US3240930A - Retarder control systems - Google Patents

Description

March 15, 1966 R. E. PORTER ETAI.

RETARDER CONTROL SYSTEMS '7 Sheets-Sheet 2 Filed Jan. 13, 1965 .wwfoz Op.

INVENTORS ARTHUR R. CRAWFORD 1\CHP\RD E. PORTER M,

March 15, 1966 R, E PORTER ETAL 3,240,930

RETARDER CONTROL SYSTEMS '7 Sheets-Sheet 4 Filed Jan. 13, 1965 INVENTORS ARTHUR. R. CRAWFORD \C|\/-\RD E. PORTER 5f PM ZONE v m@ l l l I I l l l NUL w zo.:

March 15, 1966 R E, PORTER ETAL 3,240,930

RETARDER CONTROL SYSTEMS '7 Sheets-Sheet 6 F'iled Jan. l5, 1965 March 15, 1966 R E, PQRTER ETAL 3,240,930

RETARDER CONTROL SYSTEMS 7 Sheets-Sheet 7 Filed Jan. 13, 1965 IoJmDOw OP .M M E. mm WT ,f7 AW H MP R5 0 www AH mwhllllh 55E \0tm n.355 \\mtm n nv lm United States Patent O 3,240,930 RETARDER CONTROL SYSTEMS Richard E. Porter and Arthur R. Crawford, Columbus, Ohio, assignors to American Brake Shoe Company, New York, NY., a corporation of Delaware Filed Jan. 13, 1965, Ser. No. 427,537 19 Claims. (Cl. 246-182) This invention relates to a new and improved speedsensitive control system suitable for use in the control of a railway car retarder or like apparatus. This application is a continuation-in-part o-f application Serial No. 228,- 189, led October 3, 1962, now abandoned.

In the operation of a railroad classification yard, railroad cars are ordinarily released from the top of an incline or hump to roll down the incline into the branching tracks of the classification yard. Frequently, it is necessary to provide some means for braking the cars at one or more points along the gang or feeder track. Braking may also be required on other tracks in the classification yard. The track brakes or car retarders used usually include one or more pairs of brake shoes of elongated rail-like construction that engage the sides of the wheels of the cars.

In braking installations of this kind, it is frequently desirable to vary the braking force applied by the retarder to each car in accordance with the speed of the car as it enters the retarder. Thus, if a car is rolling at a speed less than Ia predetermined safe speed for movement beyond the retarder, it may be permitted to pass on to the remainder of the yard without braking; that is, the car retarder should permit the car to pass without braking engagement. A car rolling at a speed above the safe classification speed, however, must be subjected to a substantial braking pressure, the brake being relieved when the car has been slowed to the desired exit speed.

Deceleration of the car in the retarder depends on a variety of factors, including the weight of the car, the condition of its bearings, moisture on the braking rails of the retarder, and the like. Thus, one car may be braked to a safe speed after it has traversed only onehalf of the retarder. Another and heavier car entering the same retarder at the same speed may require braking for virtually the entire length of the retarder in order to achieve a safe exit speed. For this reason, accurate and reliable measurement of the railroad car speed is highly desirable in controlling a railroad car retarder, and it is advantageous to provide for continuous monitoring of the car speed throughout the length of the retarder.

One system that has been employed in the past for the determination of car speeds, in a retarder installation, er1- tails the segmentation of the traflic rail along which the car rolls into a plurality of relatively short sections that are insulated electrically from each other. This makes it possible to measure the speed of the car, periodically, in accordance with signals derived from engagement of the rails by the car wheels, speed determination being based upon the transit time required by the car in passing over individual sections of the segmented rail. Other similar arrangements have utilized a plurality of treadles mounted along the rail and engageable by the car wheels, a plurality of photocells or sensing switches, or like means for checking the position and speed of the car as it enters or as it passes through a car retarder installation.

It is a primary object of the present invention to provide a new and improved speed-sensitive control system, suitable for control of a railway car retarder or the like, that provides for reliable and accurate speed determination on a continuous basis.

A particular object of the invention is to provide a new and improved speed-sensitive system for controlling a railp ice way car retarder or the like that does not require physical segmentation of the traffic rail or the provision of multiple auxiliary devices along the rail, yet which affords a substantially continuous spe-ed determination sensitive to small changes in car speed over relatively short distances.

A specic object of the invention is to provide a new and improved continuous operating speed-sensitive control system in which the essential data for speed determination are obtained directly from the traic rail of a railway, in response to vibration of the rail by an incoming Vehicle.

An additional object of the invention is to afford a new and improved control system for a railway car retarder, and particularly a speed-determining system for continuously monitoring the speed of a railway car, which requires no moving parts at the rail itself and entails no electrical connection to the rail, yet uses the rail as the initial input member to the system.

An additional object of the invention is to provide a new and improved speed-sensitive control system for a railway car retarder that does not sense or Contact any part of the car being retarded and hence is independent of variations in car construction.

A corollary object of the invention is to provide reliable and accurate speed control of a railway vehicle retarder, based on control apparatus that is rugged and substantially maintenance-free, yet relatively inexpensive in construction. v

A further object of the invention is to provide a new and improved speed-sensitive control system for a railroad car retarder, in which the speed of an incoming car or cut of cars is determined by sensing vibration of a traffic rail, and to protect that system against erroneous operation due to vibration of the traffic rail caused by sources other than the incoming cars. Typical extraneous sources ofl vibration of the traffic rail include the actuation of switches on the rails near the retarder, passage of cars or locomotives along adjacent tracks, and the like.

Still anotherrobject of the invention is to protect a rail-vibration actuated speed sensing control system for a railroad car retarder against erroneous operation due to the presence of at portions on the wheels of cars passing through the retarder.

The present invention therefore provides a speed-sensitive control system for a railway car retard-er or the like comprising: a traic rail having a series of surface discontinuities at equally spaced intervals along a wheelengaging surface thereof; vibration-sensitive transducer means, mounted on said rail, for developing an electrical signal having a fundamental frequency determined by the velocity of a car wheel engaging said surface discontinuif ties; and electrical control means, responsive to said sig# nal, for actuating said retarder between braking and released conditions in response to variations of said fundamental frequency above and below a frequency representative of a given release velocity.

In the preferred construction described hereinafter, the surface discontinuities in the traic rail comprise shallow linear grooves formed transversely of the rail, but they could also constitue notches, pits, or grooves in the central bearing surface or in the outside corner of the rail, or ridges on the rail, if desired. The frequencysensitive control means employed in theV system may t-ake several different forms, as described in detail hereinafter. In general, the control means may 4be considered to represent a form of band-selection and noise discrimination circuit capable of distinguishing the aforementioned repetitive components from extraneous vibrations produced by movement of the car along the rail. The control means should 4be capable of making a relatively accurate determination of the car speed, from the frequency of the repetitive components, so that the Control signal can lclose and open the retarder to release the car at a given pre-set speed.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompany drawings which, by way of illustration, show preferred embodiments of the present invention yand 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 used and structural changes 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 schematic plan view and :block diagram of a railway car retarder including contr-ol apparatus comprising a speed-determining system conslructed in accordance with one embodiment of the present invention;

FIG. 2 is a detail circuit diagram illustrating the initial circuits of the speed-determining system of FIG. 1;

FIG. 3 is -a detail circuit diagram showing gain-conirol circuits and the principal speed-selection circuits used in the control system of FIG. 1;

FIG. 4 is a detail circuit diagram of the principal noisediscrimination and control circuits incorporated in the system of FIG. l;

FIG. 5 illustraes the operating characteristics of an adjustable low-pass tilter used in the system;

FIG. 6 is a block diagram, partly schematic, of another embodiment of the invention;

FIG. 7 is a schematic plan view and block diagram of another embodiment of the invention; and

FIGS. 8 and 9 are detail schematic views of certain circuits utilized in the embodiment of FIG. 7.

FIG. 1 illustrates the application of one embodiment of the Ipresent invention to the Control `of a railway car retarder 10. As shown in FIG. l, car retarder 10 may include a Ipair of traffic rails 11 and 12 along which a car may roll in the direction indicated by the arrow A. A pair of car-retarding rails or brake shoes 13 are disposed immediaiely adjacent rail 11 in position t-o engage the opposite sides of a car wheel as it traverses this portion of the trafc rail. A similar pair of retarder rails 14 may be disposed adjacent traic rail 12 in position to engage the sides of the car wheels on rail 12 as they traverse retarder 10. Suitable means are provided for acuating retarder rails 13 and 14 conjointly, this mechanism being generally indicated in FIG. 1 by the retarder actuating mechanism 1S. It is not necessary to use both sets of retarder rails 13 and 14; one set may be employed, braking only the wheels on one side of a car. If only one set of retarder rails is used, it may -be desirable to use a guard rail along the other traic rail.

Retarder actuating mechanism 15 may be any suitable electrical, mechanical, pneumatic or hydraulic mechanism capable of moving retarder rails 13 and 14 between an open or released position and a closed or retarding position. When the retarder rails are in the open position, a car rolling along the track 11, 12 is permitted to pass through retarder 10 without substantial braking. When the retarder rails are in their closed position, however, the rails engage the sides of the car wheels and provide a substantial 'braking etIect on the rolling car.

In rearder 10, traiiic rail 12 may be of conventional construction. Traliic rail 11, however, is provided with a series of surface discontinuities at equally spaced intervals along the surface of the rail. In the illustrated apparatus, these surface discontinuities comprise a series of shallow grooves 16 in the upper or bearing surface of rail 11, the grooves extending transversely of the rail surface. By way of example, the grooves 16 in rail 11 may be of the order of one-eighth to one-quarter inch wide; preferably, these grooves are made quite shallow in order to avoid any weakening of the rail. The spacing S of the grooves or discontinuities 16 along the length of rail 11 is not particularly critical, except that this spacing must be made substantially smaller than the circumference of a railway Wheel and also must be substantially smaller than the spacing -between any two adjacent wheels on a railway track. Typically, the spacing S between the grooves 16 may be of the order of one to tive inches. Whatever the selected spacing for the discontinuities or grooves 16, the spacing should be maintained constant to alford an effective means for causing rail 11 to vibrate at frequencies representative of the speed of a car moving into and through retarder 10.

It is not essential that the discontinuities 16 take the form `of shallow grooves `in the upper surface of trafiiC rail. 11. Instead, these discontinuities may comprise relatively shallow notches or pits formed in the upper surface of the rail or in the corner of the rail adjacent `the wheel flange. Conversely, relatively small projections could be formed on the rail surface, since the purpose of the rail disconlinuities is to set up a vibration in the rail that is proportional to the speed of a railway car wheel moving along the rail. The grooved construction described hereinabove is preferred, however, because it affords the least problems with respect to machining of the rail, wear of the rail, and maintenance of the requisite regular and consistent series of surface discontinuities.

