Abstract:
Apparatus, methods and a communication system for providing relatively constant warning time at a rail grade crossing for trains with prediction of the approach of a train from a remote controller via rail-based communications to a crossing controller. A first communication signal is generated when a prediction occurs and a second communication signal is generated for slower moving trains, with the second signal temporarily overriding the first signal to provide relatively constant warning time at the crossing. Cancellation timers with timing intervals are used to resolve situations where the train does not enter the approach or where the train leaves by way of a switch or backs out. Directional logic is used to determine the direction of movement of the train and, in conjunction with cancellation timers, causes the warning devices to be activated when the timers expire.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to apparatus, methods and communication systems for highway-rail grade crossing warning systems. More particularly, the present invention relates to improved communications apparatus, methods and systems for such crossing warning systems that provide for relatively constant warning time through the use of rail-based communications.  
       BACKGROUND OF THE INVENTION  
       [0002]     A Constant Warning Time (CWT) device is a train detection device for a highway-railroad grade crossing warning system that provides a relatively uniform warning time. The CWT device electrically connects to the track and forms a track circuit between the crossing and a termination shunt located a predetermined distance from the crossing. The distance to the shunt is dependent on the maximum train speed and the desired warning time of the crossing warning system. The CWT device monitors its transceiver signal level on the track and predicts the arrival of a train based on an impedance change caused by the axles of the train as it approaches the crossing.  
         [0003]     In highway railroad grade crossing warning systems that utilize CWT, frequently the CWT track circuit at the crossing cannot extend a sufficient distance due to other signal requirements in the approach to the crossing circuit. When this situation is encountered, it is necessary for a remote CWT device to predict the arrival of the train at the distant crossing. A common term in the signal industry for the remote CWT prediction is “DAX”, meaning control of a Downstream Adjacent Crossing (Xing).  
         [0004]     Conventionally, the DAXing control information is conveyed between the locations via buried cable. When the train reaches a prediction point in the DAX approach, the remote unit will de-energize its DAX output circuit, which is communicated via the cable circuit to an input on the CWT device at the crossing. The input on the CWT device at the crossing is commonly known by the acronym “UAX” input since it generally came from an Upstream Adjacent Xing.  
         [0005]     A general object of the present invention is to improve the constant warning time provided by highway-rail grade crossing warning systems through the use of rail-based communications.  
         [0006]     Another object of the present invention is to improve the relatively constant warning time provided at a highway-rail grade crossing warning system where a remote device predicts the arrival of a train at the crossing and communicates the prediction through the use of rail-based communications.  
         [0007]     A further object of the present invention is to provide improved communication between a remote device and a highway-rail grade crossing warning system for prediction.  
         [0008]     Yet another object of the present invention is to provide a first signal to predict the approach of a train to the highway-rail grade crossing and a second signal that overrides the first signal, if a slow moving train is detected, to prevent the crossing warning system from being activated too early.  
         [0009]     Another object of the present invention is to provide directional logic that can determine the direction of motion of a train after it has stopped and then resumes motion.  
         [0010]     A still further object of the present invention is to provide methods for communicating between a remote device and a highway-rail grade crossing warning system for prediction of trains by rail-based communications.  
       SUMMARY OF THE INVENTION  
       [0011]     One aspect of this invention is directed to apparatus for providing a relatively constant warning time at a highway-rail grade crossing through the use of rail-based communications. The apparatus includes a crossing controller for monitoring a track of the rail grade crossing, a warning device that is actuated by the crossing controller when an approaching train is predicted by the crossing controller, a remote controller for sensing the approach of a train, the remote controller communicating the approach of a train to the crossing controller. The remote controller also determines if the approaching train is a slower moving train and communicates any determination that the train is slower moving to the crossing controller, the crossing controller responds to the communication that the train is slower moving by preventing activation of the warning device too early.  
         [0012]     A transmitter associated with the apparatus generates a first communication signal, the first communication signal changes when an approaching train is sensed by the remote controller, the change in the first communication signal is communicated via rail-based communications to a receiver which is in communication with the crossing controller, and the crossing controller responds to the change in the first communication signal to activate the warning device. The transmitter also generates a second communication signal, the second communication signal changes when the approaching train is determined by the remote controller to be a slower moving train, the change in the second communication signal is communicated via rail-based communications to the receiver which is in communication with the crossing controller, and the crossing controller responds to the change in the second communication signal to prevent activation of the warning device too early. For example, the first and second communication signals may both be different audio frequency communication signals. Preferably, the first communication signal is normally energized and becomes de-energized when the remote controller senses the approach of a train and communicates that to the crossing, and the second communication signal is normally de-energized and the second communication signal becomes energized when the remote controller senses the approach of a slower train and communicates that to the crossing, thereby causing the crossing controller to temporarily bypass the de-energized first communication signal.  
