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Патент USA US3078957

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Feb. 26, 1963
G. w. GRAY
Filed April 28. 1960
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United States Patent O
George W. Gray, Lamhertville, NJ., assigner to Radio
Corporation of America, a corporation of Delaware
Filed Apr. 28, 1%0, Ser. No. 25,443
47 Claims. (Cl. 18o-S2)
Patented Feb. 26, 1963
generating and p-ropagating means are also provided.
These signal generating and propagating means are op
erative to transmit control and/or warning signals along
the highway. The signal generating and propagating
means are responsive to the detecting means and trans
mit, between pairs of successive vehicles, tails of con
trol and/or warning signals related to the distance be
The present invention relates to vehicle control sys
tween the pairs of successive vehicles and the speed of
the leading vehicles in each of the pairs of successive
tems, and more particularly to electronic systems for
transmitting warning or control signals to vehicles as 10 vehicles.
they travel along a highway and for receiving such sig
The detecting means are also operative lto provide con
trol voltages. The detecting means and the signal gen
nals in these vehicles so as to increase highway safety.
erating and propagating means are connected in a man
The invention is especially suitable in providing an
ner such that the control voltages are of different ampli
automatic control system of the type disclosed in Zwory
kin, Flory and Pike United States Paten-t No. 2,847,080, 15 tudes depending upon the distance between the signal gen
erating and propagating means and >the vehicle which
issued August l2, 1958, wherein means are provided along
a highway which are actuated behind -a vehicle traveling
on the highway to create a “tail” of warning or control
otuates the detecting means.
A plurality of detecting means may be provided to
gether with a plurality of signal generating and propagat
signals. The system of the present invention provides
improved means for generating, transmitting and receiv 20 ing means. Each detecting means provides a control
ing a tail of warning or control signals.
voltage in response to the presence of the vehicle.
detecting means and the signal generating and propagat
Although the invention is especially suitable in pro
ing means are connected in a manner to actuate a num
viding safer and automatic driving for road vehicles such
ber of signal generating and propagating means with
as automobiles, trucks, buses, and the like, features of
the invention may be useful in control, warning or guid 25 control voltages of diíferent amplitudes depending upon
the distance between the signal generating and propagat
ance of aircraft, Ships and missiles, for example. Thus
ing means and the detecting means which is actauted by
a vehicle. The signal generating and propagating means
are operative in response to the control voltages to pro
moves along a path.
It is an object of the present invention to provide an 30 vide the tails of control and/ or warning signals.
the term “vehicle,” as used herein, is intended to em
brace, generally, driven equipment of any sort which
improved system for the control of vehicles which travel
along a highway or other path.
It is another object of the present invention to pro
vide an improved system for generating and transmitting
warning or control signals to vehicles which travel along
a path, as on a highway.
It is a further object of the present invention to pro
vide an improved system for signaling between vehicles
Further in accordance with the present invention, the
signal generating and propagating means includes means
for providing a repetitive signal varying in duration or
duty cycle in accordance with ythe amplitude of the sig~
nal applied from the detecting means to the generating
means. This repetitive signal is referred to hereinafter,
at times, as the distance signal.
More particularly, there may be produced in the sig
nal generating and propagating means a repetitive wave
which follow one another along a path information as
to the distance separating the vehicles and as to the 40 which has a form depending upon road conditions in the
speed thereof.
section of the highway in which the system provided by
the invention is to be used. This wave is compared with
It is a still further object of the present invention to
the control voltages from the detecting means and a por
provide an improved sys-tem for generating a tail of con
tion of the wave is propagated which varies in duration
trol or warning signals along a highway in response to
or duty cycle in accordance with the amplitude of the
the passage of a vehicle.
control voltages from the detecting means.
It is a still further object of the present invention to
By changing the wave form of the control voltage, its
duration, or other characteristics thereof, the nature of
a control or warning signal which is propagated down
changed for accommodation to Various road conditions, 50 the highway to following vehicles is controlled in accord
ance with road conditions at the particular time. More
such as rain, snow, ice, fog, and the like.
It is a still further object of the present invention to
over, the system of signaling provided in accordance with
provide an improved control system for vehicles which
the present invention isvmore stable than previous elec
provide an improved control system for vehicles by
means of which the vehicles can be caused to maintain
a safe distance of separation, which distance can be
is generally fail-safe in its operation in transmitting and
tronic systems wherein amplitude information may be
receiving warning or control signals.
transmitted directly.
It is a still further object of the present invention to
Further in accordance with -the present invention, means
provide an improved electronic system suitable for
are provided for transmitting information as to the speed
vehicle control and warning purposes which is more
of a vehicle as it travels down the highway. The signal
stable in operation than prior electronic systems for vehi
cle control and warning.
lt is a still further object of the present invention to
provide an improved system for signaling among vehicles
representing the speed is referred to hereinafter, at times,
as the speed signal. Means are provided responsive to
»the actuation of each detecting means for operating a
number of signal generating means to produce an impulse
which travel along a highway in which the need for a
when a vehicle actuates any detecting means. Impulses
reference signal is eliminated.
will be produced in succession at a rate determined by
It is a still further object of the present invention to
the vehicle’s speed. The signal generating means may
provide an improved system for transmitting and re 65 include means for detecting the variations in amplitude
ceiving signals corresponding to the speed of a vehicle
of the control voltages from the successive vehicle ac
as it travels along a highway.
tuated detecting means. As the Vehicle travels along
Brieñy described, a vehicle control system provided in
the highway past the location of each detecting means,
accordance with the present invention utilizes detecting
the amplitude of the control voltage applied to each of
means disposed at spaced locations along a highway for 70 the generating and propagating means will vary in steps.
detecting the presence of vehicles on the highway. Signal
-It will be recognized that the vehicle moves a distance
equal to the separation of the detecting means upon occurrence of each amplitude step. Thus, »the signal gen
erating means is operated to transmit a series of impulses
which vary in repetition rate depending upon the speed
of the vehicle initiated impulses.
A signal receiver may be provided in the vehicles which
travel along the highway for responding to the distance
signals and the speed signals from Ithe signal generators.
vided by the present invention, electronic control or warn
ing signals are transmitted along the highways and are
received by the vehicles traveling along the highway.
The drivers are thus warned of a dangerous condition,
or their vehicles are automatically slowed down. Chain
collisions and other types of rear-end collisions are there
by reduced or eliminated.,
In the illustrated system, a'plurality of loops or coils
12 are spaced from each other along the highway. Al
These receivers are fail-safe in operation and include
indicating means which indicate a danger condition upon 10 though the loops 12 are illustrated spaced somewhat
apart, they may, in practice, be placed in adjacent blocks.
the failure of any component in eitherrthe signal gen
These blocks may be o-f various lengths depending on the
erating or signal receiving portions of the system.
expected speed of the vehicles and the cost of the system.
The invention itself, both as` to its organization and
Blocks approximately 20 feet long may be found suit
method of operation, as well as the foregoing and other
objects and advantages thereof, will become more readi 15 able. The loop in each block may extend almost to the
limits of its block. The loops 12 are desirably buried
ly apparent from a reading of the following description
in connection with the accompanying drawings in which:
FIGURE l is a partially schematiq, partially block
diagram of signal transmitting apparatus in a system pro
just below the road surface of the highway. The loops
12 and other components of the illustrated system are
further identified with subscripts which will enter into
vided in accordance with the present invention; ‘
20 a discussion of the operation of the system appearing here
FIGURE 2 is a block diagram of means included in
.the system shown in FIG. l for generating signals indica
tive of the speed of vehicles passing along a highway
The loops 12 are each coupled to separate detecting cir»
cuits 14. These detecting circuits 14 may be referred to
hereinafter as detectors. The detectors 14 are illustrated
and the distance between vehicles;
FIGURE 3 is a detailed circuit diagram of the signal 25 as >blocks »including switches 16. The detectors 14 are
essentially phase o-r impedance sensitive circuits. A pre
generating means shown in FIG. 2;'
ferred type of detector is illustrated and described in a
FIGURE 4 is a series of waveformsof signals appear
copending patent application tiled' in the name of the
ing in -the systems and circuits shown in FIGS. l, 2 and 3;
present inventor, Serial No. 693,763, tiled October 3l,
FIGURE 5 is another series of waveforms of signals
appearing in the signal generating means shown in FIGS. 30 1957, now 'Patent No. 2,983,852, issued May 9, 1961.
This detector includes a phase shifting network in which
2 and 3 and representing a mode of operation of the
the detecting loop (such as any of the loops 12) is a
illustrated systems and circuits provided by the invention;
phase-shift producing element. The change in inductance
, FIGURE 6 is a block diagram of ’a receiver accord
of the loop 12, as the vehicle passes over the loop, pro
ing to the present invention;
FIGURE 7 is another block diagram showing another 35 duces a phase shift which may be detected as an output
pulse having a sense and magnitude which is a function of
embodiment of a receiver according to the present in
the sense and magnitude of the change in the impedance
of the loop from its quiescent value. This output pulse
FrGURE 8 is a partially schematic, partially block dia
is adapted tooperate a relay circuit in which the switch
gram of a system for generating a tail of signals along
a highway in accordance `with another embodiment of 40 16 may be provided by a set of relay contacts.
More particularly, the detector includes an oscillator
the invention;
which produces a continuous wave oscillation at several
FIGURE 9 is a circuit diagram of a part of the system
hundred kilocycles per second. A phase detector and a
shown in FIG. 8;
phase shifting network is also provided. This network
FIGURE l0 is a series of waveforms of signals ap
pearing in the system and circuit shown in FIGS. 8 and 9; 45 includes the detecting loop. The signals from the oscil
lator are applied to the phase detector and to the phase
FIGURE 1l is a waveform diagram of a signal appear
ing in the system shown in FIG. 8, the waveform being
depicted in a manner to illustrate a moderof operation
shifting network. The phase shifting network is also
coupled to the phase detector. The phase detector is
coupled through a coupling circuit to a relay circuit. The
FIGURE l2 is a ‘block diagram ofthe system of a 50 relay circuit may include a relay driving amplifier stage.
