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Патент USA US2123966

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July 19, 1938.
`
F_ X, REES
TRACK CIRCUIT
Original Filed Aug. 21, 1955
.
2,123,966
Patented July 19, 1938
’ 2,123,955
UNITED STA’FES PARENT QFFICE
2,123,966
TRACK CIRCUIT
Frank X. Rees, Albany, N. EY., assignor to Genera-1
Railway Signal Company, Rochester, N. Y.
Original application August 21, 1936, Serial No.
97,2011. Divided and this application Gctober
27, 1937, Serial No. 171,379
5 Ciaims.
10
(Cl. 246-34)
This invention relates to improvements in the
Well-known track circuits for railroads, and more
the average or eifective relay energizing current,
thereby serving to break down or ionize the film
particularly to rectified alternating current track
circuits.
The primary object of the present invention is
to improve the shunting operation of the usual
tractive soft iron armature track relay of direct
current track circuits under varying conditions
or coating on the rail surface and render more
of rail surface and ballast resistance.
This invention is in the nature of a variation
or modification for carrying out the principles
and mode of operation characteristic of the track
circuit organization disclosed and claimed in my
effective the shunting action of the Wheels and
axles of a train or trains Without increasing the
average current.
Various characteristic features, attributes, and
advantages of the invention will be in part ap
parent, and in part pointed out, as the descrip
tion progresses.
10
tion disclosed in said prior application. The
present application is also a division of my prior
The accompanying drawing illustrates in a sim
pliñed and dragrammatic manner certain specific
embodiments of the invention, the parts and
circuits being shown more With the View of
facilitating an explanation and understanding of 15
the invention than for the purpose of showing in
detail the structural organizations to be employed
application Ser. No. 97,204 filed August 21, 1936
in practice.
prior application Ser. No. 24,074, ñled May 29,
15 1935, and no claim is made herein to the inven
and no claim is made herein to the invention
20 disclosed in the parent application as noW
amended.
The reliable operation of the usual track cir
cuit depends upon establishing a conducting path
of low resistance through the axles and Wheels
of a car or train; and the Weight of the equipment
and condition of the rail surface are important
factors affecting the resistance of a Wheel shunt.
For example, Where the track rails of sidings,
Crossovers, and the like are infrequently used, a
coating of rust, usually an iron oxide, accumu
lates on the rail surface, and makes any Wheel
shunt of high resistance for the relatively small
inter-rail voltages commonly employed; and even
Where train movement is frequent and the rail
surface appears clean, a coating or film in the
form of an oxide of silicon, or some other stable
compound, is present on the rail surface, and
offers a relatively high effective resistance for low
voltages. It is found that these various coatings
40 or films on the rail surface, apparently because
they are in the nature of a stable chemical com
pound or composition, will break down and be
come a low resistance conducting path upon the
application of sufficient voltage, Which may be
45 termed an ionization voltage.
Generally speaking, and Without attempting to
denne the exact nature and scope of the inven
tion, it is proposed to provide a transformer of
special construction, conveniently termed a
peaker- voltage transformer for supplying rectified
current from an alternating current source to the
ordinary direct current track circuit, so that rela
In the drawing, Fig. 1 illustrates one form of
the invention, and 1Eig. 2 is an explanatory dia
gram illustrating how the negative Waves of the
current are blocked out by the rectifier shownin
Fig. 1.
One important characteristic of this invention
is that it assures reliable shunting of the ordi
nary track circuit under unfavorable conditions
of rail surface, Weight of equipment, and ballast
conditions. This desirable characteristic is due
to the application of high peaked voltages to
break down the ñlm or coating on the track rails,
thereby assuring a shunting effect of the Wheels
and axles of a car or train under conditions Where
a lower voltage would be insuiiicient.
In accordance with the invention illustrate-d in
Fig. l., it is proposed to employ a track relay 35
of the usual direct current tractive armature type
but having a substantial value of inductive react
ance, and to supply the track circuit with time
spaced unidirectional voltage pulses, instead of
voltage pulses in opposite directions as shown in 40
Fig. l. These unidirectional voltage pulses are
preferably derived from alternating current but
preferably have their peaks materially in excess
of that of the usual sine Wave of alternating cur
rent, these peak voltages also being in excess of
the steady operating voltage that Would be neces
sary for operating the track relay, thus tending
to more easily overcome the resistance of the
Wheel contact and establish a better ratio be
tween maximum voltage and wheel shunt resist 50
ance. In this construction the ballast resistance
between the track rails, together with an addi
tively high peak voltages of short duration are
tional shunt or bleeder resistance as may be rc
obtained, as compared With a rectified Wave of
quired, constituting a conducting path into which
the relay may discharge current during the time 55
55 the usual sine Wave shape of voltage required for
2
2,123,966
intervals between the impressed voltage pulses;
Fig. 2.
