US3413930A - Railroad retarder control systems - Google Patents

Description

Dec. 3, 1968 Filed Feb. 21, 1966 4 Sheets-Sheet 1 CONTROL 2/ CONTROL 2 f SPEED RETARDER RETARDER ACTIVITY I mT W SELECTOR I I APPARATUS, SPEED RETARDER CONTROL COMMAND RETARDER CONTROL RETARDER UNIT l4 RETARDER 0 7 /7 /5) [Z3 3 I I RETARIDER 5 27 I UNIT RETARDER A I I v, \/0

$752358 IDENTIFICATION 244 CONTROL COMMAND STORE I INVENTORS ROBERT 8. Mc CUNE ROSSER LW/LSON /M W! M El Eff? Dec. 3, 1968 R. B. MCCUNE ET 3,413,930

RAILROAD RETARDER CONTROL SYSTEMS v 4 Sheets-Sheet 3 Filed Feb. 21, 1966 must/tum imam/Rum INVE/VTORS ROBE/F78. ROSSER L R B. M CUNE ET AL RAILROAD RETARDER CONTROL SYSTEMS' Dec. 3, 1968 Filed Feb. 21, 1966 4 Sheets-Sheet 4 INVENTORS ROBE/P T 8. Mc- CU/VE' ROSSER 1.. WILSON 1 f FL MON 1 m0 wmOkomJmm mom United States Patent 3,413,930 RAILROAD RETARDER CONTROL SYSTEMS Robert B. McCune, Allendale, and Rosser L. Wilson,

Mahwah, N.J., assignors to Abex Corporation, a corporation of Delaware Filed Feb. 21, 1966, Ser. No. 528,712 9 Claims. (Cl. 104--26) ABSTRACT OF THE DISCLOSURE A selective control system for the car retarders in a railroad freight classification yard, in which a single control unit may serve a substantial number of diiferent retarders. The control system comprises several independent retarder pressure control units, the number of control units being substantially smaller than the number of car retarders in the yard, but each control unit being capable of controlling the operation of any one of the retarders. A selector apparatus is interposed between the control units and the car retarders and is used to complete operating connections, individually and selectively, between any one of the control units and any one of the car retarders. The system further includes sequence control means that determines which control unit is to be connected to an individual retarder when control of that retarder is required.

This invention relates to a new and improved selective control system for railroad retarders and more particularly to an automatic selector system for controlling a substantial number of car retarders, located in one or more classification yards, from a central location.

Increasing emphasis on automation of the operation of classification yards and other railroad installations has led to frequent use of automatic control systems for track brakes or, as they are more frequently termed, railroad car retarders. Some control systems are based entirely upon the speed of the cars entering and leaving the retarder. A particularly advantageous example of an automatic speed control for a railroad car retarder, in which the speed of a car or cut of cars is continuously monitored from a time preceding entry into the retarder until the time of exit from the retarder, is described and claimed in the co-pending application of Richard E. Porter and Arthur R. Crawford, Ser. No. 427,537 filed Jan. 13, 1965, now Patent No. 3,240,930. Other known control systems are actuated in response to additional factors affecting car movement, such as the weight of the car, wind velocity, and the like. In virtually all of these systems, however, the common denominator is the requirement for release of the car or cut of cars from the retarder at a particular exit velocity.

In a large classification yard, a substantial number of individual retarders may be employed to control movements of individual cuts of cars through the yard. By way of example, the number of retarders in a given classification yard may frequently be in excess of twenty. Each of these retarders requires individual control and, for maximum efificiency, it is usually preferable to afford automatic control for each of the retarders. Thus, the investment in control systems for the car retarders in a major classification yard is quite substantial.

On the other hand, in virtually any yard only a limited number of retarders are actually in operation at any given time. Thus, in a yard containing as many as twenty individual retarders, there may never be more than five retarders actually in operation even during peak operations. In that same yard, normal working conditions may well be such that no more than three or four retarders function simultaneously. It is thus seen that the control equip- "Ice ment for regulating operation of the retarders is quite redundant where, in accordance with normal practice, a complete control system is provided for each retarder.

It is not ordinarily possible to provide a single control system for simultaneously controlling all retarders because the control requirements with respect to individual retarders located at different points within a classification yard may be subject to substantial variation. For example, the safe release speed from one retarder in a given yard may be approximately five miles per hour whereas the permissible release speed for another retarder in the same yard may be only three miles per hour. Furthermore, the desired and permissible exit speeds for individual retarders may vary with changing conditions in the yard. These variations may be even more pronounced with respect to retarders located in a series of small classification yards, as might be the case in the environs of a large metropolitan center.

It is an object of the present invention, therefore, to eliminate excessive duplication of retarder control equipment, and at the same time provide for individual regulation of operation of each car retarder, in a large automated railroad classification yard or any other railroad installation entailing a substantial number of car retarders located in reasonable proximity to each other.

Another object of the invention is to provide for individual automatic control of each of a relatively large number of railroad car retarders in a selective control system affording only a limited number of control units, the number of control units being substantially smaller than the number of controlled car retarders.

A further object of the invention is to provide a new and improved selective automatic control system for railroad car retarders that can be readily adapted to individually set control levels for each controlled retarder, to selective exit speed control in accordance with destination, or to virtually any other basic form of exit speed determination without requiring substantial modification of the control system itself.

A specific object of the invention is to provide for automatic control of a large number of car retarders from a limited number of individual control units that may be adapted to direct speed control or to control in accordance with a wide variety of dilferent environmental factors without basic change of the selection system.

Accordingly, the invention relates to a selective control system for a given number m of railroad car retarders in a freight car classification system. The control system comprises a plurality n of retarder control units each capable of controlling operation of any one of the retarders, n being substantially smaller than m. The system also comprises 11 selector means, each coupled to an individual one of the retarder control units and each also coupled to all of the railroad car retarders. Each of the selector means includes means for selectively connecting its one control unit to any one of the retarders to control operation of that retarder. The system further includes sequence control means, connected to each of the retarders and to each of the selector means, for actuating the selector means in sequence and in response to the presence of a cut of cars in any one of the retarders, causing the actuated selector means to connect its control unit to the retarder in which a cut is present so that the control unit controls operation of the retarder during movement of the cut through the retarder.

Other and further objects of the present invention will be apparent from the following-description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIG. 1 is a functional block diagram of a selective automatic control system for railroad car retarders constructed in accordance with one embodiment of the pres ent invention;

FIG. 2 is a more detailed block diagram of a part of the system of FIG. 1, showing the selective control system in more complete form;

FIG. 3 is a detail circuit diagram of a selector means that may be incorporated in the control system of FIG. 2; and

FIG. 4 is a detail circuit diagram of a sequence control circuit that may be used in the control systems of FIGS. 1 and 2.

FIG. 1 illustrates a selective automatic control system for controlling the operations of a series of individual railroad car retarders illustarted by retarders 11, 12, 13, 14, and 16. In a typical system, the number of retarders actually present might be, and usually would be, substantially larger. Thus, in a major classification yard, it is not uncommon to have twenty or more retarders present.

