve to effect a reduction in brake cylinder
pressure and including an electrical relay, means
is
for supplying alternating current to said relay
at a frequency corresponding to the speed of a
car wheel, said relay being so tuned as to be
come energized when supplied with alternating
current above a predetermined frequency and un
energized when supplied with alternating cur
rent below said predetermined frequency.
55
7. In a brake equipment for vehicles, in com
bination, a brake cylinder, a control pipe, means
for supplying ?uid under pressure to said brake
eviinder at control pipe pressure, a valve device
for interrupting communication between said
control pipe and said brake cylinder and for
venting ?uid under pressure from said brake cyl
inder to a predetermined low value, said valve
device comprising a valve and a piston for mov
65
ing the valve, said piston being constantly subject
on one side to the pressure in the control pipe and
normally subject on the other side to the pres
sure in the control pipe and also to an additional
biasing force, electroresponsive means for releas
ing ?uid under pressure from the second named
sir'e of said piston for causing movement of said
valve to effect a reduction in brake cylinder‘pres
sure, an alternating current tuned relay respon
sive to alternating current above a-predetermined
70
4
2,109,168
. frequency for effecting the energization of said
munication through said pipe to permit the flow
said relay including a transformer a secondary
winding of which is connected to said relay and
a primary winding of which is supplied with di
operative to a second position to cut off commu
rect current, and means for interrupting the pri
mary winding circuit intermittently at a rate cor
responding to the speed of a vehicle wheel.
8. In a brake equipment for vehicles, in com
10 bination, a brake cylinder, means for supplying
?uid under pressure to said brake cylinder, valve
means for effecting a reduction in brake cylinder
pressure to a predetermined value, electrical
means for controlling said valve means, an alter
nating current tuned relay operatively responsive
only to alternating current above a predetermined
frequency for effecting energization of said elec
trical means, means for controlling said relay
including a transformer a secondary winding of
20 which is connected to said relay and a primary
winding of which is supplied with direct current,
and means for intermittently interrupting the
primary winding circuit at a rate corresponding
to the speed of the vehicle.
25
9. In a brake equipment for vehicles, in combi
nation, a brake cylinder, means for supplying ?uid
under pressure to said brake cylinder, valve means
for effecting a reduction in brake cylinder pres
sure to a predetermined value, electrical means
30 for controlling said valve means and including an
electrical relay, means for supplying alternating
current to said relay having a frequency corre
sponding to the speed of a car wheel, said relay
being so tuned as to become energized when sup
35 plied with alternating current above a predeter
mined frequency and unenergized when supplied
with , alternating current below said predeter
mined frequency.
.
10. In a vehicle brake equipment, in combina
40 tion, a brake cylinder, a pipe through which ?uid
under pressure may be supplied to effect an ap
plication of the brakes, electroresponsive means
effective when energized to cause communication
to be opened through the said pipe to the brake
cylinder and when deenergized to cause commu
$1.5 nication
through the pipe to the brake cylinder
to be closed and a communication from the brake
cylinder to atmosphere to beopened, and elec
trical means operative to complete the circuit of
5.0 the electroresponsive means and cause energiza
' tion thereof only so long as the frequency of
nication through said pipe to the brake cylinder
and to establish a communication through which
?uid under pressure is released from the brake
cylinder, electrical means effective as long as al
ternating current of a frequency above a certain
uniform frequency is supplied thereto for causing 10
the valve means to be maintained in the said
one position thereof, and means subject to the ‘
pressure in said pipe for shifting the valve means
to the said second position thereof when the fre
quency of the alternating current supplied to the 15
said electrical means is less than said certain fre
quency.
’
13. In a vehicle brake equipment, in combina
tion, a brake cylinder, a pipe through which ?uid
under pressure may be supplied to the brake cyl 20
inder to effect an application of the brakes, valve
means effective in one position to open communi
cation through said pipe to permit the ?ow of
?uid under pressure to the brake cylinder and op—
erative to a second position to cutoff communica 25
tion through said pipe to the brake cylinder and
to establish a communication through which ?uid
under pressure is released from the brake cylin
der, and electrical means effective as long as
alternating current of a frequency above a certain 30.
uniform frequency is supplied thereto for causing
the valve means to be maintained in the said one
position thereof, means subject to the pressure in
said pipe for shifting the valve means to the said
second position ‘thereof when the frequency of the 35
alternating current supplied to the said electrical
means is less than said certain frequency, and
means for supplying alternating current to said
electrical means at a' frequency corresponding to
the rotative speed of a vehicle wheel.