When a vehicle passes over the detecting coil or loop,
eceiver which may be installed -in a vehicle for` thev
of the system according to the present invention;
purpose of receiving control andwarning signals trans
mitted by the transmitting system shown in FIG. 8;
4FIGURE. 13 isa more detailed circuit diagram of a
portion of the receiver systemV shown in FIG.` l2;
FIGURE 14 is a diagram of a circuit which may be
used -in conjunction with the circuit shown in FIG. 13;
an output pulse is produced by a phase detector. This
output pulse operates the relay circuit. Accordingly, the
relay contacts are‘actuated, as by being closed, upon sens
ingof a vehicle. The contacts remain closed so long as
the vehicle remains over the loop. Thus, the contacts
will be closed for a period determined by the speed of
the vehicle.
In the event that a vehicle is stalled over a
loop, the contacts 16 (FIG. l) of the detector associated
with the loop will remain closed until the vehicle is re-V
tem for transmitting a tail of signals along a highway 60 moved.
in accordance with lstill another embodiment of the in
A voltage attenuating transmission line 18 is disposed
along the highway and interconnects the detectingcir
Referring to FIG. 1 of the drawings, a portion of a
cuits 14. The voltage transmission line 18 includes sec
highway 10 is depicted. This portion may, for'example, .
tions having series resistors 20 and shunt resistors 22.
FIGURE l5 is a schematic circuit diagram of a sys
«be one lane of a multi-lane highway, such as one of
the modern turnpikes. In driving :an automobile on
such highways, the driver usually must stay in a selected
lane and hold his speed withinyclose limits. Thus, vehi
The shunt resistors are connected to the series resistors
and to a point of reference potential, such as ground.
Diodes 24 are connected between adjacent ones of the
detecting circuits 14 and in series with the series resistors
29.y The values of the series resistors 20 may be the
cles usually follow one another rather closely as they
travel alongthe highway. A common »accident on mod 70 same, and similarly the values of the shunt resistors 22
ern highways is, therefore, the rear-end collision. Some
may be the same. Thus, the attenuation in each sec
times, one or more vehicles rwhich follow each other
tion is equal.
along the highway collide with each other in what is
A direct current transmission line 28 extends along the
highway 10, as, for example, at the roadside. A source
commonlyreferred to as. a “chain” collision..
In highways equipped with a system of the type pro 75 of negative direct current voltage indicated at _D_C.,
may be applied to this transmission line 2S. The high
potential side of this negative direct current voltage source
may be connected to the reference potential point which
is illustrated as ground. The switches Ilo are connected
to the direct current transmission line 2S and to the junc
The signal transmission lines 32, 34 and 36 serve a
section of the highway. The length of the section of the
highway served by the same group of oscillators and asso
ciated circuits will depend upon the signal transmission
characteristics of the lines 32, 34 and 36. It may be de
tion of the series and shunt resistors 2i) and 22 of the
sired to use dilierent function generators in ditterent sec
voltage attenuating transmission line 1S. When any of
tions of a highway depending upon the types of road sec
the switches 16 closes, a control voltage from the line
tions, such as curves, hills, and straight sections. Ac
2e’ is appl'ed to the voltage attenuating transmission line
cordingly, the signal transmission line 36 may serve a
1S. This voltage is nevative with respect to ground. As 10 longer or shorter section of the highway than the other
will become apparent, the direct current voltage estab
transmission lines 32 and 34.
lished by the detectors on the attenuating transmission
line iS has amplitude characteristics which are indica
tive of the distance along the highway between a vehicle
and any block, as well as of the speed of a vehicle. Thus,
this direct current voltage may be availed of, and will be
hereinafter referred to, as a control voltage.
The transmission line i8 transmits the negative control
voltage in a direction opposite to the direction of travel
of the vehicles along the highway. The direction of travel 20
of the vehicles is indicated by the arrow 26 on the high
way 10. The direction of current transmission is estab
lished by the polarization of the diodes 24. It will be
noted that the transmission line 1S is adapted to transmit
Different antennas 52 are associated with different
blocks along the highway. In other words, the antennas
correspond in number and location to the detecting loops
The antennas 52 are grounded at one end and are
adapted to radiate energy primarily by induction. Ac
cordingly, the radiation field of each antenna is limited
approximately t0 the block of the highway in which the
antenna is disposed.
The antennas may be located, in
practice, along the roadside rather than along the center
of the road, as illustrated in the drawing.
The antennas are fed by signals from signal generating
networks 54. These networks may be referred to here
inafter simply as generators 54. The generators 54 are
current in a direction opposite to the direction of travel 25 connected to the signal transmission lines 32, 34 and 36
of the vehicles alonor the highway le.
and to the voltage transmission line 18. Connections are
Three other signal transmission lines 32, 34, and 35
made from associated detectors 14 and generators 54 to
are provided which are adapted to transmit high fre
different sections of the transmission line 18 at the junc
quency alternating current signals. Voice modulated
tions of diiferent pairs of series and shunt resistors 2d and
signals are adapted to be applied to the signal trans 30 22. lt will be observed that each generator 54 is connected
mission line 32. An oscillator 38 operating, for example,
to the antenna 52 associated with the block immediately
at one-hundred kilocycles (kc.) is coupled to a modulator
preceding the block containing the loop 12 of its asso
at). The output of the modulator is connected to the line
ciated detector 14.
32. Voice signals from a microphone 42 are applied to
Each of the generators 54 is operative in response to
the modulator 4t?. The one-hundred kilocycle oscillators 35 control voltages from its associated detector and from the
act as a carrier. Highway oiiicials may, desirably, use
line 18, and to signals from the signal transmission lines
the microphone to transmit messages of interest, such as
32, 34 and 36. Each generator 54 is adapted to produce
those relating to the conditions of the road several miles
control and warning signals for transmission by its an
ahead, to the vehicles passing along the section of the
tenna 52. These control and warning signals have char
highway l0.
40 acteristics determined and ascertained by the control volt
Another oscillator 4d which operates at a freouency
ages from the detectors due to the distance between ve
above the frequency of oscillation o-f the oscillator 38 (for
hicles on the highway and vehicle speed. However, the
example, one hundred and ten kilocycles) is coupled to
signals produced by the generators and radiated by the
another of the signal transmission lines, such as the line
34. The oscillations from the oscillator 44 are used to 45 antennas are in a form most suitable for accurate trans
mission and reception of warning and control informa
transmit information as to the speed of the vehicles pass
tion by the vehicles as they travel along the highway.
ing along the highway 10, as Will be explained more fully
The details of the generators 5d are discussed below in
connection with FÍGS. 2 and 3 of the drawing.
Another oscillator 45, which operates at a frequency
As a vehicle passes over a particular loop 12, the
diiîerent from the frequencies of oscillation of the oscilla 50
switch i6 of the detector 14 associated with the loop will
tors 3S and 44 (for example, one hundred and ñve kilo
close for the time interval that the vehicle is present on
cycles) cooperates with a function generator d8 to pro
the loop 12. To clarify the following discussion, the vari
vide signals of special waveform for application to the
ous sensing loops, detecting circuits 14 and generators 54
third signal transmission line 36. The function generator
49, in the system illustrated in FÍG. l, generates a step 55 are identiiied by letter subscripts in accordance with the
letters in the alphabet. Thus, as a vehicle travels along
wave which is repetitive at a frequency much lower than
the highway 10, it will pass over the loops 12a, 12b and
the frequency of oper-ation of the oscillator do. A suit
lic in succession. The detector Ma is iirst actuated and
able frequency may be in the range of 10() to 200 cycles
the switch 16a is closed. A negative control voltage is
per second. While the function generator 48 is described
herein in connection with the embodiment of the inven 60 applied from the line 28 to the generator 54a.
The vehicle then passes over the second loop 12b. The
tion shown in FIG. 1 as a step wave generator, it may,
switch toa in the detecting circuit 14a opens and the
as will be explained more fully hereinafter, be adapted to
switch ldb in the detecting circuit 1411 closes. A voltage
generate other waveforms such as triangular, sawtooth
from the line 28 is applied to the generator Séb. A con
or exponential waves.
trol voitage will appear across the shunt resistor 22h in
The waveform generator may be of any conventional
the transmission line 18 which is effectively connected
design. The design of generators of special waveforms
across the control voltage input of the generating network
is known in the art and is described in the textbook en
Selb. Some of the voltage across the shunt resistor 22h
titled “Waveforms” by Chance et al. (M.I.T. Radiation
appears across the first resistor 22a which is, similarly
Laboratory Series-McGraw-Hill Book Company, 1949).
with the resistor Z217, connected across the control voltage
The oscillations from the oscillator 45 are additively corn
bined with the wave from the function generator in an
adding circuit 5t). This adding circuit 50 may be a re
input of the generating network 54a. The amplitude
of the control voltage across the first shunt resistor 22a
is determined by the Values of the resistors 20a and 22a
and the forward resistance of the diodes 24 in the line 18.
Thus, a voltage will appear across the resistor 22a, when
sistive adding network, as will be described in detail here
inafter. The output of the adding circuit is connected
to the signal transmission line 36.
76 the vehicle passes over the detecting loop 12b, which is
a predetermined fraction of the voltage which appeared
across the resistor 22a when the vehicle passed over the
detecting loop 12a.
As the vehicle proceeds down the highway, it passes
over the detecting loop’lZc. The switch 16b opens and
the switch 16e closes. A control voltage equal in mag
nitude to the voltage which was applied to the generating
networks 54a, 54b when the vehicle passed over the de
tecting loops ìZa, 12b now appears across the shunt re
sistor 22e. A predetermined fraction of this voltage is
transmitted through the voltage transmission line lâ and
appears across the resistor 22h. A still smaller fraction
of this voltage appears across the resistor 22a. Accord
ingly, the control voltage at the inputs of the generators
54a, 54b, 54o will therefore vary in steps as the vehicle
proceeds down the highway 1l). The amplitude of the
gate circuit 66. The gate circuit 66 is operative totransmit signals therethrough so long as the signals from
the function generator are greater in amplitude than
the control voltage, when the amplitudes thereof are
measured in the same sense.
In the illustrated case,
the voltages are measured in the negative sense. Thus,
where a first voltage is of greater negative value than
another voltage of lesser negative value, the lirst voltage
is considered of greater magnitude than the other.