In the control system 10 of FIG. 1, there are three individual retarder control units 21, 22 and 23. Each of the retarder control units 21-23 is capable of controlling the operation of any one of the individual retarders 11-16. However, the number of retarder control units is substantially smaller than the number of retarders and the control units are not permanently connected to the retarders. Instead, the retarder control units are selectively connected to individual retarders through a selector apparatus 17.

Selector apparatus 17 includes a plurality of selector means, one for each of the retarder control units 21-23, together with a sequence control means for actuating the individual selector means, as described more fully hereinafter in connection with FIG. 2. The operating units within selector apparatus 17 are employed to connect the retarder control units to the retarders in accordance with activity occurring at the retarders, and exercise control over the retarders pursuant to commands stored in a control command storage unit 18.

In a given instance, for example, a cut of cars may be passing through retarder 11. As the cut enters the retarder, an indication of this activity is transmitted to selector apparatus 17 by means of an electrical connection 24 and the activity is also signalled to the control command store 18 through an electrical connection 24A. Selector apparatus 17 identifies an idle retarder control unit. In this instance, it is assumed that retarder control unit 21 is idle. The selector apparatus then establishes operating connections between retarder 11 and control unit 21 as indicated by the dash lines 25 and 26 in FIG. 1. The electrical connections 25 and 26 transmit speed information from retarder 11 to control unit 21 and transmit control information for operation of the retarder from unit 21 back to retarder 11. In addition, a connection is completed from the control command store 18 to retarder control unit 21, as indicated by the dash line connection 27, to condition the retarder control unit for the specific release speed requirements of retarder 11.

A second cut may enter retarder 15, for example, while the first cut is still passing through retarder 11. Under these circumstances, activity in retarder 15 is signalled to selector apparatus 17 and to control command store 18 as before. The selector apparatus establishes the necessary operating connections between retarder 15 and the next available control unit, retarder control unit 22. In addition, an operating connection is made from the control command store 18 to retarder control unit 22 to condition unit 22 for a release speed corresponding to the particular requirements of retarder 15. These electrical connections are also indicated by appropriate dash lines within selec- 4 tor apparatus 17, dash lines having been used because the connections are temporary in nature and are maintained only while the cut is moving through the retarder. In subsequent cycles of operation, any one of retarders '11 through 16 may be connected, at a given time, to any one of retarder control units 21, 22 and 23.

The selective control system 10 illustrated in FIG. 1 is based upon individual manual or other settings for release speeds for the retarders, the settings being stored in command store 18. The control command store could be eliminated entirely if the construction of the classification yard containing retarders 11-16 were such that a single fixed speed of release could be employed for all retarders. On the other hand, in some yards the release speeds for the retarders may vary in accordance with destination; that is, a particular retarder such as retarder 11 might require operation for two or more ditterent release speeds depending upon the ultimate destination of a given out of cars passing through the retarder. A similar variable situation is presented where it is desired to control operation of the retarder on the basis of other factors such as the weight of the car or cars. Where such variations are to be taken into account, through either automatic or pre-set release speed determining apparatus, the release speed determination equipment may be coupled to control command store 18 to determine the control commands supplied to retarder control units 21-23.

FIG. 2 illustrates a larger selective control system 30 for a classification yard or other railroad installation including a larger number of retarders. In this instance, twelve retarders are incorporated in the system, being represented in FIG. 2 by retarders 31, 32, and 33, and retarders 41 and 42, with the intervening retarders being omitted from the drawing.

Retarder 31 is electrically connected to a cut detector circuit 51. Similarly, retarders 32, 33, 41 and 42 are individually electrically connected to detector circuits 52, 53, 61 and 62 respectively. That is, there is a separate out detector for each of the retarders. Cut detector 51 is electrically connected to each of a series of five selector devices identified by reference numerals A, 70B, 70C, 70D and 70E. Each of the remaining cut detectors for the retarders is individually electrically connected to each of the separate selector means 70A through 70E. In addition, each of the cut detectors is individually electrically connected to a sequence control unit 67. The sequence control means 67 is in turn connected to each one of the separate selector means 70A through 70E.

Each of the selector means 70A through 70E is individually electrically connected to a particular retarder control unit, the retarder control units being identified by reference characters 71A through 71E. That is, selector means 70A is connected to retarder control unit 71A but is not connected to the other retarder control units of the system. Similarly, selector means 70B is connected only to retarder control unit 71B, etc. In addition, output connections are provided from each of the selector means 70A through 70E back to all of the retarders in the system as generally represented by retarders 31, 32, 33, 41 and 42. It will be understood that corresponding connections from the selector means are provided to the remaining retarders that have been omitted from FIG. 2.

In considering the operation of the selective control system illustrated in FIG. 2, it may first be assumed that a car or cut of cars enters the portion of track in the system encompassing retarder 31. The presence of the cut is detected by device 51, which signals sequence control means 67 of the presence of a cut in retarder 31. The sequence control means identifies one of the selector means 70A through 70E that is not presently in use and completes an internal connection within the selector means to couple the cut detector 51 to the retarder control unit that is connected to the selector means. For example, sequence control means 67, in the instance under consideration, may actuate selector means 70A to connect retarder control 71A to cut detector 51 and hence to retarder 31. Only one of the selector means is actuated by sequence control means 67 in response to any one signal from a cut detector; consequently, only retarder control unit 71A is effectively connected to retarder 31 to control its operation while the cut passes through the retarder. When the cut leaves the retarder, its departure is signalled to selector means 70A through out detector 51 and the selector means operates to break the connection between control unit 71A and retarder 31, leaving the control unit free for use with another retarder.

The process described above is carried on continuously by control system 30. Each time a car or cut of cars enters one of the retarders, that retarder is automatically connected to one of the retarder control units by means of the sequence control 67 and the individual selectors 70A through 70E. The selected retarder control unit maintains control of the retarder until the car or cut of cars leaves the retarder, at which time the selector automatically disconnects the operating connection and releases the retarder control unit for subsequent operations.

FIG. 3 illustrates operating circuits that may be utilized for the cut detectors 51 and 52, together with an operating circuit that may be employed for the selector means 70A in FIG. 2. It should be understood that selector means 70A, as illustrated in FIG. 3 is generally typical of the selector means 70B through 70E, since all of the selectors in a given installation would usually be of the same construction.

Cut detector 51, as illustrated in FIG. 3, comprises a track relay having an operating coil ITRR. One terminal of coil lTRR is connected to a suitable power supply, designated as V+, through a normally open test switch 1TSW. The other terminal of coil 1TRR is returned to system ground. A switch lRSW is shown connected in parallel with test switch 1TSW. Switch 1RSW would normally constitute a set of relay contacts or other appropriate track circuit means capable of maintaining the energizing circuit for the track relay .ITRR as long as a car or cut of cars remains in the section of track encompassing retarder 31. If automatic route switching is employed in the classification yard, switch 1RSW may be a part of the detection and control apparatus used for route switching. An appropriate indicator light 81 may be connected in parallel with coil 1TRR to give a visual indication to the system operator that a car or cut of cars is present in retarder 31.

