US2834001A - Traffic cycle selector - Google Patents

Description

May 6, 1958 H. A. 'wlLcox 2,834,001

TRAFFIC CYCLE SELECTOR Filed March 25, 1956 2 Sheets- Sh eet 1 INVENTOR HARRY A.Wu.cox BY ATTORNEEY ay 6, 1958 H. A. wlLcox TRAFFIC CYCLE SELECTOR 2 Sheets-Sheet 2 Filed March 23, 1956 CVCZE SEL EC TO I? LL fl nR w w w HR .4 1. D 86k 36 5 z 3% n U 2 R E M w m w R M M m as E H M INVENTOR HARRY A.Wu..cov-

ATTORNEY TRAFFIC CYCLE SELECTOR Harry A. Wilcox, Westport, Conn., assignor to Eastern Industries, incorporated, East Norwalk, Conn, a corporation of Delaware Application March 23, 1956, Serial No. 573,465 9 Claims. (Cl. Mil-41) This invention is an improvement on the invention disclosed in Patent No. 2,288,601, which was granted to John L. Barker on July 7, 1942, and relates to traffic signal control apparatus and especially to cycle selecting apparatus for use in conjuntion with a master controller or master timer which governs a number of local or individual intersection traflic signal controllers for control of tralfic right of way at individual intersections. The master controller may also serve directly or indirectly as a traffic signal controller for one intersection.

The cycle selecting apparatus is arranged to periodically effect a choice from a number of available master timer operating cycles of one cycle whose length or control features shall be best suited in accordance with the general level of trariic density for most effective dispatch of such trafiic thru the area served by the master timer.

In addition the cycle selector embodies apparatus to select and render effective various ones of a number of available difierent plans of operation for the master controller. For example the individual local controllers at several intersections of cross roads along a main road may be co-ordinated by the master controller in accordance with a progressive traffic control system in which accord of right of Way to the main road is made progressively by the several local signal controllers, or may be co-ordinated with a synchronized system in which accord of right of way at the several intersections is substan tially simultaneous, or the local controllers may be freed from co-ordination, all depending on which cycle of the master controller is being rendered effective by the cycle selecting apparatus.

The individual intersection controllers may be of the full or semi-traific actuated type in which the transfer of right of way to one road from another to initiate a right of Way signal cycle is made responsive to traffic actuation of a traiiic detector in such one road, or may be of the fixed time (non-traflic actuated) type, or some may be of one and others of another type, or they may be changed over from one type to another under various conditions.

Accordin ly it i an object of the invention to provide an improved cycle selecting apparatus for use in conjunction with a master tratfic signal timer having a number of different operating cycles to effect periodically a selection of such available cycles in accordance with the trafiic density level as determined by the number of trafiic detector actuations over a cyclically repeated counting period.

Another object is to provide an improved cycle selector of this type having a scale of cycle positions. for such different cycles and which, in the event of traffic reaching a predetermined count within a preset cyclic counting period while operating in one cycle position will hold such cycle position for the succeeding such counting period, and in the event trathc reaches only a substantially lower predetermined atcnt O count will cause operation in Patented l t lay 6, llllib the next lower cycle position in the succeeding such counting period.

A further object is the provision of an improved cycle selecting apparatus for use in conjunction with a master tralfic signal controller having a number of operating cycles of ditierent time lengths, to count traffic during a time period while the master controller is operating on one selected cycle and to select the next longer cycle or next shorter cycle or the same cycle respectively for the next counting period in accordance with whether the tratfic count is materially greater or less or substantially equal to respectively a predetermined amount to which such time cycle is suited.

Another object is to provide traffic signal cycle selecting apparatus for control of a master controller for a series of individual intersection traific signal controllers along a road and having a number of different traflic signal cycles including one minimum cycle providing independent control of the individual controllers responsive only to traffic actuation of a traffic detector at the individual intersections, a number of other cycles of successively longer time length providing co-ordinated control of the several individual controllers to have accord of right of way proceed progressively along the road at successively lower trafiic speeds, and a cycle of maximum length providing synchronized co-ordinated control of the individual controllers for substantially simultaneous accord of right of way, the cycle selector counting tratfic actuations over a time period while providing one selected intermediate cycle for example, and shifting to the next longer cycle or the next shorter cycle or retaining the same cycle in accordance with counting more or less trafiic or substantially the same traffic respectively as a predetermined amount or" traffic to which the cycle is suited.

A still further object contemplates the use of a condenser and gas filled triode counting means for registering the number of actuations of tratlic sampling detectors over a counting period for determining the density of trafiic.

Still another object provides that the present cycle selector equipment in addition to determining master timer cycle length is eiiective also in determining in accordance with the level of traflic density Whether individual local intersection controllers shall operate under one or another of various co-ordination plans under the master timer or shall operate free and independently of the master timer.

Another object provides that the cycle selecting equipment cause a unit shortening change in master timer cycle length if the trafiic falls below a predetermined required tratfic level in a single counting period or cause a unit lengthening change in cycle length if the traffic attains a higher level than the predetermined level in a single counting period, or cause the cycle length to remain unchanged if the trafiic level so Warrants it.

In a number of instances where a plurality of individual intersection trafiic signal controllers are located at related intersections along a main road continuous movement of platoons of traffic is facilitated by rendering the cycles of operation of the local controllers subject to the governing influence of a master timer which determines when each local controller may start its cycle of operation. Local controllers of both full and semi-actuated type as Well as fixed-time cycle controllers have been co-ordinated under a master timer.