         [0013]     Preferably, the apparatus also includes a first timer to provide a first predetermined time delay, the first timer initiated after the second communication signal is energized, and if the first communication signal does not remain de-energized for the length of the first predetermined time delay, temporary bypass of the first communication signal is terminated and the crossing controller activates the warning device. A second timer may provide a second predetermined time delay greater than the first predetermined time delay, the second timer is initiated after the second communication signal is energized, and if the first communication signal does not remain de-energized after the second predetermined time delay or if a track signal monitored by the crossing controller exceeds a predetermined level indicative of a train on a monitored portion of the track, the crossing controller deactivates the warning device.  
         [0014]     The apparatus further includes directional logic. The directional logic determines that motion of a train is in an outbound direction if the crossing controller determines that the magnitude of track circuit signal is indicative of the train being near the island and if the crossing controller subsequently determines that an island circuit is de-energized. The directional logic then overrides de-energization of the first communication signal and deactivates the warning device. The directional logic continues to remain in an outbound state as long as outbound motion of the train continues to be detected. A cancellation timer with a first predetermined cancellation time cancels the outbound state of the directional logic if the crossing controller senses a relatively large track signal magnitude, if no outbound motion of the train is detected and if the first communication signal is de-energized at the end of the first predetermined cancellation time. The cancellation timer also has a second predetermined cancellation time and cancels the outbound state of the directional logic if the crossing controller senses that the train stopped on the outbound move for a time greater than the second predetermined time and if the first communication signal is de-energized at the end of the second predetermined cancellation time.  
         [0015]     Yet another aspect of the present invention includes related methods. One of the methods includes the steps of monitoring a track of the rail grade crossing with the crossing controller, actuating a warning device with the crossing controller when an approaching train is predicted by the crossing controller, sensing the approach of a train at the remote controller, communicating the approach of a train from the remote controller to the crossing controller via a track circuit, determining if the approaching train is a slower moving train at the remote controller, communicating via the track circuit any determination that the train is slower moving to the crossing controller, and responding to the communication that the train is slower moving by preventing early activation of the warning device for slower moving trains.  
         [0016]     Additional methods include the steps of providing a first communication signal via a track circuit, changing the first communication signal when an approaching train is sensed by the remote controller, communicating the change in the first communication signal to the crossing controller, responding to the change in the first communication signal at the crossing controller to activate the warning device, providing a second communication signal via a track circuit, changing the second communication signal when the approaching train is determined by the remote controller to be a slower moving train, communicating the change in the second communication signal to the crossing controller, and responding to the change in the second communication signal at the crossing controller to delay activation of the warning device for slower moving trains. Further steps include normally energizing the first communication signal, normally de-energizing the first communication signal, de-energizing the second communication signal when the remote controller senses the approach of a train, energizing the second communication signal when the remote controller senses the approach of a train, and using the energization of the second communication signal to temporarily bypass the de-energization of the first communication signal at the crossing controller, thereby delaying activation of the warning device for slower moving trains.  
         [0017]     The present invention is further directed to methods including the steps of providing a first timer with a first predetermined time delay, initiating the first timer after the second communication signal is energized, terminating temporary bypass of the first communication signal if the first communication signal does not remain de-energized for the length of the first predetermined time delay, and activating the warning device if the first communication signal does not remain de-energized for the length of the first predetermined time delay. Preferably, the steps also include providing a second timer with a second predetermined time delay greater than the first predetermined time delay, initiating the second timer after the second communication signal is energized, and activating the warning device if the first communication signal does not remain de-energized after the second predetermined time delay or if a track signal monitored by the crossing controller exceeds a predetermined level indicative of a train on a monitored portion of the track.  
         [0018]     Preferably the methods include the steps of providing directional logic, determining that motion of a train is in an outbound direction if the crossing controller determines that the magnitude of a track circuit signal is indicative of the train being near the island and if the crossing controller subsequently determines that an island circuit is de-energized, using the directional logic to override the first communication signal if the first communication signal does not remain de-energized for the length of the first predetermined time delay, deactivating the warning device, and continuing to keep the directional logic in an outbound state as long as outbound motion of the train continues to be detected. Still another method provides a cancellation timer with a first predetermined cancellation time, cancels the outbound state of the directional logic if the crossing controller senses a relatively large track signal magnitude, if no outbound motion of the train is detected and if the first communication signal is de-energized at the end of the first predetermined cancellation time, provides the cancellation timer with a second predetermined cancellation time, and cancels the outbound state of the directional logic if the crossing controller senses that the train stopped on the outbound move for a time greater than the second predetermined time and if the first communication signal is de-energized at the end of the second predetermined cancellation time.  