The output of the gate circuit 66 is applied through
an alternating current coupling device (for example, a
capacitor) to the input of an amplifier `68. The direct
current component of the signal transmitted by the gate
circuit 66 is removed due to the capacitive coupling to
the amplifier 63. The 105 kc. signal which is superim
posed on the signal from the function generator is there
fore transmitted by the amplifier 68 to the adder 64»,
so long as the amplitude of the signal from the function
control voltage at any block on the highway depends on
the distance of the vehicle from the block. The width of
each step will depend upon the speed of the vehicle. The
generator is greater, in the same sense, than the amplitude»
rate of occurrence of the steps is related to the speed of 20 of the control voltage.
The amplitude relationships of the signals will be more
the vehicle.
Assuming, for example that the vehicle> travels about
apparent from PEG. 4- ofthe drawings. The step wave
sixty mph., it will pass over each loop in approximately
signal from the function generator is shown as waveform
0.25 second. Because of the action of the diode voltage
a having 10‘5 lic. oscillations superimposed thereon. The
transmission line 1S, the vehicle leaves behind it a tail 25 control voltage, shown in waveform b, is also a step
of control voltages appearing at each of the generators
wave. As indicated above, this control voltage is nega
54a, 54b, and S40. This tail is preferably adjusted in
tive with respect to ground as measured at the input
practice to correspond to a distance of several hundred
terminal 56 of the generator 54. Negative going volt
feet in order to provide sufficient time and distance to
ages are selected for the control voltage and for the volt
bring following vehicles to a stop even though the lead 30 age wave generated by the function generator in view of
ing vehicle is stopped. lt will be appreciated that any
the characteristics of the circuitryrin the generator 54.
number of detecting loops and their associated circuitry
It will be pointed out hereinafter that the circuits in the
and networks may be employed and that only three are
generator 54 are transistorized. It is desirable to use
shown to simplify the illustration.
P-N-P‘transistors, since they are more readily available.
The control voltage applied to each of the generators 35 Since these transistors are operated with negative signals,
S4 is compared in the networks thereof with the Wave
the control voltages are generated from a negative source
from the function generator 48 and oscillator 46 which
in order to accommodate these transistors. It will be
is applied to the signal transmission line 36. The gen
appreciated that vacuum tube circuits and other types
erators are therefore operative to convert a control volt
of transistors may be used in the system provided by
age into control and warning signals having certain de
the invention. Where electron tubes are employed, it
sired characteristics: These signals are propagated by
would be desirable to generate control voltages and
the antennas S2 for reception'in vehicle carried receivers
waves which increase in a positive sense rather than in
of the type to be described hereinafter. Since the con
the negative sense as in the case illustrated above.
trol voltage is related to the distance of the vehicle ahead 45
The wave from the function generator is desirably
on the highway and the speed thereof, the control and
of such frequency that several cycles of the step wave
warning signals will also be related to the distance and
occur during each step of the control voltage. ln the
speed of the vehicle.
case of aivehicle traveling l0() miles per hour, which is
Referring to -FlG. 2; a block diagram of one of the
higher than would be expected even on a high-speed
generators '54 is shown. Four input terminals 56, S8, 50 turnpilre, each step of the control voltage shown in the
643 and -62 are indicated in this figure.` The control
waveform b of FlG. 4 would be approximately 1f; of a
voltage from the ,detecting networks ld‘and diode trans
second. Accordingly, it is desirable for several cycles
mission line 18 is applied tothe input terminal 55. The
of the function to occur within the period of one step
signal transmission vline 34' is connected to the input
of the control voltage wave. Fewer cycles of the step
terminal 58 andfapplies 110 kc. oscillations to the termi
wave from the function generator than may appear in
nal 58. The signal transmission line 36 is connected to
practice are shown occurring during each of the steps
the input terminal 'Gil and applies'th'ereto a `step wave
inthe control voltage in FIG. 4 to simplify the drawing
form having a lGS kc. signal superimposed thereon as
of the waveforms.
indicated by the waveform shown immediately adjacent
As the vehicle travels away from the loop of the
the terminal dit. The signal transmission line 32 is con 60 detector coupled directly to the generator shown in FIG.
nected to the last of the terminals 62 for the application
2, the control voltage, Waveform b, decreases in steps,
of the voice modulated 100 kc. oscillations to the gen
erator. The generator provides three signals which are
each step corresponding to a passage over a successive
one of the blocks. lt will be observed that the wave a
combined in an adder circuit 64 for transmission to the
and control voltage wave b are of equal amplitude. The
antenna 52 associated with the related generating net 65 height of each step in the control voltage b is equal to
work. These signals are (l) a iirst control and warning
the height of each' step in the step wave a. The first
signal indicative of the distance between vehicles, (2)
step in time occurs when the vehicle passes over the loop
another control or warning signal indicative of the speed
of the detector i4 which is directly coupled to the gen
of a vehicle, and (3) a voice-modulated signal to carry
erator of FlG.- 2.- lt will be recalled that the gate 66
information of interest.
70 transmits the step wave when the step wave is greater
The generation of the distance control or warning
signal will be considered lirst. The control voltage is
applied to an amplifier 63. This ampliñer is a direct
current amplilier which applies the control voltage to
one input.of'a_gate circuit.66. The signals from the
function generator are applied to another input of the
in amplitude than the control voltage.
Because of the
amplitude relations of the waves a and b, the step Awave
a is blocked during the period that the vehicle passes
over the block containing'the loop of the detector which
is directly coupled to the generator shown in FlG. 2.
When the vehicle proceeds to the next adjacent block,
the iirst and greatest amplitude step of the control voltage
Wave b is transmitted. When the vehicle reaches the
third block, two steps of the step wave tz are transmitted.
Finally, as the control voltage decreases to approximately
“Zero” volts, or ground potential, three steps of the step
wave è are transmitted.
The direct current component of the signal is elimi
nated in the circuit which couples the gate 66 to the am
pliiier 63. Thus, only bursts of oscillations of 105 kc.
are amplified by the ampliiier 66 and applied to the
adder 6d for application to the antenna 52. These bursts
of signals are shown in waveform c of FIG. 4. It will
be noted that since the steps in each staircase in the step
mitted control or warning signal. The receivers will be
described in detail hereinafter. The receivers respond
by indicating the distance separating the vehicles or by
automatically controlling the braking system of the ve
hicles. Since a signal or shorter duration and duty cycle
is produced when there is a longer distance between ve
hicles than under normal conditions, the following ve
hicle will slow down sooner and maintain a greater dis
tance behind the car ahead. Thus, under slippery road
conditions, the vehicles may be kept farther apart than
under dry or normal road conditions.
Signals are obtained in the generator shown in FIG. 2
from the control voltage representing the speed of the
Vehicles traveling along the highway. The control volt
wave a and the steps in the control voltage b are of equal
age is applied to a difïerentiating circuit 7i).
amplitude, only the duty cycle of the bursts will vary.
The duty cycle will be l0() percent when the duration
of each burst equals the period of a cycle of the step
entiated control voltage output from the diiierentiating
The diiîer
distance separating vehicles, in terms of signal duration.
ative-going pulse is produced on the descending portion
circuit 7h is in the form of a series of pulses. These pulses
are amplified in an amplifier and applied to a gate circuit
wave. The duty cycle is zero percent when the control
74. The 110 kc. oscillations from the signal transmis
voltage and step wave are of equal amplitudes. When 20 sion liney 3d are also applied to the gate circuit 74.
the vehicle speeds up or slows down, the duty cycle will
The ditierentiated control voltage therefore serves to gate
not vary. However, bursts of the same duty cycle will
the 110 kc. oscillations so that bursts of ll() kc. oscilla
be available for a longer period of time.
tions are transmitted upon occurrence of the pulses from
Thus, it will be seen that the control voltage due to
the diiterentiating circuit 7G. These bursts are applied
the passage ot’ chicles along the hiùhway is translated
to the adder network ed for application to the antenna.
or converted from a representation of distance separating
Referring to FIG. 4 again, waveform e thereof illus
vehicles, in terms of amplitude, to a representation of
trates the output of the diñerentiating circuit 7d. The neg
In other words, the duration of the signal, such as rep
of the control voltage. Fositive pulses are reproduced
resented by waveform c in FïG. 4, varies from a mini 30 at the beginning of each step of the control voltage. The
mum of a predetermined maximum in accordance with
negative-going pulse does not contain any useful speed
the distance separating successive pairs of vehicles. 'Ihe
information and is suppressed by components of the sys
longer the duration of the signal, the farther apart are
tem which will be described in connection with FIG. 3
the vehicles.
of the drawing. Each of the positive pulses of the differ
The system provided by the invention therefore has 35 entiated control voltage is produced after the vehicle has
certain advantages. The system is more stable than pre
vious systems in which the amplitude of a control voltage
was the significant characteristic of the transmitted signal.
Ambient conditions and variations of circuit characteris
tics as the circuit components age which might alter the 40
signal amplitude do not adversely aiîect the system pro
vided by the present invention. Moreover, no reference
signals need be transmitted. In addition, the system pro
moved the length of a block (i.e., twenty feet in an eX
ernplary case) along the highway in which diiîerent de
tecting loops are located. The number of positive pulses
in the ditferentiated output produced for a given period of
time is therefore an indication of the speed of the ve
hicle. These voltage pulses gate the 110 kc. oscillations
in the gate circuit 54 so that bursts of 110 kc. oscilla
tions are transmitted as warning and control signals which
represent the speed of a vehicle to a succeeding vehicle
vided by the present invention is more flexible in its use.