It-has long been appreciated by trafiic authorities that the Widely varying conditions of traflic flow or distribu tion during a 24 hour period cause considerable maladjustment and loss of efiiciency in many tratfic signal systems in which the same co-ordination pattern or master timer cycle is imposedv continuously on the local con trollers and some automatic selection among several different cycles would be desirable. ordinary trafiic densities a progressive co-ordination system in which the several local controllers are each. permitted to transfer right of way from-the main road at progressively staggered intervals in the mastertimer cycle may be found most satisfactory for traffic movement, While in periods of very heavy traffic concentra tion a synchronized co-ordinated system wherein all local controllers simultaneously make'transfers of right of wayfrom the main road may be desirable to provide a sufli ciently long cycle to care for the heavy traffic without excessive reduction of traflic speed. in some instances of very heavy traflic it is desirable to insert an exclusive pedestrian period in the cycle but such an addition to the cycle may make the cycle too long for proper progressive operation so that a change to synchronized operation may be necessary.

Further, in periods of very light tratlic the individual controllers cause least delay to traffic if each is free of co-ordination and arranged to operate as an independent tratiic actuated controller. Additionally it has been demonstrated that when operated as a progressive coordinated system greatest facility of traffic movement is obtained by utilizing master timer cycles of increased length as the density of traiiic increases and its speed decreases, since the proper cycle-length for progressive systems is inversely proportional to the speed of traffic through the system.

The present invention provides cycle selector equip: ment responsive to traffic actuation for use in conjunction with a master'timer in a system of this character and in which the local controllers will be operated on a master timer cycle'of suitable length and character depending.

upon the density level of traffic, the local controllers being For example for" freed from co-ordination on the shortest cycle being.v

co-ordinated on a synchronized plan on the longest cycle, and being co-ordinated on a progressive plan on intermediate length cycles.

For the purposes ofthis application the master-controller or timer controlled by the cycle selector may be considered to be for example a circuit controller driven through gearing by an induction disc type motor at any one of a number of different speeds by one of a number of suitable driving coils depending upon which one of 4 the coils is energized. From suitable cam controlled contacts, operated by such motor, circuits are closed to each of the individual intersection controllers for governing their operation.

A local controller may for example be. of the type@ which normally rests in ,a position where right of way is accorded to the main road, but upon actuation of an associated cross road trafiic actuatable device the con-:-

troller operates through a cycle in which right of way is transferred to the cross. road and subsequently re-.

tion from the master timer, the interruption of this. pro-.-

ventive impulse at a predetermined point. inthe master timer cycle being the signal for permitting transfersof. right of way fro-m the main road by the local controller:

in response to actuation. Many other suitabletypes of master timers or local controllers are well-known. in the t.

art and readily adapt themselves for substitution for the ones mentioned for purpose of example. For instance instead of transmitting to the local controllers a con tinuous preventive impulse which is interrupted once in each cycle to allow each local controller totransfer right of Way from the mainroad, the master'tinier may" be arranged to send out permissive impulsesf'of' short duration atthe. desired; cyclic intervals. In' this; case -the terminal equipment;in'rtheszlocal controllers would be nextlower'one underconditions of falling traflic volume 4... arranged to complete operating circuits upon receipt of such impulsesrather than upon cessation of the preventive impulse.

Examples of systems illustrating local traffic actuated signal controllers subject to preventive impulses from a master timer are disclosed in Patent 2,241,047, issued May 6, 1941, to H. A. Wilcox. Examples of systems having local traific actuated signal controllers subject to periodic permissive impulses from a master timer are disclosed in Patent 2,110,723, issued March-8, 1938, to

C. D. Geer and I. L. .Blach; Patent 2,122,411, issued July 5, 1938, to E. H. Barnes; and also in Patent 2,105,443, issued January 11, 1938, to A. P. B. Renshaw, the latter patent also disclosing a local cyclic controller of the non-tratiic actuated which is subject to recycling permissive impulses from the master timer.

The cycle selector according to the present invention is arranged to cause operation of the master timer on any. one of its available cycles. in accordance with the trafiic density level which is determined by the number of actuations of a tratiic actuatable device or devices suitably. located for sampling traffic movement within a predetermined counting period.

While any one of the several cycles, except the shortest, is ineffect, a predetermined appropriate level of traffic is required over a single counting period in order'for the selector to retain such cycle for another counting period. The level required to hold on one cycle is preferably different from that required to hold on another cycle. If'at the end of a counting period the predetermined required .traffic level has not been reached the selector will place in effect the next shorter master timer cycle. Should, however, the predetermined required traffic level be sufficiently exceeded, the selector will render effective the next longer cycle for at least the duration ofthe. next counting period. that the cycle in effect is the best cycle for the counted trafficlevel, the samecycle length will be retained.

The counting period utilized is preferably several times as long as the longest master timer cycle, a six-minute counting. period being particularly convenient as it is sufficiently long to average out the relatively large momentary fluctuations in trafiic flow often experienced, and to avoid abrupt changes, and to permit four ninety secondmaximum cycles to occur within .the counting period for example. The six minute counting period is sufficiently short, however, to permit the cycle selector to change from the minimum cyclethrough the four successive traffic intermediate cycles to themaximum cycle in thirty minutesin case the traificshould, in an unusual case, increase as rapidly as this.

Connection is also made by the cycle selector so that whentheshortest master timer cycle is being rendered effective, circuit is completed to permit operation of the local controllers as free and independent of coordination by themaster timer. When the master. timer is made to operate on its longest cycle the cycle selector causes completion of a circuit to switch over to a synchronizedplan of coordinated operation in which all of the local controllers. are permitted to transfer right of way to their respective cross roads simultaneously. On the other available cycles the master timer shown is arranged to govern the local controllers in accordance with a progressive coordinated system, but any desired plan of operation may be set up. Other changes in the form of local controller cycles or in the pattern of coordination, as for instance inclusion under one or more cycle plans of pedestrian periods in the local controller cycles, may be arranged to be effective as desired will hereinafter appear.