The speed-determining system of FIG. 1 also includes transducer means for generating an initial electrical signal that is representative of vibration of the traiiic rail 11. This transducer means comprises a pair of individual sensing or pickup devices 17A and 17B that are mounted on the base or web portion of traffic rail 11 between points 11A and 11B defining the limits of the serrated portion of the traffic rail. A variety of ditcrent specific forms of vibration-sensitive pickup may be utilized for the devices 17A, 17B. Typically, these devices may comprise conventional velocity-actuated transducers each capable of producing an electrical output signal directly representative of vibration of the member upon which they are mounted, the rail 11. Inasmuch as pickup devices of this kind are Well known in the art and are commercially available, construction of the pickups is not described in detail herein.

The notched portion of rail 11 extends well ahead of the retarder rails 13 and 14. In the illustrated arran-gement, the retarder rails are of given length L and the notched section of rail 11 ahead of the retarder rails is of a corresponding length. Transducer 17A is 4located a distance D from the initial end 11A of the notched portion of rail 11. Transducer 17B is located a corresponding distance D from the outlet end of the retarder. This spacing is not critical, however, and is shown only to afford a complete illustration of this embodiment of the invention.

The transducers 17A and 17B are both electrically connected to a speed control unit 18. The speed control unit 18 includes frequency-sensitive means for segregating, from the initial electrical signals from the transducers 17A and 17B, speed-representative signals comprising repetitive components of the initial electrical signal produced by engagement of a car wheel with the surface discontinuities or grooves 16 Iin the traffic rail 11. That is, speed control unit 18 provides for the effective elimination of extraneous vibrations of notched rail 11, in the signals from the transducer means 17A, 17B, such as might be produced by a flat spot or spots on a vehicle wheel, by irregularities in the traffic rail 11 at some point other than the grooves 16, or by other similar sources of extraneous vibration. Speed control unit 1S also includes means for utilizing the speed-representative signals to develop a control signal, suitable for controlling operation of retarder actuating mechanism 15.

In control unit 18 the two pickups 17A and 17B are connected to an automatic signal level switching circuit 21. Switching circuit 21 is employed only to select the signal of maximum amplitude, from the two pickup devices, so that a single signal may be utilized to actuate the remaining circuits of control unit 18. It is not es.

sential that two pickup devices be employed; instead, a single pickup may be utilized, in which case the automatic signal level switch 21 may be eliminated. On the other hand, additional pickups may be included in the system if desired. Selection of a single pickup from multiple transducers, in a given application, is dependent primarily upon the sensitivity of the transducers utilized and the damping characteristics of traffic rail 11 with respect to vibrations caused by movement of a car wheel along the rail.

The output of switching circuit 21 is coupled to a cornpressor amplifier 22 that functions primarily as an automatic gain control for the system. The compressor amplifier includes, in its output stage, a high-pass filter with a relatively low cut-off frequency, this filter being employed to eliminate, to a substantial extent, the effect of verylow-frequency signals produced by flat spots or other.

irregularities in car wheels. The compressor amplifier Iis coupled, in t-urn, to a clipper circuit 23 that is connected to an adjustable low-pass filter 24. Adjustable filter 24 is the speed-selection device of the systemV and is employed to adjust the system to release cars from retarder at varying speeds dependent upon the requirements of the classification yard. It is essential that fil-ter 24 have a sharp cut-off characteristic in order to afford adequate differentiation between different desired output speeds.

The output of filter 24 is coupled to a driver amplifier 25 utilized to actuate a signal relay and control circuit 26. Circuit 26, in turn, actuates a brake relay circuit 27 that is electrically connected to retarder actuating mechanism to control the operation of the retarder.

In addition toV the connection to clipper circuit 23, the output of compressor amplifier 22 is coupled to a lowpass filter 28 that is connected in series with a high-pass filter 29 to a noise amplifier and relay circuit 31. Noise amplifier and relay circuit 31 is coupled to signal relay circuit 26. A portion of the signal relay of circuit 26 is incorporated in a bypass circuit that shunts low-pass filter 2S for certain operating conditions, as described ,more fully hereinafter.

In c-onsidering operation of the system illustrated in FIG. 1, it may first be assumed that there is no car ,entering retarder 10. Retarder actuating mechanism 15 is set to maintain the retarder open. Since no car is rolling over the notched traffic rail 11, the only output signals from transducers 17A and 17B are extraneous noise signals of short duration. These signals are not effective to actuate control system 18, so that the retarder remains in its open or released braking condition.

A car entering retarder 10 first engages the notched trafhc rail 11 at point 11A, the direction of car entrance being indicated by arrow A. Movement of the car wheels along the serrated tra'ic rail produces a vibration in the traffic rail having frequency components determined by the spacing of notches 16 and 'by the speed at which the car is moving, but with many harmonics. Vibration of the rail is sensed by transducers 17A and 17B, producing initial electrical signals having repetitive components at frequencies corresponding to the frequencies at which the traffic rail .is vvibrated. When the car first enters the retarder, at point 11A, the signal produced by the first transducer 17A is substantially stronger than that produced by the second pickup 17B, since the car is closer to transducer 17A and, accordingly, the damping effect of transmission of vibration along the rail is less with respect to the first pickup unit.

The output signal from transducer 17A, accordingly, is selected by switch 21 and supplied to compressor amplier 22. The compressor amplifier and clipper 23 serve primarily to maintain a constant amplitude output despite substantial variations in the amplitude of the signal received from the transducer. This automatic gain con- 5, trol effect is desirable because the amplitude of the output signal from the transducer will vary to a substantial extent as the car moves aiong traffic rail 11.

Filter 24 is set, in advance, to a given frequency determined by the desired maximum speed for cars leaving the retarder. Assuming that the car enters at a speed above the pre-set exit speed, the signal from clipper 23 is composed primarily of frequencies higher than the setting of the adjustable low-pass filter 24. Consequently, the signal is substantially attenuated and does not effect operation of the signal relay and control circuit 26. The same signd, however, is supplied to noise amplifier 31 through filter circuits 28 and 29. The signal supplied to noise amplifier 31 actuates a relay, referred to herein as the noise relay, completing an energizing circuit for the signal relay of unit 26.V Upon actuation of the signal relay, brake relay 27 is energized -to complete an operating cir- Vcuit that supplies a control signal to retarder actuating mechanism 15. Accordingly, actuating mechanism 15 is energized to close retarder 10.

Closing of the retarder is preferably accomplished before the railroad car reaches retarder rails 13 and 14. It

lis for this reason that the serra-ted trafiic rail 11 is extended well ahead of the retarder mechanism, giving sufficient time to close the retarder before the car reaches braking position.

When the car is engaged by retarder rails 13 and 14, it is decelerated at a rate depending upon the weight of Vthe car, its initial speed, the braking force applied to the retarder rails by the retarder actuating mechanism, and other factors common to railretarder systems. When the car is decelerated to a speed below the exit velocity for which filter 24 is adjusted, the filter applies a signal to driver amplifier 25, which in turn actuates circuit 26 to de-energize the signal relay. When the signal relay drops out, the operating circuit for brake relay 27 is interrupted, with the result that the control signal applied to actuating mechanism 15 is changed and mechanism 15 restores the retarder to its open or released position.

When signal relay 26 drops out, at the time that braking of the car is completed, the bypass circuit normally effective for low-pass filter 28 in the noise channel of the system is opened, effectively placing the low-pass filter in the signal channel to the noise amplifier 31. This is done to prevent high order harmonic signals from holding the noise relay energized at speeds below a predetermined minimum setting established as the lower limit of retarder control.' In a typical system, this minimum setting may be of the order of three miles per hour, with retarder control afforded over a range of three to fifteen miles per hour as determined by the setting of adjustable t filter 24.

As noted above, retarder 10 is opened or released while the car is still moving. Consequently, under ordinary circumstances the car continues its movement through the retarder, at its reduced speed, and eventually passes beyond the exit end 11B of notched rail 11. When this occurs, the signal supplied to the control system 18 is l no longer adequate to energize noise relay 31, with the result that the noise relay drops out and the system isready for a subsequent operation. The noise relay also drops out if the car speed drops below the minimum range of retarder operation, as noted above, due to the operation of high-pass filter 29. 65-

In some instances, if retarder 10 is established on a substantial grade, and extends for a substantial length along traffic rails 11 and 12, a given car of free rolling characteristics may be braked to the desired speed but may accelerate substantially after the retarder has been released and before the car leaves the retarder. If this should occur, the output signals from transducers 17A and 17B again increase in frequency above the frequency setting of adjustable low-pass filter 24. This `cuts off the actuating signal for driver amplifier 25 and permits the signal relay of circuit 26 to be energized again under control of the noise amplifier and relay circuit 31. Accordingly, -the retarder is again actuated by the control signal supplied by the operation of the signal relay and brake relay 27.

When a car first enters the retarder control system, at point 11A, the predominant signal is that supplied by transducer 17A. Movement of the car through the retarder, however, eventually results in production of a signal at transducer 17B that is of greater amplitude than the signal from the initial pickup 17A. When this happens, switch 21 is actuated automatically to transfer control of the system from the initial transducer 17A to the second or outlet end transducer 17B.

FIG. 2 illustrates a specific circuit that may be utilized for the automatic level switch 21 of FIG. 1. Switch circuit 21, as shown in FIG. 2, comprises a first pre-amplifier 41 connected to pickup transducer 17A by means of a coupling capacitor 42. Capacitor 42 is connected to the center terminal of a voltage divider comprising two resistors 43 and 44 connected in series between a negative polarity unidirectional supply, designated as C-, and system ground. The coupling capacitor is also connected -to the base electrode of a first transistor 45. The emitter of transistor 45 is connected to ground through a bias resistor 46. The collector electrode of transistor 45 is returned to the C- supply through a load resistor 47 and is connected to the base electrode of a second transistor 48.

Transistor 48 is connected in an emitter follower circuit. The collector of this transistor is connected directly to the C supply and the emitter is returned to ground through a load resistor 49. The output from the second stage of pre-amplifier 41 is taken `through a coupling capacitor 51 connected to the emitter of the transistor.

The output stage of pre-amplifier 41 includes a first diode 52 connected from capacitor 51 to ground and a second diode 53 connected in series with the capacitor to afford a half-wave voltage doubling rectier circuit. The voltage doubler is completed by a capacitor 54 connected from diode 53 to system ground. A resistor 55 connects the capacitor to an output terminal 56.