and the voltages and resistances being so propor
tioned that the rate of decay of current through
the relay varies with the ballast resistance in such
a way as to compensate for the change in the
Wel1~known copper-oxide dry plate type, have the
inter-rail impressed voltage with changes in
ballast resistance, thereby maintaining a substan
tially constant average operating current through
the track relay throughout a wide range of varia
10 tions in ballast resistance.
Referring to Fig. 1 of the drawing, it is con
templated that the track rails H wil be joined
together in the usual way, with insulated joints
l2 designating the ends of the track sections, one
of which only is illustrated.
At one end of the
track circuit, preferably at the entering end, the
direction of traffic being in the direction of the
arrow, the direct current track relay T4 of the
usual tractive armature type construction is con
20 nected across the track rails Il, the resistance
property or characteristic that the resistance to
the ñow of current in the direction in which the
rectifier is conducting, varies invariably with the
current induced, such forward resistance of the
rectifier increasing as the conducted current de
creases. This characteristic or property of the
rectiñer I5 is a factor in connection with other
features of this form of the invention to compen
sate for variations in ballast resistance.
Considering now the operation of the track
circuit organization of the construction shown in
Fig. l, and the theory believed to underlie the re
sults obtained, the impressed Voltage applied to
the track rails at the feed end comprises uni
directional time spaced pulses or waves. These
voltage pulses supply current to the ballast re
sistance and to the track relay through the limit»
ing resistance I9; and each wave causes a cor
and/or inductance of this track relay T4» being
responding temporary increase in the current
dependent. upon the nature of the ballast resist
ñowing in the track relay. As an impressed volt
age wave is applied to the relay current through
this relay increases, with a time lag due to the
inductive reactance of the relay; and as this
ance and a number of other factors, as will pres
251
Certain types of rectifiers, such as the
ently appear.
It is contemplated that the impedance of
track relay T4 and its connections to the track
rails will be some two or six times greater than
ordinarily used, as for example, where ordinarily
aV 4 ohm track relay7 would be used, a track relay
The pur
30 of about 25 ohms would be employed.
pose for'such relatively large impedance of the
track relay and its connections is to permit the
use of a greater inter-rail potential for overcom
ing the resistance of the wheel contact, and fur
35 Vther to supply sufficient energy to the track relay
by smaller average current than would be neces
sary for the'usual 4 ohm relay.
In accordance with the invention the track re
lay is supplied with current of unidirectional time
kspaced pulses, the direction of the pulses and
space between them, as well as the peak voltage,
being chosen with due regard to the other char
acteristics of the circuit., so as. to obtain the de
sired operating characteristics of the track cir
In the embodiment shown in Fig. 1, a
45 cuit.
source of alternating current of an ordinary
frequency, such as 60 cycles, is employed. Such
source of current is shown conventionally by the
generator G4. This source of alternating current
50 G4 is supplied directly to the primary winding 'i4
of a peaking transformer PT4. The secondary
winding 84 of this peaking transformer PT4 is
connected to the track rails through an adjusta
ble resistance IQ and a rectifier l5 connected in
55 series. This adjustable resistance I9 constitutes
the usual limiting resistance. In certain appli
cations of the invention, for reasons hereinafter
explained, it is also desirable to employ a bleeder
or regulating shunt resistance 2|, preferably ad
60 justable, which is connected across the track rails,
as shown, preferably at the feed end of the track
circuit'.
In the arrangements shown in Fig. 1, the rectiñer
i5 serves to impress across the track rails waves
65 or half-cycles of peaked alternating current Volt
age supplied by the secondary winding 84 of the
peaking transformer PT4, thereby providing a
single unidirectional impulse for each cycle of al
ternating current as shown by the Waves C5 of
70 Fig_ 2. It may be pointed out that the curves
shown in Fig. 2 are substantiallx7 the same as those
shown in Fig, 3 of the parent application except
that the negative voltage waves shown in Fig. 3
of the- parent application have been blocked out
75 "by the rectifier l5 and are therefore not shown in
20
impressed voltage wave falls, the current through
the relay decreases. As thc relay current de
creases, the collapse or decay of flux in the relay
induces a voltage in its winding in a direction to
sustain current flow in the relay, and in accord 30
ance With established principles, the rate of
decrease or decay of current is dependent upon
the inductance of the relay and the resistance of
the multiple path which in the present instance
is the ballast resistance of the track circuit. It
is found that the rate at which the relay current
will flow between two successive waves of uni
directional potential, depends upon the. joint
effect of the ballast resistance and the bleeder
resistance 2l (which bleeder resistance in track
circuits may be omitted).