The cycle selector disclosed herein differs from that disclosed in Patent "288,631, primarily in the method or means by which itsteps down from one cycle to the andthdmetho'd or means which the system employs to If it is observed determine the stepping up, holding or stepping down operation from trafiic counted in the counting period. Since the major amount of crcuitry in either selector is associated with the step-down function the invention disclosed herein is considerably different than the invention disclosed in Patent 2,288,601.

The counting function, the step-up function, and the stay function of the invention disclosed herein and that disclosed in Patent 2,238,601 are somewhat alike but employ different means for accomplishment.

The step-down function is also accomplished dirTerently. In connection with the latter this improved device includes six individual relays, one associated with each cycle position. When the ep-down function starts, the relay associated with the former cycle position pulls in and locks in through its own contacts, thus indicating the position from which it started. The stepping switch is then notched rapidly around by means of a self-interrupting circuit until it arrives at the position next lower than the one from which it started.

A description of the cycle selector according to the invention and its manner of operation will now be presented with reference to the accompanying sheets of drawings in which:

Figures 1 and 2 when placed one over the other form a circuit drawing for an embodiment of the cycle selector together with connections to a form of master timer in conjunction with which the cycle selector may advantageously be employed. Connections to terminal equipment to be provided in each of several local intersection controllers are also indicated in Figs. 1 and 2. Fig. 3 is a schematic diagram outlining illustrative connections between the cycle selector and master timer and local controllers for three intersections. Figure 1 illustrates the cycle selector proper and Figure 2 shows the connections to an illustrative master controller and associated cycle function change over means. Fig. 3 shows three intersections of cross roads I, II and III respectively with a main road. The trafiie signals S at the respective intersections may be of any well known type for controlling the right of way of traffic under control of the local signal controllers indicated schematically in the drawings.

The local signal controller at cross road I is illustrated as of the fixed time or non-tralfic actuated type. The controll rs at cross roads II and III are illustrated as of the traific actuated type connected with trafiic detectors 2131, 2132 and 3B1, 3132 in their associated cross roads, and may he of a number of different forms known in the prior art some of which are represented by the several patents mentioned above for example.

The connections for the detectors and signals are outlined in single line form for simplicity as the details of such connections for detectors D1 and D2 are disclosed in Fig. l, and examples of connections of the signals and of the cross road detectors are disclosed in the prior patents mentioned above.

Leads 94, 95 and 96 are energized by the master timer during the part of its cycle in which it is desired to prevent local controller cycle initiation and are deenergized during the remainder of the master timer cycle in which it is desired to permit local controller cycle initiation.

Direct connection of lead 96 from the master timer to the local signal controller at cross road III is illustrated in Fig. 3 and this controller is assumed to be adapted to have its trafiic signal control cycle initiated by deenergization of the preventive impulse lead 96. Connection to the signal controllers at intersections I and Ii is illustrated by way of terminal relay lCR and ZCR from preventive imaulse leads )4 and 95 respectively to convert to permissive impulse for these latter controllers which are assumed to be of the type adapted to have their traffic signal control cycle initiated by a permissive energizing impulse for example.

Relays ICR and ZCR are energized by the preventive impulse energization of leads 94 and 95 respectively and are deenergized between preventive impulses to close their respective back contacts lcrl and 2cr1 to connect one or the other of the power supply leads to provide permissive energization impulses to the respective local controllers at I and II.

The embodiment of the cycle selector in accordance with the invention disclosed herein is set up to efiFect a choice from six available cycles of different lengths obtained through separate driving coils in the master timer. These cycles will be denoted as cycles A, B, C, D, E, and F respectively. Obviously more or fewer cycle lengths or plans of operation for the local controllers may be utilized by constructing the master timer with a different number of driving coils. Connection to the several coils is made by a switch finger or wiper over one bank of a step-by-step multi-pcsition switch of the type ordinarily employed in automatic telephony as a line switch.

The line switch is a 6 bank 20 position type. The Wipers for certain of the banks are shown as two arrows contacting the fixed contact. The two arrows indicate that this is a bridging wiper, which makes connection with the next fixed contact before it breaks connection with the previous one. The wipers of other of the banks are shown as single arrows, which means that these wipers are the non bridging type, breaking connection with one contact before making connection with the next contact.

Operating in conjunction with this stepping switch is a group of four cam operated contacts which are driven for example by a synchronous motor.

For purposes of describing the invention a 6 minute cycle has been assumed, however other time periods may selected. Near the end of the 6 minute cycle the cam designated N closes contacts 157 associated therewith for about 2 seconds thereby applying A. C.power for the step-up test. As this power is removed the cam designated T closes contacts 164 associated therewith for about 7 2 seconds thereby applying A. C. power for the stay test. As this power is removed the cam designated V closes contacts 166 associated therewith for about 3 seconds thereby applying A. C. power for the step-down test.

After contacts 166 open cam S which had maintained contacts closed since the beginning of the 6 minute cycle allows contacts s to open for a period of 2 seconds and then closes contacts s again.

The time periods given for the cam operation are approximate and the proper sequence of operation is critical only. This series of tests may take place within the last 10 seconds of the 6 minute period.

Each actuation of the traflic-sampling detectors adds an increment of charge to a condenser. If the traffic level is suffieiently high to cause the charge on the condenser.

to attain a predetermined value required for discharge through a gas-discharge tube by the instant the contacts 157 are closed by the N cam the stepping switch is operated to advance its wipers one contact position to set up the next longer master timer cycle (excepting when the longest cycle is already in use). This condition thus eifects an increase in cycle length by the selector in order to facilitate traffic movement at the new higher 'traflic level.

