US3394250A

US3394250A - Retarder control apparatus

Info

Publication number: US3394250A
Application number: US426084A
Authority: US
Inventors: Robert B Mccune
Original assignee: Abex Corp
Current assignee: PepsiAmericas Inc
Priority date: 1965-01-18
Filing date: 1965-01-18
Publication date: 1968-07-23
Anticipated expiration: 1985-07-23

Description

July 23, 1968 2 Sheets-Sheet 2 Filed Jan. 18, 1965 INVENTOR ig H.- 5-

United States Patent O 3,394,250 RETARDER CONTROL APPARATUS Robert B. McCune, Allendale, NJ., assigner to Abex Corporation, a 'corporation of Delaware Filed Jan. 18, 1965, Ser. No. 426,084

8 Claims. (Cl. 246--182) ABSTRACT OF THE DISCLOSURE A speed-sensing control system for a railway car retarder actuata-ble between braking and released conditions. A series of n track switches or other sensing devices are located along the traffic rail of the car retarder at uniform spaced intervals less than the minimum spacing between car axles; each track switch develops an initiating signal when actuated by a car wheel. A series of n-l timing devices are each individually connected to a respective adjacent pair of the track switches; thus, each track switch is connected to two timing devices, except for the rst and last track switches which are connected to only one timing device. The timing devices develop individual timing signals representative of the time required for a wheel to traverse the space between the two track switches to which it is connected. A single comparison circuit is connected to all of the timing devices and compares the timing signals with a given standard signal amplitude to ascertain whether a car passing through the retarder is above or below a given release speed. The comparison circuit develops overspeed and underspeed actuating signals which are applied to the actuating mechanism for the retarder to control its operation. A time delay release is provided for re-actuating the retarder to released condition upon elapse of a predetermined time interval with no overspeed actuating signal.

This invention relates to a new and improved braking apparatus to be used in a railroad classification yard or like application. More particularly, the invention relates to a new and improved speed-sensitive control system for a railroad vehicle retarder.

In the operation of a railroad classification yard, railroad cars are ordinarily released at the top ofV an incline or hump and roll down the incline and into the branching classification tracks of the yard. It is usually necessary to brake the cars at one or more points along the gang or feeder track and it may also be necessary Ato provide additional braking along the classification tracks of the yard. The track brakes or car retarders used for this purpose ordinarily comprise pairs of elongated rail-like brake shoes, sometimes referred to herein as retarder members, that engage the sides of the car wheels. The car retarders are necessary to prevent coupling at excessive speeds, in the use of the classification yard, with resultant damageto the railroad cars and their contents.

Relatively elaborate control systems have been utilized for centralized control of all of the car retarders in 4a classification yard. These control systems have frequently utilized radar or other costly speed-sensing devices, together with car weighing apparatus and other mechanisms for determining various factors that affect the rollability of individual cars. Control systems of this kind, however, are not usually suitable for use with individual track brakes located on the classification tracks of the yard, since there are usually many such classification tracks and the cost would be prohibitive. By the same token, radar speed control and similar arrangements are not economically feasible in relatively small yards.

Other car retarder control systems have also been proposed, some of which are based upon the actuation of 3,394,250 Patented July 23, 1968 relatively simple sensing devices located at spaced intervals along the traic rail of the retarder. Thus, relatively simple and inexpensive control systems have been proposed in which the primary sensing devices constitute ordinary track switches that are engaged and closed tnomentarily 4by each wheel of the railway vehicle. A particularly advantageous system of this kind is described and claimed in the co-pending application of Erwin R. Knauer and Robert B. McCune, Ser. No.' 348,734, tiled Mar. 2, 1964. In the control system disclosed in that application, initiating signals developed by a series of track switches are all supplied to one signal-operated timing apparatus, preferably comprising a slow-release relay. The timing apparatus completes and maintains an energizing circuit for a predetermined time interval inresponse to each initiating signal. The system also includes control and interlocking means for establishing and maintaining the retarder in braking condition only so long as the timing apparatus continuously maintains the aforesaid energizing circuit in completed conditon.

The aforesaid car retarder` control system of Knauer and McCune, although economical in construction and `effective in operation, presents some difiiculty with respect to protection of the system against erroneous operation in the event of failure of one ofthe trackswitches. Moreover, the system is difficult to adapt toa multi-speed level operation entailing determination of separately and independently established overspeed and underspeed thresholds, as may be necessary or desirable in some installations.

It is a principal object of the present invention, therefore, to provide a new and improved speed-sensitive control system for a railway vehicle retarder that is relatively simple and inexpensive in construction yet highly Vdependable in operation and that affords .a direct determination of both overspeed and underspeed conditions.

An additional object of the invention is to provide a new and improved speed-sensitive control system in which the movement of a railway car along a track is sensed periodically by track switches or similar conventional sensing devices and which requires Vonly a minimum of speed-determination apparatus, yet is effectively protected lagainst malfunction due to failure in operation of any of the sensing devices. v

A specific object of the invention is to provide for direct determination of an underspeed condition, as well as time-delay determination of such an underspeed condition, in the operation of a railway vehicle retarder control system, thereby avoiding any delay in recognition Vof the need to release the retarder.

or a multiple cut of cars yet which operates directly from the wheels of the cars .as they traverse the retarder without introducing confusion in operation.

Y `An additional object ofthe invention is the production of a speed-sensitive control system :actuated by track switches against the possibility of erroneous operation from stoppage of a car in the retarder, whether or not a car wheel is in contact with one of the track switches.