FÍGURE 5 shows a series of waveforms which indi 45 traveling along on the highway.
cate how the system may be controlled or adjusted to
The bursts of 110 kc. oscillations are used in the re
accommodate changing road conditions. Under ordinary
circumstances, a certain safe separating distance will be
acceptable. However, when the highway becomes wet,
icy, or covered with snow, for example, the minimum
safe separation distance is desirably increased. This can
be accomplished with the present invention by somewhat
changing the waveform generated by the function genera
tor. Waveform a in FIG. 5 represents the output of
the function generator. The 165 kc. signal is not shown
in FES. 5 to simplify the illustration. it will be ob
served in FlG. 5c that the two top steps of each of the
ceiver of the following vehicle to ascertain and indicate
the speed of the vehicle ahead of the following vehicle
on the highway and for warning and/or control pur
The voice modulated signals are ampliiied in an ani
pliiier 7o and applied to the adder circuit 64 for transmis
sion by the antenna 52 associated with the generator 54,
as illustrated in FiG. 2 ot the drawings. It will be no
ticed that the speed signals are bursts of ll() kc. oscilla
tions. The distance signals are bursts of 105 kc. oscilla
tions and the voice modulated signals are transmitted on
cycles of the waveform are approximately one-half as wide
a 100 irc. carrier. Each control signal is therefore in
as the other step. A control voltage generated by a
a different frequency band so that the various signals can
'vehicle traveling at a unifor n speed is portrayed in wave 60 be separated in the receiver, as will `be explained herein
form ZJ in
5. Upon application of waveforms a
and b ot FiG. 5 to the gate circuit 61S, output signal bursts
Referring to FIG. 3, it will be seen that the circuit
are provided after removal of the direct current compo
elements and components of the generating network
nent, as shown in waveform c of FlG. 5. It will be
shown in FIG. 2 are illustrated as semiconductor circuits.
observed that signal bursts of longer duration are pro 65 It will be appreciated, however, that the principles of the
duced later in time in waveform c of FIG. 5 than in
invention may be applied to circuits using other types of
waveform c of
4. Since steps of the wave a have
amplifying devices and unilateral conductive devices,
been purposelv made or" shorter than normal duration,
such as electron tubes.
control and warning signals of longer duty cycle are
rEhe control voltage `from the highway is applied to a
generated later in time than usual. This indicates that 70 transistor stage providing the ampliñer 6.3 which is con
the distance between the vehicles is shorter than is ac
tually the case. However, this is desirable when the road
conditions are dangerous.
nected in an emitter-follower circuit. lhis ampliiier in
cludes a type P-N-F transistor ’78. The emitter of this
transistor 7S is connected through a resistor 8@ to the
rille vehicles traveling along the highway are equipped
point of reference potential (ground). The collector is
with receivers which respond to the duration of the trans 75 connected to a source of energizing potential which, `in
the'case of P-N-P transistors, is a negative voltage source
indicated as -B. The base of the transistor 7S is con
nected to the input terminal do so that the control volt~
ages from the highway are applied to the base of the
transistor. Since the transistor '7S operates as an emitter~
follower, these control voltages appear across the emitter
resistor' Si?. The emitter resistor 8G is connected through
a resistor S2 to a diode S4 which constitutes the gate cir
cuit 66. The diode dit acts as a gate'since current passes
resistor 124.». The resistors Il@ and 121i set the operating
voltage on the emitter of the transistor H4.
The llt) lrc. oscillations are applied to the terminal
Si?. The terminal Sâ is connected to the secondary wind
ing of the coupling transformer 116 and provides one
input to the gate circuit 74. The output of the gate cir
cuit ’îd is obtained from the secondary of the other con»
pling transformer 120. This secondary is connected to
the resistor 1€=2 in the adder 64.
The differentiated pulses produced by the 4differentiating
through the diode only when the voltage across the resis 10
circuit '70 are applied to the base of the transistor 114.
tor Sti is more positive than the voltage at the input ter
The transistor H4 is operated normally «cut oli by virtue
minal 60. The step wave from the function generator to
of thepote'ntial applied to its emitter through the voltage
which 105 kc. oscillations are added is applied to the input
divider comprising the resistor H8 and Íthe resistor 124.
terminal 56. It follows that the diode gate circuit 66
It is a well kno-wn characteristic of N-P-N transistors that
functions to block the transmission of the signals from
they are rendered conductive in their collector-to-cmitter
the function generator, when the control voltage is greater
path when a positive voltage is applied to their base. Ac
in amplitude in the same sense (negative in the illustrated
cordingly, negative pulses such as result from differentia~
case) than the step wave from the function generator
tion of the first step of the control voltages, as shown in
4S (FIG. l).
The current transmitted through the diode circuit 66 20 'waveform e in FIG. 4, are automatically suppressed in the
circuit. The resistor H2 drops the voltage due to the
when the diode 84- condncts results in a voltage drop
negative pulses to a low amplitude and thereby insures
across the emitter-resistor S0. A coupling capacitor S6
that the pulses will not be of suíiicient .amplitude to dam
is connected to the base of a transistor Se which is'in
age the transistor 114. The positive pulses are, however,
cluded in the ampliñer stage de. This capacitor 86 re
moves the direct current component from the current 25 ïsuiiicient to render the transistor H4 conductive from
emitter to collector. Accordingly, the 110 kc. oscillations
passed by the diode gate 66. Accordingly, a waveform
applied to the emitter are transmitted in bursts through
similar to the waveform c shown in FIG. 4 is applied to
the transistor to the transformer llo and are coupled to
the input of the ampliiier 63.
the adder circuit 64. These bursts of 110 kc. provide the
The amplifier 63 includes a P-N-P transistorv 8S having
a tank circuit 90 tuned to 105 kc. The tank circuit 90 30 control or warning signal indicative of the speed of the
vehicles on the highway.
is connected to the collector of the transistor S8. The
The voice modulated 1l() kc. carrier is applied to the Y
tank circuit is also connected to the source of operating
input terminal 62. The input terminal 62 is connected
voltage -B and provides a path for operating current
to a substantially conventional P-N-P transistor amplifier
for the transistor 8S. The emitter is connected to ground
through a self-biasing resistor 92. A biasing network 35 ‘76, which is connected as a biased emitter-follower. The
including two' resistors 94 and 96 is connected, at the
junction of these resistors, to the base of the transistor
38. The coil in the tank circuit 90 constitutes the pri
ampliñer 76 includes a transistor lité. The emitter of
the transistor 125 is connected to the adder circuit through
the resistor 1&4 thereof` Accordingly, the distance
control and warning signals. This differentiating circuit
filter passes only the voice signals, The output of the
kc. . Theresistor 11S is connected to ground throughV a
direct current voltage pulses of the type illustrated im
signal, speed signal and the voice modulated signal may
mary of a coupling transformer 9d. The secondary of
this coupling transformer is coupled to the adder cir 40 be simultaneously propagated by the antennas 52..
A receiver which may be installed in vehicles which
cuit 64.
travel along the highway i0 is shown in FiG. 6 of the
The adder circuit 6d is provided by three resistors 160,
drawings in block form. A receiving antenna 128 is
102 and 104 connected to a common junction point ille.
connected to a radio frequency ‘amplifier 130. The out
The sum or total or” the voltages applied to each of the
put of the radio frequency ampliiier is detected in a detec
resistors is obtained at this junction N6, and this total
tor circuit 132 which removes the audio frequency com
voltage provides the output of the generator. This out
ponents of the signal. In other Words, the 100 kc. corn
put may be connected tothe antenna through suitable
ponen-t of the transmitted signals is treated as a carrier,
coupling circuits (not shown). It will be recalled that
and the lower frequency components which carry the
the antennas 52 are connected to groundto complete
voice signals, the speed signals, and the distance signals
the output circuit of the adder. Accordingly, bursts of
are detected and derived as carrier modulating signals.
105 kc. varying in duration corresponding to the distance
It should be pointed out at this juncture that itis desirable
of a vehicle on the highway from the generator are trans
to restrict the frequency range or” the voice signals to
mitted as a control and warning signal after amplification
below 4,000 cycles in order to prevent any possibility of
in the amplifier ed. These 105 lic. bursts are transmitted
interference with the speed and distance signals.
together with other signals combined in the adder 6d.
The signals are applied Ito a low pass ñlter E34 which
The control voltage from the highway is also applied
cuts oil? at approximately 4,000 cycles. This low pass
to a differentiating circuit 7G in order to obtain the speed
includes a capacitor ïâlâ and a resistance provided pri 60 low pass filter is amplified in an audio ‘amplifier 135 and
applied to aloud speaker L33.
marily by a resistor liti which is connected from the
The detector also provides signals for a band~pass
capacitor .E08 to ground through the source of negative
ñlter lith tuned to pass the band of approximately 4,000
voltage at -B, which source is, of course, grounded.` A
to 9,000 cycles. Alternatively, a simple ñlter tuned to
resistor i12 couples the differentiating circuit 70 to the
input of the gate circuit 74. This resistor M2 has a 65 approximately 5,000 cycles may be used. The distance
control or warning signals are transmitted by the band
high value of resistance, for example l0 lfiilohrns.
pass ñlter M0 as pulses or” 5,000 cycle oscillations. These
The 4gate circuit 7d is provided by a type N-P-N tran~
pulses are limited in a conventional limiter circuit 142.
sistor H4. The emitter of this transistor is connected
The limiter circuit removes any amplitude variations due
to the secondary winding of a coupling transfírmer 116
and, through a by-pass resistor HS, to the source of op 70 »to transmission characteristics. Amplifiers may desirably
be inserted before or after the lim-iter circuit, as desired.
erating potential at -B. The collector of the transistor
The limiter output is applied to a rectifier 144 which may
114 is connected to ground through a tank circuit includ
be a bridge type of rectifier. The rectilier 144 converts
ing the primary winding of a coupling transformer §20
the bursts of the pulses of 5,000 cycle oscillations into
and a capacitor îZZ. This tank circuit is tuned to llO
mediately above the rectifier- in FIG. 6 of the drawings.
lt will be noted that these pulses vary in duration (i.e.,
duty cycle) in accordance with the dis-tance of the leading
constant of about ten seconds. The output pulses from
vehicle from the vehicle carrying the receiver.
- aroup of pulses is produced by each generating net
work Sii». This is because the frequency of the waveform
from the function generator is much higher than the fre-
speed is indicated on a rneter 16d.
tem such as lights, counters and the like may be used.
may be used to control the vehicle to maintain a certain
the rectifier circuit are direct current puls-es as indicated
by the waveform above the rectifier circuit 15S.
The meter may be
calibrated so that it reads speed directly.
ln order to indicate the relative speeds of a following
vehicle and the vehicle ahead of it, a tachometer gen
erator 166 may be used to provide a voltage indicative
quency of the steps of voltage in the control voltage.
of the speed of the following vehicle. The voltage in
Since groups of pulses are generated, and since pulses do
not vary in duration from pulse to pulse, a conventional 10 dicative of the speed of the vehicle ahead is obtained
from the receiver and app-ears across the capacitor 162.
integrating circuit 1416, constituted of a resistor 14d and a
This signal is applied to a difference amplifier 168 to
capacitor 150, may be used to derive a voltage which
gether with the signal from the tachometer generator
varies in amplitude in accordance with the distance be
166. A meter 170 is connected in the output of the
tween vehicles. This Voltage is shown operating a meter
152 to provide an indication of distance to the driver of 15 difference amplifier 16S and may be calibrated to read
relative speeds of adjacent vehicles. A control servo des
the vehicle. This indication should warn the driver to
ignated schematically by the block 172 labeled “Control"
slow down or stop his vehicle. However, a warning sys
relative speed between it and the vehicle ahead.