4 (i
It is thus seen that the
decay of current ñowing in the relay T‘1 during
the time interval between voltage pulses is at a
slower rate with a lower ballast resistance, and
that the greater rate of decay of current will
take place for higher ballast resistance.
The pick-up and drop-away current value of
the track relay T4 Adepends upon what may be
termed the average current through it; and it
can be seen that the magnitude of this average
current depends upon the rate at which the relay
current decreases or decays during the half-cycles
where the impressed voltage is cut oí, as well as
upon the value of the voltage pulses. In other
50
Words, the higher the pulses of impressed voltage,
the greater the instantaneous current; and also
the slower the rate of decay of relay current, the
greater will be the average current through the
relay; and vice versa.
In the ordinary track circuit, when the battery 60
voltage and limiting resistance has been selected
or adjusted to provide sufficient current for the
track relay under wet ballast conditions, that is,
low ballast resistance, if the ballast dries out and
its resistance increases, less current flows through
the ballast and the limiting resistance, the volt
age drop through the limiting resistance then
becomes smaller, and a greater voltage is im
pressed across the track rails to increase the cur
rent through the relay. It can thus be seen that,
if once the ordinary track circuit has been ad
justed to hold up the relay under wet ballast con~
ditions, there will be excessive current through the
relay under dry ballast conditions, which mate
rially interferes with the shunting of the track
3
2,123,966
relay. For this reason, it is desirable to provide
something Which will act automatically to main
tain a uniform normal current through the track
relay under varying ballast conditions, so that the
energization of the relay is substantially the same
at all times, and so that the relay can be shunted
quickly and reliably under both wet and dry bal
last conditions. An important feature of the
invention shown in Fig. l is the automatic corn
pensation provided to maintain the relay current
substantially uniform for various ballast resist
ances throughout a wide range at the higher
ballast resistances and above what may be termed
the zone of Wheel shunt resistance.
Explaining the theory apparently underlying
the operation accomplishing this result, it appears
that changes in the voltage applied to the relay
with variation in ballast resistance are accom
plished by compensating change in the rate of
20 decay of the relay current between the voltage
pulses, in such a way that, with suitable propor
tioned parts, the average operating current
through the relay is maintained substantially uni
form throughout a Wide range of ballast resist
25 ances above the lower values, around 2 ohms per
thousand feet of track.
In practicing this invention, the parts are
selected and proportioned to provide adequate
operating current for the track relay T"z under the
30 most unfavorable or Wet ballast conditions to be
encountered; but as the ballast dries out, less
current is supplied to the track circuit as a whole,
and the voltage drop through the limiting resist
ance is decreases to raise the voltage impressed
35 upon the relay T4, such increase in ballast resist
ance is accomplished by a more rapid decay of
relay current between the pulses of impressed
voltage, so that the average current iiowing in the
track relay T4 remains substantially constant,
40 rather than to increase steadily with. an increase
in 1ballast resistance as is the case in the ordinary
track circuit. Consequently, the track relay T4 is
not overenergized under dry ballast conditions
and may be shunted as surely
as quickly
45 under dry as under wet ballast conditions.
In some applications of the invention, it is
found that there is what may be termed over
compensation, such that the average current
through the relay of an unoccupied track circuit
50 decreases at the higher ballast resistances to the
point where it will fail to hold up its armature.
This appears to be due to a relatively greater
change in relay current between the voltage
pulses for higher ballast resistances, than changes
55 in the impressed voltage, with the result that the
average current actually decreases for higher
values of ballast resistances. In such cases, the
shunt or bleeder resistance 2l across the track
relay is employed to provide what may be consid
60 ered to be an artiiicial ballast resistance or leak
age path for the purpose of maintaining a suñ'i
ciently low resistance for the discharge circuit for
the track relay T4 under very dry ballast condi
tions to avoid too quick a decay in the relay cur
65 rent between the voltage pulses and thereby main
tain the average current. This shunt or bleeder
resistance 2i is preferably adjustable, and with
the proper selection or adjustment thereof, to
gether with the adjustment aiiîorded by the usual
70 limiting resistance i9, it appears that the desired
regulation of relay current may be obtained for
track circuits for various lengths and ballast
materials throughout the full operating range
encountered in practice.