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 a preferred embodiment of the present invention and the principles thereof and what is now considered to lbe 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. v

In the drawings:

FIG. 1 is a combined block diagram and plan view of a railway car retarder including a control system constructed in accordance with one embodiment of the present invention;

FIG. 2 is a detailed schematic diagram of the timing devices and comparison circuit for the control system of FIG. 1; and p FIG. 3 is a detail schematic diagram of the overspeed and underspeed actuator circuits and a part of the retarder operating mechanism employed in the control system of FIG. 1.

FIG. 1 illustrates a substantially conventional railway car retarder which incorporates a control system 20 constructed in accordance with one embodiment of the present invention. Retarder 10 includes a relatively short section of a railway traffic rail 11. Of course, there is a second traic rail parallel to rail 11, but the second rail has been omitted from the drawing due to space considerations. The railway track in which the rail section 11 is incorporated is usually an inclined track permitting cars to roll through the retarder. The direction of movement of the cars through the retarder is as indicated by the arrow A.

A pair of car retarding rails or brake shoes 13 are disposed immediately adjacent rail section 11 in position to engage the opposite sides of a car Wheel as the Wheel traverses retarder 10. The retarding rails 13 are sometimes referred to hereinafter as retarder elements. If desired, a similar pair of retarder elements (not shown) may be disposed along the corresponding section of the other rail of the railway track in which retarder 10 is incorporated. Suitable means are provided for actuating retarder rails 13 between braking and released positions, the retarder operating means being generally indicated in FIG. l as the retarder operating mechanism 15. The retarder operating mechanism 15 may comprise any suitable electrical, mechanical, pneumatic, or hydraulic lmechanism capable of moving the retarder rails 13 between an open or released condition and a closed braking or retarding condition. Regardless of the basic drive apparatus incorporated in operating mechanism 15, this mechanism is constructed for electrical actuation, as described hereinafter.

In order to provide for effective operation of the retarder control system 20, in controlling retarder operating mechanism 15, it is necessary to afford some means for sensing the movement of a railroad car or cars along track section 11. In FIG. l, the sensing means constitutes a series of

sensing devices

21, 22, 23, 24, 25, 26, 27, 28 and 29. The individual sensing devices 21-29 preferably comprise conventional track switches; the switches are located along the trafiic rail section 11 at uniformly spaced intervals. The spacing between adjacent sensing devices is made less than the minimum spacing between railway vehicle wheels so that it is not possible to actuate two adjacent switches simultaneously. There is no -critical number of sensing switches or other sensing devices; though nine sensing switches are shown, a greater or lesser number may be employed as desired.

yControl system further includes a series of

timing devices

31, 32, 33, 34, 35, 36, 37 and 38. Timing device 31 is electrically connected to the rst pair of

sensing devices

21 and 22. Timing device 32 is electrically connected to the next pair of adjacent sensing devices, constituting

track switches

22 and 23. This arrangement is carried out uniformly for each of the timing devices; thus, each timing device is individually connected to a respective pair of the sensing switches. The timing devices are each constructed to develop a timing signal having an amplitude or other parameter representative of the time required for a railway car wheel to traverse the space between the sensing devices to which that timing device is connected. Thus, timing device 31 produces a timing signal representative of the time required for the wheel of a car traversing track section 11 to move from sensing switch 21 to sensing switch 22. Similarly, timing device 32 develops a timing signal representative of the time required for the car wheel to pass from sensing switch 22 to switch 23. The same arrangement is maintained throughout the series of timing devices, the last timing device 38 being effective to generate a timing signal that is representative of the time interval required for the car wheel to traverse the space between sensing switches 28 and 29. From the foregoing description, it can be seen that the pairing of the sensing switches 21-29 with the timing devices 31-38 requires that for each series of n sensing switches (nine are illustrated) there must be 11-1 timing-devices (eight are shown).

Each of the timing devices 31-38 is individually electrically coupled to a comparison circuit 39. Comparison circuit 39 compares the individual timing signals with a given threshold velocity to determine whether the speed of a railway car or other vehicle passing through retarder 10 is above or below a desired release speed. Comparison circuit 39 develops either an overspeed signal or an underspeed signal, depending upon the results of the comparison operation.

The overspeed signal output of comparison circuit 39 is electrically connected to an overspeed lactuator circuit 41. The underspeed signal output of device 39 is electrically connected to an underspeed actuator 42. The

actuator devices

41 and 42 `develop appropriate actuating signals that are applied to an output control circuit 43 that is in turn coupled to retarder operating mechanism 15 to actuate that mechanism to braking condition or to released condition, depending upon the actual speed of the railway car or other vehicle traversing retarder track section 11.

FIGS. 2 and 3 afford a complete schematic illustration of typical operating circuits that may be incorporated in control system 20, affording the timing devices 31-38, the comparison circuit 39, the overspeed and

underspeed actuator circuits

41 and 42, and the output control circuit 43. Referring to FIG. 2, it is seen that one terminal of each of the normally open track switches constituting the sensing devices 21-29 is connected to a power supply, designated in FIG. 2 as the B+ supply. The B+ supply may constitute any conventional DC power supply and, accordingly, is not shown in the drawings.

The remaining terminal of track switch 21 is connected in a circuit that includes, in series, a capcitor 51 and the operating coil of a first control relay 61. The coil of relay 61 is returned to system ground. A resistor 54 is connected with capacitor 51. An additional resistor 55 is also connected in parallel with capacitor l51 in a circuit that includes, in series, a pair of normally open contacts 56 from a second control relay 62.

The first timing device 31, in the form illustrated in FIG. 2, includes contacts in yboth of the relays 61 and 62. Timing device 31 comprises a capacitor 71 having one terminal connected to a suitable DC power supply designated as C+. The other terminal of capacitor 71 is returned to system ground through a series resistor S1. A relatively small resistor 91 is connected in a shunt circuit, relative to capacitor 71, this shunt circuit also including, in series, a pair of normally open contacts 57 in control relay 61.