40
14. In a vehicle brake equipment, in combina
tion, a brake cylinder, a pipe through which ?uid
under pressure may be supplied to the brake cyl
inder to effect an application of the brakes, a
valve having one position for opening communi 45
cation through the pipe to the brake cylinder and
a second position in which the communication
through the said pipe is closed and a communi
cation ‘established through which ?uid under
pressure is released from the brake cylinder, ?uid 50
pressure responsive ' means for operating said
valve and subject in opposing relation to the
means exceeds a certain uniform frequency.
pressure in the said pipe and the pressure in a
11. In a vehicle brake equipment, in combina
plication of the brakes, electroresponsive means
effective when energized to cause communication
to be opened through the said pipe to the brake
cylinder and when deenergized to cause commu
nication through the pipe to the brake cylinder
to be closed and a communication from the brake
cylinder to atmosphere to be opened, electrical
means operative to complete the circuit of the
65 electroresponsive means and cause energization
thereof only so long as the alternating current
supplied to the electrical means exceeds a certain
uniform frequency, and means for supplying al
ternating current to said electrical means at a fre
15
of ?uid under pressure to the brake cylinder and
the alternating current supplied to the electrical
tion, a brake cylinder, a pipe through which ?uid
.55, under
pressure may be supplied to effect an ap
w
valve means effective in one position to open com
electroresponsive means, means for, controlling
quency corresponding to the speed of rotation of
a vehicle wheel.
12. In a vehicle brake equipment in combina
tion, a brake cylinder, a pipe through which ?uid
under pressure may be supplied to the brake
cylinder to effect an application of the brakes,
chamber, means for biasing the valve to the said
one position thereof when the pressure in the 55
pipe and the pressure in the chamber are sub
stantially equalized, electroresponsive means ef
fective when energized to cause the pressure in
the said pipe and in said chamber to be substan
tially equalized and effective when deenergized
to reduce the pressure in the said chamber and
cause the higher pressure in said pipe acting on
the ?uid pressure responsive means to shift the
said valve from the said one to the said’ second
position thereof, and electrical means controlling
the circuit of the electroresponsive means and
effective to cause energization of the electrore
sponsive means only so long as the frequency of
the alternating. current supplied thereto exceeds
a certain uniform frequency.
15. In a vehicle brake equipment, in combina
tion, a brake cylinder, a pipe through which?uid
under pressure may be supplied to the brake cyl
inder to effect an application of the brakes, a
valve having one position for opening'communi
75
5
2,109,168
cation through the pipe to the brake cylinder and
uniform frequency is supplied thereto for causing
a second position in which the communication
through the said pipe is closed and a communi
the valve means to be maintained in the said one
cation established through which ?uid under
pressure is released from the brake cylinder, ?uid
pressure responsive means for operating said
valve and subject in opposing relation to the pres
sure in the pipe and the pressure in a chamber,
means for biasing the valve to the said one posi
10 tion thereof when the pressure in the pipe and
the pressurev in the chamber are substantially
equalized, electroresponsive means effective when
energized to cause the pressure in the pipe and in
the said chamber to be substantially equalized
15 and effective when deenergized to reduce the
pressure in the said chamber and cause the high
er pipe pressure acting on the ?uid pressure re
sponsive means to shift the said valve from the
said one to the said second position thereof, elec
20 trical means controlling the circuit of the electro
responsive means and effective to cause energiza
tion of the electroresponsive means only so long
as the frequency of the alternating current sup
plied thereto exceeds a certain frequency, and
25 means for supplying alternating current to said
electrical means at a frequency corresponding to
the speed of rotation of a vehicle wheel.
16. In a vehicle brake equipment, in combina
tion, a brake cylinder, a pipe through which ?uid
30 under pressure may be supplied‘to the brake cyl
inder to effect an application of the brakes, valve
means effective in one position to open communi
cation through said pipe to permit the ?ow of
?uid under pressure to the brake cylinder and op
35 erative to a second position to cut off communi
cation through said pipe to the brake cylinder and
to establish a communication through which ?uid
under pressure is released from the brake cylin
der, and electrical means effective as long as al
ternating current of a frequency above a certain
position thereof, means subject to the pressure in
said pipe for shifting the valve means to the said
second position thereof when the frequency of 5
the alternating current supplied to the said elec
trical means is less than said certain frequency,
and means for rendering the electrical means in
effective to control the valve means regardless
of the frequency of the alternating current sup 10
plied thereto unless the pressure in the said pipe
exceeds a certain uniform pressure.
17. In a vehicle brake equipment, in combina
tion, a brake cylinder, a pipe through which ?uid
under pressure may be supplied to the brake cyl-. 15
inder to effect an application of the brakes, valve
means effective in one position to open communi
cation through saidpipe to permit the ?ow of
?uid under pressure to the brake cylinder and op
erative to a second position to cut off communica 20
tion through said pipe to the brake cylinder and
to establish a communication through which ?uid
under pressure is released from the bra-kecylin
der, and electrical means effective as long as al
ternating current of a frequency above a certain 25
uniform frequency is supplied thereto for causing
the valve means to be maintained in the said one
position thereof, means subject to the pressure
in said pipe for shifting the valve means to the
said second position thereof when the frequency 30
of the alternating current supplied to the said
electrical means is less than said frequency, and
means effective when the said valve means is in
its second position for preventing further release
of ?uid under pressure from the brake cylinder 35
through the said release communication when the
pressure in the brake cylinder reduces to a certain
uniform pressure.
RAYMOND E,
40
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