The maintenance of substantially constant
75
average current through the relay for different
ballast resistances seems to be helped also by the
current-resistance characteristics of the copper
oxide rectifier l5 in the arrangement shown in
Fig. l, the eifect of the rectifier in this respect,
however, being apparently dependent upon a
number of related factors and diñìcult to explain
and evaluate. A source of alternating current
derived from a peaker transformer when used in
combination with a half-wave rectifier l5, affords 10
a convenient way of obtaining the time spaced
impulses of impressed Voltage, and with such an
arrangement the operating characteristics of the
rectifier may also be taken advantage of to modify
the current regulating characteristics of the track
circuit. For example, assuming a setting for Wet
ballast conditions, when the ballast dries out and
less current is supplied to the track, the forward
resistance of the rectiñer, i. e. the resistance in the
direction in which it is conducting, increases and 20
in effect adds to the limiting resistance i9 to
maintain a voltage drop wth a smaller current to
give nearly the same impressed voltage across the
track rails. For this reason, and in this way, the
characteristics of the rectifier are helpful in 25
obtaining the desired current regulation.
Another important feature of this invention is
that the peak voltage of the half-cycles of peaked
alternating current are much in excess of the
steady direct current voltage that would be re 30
quired to produce the same general operating cur
rent through the relay. In other words, the peak
voltages applied across the track rails in accord
ance with the form of invention shown in Fig. 1
are much greater than the steady voltage that
would be used with the same type of track relay in
a continuous direct current track circuit.
Such
peak voltages very materially assist in reducing or
breaking down the resistance of the wheel con
tacts and establish an effective low resistance
wheel shunt, this being true more particularly
with dirty or rusty track rails, or with light
weight equipment, such as gas-electric cars.
'
'I‘he resistance of the Wheel Contact is found
to vary greatly with the conditions of the rail
surface and the weight of the equipment; and
it appears that in many cases voltages much
higher than the relatively small voltages, of about
2 volts normally employed for track circuits,
are necessary to break down the resistance of
the Wheel contact to a point where ionization
and actual shunting of the track relay takes
place.
'I‘he peak voltages provided by this in
vention, which are many times those commonly
used in track circuits, apparently break down 554
the resistance at the wheel contact by an ioniza
tion eifect, and enable effective shunting with
dirty or rusty track rails and light-weight equip
ment in a manner not obtainable with the ordi
nary track circuit arrangement.
In this connection, it will be noted that the
peak voltages are periodically applied at fre
quent intervals and are available to break down
the resistance of the Wheel contact, as the car
or train moves along the track and its Wheels
contact with successive points on the rails, and
with the resistance once broken down it will
remain of low value until the train has left and
an opportunity for soiling and oxidization of
the rail surface has been presented.
Further, the use of a pulsating current ob
taining from a peaked alternating current source
through the medium of a half-wave rectifier,
as distinctive from a steady current for energiz- '
ing the track relay, acts to improve the pick-up
60
4
2,123,966
and drop-away characteristics of the high im
section, a peaking transformer having an in-put
pedance soft iron armature track relay T4. In
other Words, a direct current „tractive arma
ture type relay of the usual construction will
current connected to the in-put Winding of said
peaking transformer, means including a half
and an out-put Winding, a source of alternating
pick up on less current and drop away on a
Wave rectifier and a limiting resistance in series
greater current When energized with half-cycles
for connecting the out-put Winding of said peak
of rectified alternating current or equivalent
time spaced current impulses, than When ener
gized With an ordinary unidirectional voltage
ing transformer to the track rails at the other
end of said track section to impress peak volt
from a battery or the like, and this effect is
still more pronounced When these half-cycles
are of extremely peaked Wave form. This is
attributed to the fluctuating nature of the ener
gizing current which tends to initiate armature
movement at critical current values in a man
ner that does not occur with steady energiza
tion. Also, the movement of the armature of
the relay is accompanied by a flux change Which
appears to be a contributing factor to the su
perior ratio of drop-away current to pick-up
current obtained by the use of pulsating ener
gization of the track relay in accordance with
this invention.
From the foregoing it will be appreciated
25, that this invention involves certain selection and
proportioning of parts in the complete organi
zation; and the various voltages, resistances, and
inductive reactances are so completely inter
related that a variation in the change in one
30"; factor tends to modify one or more of the other
factors.