The timing signals derived from timing device 31 are taken from the common terminal 64 of capacitor 71 and resistor 81. The output circuit for the timing signals extends from terminal 64 through a further pair of normally open contacts 65 in relay I62 to a pair of blocking

diodes

66 and 67 that are connected in the circuit with opposite polarities. The timing signal output circuits comprising the

diodes

66 and 67 Iare described in greater detail hereinafter.

The second sensing ldevice, switch 22, is connected between the B+ supply and a capacitor 52. Capacitor 52, in turn, is connected to one terminal of the operating coil of relay 62, the other terminal of the coil being returned to system ground. A resistor 74 is connected in parallel with capacitor 52. A resistor 75 is connected in another parallel circuit with respect to capacitor 52, this circuit including, in series, the normally open contacts 76 of a third control relay 63.

The second timing device 32, in the circuit arrangement illustrated in FIG. 2, includes a timing capacitor 72 that is connected in .series with a resistor 82 between the C+ supply and system ground. A relatively small resistor 92 is connected in parallel with capacitor 72 in a circuit that includes, in series, a pair of normally open contacts 77 in control relay 62. The common terminal y84 of capacitor 72 and resistor 82 is connected through a pair of normally open contacts 85 in relay 63 to an overspeedunderspeed timing signal output circuit comprising a pair of

diodes

86 and 87.

The operating coil of the third control relay `63 is connected in a circuit essentially identical with that for relay 62, the coil being in series with a capacitor 53 and with sensing switch 23 between the B+ supply and ground. Control relay 63 is also connected to the third timing device 33, comprising a timing capacitor 73 and resistor 83, in the same manner as the previously described circuits.

FIG. 2 illustrates the rst two stages of the timing apparatus of control :system 20, comprising timing de

vices

31 and 32, complete, and also shows a part of the third timing device 33. In addition, this figure illustrates the linal timing device 38, which is controlled by the last two

sensing switches

28 and 29.

Thus sensing `switch 28 is connected in series with a capacitor 58 and with the operating coil of a control relay 68 ybetween the B+ supply and ground. A resistor 94 is connected in parallel with capacitor 58. Another resistor is connected in a circuit that parallels capacitor 58, this circuit including in series therewith a pair of normally open contacts 96 in the last control relay 69.

Timing device 38, as illustrated in FIG. 2, is substaa tially identical in construction to the other timing devices. It includes a series RC circuit including a capacitor 78 and a resistor 88 connected in series with each other between C+ and system ground. A resistor 98 is connected in series with a pair of normally open contacts 97 in relay 68 between the C+ supply Iand resistor 8S. The common terminal 101i of capacitor 78 and resistor 88 is connected through a pair of normally open contacts 105 in relay 69 to a pair of oppositely

polarized diodes

106 and 107. The operating coil ofthe final control relay, relay 69, is connected in series with a capacitor 59 and the iinal sensing switch 29 between ground and B+. A resistor 108 is connected in parallel with capacitor 59.

The comparison circuit 39, in the form illustrated in FIG. 2, comprises a three-element resistive voltage divider. Beginning at the C+ supply, this circuit includes. in series, a resistor 111, a resistor 112, and an adjustable resistor or potentiometer 113, potentiometer 113 'being returned to system ground. A iirst output transformer 11d, constituting a pulse transformer of conventional construction, is incorporated in comparison circuit 39. The primary winding 115 of pulse transformer 114, sometimes referred to hereinafter as the underspeed transformer, is connected from the common terminal 116 of resistors 111 and 112 to all ofthe similarly

polarized diodes

66, 86, and 106 (and to the correspondingly polarized diodes in other stages of the system). The secondary winding 117 of the underspeed transformer 114 is connected to the

actuator circuits

41 and 42 described hereinafter in connection with FIG. 3.

Comparison circuit 39 (FIG. 2) further includes a second output transformer 121, sometimes referred to hereinafter as the overspeed transformer. One terminal of the primary winding 122 of transformer 121 is connected t-o the common terminal 123 of resistor 112 and potentiometer 113. The other terminal of primary winding 122. is connected to each of the similarly

polarized diodes

67, 87

and 107 (and to the corresponding diodes in other stages). The secondary winding 124 of transformer 121 is connected to the overspeed actuator circuit 41 (FIG. 3).

At this point, it is possible to consider in detail the operation of the timing devices and comparison circuit in the particular form illustrated in FIG. 2.. It will be recalled that a car approaches the sensing devices 21-29 in the direction of the arrow A. The first action that takes place is the closing of the initial sensing switch 21, completing a circuit from the B+ supply through capacitor 51 and through the operating coil of relay 61 to system ground. The operating current through capacitor 51 is of suicient amplitude to energize relay 61 momentarily. It should be noted that the circuit parameters are selected to assure actuation of the relay regardless of the fact that switch 21 may be closed only instantaneously. Resistor S4 is selected to have a resistance much larger that the coil resistance of relay 61 so that the steady state voltage drop across the relay coil is substantially less than its drop-out voltage.

As a consequence of energization of relay 61, contacts 57 are closed and the timing capacitor 71 in timing device 31 is rapidly discharged through the relatively small resistor 91.