The second pickup transducer 17B is connected by a coupling capacitor 60 to a pre-amplifier circuit 61 that is essentially identical with the preamplifier 41. The only difference between circuits 41 and 61 is that in the voltage doubler circuit comprising the output of amplifier 61 the two diodes 62 and 63 are reversed in polarity as compared with the corresponding diodes 52 and 53 in the pre-amplifier for the first stage of the circuit. The voltage doubler circuit includes a capacitor 64, the voltage doubler being connected to terminal 56 by means of a resistor 65.

The common output terminal 56 of the two pre-amplifiers 41 and 61 is returned to ground through an output resistor 67 which is connected in parallel with a capacitor 68. A resistor 69 connects terminal 56 to the control electrode of a single-controlled silicon rectifier 71. Rectifier 71 is connected in the energizing circuit for the operating coil 72 of a level-switching relay 73. The cathode of rectifier 71 is returned to ground through a self-biasing diode 74, the anode of the rectifier being connected to coil 72. The other end of coil 72 is connected directly to a suitable A.C. supply (not shown). A damping circuit, comprising a diode 75 connected in parallel with a capacitor 76, is connected across coil 72 to protect rectifier 71 and relay 73 against transient over-voltage condit-ions.

Relay 73 includes a first movable contact 81 engageable with either of two fixed contacts 82 and 83, depending upon whether or not the relay has ybeen actuated. A second set of contacts is incorporated in the relay and comprises a moving Contact 84 engageable with either of two fixed contacts 85 and 86. Movable contacts 81 and 84 are shown in the positions maintained when relay 73 is de-energized.

Movable contact 81 comprises the principal output terminal for automatic switch circuit 21 and is connected to compressor amplifier 22, as described in detail hereinafter in connection with FIG. 3. Contact 82 of relay 73 is connected directly to the output of transducer 17B, whereas contact 83 is connected directly to the output of pickup device 17A.

Contacts 8486 of relay 73 are connected in a safety circuit, the operation of which is described in substantial detail hereinafter. Contact 86 is directly connected by a line 87 to a noise amplifier (FIG. 4). Contact 85 is connected through a resistor 88, in series with a diode 89, and by a conductor 91, to the noise relay that cornprises a part of the circuit 31 of FIG. 4. The movable contact of this portion of the relay is connected to a capacitor 92 that is returned to system ground.

Operation of the automatic level switch 21 of FIG. 2 is relatively simple, and in effect, constitutes a comparison of the amplitudes of the output signals from transducers 17A and 17B to couple the signal having the greatest instantaneous amplitude to the compressor amplifier 22 through movable contact 81 and the output conductor 93. Thus, when a car first enters the retarder section, engaging rail 11 at point 11A (FIG. 1), the traffic rail is vibrated and an output signal yis produced by each of transducers 17A and 17B. At first, the signal from transducer 17A is substantially higher in amplitude than that from transducer 17B, due to the proximity of transducer 17A to the leading end 11A of the serrated traffic rail. Accordingly, when the two output signals from amplifiers 41 and 61 (FIG. 2) are added together in opposite polarity across resistor 67, the net signal across the resistor is of positive polarity, the polarization of the voltage doubler 52-'54 in the output of pre-amplifier 41. The resulting positive-polarity signal at terminal 56 is supplied to the control electrode of rectifier 71 and triggers the rectifier to conduction. With the rectifier 71 in its conductive state, relay 73 is energized, closing movable contact 81 on contact 83 and directly connecting transducer 17A through line 93 to the succeeding stage, compressor amplifier 22.

Subsequently, as the car passes through the retarder, a condition is reached in which the output signal from pickup 17B is of greater amplitude than that from transducer 17A. When this condition obtains, the summation signal appearing at terminal 56, and resulting from the addition of the output signals from pre-ampliers 41 and 61 across resistor 67, swings negative in polarity. This is effective to cut off conduction through rectifier 71, with the result that relay 73 is de-energized. When the relay drops out, movable contact 81 returns to its normal position in engagement with contact 82, connecting the compressor amplifier 22 directly to the output of transducer 17B.

In the illustrated circuit, it is preferable that capacitors 54 and 64 be relatively large. The object in selecting capacitors of substantial size is to obtain a charging time for the capacitors covering several cycles at the fundamental frequencies of input signals within the normal operating range of car speeds for the retarder system. That is, the capacitors 54 and 64 establish a relatively long time constant for this portion of the circuit. This prevents triggering of relay 73 in response to short-duration, high-amplitude noise pulses. The relatively long time constant also serves to prevent chattering of the relay between its energized and de-energized conditions during time intervals in which the output signals from the two transducers are quite close in amplitude.

FIGS. 3 and 4, taken together, illustrate the remaining control circuits of system 18. Inasmuch as the individual circuits in these two figures are interconnected in several different instances, it is desirable to consider the two figures conjointly, both in the discussion of construction and in the description of operation.

FIG. 3 illustrates one construction that may be utilized for compressor amplifiers 22. In this circuit, the conductor 93 from signal level switch 21 (see FIG. 2) is returned to ground through a potentiometer 101. The tap on potentiometer 101 is coupled by a capacitor 102 to the base electrode of a transistor 103 in the first stage of the compressor amplifier. This first stage of the compressor amplifier is an emitter follower circuit, the collector electrode of the transistor being connected through a de-coupling resistor 104 to the C- supply and the emitter being connected through a load resistor 105 to system ground. Resistor 104 is y'by-passed to ground by a de-coupling capacitor 110. A degenerative feedback circuit comprising a capacitor 106 and a resistor 107 connects the emitter of transistor 103 back to the base electrode. In addition, capacitor 106 is connected to the center terminal of a voltage divider comprising two resistors 108 and 109 connected from system ground back through resistor 104 to the C- supply.

The output from the first stage of compressor amplifier 22 is taken through a capacitor 111 connected to the emitter of transistor 103, on one hand, and to the center terminal of a voltage divider comprising two . resistors 112 and 113 connected in series with resistor 104 from the C- supply to ground. A connecting resistor 114 is connected from capacitor 111 to the base electrode of a transistor 115 in the second stage of the compressor amplifier. The emitter of transistor 115 is returned to system ground. The collector of this transistor is connected through a resistor 116 in series with resistoi` 104 to the C- supply. The output from transistor 115 is taken through a coupling capacitor 117 connected from the collector electrode of the transistor to the base electrode of a transistor 118 comprising the next stage of the amplifier. The base electrode of transistor 118 is also connected to a voltage divider comprising two resistors 119 and 121 connected in lseries from the C- supply to system ground.

The emitter circuit for transistor 118 comprises a resistor 122 that is connected in parallel with a capacitor 123 from the emitter to system ground. The collector circuit includes a load resistor 124 by means of which the collector is connected t the C- supply. The output signal from transistor 118 is taken through a resistor 125 connected to the collector and connected in series with a coupling capacitor 126 that comprises a part of a highpass filter 127. Resistor 125 is used to match the input of the filter to the output of the amplifier.

Filter 127 includes a further series capacitor 128 connected to capacitor 126, the common terminal of the capacitors 126 and 128 being returned to ground through the series combination of an inductance coil 129 and a capacitor 131. A further series capacitor 132 is connected to capacitor 128, the common terminal of capacitors 128 and 132 being returned to ground through a resistor 133. Resistor 133 is the proper load termination for the high pass filter 127. Resistors 125 and 133 are terminating resistors selected to make filter 127 give a fiat response above the cut-off frequency of the lter. Capacitor 132 couples filter 127 to the base electrode of a transistor 134 that comprises the final stage of compressor amplifier 22.

Transistor 134 is connected in a circuit similar to that for transistor 103, this being an emitter follower utilized primarily to obtain a high input impedance, to avoid loading the filter 127, but having a relatively low output impedance. The collector electrode of transistor 134 is connected d-irectly to the C- supply. The emitter electrode is returned to ground through two series-connected load resistors 135 and 136 used to provide proper signal level to the clipper circuit 23. To achieve the desired impedance characteristics, this stage of the amplifier includes a de-generative feedback circuit including a coupling capacitor 137 connected in series with a resistor 138 from the emitter of transistor 134 to its base electrode. Capacitor 137 is also coupled to a voltage 10 divider comprising two resistors 141 and 142 connected from the C- supply to ground for operating bias.

There are two output connections to transistor 134. The first output connection is taken directly from the emitter of the transistor, through a coupling capacitor 143 and a conductor 144 to the signal relay of circuit 26 and to the filter 28, as described more fully hereinafter in connection with FIG. 4. The second output connection is taken from the common'terrnina-l of resistors and 136 in the emitter circuit, this output extending to clipper circuit 23 and specifically to a coupling capacitor 145 in the input of the clipper.

Compressor amplifier 22 is provided with a negative feedback circuit from the final stage, comprising transistors 134, back to the initial compressor stage, transistor 115. This negative feedback circuit includes a coupling capacit-or 146 that is connected to the emitter of transistor 134 and to a series resistor 147. Resistor 147, in turn, is connected to a half-wave voltage doubler circuit including a diode 148 connected from the resistor to ground and a second diode 149 connected, from the resistor, in series with a capacitor 151, to ground. Diodes 148 and 149 are oppositely polarized. The common terminal of diode 149 and capacitor 151 is connected through two limiter diodes 153 and 154 and a resistor 155 to the base electrode of transistor 115 to complete the feedback circuit. A fixed bias circuit is also provided for the base electrode of transistor l115, this fixed lbias circuit including -a filter circuit 157 connected by a conductor 158 to a low-voltage D.C. supply shown as a part of brake relay circuit 27 in FIG. 4.

Clipper circuit 23 is of conventional construction. It comprises a resistor 161 that is connected to the input coupling capacitor 145 and returned to system ground through a pair of back-to- back diodes 162 and 163. The output of the clipper comprises a coupling capacitor 164 connected from the common termina-l of circuit elements 161-163 to the center terminal of a voltage divider including two resistors 165 and 166, the voltage divider being connected from the C- supply to ground. The output terminal of the clipper is indicated by reference numeral 167.

A preferred form of adju-stable low-pass filter 24 is shownA in FIG. 3. The first stage of this circuit comprises a pair of transistors 168 and 169 each connected in an emitter follower configuration with a feedback circuit from the output of transistor 169 back to the input of transistor 168, this feedback circuit including a twin-T filter 171.