A modified receiver of lower cost than the receiver
159 may =be used in a servo system of generally conven 20
shown in FlG. 6 is illustrated in FIG. 7. This receiver
tional design for controlling the brakes of the vehicle and
includes an antenna 174, a radio-frequency (RF.) ampli
therefore will be operative automatically to stop the vehi
ñer 176, the detector 17S and a bandpass filter 1%. The
cle when the vehicle approaches the minimum safe
RF. amplifier 176, the detector 17 8 and the bandpass filter
distance behind the vehicle ahead of it.
lt will be recalled that the plurality of spaced antennas 25 18@ may be similar to the R15. amplifier 130, detector 132
and the bandpass filter 140 (FIG. 6), respectively. A
52 generates la tail of control or warning signals. These
tuned circuit tuned to 5,000 cycles may be used instead of
signals will be, when received, bursts of 5,000 cycle oscil
a bandpass filter 13%. The output of the bandpass filter is
lations of duration varying to a maximum duration de
rectified in a rectifier 182 and integrated in an integrating
pending upon the distance of the vehicle carrying the re
ceiver from the vehicle ahead of it. As the distance be 30 circuit 184. The rectifier and the integrating circuits 1S2
and 184 may be similar to the rectifier 144 and the inte
tween the vehicles increases, the duration of the 5,000
grating circuit 1156 (FIG. 6). Thus, a voltage will be
cycle signals received by the following vehicle will in
`developed from the output of the integrator 18d which
crease. Thus, the absence of control signals indicates
is a function of the separation between the vehicles. This
that the vehicles are adjacent to each other. More partic
35 voltage may be differentiated in a differentiating circuit
ularly, they will be in adjacent blocks on the highway.
it will be noted that the warning or control signals de
The differentiated distance signal is a function of the
rived by the receiver decrease in amplitude as the vehicles
relative speeds of the leading vehicle and of the following
come closer together on the highway. Thus, in the event
vehicle which is equipped with the receiver shown in
of a failure of signal, a warning indication will be pro
vided. This añords fail-safe operation for the system 40 FIG. 7. A tachometer generator, as illustrated in FIG.
6, is not used in the system of FlG. 7. The differentiated
of the invention.
signal is applied to a control device 190. This control
it is, of course, desirable to maintain a separation
device may be a servo for controlling the acceleration
of at least several blocks. The separation distance will
and the braking system of the vehicles so as to maintain
depend upon the speed of »the vehicles. Thus, on a
turnpike where the vehicles may travel at speeds of 45 the vehicle at a particular speed with respect to the speed
ofthe vehicle ahead of it.
60 miles per hour or higher, the separation distance
Another embodiment of a system provided in accord
may be l0 or l5 blocks, so that the cars are separated
ance with the present invention is illustrated in FiG.
by at least 200 feet. On slower speed highways, such
8 of the drawings. FIG. 8 shows the equipment which
as in tunnels and on bridges, a smaller separation of
just a few ‘blocks may be sufûcient. A warning indi 50 may be located in or along the highway for the purpose
of generating and transmitting the control and warning
cation or controlled operation is, therefore, provided
signals. The highway is not depicted in FIG. 3 in order
to indicate `when the minimum safe separation distance is
to simplify the illustration. The system illustrated in
achieved. This may be accomplished by flashing of
FIG. 8 includes a plurality of detecting loops (not shown
lights or operation of the servo system automatically to
apply the brakes.
55 in this figure) for sensing the passage of vehicles along
the highway. These loops are coupled to detecting cir
Conventional servo systems and integrating circuits
cuits or detectors 11i. Antennas 52 associated with
such as illustrated in FIG. 6 may be used, since the 5,000
diñerent of the successive blocks along the highway are
cycle bursts vary in duration at a relatively slow rate.
also used. A diode Voltage transmission {attenuating}
Thus, it is an important feature of the invention to pro
vide a suitable frequency relationship between the fre 60 line 1S is disposed along the highway for cooperation with
the detectors. This diode line 18 includes series resistors
quency of occurrence of the steps of the control voltage
Ztl which are of equal value and shunt resistors Z2 which
and the frequency of the waves from the function gen
are also of value equal to each other. The shunt resistors
erator such that the function generator produces waves
22 may have a much higher resistance than the series
at a frequency higher than the frequency of the steps in
the control voltage.
65 resistors 2d. In series with the shunt resistors are addi
tional diodes 2li@ which cooperate with a clamping cir
The signals from the detector are also applied to a
cuit as will be described hereinafter. However, the
high pass filter 154 which passes signals of higher than
diodes 2410 may be omitted when a level setting circuit
9,090 cycles in frequency. Alternativ-ely, a tuned circuit
of a type other than the clamping circuit 216 is used.
tuned to 10,000 cycles may be used. The speed signals
are separated in the filter 154» as bursts of 10,000 cycle 70 These diodes 2150 are polarized to transmit negative cur
oscillations. These bursts are limited in a limiter circuit
rent through the shunt branches of the line 1S. Instead
156 and rectified in a rectifier 15S which may be a bridge
of being connected to ground, the shunt resistors are
type rectiñer. The rectifier 15S is coupled to an integrat
connected to a source of positive voltage which, for
ing circuit including a resistor 160 and a capacitor 162.
purposes of illustration, is designated as being of +20
This integrating circuit desirably has a fairly long time
volts. A direct current transmission line 2d is connected
Alternatively, the voltage appearing across the capacitor
to a source of negative voltage indicated solely for pur
wave in the diode line 1S as will be explained more
poses of illustration as being _l5 volts. The detectors
l@ are connected so that the switches id thereof are cach
between the direct current transmission line 26 and the
diode line lâ at the junction of a diode Ztl@ and a series
resistor Ztl.
fully below in connection with FIG. l0.
Waveform B of FIG. l0 shows the step wave of control
voltage which would be generated at each of the junctions
of one of the resistors 2l) and the associated diode 2&0 oÍ
the line IlS as a vehicle passes over the loops of the de
tector connected to these junctions. When the vehicle
passes over the loop, the detector switch 16 closes and
thus a negative voltage appears across the shunt branch
18 and with a generator 2li/»i of waves ot predetermined
waveform or which varies in amplitude as a predeter 10 including the diode 2&9 and shunt resistor 22. Since
the DC. transmission line 28 is negative with respect to
mined function of time. rl'his generator
is called a
A signal generator network or generator 2S?, is also
provided. This generator cooperates with the diode line
function generator herein. The function generator 28d
functions to convert the control voltage from the detectors
ground and since the bottom of the shunt resistor is posi
tive with respect to ground, the voltage across the shunt
branch, in the absence of the diode 214 which is connected
ld and the diode line lâ into control and warning signals
for transmission by the antennas 52. A plurality of the 15 to ground across that branch, would be the sum of the
source voltages which, in the illustrated case, is 35 volts.
generators 292 may be provided. Each of the generators
As the vehicle passes over successive loops as it travels
292 is associated with a dilierent block or" the highway
down the highway, the voltage acrossy any of the shunt
and is connected to a didercnt one of the antennas 52.
branches will vary in steps determined by the attenuating
Two generators Zr'âî are shown in FIG. 8. One of these
generators is shown in greater detail than the other in 20 characteristics ot the line lli. The attenuation in each
block of the diode line 1S (constituted of a series and
two parts labeled 2G26: and 245215. A function generator
shunt resistor 2€) and 22, respectively) is the same. Thus,
2&4 may be connected to a signalV transmission line 21%
the steps of voltage gradually decrease in amplitude.
and serves to provide predetermined waveform signals to
This decrease is approximately equal over the first several
a number of the generators» 2M.
The function generator 264i includes a generator 2li? of 25 blocks along the highway. However, as the input volt
sawtooth waves. lt will be understood that other waves
such as triangular waves, may be used. This generator
Zîil. may be a conventional Miller or boot strap circuit.
rihre waves are illustrated in waveform A of FlG. 10i.
The waves increase in a negative sense and vary in mag
nitude between Zero volts «and minus ñfteen volle. The
voltage magnitude of the wave is merely a typical suit
able value, indicated herein solely for the purpose of
illustration. The waveform A is selected to be of nega~
tive polarity to :accommodate the use or? transistor and
semiconductor circuitry in the generator 262. This cir
cuitry is adapted to use type'P-N-P transistors, primarily.
Type P-l‘l-l’ transistors are of lower cost and are more
age to blocks of the line 18 which are somewhat distant
from the vehicle decreases, the steps of voltage also de
crease and depart from uniformity. The steps of vol*
age decrease in a somewhat exponential manner.
Waveform B of FIG. _l0 shows three steps of approxi~
mately uniform height or amplitude and a fourth step of
lesser amplitude. It will he appreciated, however, that
many more steps are produced in practice before the
amplitude of a step decreases from its adjacent step to an
appreciable extent. It will be noticed, however, that the
step at which an appreciable decrease in amplitude takes
place varies from zero or ground potential to positive po
tential. This step would, in the absence of the diodes 214,
appear across one of the shunt branches of the line 18.
The function generator 294 also includes an oscillator 40 However, the diodes 21d prevent the transmission of volt
ages which are positive with respect to ground. Accord
2% which, for purposes oi' illustration, isV designated as
generally available at this time.
ingly, the significant portion of the control voltage which
has steps which are substantially equal in amplitude is
used to the exclusion of the portion of the control volt
generator [au in an adding circuit 2&2. Thus, 4.5 kc.
oscillations are supe
posed on the sawtooth waves, as 45 age having non-uniform amplitude steps. Since these
steps of control voltage which are of lesser height than
illustrated in the wave rm A of EEG. lll. The frequency
the steps in the significant portion are usually well beyond
of the sav/tooth waves is desirably much greater than the
the safe minimum distance which should be maintained
frequency of the steps of the control voltage produced in
providing oscillations at 4.5 kc. (4560l cycles). These
oscillations are added to the sawtooth waves from a
the diode transmission line i8 for the reasons pointed out
between cars, the elimination of these latter steps does not
above, namely, more stable operation of the transmitting 50 aiîect the operation of the system.