The initial wheel of the car moving into the retarder next engages and closes the second sensing switch 22. The momentary closing of switch 22 is eiective to energize the second relay 62 in the manner described hereinabove for relay 61. The resultant closing of contacts 56 in relay 62 completes a circuit, through resistor 55, in parallel With capacitor S1. Accordingly, capacitor 51 is discharged and is thus made ready for a subsequent actuation of relay 61 as described above. It should -be noted that the closing of switch 22 and the consequent discharge of capacitor 51 through relay contacts 56 takes place before the next wheel of the car can contact switch 21, since the spacing between

switches

21 and 22 is made smaller than the minimum spacing between railway vehicle wheels. In the event that there is a failure of actuation of switch 22, so that capacitor S1 is not discharged by the closing of relay contacts 56 as just described, the charge on capacitor 51 is discharged more slowly through the larger resistor 54.

Continuing progress of the car through the retarder causes the sequential actuation of sensing switches 23 through 29. Each time the car wheel engages one of these switches, the corresponding control relay is energized momentarily by the charging current through the associated capacitor in the manner described above. The control relays are actuated, momentarily, only when the car wheel engages the associated switch. Depending upon the spacing of the car wheels, it may lbe noted that simultaneous operation of several of the control relays 6169 is possible. However, adjacent control relays are never operated simultaneously, due to the aforementioned maximum spacing requirement with respect to the sensing switches.

Consideration may now be -given to the operation of timing circuit 31 in developing a timing signal representa tive of the interval required for the car wheel to traverse the space between the two

sensing switches

21 and 22 employed to actuate this intial timing device. 1t will be recognized that the elapsed time between closing of

switches

21 and 22 is inversely proportional to the average speed ofthe railway car as it traverses the distance between the two switches. It is this time interval that is actually measured by timing device 31 and that is utilized to develop the requisite timing signal.

As noted above, the momentary closing of contacts 57 upon energization of relay 61 discharges capacitor 71 through resistor 91; the time constant of the RC circuit comprising capacitor 71 and resistor 91 is made substantially smaller than the time interval during which relay -61 remains energized in order to accomplish this desired discharge of the timing capacitor. The subsequent opening of contacts 57 initiates the timing period that is measured to establish the velocity of the car traversing the retarder.

- `At the time that contacts 57 open, the effective voltage across resistor 81 is approximately the C| voltage. The active circuit now consists of capacitor 71 and resistor 81, the voltage across resistor 81 decreasing as an exponential function of the-product of the resistance of resistor 81 and the capacitanceof capacitor 71.

Thereafter, contacts 65 of relay 62 are closed as a result of closing of sensing switch 22 by the same car wheel that" previously closed switch 21.`The closing of contacts 65 momentarily supplies an output signal to the two

diodes

66 and 67. The amplitude of the pulse voltage applied to the'two diodes is, of course, equal to the instantaneous voltage across resistor `81. Thus, the voltage amplitude of the signal supplied to

diodes

66 and 67 is 'representative of the speed of 4the car moving through the distance between

switches

21 and 22, sincethe voltage across resistor 81 is a functionofthe time constant of the

RC circuit

71, 81 and 'of the C+ Voltage. I-t will be understood that the voltage across resistor 81, and hence the voltage supplied to

diodes

66 and 67 is not linearly proportional to the average speed of the car as it moves between

switches

21 and 22. However, there is a fixed relationship between the time interval being measured and the voltage across resistor 81 so that any given voltage value represents but one value of average speed.

At the time that the car wheel engages switch 22, energizing relay 62 as aforesaid, the relay contacts 77 are also closed. Closing of contacts 77 discharges the timing capacitor 72 in the Isecond timing circuit 32. When the contacts 77 re-open, the timing cycle for device 32 is initiated. That is, the voltage across resistor 82 begins to decrease as an exponential function of the impedances of circuit elements 72 and 82. It is thus seen that the voltage across resistor S2 affords a measure of the time required for the car wheel to traverse the distance between switches V22 and 23. The subsequent energization `of relay 63 upon closing of switch 23 supplies to the diodes 86 and 87 a pulse voltage having an amplitude representative of the voltage across resistor 82. Resistor 82 is of the same value as resistor 81,

resistors

91 and 92 are equal in resistance', and

capacitors

71 and 72 are of corresponding capacitance. Thus, output signals of corresponding amplitudes are applied to the diode output circuits whenever the average speed between adjacent sensing switches remains constant. Moreover, the amplitude of the output signals varies as a function of the time required for the car to move between adjacent switches and hence as a function of the average speed of the vehicle between each pair of switches.

The same timing action, producing timing signals representative of the time required for each wheel of the car to traverse the space between adjacent sensing devices in each pair, is repeated progressively as each car wheel moves through the retarder. Since more than one wheel can be present in vthe retarder at a given time, it will be understood that this action can occur simultaneously for as many wheels as are present within the retarder.

The comparison action required to determine whether an overspeed or underspeed condition exists is carried out in comparison circuit 39 in which the principal elements constitute the voltage divider afforded by

resistors

111, 112 and 113 and the two pulse Atransformers 114 and 121. Potentiometer 113 may be adjusted to modify the steady stage voltages at the two

central terminals

116 and 123 of the voltage divider. This adjustment establishes a voltage relation representative of the standard release speed to be utilized as a basis of comparison.

In considering the operation of comparison circuit 39 ('FIG. 2) it may first be assumed that in a given instance the voltage across resistor 8'1, at the time of closing of relay contacts 65, exceeds the voltage across resistor 113 in the comparison circuit. Under these circumstances, a pulse`signal is developed across the primary winding 122 of the overspeed transformer 121. This overspeed actuating signal is supplied from the secondary winding 124 of the transformer to the overspeed actuator 41, the operating circuit of the actuator being described in detail hereinafter in connection with FIG. 3. I-t should be noted that the blocking diode 66 effectively prevents a corresponding signal from being developed 'at the underspeed transformer 114.