Filter circuit 171 includes an adjustable input resistor 172, used for input matching to give fiat response in the pass-back of the filter. Resistor 172 is connected to the output terminal 167 of clipper stage 23 and is further connected in series with two adjustable resistors 173 and 174 to the base electrode of transistor 168. A pair of capacitors 175 and 176 are connected in series with each other across resistors 173 and 174 and the common terminal of the two capacitors is connected through an adjustable resistor 177 in series with a resistor 178 to the C- supply. Resistor 178 is the load resistor in the emitter circuit of transistor 169.` The vfilter cir-cuit is completed by a capacitor 179 connected from the common terminal of resistors 173 and 174 through resistor 178 to the C- supply.

The collector electrode of transistor 168 is connected to system ground. The output circuit of the transistor comprises a Kload resistor 181 connected in series with resistor 178 to the C- supply. The emitter of transistor 168 is connected to the base electrode of transistor 169, the collector electrode of transistor 169 being grounded.

The succeeding stage of filter 24 is of more conventional configuration. It comprises a pair of resistors 183 and 184 connected in series with each other from the emitter of transistor 169 to the base electrode of a transistor 185. The common terminal of resistors 183 and 184 is returned to the C- supply through an adjustable capacitor 186. The input terminals to this stage, however, which is connected to the emitter of transistor 169, is connected to a capacitor 187 that is not returned directly to the C- supply, instead being connected thereto through a resistor 188 that comprises the output resistor for the filter circuit 24. This feed-back gives a sharper fall-off about the knee of the low-pass filter characteristic.

Transistor 185 is connected in an emitter follower impedance matching stage. The collector electrode is grounded and the emitter is connected to the C- supply through a load resistor 189. The collector electrode of transistor 185 is also connected through a low-pass filter 191 to the base electrode of a transistor 192 in the output stage of circuit 24. Filter 191 may be essentially identical with the filter circuit in the input to transistor 185, except that both capacitors are returned directly to the C- supply. Transistor 192 is again connected in an emitter follower impedance matching configuration with the collector connected to system ground and the emitter returned to the C- supply through load resistor 188. In addition to the feedback connection to capacitor 187, the emitter of transistor 192 is connected by a conductor 193 to the noise relay in circuit 31 (FIG. 4).

FIG. 4 shows the remaining control circuits of system 18. As shown therein, low-pass filter 28 is provided with an input terminal 201 connected by the conductor 144 to the output stage of compressor amplifier 22 (FIG. 3). Low-pass filter 28 includes first and second inductances 202 and 203 connected in series with each other from `input terminal 201 to the filter to an output terminal 204. A capacitor 205 is connected in parallel with coil 202. The common terminal of inductances 202 and 203 is returned to system ground through a capacitor 206. The input and output terminals 201 and 204 are returned to ground through two capacitors 207 and 208 respectively. In the output of the filter, a resistor 209 is connected from output terminal 204 to ground. Resistor 209 matches the characteristic impedance of the filter to give a flat response in the pass-band.

High-pass filter 29 comprises an impedance-matching resistor 211 connecting the filter to the output terminal 204 of low-pass filter 28. Resistor 211 is connected in series with two capacitors 212 and 213, capacitor 213 being returned to ground through a potentiometer 214 that terminates the filter. The movable tap 215 on the potentiometer constitutes the output terminal of the highpass filter. The common terminal of capacitors 212 and 213 is returned to ground through a series circuit comprising an inductance coil 216 and a capacitor 217.

A coupling capacitor 219 connects the output terminal 215 of high-pass filter 29 to the base electrode of a transistor 221 in the input stage of the noise amplifier and relay circuit 31. Transistor 221 is connected in an emitter follower circuit similar to that provided for transistor 103 in the input of compressor amplifier 22 (see FIG. 3) to afford a relatively high input impedance with a relatively low output impedance. Thus, the collector electrode of transistor 221 is connected to the C- supply. The emitter electrode is returned to ground through a load lresistor 222. A 'de-generative feedback circuit is connected from the emitter to the base electrode, this feedback circuit comprising a capacitor 223 connected in series with a resistor 224. The common terminal of capacitor 223 and resistor 224 is connected to the center of a voltage divider comprising two resistors 225 and 226 connected from the C- supply to ground.

The output from the first or impedance-matching stage of noise amplifier and relay circuit 31 is taken from the emitter of transistor 221 through a coupling capacitor 227. Coupling capacitor 227 is connected to a voltage doubler half-wave rectifier comprising a diode 229 connected in series with a capacitor 230 from capacitor 227 to ground, a further diode 231 being connected in opposite polarization directly from capacitor 227 to ground. The output terminal 220 of the voltage doubler circuit is connected to resistor 232 that is returned to ground. Terminal 220 is also connected by conductor 87 to contact 86 of the signal level relay 73 (FIG. 2). A gate current limiting lresistor 233 is connected from terminal 220 to the control electrode of a signal controlled silicon rectifier 234.

Rectifier 234 is connected in the energizing circuit for the operating coil 235 of a noise relay 236. A self-biasing circuit comprising a diode 237 is connected from the cathode of rectifier 234 to ground. A diode 238 and a parallel capacitor 239 are connected across relay coil 235 to protect the relay and diode 234. The remaining terminal of the relay coil is connected to the secondary winding 240 of an input transformer 250 in the brake relay circuit 27, the primary winding of transformer 250 being connected to a suitable A.C. supply.

Noise relay 236 is provided with a first set of contacts comprising a movable contact 241 that engages a fixed contact 244 when the relay is de-energized but moves to engagement with a contact 243 when the relay is actuated. Contact 243 is connected to terminal 220 in the input circuit to control rectifier 234. Movable contact 241 is connected to a capacitor 242 that is returned to ground. Contact 244 is connected through a coupling resistor 253 to a low-voltage D.C. supply circuit including a pair of resistors 254 and 255 connected as a voltage divider, in series with a diode 256, across the secondary winding 240 of transformer 250. The voltage divider is shunted by a capacitor 260. It is thus seen that capacitor 242 is charged from the rectifier circuit, through resistor 253, during intervals in which the noise relay is de-energized, and may be discharged into the input circuit to signalcontrolled rectifier 234 when the relay is actuated. This increases the time constant of capacitor 230 and resistor 232 and tends to lock in the relay once it has closed.

Relay 236 includes a second set of contacts comprising a movable contact 246 engageable with a fixed contact 245 when the relay is de-energized and movable into engagement with a second fixed contact 247 when the relay is actuated. Contact 247 is connected to the output of adjustable low-pass filter 24 (FIG. 3) by means of conductor 193. Contact 246, the movable contact, is connected to a coupling capacitor 261 in the input of driver amplifier 25. Contact 245 is connected to the movable tap of a potentiometer 262, shown as a part of brake relay circuit 27. Potentiometer 262 is connected across a pair of diodes 263 that are connected in back-to-back relationship to afford a clipper circuit. The clipper circuit is connected in series with a resistor 264 back to the secondary winding 240 of transformer 250 to afford a fixed-voltage A.C. bias circuit.

Noise relay 236 includes one further set of contacts comprising a movable contact 251 that engages a fixed contact 248 when the relay is tie-energized but moves into engagement with a second fixed contact 249 when the relay is actuated. Contact 248 is connected, by conductor 91, to the contacts of switching device 73 in the automatic level switch circuit 21 (FIG. 2). Movable contact 251 is connected to the A.C. supply, in this instance being connected to transformer secondary 240 in brake relay circuit 27. Contact 249, on the other hand, is connected to one terminal of an operating coil 269 for a signal relay 271 constituting a part of control circuit 26.

Considering next the driver amplifier circuit 25, it is seen that the coupling capacitor 261 in the input to this circuit is connected to a voltage divider comprising two resistors 272 and 273 connected from the C- supply to ground. Capacitor 261 is also connected by a resistor 274 to the base electrode of a transistor 275.

The emitter circuit of transistor 275 comprises a bias resistor 276 that is returned to ground in parallel with a by pass capacitor 277. The emitter is connected to the C- supply by a load resistor 278 and is also connected to lboost circuits.

input of control circuit 26.

13 the base electrode of a second transistor 279 included in the amplifier.

Transistor 279 is connected as an emitter follower with the collector connected directly to the C- supply. kThe emitter is returned to ground through a load resistor 281. There is a feedback circuit from the emitter of transistor 279 to the base electrode of transistor 275, this feedback circuit including, in series, a resistor 282 and a capacitor 283. The resulting circuit is essentially similar to circuits used in the communication field for emphasizing lowfrequency components with respect to high-frequencies, devices of -this'kind generally being referred to as bass- Thus, driver amplifier 25 affords greater Vamplification at relatively low frequencies than at high frequencies.

The output from driver amplifier 25 is taken through a resistor285 connected to the emitter of transistor 279. Resistor 285 is connected in series with a capacitor 286 that is coupled to a half-wave voltage doubler rectifier circuit. The voltage doubler comprises a diode 287 connectedfrom capacitor 286 to ground and a second diode 288 connected with opposite polarization and in series with a capacitor 289 from capacitor 286 to ground. The common terminal of diode 288 and capacitor 289 is identified by reference numeral 291.

Voltagey doubler circuit 287-289 is shown as a part of Ithe signal relay and control circuit 26. A potentiometer 292 is connected in parallel with the capacitor 289 of the voltage doubler circuit. The movable tap of the po- Stentiome'ter is connected through a resistor 293 to the lcontrol electrode of a signal-controlled `silicon rectifier 294'." Diode 294 is connected in series with the operating coil 269 of signal relay 271.

There is another circuit connection to the control electrode of lrectifier 294, this second circuit connection being utilizedto afford a fixed bias circuit for the control electrode. yThe bias circuit includes a current limiting resistor296 and a b ias resistor297 connected in series with each other from the control electrode of rectifier 294 back to diode 256l in brake relay circuit 27. A`Zener diode '298 is connected from the common terminal of resistors 296 and 297 to groundv to complete thebias circuit.

, Signal relay 271 is provided with three sets of operating contacts. The first set comprises a movable conn tact 301 that engages, a fixed contact 304 when the relay is de-venergized but moves to engagement with a second fixed contact 303 when the relay is actuated. Contact 3 01 is returnedto ground through a capacitor 315. Conoutput terminal 2 91 of the voltage Adoubler circuit in the The next set of contacts in relay 271 comprises a movj able contact 306 that engagesra fixed Contact 305 when the relay is not energizedl butengages a second fixed contact 307 lwhen the relay is actuated. Contact 305 is open-circuited. Contact 306 is connected to output teryminal 204 of low-pass filter 28. Contact 307 is connected'to the input terminal 201 of the low-pass filter.