Cut detector 51 further includes an auxiliary track relay comprising an operating coil ITXR. One terminal of coil lTXR is grounded and the other terminal is connected through a resistor 91 and a pair of normally open track relay contacts lTRRl to the V+ supply.

The second cut detector 52 shown in detail in FIG. 3 is similar in construction to detector 51. It comprises the operating coil 2TRR of a track relay which is arranged for energization through either a test switch 2TSW or a retarder occupancy sensing switch ZRSW. As before, an appropriate indicator light 82 may be connected in parallel with coil 2TRR. In detector 52, there is an auxiliary track relay operating coil ZTXR that is energized through the series combination of a resistor 92 and a pair of normally open contacts 2TRR1.

Selector means 70A, as illustrated in FIG. 3, comprises a multiple stage rotary stepping switch ISSA. In the illustrated arrangement, the rotary switch 1SSA has five stages, each with a total of twelve operating contacts and a home contact; the wiper arm for each stage is shown in the home position. The rotary switch 1S-SA may be of a type fre quently used for telephone and other communication applications and is stepped from one position to another, with all stages moving simultaneously, by means of an electromagnet MISSA. In a typical switch of this kind, each of the five wiper arms 101, 102, 103, 104 and 105 of the selector switch 1SSA is advanced, simultaneously with the other arms, by one step each time the electromagnet MISSA is energized and subsequently deenergized. That is, stepping of switch ISSA occurs upon de-energization of its coil MISSA.

The first stage of stepping switch ISSA, comprising wiper arm 101, has its initial operating contact, after the home contact, electrically connected to the terminal 111 in cut detector 51 between resistor 91 and coil ITXR. Similarly, the second operating contact engageable by wiper arm 101 is connected to the terminal 112 in cut detector 52 between coil ZTXR and resistor 92;. Corresponding connections are made from the remaining ten terminals of the first stage of stepping switch 1=SSA to the other cut detectors 53-62, respectively (see FIG. 2). Wiper arm 101 is connected through a pair of normally open homing relay contacts AHRI to system ground.

The second and third stages of stepping switch ISSA, comprising the wiper arms 102 and 103, are employed to connect a speed controller 121 to the individual retarders in the system. Thus, the initial contact engageable by wiper arm 102, upon stepping of the wiper arm from the home position as illustrated, is electrically connected to retarder 31. The second operating contact of the stage of stepping switch ISSA comprising wiper arm 102 is electrically connected to retarder 32. The third operating terminal of this stage of the stepping switch lSSA is electrically connected to retarder 33. The initial operating terminal of the third stage of stepping switch ISSA, comprising wiper arm 103, is electrically connected to retarder 31. The second operating terminal is connected to retarder 32 and the third operating terminal is connected to retarder 33. Similar connections are made from the remaining operating terminals of these two stages of stepping switch A to the other retarders controlled by the system. The home or normal contact in each of the first three stages of switch ISSA is left open-circuited.

The wiper arm 102 in the second stage of stepping switch ISSA is electrically connected to the speed controller 71A through a pair of normally open main relay contacts AMRI. Similarly, wiper arm 103 in the third stage of the stepping switch is electrically connected to retarder control unit 71A through a pair of normally open relay contacts AMRZ. The construction of controller 71A is not critical with respect to the present invention; it may be of the kind described and claimed in the aforementioned application of Porter and Crawford Ser. No. 427,537, but other forms of speed control apparatus may be utilized. The provision for two electrical connections from each retarder to the control unit makes it possible to transmit actual speed measurements from the retarder to the controller as well as to transmit control signals to the retarder from unit 71A. In a given installation, more than two electrical connections may be required to effect the requisite control of the retarder; selector means 70A can be readily modified to provide additional connections as described more fully hereinafter.

The fourth stage of stepping switch ISSA, comprising wiper arm 104, has the home contact for the wiper arm returned to system ground through a pair of normally closed relay contacts APR]. The initial contact of this stage of the stepping switch, following the home contact, is connected by a conductor 131 to the sequence control means 67 described more fully hereinafter in conjunction with FIG. 4. The second and third contacts of this stage of the stepping switch 1SSA are similarly connected, by conductors 132 and 133 respectively, to sequence control means 67. Corresponding connections are provided for each of the twelve individual operating contacts of the fourth stage of stepping switch 158A. The wiper arm 104 of this stage of the stepping switch is connected to one terminal of the operating coil -1ASR of a first selector relay connected in selector means 70A, the other terminal of coil lASR being connected to the V+ supply for the system.

One terminal of the electromagnet 'MISSA for stepping switch ISSA is connected to system ground. The other terminal of the coil is connected to the V+ supply through the internal stepping switch contacts 1SSA1 and through the series combination of a pair of normally closed main relay contacts AMR3 and a pair of selector relay contacts IASRI. Contacts 1SSA1 are of a kind normally provided in communication stepping switches of the type described above, and are opened each time electromagnet MISSA is energized.

Selector means 7tiA further includes a first auxiliary relay having an operating coil AXR located in FIG. 3 immediately to the right of electromagnet MISSA. One terminal of coil AXR is connected to system ground. The other terminal of the coil is connected to the V+ supply through a pair of normally open homing relay contacts AHRZ. This terminal of relay coil AXR is provided with a holding circuit comprising a normally open pair of contacts AXRl in the same relay and a pair of contacts ISSAZ controlled by the stepping switch magnet MISSA. Contacts 1SSA2 are of the kind normally identified as olf normal springs contacts in a conventional stepping switch and remain open only as long as the stepping switch is in its home or normal position as illustrated in FIG. 3. For all other positions of the stepping switch, contacts 1SSA2 are closed.

Selector means 70A further includes a homing relay comprising an operating coil AHR. One terminal of coil AHR is connected to system ground and the other terminal is connected to the V+ Supply through an energized circuit, comprising in series, a pair of normally open selector relay contacts IASRZ and the stepping switch off normal contacts 1SSA2.

The fifth stage of stepping switch 1SSA, comprising wiper arm 105, is employed to couple stepping switch 1SSA to a second stepping switch ZSSA. The wiper arm 105 in this stage is connected directly to system ground. The home or normal contact is left open-circuited. The initial operating contact, following the home contact in this stage of switch ISSA, is electrically connected to the first operating contact of the stepping switch ZSSA. The second operating contact engageable by wiper arm 105 is connected to the second operating contact engageable by the wiper arm 135 of stepping switch ZSSA. A similar pattern is maintained for the remaining contacts of the fifth stage of stepping switch 155A and the operating contacts of switch 255A. The home or normal contact of stepping switch ZSSA is connected to system ground through a pair of normally closed homing relay contacts AHR3.

The wiper arm 135 of stepping switch ZSSA is connected to a pair of auxiliary relay contacts AYRl that are returned to system ground. The wiper arm is also electrically connected to one terminal of the operating coil ZASR of a second selector relay, the other terminal of coil ZASR being directly connected to the V+ supply.