The elimination of the nonlinear portieri of the con
portion of the system provided by the invention and bet
trol voltage is also illustrated in FIG. 1l. lt will be
ter adaptability to integration in the integrator circuits in
noted that the heights of thc steps above ground poten<
the receiver with which the vehicles traveling along the
tial varies somewhat exponentially in amplitude. By
highway may be equipped.
lt may also be desirable to synchronize the sawtooth 55 elimination of the steps through use of the diodes 214,
only the more linear, significant portion of the control
enerator 2li) with oscillations from the oscillator Zilë'l.
voltage is used.
lt is desirable to initiate each cycle of the sawtooth wave
The generating networks 262 serve to transmit distance
at the beginning of a cycle of the 4.5 kc. oscillations. ln
control and warning signals indicative of the speed of
this manner, the ma rnurn amplitude of the sawtooth
wave is not altered. As is apparent from waveform A of 60 the vehicle. The distance control and warning signals are
formed and »transmitted by a system of components in
FlG. l0, the amplitude of the 4.5 itc. oscillations is much
cluding a clamping circuit Zlá, a gate circuit Zlíâ, an
smaller than the amplitude of the sawtooth wave and may,
ampliñer 220 and an adding network 222., these circuits
for example, be ot about one-halt volt pcak-to-peak. Syn
being connected in tandem. The clamping circuit 2id is
chronizing circuits tor sav/tooth genenators are well
known in the art and may be found in many texts such as 65 also operative as an impedance transforming device to
prevent loading of the diode line t3 due to the generating
the “waveforms” text referenced above. Accordingly,
networks Edil. The diode 2% serves to provide biasing
such circuits will not be described in detail herein.
potentials for the clamping circuit as will be explained
lt will be noted that each junction between a series re
hereinafter. The signal transmitting line Ztiä, which car
sistor Ztl and its vassociated diode 20d on the diode trans
mission line lâ is connected to ground potential through 70 ries the sawtooth wave and its superimposed oscillations,
is connected to the clamping circuit Zio. The clamping
a diode 2id which is polarized to transmit positive cur
circuit functions to clamp the waves from the line 2%
rent to ground. Thus, the junctions of the respective re
to the voltage of the control voltage.
sistors 2li and diodes 2&9 cannot rise above ground po
tential. This circuit arrangement permits utilization of
only the more linear portion of the control voltage step
The operation of the clamping circuit 2li? will be ap
parent from waveform C of FlG. l0. The sawtooth wave
is raised in amplitude progressively and step-wise as it
is clamped to the voltage of each step of the control volt
signals are both transmitted simultaneously by the antenna
52 coupled to the generator 262.
Referring to FEGURE 9, the generator is shown in de
tail. A portion of the diode transmission line i8 is also
shown. The signal generating network includes a pair of
age. If, for any reason, the control Voltage wave fails,
the sawtooth wave drops in amplitude or resumes its ini
tial amplitude, which is, in the illustrated ease, -15 volts.
'[his will operate the generator to transmit signals to fol
input connections 234 and 236 which are connected across
lowing cars that the leading car is just ahead (a danger
the diode 2%'. The control voltage from the line 1S ap
ous condition). Thus, the system is fail-safe in case of
pears -on the upper one of these connections 234. The
loss or” the control voltage. lt will be noted that the peak
general wave form of this control voltage is depicted adja
to-peak amplitude of the sawtooth Wave is equal to the 10 cent the connection 231.1. The connection 234 leads to
peak-to-peak amplitude of the control wave, which, in the
the base of a transistor 23S. The connection 236 leads
illustrated case, is l5 volts. Both waves increase in the
to the base of another transistor 240. 'Ihe transistor 236
same sense, that is to say, in the negative sense.
is' of the P-N-P type and the transistor 246` is of the
The clamped output signal in the clamping circuit 216
N-P-N type. Thus, the transistors 23S and 241i are corn
is applied to the gate 218. The gate ZlS is, as will be 15 plementary to each other.
described in detail hereinafter, a circuit which transmits
These transistors 238 »and 240 form part of an imped
or gates voltages which are above ground potential (zero
ance transformation circuit. The collector of the upper
volts in the illustrated example). Thus, only those por
transistor 238 is connected to a source of operating volt
tions of the sawtooth Wave which are raised and clamped
age indicated at -B. The emitters of the transistors are
above Zero volts are transmitted. The higher in ampli 20 connected together. The collector of the N-P-N transis
tude the control voltage, the smaller the portion of the
tor 240 is connected to a source of bias voltage indicated,
sawtooth wave which is transmitted when both the saw
solely for purposes of illustration, as +3 volts. The
tooth wave voltage and the control voltage are consid
output of the complementary transistors 238 and 240 is
ered to increase in amplitude in the same sense (negative
obtained at the emitters thereof. The output voltage of
in the illustrated case) .
The gate portion of the sawtooth wave is applied to the
ampliiier 220. Amplilier 22€) incorporates alternating cur
rent coupling circuits whichare operative to transmit only
25 these transistors will be the same as the input voltage.
In the other words, »the control voltage appears at the
output of the transistors 238 and 240.
ln operation, the circuit including the transistors 238
the 4.5 kc. oscillation which is superimposed on the saw
and 249 provides an impedance transformation so that
tooth Wave. Accordingly, bursts of 4.5 kc. oscillations 30 the impedance at the output of the circuit is many times
will be transmitted which vary in duration in accordance
lower than the impedance of the input thereof. The con
with the portion of the sawtooth wave which is trans
trol voltage which appears at the output of the circuit
mitted or gated throughthe gate circuit‘2l8. The trans
therefore will not vary with changes in load due to the
mitted wave is illustrated in wave form D of FIG. 10.
operation of the other system components of the gener
it will be observed that the bursts vary in duration or 35 ator 202.
duty cycle from 1G()l percent duty cycle to zero percent
Since a voltage drop appears across the diode 200,
duty cycle which correspond, respectively, to the tran-smis
Vthe P-N-P transistor 238 is biased slightly into its con
sion of a burst equal in duration to the period of the
ducting region. However, this bias is insufficient to cause
sawtooth wave to transmission of a burst of Zero duration,
»full conduction in the P-N-P transistor. The voltage
40 across the diode Zilli also causes the N-P-N transistor
or no burst.
The duration of the bursts varies in accordance with
-249 to be biased into its conducting region. However',
the distance of the vehicle from the block associated with
the bia-s is also insufficient to cause full Conduction in
the generating network which generates the bursts. Thus,
the N-P-N transistor 24d. When the control voltage
the 4.5 kc. oscillations will be continuously transmitted if
appears across the shunt branch, either the transistor
the vehicle is a considerable distance from the particular
23S or the transistor 246 will conduct so that the volt
generating station. if the vehicle is in the block adjacent
age at their common emitters will follow the control
to the detector 14 which is directly connected to the gen
voltage. 'The P-N-P transistor 23S provides low output
erating network 202, no burst will be transmitted. The
impedance for negative input signals and 'prevents the
same condition results if the control signal fails as was
output of the pair of transistors 23S and 24@ from be
pointed out above. rl'he receiver which responds to the 60 coming more positive than the input. The N-P-N tran
control signals is operative to indicate a minimum vehi
sistor 249 provides low output impedance for positive
cle separation in the absence of signal. This, of course,
input signals and prevents the output from becoming
will be a danger condition and the driver will be warned
more negative than the input. .As will he explained here
to stop the vehicle, or the vehicle will be automatically
inafter, signal. waves are applied to the clamping cir
stopped. Since the same operation is obtained when the
cuit 216. These waves may cause voltages to appear
at the output of the transistors 238 and 240 which would
control voltage fails, the system is fail-safe in operation.
be higher than the control voltage such that transistor
The bursts of 4.5 kc. oscillations are added to other
signals in an adding network 2272. The adding network
output voltage is applied to an amplifier 22d which drives
the antenna 52 associated with the generator 262.
The generator 262 is mso operative to produce signals
indicative of the speed of a vehicle on the highway. This
cut-olf would result and the control signal might pos
sibly be blocked. However, the action of the N-P-N
and P-N-P transistors obviates this possibility.
As an alternative, a resistor may be used in place of
one of the transistors and the biasing diode 200 may be
omitted. For example, this resistor may be connected
portion of the system (253215 in FIG. 8) is generally simi
from the emitter of the transistor 238 to the source of
lar to the speed signal generating system shown in FIG. 2
voltage (+20 volts). This provides a suíiiciently
of the drawings. The speed signal producing system is
high voltage at the emitter of the transistor 238 to pre
constituted of a diiîerentiating circuit 226, a direct current
amplifier 22S and a gate circuit 23%. An oscillator 232
vent cut-otî of the transistor and blocking of the control
which produces oscillations at 8 lic., for example, is con
it should be noted that the input connection 234 from
nœted to the gate circuit 236, and the gate circuit is op 70 the diode line is also connected to the linearizing diode
erative to gate the oscillations so as to produce bursts of
211i. The operation of the linearizing diode was described
8 kc. oscillations upon occurrence of each pulse from the
in connection with FlG. 8 of the drawings.
differentiating circuit. These bursts of oscillations are
The output of the impedance transformation circuit
applied to the adding network 222 in addition to, the 4.5
including the transistors 23S and 240 is connected to the
kc. signals. Thus, the speed signals and the distance 75 clamping circuit 216. lThis clamping circuit includes a
clamping diode 242 shunted by a discharge resistor 244.
The circuit also includes a charging capacitor 246. The
sawtooth wave having the 4.5 kc. oscillations superim
posed thereon passes through the capacitor 246. The
clamping circuit 2î6 functions to clamp the bottom of
284. A negative operating voltage is applied to the emit
ter of this transistor 234 by a voltage divider 286. The
voltage divider 286 is connected between the source of
negative operating voltage at -B and ground. Output
voltage from the transistor 284 appears across a collector
the sav/tooth wave to the voltage at the output of the
resistor 288. A capacitor 29u is connected across the
resistor 28S. This capacitor and the collector resistor 28S
provide a charging circuit having a longer time constant
impedance transformation circuit. This is the output
>voltage which appears at theV emitters of the transistors
238 and 24d. rThe clamping circuit 216 operates in the
'conventional manner.
than the pulses ampli-fied by the amplifier 228 and con
stitute a pulse stretching network.