The foregoing action, developing an actuating signal at the overspeed transformer 121, is representative of the operation of the comparison circuit 39 for an overspeed condition. For an underspeed situation, the voltage across resistor 81 is substantially lower due'to the greater lapse of time in movement of the car wheel between sensing switches 21 and 22. If the voltage across resistor 81, at the time of closing of relay Acontact 65, is less than the combined voltage across resistors 111 and 112, a pulse signal is developed across the primary winding 115 of the underspeed pulse transformer 114. As a consequence, an actu-ating signal is generated 'in the secondary winding 117 of the transformer and is supplied to' the underspeed actuator 42 described hereinafter in connection with FIG. 3. The circuit arrangement is such that, for an underspeed condition, the voltage across resistor 81 is less than the voltage across potentiometer 113 so that no pulse signal is developed in the overspeed transformer 121. The multiple arrangement of the blocking diodes permits effective segregation and recognition of pulse signals that are very nearly coincident with each other and precludes confusion between the various .timing signals supplied to the transformers. It will be understood that the operation of thepulse transformers and the comparison circuit is essentially the same for all stages of the control system. f

The yoverspeed actuator circuit 41 and the underspeed actuator 42 are both shown in detail in FIG. 3, together with the output control circuit 43. The underspeed actuator 42 is illustrated at the top of FIG. 3 and comprises the secondary winding 11'7 of the underspeed pulse transformer 114. One end of secondary winding 117 is connected through a potentiometer 131 to the C+ supply. This same terminal of winding 117 is connected through a parallel RC circuit, comprising a capacitor 132 and a resistor 133, and through a diode 134 to system ground. The other terminal of coil 117 is connected to the emitter of a silicon unijunction transistor 135.

Transistor 135 is connected in a one-shot lmultivibrator circuit employed to extend the duration of the pulse output signals from comparison circuit 39 that appear as actuating signals across the secondary winding 117 of pulse transformer 114. Transistors of this kind, which have lbeen commercially known since at least 19-59, are provided with two base electrodes. In the illustratedcin cuit, one base electrode of transistor 135 is connected through a load resistor 136 to the C-lsupply. The remaining base electrode is connected through a resistor 137 to system ground. The outputfrom `transistor 135 is taken through a series RC circuit comprising acapacitor 138 and a resistor 139 connected from the load resistor 136 to the base electrode of a conventional PNP transistor 141. A diode 140 is connected from ,the common terminal of capacitor 138 and resistor 139 back to the C-I- supply.

Transistor 141 is connected in a power amplifier circuit utilized as a relay driver. 'The emitter of transistor 141 is connected to the C+ supply. The collector is 'returned to system ground through a circuit that includes, in series, the operating coil of an underspeed operating relay 142. A diode 143 may be connected in parallel with the relay coil.

A similar circuit arrangement is employed for the overspeed actuator 41, illustrated in the bottom portion of FIG. 3. Thus, in overspeed actuator 41 one terminal of the secondary winding 124 of the overspeed pulse transformer 121 is connected to the C-I- supply through a potentiometer 151. This same terminal of coil 124 is also returned to system ground through a parallel RC circuit comprising a capacitor 152 and a resistor 153, a diode 154 being incorporated in series in the circuit. The remaining terminal of coil 124 is connected to the emitter of a silicon unijunction transistor 155. Transistor 155 is again connected in a one-shot trigger circuit. One base electrode of the transistor is returned to system ground through a resistor 157. The other base electrode is connected through a load resistor 156 to the C+ supply. As before, a series RC circuit comprising a capacitor 158 and a resistor 159 connects the load resistor 156 to the base electrode of a power amplifier transistor 161. A diode 160 is connected from the common terminal of capacitor 158 and resistor 159 to the C+ supply. Transistor 161 has its emitter connected directly to the C+ supply. The collector of this transistor is returned to system ground through a circuit that includes, in series, the operating coil of an overspeed operating relay 162. As before, a diode 163 may be connected in parallel with the relay coil.

The central portion of FIG. 3 illustrates the output control circuit 43, which is controlled by operation of the underspeed and overspeed operating relays 142 and 162. Circuit 43 includes a unijunction transistor 172 that is incorporated in a timing circuit and a conventional PNP transistor 173 that is utilized as a relay driver. The input to output control circuit 43 is applied at the emitter electrode of transistor 172. This emitter electrode is connected through a resistor 174 to a pair of normally open contacts 175 in the underspeed relay 142, the contacts 175 being returned to system ground. A similar connection is made from resistor 174 through a pair of normally open contacts 176 in the overspeed operating relay 162 to ground. A timing capacitor 184 is connected from the emitter of transistor 172 to ground. The emitter of transistor 172 is also connected through a potentiometer 177 to a conductor 178 that affords a power supply connection for circuit 43 as described more fully hereinafter.

One of the two base electrodes of transistor 172 is connected to the power supply conductor 178 through a resistor 179. The other electrode of transistor 1'72 is returned to system ground through a load resistor 131 and is also connected through a parallel RC circuit, comprising a resistor 182 and a capacitor 183, to the base electrode of transistor 173.

The relay driver transistor 173 has its emitter electrode connected to the power supply conductor 178. The collector electrode of this transistor is returned to system ground through a diode 185. The collector electrode is also connected back to the C+ supply through a circuit that includes, in series, a pair of normally open contacts 186 in the overspeed operating relay 162.

Output control circuit 43 further includes a delay release relay 191. One terminal of the operating coil of relay 191 is connected to the normally open contacts 136 in the overspeed operating relay 162 and thence to the C+ supply. The other terminal of the relay coil is returned directly to system ground.