Stepping switch 2SSA is preferably of the same basic construction as described above for switch ISSA, and is actuated by an electromagnet MZSSA. One terminal of the stepping switch magnet is connected to system ground and the other terminal is connected to the V+ supply through a pair of normally closed internal contacts 2SSA1 for the stepping switch connected in series with a pair of normally closed selector relay contacts 2ASR1.

Selector means 70A further includes a failure or cancellation relay comprising an operating coil AFR. One terminal of failure relay coil AFR is connected to system ground and the other terminal is connected through a switch PB to two of the contacts for one pole ASWl of a three-pole three-position control switch. Two poles ASWl and ASWZ for this control switch are illustrated in FIG. 3; the third pole of the switch is shown in FIG. 4. The third contact of switch ASWl is left open-circuited. The three positions for switch ASWl, relating to the three contacts of the switch proceeding from left to right as seen in FIG. 3, are an off position, a test position,

and an active position, switch PB being connected to both the test and active contacts of the switch. A holding circuit for failure relay coil AFR is provided by the normally-open relay contacts AFRI connected in parallel with switch PB. An indicator light 136 may be connected in parallel with coil AFR to give the system operator a positive indication of energization of the failure relay.

The auxiliary relay coil AYR is illustrated in the lower right-hand corner of FIG. 3. One terminal of this coil is connected to system ground and the other terminal of the coil is connected to an energizing circuit comprising, in series, the normally open selector relay contacts 2ASR2, a diode 137, a pair of normally open stepping switch contacts ZSSAZ, and a pair of normally open homing relay contacts AHR4. Contacts ZSSAZ are off normal contacts for the stepping switch ZSSA and are closed for all positions of the stepping switch except its home or normal position. A holding circuit is pro vided for coil AYR comprising, in series, two pair of normally open auxiliary relay contacts AYRZ and AXRZ.

The main or master operating relay for selector means 70A comprises a coil AMR illustrated in the lower righthand corner of FIG. 3 and the contacts AMRl-AMR3 described above. One terminal of coil AMR is connected to system ground. The other terminal of this coil is connected to the right-hand or active contact of control switch ASW2. The movable contact of switch ASW2 is connected, through a pair of normally open auxiliary relay contacts AYR3 and through the homing relay contacts AHR4, to the V} supply. An indicator lamp 141 may be connected in parallel with the main relay coil AMR to afford the operator a positive indication that the main operating relay of the selector is energized, thereby indicating that the selector is in use connecting a retarder control unit to a retarder.

The test contact of switch ASW2, the middle one of the three contacts, is connected to an indicator lamp 142 that is returned to ground. The remaining contact of switch ASWZ, the off contact is opcn-circuited, as is the 01f contact for switch ASW1.

FIG. 4 illustrates minor portions of the selector means 70A and a corresponding part of selector 70B, together with the sequence control means 67 and the external connections to the sequence control means. Sequence control means 67 comprises a multiple-stage stepping switch SS1. Two stages of switch SS1, comprising wiper arms 145 and 146, are shown in FIG. 4. Stepping switch SS1 may be of the same general kind as stepping switches A and ZSSA (FIG. 3) except that its stages need not include a home position contact, employing only the twelve operating contacts necessary to afford one contact for each retarder in each stage of the stepping switch. Although only two stages of stepping switch SS1, connected to selector means 70A, are shown in FIG. 4, there are eight additional stages including in this switch,

providing two corresponding stages in the stepping switch for each of the individual selector units 70B through 70E.

The initial operating terminal in the first stage of stepping switch SS1, comprising wiper arm 145, is connected to a pair of normally closed auxiliary track relay contacts lTXRl. Contacts 1TXR1 are returned to system ground. Similarly, the second contact of this stage" of stepping switch SS1 is connected through a pair of normally closed auxiliary track relay contacts 2TXR1 to system ground. Each of the remaining contacts in this stage of the stepping switch is similarly returned to system ground through a normally closed pair-of auxiliary track relay contacts.

The first operating contact engageable by the wiper arm 146 in the second stage of stepping switch SS1 is electrically connected to the conductor 131 leading to the first operating contact in the fourth stage of the stepping switch ISSA in selector means 70A, FIG; 3.

This same contact is connected through a pair of normally open track relay contacts 1TRR2 to a diode 151. Diode 151, in turn, is connected through the series combination of a pair of normally open homing relay contacts AHRS and a pair of normally open failure relay contacts AFR2 to system ground.

Similarly, the second contact engageable by wiper arm 146 is connected to the conductor 132 leading to the selector means 70A in FIG. 3. This contact of switch SS1 is also connected through a pair of normally open track relay contacts 2TRR2 (a part of cut detector 52) and a diode 152 to the conductor 159 connected to homing relay contacts AHRS. Corresponding connections are provided for the succeeding contacts of this stage of switch SS1. Moreover, a similar circuit arrangement is utilized for each of the stepping switch stages (not shown) included in sequence control means 67 and connected to selector means 70B-70E.

The wiper arm 146 in the second stage of stepping switch SS1 is electrically connected to a pair of normally closed auxiliary relay contacts AXR3 which are in turn connected to a pair of normally open failure relay contacts AFR3, the latter being returned to ground.

One of the principal operating relays of sequence control relays 67, FIG. 4, is a track sequence relay comprising an operating coil TSR. One terminal of coil TSR is connected to system ground and the other terminal 161 is connected to the V+ supply through a resistor 162. Terminal 161 is also connected to the wiper arm 145 of stepping switch SS1 and to the wiper arms of the other stages of stepping switch SS1 (not shown) incorporated in sequence control means 67 for connection to selectors 70B through 70E.

The electromagnet MSS1 for actuating the multiple stage stepping switch SS1 is shown in FIG. 4 immediately to the right of relay coil TSR. One terminal of electromagnet M581 is connected directly to the V+ supply. The other terminal is connected to a pair of normally closed internal stepping switch contacts $811 which are in turn connected through a pair of normally closed track sequence relay contacts TSR1 to conductor 163. Contacts 5811 open each time the electromagnet MSSI is energized. Conductor 163 is provided with a plurality of return circuits to system ground, each including a pair of normally open contacts in one of the retarder cut detector circuits. That is, conductor 163 is connected to a pair of normally open auxiliary relay contacts 1TXR2 from the first cut detector, these contacts being returned to ground. The same arrangement is employed for auxiliary track relay contacts 2TXR2 and 3TXR2, one such pair of contacts from each cut detector.

Sequence control means 67 further includes a fourstage rotary stepping switch SS2, the individual stages of which are illustrated at the right-hand side of FIG. 4. The electromagnet MSS2 for switch SS2, which may be similar in construction to stepping switch SS1, is located in the central portion of the drawing. One terminal of electromagnet MSS2 is connected to system ground. The other terminal of the electromagnet is connected through a pair of normally closed stepping break relay contacts SBRl to a conductor 164.