Should the condenser charge not have attained the predetermined tube discharge value required for the in stant when the contacts 157 are closed, the stepping switch maintains its position and the contacts 164 are closed by the cam associated therewith. If the condenser has achieved sufficient charge to require the stepping switch to remain in its present position closure of the contacts I to discharge. the gas tube at closure of the contacts 157 ass-mor or the contacts 164, indicating that =the tratiicdensity has diminished since the preceding counting period, the contacts 166 upon closurethereof 'by the'cam associated therewith will cause the'wipers of the steppingiswitch' to be'advancedrapidly forward and come to rest in a position energizing the master timer driving coil for a cycle next shorter than the one effectiveduring the in stant counting period.-

Provision is made-for varying the relative weight or effect of-each'detector actuation while the cycle selector is renderim any one of the six available cycles effective so that-the required level of traiiic to cause an increase incycle length from the E or next longest cycle" to-the F or longest cycle for example may be considerably greater (or less) than-that required to shift for instance from the-A or shortest cycle to theBor next shortest intermediate cycle. These density values may be adjusted in dependentlyas desired by-manipulating dials provided for this purpose andcalibrated in number of cars per hour required to hold on B-c'ycle, for example,=these dials controlling potentiomcters which determine the grid biasvoltage required to operate the gas-filled triode.

Referring now to the figures of drawings which when placed Fig. 1 above Fig. 2 constitute a circuit drawing for the cycle selector apparatus and its connection to one form ofmaster timer. A six-bankswitch having twenty V contacts on each bank is shown=although a switch having a different number of banks might be used, or one with only six contacts per bank for instance.

Each bank is provided with a corresponding wiper arm or connecting finger which rotates over contacts 1 through 20- in turn and then ire-engages contact 1 again,. All

wipers are simultaneously advanced one step or position ata timeupona cycle of energization and deenergization of motormaguet MM. Driving magnet MM is op tacts' 2, 3 or the B-cycle 'coil MB is energized and so on.

Direct' current forcharging condenserKC by units of traffic isifurnished-from rectifier tubeRFl suitably connected to.the secondary oftransformer TF; Filter condenser KF serves to provide a steady curren't'on the D..C. output. Lead 51 is :the common groundedside of bothnthe' -A. C. sourceandD. C., is indicated by a minus. sign in a circle, and corresponds to point 85 on the potential divider 122122"in the lower part of Fig. i

1. Lead 52, also identified by. a plus sign in a circle, is

the ungrounded side of the .A. C. source and lead 53 the positive side of the D. C. circuit, the lead 53 also being identified with a plus ina square; Also negative D. C. lead 53 is identified'with'a minus in a square, which provides a negative biasivoltage source with respect to ground siredlocation in one or more of the roadways involved in the traffic signalling system and any desired number of detectors may be employed to obtain a representative traffic count.

The manner of counting cars by means of detector actuations will now be described. Cars are counted by having each actuation of detector D1 or D2 apply power tothe coil of relay DR, thus placing a smallcharge.

of' electricity into condenser KC. For purposes of this illustration KC has a value of 5 told. it is, of course, understood that this particular value is illustrative only. in the present embodiment, separate unit condensers are employed 'for each cycle-in order that different values of trafiic level required to hold a cycle may be assigned for each cycle. When any one cycle is in operation the effect of a single detectoractuation toward retaining such'cycle in operation, or changing the cycle, is independent of the other cycles. Since fewer actuations per 6 minutes would be required to keep the cycle selection resting on low cycle indication the capacitor for the lower cycle indication positions is larger than the capacitor for the higher cycle indicating positions. Thus, for example, K2 which is the bucketing condenser for cycle B has a .059 mfd. value while K5 which is the bucketing condenser for cycle E has a .035 mfd. value and therefore would require almost twice as' many actuationsto build up an equivalent voltage in condenser KC.

The action of the condenser to bucket charges into condenser KC will now be explained. The circuit-drawing' shows the line switch wipers in the position which corresponds "to cycle B..

It will'be noted that'wiper W5 of bank L5 is feeding voltagerthrough contact No. 2 by means of lead 60 and thus energizing cycle B; The line switch could be in position 2, 9,.or 15 for cycle B since there are three complete sets of 'cycleindications in the 20 points of the line switch, plus 2 skip positions 7 and 20. Tracing now the action resulting from an actuation it is observed that relay. coil DR has one of its terminals connected too at :lead 51 and at thepoint 85-on the potential divider v 122-122 as more fully described below.

The counting periodis established by a plurality of cyclically operated contact pairs shown herein as'camoperated contacts 157, 166, 164, 155 operated respectively by .cams N, V, T, S on shaft rotated by gearing or otherwise by .a synchronous type motor 54 which is continuously driven at constant-speedby a circuit/from plusi lead 52 Jviaxleads 55,, 56,:to minus lead.51-. The

shaftr 75and. cams are :arranged to make one revolutionevery six minutes to constitute-the counting period previously mentioned.