The delay release relay 191 includes two pairs of normally open contacts 192 and 193. The normally open contacts 192 are connected in series in a circuit that extends from the power supply conductor 178 through contacts 192 and through a pair of normally closed contacts 194 in the underspeed operating relay 142 to the C+ supply. The other pair of normally open contacts 193 in delay release relay 191 are connected in series with the operating coil of a retarder actuating relay 196 between the C+ supply and ground.

The overspeed actuator circuit 41 and the underspeed actuator circuit 42, -as illustrated in FIG. 3, each provide three basic functions. Thus, in each of these circuits the incoming pulse signal, the actuating signal from comparison circuit 39, is extended in time in order to afford effective operation of a relay. The pulse actuating signal is also amplified substantially for the same purpose. In addition, each of these circuits provides a means for adjusting the threshold level for actuation of its operating relay, permitting independent adjustment of the effective thresholds for overspeed and underspeed conditions.

Referring to the overspeed actuator circuit 41 at the bottom of FIG. 3, potentiometer 151 is adjusted to establish a threshold value for triggering of the transistor 155 that is driven by the pulse signals from the overspeed pulse transformer 121. The impedances in the one-shot trigger circuit in which transistor 155 is incorporated are selected to provide an operating period for the trigger circuit that is sufficient to permit effective operation of the overspeed operating relay 162. In a typical installation, this operating period for the monostable trigger circuit may be of the order of thirty milliseconds. In any event, the trigger circuit period must be long enough to assure energization of relay 162. Transistor 161, on the other hand, is employed only to afford power amplification and requires no specific description of operation.

The underspeed actuator circuit 42 functions in the same manner as the overspeed actuator. Potentiometer 131 is adjusted to determine a desired threshold for triggering of the one-shot multivibrator comprising transistor and thus is effective to control actuation of the underspeed operating relay 142 with respect to the amplitude of the actuating signals applied to the secondary winding 117 of pulse transformer 114. Again, the one-shot trigger circuit is employed to extend the pulse time and is constructed to have an operating period sufficient to assure energization of the underspeed operating relay. Power amplification is provided by transistor 141.

In considering operation of output control circuit 43, it is helpful to remember that the overspeed operating relay 162 and the underspeed operating relay 142 never operate simultaneously. Moreover, the duration of operation of these relays is fixed, being determined by the operating periods of the two one-shot trigger

circuits comprising transistors

135 and 155. As noted` above, this period may be of the order of thirty milliseconds. The principal purpose of circuit 43 is to utilize the momentary actuation of the

relays

142 and 162, effected by the pulse actuating signals from

transformers

114 and 121, to provide a continuous control signal that may be employed to actuate the retarder to its released or its braking conditions. Actual control of the retarder is effected by relay 196.

For an overspeed condition as described above, a pulse signal is developed across the secondary winding 124 of the overspeed pulse transformer 121. Assuming that this pulse signal is of sufficient amplitude to exceed the threshold level established by adjustment of potentiometer 151, it is effective to trigger the unijunction transistor 155. The output signal from the monostable circuit comprising transistor is amplified and is effective to energize and actuate the overspeed operating relay 162. Thus,

contacts

176 and 186 of relay 162 are closed, in response to an overspeed actuating signal, for a time interval determined by the operating period lof the trigger circuit comprising transistor 155.

Closing of -contacts 176 in relay 162 is effective to ground the emitter of transistor 172 through resistor 174. In addition, capacitor 184 is now discharged through the resistor.

The closing of contacts' 186 in relay 162 is effective to energize the operating coil of the delay release relay 191 through a circuit that extends from the C+ supply through contacts 186 to the operating coil and then to ground. Thus, when relay 191 is actuated, the unijunction transistor 172 is cut off whereas transistor 173 is effectively connected to the C+ supply by closing the relay contacts 192 and is established in saturated conductive condition. With transistor 173 conductive, the operating coil of relay 191 is maintained energized through a circuit beginning at the C+ supply and extending through the normally closed contacts 194 of relay 142, its own contacts 192 (now closed), and the emitter-collector conduction path of transistor 173. Accordingly, subsequent dropout of the overspeed operating relay 162 does not deenergize the delay release relay 191.

With relay 191 in energized condition as described, capacitor 184 begins to charge through the charging circuit afforded by conductor 178 and potentiometer 177. The rate of charge is, of course, dependent upon the relative impedances of a resistor 174 and capacitor 184. When the charge on capacitor 184 reaches the peak tiring point voltage for the emitter of transistor 172, the transistor becomes conductive and discharges capacitor 184 through resistor 181. The pulse signal generated upon discharge of capacitor 184 through resistor 181 is applied to the base electrode of transistor 173 and drives this transistor from its saturated conductive condition to cut-off. With transistor 173 cut off, the relay 191 drops out, restoring the entire -circuit to the condition existing before actuation of overspeed operating relay 162.

Each time contacts 193 `of delay release relay 191 are actuated, retarder control relay 196 is energized, closing its contacts and actuating the retarder operating mechanism 15 to braking condition. Due to the delay characteristics of the operating circuit for relay 191, this being the output control circuit 140, movement of an overspeed car through the retarder maintains relay 191 energized continuously and keeps the retarder in braking condition. On the other hand, if the car is slowed below the overspeed threshold by an amount sufficient to allow relay 191 to drop out, then the retarder returns to released condition as a result of de-energization of relay 196.