Three different circuits are provided for connecting conductor 164 to the V+ supply. The first of these circuits comprises a pair of normally open contacts TSR2 of the track sequence relay, which are connected directly between conductor 164 and the V+ supply. The second circuit is provided by a normally open pole SPB1 of a manually operated sequence switch. The third circuit is afforded by a normally closed pole SPB2 of the same switch which connects conductor 164 to the wiper arm 171 in the first stage of stepping switch SS2. The first five contacts engageable by wiper arm 171 do not afford a connection to the V+ supply, but are left open-circuited. However, the last five contacts engageable by wiper arm 171 do afford a connection to the V-lsupply. It should 10 be noted that switches SPB1 and SPB2 act conjointly, pole SPB1 opening each time pole SPB2 is closed.

The wiper arm 171 in the first stage of stepping switch SS2 is also connected directly to the wiper arm 172 in the second stage of this switch. The initial operating contact engaged by wiper arm 172 (there are no home contacts in stepping switch SS2) is electrically connected to the two right-hand contacts of the third pole ASW3 of the main control switch, these being the active and test contacts for this switch. The left-hand contact for switch ASW3 is again the off contact. The movable contact of switch ASW3, which is actually a part of selector 70A, is electrically connected through the series combination of two pair of normally closed stepping switch contacts 1SSA3 and 2SSA3 to a pair of normally open position relay contacts APR4, the contacts APR4 being returned to the conductor 164. Contacts 1SSA3 are off normal contacts for the stepping; switch ISSA (FIG. 3) and are open whenever that stepping switch is not in its home or normal position. Contacts 2SSA3 are a similar pair of olf normal contacts for the stepping switch ZSSA (FIG. 3) and are open for all positions of that stepping switch except the home position.

The operating coil APR for the position relay of selector means 70A is also shown in FIG. 4 near the lower right-hand corner of the figure. One terminal of coil APR is connected to system ground and the other terminal is connected to the conductor 164 through the series combination of a pair of normally open failure relay contacts APR4 and the position relay contacts APR4, contacts APR4 affording a holding circuit for the APR relay. Initial energization of coil APR is achieved through the circuit comprising contacts 2SSA3 and 1SSA3 and switches ASW3 and SS2, as described more fully hereinafter.

The connection afforded for the contact engaged by wiper arm 172 in the second stage of stepping switch SS2 is the same as described above for the first contact except that the second contact is connected to circuit components in the second selector means 70B. Thus, the second operating contact engageable by wiper arm 172 is connected through a switch BSW3 and two pair of normally closed off normal stepping switch contacts 188133 and 2SSB3 to a pair of normally open position relay contacts BPR4 that are returned to the conductor 164. The same circuit extends from the terminal of contacts 2SSB3 and BPR4 and through a pair of normally open failure relay contacts BFR4 to the position relay coil BPR in the second selector means 70B and thence to ground. Corresponding connections (not shown) are provided to selectors 70C, 70D and 70B from the third, fourth and fifth contacts in the second stage of switch SS2. The remaining five contacts engageable by wiper arm 172 remain open-circuited.

The wiper arms 171 and 172 in stepping switch SS2 are connected to the third stage wiper arm 173 of the stepping switch through a circuit comprising, in series, a pair of normally open internal stepping switch contacts SS22 and a stepping break relay coil SBR. Contacts SS22 are actuated each time the stepping switch electromagnet MSS2 is energized.

The first operating terminal in the third stage of switch SS2, comprising wiper arm 173, is returned to ground through a pair of normally closed position relay contacts APR3 of selector means 70A. The second terminal in this stage of the stepping switch is similarly returned to ground through a pair of normally closed position relay contacts BPR3 in the second selector means 70B. Corresponding connections, through selector means 70C, 70D

internal stepping switch contacts 1SSA4 that are controlled by the stepping switch ISSA of selector means 70A (FIG. 3). As shown in FIG. 4, contacts 1SSA4 are connected to the V+ supply to provide energization of lamp 175A. A similar circuit including an indicator lamp 1758 and internal stepping switch contacts 1SSB4 is connected between the second contact of this stage of switch SS2 and the V+ supply. Corresponding indicator lamp circuits (not shown) are provided for the third, fourth and fifth contacts of this stage of stepping switch SS2, the connections being incorporated in selector means 70C, 70D and 70E respectively.

In considering operation of the cut detector, selector means, and sequence control circuits illustrated in FIGS. 3 and 4, it may first be assumed that track relay coil 1TRR (FIG. 3 upper left-hand corner) in cut detector 51 is energized. This is effected by closing of switch IRSW, for an actual detection of cut presence, or may be simulated for test purposes by closing of switch ITSW. Upon energization of the track relay coil, contacts 1TRR1 close, completing an operating circuit for the auxiliary track relay coil 1TXR through resistor 91.

It may happen that the position of switch SS1 (FIG. 4) is already such that wiper arm 145 is aligned with the initial contact in this stage of the stepping switch, connecting the wiper arm to auxiliary track relay contacts lTXRl. Under these circumstances, the opening of contacts 1TXR1 is effective to energize the track sequence relay coil TSR, since the opening of these contacts removes the shunt to ground that was previously present with respect to coil TSR. Moreover, although the auxiliary track relay contacts 1TXR2 are closed, energization of the track sequence relay coil TSR and the consequent opening of its contacts TSR1 prevents completion of an energizing circuit for the stepping switch electromagnet MSSl, even though contacts S811 are already closed. The track sequence relay TSR is a fast-operating relay and is effective to open contacts TSRl before coil MSSl can be energized, by closing of contacts 1TXR2, for a time sufficient to step switch SS1. Under these circumstances, the stepping switch SS1 does not move, having already and previously been aligned at the position for connecting the active retarder, retarder 31, to the retarder control unit 71A through selector means 70A as described more fully hereinafter.

,More typically, selector switch SS1 may be at some other position than that illustrated in FIG. 4. For example, if it is assumed that wiper arm 145 initially engages one of the other contacts clockwise from the position shown, it will be seen that coil TSR is not affected by the opening of contacts 1TXR1 in the cut detector for the first retarder and hence remains unenergized. Under these circumstances, the closing of contacts 1TXR2 signifying the entrance of a cut of cars into retarder 31 completes an operating circuit to the stepping switch electromagnet MSSl. The stepping switch magnet is energized and upon energization, opens its own contacts SS11. Opening of these contacts de-energizes the stepping switch solenoid and advances the stepping switch one position. This operation continues through as many steps as are necessary to bring wiper arm 145 into engagement with the first contact, connected to the auxiliary track relay contacts 1TXR1, which are now open. When that position is reached, sequence relay coil TSR is energized and further advancement of the stepping switch is prevented as described above.

It is quite possible for more than one retarder to be active at the same time. When this occurs, switch SS1 advances as described above until it reaches the first contact connected to a pair of auxiliary track relay contacts that have been opened by the cut detector circuit associated with one of the active retarders. Thereafter, there is no further stepping of switch SS1 until the first active retarder has been connected to a speed controller, at which time switch SS1 moves on to find the next active retarder.