The traflic-sampling idetectors "D1, '.D2; :shown'as pairs of contacts-for illustration may: be zlocatedalinr.any de source-of A. C. potential indicated'by plus in a circle. The other terminal of coil DR is connected to lead 120 which is connected to the lead wire of pressure-indicator D1 or D2 located in the highway. When a car crosses the indicator lead 120 will be grounded and therefore relay coil DR will have A. 'C. applied to it and therefore will be energized. Since the line switch is in position 2 condenser K2 will be in use. Point 121 on the potential divider 122122, which is fed from a source of D. C.

potential by means of leads 53 and 53', feeds D. C.'po-

tential via lead 192 through contacts 127 of relay DR,

up through resistor R2, to capacitor KS and via lead 197 back through, the ground at line 51 and at point between potentiometer 122 and resistor 122, thus charging capacitor KZL When relay coil DR is energized contact =129is closed and contact 127 is opened, and the charge which had been placed in K2 feeds through'contact W3, lead E31, through contacts 129, through condenser KC and to ground thus charging KC slightly. When the wheel of the car goes off the detector D1 or D2, contacts 132", 133" and 1341' respectively and the commonv adjusting resistors or potentiometers136aud 137. The" iadjustrn'ent at 132 is for-"cycle Aand'the"adjustmentht' 129 open and contacts 127 close again, thus permitting 134 is f or cycle F while the adjustment at 133 is for cycles 13, C, D, and E. These adjustments permit an operator to enable the cycle selector to arrange the number of actuations per timing interval which corresponds to the various cycle selections. Each potentiometer is part of a potential divider system by means of which the grid voltage of gaseous triode tube 135 can be adjusted. Tube 135 is a gas filled triode tube, the breakdown voltage of the gas being controlled by grid 142 in the usual manner. In the drawings a minus sign in a square represents negative D. C. voltage which is approximately 40 volts more negative than the minus sign in a circle which represents ground. The potential divider system just described is connected between extreme negative D. C. Voltage, through resistor 133, through the body of potentiometer 133, through potentiometer 136, through potentiometer 137 and resistor 138 in parallel, to ground. Thus the arm on potentiometer 133 will pick off a potential which is more negative as the knob is rotated to the left or a less negative if the knob is rotated to the right. The selection as to which potentiometer 132, 133 or 134 is to be used is made by Wiper W2 of the line switch bank L2. in the figures where cycle position B is shown in operation wiper W2 is in such position that potentiometer 133 has been selected. The center arm of potentiometer 133 is therefore connected through the line switch, and through a filter network consisting of resistor 139 and resistor 14% and condenser 141, to the grid of tube 135. It is seen that lead 142 connects wiper W2 to the filter network. Tube 135 as indicated previously is a gaseous triode. For any given potential on grid 142 no current can flow between plate 143 and cathode 144 until the plate voltage exceeds a critical value of approximately times the value of the grid voltage. For example, if the grid voltage were volts negative with respect to the cathode and the plate were 150 volts positive with respect to the cathode, the tube would be in theoretical balance. Any additional voltage on the plate would cause current to start to how from the plate to the cathode, and as soon as this current starts to flow, grid 142 would lose control and the current would continue to flow until toe plate voltage drops nearly to zero. Since the coil of relay CS is in series with output condenser 145 and plate 143, the pulse of current flowing through tube 13% operates relay CS momentarily, causing it to close its contacts 146 which in turn completes a circuit through relay coil AS by means of lead 51, lead 147, contacts 1 .6, lead 14%, lead 149, and lead 150. i

The operation of the system will now be explained by considering a typical cycle. Let us assume that an unknown number of actuatio-ns have bucketed charges into condenser KC so that the voltage on KC has risen to some value. Since cycle B has been used, it is now necessary for the system to determine whether or not cycle B should remain in operation for another cycle or whether cycle A or C should be utilized.

If there had been a large number of actuations during the counting period, at the end of this period, the voltage on KC would have risen to a high enough value to overcome the effect of the selected grid bias as determined by the setting of potentiometer 133, and tube 135 would have flashed, thus permitting relay CS to operate momentarily. Contacts 146 would have applied power to coil AS and contacts 151 of coil AS would have closed, thus permitting power to be fed from lead 51 by means of lead 153, lead 154, contacts 155 (which had been closed by cam S), lead 156, contacts 151, lead 149 and lead 150 thus locking relay AS in and causing it to remain in an energized state.

Near the end of a cycle and while contacts 155 are maintained in a closed position by cam S, cam N will close contacts 157. Relay HF will be in a de-energized condition since it is energized only in the cycle F position (the only function of relay HP is to prevent the cycle selector from stepping up from cycle F, since there is no cycle higher than cycle F). Power is therefore fed from lead 51, through lead 153, contacts 157, lead 158, contacts 159, through contacts of relay AS (which are closed because relay AS is locked in), and to terminal 161 of bridge rectifier RFZ. Terminal 162 of bridge rectifier RFZ is connected to lead 52 and therefore the line switch motor magnet MM becomes energized with D. C. voltage and attracts line switch armature 163 and opens its contact 184. When cam N causes contacts 157 to open, motor magnet MM is deenergized and line switch armature 163 retracts and closes its contact 184 due to the energy stored in a spring of the switch, and the line switch rotor is moved forward into position 3 and cycle C has been selected.

The above has been a description of the step-up function of the system. The step-up can occur only if sulficient quantity of charge has been placed in condenser KC by the time cam N closes contacts 157. If suificient charge for step-up has not been placed in condenser KC then closure of contacts 157 by cam N cannot cause a step-up operation.

Cam T which closes contacts 164 immediately after contacts 157 open serves to operate the stay function portion of the system. This function will be considered now. After contacts 157 open ground is applied to lead 165 by operation of cam T and contacts 164. This re duces the amount of resistance between the center arm of potentiometer 133 and ground, the amount of resistance between the center arm of potentiometer 133 and extreme negative D. C. voltage remaining the same. Therefore grid 142 of tube 135 is made less negative than it was before. If the tube had operated during the stepup function portion of the cycle, this change in grid bias will not have any efiect. However, if the voltage in KC had not been high enough to let the tube flash during or before the brief period in the cycle when contacts 157 are closed by cam N, the making of the grid slightly less negative during the following stay function portion of the cycle when contacts 164 are closed by cam T may cause tube 135 to be operated.