         [0019]     The present invention further includes a communication system for apparatus for providing relatively constant warning time for a rail-grade crossing. The apparatus includes a crossing controller, a remote controller and a warning device. The communication system includes a first transmitter for transmitting a first communication signal via rail-based communications, the first communication signal changes when an approaching train is sensed by the remote controller, the change in the first communication signal is communicated to the crossing controller, and the crossing controller responds to the change in the first communication signal to activate a warning device. A second transmitter in the communication system transmits a second communication signal via rail-based communications, the second communication signal changes when the approaching train is determined by the remote controller to be a slower moving train, the change in the second communication signal is communicated to the crossing controller, and the crossing controller responds to the change in the second communication signal to prevent early activation of the warning device.  
         [0020]     The first and second communication signals in the communication system are preferably audio signals of different frequencies. The communication system further includes a first receiver for receiving the first communication signal via rail-based communications, and a second receiver for receiving the second communication signal via rail-based communications, and the first and second receivers are in communication with an input of the crossing controller. The first communication signal is normally energized and said first communication signal becomes de-energized when the remote controller senses the approach of a train. The second communication signal is normally de-energized and the second communication signal becomes energized when the remote controller senses the approach of a slower train, thereby causing the crossing controller to temporarily bypass the de-energization of the first communication signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The invention, together with its objects and the advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures, and in which:  
         [0022]      FIG. 1  is a diagrammatic illustration of a highway-rail grade crossing including a warning system that communicates between a remote controller and a crossing controller in accordance with the present invention;  
         [0023]      FIG. 2  is a state transition model diagram that illustrates representative steps that may occur during communication between the remote controller and the crossing controller in accordance with the present invention;  
         [0024]      FIG. 3  is a diagrammatic illustration of a highway-rail grade crossing with a warning system that is related to the warning system in  FIG. 1 , except that the embodiment shown in  FIG. 3  includes a third transmitter for bi-directional circuits; and  
         [0025]      FIG. 4  is a diagrammatic illustration of a highway-rail grade crossing with a warning system that is related to the warning system in  FIG. 1 , except that the embodiment shown in  FIG. 4  includes a bi-directional remote controller. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     It will be understood that the invention may be embodied in other specific forms without departing from the spirit thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.  
         [0027]     With reference to the drawing Figures,  FIG. 1  illustrates a highway-rail crossing, generally indicated by reference numeral  20 , at the intersection of a road  21  and a railroad track  22 . A Grade Crossing Predictor (GCP) system  40  is in general proximity to railroad track  22 . The GCP system  40  will also be hereinafter referred to as a controller or a crossing controller. The GCP system or controller  40  is an integrated system that includes all of the control, train detection, and monitoring of a highway-railroad grade crossing warning system, such as for the highway-rail crossing  20  shown in  FIG. 1 . The railroad grade crossing shown in  FIG. 1  may include a plurality of tracks, instead of the single track  22  shown. Likewise, controller  40  may monitor and control a plurality of tracks; for example, typically up to six tracks.  
         [0028]     In a conventional manner, at least that portion of railroad track  22  that intersects with the road  21  includes an island circuit  24  that is monitored by controller  40 . Similarly, those portions of track  22  that lie to the right and to the left of the island circuit  24  are included in an approach circuit are identified by reference numerals  27  and  26 , respectively. Approach circuits  26  and  27  are also monitored by the controller  40 . Traffic warning devices  30  are typically placed on both sides of track  22  and adjacent to road  21 . Warning devices  30  are provided with flashing lamps, and may be provided with gates that may be lowered, and/or may be provided with audible devices, such as bells, or the like, in a known manner. When a train is detected in the approach circuits  26  and  27  or in the island circuit  24 , controller  40  activates the traffic warning device  30 .  
         [0029]     The present invention in the GCP system  40 , utilizes audio frequency track circuit technology to communicate the DAX information from a remote controller  42  to the crossing controller  40  at the crossing via rail-based communications. Audio frequency track circuits utilize a transmitter connected across the rails that, when ‘keyed-on’, communicates an electrical signal to a receiver connected to the track at another location. The receiver is de-energized whenever the transmitter is off, or when a train is shunting the track circuit between the transmitter and receiver. When train axles are in the approach circuit  26 , the axles form a short circuit across the track that shunts the transmitted signal away from the receiver.  
         [0030]     In accordance with one aspect of the present invention, the remote controller  42  keys a first phase shift overlay (PSO) transmitter  34  and a second PSO transmitter  35 . A first PSO receiver  36  receives the PSO signals from the first transmitter  34 , and a second PSO receiver  37  receives the PSO signals from the second transmitter  35 . These PSO signals are typically of different audio frequencies. Receivers  36  and  37  provide output signals to the crossing controller  40 , which is located at the crossing  20 . For example, the output signal from PSO receivers  36  and  37  may be received at a UAX input of controller  40 .  