Having identified an active retarder by the stepping of switch SS1, as described above, the next function of the sequence control circuit 67 of FIG. 4 is to locate an idle retarder control unit, one of units 71A-71E. The search for an idle control unit is conducted by stepping switch SS2, the position of which identifies the control unit next scheduled for operation. In FIG. 4, the position of stepping switch SS2 indicates that retarder control unit 71A is the next to be utilized and is to be connected to the active retarder through selector means 70A.

As indicated above, the identification of activity in retarder 31 requiring control has resulted in energization of the track sequence relay TSR. As .a consequence, contacts TSR2, located in the upper right-hand portion of FIG. 4, are closed. This completes an operating circuit for the position relay APR of selector means 70A, the circuit extending from the V+ supply through contacts TSR2 and through the normally closed switch SPB2 to wiper arm 172 of switch SS2, which, as noted above, is presently engaged with the first contact as shown in the drawings. From wiper 172, the circuit extends through the active contact of switch ASW3 (the switch is assumed to be in its active position) and through the normally closed contacts 1SSA3 and 2SSA3 to the failure relay contacts AFR4. The failure relay is continuously energized during normal operation (its failure function is described hereinafter) so that a complete operating circuit is established for the position relay coil APR. The energization of coil APR and consequent actuation of the APR position relay indicates that selector means 70A and its associated retarder control unit 71A are idle and available.

Next in time sequence, stepping switch electromagnet MSS2, located in the center portion of FIG. 4, is energized. The operating circuit is established through the normally closed contacts SBR1 and through the closing of the track sequence relay contacts TSR2 as noted above. To asure energization of stepping switch magnet MSS2, it is necessary that contacts SBR1 remain closed. To this end, the position relay APR is made a fast-acting relay, relative to the SBR stepping brake relay so that contacts APR3 of the position relay open before coil SBR can be energized long enough to actuate its relay .and before the contacts SS22 in series with the SBR coil are closed by energization of electromagnet MSSZ. The position relay APR completes its own holding circuit by closing of its contact APR4 in series 'with the coil APR. But electromagnet M852 is not de-energized at this time and switch SS2 is not stepped. This completes the operations for recognition of the availability of speed controller 71A through its selector means 70A.

The situation is substantially different if the selector means 70A is already in operation and has been actuated to connect its speed controller 71A to some other retarder that is already active. This situation is indicated by the fact that either one of both of stepping switches ISSA and 255A (FIG. 3) are displaced from the home or normal position. Under these circumstances, referring again to FIG 4, it is seen that the position relay coil APR cannot be energized because either one or both of the off nonma contact pairs 1SSA3 and 2SSA3 in the energizing circuit would be open. Since the position relay APR has not been energized, the closing of the track sequence relay contacts TSR2 and consequent energization of stepping switch magnet MSS2, as described above, cornpletes an operating circuit to the stepping brake relay coil SBR upon closing of the contacts SS22 (actuated by the stepping switch solenoid) because contacts APR3 in series with the coil SBR remain closed. Energization of coil SBR causes the normally closed contacts SBR1 in series with stepping switch electromagnet MSS2 to open. The consequent de-energization of electromagnet MSS2 causes stepping switch SS2 to advance one step in search of an idle retarder control unit. As soon as stepping switch SS2 reaches a position connected to a selector means 70B-70E in which the position relay coil such as coil BPR can be energized, the stepping of switch SS2 stops as described above.

' It can be seen that if the control switch ASW has been turned to its off position, engaging the left-hand contact of the switch, then the energizing circuit for position relay coil APR is open at switch ASW3 (FIG. 4) and stepping switch SS2 will operate in the same manner as described above fior a situation in which the first retarder control unit 71A is already in use. For convenience, the sequence control means 67 is also provided with a manual indexing circuit for stepping of switch SS2. This is accomplished by actuation of switch SPB1-SPB2, which energizes the stepping switch magnet MSS2 directly and independently of the track sequence relay contacts TSR2. It will be noted that the opening of pole SPB2 in this switch prevents undesired actuation of the selector means position relays such as the APR and BPR relays and also prevents energization of the stepping break relay comprising coil SBR.

In the illustrated arrangement, the last five positions on stepping switch SS2 are not utilized and the switch is advanced directly from the fifth position to the first position by the power supply connection for the last five contacts engageable by wiper mm 171.

Assuming that speed controller 71A and its associated selector means 70A have been recognized as being idle, as indicated by energization of position relay coil APR (FIG. 4), stepping switch 158A of selector means 70A (FIG. 3) starts to advance. The stepping movement of switch ISSA is initiated upon opening of the position relay contacts APRl connected to the home position contact in the fourth stage of the switch comprising wiper arm 104. Opening of these contacts de-energizes the selector relay coil 1ASR and permits the closing of its con tacts lASRl. The closing of contacts 1ASR1 completes an operating circuit to the stepping switch magnet M1SSA. Upon energization of the electromagnet MISSA, its contacts 1SSA1 open, causing the switch to advance one step. This process is repeated for as many steps as are necessary until such time as the master relay contacts AMR3 are opened as described hereinafter.

The fourth stage of stepping switch 1SSA, comprising wiper 104, searches for a ground connection through the interconnection of its individual contacts with the second level of the stepping switch SS1 in the sequence control means 67, these interconnect-ions being afforded by the conductors 131-433. As noted above, the position of switch SS1 represents the location of an active retarder; by stopping switch 188A at the same position as already occupied by switch SS1, the first step in connecting the retarder control. unit to the active retarder is accomplished. In the present instance, where switch SS1 is at its initial position representative of activity in retarder 31, alignment of the two switches is achieved as soon as switch 1SSA advances one step to bring wiper 104 into engagement with the contact connected to line 131 (FIG. 3), since this completes a circuit to ground from conductor 131 through wiper 146 (FIG. 4) and contacts AXR3 and AFR3. It should be remember that contacts AFR3 are normally closed except in event of a power failure as described more fully hereinafter.

As soon as switch ISSA advances into alignment with switch 1881, as described above, completing an eifective connection from wiper 104 to ground (see FIG. 3)' selector relay coil 1ASR is again energized. Upon energization of coil 1ASR, its contacts 1ASR1 are opened, preventing further stepping of switch 1SSA because it is no longer possible to energize the electromagnet MlSSA for the stepping switch.

Ene-rgization of the selector relay coil 1ASR also closed contacts 1ASR2, in theupper right-hand corner of FIG. 3. Closing of these contacts completes an operating circuit for the homing relay coil AHR, since switch ISSA has movedYaway from its normal position and contacts 1SSA2 are closed for all positions of the stepping switch other than the normal position. Energization of coil AHR closes contacts AHR2 and energizes the auxiliary relay coil AXR. Actuation of the auxiliar relay closes its contacts AXRI to establish a holding circuit that is independent of the homing relay.

Energization of the auxiliary relay coil AXR also causes the opening of contacts AXR3 in the sequence control means 67 (FIG. 4). However, opening of these contacts occurs after actuation of the AHR homing relay and hence after closing of contacts AHRS. Recalling that track relay 1TRR2 is previously energized, retarder 31 being active, and that contacts AFR2 are closed because the failure relay is normally held energized, it is seen that the actuation of the homing relay coil AHR and the consequent closing of contacts AHRS prior to actuation of the auxiliary relay coil AXR and the resultant opening of contacts AXR3 maintains the necessary ground connection for the sequence relay 1ASR through conductor 131.