The circuits controlled by the underspeed operating relay 142 are so arranged that, upon energization of this relay in response to an underspeed actuating signal developed across the transformer secondary 171, the delay release relay 191 is immediately dropped out. Thus, energization of the underspeed relay 142 in response to an underspeed actuating signal opens contacts 194 and prevents energization of relay 191 through its contacts 192. If relay 191 has previously been energized as described above, by lan overspeed signal, the presence of an underspeed signal immediately de-energizes this relay and, as a consequence, is effective to de-energize the retarder actuating relay 196. Moreover, the closing of contacts 175 in relay 142 is effective to discharge capacitor 184 through resistor 174 and thus resets the timing circuit in the output control 43 for subsequent operation.

There are two practical reasons why it is desirable to provide timing control through circuit 43 and also to provide direct and positive underspeed control through actuator 42. Thus, a particular car or cut of cars may pass through the retarder without being braked sufficiently to reduce the car speed to the level at which an underspeed signal is developed. If this occurs, the timing operation of circuit 43 is nevertheless effective to drop out the release relay 191 and restore the retarder to released condition after a predetermined time interval. Accordingly, the retarder is not left in braking condition when unoccupied.

On the other hand, the failure of a track switch at about the time that a car reaches an underspeed condition could result in a failure to develop an underspeed actuating signal. Again, however, the timing operation of circuit 43 is effective to restore the retarder to its released conditionl ready for the next car or group of cars. The timing circuit of output control 43 operates conjointly with the underspeed detection circuit, either being effective upon failure of the other to restore `the retarder control to'the required condition for a subsequent operation. The principal purpose of the underspeed detecting and actuating circuits is to eliminate delay in recognition of an underspeed condition and to restore the retarder to released condition more promptly than would be possible where only timing is relied upon for this purpose.

To summarize the effective adjustments available in the system described hereinabove, it should vbe noted that the basic speed control adjustment is effected by adjustment of potentiometer 113 (FIG. 2). The setting of this variable y J i., r impedance determines which of the actuating signal pulses (proportional in voltage to speed of the car) are transmitted to the overspeed actuator 41 and which are transmitted to the underspeed lactuator 42. On the other hand, independent adjustments of the ove-rspeed threshold and the underspeed threshold are provided by the

potentiometers

151 and 131, respectively, in FIG.` 3. That is, these two potentiometers deter-mine the threshold values. for operation of the overspeed. operating relay 162 and the underspeed operating relay 142, permitting establishment of a control dea-d zone inter-mediate the underspeed and overspeed thresholds. Finally, in FIG. 3, adjustment of potentiometer 177 determines the timing delay afforded by the output control circuit 43 and thus establishes an interval requiredto restore the retarder to released condition when no underspeed signal is present.

The control system of the present invention, 'as described hereinabove, despite its relative simplicity and inexpensive construction, is highly dependable in operation and affords direct determination of both underspeed and overspeed conditions. The system is effectively protected against malfunctions of the sensing switches or other comparable inexpensive sensing devices employed to detect movement of the car wheels through the retarder. In particular, the system cannot operate to maintain a car speed in the 4retarder with the retarder in braking condition. Direct determination of underspeed conditions avo-ids the` delays inherent in systems depending solely upon timing to determine that an underspeed condition exists.

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 I therefore do not wish to be limited to lthe precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims. i

I claim:

1. A speed-sensitive control system for a railway vehicle retarder comprising a. traffic rail, at least one Iretarder member, and operating means for actuating salid retarder member between braking and released conditions comprising a series of pairs of individual sensing devices, located along said traffic rail and 4having uniform spacing between the devices in each pair, that is less than the minimum spacing between railway vehicle wheels, each sensing device being effective to develop -an initiating signal indicative of the presence of a railway vehicle wheel at the sensing `device location;

ya series of independent timing devices, each individually connected to a respective pair of said sensing devices and each effective to develop va timing signal representative of the time required for a wheel to traverse the space between the sensing devicesin the pair to which the timing device is coupled;

comparison -means for comparing said timing signals from all of said timing devices with a given standard to ydetermine whether the velocity of each of one or more railway vehicle wheels passing through the retarder is above a given release speed and for developing an actuating signal based upon such comparison whenever any one wheel exceeds said release speed;

and actuating means for actuating said operating means to braking condition in response to said actuating signal.

2. A speed-sensitive control system for a railway vehicle retarder comprising a traffic rail, at least one tretarder member, and operating means for actuating said retarder member between braking and released conditions, comprising:

a series of pairs of individual sensing devices, located along said trafc rail and having uniform spacing between the devices in each pair, that is less than the minimum spacing between railway vehicle wheels, each sensing `device being effective to develop an `initiating signal indicative of the presence of a rail- `way vehicle wheel at the sensing device location;

a series of independent timing devices, each individually connected to a respective pair of said sensing devices Vand each `effective to develop a timing signalrepresentative of the time required for a wheel to traverse the space between the sensing devices in the pair to which the timing device is coupled;

, comparison means for comparing said timing signals from all of said'timing deviceswith a given standard to determine whether the velocity of each of one .or more railway vehicle wheels passingthrough the retarder is below a given release speed and for developing an actuating signal based upon such comparison whenever any one wheel is below said release speed; l and actuating means for actuating said operating means i to released condition in response to said actuating signal.

3. A speed-sensitive control system for a railway vehicle retarder comprising A a traiic rail, at leas-t one retarder member, fand operating means for actuating said retarder member lbetween braking and released conditions, comprising:

a series of n sensing devices, located along said traic rail at uniform spaced intervals less than the minimum spacing between railway vehicle wheels, each effective to develop an initiating signal indicative of the presence of a railway vehicle Wheel at the sensing device location;

a series Iof n-l independent timing devices, each individually connected to a respective, pair of sensing ldevices adjacent to each other, and each elective to develop an -individual timing signal representative of the time required for a wheel to traverse the space between the sensing devices in the pair to which the timing device is coupled;

comparison means for comparing said timing signals from all of said timing devices with a given standard to determine whether the velocity of each of one or more railway vehicle wheels passing through the retarder is above or below a -given release speed and for developing overspeed and underspeed actuating signals based upon such comparison Whenever any wheel exceeds or drops below said release speed;

iirst actuating means for 'actuating said operating means to braking condition in response to said overspeed actuating signal; and

second actuating means for actuating said operating means to released condition in response to said underspeed actuating signal.