Thus, itcan'be seen that when' signal relay 27,1,is enerand 311 of relay 271 to afford a means for actuating the system to close the retarder on a manually controlled basis'.

Brake relay 27 may be connected to retarder actuating mechanism 15 in any one of a variety of ways, depending upon the construction of the retarder operating mechanism and the kind of control system required for its operation. In the arrangement shown in FIG. 4, the control signal connection to the retarder operating mechanism is made through a single set of contacts 325 of the brake relay. However, this connection may be considerably more complex if it is necessary or desirable to open or close more than one circuit for the retarder actuating mechanism to put the brakes on or off.

In addition, 'the brake relay may be provided with a second set of contacts 326 and appropriate indicator lights 327 and 328 to show whether the brake relay has been actuated.

To facilitate description of the operation of the control system of FIGS. 2-4, it is desirable first to consider typical examples of notch spacing and other factors affecting system operation. For example, the notched spacing S (FIG. 1) may be established at 1`. 5 inches, thereby establishing an approximate frequency-to-speed relation of eleven cycles'per second per mile per hour. It will be understood, of course, that this particular notch spacing is given only by way of example and that other spacing may be selected with consequent revisions in the operating circuits.l In a typical installation, the length L is thirty-nine feet, the distance D fifteen feet (FIG. 1).

FurtherV to establish the operating characteristics for the system asl shown in FIGS. 2-4,` it may be assumed that'the compressor amplifier 22 is provided with an output filter 127 affording an attenuation of three decibels at twenty cycles per second, a frequency representative of approximately two miles per hour, with virtually infinite rejection -for frequencies below fourteen cycles per second. Low-pass filter 28 may be constructed to have a cut-off'frequency of approximately one hundred sixty-five cycles per second, corresponding to about fifteen miles per hour with the aforementioned notched spacing of 1.5

As noted above, the lower limit of the operating' range for the system is determined primarily by the construction *of high-pass filter 29. In the following operational description, it is assumed that this filter is constructed to have a cut-offA frequency of about thirty-.three cycles per second, corresponding to a lower speed limit, for retarder control of three miles per'hour'.

The exit:` speed for the car is established, as noted above, by adjustment of low-pass filter 24. In the' followther amplified by driver amplifier 25.

Y Initially, before a car enters the immediate area. of the retarder, all ofthe operating relays of the system are deenergized. All relays are illustrated in thiscondition.

ySwitching relay 73 in the automatic level switching circuit 21 (FIG. 2) is held de-energized by the self-biasing circuit for diode 71, comprising diode 74, which maintains diode 71 in cut-off condition. Similarly, noise relay 236 is maintained de-energized by the small self-bias afforded by diode 237 (FIG. 4). Signal relay 271 is vmaintained def-energized by the ope'n circuit win the operating circuit for coil 269 thatY appears at contacts 249 and 251 of the noise relay. Brake relay 27, on the other hand, is held in its unactuated condition due to the fact that operating coil 321'is open-circuited at contacts 309 and 311 of signal relay 271.

`With operating conditions as described above, a car 'may enter the retarder control system at point 11A(FIG.

1) at a speed substantially above the setting of adjustable low-pass filter 24. The entering car, as it passes over notches 16, vibrates rail 11 at a fundamental frequency determined by the car speed. Thus, with a notch spacing S of 1.5 inches, a car entering the retarder at six miles per hour vibrates the rail at a fundamental frequency of approximately sixty-six cycles per second. A car travelling at eight miles per hour would vibrate the rail at a fundamental frequency of eighty-eight cycles and a car travelling twelve miles per hour would produce a vibration having a fundamental frequency of one hundred thirty-two cycles per second. However, vibration of the rail 11 is not limited to the fundamental frequency by any means. Rather, the rail also vibrates at frequencies representative of multiple harmonics of the fundamental Consequently, the vibration of the rail is a quite complex phenomenon.

Initially, with an over-speed car entering the retarder system, relay 73 is actuated, as described above, to connect only transducer 17A to compressor amplifier 22. The compressor amplifier amplifies the signal from transducer 17A, producing an -output signal that is maintained within a limited amplitude range despite substantial variations in the amplitude of the input from the pickup device. It should 'be noted, in this regard, that diodes 153 and 154 in the negative feedback circuit of amplifier 22 are conductive only when the output signal exceeds one .volt.

The particular circuit illustrated in FIG. 3 for compressor amplifier 22 provides an output signal amplitude variation limited to approximately twelve decibels, with an input variation of forty decibels. At the same time, amplifier 22 affords positive gain, the output signal for a one-half volt input being approximately two volts R.M.S. The working range of compressor amplifier 22, with respect to input signal amplitude, is approximately 1.5 volts to 100 millivolts.

Not all of the input signal is effectively translated through the compressor amplifier. Filter 127 effectively attenuates very low-frequency components in the signal, these being components representative of car speeds below approximately two miles per hour.

The output signal from compressor amplifier 22 is supplied, through the circuit comprising coupling Capacitor 143 and conductor 144, to the input terminal 201 of lowpass filter 28 (see FIG. 4). The repetitive components of the signal below the cut-off frequency of filter 28, in this instance below one hundred sixty-five cycles (l m.p.h.) .are translated to the output terminal 204 of the filter and, accordingly, supplied to high-pass filter 29. Filter 29 attenuates the frequency components below approximately thirty cycles (3 m.p.h.) and supplies the remaining signal components to noise amplifier 31 through the connection afforded by coupling capacitor 219. This signal is supplied to the control electrode of rectifier 234, rendering rectifier 234 conductive and completing an energizing circuit for noise relay 236.

As soon as noise relay 236 is actuated, contact 241 closes upon contact 243, connecting capacitor 242 to the input terminal 220 of the control circuit for rectier 234. Capacitor 242, which has previously been charged through its connection to the D.C. supply circuit comprising rectifier 256, discharges, maintaining the noise relay 236 energized for a short time interval. This momentary holding circuit arrangement is utilized to make sure that noise relay 236 is energized; it also increases the time constant of the circuit to guard against drop-out of relay 236 on momentary interrupting of the incoming signal.

Actuation of the noise relay also causes contacts 245 and 246 to open and close contacts 246 and 247. Opening of contacts 245 and 246 interrupts the A.C. bias signal previously supplied to driver amplifier 25 fr- om clipper circuit 262, 263. The ybias circuit keeps capacitor 289 partially charged in the absence of pick-up signal. Thus, a delay Yin initial brake appljatin gan be effected by adjustment of potentiometer 262. Also, momentary dropouts of noise relay 236 due to loss of signal will not allow the brake to be re-applied when signal again act-uates relay 236 if there is some delay set in by this bias. Closing of contacts 246 and 247 completes an operating circuit to the input of driver amplifier 25 from the output circuit of filter 24 through the connecting conductor 193 (FIGS. 3 and 4). At this point, however, no significant signal is supplied to the driver amplifier from filter 24, since the available signal is well above the cut-off frequency to which the low-pass filter has lbeen affect actuation of signal relay 271 at this point.

Actuation of the noise relay, in response to signals indicative of movement of the over-speed car into the retarder control system, also closes contacts 249 and 251. Closing of these contacts completes an operating circuit for the coil 269 of signal relay 271. The controlled rectifier 294 in the operating circuit of this relay is normally biased toward conduction by the circuit cornprising Zener diode 298. Consequently, the signal relay is actuated in response to actuation of noise relay 236.

When signal relay 271 is actuated, contacts 309 and 311 close. This establishes an energizing circuit for the operating coil 321 of brake relay 27. Thus, the brake relay is actuated and supplies a control signal to mechanism 15 that causes retarder 10 (FIG. 1) to be actuated to its braking condition.

Actuation of signal relay 271 also closes contacts 301 and 303. This connects capacitor 315 to the charging circuit 316, 317, charging the capacitor for a purpose described hereinafter. Furthermore, contacts 306 and 307 are closed, shorting out low-pass filter 28. Thus, as long as signal relay 271 remains actuated, and the brakes are on, high harmonics present in the output signal from compressor amplifier 22 are passed directly to noise amplifier circuit 31 to hold noise relay 236 in its energized condition. These high frequencies are more easily transmitted down the track than lower frequency signals, a consideration that is especially important in turning the brake on initially.

Retarder 10 is actuated, lby mechanism 15, to its closed or braking condition before the incoming car reaches retarder rails 13 and 14 (FIG. 1). Hence, when the over-speed car reaches the retarder rails it is decelerated at a rate dependent upon the friction characteristics of the rails and the wheels engaged thereby and also dependent upon the force applied to the retarder rails by mechanism 15.

As long as the car speed remains above the setting of adjustable low-pass filter 24, circuit conditions are not changed from those described immediately hereinabove. When the car has been decelerated to the release speed established by the setting of filter 24, however, a signal of substantial amplitude is translated through the filter and is supplied to driver amplifier 2S through the circuit comprising conductor 193, nose relay contacts 246 and 247, and coupling capacitor 261 (FIG. 4). This signal is amplified in circuit 25, which emphasizes the low-frequency components thereof as noted hereinabove. The

output signal from the driver amplifier is rectified in the voltage doubler circuit 287-289 and is supplied to the control electrode of rectifier 294 through the circuit comprising potentiometer 292 and current-limiting resistor 293. As a consequence, rectifier 294 is driven to cut-off, de-energizing signal relay 271.

When signal relay 271 drops out, contact 301 returns to engagement with contact 304. This change is effective to interrupt the charging `circle to capacitor 31S and connects the capacitor to terminal 291. Thus, capacitor 315 is discharged through potentiometer 292, helping to maintain the signal relay in de-energized condition. It also increases the circuit time constant about 5:1 so that subsequent signal drop-outs will not re-apply the brake. Also, it delays re-application of the brakes in case the car speeds up; hence the retarder doesnt chatter on and off if speed is near the filter cut-off frequency. As it is discharged, capacitor 315 charges capacitor 289 more negatively. The illustrated circuit arrangement gives rapid response to changes in signal condition in the output of drive amplifier 25, yet is effective to prevent premature reapplication of the brake on slow-speed cars.

Of course, as soon as signal relay 271 drops out, contacts 309 and 311 open. This interrupts the operating circuit for brake relay coil 321 and the brakes go ofi.

Contacts 306 and 307 are opened, when signal relay 271 drops out, removing the shunt across low-pass ilter 28. That is, filter 28 is eectively re-connected in the input circuit of noise amplifier 31 whenever the signal relay is de-energized and the brakes are off. The lowpass lilter prevents high order harmonics of the repetitive vibration signals from keeping noise relay 236 actuated after the car speed drops below the minimum value established by high-pass filter 29.