Energization of the homing relay coil AHR (FIG. 3) also closes the homing relay contacts AHR1 that are connected to the wiper arm 101 in the first stage of the stepping switch 1SSA. Recalling that the actuation of the homing relay occurs upon stepping of switch ISSA to its first operating contact away from the home position, it is seen that the closing of the contacts AHR1 effectively shunt the operating coil 1TXR of the auxiliary track relay in the first cut detector 51 to ground. As a consequence, the lTXR auxiliary track relay drops out and its contacts 1TXR1 (FIG. 4 upper left-hand corner) close. The closing of these contacts completes a shunt circuit to ground that is effective to tie-energize the track sequence relay coil TSR. The consequent dropping out of the track sequence relay closes contacts TSR1 in the operating circuit for the electromagnet MSSI that actuates stepping switch SS1. This permits stepping switch SS1 to resume the search for an active retarder, if in fact there is an active retarder as would [be indicated by closing of one of the other sets of auxiliary track relay contacts ZTXRZ, 3TXR2, etc.

Of course, the other set of track sequence relay contacts TSR2 now open, effectively disconnecting conductor 164 from the V+ supply and de-energizing the stepping switch magnet MSSZ. This permits stepping switch SS2 to advance one step and thus prepares the stepping switch for connection to the next speed control unit when such connection is required by occurrence of activity in another retarder.

The operating cycle for selection and maintenance of operating connections between retarder control unit 71A and a retarder 31 is completed when track relay 1TRR is de-energized by opening of the switch IRSW or 1TSW that initially energized the track relay to indicate activity in retarder 31. When this occurs, it is necessary to bring switch 1SSA back to its home position to condition selector me'ans 70A for subsequent operations. This action is initiated by the opening of contacts 1TRR2 (FIG. 4 lower left-hand corner), which breaks the existing ground connection to conductor 131 and thus de-energizes selector relay 1ASR (FIG. 3). When the selector relay comprising coil 1ASR drops out, its contacts 1ASR1 again close. This permits energization of stepping switch magnet MlSSA which, when energized, opens its own contacts 1SSA1. The opening of contacts 1'SSA1 effectively de-energizes the stepping switch magnet and causes the stepping switch to advance one step.

This self-interrupted stepping is maintained until switch ISSA reaches the home position in which it is illustrated in FIG. 3. At that position, with the position relay coil APR de-energized in the manner described above, and with position relay contacts APRl consequently closed, selector relay 1ASR is again energized because a ground connection is available through wiper arm 104. Consequently, contacts 1ASR1 open and the stepping action of switch 1SSA is interrupted because electromagnet MISSA cannot again be energized. The stepping switch ISSA remains in the home position until again required to locate an active retarder as described above.

When the stepping switch 1SSA returns to its home position, contacts 1SSA2 open. This is effective to deenergize the homing relay coil AHR and the auxiliary relay coil AXR.

The basic role of the failure relay comprising coil AFR (FIG. 3 lower right-hand corner) is to prevent stepping switch SS2 (FIG. 4) from hanging up in a position associated with a malfunctioning selector means 70A70E. For example, a failure in the power supply for one of the individual selector means, and specifically the selector means 70A, is effective to de-energize the failure relay coil AFR. With the failure relay de-energized, stepping switch SS2 cannot stop on its first position, in which it connects to selector means 70A, because the consequent opening of contacts AFR4 prevents energization of the position relay coil APR. It will be recalled that switch SS2 can only remain in position with a selector means where it is possible to energize the position relay coil of the selector means.

When the system is first placed in operation, the failure relay coil AFR (FIG. 3) is initially energized by closing of switch PB and remains energized thereafter by means of a holding circuit established through its own contacts AF'RI. Whenever a power supply failure occurs, with consequent drop out of the AFR relay, the circuit is reset for operation by momentarily closing switch PB. This action is also necessary if the system has been taken out of operation, as by actuation of the ASW switch to its off position, for any reason. Automatic reset upon restoration of power can be provided if desired.

The second stepping switch 2SSA that is incorporated in selector means 70A is provided primarily to afford additional stages for multiple circuit connections between retarder control unit 71A and the selector means, although further stages of switch ZSSA have not been illustrated in the drawings. Consequently, switch 2SSA is arranged to step to the same point as switch ISSA in the course of connecting the selector means and its associated retarder control unit to an active retarder. The main or master relay comprising coil AMR is placed under control of stepping switch vZSSA to complete the operating connections between the active retarder and the retarder control unit.

As noted above, the homing relay coil AHR is energized at the time stepping switch ISSA stops its stepping at the active retarder (retarder 31 in the example given above). Upon energization of the relay coil AHR, contacts AHR3 in the lower central portion of FIG. 3 open, interrupting the operating circuit for the second selector relay coil ZASR. De-energization of this selector relay is effective to cause self-interrupted stepping of switch 2SSA until wiper arm 135 again reaches a contact at ground potential to energize coil ZASR. That is, stepping switch 2SSA advances by the opening and closing of its own contacts 2SSA1 occasioned by energization of coil MZSSA, since contacts 2ASR1 are now closed. The stepping action is interrupted when wiper arm 135 reaches a point corresponding to the point of advancement of wiper arm 105 in switch ISSA, since wiper arm 105 is connected to ground and completion of the ground connection again effects energization of coil ZASR and opens contacts 2ASR1 to break the operating circuit to the stepping switch solenoid.

At the time that selector relay 2ASR is again energized, its contacts 2ASR2 in series with auxiliary relay coil AYR close. When this occurs, the contacts 2SSA2 in series with contacts 2ASR2 are already closed; it will be recalled that contacts 2SSA2 are closed for every position of stepping switch 2SSA other than its home or normal position. Moreover, contacts AHR4 are closed 16 because the homing relay has been energized as discussed above. Consequently, the auxiliary relay coil AYR is energized. It establishes a holding circuit by the closing of its contacts AYR2, the series contacts AXR2 already being closed because auxiliary relay AXR has been energized as described before.

Energization of the auxiliary relay coil AYR also closes the contacts AYR3 of this relay. Inasmuch as contacts AHR4 are already closed, this completes an energizing circuit for the main or master relay coil AMR, as suming that the ASW switch is in its active position as shown in FIG. 3. Energization of the main relay coil closes contacts AMRI and AMR2 and thus completes two operating circuits between retarder control unit 71A and the active retarder, in this instance retarder 31. Of course, it will be understood that the AMR relay may contain additional contacts connecting additional stages in stepping switch ZSSA to the retarder control unit and to the retarder if additional control functions are required.

The main relay AMR should be dropped out before homing of the stepping switches 188A and ZSSA upon completion of a control cycle, triggered by the exit of the cut of cars from the previously active retarder as described generally above. This is accomplished by incorporating contacts AMR3 in series in the operating circuit of stepping switch magnet MISSA (FIG. 3). As long as the master relay is energized, contacts AMR3 are open and the stepping switch 1SSA cannot resume stepping action to bring it to home position. Stepping of swtch 2SSA is dependent upon operation of switch ISSA and hence cannot occur prematurely.