4. A speed-sensitive control system for a railway vehicle retarder comprising a traflic rail, at least one retarder member, and operating means for actuating said retarder member between braking and released conditions comprising:

a series of pairs of individual sensing devices, lo-

cated along said traic rail and having uniform spacing between the devices in each pair, that is less than the minimum spacing between railway vehicle wheels, each sensing device being eifective to develop an initiating signal indicative of the presence of a railway vehicle wheel at the sensing device location;

a series of timing devices, each individually connected to a respective pair of said sensing devices and each eiTect-ive tot develop a timing signal having an amplitude representative of the time required for a wheel to traverse the space between the sensing devices in the pair to which the timing device is coupled;

comparison means for comparing said timing signals from all of said timing devices with a given standard signal amplitude to determine whether the velocity of a railway vehicle passing through the retarder is above or below'a given release speed and for developing overspeed and underspeed actuating signals based upon such comparison;

first actuating means for actuating said operating means to braking condition in response to an overspeed actuating signal;

time delay release means, in said operating means, for

re-actuating said operating means to released condition upon elapse of a predetermined time interval v in which no overspeed actuating signal occurs;

. and second actuating means for actuating said operating means to released condition immediately in response to occurrence of an underspeed actuating signal, independently of said time delay release means.

5. A railway vehicle retarder control system according to claim 4 in'which said first and second actuating means `each includes a relay energized for a predetermined short time interval in response to the appropriate actuating signal, said time interval being substantially `independent of the duration of the actuating signals.

6. A railway vehicle retarder control system according to claim 4 in which said tirstactuating means includes rst limiting means for limiting operation thereof to overspeed actuating signals exceeding a given overspeed threshold amplitude, and in which said second actuating means includes second limiting means for limiting operation thereof to underspeed actuating signals exceeding a given underspeed threshold amplitude.

7. A speed-sensitive control system for a railway vehicle retarder comprising a traic rail, at least one retarder member, and operating means for actuating said retarder member between braking and released conditions comprising:

a series of pairs of individual sensing devices, located along said trafc rail and having uniform spacing between the devices in each pair, that is less than the minimum spacing between railway vehicle Wheels, each sensing device being effective to develop an initiating signal indicative of the presence of a railway vehicle wheel at the sensing device location;

a series of independent timing devices, each individually connected t-o a respective pair of said sensing devices and each eiective to develop a timing signal voltage having an amplitude representative of the time required for a wheel to traverse the space between the sensing devices in the pair to which the timing device is coupled,

each timing device including a capacitor, a charging circuit for the capacitor, and means for momentarily opening and cl-osing the charging circuit in response to the initiating signals from the associated pair of sensing devices whereby the charge on the capacitor at the time of the second initiating signal, constituting said timing signal voltage, is proportional to the elapsed time between the initiating signals from the associated pair of sensing devices and hence proportional to the average speed of the vehicle wheel moving between said pair of sensing devices;

comparison means, including a constant voltage supply, for com-paring said timing signal voltages from all of said timing devices with a given standard voltage representative of a given release speed to determine whether the velocity of each of one or more railway vehicle wheels passing through the retarder is above a given release speed and for developing an actuating signal based upon such comparison whenever any one lwheel exceeds said release speed.;

8. A speed-sensitive control system for a railway vehicle retarder comprising a traic rail, at least one retarder member, and operating means for actuating said retarder member between braking and released conditions comprising:

a series of pairs of individual sensing devices, located along said traiiic rail and having uniform spacing between the devices in each pair, that is less than the minimum spacing between railway vehicle wheels, each sensing device being eitective to develop an initiating signal indicative of the presence of a railway vehicle wheel at the sensing device location;

a series of timing devices, each individually connected to a respective pair of said sensing devices and each effective to develop a timing signal voltage having an amplitude representative of the time required for a wheel to traverse the space between the sensing devices in the pair to which the timing device is coupled,

each timing device including a capacitor, a charging circuit for the capacitor, and means for momentarily opening and closing the charging circuit in response to the initiating signals from the associated pair of sensing devices whereby the charge on the capacitor upon occurrence of the second initiating signal, constituting said timing signal voltage, is piroportional to the elapsed time between the initiating signals from the associated pair of sensing devices and hence proportional to the average speed of the vehicle wheel moving between said pair of sensing devices;

comparison means, including a constant voltage supply and a voltage divider coupled to said timing `devices, for comparing said timing signal voltages from all of said timing devices with a given standard voltage representative of a given release speed to determine whether the velocity of a railway vehicle passing through the retarder is above or below a given release speed and for developing overspeed and underspeed actuating signals based upon such comparison;

rst actuating means for actuating said operating means t-o braking condition in response to said overspeed actuating signal;

time delay release means, in said operating means, for re-actuating said operating means to released condition upon elapse of a predetermined time interval in which no overspeed actuating signal occurs;

and second actuating means for actuating said operating means to released condition immediately in response to Occurrence of an underspeed actuating signal, 'independently of said time delay release means.

References Cited UNITED STATES PATENTS 5/1937 Livingston 246-182 6/1959 Yalich et al. 246-182 FOREIGN PATENTS 3/1963 Great Britain. l/l947 France.