The pulses after being stretched or extended somewhat
The sawtooth wave charges the
capacitor to the control voltage which appears at the out
put of the transistor circuit.
The clamped rsawtooth wave and its superimposed 4.5
kc. oscillation passes through a resistor 248 to the gate
circuit 218. The gate circuit 218 includes a diode 25d
polarized to transmit positive current,V and a tank circuit
252 which is resonant at 4.5 kct or the frequency of the
oscillations superimposed on the sawtooth wave. . A
dampening resistor 254 is shunted across the tank vcir
in duration are coupled by means of a coupling resistor
292 to the gate circuit 230. The 8 kc. oscillations from
the source of oscillation 232 (FîG. 8) are applied through
a capacitor 294 and a resistor 296 to the gate circuit 239.
A negative voltage appearing across a voltage divider 298
is Aapplied through an inductor 390 of a tank circuit 392
Vto the anode of the diode 299 in the gate circuit 230.
Accordingly, the diode 299 is biased to cut-oli.
cuit to prevent ringing. The gate circuit operates .so 20
A polarity inversion of positive pulses applied to the
that only voltages which are positive with respect to
base of the transistor 2184 occurs in the amplifier circuit
ground are transmitted through the diode 250. Thus,
228. Thus, negative pulses appear across the collector
portions of the sawtooth wave of duration depending up
resistor 288. These negative pulses are of sufficient mag
on the amplitude of the control voltage appear across
nitude to make the cathode of the diode 299 negative with
the tank circuit 252. Since the tank circuit is resonant 25 respect to its anode and therefore cause conduction through
at the frequency of the oscillations superimposed on the
the diode. When the diode 299 conducts, the 8 kc. oscil
sawtooth wave, only these oscillations appear across the
lations are transmitted or gated through the diode 299 to
tank circuit 252. The tank circuit effectively ñlters and
the adding network 222. The 8 kc. oscillations pass
through a circuit including a coupling capacitor 304 and
The tank circuit is connected to a` transistor ampli 30 the resistor 264 of the adding network. Thus, speed con
iier 220 of conventional design which utilizes a P-N-P
trol warning signals are added to the distance control warn
.transistor 256. The circuit including the transistor 256
ing signals in the adding circuit 222.
ampliñes the bursts of 4.5 kc. oscillations. The ampli'
The additively combined speed and distance control and
4tier 220 inQludes an alternating current coupling network
warning signals are then amplified in the amplilier 224
provided by a capacitor 258. This coupling network 35 and fed to the antenna 52 for transmission to vehicles as
insures the elimination of any direct current component
they travel along the highway.
in the output signal passed through the gate circuit 218.
A receiver for the control and warning signals trans
The output of the amplifier 229` is connected to the
mitted by the antennas 52 is shown in FIG. l2 of the draw
adding network 222. The adding network `222 is pro
ings in block form. This receiver includes means for
vided by a plurality of resistors 269, 262 and 264. 40 deriving the distance signal and the speed signal from the
Accordingly, the distance control and warning signal
tail of signals propagated by the antennas 52.
constituted of bursts of. 4.5 kc. oscillations is combined with
The signal which corresponds to the distance from the
speed control and warning signals which appear across
vehicle generating the tail of warning signals to the fol
the resistor 264. These signals are bursts of 8 kc. oscil
lowing vehicle is derived by circuitry similar to the cir
45 cuitry shown and described in connection with FIG. 6 of
The additively combined signals are amplified in an
the drawing. Antennas 310 and 318 on the trailing ve«
amplitier 224. This amplifier includes two transistors
hicle pick up the 4.5 kc. signal and the 8 kc. signal which
V266 and 26S. The transistor 266 is a P~N-P transistor
are transmitted as control and warning signals representa
connected in an emitter follower ampliñer circuit. Spuit~
tive of distance and speed of the leading vehicle, respec
-able biasing potentials are applied to the base oli the 50 tively. These antennas may, for example, be loops which
transistor 266 with a biasing resistor 270. The emitter
respond to the inductive iield around the transmitting an
of the transistor 266 is coupled through a capacitor 272
termas 52.
to the base of the other transistor 268.
The antennas 310 is connected to an amplilier 312
An antenna coupling network including resistance
which ampliñes the 4.5 kc. signal picked up by the antenna
-capacitance iilter circuit 274 and a tank circuit 276 is 55 310. The antenna 318 is connected to an ampliñer 330.
connected between the emitter of the transistor 26S and
The amplifier 312 is coupled to a system 314 of circuits
removes the sawtooth wave.
the antenna 52. The tank circuit acts as a trap to pre
which measure the distance between vehicles.
The am
vent spurious signals which might be picked up by the
plifier 330 is coupled to another system 316 of circuits
antenna 52 from aifecting the circuit. The antenna is
for measuring the speed of the leading vehicle.
driven by the amplifier 224 and propagates the signals 60 The ampliñer 312 is coupled to a limiter 320 which
in the output of the adding network 222.
limits the amplitude of the bursts. The limited signals are
The speed signal generating portion of the network
illustrated in FIG. 9 includes the differentiating circuit
226, the amplifier 22.8 and a gate circuit 23€).
rectified in a rectifier 322 and integrated in an integrating
circuit 324. The output of the integrating circuit is con
nected to a terminal 326 and to a meter 328.
The ter
The differentiating circuit is provided by a capacitor 65 minal 326 may be connected to the interlock or speed
278 and by a pair of resistors 280 and 282.
The re
override circuit illustrated in FIGURE 14 and described
in detail hereinafter. For purposes of accommodating
the transistor circuitry in the override circuit it will be
desirable to polarize »the rectifier 322 with respect to
which might otherwise damage4 the amplifier 228. The 70 ground so that increasingly negative voltages are produced
dilîerentiating circuit therefore produces a positive pulse
with increasing distance of the vehicle ahead from the
at each step of the step wave. The leading edge of each
vehicle carrying the receiver, instead of increasing posi
step Wave produces a negative pulse which is disregarded
tive voltages. When the distance from the leading ve
sistors 280 and 282 are returned to ground through the
source of negative voltage at -B. The resistor 280
also serves to suppress transient negative peak voltages
bythe amplifier circuit 223.
hicle is short the absolute amplitude of the voltages will
>The aiiipli?ierv circuit 228 includes an N-P-N transistor 75 be small in any case.
The limiter 320, the rectifier 322, the integrating circuit
324 and the meter 328 serve to measure the distance be
tween vehicles, as was explained in connection with FIG.
charge to this certain magnitude before the relay driv~
ing circuit operates to permit transfer of the voltage from
the timing capacitor to the storage capacitor. The volt
6 of the drawing in the case of the limiter 142, the recti
age on the storage capacitor will then decrease to a
fier M4, the integrating circuit 146 and the meter l5?. Ul voltage magnitude less than the certain magnitude Of
shown in that figure. The output of the integrating cir
cuit may be coupled to a servo system for automatically
controlling the accelerator and brakes of the vehicle to
slow and stop the vehicle before a minimum safe dis
tance between the vehicles is reached.
The 8 kc. signal corresponding to the speed of a vehicle
which leads another vehicle along the highway is limited
in a limiter circuit 332 and produces bursts of limited 8
kc. oscillations corresponding in time of occurrence to
times of occurrence of the leading edges of each of the
steps of the control voltage.
These bursts trigger a monostable multivibrator 334-.
Such multivibrators are well known and produce a single
voltage previously maintained thereon. Therefore, if a
constant speed is held by the leading vehicle, the storage
capacitor is kept at the same voltage and only leakage
losses in voltage across the storage capacitor is recovered.
if the vehicle speeds up or slows down, the storage capaci
tor is discharged or charged, respectively, to the voltage
across the timing capacitor.
An anticipation circuit 346 is connected between the
storage capacitor and the transfer circuit. Conceivably,
a vehicle may stall on the highway so that the next suc
cessive burst of 8 kc. oscillations does not occur, or the
vehicle may slow down to a speed such that the timing
capacitor may be completely charged before the next
square wave pulse for each trigger pulse. Such square
successive burst of 8 kc. oscillations is transmitted. In
wave pulses are illustrated in the wave form shown adja 20 the event that a vehicle stalls or slows down rapidly,
cent the output connection extending from the multivi
the voltage across the timing capacitor and the voltage
brator 334. The pulses from the multivibrator operate a
across the storage capacitor will assume different levels.
relay driving circuit 336 which includes a relay. The re
The anticipation circuit responds to these different levels
lay and the relay driving circuit control a timing circuit
in voltage and permits transfer of voltage from the timing
338 which is operative to decode the pulses and provide 25 capacitor to the storage capacitor. The storage capacitor
the speed information. More particularly, the timing cir
is then permitted to charge in anticipation, to a Voltage
cuit 33í5 provides a Voltage which varies in accordance with
which indicates a stalled or Very slowly moving vehicle
the speed of a vehicle which leads the vehicle equipped
on the highway.
with the illustrated receiver, as both vehicles travel along
The voltage across the storage capacitor is amplified
the highway.
30 in an ampliiier 31th and applied to a metering circuit
A voltage corresponding to the speed of a leading ve
351i. The metering circuit is operative to supply in
hicle may be obtained by integration or differentiation
creasing voltage output with increasing speed of the
of the distance or speed signals, respectively, as was de
vehicle. For example, in the circuit to be described here
scribed in connection with FIGS. 6 and 7 of the drawings.
inafter, a more negative voltage indicates increasing
However, such differentiation and integration operations
speed. lt is desired to provide a less negative voltage as
are not altogether desirable, particularly in the case where
an indication of increasing speed. This circuit essentially
the speed of relatively slowly moving vehicles is being
therefore reverses the phase of the voltage developed
detected. The decoding or timing circuit 33S which is
across the storage capacitor. The metering circuit there
shown in FIGURE l2, and which will be described in de
fore provides fail-safe operation of the speed receiving
tail in connection with FIGURE 13 of the drawings, op 40 system since it provides an output indicative of minimum
crates to derive, from the S kc. distance signal, a voltage
speed in the absence of a signal voltage. Thus, any fail
which increases uniformly with increasing speed of the
ure in the receiver or transmitter portions of the system
vehicle regardless of the speed at which the vehicle is trav
will produce a danger or Warning response or control
voltage. The output of the metering circuit may be con
This timing circuit 333 includes a timing capacitor 45 nected to a terminal 354 and to a meter 352. The termi
The charging and discharging of this capacitor is
nal 354i is connected to the interlock or speed override
controlled by the relay in the relay driving circuit 336.
circuit which will be described hereinafter in connection
rl`hus, the capacitor may, for example, be permitted to
with FIG. 14 of the drawings.
charge or discharge to a voltage determined by the fre
Referring, now, to FIG. 13, the details of ’the timing
quency of the bursts of oscillation produced when the 50 circuit 33d, the ampliñer 348 and the metering circuit
vehicle passes over a block on the highway. The voltage
across the timing capacitor is transferred by a transfer
circuit 343-2 to a storage capacitor 344. The transfer
circuit may be an impedance transformation network
35h are illustrated.