If this occurred, it would indicate that sufficient actuations had been received during the cycle to require that cycle B be maintained. If tube 135 flashes when the new grid potential is applied by the closing of contacts 164, relay CS will operate momentarily. Contacts 146 will close and relay coil AS will be energized and locked in through its own contacts 151 being grounded through contacts 155. Closing contacts 160 now does nothing because contacts 157 are open and therefore MM will not be energized and the cycle selector switch will remain in the same position.

The operation of the system for step-down will now be considered. If the number of actuations on D1 and D2 received during the counting period was too small to bucket enough charge into condenser KC to allow tube 135 to flash by the time of closure of the contacts associated with the N cam or the T cam, then relay coil AS will still be de-energized when cam V closes contacts 166, the contacts associated with cam S remaining closed. Since cam V operates to close the contacts associated therewith after the operation of the step-up and stay functions it is observed that cam V controls the step-down function of the system.

In the situation assumed, where cycle B has been in operation, it becomes desirable that the line switch be placed in the next lower position which corresponds to cycle A. Since the line switch wiper cannot move in the reverse direction the manner in which cycle A position is achieved is to have the switch step forward until'it arrives at a cycle A position which will be position 8 of the line switch. When cam V closes contacts 166,

relay SD will become energized through leads 167,168,

and 169. Contacts of relay SD will close shorting condenser KC'vialead 193' and contacts 170' through our rent 'limiting resistor 171 so that when the counting is resumed in the next counting period,condenser KC will begin with zero charge thereon. Also lead 156 will be -grounded -throughcontacts 155associated with cam S andwill thusgroundlead 172 through contacts 152 of coil'AS. This ground connection will be continued through contacts 173 of relay SD, contacts 174 of relay RS 'lead 198 'and wiper W4 of L4 thereby causing relay BL to become energized. Contacts 175 of relaySD have been closed and ground will be achieved via lead 194 throughcontacts 176 of relay BL thus locking in coil BL so-that it'will remain-energized after wiper W4 leaves position 2. Contacts 177 of relay BL having closed will cause relay coil RS to become energized. This energization will be effected by a circuit from lead 51 through lead '178, contacts 177, lead 179, the coils of RS, lead 180-and lead 52. The operation of this relay will open contacts 174 of relay RS, thus preventing relays CL, DL, EL, FL and AL from being energized as the wipers move forward in their step-down operation. Contacts 181 of relay RS close permitting ground to be applied through contacts 175, lead 194 contacts 182 associated with-relay coil CL and through contact 2 of bankLG,

through wiper W6, lead 183, contacts 181, lead 196, conmots-184 associated with relay MM and to point 161 of bridge rectifierRFZ thereby energizing magnet MM. As the motor magnet armature 163 moves toward coil MM it opens contact 184; but the inertia of the armature causes it tomake a full stroke before dropping out and notching the line switch into position 3. As contact 184 7 doses again, with theline switch in position 3 ground is applied-through contacts 185 associated with coil DL through contact 3, through wiper W6 and through the same path to energize MM again, thus moving the wipers into position 4. In position 4 ground is applied to wiper W6 through contacts 186, which are associated with coil EL, thus causing the line switch to move to position 5.

In position ground is applied through contacts 187 as-' the line Jswitch stop there; The motion is halted in posi-.

tionuS because this is a cycle A position. In order: to

feed power to thisposition both AL and BL would have to bode-energized. When coil BL is energized indicating .that the step-down operation started from cycle B,

cycle A is the position at which the wiper is stopped.

It 'is'noted' that contacts 188 associated with'coil BL and contacts 189 associated with coil AL are in series,

whereas the contacts 182, 185, 186, and 187 each furnish power to a contact representing the next lower cycle to stay oncycle' A if it is already there, or to stop when it gets therein its step-down operation from cycle". B.

The relay BL is released after the step-down operation by theaction of cam.V opening its contacts l66 which in turnreleases relay SD, which opens its contacts to open the lock-in circuit for relay BL previously de scribed.

While .the step down .operation has been...des'cribejd.

abo'vein 'detail "from the cycle" B position itwill be understood thatthe'operation is"similar"for"the cycleC,"

D;=:E,"and -F positions'as a starting point, with the appropriate-relays'CL, DL, EL, and FL serving to remem-. ber-such starting point respectively in place of the relay.

BL in the detailed description above, and the stepping switch'stopping in the next lower cycle respectively.

The system is provided with a safety circuit since if one of the counting detectors should become shorted, or if a car shouldstop with a Wheel on a detector, the bucketing circuits could no longer operate. The cycle selector would react as though there were no more traffic movement and would cause a step-down operation at the end of each 6 minute interval unit-cycle A was'reached. However, it would be best under these conditions to have the selector step up to cycle F thus giving the longest possible cycle.

in order to accomplish this, resistor 190 of high resist-- ance (in the order of 40 meghoms) is connected through contacts 130 associated with relay coil DR to condenser KC. which contacts 130 are closed due to regular actuations is so-small that this resistor cannot have any appreciable eifect on the counting. However, if the detector relay should remainclosed continuously the current through resistorlQil-would eventually charge condenser KC so that it would have sufiicient charge to cause the system tostepup zone-cycle at the end of each counting interval until cycle F was arrived at. This is a safety device incorporated-into the system to insure proper operation.