If, in the course of braking, the speed of the car moving through the retarder drops below the cut-off speed established by high-pass filter 29, noise relay 236 usually drops out, although harmonic signals may keep the noise relay energized for a short interval. In any event, when the car clears the end 11B of the retarder, the input signal to the noise amplifier is insufficient to maintain the noise relay energized. Thus, the noise relay drops out and the system is ready for the next operation.

In some instances, a car entering the retarder may be travelling at a speed below the speed for which adjustable low-pass t'iiter 24 is set. If this occurs, the sequence of operations is essentially as described above except that lter 24 immediately passes a signal of substantial amplitude. As a consequence, a de-energizing signal is immediately available, from driver amplilier 25, operating to cut oft signal relay 271. Thus, although noise relay 236 is actuated, signal relay 271 remains effectively opencircuited at the signal-controlled rectifier 294. Since the signal relay cannot be actuated, the brakes are not applied and the car rolls through the retarder without braking.

As each car moves along rail 11, and into the retarder, it causes switching circuit 21 to actuate relay 73 to connect first pickup 17A and subsequently pickup 17B to the remaining circuits of the control system. In addition to switching the input connections to compressor amplifier 22, relay 73 controls a safety circuit, connected to contacts 84-86, that protects the system against cars approaching the retarder at very high speeds.

With reference to FIGS. 2 and 4, it can be seen that capacitor 92 is initially charged through resistor 88 and diode 91 by means of the connection extending back through contacts 248 and 251 of the noise relay to the A.C. supply. The contacts 84 and 85 of relay 73 are in series in this charging circuit.

When a car enters the retarder at point 11A, actuating relay 73, the charging circuit connection to capacitor 92 is interrupted. At the same time, the capacitor is effectively connected, through contacts 84 and 86 and conductor 87, to the input terminal 220 for the signal-controlled rectifier 234 of the noise amplifier and relay circuit 31. Discharge of capacitor 92 drives rectifier 234 conductive. As a consequence, noise relay 236 is energized long enough to actuate signal relay 271 and establish a momentary shunt for low-pass filter 28. Otherwise, if a really high speed car were coming in, the speed of the car being over the cut-off for low-pass filter 28, the filter might prevent transfer of an adequate energizing signal to noise amplifier and relay circuit 31 with the result that the brakes would not be applied. On the other hand, in a given installation it may be desirable to construct the retarder control deliberately to pass any car at speeds over, for example, fifteen miles per hour, in which case the safety circuit described immediately above may be omitted. As long as relay 236 remains energized,

18 capacitor 92 cannot be charged, and further operations of relay 73 have no undesirable effects.

In order to afford a complete illustration of the invention, circuit parameters for the circuits of FIGS. 2-4 are listed hereinafter. It should be understood that these data are set forth only by way of example and not as a limitation on the invention.

Resistors and potentiometers 43 kilohms 180 44 do 18 46, 113, 147 do 1 47, 55, 65, 278 do 4.7 49, 161, 297 do 2.2 67, 165, 166, 189, 232 do 47 69, 233 do 27 88, 101, 107, 133, 138, 184, 214, 224, 293,

296 ki1ohms 100 105, 116, 124, 183, 188, 178, 222 do l0 108, 109, 141, 142, 225, 226 do 68 112 do 120 114, 209, 274 do 2.7 104 ohms 680 119, 272 kilohms 150 121 do 3.9 122, 276 ohms 470 125, 209, 282 kilohms 56 135, 136 do 1.5 172 do 82-200 173, 174 do 8.1-27 177 do 1.8-13.3 253 do 6.8 273, 317 do 8.2 281 do 1.8 285 do 1.2 292 do 33-83 316 do 39 Capacitors Microfarads Inductors Henries Transistors, diodes, rectifz'ers 45, 118, 275 2N383 48, 134, 279 2N586 52, 53, 229, 231 1N56A 71, 234, 294 3A15A 74 S1010 103, 115, 221 2N1309 148, 149, 153, 154, 162, 163, 237, 287, 288 1N456 168, 169, 185, 192 T1495 298 1N1507 19 Operating voltages Transformer secondary 240, volts A.C 6 C-, volts D.C. 22.5

In considering the basic characteristics of speed control system 18, as described in detail hereinabove, it should be noted that automatic signal level switch 21 serves primarily to select the maximum amplitude signal from transducers 17A and 17B and is not necessary to the system if only a single transducer is employed or if other means are afforded to accommodate multiple transducers as in the system of FIG. 7, described hereinafter. Compressor amplifier 22 serves primarily to reduce the initial signal from the transducers to a limited amplitude range suitable for further use in the control system, the AGC effect being further assisted by clipper 23 before the signal is passed on to low-pass filter 24.

The high-pass filter 127 in the output of compressor amplifier 22 (FIG. 3) is not essential to operation of the system, since it serves primarily to set a lower frequency limit for signals passed on to other portions of the control circuit. However, this high-pass filter is desirable because it affords positive protection against erroneous actuation of the retarder as the result of low-frequency vibration of rail 11 that would not be attributable to the movement of a railway vehicle along the rail. An example of a source of such spurious low-frequency signals would be the operation of a spike driver somewhere along the track, engagement of car wheels with track joints ahead of the serrated rail, and fiat spots on the car wheels, any of which can produce high-amplitude low-frequency vibration signals along the track. All of these troubles are most noticeable before a car reaches the notched rail. Once the car is on notches 16 the signal from the notches overrides everything else. Filter 127 also helps speed up the response of the AGC circuit, compressor amplifier 22.

The most important control element in system 18 is adjustable low-pass filter 24; since this device establishes the release speed for the cars, it must have a sharp cut-off characteristic and must be adjustable to any release speed desired for the system. The output signal from filter 24 may aptly be termed a release signal, and it is this release signal that is supplied to driver amplifier 25 to deenergize the signal relay 271 of circuit 26 and actuate relay 27 to release the retarder. In connection with driver amplifier 25, the low-frequency emphasis afforded by the operating characteristic of this amplifier is quite desirable because it is essential to release retarder as soon as the car is slowed to the desired exit speed. There are always some losses at low frequencies, due to the velocity-dependent pick-ups. Also, at low frequencies the periods of signal drop-out are longer, due to the longer time it takes the car to get from one pick-up to the other, and capacitors 289-315 must be charged to a higher level to maintain control during such drop-outs.

Control of signal relay 271 of circuit 26 is actually effected by signals supplied through two different channels, as will be apparent from the foregoing description. Thus, initial control of the relay is effected by a first channel comprising filters 28 and 29 and the noise amplifier and relay circuit 31. The signal supplied to circuit 26 through this channel tends to actuate the signal relay to its actuated or brake-applying condition in response to both low and high frequency signals, the operating range of the signal channel being established by the filters 28 and 29. The control effected through this channel, hov ever, is over-ridden by the signal supplied to circuit 26 through the alternate channel comprising clipper 23, lowpass filter 24, and driver amplifier 25, whenever the speed of a car is reduced to a level below the speed setting of filter 24. In this connection, noise relay 236 functions as an auxiliary switching device with respect to signal relay 271; the two relays cooperate to afford the necessary control function.

The operating circuits shown in FIGS. 2-4 can, of course, be modified substantially without departing from the present invention. By way of example, it should be noted that it is not essential to use relays as the principal control elements in circuits 26, 27 and 31. Instead, other signal-actuated control devices, preferably switching devices, may be employed in all of these circuits. Changes of a similar nature can be made in Virtually all of the individual operating circuits.

In sorne installations, it is possible to utilize a retarder 10 that is normally maintained in a closed or braking condition. Where the installation permits operation on this basis, system 18 may be simplified substantially by eliminating the signal channel comprising filters 28 and 29 and noise circuit 31. Control of the retarder is then effected oniy by the speed-control channel comprising clipper 23, filter 24, and driver amplifier 25. However, a system of this kind, if set for a low release speed, could operate to lock a car in a retarder, a condition that would not be desirable in most installations because of the possibility of damage from a second car entering the retarder. The signal channel comprising circuits 23, 29 and 31 prevents this completely; in effect, this signal channel controls the entire system and is effective to release the brakes when a car is below the minimum speed for which high-pass filter 29 is constructed (in this instance 3 m.p.h.) even if the main speed control comprising the channel including filter 24 fails to operate.

As noted hereinabove, one of the most critical elements of the control system is the adjustable low pass filter 24. FIG. 5 illustrates operating characteristics for circuit 24, and specifically for the particular circuit arrangement illustrated in FIG. 3, at three different speed settings. The initial curve 561 in FIG. 5, a plot of the output signal amplitude of the filter in volts as a function of frequency in cycles per second, shows a three mile per hour setting of the low pass filter. As can be seen from curve 501, the amplitude of the signal output from the filter remains substantially constant until the frequency reaches approximately thirty cycles, at which point the signal amplitude begins to drop o. The output signal is down three decibels at a frequency of approximately 33.8 cycles per second, corresponding substantially to a car speed of three miles per hour.

The second curve 562 in FIG. 5 illustrates the operation of filter circuit 24 when adjusted for a speed of four miles per hour. In this instance, the signal is down three db for a frequency of approximately forty-six cycles per second. The third curve 503 in this figure pertains to a filter setting for seven miles per hour, the signal being attenuated approximately three db at a frequency of about 81.5 cycles per second. In each instance, the output signal employed drops off very sharply after the cutoff frequency is reached, a characteristic that is necessary in the low pass filter if the system is to function properly.

FIG. 6 illustrates a speed-sensitive control system 368 for a railway car retarder that comprises a second embodiment of the present invention. In many respects, system 368 is substantially similar to the control system described in detail hereinabove. Thus, it comprises the two pickups 17A and 17B that are mounted at suitable positions along a notched or serrated rail in the same manner as in the embodiment of FIG. 1. Pickup devices 17A and 17B are again connected to an automatic signal level switch 21 that may be constructed in the same manner as illustrated in detail in FIG. 2.

The output of switching circuit 21 is again coupled to a compressor amplifier 22 that .is in turn coupled to a clipper circuit 23. The output of the clipper is coupled to the adjustable low pass filter 24, the low pass filter again being connected to a driver amplifier 25. Circuits 22-25 may be essentially similar in construction to the corresponding circuits described in detail hereinafter in connection with FIGS. 3 and 4.

The output of driver amplifier 25 is connected to a rectifier circuit 369 that may be essentially similar to the rectifier circuit 287, 288 in the input of circuit 26, FIG. 4. Rectifier 369 is connected to a signal relay control circuit 370 that may be essentially similar in construction to the signal controlled rectifier circuit shown in FIG. 4 in connection with relay 271. As before, a capacitor 289 is incorporated in the signal relay control circuit, being returned to ground.