The circuits are shown entirely as
transistor and semiconductor circuits. It Will be appre
ciated, however, that electron tube circuits suitable for
performing similar operations may be used. The timing
which prevents loading and unwarranted discharge of the 55 capacitor 34h is connected through a charging resistor
timing capacitor 34d due to variations in impedance in
36@ to a source of operating voltage indicated at -B.
the circuit of the storage capacitor. Such variations in
Negative voltages are used to operate the circuits since
impedance may result in the charging and discharging of
the circuits use primarily type P-N-P transistors which
the storage capacitor.
are more readily available with a wider variety of oper
The relay driving circuit is connected to the storage 60 ating characteristics at the present time.
capacitor and operates to permit transfer of the voltage
One side of the timing capacitor 3426 is connected to a
across the timing capacitor to the storage capacitor on
point of reference potential such as ground. The other
occurrence of each burst of 8 kc. oscillations. Since
side of the timing capacitor 349 is connected to the ñrst
the rate of occurrence of the bursts of 8 kc. oscillation
of three transistor amplifier stages constituting the trans
depends on the speed of the leading vehicle, the timing 65 fer circuit 342. rl`hese amplifier stages include three type
capacitor will have charged to some magnitude or" voltage
l>-N-P transistors 362, 354i and 366. Each of the stages
at the time a succeeding burst occurs. This voltage will
is connected as an emitter follower stage and serves to
be a certain magnitude if the leading vehicle maintains
progressively reduce the impedance of the output of the
a constant speed. If the leading vehicle decreases in
transfer circuit with respect to the input thereof. The
speed, the magnitude of the voltage transferred to the 70 input of the transfer circuit is the base of the transistor
storage capacitor will increase, since the timing capacitor
352 in the first stage and the output of the transfer cir
will have charged to a voltage magnitude higher than
cuit is the emitter of the transistor 3% in the third stage.
the certain magnitude of voltage stored on the storage
A discharge circuit for the timing capacitor 346` is pro
capacitor. On the other hand, if the leading vehicle in
vided by a transistor 368. The collector of this tran
creases in speed, the timing capacitor is not permitted to
sistor is connected to the timing capacitor 340. The
emitter of the transistor is connected through a resistor
lat ---B. A portion of this resistor 406 may be a variable re
370 to ground. Thus, the emitter collector path of the
sistor which is useful in Calibrating the measuring circuit.
transistor 36S is connected across the capacitor 34d. rline
emitter of the transistor 36S is also connected through a
resistor 372 to the source of operating voltage at -~B.
The discharge circuit is controlled by a switch 374 oper
The collector of the transistor 432 is connected «to ground
through a resistor 4tl8. A voltage divider 410 is con
nccted between ground and the source of operating volt
age at -B. The base of the transistor 402 is connected
to this voltage divider so that the voltage at the base of
ated by a relay 376 which is in the relay driving circuit
335 shown in FÍG. 12. This relay 376 also operates
another switch 373 which is connected in circuit with
the storage capacitor 344, as will be explained hereinafter.
The tongue of the switch 374 is connected to a capacitor
the N-P-N transistor 462 is normally maintained posi~
tive with respect -to the emitter thereof. A potentiometer
412 is connect-ed across the resistor 438. The meter
352 is connected from the arm of the potentiometer to
charge circuit through a resistor 382. The base of the
transistor 368 is also returned to ground through another
resistor 384. The capacitor 38@ is charged to a negative
ground. The output voltage to be measured appears
across the potentiometer 412. The terminal 354 is also
connected to the ungrounded side ofthe meter 352. This
terminal is provided for connection to the override cir
cuit which will `be described hereinafter in connection
with FIG. 14.
in operation, the relay 376 is energized to pull in on
voltage when the relay 376 pulls in, since the tongue of
occurrence of a burst of the 8 kc. oscillations which ener
the switch 374 then contacts the fixed Contact 375 which
is connected through a resistor 386 to the source of op
336 as was explained above in connection with FlG. l2.
380. One side of the capacitor 380 is grounded. The
tongue is normally (before relay pull-in) on a iixed
contact 373 of the switch 374. This fixed contact 373
is connected to the base of the transistor 3x38 of the dis~
gizes the multivibrator 334 and the relay drive circuit
The capacitor 380 is then charged to a negative voltage
above ground by way of the circuit including a set of con
tacts 374 and the resistor 386. When the relay 376 re
storage capacitor 344 through the switch 373 of the
relay 376. The storage capacitor 344 may be of larger 25 leases vafter the pulse from the multivibrator terminates,
the capacitor 380 discharges through resistors 382 and
value of lcapacitance than the timing capacitor 340 so
384. A negative voltage then appears on the base of
that its time constant is longer. Charge will therefore be
the transistor 368. This transistor 36S is normally cut
Vstored in the storage capacitor 344 for a longer period
off, because of the negative bias applied to its emitter
of .time than charge is stored in the timing capacitor 340.
The anticipation circuit 346 is provided by .a diode 388 30 through the resistor 372, and is rendered conductive only
when the relay 376 releases. A low impedance dis
connected between the emitter of the transistor 366 in
charge path through the resistor 370 and the emitter-to
the transfer circuit and the storage capacitor 344. The
collector path of the Átransistor 368 therefore is established
anticipation circuit 388 eiiectively shunts the switch 37S.
across the timing capacitor 340. This capacitor 340 then
The diode 388 is polarized so that it conducts only when
discharges almost to ground potential. The capacitor
the voltage across the storage capacitor is greater than
380 discharges quickly and in a minute fraction of the
the voltage at the output of the transfer circuit. Since
erating voltage at -B.
The Voltage transfer circuit 342 is connected to the
the voltage at the output of the transfer circuit corre
time up to when the next burst of 8 kc. oscillations might
occur. The timing capacitor 340 therefore begins to
charge through the resistor 360 to -a negative potential.
the diode 33S wil-1 conduct when the voltage across the
timing capacitor 340 is more negative than the voltage 40 This negative potential appears- on the base input of the
impedance .transforming circuit 342. A voltage corre
-across the storage capacitor.
sponding to the voltage across the timing capacitor 340
The storage capacitor 344 is connected to the input
»therefore continuously appears during the discharge of
of the ampliiier 348. The amplifier 348 includes a pair
the timing capacitor 340 at the emitter of the transistor
vof transistors 399 and 392 of the P-N-P type. These
sponds to the voltage across the timing capacitor 340,
transistors are connected in cascaded emitter follower 45 356.
Upon occurrence of the next pulse `due to the 8 kc.
circuits. Accordingly, the impedance at the output of the
amplilier 348 is lower than the impedance at the input
burst oi oscillation, the relay 376 again pulls in. The
set of contacts ‘373 connects the storage capacitor 344
thereof. The output of the amplifier 348 is derived across
to the emitter of the transistor 366. The storage capac
the emitter resistor' 394 of the transistor 392, The input
of the amplifier is at the base of the iirst transistor 399. 50 itor 344 is .then quickly charged through a charging
circuit having a low time constant to a voltage approxi
A resistor 396 is connected to a -point on an emitter
ma-tely equal to the voltage across the timing capacitor
resistor 398 in the iirst emitter follower stage of the
341). The impedance transformation in the impedance
amplifier 343. This resistor 396 and a porti-on of the
.transforming network 342 provides a low value of resist
emitter follower resistor 39S provide part of a discharge
ance in the charging circuit of the storage capacitor 344.
circuit .for the storage capacitor 344. This discharge
This low time constant makes the time of charging of
circuit includes the -base-to-emitter path in the transistor
the storage capacitor a minimum.
390. The resistor 396, which is connected to the source
After Ithe pulse terminates, the relay 376 releases. The
of operating voltage at -B, sets the minimum voltage
tongue of the switch 378 breaks its connection before
'to which the storage capacitor 344 may discharge. A
portion of the resistor 398 may be provided by a poten-ti 60 connection is made in the other switch 374. The stor
age capacitor holds the charge. The timing capacitor
ometer in order to calibrate the measuring circuit 359.
349 is »discharged by the `action of the discharge circuit
The measuring circuit ‘359 includes a P-N-P transistor
including the Itransistor 368, and a voltage equal to the
409 and an N-P-N transistor 4il2. The base of the tran
peak voltage across the capacitor 34@ is maintained
sistor 400 is .connected to the output ot the amplifier 348.
lacross .the storage capacitor î344». After discharging, the
The emitter of the transistor 40@ is connected through
timing capacitor 346 again lbegins charging towards a
a resistor 464 to the same point on the emitter resistor
338 of the transistor 39B as is the resistor 3%. The
transistor ¿filû is eiiectively in a D.C. ampliiier stage
kwhich is operated at a potential somewhat above ground
`equal to the voltage to which the timing capacitor 349
is discharged. rI'his improves the linearity of operation
_"of the amplifier.
The emitter of the N-PLN transistor 4iì2 andtheicol
I»lector of the P-N'-P transistor' 40G areV connected', through
a common resistor 436, to .the source of operating voltage
Anegative voltage.
Upon occurence of the next pulse due to the 8 kc. oscil
lations, the relay 376 again pulls in. Puilses of 8 kc. oscil
lation occur at equal time intervals if the vehicle main
tains constant speed. It the vehicle speeds up, the pulses
will occur sooner in time; if the vehicle slows down, the
pulses will occur later than would be the case if the vehicle
maintained a constant speed. Thus, when the relay 376
pulls in, the capacitor 349 will have charged to the same
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