The relays Z, P and Q control the output power for the ."preventive"-permissive pulses of the master timer and. to the local intersection signal controllers in the coordinated system, and control the optional systems of progressive, simultaneous and free operation, via wires 94,. 95,96 and 93 and 181 in a manner similar to the i. LQBarker Patent 2,288,601 referred to above, and reference may be had to that patent for a more detailed description, except that in Fig. 1 of the present application these relays are under the control of bank L1 and wiper Wlxc-f thestepping switch, and the wiper is connected to the negative A. C. power (same as wire 51) via a back contact 201' of relay RS, so that the power for the system selecting relays P and Q will be interrupted by open ing of contact 2531 during the rapid step-down operation. Obviously if .therelays P and Q were made sufficiently slow acting the wiper W1 could be connected directly to negative A. C. power instead of via contact 201, in view of the, very brief timein passing through any one step or position inthe rapid stepping of the step-down operation.

The relay. Q maybe arranged as shown to be operated in theA cycle 1, 8 and 14 positions with switch SA closed, and switch SQ closed to free the local controller from the master timer control, and the relay P may be arranged to be operated inthe cycle F positions 6, 7, 13 19 and 20 by the switch SP to change from progressive system control of the signalsto simultaneous system control.'- The relay Z is released by operation of relay P to accomplish this.

The output circuits 94,-95, 96, 93 and 101 connect with the corresponding wires in Fig. 2.

Still other arrangements are readily apparent to those skilled in the art; for examplethe -preventive circuits to the local controller might be replaced by permissive circuits under which transfer of right of way from the main road by each local controller could be made only while the impulse was being received, instead of only while interrupted as in the arrangement shown. Substitution of such. permissive circuits would involvea different arrangement of master timer contacts, switches, and change-over relays in lieu of the ones shown.

Under another plan of operation it may be arranged forexample to change-over operation of the individual intersection controllers from traffic-actuated controllers of the full 'orserni actuated typ'e to the fixed time type.

Orthe'controllerscould be arranged to insertin their In normal operation the period of time duringnormal signal cycles a pedestrian period when operating on certain coordination plans; for example the pedestrian period could be inserted while the synchronized coordination plan is effective.

Summarizing it will be seen that cycle selecting equipment according to the present invention is provided in which selection between a plurality of operating cycles for an associated master traffic signal timer is automatically accomplished in accordance with the level of traflic density as determined by traflic detectors situated at a representative trafiic sampling point.

It will be appreciated that the ratio of capacities of the unit charge condensers on successive cycles determines the ratio of traffic to hold on a given cycle (or stepdown from such cycle) to traific to hold on the next lower cycle (or step down from such lower cycle), because the relative capacities of the unit condensers determine the relative weight of each actuation on the successive cycles in charging the cumulative condenser KC.

The cycle selector herein has incorporated in it a multi-position stepping switch and operation of the master timer on the latters next longer cycle is obtained by advancing the switch one position. Operation of the master timer on the latters next shorter cycle is secured by advancing the stepping switch rapidly through a number of positions one less than the total number of available cycle lengths whereupon it comes to rest in the position for causing the desired shorter cycle operation, through relay circuits insuring stopping in the proper position of the scale of cycle positions. Provision is made for preventing jamming or false operation on the longest and shortest cycles.

An arrangement believed novel is also provided in which a condenser and grid-controlled gas-discharge tube circuit normally is used for responding selectively to different volume levels of traffic by providing a normal high grid bias for the step-up level of traffic to substantially the end of the counting period, and then supplanting this with a lower grid bias for the lower stay level of tramc near or substantially at the end of the counting period before the potential step-down and the reset functions at the end of such counting period.

Provision is also made for a relay group which is effective to change over from one master timer coordination plan to another as from synchronized to progressive operation, or to free local controllers altogether from the master timer when the master timer is being operated on one or another of its available cycle lengths in accordance with tratfic requirements.

For purposes of test or control of external apparatus the contacts 191 of relay RS connect positive A. C. power (same as wire 52) to an output lead 2% as Well as to provide a trickle current via resistor 2tl2 to assure release of relay HF after its main operating A. C. power is interrupted. It will be noted that drop-out resistors for such trickle current are provided for the A. C. relays in general to counteract any residual magnetism which might otherwise hold the relay in improperly.

Thus, resistors 22%, 204, and 205 serve as drop-out resistors for relays SD, AS, and RS respectively.

It will be appreciated that the expressions of stepping up and down or forward and backward or the like are used broadly in reference to operation of the selector switch from one cycle position to another. In the present illustrative embodiment a simple standard unidirectional selector switch is employed, which always steps forward but by a novel arrangement is made to step forward to produce the same effect as stepping backward. A two way stepping switch could be employed with separate step forward and step backward magnets but the present arrangement herein disclosed is preferred.

It is to be understood that various other modifications in the structural details, arrangements or physical values of the parts or changes in the designs herein 14 exemplified may be made without departure from the spirit of the invention as defined by the claims.

I claim:

1. In a traffic control apparatus having a plurality of traffic signalling cycles and a selector device for selecting among said cycles in accordance with the amount of tralfic, said selecting device comprising a step-by-step switch having a series of more than two switch positions and providing connections in the respective positions for the several signalling cycles, trafiic counting means, periodic timing means for periodically resetting said counting means, means responsive to the counting of a predetermined amount of traffic by said counting means during the time period of said periodic timing means to maintain said step-by-step switch in a position it has already attained to provide the same signal cycle or the following such time period, means responsive to the counting of a predetermined greater amount of traffic by such counting means during said time period to step said step-by-step switch ahead one position to provide another signal cycle for such following time period, and means responsive to the counting of a predetermined lesser amount of traffic by said counting means during said time period to step said step-by-step switch back one position to provide a third cycle for such following time period, said step-by-step switch having a uni-directional stepping mechanism and a scale of successive positions corresponding to a scale of tralfic count values and repeated cyclically in said series and said stepback means including relay circuits for predetermining stepping ahead of said step-by-step switch to the position corresponding to the next position back in said scale of positions.