Circuit 370 controls the actuation of a signal relay 371 having an operating coil 372. Relay 371 comprises three sets of contacts. The first set of contacts includes a movable contact 406 that normally engages a first fixed contact 405 but that is engageable with a second fixed contact 407 upon actuation of the relay. Another set of contacts for relay 371 includes fixed contacts 408 and 409. When the relay is de-energized contact 408 is engaged by a movable contact 411; when the relay is actuated, contact 411 moves into engagement with contact 409. A further set of relay contacts comprises a movable contact 401 that is ordinarily engaged with a fixed contact 404 but that engages a second fixed contact 403 when the relay is actuated.

Contact 405 of signal relay 371 is connected to the output of compressor amplifier 22. Movable contact 406 is connected to the input of a high pass filter 29, which may be constructed to correspond substantially to the filter circuit 29 illustrated in FIG. 4. Contact 407, on the other hand, is connected to the output of the adjustable low pass filter 24. Thus, actuation of signal control relay 371 is effective to change the input circuit to high pass filter 29 by incorporating low pass filter 24 in this circuit as described more fully hereinafter.

The movable contact 401 in the second set of relay contacts is returned to ground through a capacitor 415. The fixed contact 404 in this set is connected to a low voltage D.C. supply B-jthrough a resistor 412. Terminal 403 is connected to capacitor 289 in the coupling circuit between rectifier 369 and control circuit 370.

In the final set of contacts for relay 371, fixed contact 409 is left open circuited. Contact 411 is grounded and contact 408 is utilized to afford a signal connection to the noise relay of the embodiment, as described more fully hereinafter.

High pass filter 29 is connected yto a noise amplifier circuit 421 that may be essentially similar in construction to the initial stage of circuit 31 in FIG. 4. In the system of FIG. 6, it may be desirable to provide for additional amplification in the noise channel, in which case a further amplifier circuit may be incorporated in the signal channel, preferably ahead of filter 29. The output of noise amplifier 421 is connected to a rectifier circuit 422 that may be essentially similar to the voltage doubler 229, 231 in the circuit 31 of the initially described embodiment. Again, the rectifier is connected to a control circuit 423 that may constitute a signal-controlled rectifier, as in the relay control circuits described hereinbefore, the control arrangement comprising circuits 422 and 432 including the capacitor 230.

Circuit 423 controls actuation of anoise relay 436 having an operating coil 435 and two sets of contacts. The first set of contacts in this relay includes a movable contact 441 that is normally engaged with a fixed contact 444. Contact 441 is moved to engagement with a second fixed contact 443 upon actuation of the relay. Movable contact 441 is returned to ground through a capacitor 442. Contact 444 is connected, through a resistor 453, to the B+ supply. Contact 443 in this set is connected back to capacitor 230 in the control circuit for the noise relay.

The second set of contacts for relay 436 comprises a movable contact 446 that is normally engaged with an open-circuited contact 445. The remaining contact 447 in this set, which is engaged by contact 446 when the relay is actuated, is connected to one terminal of the operating coil 321 of the brake relay 27. The other terminal of coil 321 is connected to the AC supply. As before, the operating contacts 325 of the brake relay are connected to a retarder actuating mechanism 15 as described hereinabove in connection with FIG. 1. The movable contact 446 in this portion of relay 436 is connected to contact 40S of the signal relay 371.

Initially, and prior to the time `that a car enters the immediate area of the retarder, the operating relays of system 363 are de-energized and are in the positions shown in FIG. 6. When a railway car enters the retarder control system at point 11A (FIG. l) it vibrates the trafc rail at a fundamental frequency determined by the speed of the car. If the fundamental signal frequency is above the setting of adjustable low pass filter 24, as would be the case with a car entering above the desired release speed set for the retarder, the output signal from low pass filter 24 is quite weak and is insufficient to actuate signal relay 371. The output signal from the compressor amplifier 22, however, is of substantial amplitude; it should be remembered that circuit 22 affords a substantial AGC action and produces a signal of usable amplitude over a wide range of frequencies. This signal is passed through filter 29, which again affords attenua-tion only at frequencies below approximately thirty cycles. The signal is arnplied (circuit 421), rectified (circuit 422) and applied to control circuit 423 to energize noise relay 436.

When relay 436 is actuated, contacts 446 and 447 close to complete an operating circuit for the coil 321 of brake relay 27. Consequently, contacts 325 are actuated and produce an output signal that is supplied to mechanism 15 to establish the retarder in its braking condition.

With the retarder in braking condition, the car is decelerated as before. When the car speed is reduced to a level at which the engagement of the car wheels With the notches in serrated rail 11 occurs at a frequency beloW the setting of filter 24, an output signal of appreciable arnplitude is available from the low pass filter. This signal is supplied to amplifier 25, is rectified in circuit 369, and is applied to circuit 370 to actuate signal relay 371. AS soon as relay 371 is actuated contacts 408 and 411 open, interrupting the energizing circuit for brake relay 27 and restoring the retarder to its released condition.

Actuation of signal relay 371 also affects the input to high pass filter 29. Thus, when the signal relay is actuated, contacts 405 and 406 open, interrupting the initial input circuit to the high pass filter. Contacts 406 and 407, however, are now closed. Accordingly, high pass filter 29 is now provided with an input circuit that includes, in series therewith, the adjustable low-.pass filter 24.

By incorporating low-pass filter 24 in series in the input circuit to high-pass filter 29, upon actuation of signal relay 371, the adjustable low-pass filter is made to perform the basic function of the low-pass filter 28 in the embodiment of FIG. l. Thus, the additional low-pass filter incorporated in the noise signal channel of the initial embodirnent is eliminated, but its basic function is retained. The presence of low-pass filter 24 in the noise signal channel, after the brakes have been released but with a car still rolling through the retarder system, prevents high order harmonics of the repetitive vibration signals from keeping the noise relay actuated after the car speed drops below the minimum value established by high pass filter 29. When the car speed drops below the speed represented by the cut-off frequency of high-pass filter 29,

rnoise relay 436 is de-energized and the relay drops out.

Thus, the system is conditioned for the next operation as soon as the car passes beyond the end of the notched rail and the actuating signal for relay 371 is no longer available.

The safety circuit utilized in the initial embodiment is not required in system 36S of FIG. 6. Thus, there is no low-pass filter in the noise channel unless and until signal relay 371 is actuated. Consequently, a car travelling at very high speeds will :always actuate noise relay 436 and establish the retarder in braking condition as soon as an appreciable signal is available from pick- ups 17A and 17B.

When signal relay 371 is in its normal tie-energized condition capacitor 415 is charged through the charging circuit comprising resistor 412 and relay contacts 401 and 404. When the signal relay is actuated by a signal indicative of a car moving at a speed below the setting of filter 24, capacitor 415 is disconnected from its charging circuit and is connected to capacitor 289 in the -control circuit for the signal relay. Thus, capacitor 415 fulfills the same basic functions as capacitor 315 in the first-described embodiment; in this instance, however, the charge on the capacitor is reversed in polarity because the object is to maintain relay 371 in energized condition in order to release the retarder, the energized and de-energized operating conditions for the signal relay being reversed as compared with the initial embodiment of the invention. As before, the connection of capacitor 415 to the control circuit rfor the signal relay also increases the control circuit time constant to avoid premature reapplication of the brake.

Capacitor 442, on the other hand, carries out the same basic functions as capacitor 242 in the first embodiment of the invention (see FIG. 4). Capacitor 442 is normally connected to a charging circuit comprising resistor 453 and contacts 441 and 444 for noise relay 436. When the noise relay is actuated in response to movement of a car into the retarder, the capacitor is disconnected from its charging circuit and is connected to capacitor 230 in the control circuit for relay 436. As capacitor 442 discharges, it is effective to maintain the noise relay energized for a short time interval and increases the time constant of the relay control circuit to protect the systern against premature drop-out of relay 435 upon momentary interruption of the input signal from pickups 17A and 17B.

In other essential respects, the system 36S of FIG. 6 functions in essentially the same manner as the system of FIGS. 14. Thus, if a car entering the retarder is travelling at a speed below the setting of low-pass filter 24, signal relay 371 is actuated almost immediately and the retarder is not actuated to its braking condition. Under these circumstances, filter 24 is again incorporated in the input circuit to the noise relay control 422, 423 to provide for de-energization of the noise relay.

In each of the foregoing embodiments, a major problem is the separation of useful car speed information from extraneous in formation in the initial signal developed by the transducers such as devices 17A and 17B. This signal inherently includes many harmonics of the fundamental frequency; if this extraneous information is not effectively segregated from the desired fundamental signal, the system cannot operate properly or even safely. The systems of the present invention overcome this difiiculty, primarily through the use of the multiple lter circuits employed in both the principal signal channel and the noise channel. With the described circuit arrangements, what would appear to -be an unusable mixture of confusing signal information is effectively employed to control car speed and to assure safe and accurate operation of the retarder.

FIG. 7 illustrates a speed-sensitive control system 51S for a railway car retarder constituting another embodiment of the present invention. The car retarder controlled by system S18 is slightly different from that described and illustrated in FIG. l in that it includes two sets of retarder rails 13A and 13B that are located imrnediately adjacent each other longitudinally of the trafc rail 11. The two sets of braking elements of retarder rails, however, are controlled from a common retarder actuating mechanism 15. Moreover, the traffic rail 11 is again provided with a multiplicity of equally-spaced shallow grooves or other surface discontinuities 16 beginning at a point 11A well ahead of the retarder rails 13A and 13B and ending at the point 11B at the outlet of the retarder. Thus, the retarder mechanism is basically similar to that described above except that the retarder rails lare divided into two longitudinal segments for convenience in construction. It should be noted that the surface notches or grooves 16 need not be provided in the rail 11 along which the retarder rails 13A and 13B are mounted; rather, the other rail of the railway -rnay be provided with the requisite notches or other surface discontinuities.

Control system 518 comprises three individual pickup devices 517A, 517B and 517C mounted on rail 11. The initial pickup device 517A is located near the point 11A at which the individual cars or cuts of cars enter the retarder system. Pickup device 517B is located within the length of traffic rail 11 encompassed by the first pair of retarder rails 13A. Pickup 517C is located near the outlet end of the retarder on the portion of the trafiic rail encompassed by the second pair of retarder rails 13B. All three of the pickup units 517A, 517B and 517C are electrically coupled to an adder amplifier 519. Adder amplifier 519 is a simple adding circuit that combines and amplifies the three initial electrical signals from the pickup devices 517A, 517B and 517C to produce at combined initial signal.