It is also desirable to effect the return of switch ISSA to its home position before switch 2SSA commences homing. This is effected by maintaining selector relay coil ZASR energized as long as the auxiliary relay coil AYR is energized through the utilization of contacts AYRI in the ground circuit for coil 2ASR. Auxiliary relay coil AYR can only drop out when the counterpart relay coil AXR in the control circuit for stepping switch 1SSA is de-energized, dropout of the AYR relay coil being effected by opening of contacts AXR2. As described above, the auxiliary relay AXR is de-energized upon switch ISSA reaching home position to open contacts 1SSA2. It is clear, therefore, that the AYR relay will drop out only after switch ISSA has reached home position, at which time the interruption of the operating circuit for coil 2ASR through Opening of the relay contacts AYRl permits contacts 2ASR1 to close and complete an energizing circuit to stepping switch electromagnet 255A. The stepping action of switch 2SSA is interrupted when it reaches its home position and again finds a ground connection through contacts AHR3, which have previously closed upon de-energization of coil AHR by homing of switch A.

The principal purpose in staggering the stepping of switches 185A and ZSSA is to reduce power supply requirements. Where speed of connection of an active retarder to a control unit is critical, simultaneous stepping of switches 158A and 288A can be provided.

In the embodiments described above, stepping switches are employed for identification of active retarders by the sequence control means (switch SS1, FIG. 4), for sequential identification of an available selector means and idle control unit (switch SS2) and for selection of the active retarder by the selector means (switches ISSA, 2SSA, FIG. 3). It will be recognized, however, that conventional shift registers constructed with vacuum tubes or solid state devices such as transistors, and other forms of electrically or electronically operated stepping devices, such as the crossbar switches employed in communication networks, could be employed for these same purposes. In the ap pended claims, therefore, all references to stepping switches are intended to include such stepping devices in general, without limitation to mechanical switching members. Of course, electronically actuated gate circuits can 17 also be utilized for the relay circuits specifically described above.

As noted above, the stepping switch SS2 is used to identify the next available selector means and control unit combination. The circuit can be arranged to identify that combination in advance instead of waiting until a control unit is actually required, with some saving in search time, if this appears desirable. Of course, auxiliary circuits may be provided to indicate when all control units are in use, and also to indicate when an additional control unit is needed under these circumstances.

From the foregoing description, it is clear that the selective control system of the present invention makes it possible to control a relatively large number of retarders from a substantially smaller number of retarder control units. The number of direct electrical connections between the retarders and the control units is dependent only upon the number of stages that are provided in stepping switches 183A and 255A, so that the system can be utilized with virtually any form of basic retarder control without substantial modification. Thus, the selective control system is seen to provide a maximum in versatility and at the same time to afford optimum economy in overall system cost.

Hence, while preferred embodiments of the invention have been described and illustrated, it is to be understood that they are capable of variation and modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.

We claim:

1. A selective control system for a number of railroad car retarders in a freight car classification system comprising:

a plurality of independent retarder control units substantially smaller in number than the number of railroad car retarders, each capable of controlling operation of any one of said retarders;

selector apparatus, coupled to said retarder control units and to said car retarders, -for individually selectively completing an operating connection between any one of said control units and any one of said car retarders,

said selector apparatus including sequence control means for completing said operating connections in accordance with activity at said retar-ders and availability of said control units;

a control command store for recording at least one control command signal for each of said retarders;

and means, included in said selector apparatus, for selectively connecting said control command store to said control units to apply said control command signals to said control units in correspondence with the operating connection of said control units to said retarders.

2. A selective control system for a given number m of railroad car retarders in a freight car classification system comprising:

a plurality of n independent retarder control units each capable of controlling operation of any one of said retarders, n being less than m;

a corresponding plurality n of selector means, each coupled to an individual one of said retarder control units and to all of said railroad car retarders,

said selector means each including means for selectively connecting its one control unit to any one of said retarders to control operation of the retarder;

and sequence control means, connected to each of said retarders and to each of said selector means, for actuating each of said selector means, in sequence, in

,response to the presence of a cut in any one of said retarders, to connect said retarder to the control unit associated with said selector means to control operation of that retarder during passage of said out through said retarder.

3. A selective railroad retarder control system according to claim 2, comprising in cut detector circuits, one for each retarder and each connected to all of said selector means and to said sequence control rneans, each of said detector circuits being actuatable from an initial inactive condition to an active condition upon entry of a cut into its associated retarder and further being actuatable back to inactive condition when the cut leaves the retarder, said selector means each including means for interrupting the connection from its control unit to any given retarder whenever the cut detector circuit for that retarder reverts to its inactive condition.

4. A selective railroad retarder control system according to claim 2 in which each of said selector means provides a plurality of electrical connections between its associated control unit and a retarder controlled by the control unit.

5. A selective railroad retarder control system according to claim -4 in which each of said electrical connections is eflected through an individual stage of a multiplestage stepping switch, each stage of said stepping switch having a separate contact for each retarder in the system.

6. A selective railroad retarder control system according to claim 2 in which said sequence control means includes a multiple-stage sequence stepping switch having one contact in each stage connected to each selector means, and advancing means for advancing said sequence stepping switch one contact each time one of said selector means is actuated to connect its control unit to an active retarder.

7. A selective railroad retarder control system according to claim 6 in which one stage of said sequence stepping switch is connected back to said advancing means to actuate said advancing means and advance said sequence stepping switch an additional contact each time said switch is advanced to a contact connected to a selector means already connecting its control unit to an active retarder.

8. A selective railroad retarder control system according to claim 3 in which said sequence control means includes a retarder identification stepping switch having one contact connected to each cut detector, and advancing means for advancing said identification stepping switch one contact at a time, said advancing means being connected to all of said out detectors for actuation whenever any of said cut detectors is actuated to its active condition and remaining in operation to continue advancement of said identification stepping switch until said switch reaches the contact thereof connected to the cut detector that has been actuated to active condition.

9. A selective railroad retarder control system according to claim 8, in which said retarder identification stepping switch includes at least a plurality of stages and in which each of said selector means includes a multiple stage retarder selection stepping switch, each stage of said retarder selection switches including one contact for each retarder in the system, and advancing means for advancing said retarder selection stepping switch one contact at a time, the contacts of one stage of each of said retarder selection stepping switches being individually interconnected with the contacts of one stage of said retarder identification switch and being connectible to said advancing means to advance said retarder selection switch to a position corresponding to the position of said retarder identification switch whenever said selector means is actuated.

References Cited UNITED STATES PATENTS 3,226,541 12/1965 Brinker et al 246182 3,251,991 5/1966 Coley et a1 246-182 3,253,142 5/1966 Brown 246-182 ARTHUR L. LA POINT, Primary Examiner.

S. T. KRAWCZEWICZ, Assistant Examiner.

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