2. In a traffic cycle selector apparatus having a plurality of traffic signalling cycles and a selector device for selecting between said cycles in accordance with amount of trafiic, said selecting device comprising a step by step switch having a series of more than two switch positions and providing connections in the respective positions for the several signalling cycles, a traffic actuated device, an accumulator limit device actuatable toward its limit by said traffic actuated device and operating at its limit responsive only to accumulation of a certain amount of trafiic actuation, a cyclic timer device for resetting said accumulator device periodically at the end of its cycle, and electromagnetic means for stepping said step by step switch from one position to the next, means for operating electromagnetic means to step said step by step switch to the next succeeding position of said series responsive to operation of said accumulator device before the end of the time cycle of said timer device, and means for operating said electromagnetic means to step said step by step switch to the preceding position of said series from any one responsive to absence of operation of said accumulator device immediately before the end of said time cycle, said last named responsive means including a relay sys term for predetermining stepping ahead of said step-bystep switch the number of positions required to step only to aposition corresponding to the next position back of its original position.

3. In a traffic cycle selector apparatus having a plurality of trafiic signalling cycles and a selector device for selecting between said cycles in accordance with amount of traffic, said selecting device comprising a step by step switch having a series of more than two switch positions and providing connections in the respective positions for the several signalling cycles, a traffic actuated device, an accumulator limit device actuatable toward its limit by said trafiic actuated device and operating at its limit responsive only to accumulation of a certain amount of traffic actuation, a cyclic timer de vice for resetting said accumulator device periodically at the end of its cycle, and electromagnetic means for stepping said step by step switch from one position to "EST theznext; means for'operatingelectromagnetic means to step said step .by step switch to the next succeeding position of said series responsive to operation of said accumulator device before the end of the time cycle of said .timer device, and means for operating said electromagnetic-means to step said step'by step switch to the preceding position of said series from any one responsive to-absence of operation of said accumulator device immediately before the end of said time cycle, said stepby-stepswitch having a repeated scale of positions in said series, -and:said last named responsive means including a relay system for predetermining stepping ahead of said step-by-step switch the number of positions required to step only to a position corresponding to the next position backof its original position.

4. In a trafiic cycle selector apparatus having a plurality. of trafiic signalling cycles and a selector device for' selecting between said cycles in accordance with amount of traffic, said-selecting device comprising. a

step by step switch having a series of more than two' switch positions and providing connections in the respective positions for the several signalling cycles, a trafficactuated device, an accumulator limit device actuatable toward its limit by said traffic actuated deviceandopcrating at its limit responsive only to accumulation of a certain amount of traffic actuation, a cyclic timerdevice for resetting said accumulator-device periodically t step lsaid stepby step switch to the next succeeding position of said series responsive to operationof said accumulator device before the end of the time cycle of said timer device, and means for operating said electromagnetic means to step said step by step switch to the preceding position of said series from any one responsive toabsence of operation of said accumulator device immediately before the end of said time cycle, and said step-by-step switch having a repeated scale of positions in said series, said last named step back means including relay means for predetermining for each position a rapid stepping ahead of. said step-by-step switch to the next position back in said scale except when already in the lowest position of said scale.

5..A structure as 'in claim 4 in which said relay means includes a relay operated at the start of such step back operation to remember the starting position and circuits including contacts controlled by the stepping switchinits respective positions in :such step back operation to maintain such rapid stepping ahead until said switch .reaches the next preceding :cycle position.

6. A trafiic cycle selector including a selector switch having a series of more than two positions providing a scale of trafiic cycles for low to high traffic volumes, a capacitor, a grid controlled electronic discharge tube-controlled by the voltage on said capacitor, means actuated by traflic to vary the voltage on said capacitor progressively from: an initial value toward another value for the,

counting of traiiic, cyclic timing means for providing a traflic counting period during which .said selector switch remains in one position and a high grid bias is maintained said selector switch from said one position to the, next higher position on its scale if said memory means is operated, followed by a brief change from such high bias to a lower grid bias to then cause said/tube; to become conducting at a lower voltage change corresponding to a lower trafiic count to operate said memory means if not previously operated, and followed, by a brief period to step said selector switch down to the next lower position if insuflicient tr-affic has been counted to operate said memory means, and said cyclic timing means including means for resetting the voltage on said capacitor to in-- itial value and for releasing said memory means at the end of said counting period.

7. A trafiic cycle selector as in claim 6 and including adjustable impedance means for varying said grid bias over a range of trafl'ic count values.

8. A traffic cycle selector as in claim 6, and including a plurality of adjustable impedance means individual to certain of said cycle positions for varying said grid bias over; a range of trafiic counting values for such control of said tube conduction in the respective positions.

9. In a traffic control apparatus, a cyclic stepping switch having a multiplicity of positions and output con-,

nections from the respective positions for providing different trafliocontrol operations, a periodic timer device, and means actuated by trafiic responsive to the amount of such trafiic actuation to step said stepping switch ahead one poistion or back one position or to maintain the same position for a further such counting period 'in accordance with the amount of trafiic actuations during the period of said timer device, said stepping switch having a repeated scale of positions and said trafiic actuated responsive means including a relay system for predetermining stepping ahead of said step-by-step, switch the number of positions required to step only to a position corresponding to the next position back of its original position for such step back operation.

References Cited in the file of this patent UNITED STATES PATENTS 2,090,655 Wilcox Aug. 23, 1931

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