Control system 518 does not include an automatic level switch such as the switch 21 of the previous embodiments. It does comprise a squelch circuit arrangement comprising an lamplifier 522 having its input circuit coupled to the output of adder amplifier 519. Th-e output of squelch amplifier 522 is coupled to a rectifier and drive circuit S23 that is essentially similar to the rectifier and drive circuit for the automatic level switch 21 as illustrated in FIG. 2. Thus, drive circuit 523 is utilized to energize the operating coil 524 of a squelch relay 525.

Relay 525 comprises three sets of contacts, the contacts being shown in the normal or unenergized position for the relay. The first s-et of contacts comprises two fixed contacts 526 and 527 and a movable contact 528, movable contact 528 normally being engaged with contact 526. The second set of contacts of `the relay includes a fixed contact 532 normally engaged by a movable contact 534, the movable contact engaging a second fixed contact 533 when the relay is energized. The third set of contacts for the squelch relay comprises a movable contact 536 that is normally engaged with a fixed contact 538 but which engages a second fixed contact 537 upon energization of the relay.

In the first set of contacts of squelch relay 525, the normally closed fixed contact 526 is connected through a resistor 539 to the B+ supply for the system. Movable contact 52S is connected to a capacitor 541 that is returned to ground. The remaining Contact in this set, contact S27, is connected back to the input to recifier and drive circuit 523. The connections for the remaining sets of contacts in the squelch relay are described in detail hereinafter.

The output of adder amplifier 519, in addition to its connection to squelch amplifier 522, is also coupled to an equalizer circuit 542. The equalizer circuit, which is utilized to compensate for the frequency characteristics of the pickup devices 517A, 517B and 517C, as described more fully hereinafter, is in turn coupled to a compressor amplifier 543. The compressor amplifier may be essentially similar in construction to the compressor amplifier 22 of the previously described embodiments. Compressor amplifier 543 is also provided with internal `connections to the contacts 533 and 534 of squelch relay 525 to modify the operating characteristics of the compressor amplifier upon actuation of the squelch relay, as described more fully hereinafter.

The output of compressor amplifier S43 is coupled to a dual level clipper gate circuit 545, the two circuits affording an automatic gain control for the system. Gate circuit 545, in turn, is connected through a selector switch 544 to the input to a low pass filter 546. Low

ascenso 25 pass filter 546 performs the same basic function as filter circuit 24 in the previously described embodiments and may be essentially similar to the construction illustrated in FIG. 3. In this instance, however, low pass filter 546 is constructed as a fixed filter and changes in the critical release speed for the retarder control system are effected by switching from one filter circuit to another. Thus, a second low-pass filter 546A, having a different cut-o frequency from filter 546, can be substituted in the operating circuit by actuation of a pair of connecting switches 544 and 544A. Although only two low pass filters are illustrated in FIG. 7, it should be understood that several additional filter circuits may be employed with appropriate means for switching from one circuit to another for different retarder operating conditions to establish different desired levels for the critical release speed of the retarder system. The plural filters and connecting selector switches afford an adjustably settable filter means for setting the release speed for the retarder.

Low pass filter 546 is coupled through selector switch 544A to a drive amplifier 547 that is in turn connected to a rectifier circuit unit 548. The rectifier circuit unit 548 is provided with a main output circuit 549 that is utilized to charge a control capacitor 551. The rectifier output circuit 549 and capacitor 551 are also coupled to a signal relay control circiut 552. Furthermore, the main output circuit 549 of rectifier circuit 548 is connected back to the dual lever clipper gate 545 to actuate the gate as described more fully hereinafter in connection with FIG. 9.

The rectifier circuit unit 548 is also provided with a second output circuit that is connected to a capacitor discharge circuit 553. Circuit 553 affords a controlled discharge of capacitor 551 under certain operating conditions as described more fully hereinafter.

Signal relay control circuit 552 is utilized to energize the operating coil 555 of a signal relay 556. Signal relay 556 includes three sets of contacts, all of which are shown in the normal or unenergized condition for the relay. The first set of contacts comprises a movable contact 557 normally engaged with a fixed contact 553 but engageable with a second fixed contact 559 when the relay is energized. The second set of signal relay contacts includes a movable contact 561 normally engaged with a fixed contact 562 but movable into engagement with a second fixed contact 563. The third set of contacts for the signal relay includes a movable contact 565 normally engaged with a fixed contact 566 and engageable with a second fixed contact 567 upon energization of the relay. The movable contact 565 in the third set of contacts for relay 556 is connected to the B+ supply for the system. The normally closed fixed contact in this set is connected to capacitor discharge circuit 553. The remaining fixed contact 567 is left open-circuited.

In addition to the connection to clipper gate 545, compressor amplifier 543 is provided with an output connection to a high-pass filter amplifier 571. This circuit includes, in series, the fixed contact 55S and the movable contact 557 in the first set of contacts of signal relay 556. The remaining contact 559 in this set is left opencircuited.

The output of high pass filter amplifier 571 is coupled to a rectifier circuit 572 which is in turn coupled to a noise relay control circuit 573. The input to control circuit 573 also includes a connection to the fixed contact 538 of squelch relay 525. The related movable contact 536 of the squelch relay is returned to system ground, whereas the remaining fixed contact 537 in this set of contacts is left open-circuited.

Control circuit 573 is utilized to actuate a noise relay 575, being connected to the operating coil 576 of the relay. Noise relay 575 includes two sets of contacts. The first set comprises an open-circuited fixed contact 577 normally engaged by a movable -contact 57S, the contact 578 moving into engagement with a second xed contact Y 26 579 upon energization of the relay. The second contact set in the noise relay comprises a fixed contact 531 that is normally engaged by a movable contact 582, the movable contact being engageable with `a second fixed contact 583 upon actuation of the relay.

In noise relay 575, fixed contact 581 is returned to system ground through a resistor 585. Movable contact 582 is connected to a capacitor 536 that is returned to ground. Contact 583 is connected back to the noise relay control circuit 57 3.

The remaining sets of -contacts in noise relay 575 and in signal relay 556 are interconnected in a control circuit for the brake relay 27. Thus, the fixed contact 579 of noise relay 575 is directly connected to brake relay 27. The corresponding fixed contact 577 is left open-circuited but the movable contact 57S is connected to fixed contact 562 in the signal relay. The related movable contact 561 is connected directly to brake relay 27 whereas the remaining fixed contact 563 is open-circuited.

With control system 518 in operation, but with no car on traffic rail 11, retarder actuating mechanism 15 maintains the retarder rails 13A and 13B in their open or released positions. As in the previous embodiments, actuating mechanism 15 is energized from brake relay 27. But the operating circuit for brake relay 27 is open at contacts 577 and 579 of noise relay 575. Accordingly, the retarder remains in its open or off condition until the brake relay is energized by control system 518.

An approaching car or cut of cars entering the retarder from the direction of arrow A first engages the notched portion of traffic rail 11 at point 11A. Continuing movement of the car causes the traffic rail to vibrate at a frequency determined by the velocity of the car or cars. Vibration lof the -rail is detected by pickup devices 517A, 517B and 517C, the initial electrical signals from the three pickups being additively combined in amplifier circuit 519. At the outset, as the first wheels of the cut pass point llA on the rail, the signal from pickup device 517A predominates. t

The output signal from ad-der amplifier 519 is applied to squelch amplifier 522 and to equalizer circuit 542. Referring to squelch amplifier 522, the initial electrical signal from the pickup devices, as supplied by amplifier 519, is amplified further and then applied to 'rectifier and drive circuit 523. Circuit 523 in turn energizes relay 525, actuating movable contacts 528, 534 and 536 to their alternate operating positions, closing upon xed contacts 527, 533 and 537 respectively.

The closing of contacts 527 and 528 in squelch relay 525 connects capacitor 541 to rectifier drive circuit 523. Capacitor 541 has previously been charged to a substantial potential through the connection .to resistor 539 and to the B+ supply. Discharge of the capacitor through the rectifier and drive circuit 523 assures a sustained output signal from circuit 523 to hold squelch relay 525 energized for .a predetermined time interval, thereby precluding chattering of the relay in :the event of momentary subsequent interruption of the Isignal immediately following energization of the relay.

The closing of contacts 534 and 533 in squelch relay 525 completes a positive feedback circuit in compressor 'amplifier 543 and materially increases the gain of the comt pressor amplifier. The reason for this circuit connection is that it is undesirable to produce a high-amplitude output signal from the compressor amplifier for short-duration signals and transient-s such .as might be caused by switching along the line, by the driving of spikes at some nearby point along the same line, or by other sources. With this arrangement, the `gain for compressor amplier 543 may be held to la minimal level when there is no car yactually on the notched portion of traffic rail 11, whereas the gain of the amplifier is increased to a desired operating level once a signal of sufficient duration is available to -actuate squelch relay 525. In this regard, 4it should be noted that the rectifier and drive circuit 523 may be essentially

Claims (1)

1. A SPEED-SENSITIVE CONTROL SYSTEM FOR A RAILWAY CAR RETARDER OR THE LIKE COMPRISING: A RAIL EXTENDING THROUGH A MAJOR PORTION OF THE LENGTH OF THE RETARDER HAVING A SERIES OF SURFACE DISCONTINUITIES AT PREDETERMINED SPACED INTERVALS ALONG THE RAIL IN POSITION TO BE ENGAGED BY A RAILWAY VEHICLE WHEEL MOVING ALONG THE RAIL; A PLURALITY OF INDIVIDUAL TRANSDUCERS MOUNTED ON SAID RAIL AT SPACED INTERVALS, FOR GENERATING INITIAL ELECTRICAL SIGNALS REPRESENTATIVE OF VIBRATION OF THE RAIL, SAID INITIAL SIGNALS INCLUDING REPETITIVE SIGNAL COMPONENTS AT FREQUENCIES DETERMINED CONJOINTLY BY THE SPACING BETWEEN SAID SURFACE DISCONTINUITIES AND THE SPEED OF A VEHICLE MOVING ALONG THE RAIL; AN AMPLITUDE-SENSITIVE SWITCHING DEVICE, CONNECTED TO SAID TRANSDUCERS, FOR SELECTING THE INITIAL SIGNAL OF THE GREATEST INSTANTANEOUS AMPLITUDE; FREQUENCY-SELECTIVE CONTROL MEANS, COUPLED TO SAID SWITCHING DEVICE FOR SELECTIVELY UTILIZING SAID RE-

Images