Generally speaking, the underlying principles
and advantages of the invention shown in Fig. l
may be obtained when the limiting resistance
35.'. I9 and the shunt or bleeder resistance 2l, if
used, are selected to conform With the length
of the track circuit, condition of the ballast,
range of variation in ballast resistance, and the
like; the inductive reactance of the relay T4
40 is preferably so chosen as to require peak volt
ages suitable for reducing the resistance of the
wheel contact by breaking doWn the resistance
by ionization; and these various factors are rel
atively proportioned to provide the necessary
45. average current through the track relay of an
unoccupied track circuit under Wet ballast con
ditions, and to maintain such average current
substantially constant throughout the range of
variation of ballast resistance encountered with
changing weather conditions.
The particular embodiments of the invention
shown and described are merely illustrative; and
various adaptations, modifications, and additions
may be employed, Without departing from the
55 principles and mode of operation of the inven
tion.
What I claim isz
1. A track circuit for railroads comprising a
half-Wave rectifier, a limiting resistance, a peak
ages substantially greater than the steady op
erating voltage for said relay, a shunt bleeder 10
resistance connected across the track rails, the
magnitude of said peak voltages and their time
spacing being selected With respect to the self
induction of said track relay and the resistance
of said bleeder to provide an approximately uni 15
form operating current for said track relay
throughout a Wide variation in ballast resistance.
3. A track circuit for railroads comprising, a
direct current track relay of the usual tractive
armature type connected across the track rails 20
at one end of the track section, a source of
alternating current, a transformer having a high
leakage reactance, an adjustable limiting re
sistance, a half-Wave rectifier, and means con
necting said source of alternating current to the 25
in-put side of said transformer and connecting
the out-put side of said transformer across the
track rails at the other end of said track sec
tion through said limiting resistance and said
half-Wave rectifier, a bleeder resistance con 30.
nected across the track rails of said section, the
self-induction of said track relay and the re
sistance of said bleeder being such as to tend to
maintain current of a value in its Winding to
keep its armature attracted between the half 35;
cycles of impressed voltage, and the peak voltages
of the half cycles of impressed voltage being such
as to provide an average current through said
track relay comparable with its steady operat
ing current and being materially greater than 40
the voltage for such steady operating current,
whereby peak voltages across the track rails suit
able for breaking down anycontact resistance of
the Wheel shunt are available Without a corre
spondingly greater average energization of the
track relay which Would interfere with its shunt
ing.
Ll. A track circuit for railroads comprising, a
direct current track relay of the usual tractive
armature type having its winding connected across 50
the track rails at one end of a track section, a
limiting resistance, and means including a trans
former having high leakage reactance and a
rectifier included in its secondary Winding for
supplying time spaced uni-directional voltage 55
pulses through said limiting resistance across the
track rails at the other end of said section, a
bleeder resistance connected across the track
rails of said track section, the self-induction of
ing transformer energized from a source of al
said relay maintaining current through its -wind
ternating current for impressing voltage across
ing between such Voltage pulses by discharging
the track rails at one end of the track section
path through which the track relay having con
into the ballast resistance and bleeder resistance,
the rate of decay of said current of self-induc
tion between the voltage pulses varying with
changes in ballast resistance to compensate for 65
the variations in current supplied to said track
relay by the voltage pulses for different ballast re
siderable inductive reactance may discharge cur
sistance so as to cause approximately the same
rent during the half cycles when the impressed
`voltage is blocked by the rectifier.
2. A track circuit for railroads having the
relay of the tractive armature type connected
average current through the track relay for a Wide
variation in ballast resistance.
70
5. A track circuit for railroads having the
usual variation in ballast resistance and compris
ing, a direct current track relay of the usual trac
tive armature type having its Winding con
yacross the track rails at one end of the track
nected across the track rails at one end of a track
in series with said rectifier and said limiting
resistance, and a shunt bleeder resistance con
65 nected across the track rails to cooperate with
the ballast resistance to provide a conducting
usual variation in ballast resistance between the
track rails and comprising, a direct current track
60
2,123,966
section, an adjustable limiting resistance, a source
of alternating current, a transformer having a.
high leakage reactance and a rectifier included
in series in its secondary Winding for impressing
time spaced uni-directional Voltage pulses
through said limiting resistance across the track
rails at the other end of said track section, a
bleeder resistance connected across the track rails
5
of said track section, the time spacing and mag
nitude of said voltage pulses, the self-induction
of said track relay, and said limiting resistance
and bleeder resistance having such relation that
approximately the same average current flows
through said track relay for a Wide range of
variation in ballast resistance.
FRANK X. BEES.
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