         [0031]     Crossing controller  40  also monitors its transceiver signal level on the track  26 , which is referred to as the EZ level. This EZ level is nominally  100  without a train in the approach. As a train approaches the crossing  20 , the EZ level reduces nearly proportional to the distance that the train is from the crossing.  
         [0032]     Advanced analysis of the track circuit is required to provide fail-safe directional detection of the train, which allows deactivation of the warning devices  30  for receding trains. One of the aspects of the present invention is the reactivation of the warning devices  30  if a train stops after proceeding over the crossing  20  and then reverses direction back towards the crossing.  
         [0033]     In accordance with another aspect of the present invention, two PSO transmitters  34  and  35  are located near the remote location of remote controller  42  and two PSO receivers  36  and  37  are located near crossing controller  40 . For example, the first PSO transmitter  34  may generate PSO signal A, also indicated by reference numeral  44 , and the second PSO transmitter  35  may generate PSO signal B, also indicated by reference numeral  45 . Transmitters  34  and  35  may be combined together, if desired. Each PSO track circuit operates on a different frequency. In the following example, these frequencies are referred to as an A signal  44  and a B signal  45 . In a similar manner, a first PSO receiver  36  may receive the A signal  44  and a second PSO receiver  37  may receive the B signal  45 . PSO receivers  36  and  37  are in communication with crossing controller  40 , such as with a UAX input of crossing controller  40 .  
         [0034]     At the point at which the remote controller  42  would normally de-energize its DAX relay drive output, it will vitally drop the transmit signal for the PSO A signal  44 . The crossing controller  40  will treat the lack of a PSO A received signal  44  as an indication to activate the crossing warning devices  30 . This DAXing scheme works fine for trains that always predict further out than the remote controller  42 , but it will lead to long warning times for slower trains that do not need to activate the warning system  30  until they are well into the approach of the track circuit  26  at the crossing. This occurs because the PSO receive signal will always drop out (be shunted out) as soon as the train passes the insulated rail joints  48  near the remote controller  42  and thus will cause the crossing to activate. In some applications, where trains are generally constant speed and fast, this may be an acceptable approach.  
         [0035]     The state transition model diagram in  FIG. 2  illustrates the steps of modifying the response of crossing controller  40  during the approach of slower trains. In block  50 , crossing controller  40  is in an idle state, the various timers are stopped and the UAX signal input to controller  40  is energized. When a remote prediction of an approaching train is made at block  54 , the A signal  44  drops as the train crosses the insulated joints  48 . The dropping of the A signal  44  is detected by PSO receiver  36 , which is in communication with crossing controller  40 . At the same time, the UAX signal to controller  40  is de-energized. Crossing controller  40  then activates the warning devices  30  to warn of the approaching train.  
         [0036]     However, to avoid long warning times at the rail-highway grade crossing for slower trains, a second PSO B signal  45  is needed to tell the crossing to ignore the dropping out of the PSO A signal  44  as the train passes the insulated joints  48 . When conventional PSO circuits are being used, this will require a second PSO (PSO B signal  45 ), as illustrated in  FIG. 1 . If the remote controller  42  computes that the train is not going to predict within about the first 5 seconds after passing the insulated joints  48 , then the remote controller  42  will activate the transmitter  34  to energize PSO signal B, which is normally deactivated, but just prior to the train arriving at the insulated joints  48 . When the input of controller  40  at the crossing sees PSO signal B energized, it will know to ignore or override the de-energizing of PSO signal A. For example, the 5 second overlap may compensate for the reaction time of the crossing controller  40 . This overlap time will lead to warning time up to about 5 seconds longer for trains that predict about 5 seconds after passing the insulated joint  48 .  
         [0037]     The crossing logic also needs to prevent situations in which the DAXing is bypassed by PSO signal B  45  but not cleared by the train going through the island, such as: 
        a) PSO signal A  44  does not drop on this train move, due to the train not entering the block, or     b) PSO signal A  44  drops, but the train leaves the crossing approach via a switch or the train backs out.        
 
         [0040]     Thus, to solve situation a), a 10 second timer is started after PSO signal B  45  picks. This is seen in block  56  of  FIG. 2 . If PSO signal A  44  does not drop in this time, bypass is not allowed. However, if signal A  44  drops, bypass occurs and the UAX input to controller  40  remains energized (block  58  in  FIG. 2 ).  
         [0041]     In order to solve situation b), the bypass is ended if the EZ level goes above 80. However, a timer is needed to prevent the bypass being canceled as the train first enters the approach. Hence, a 60 second timer is started when PSO signal A  44  first drops (block  58  in  FIG. 2 ). When the 60 second timer expires (block  60 ), the remote remains bypassed and the UAX input to controller  40  remains energized. If signal A  44  returns or if the EZ level is greater than 80 for about 5 seconds, the process returns to the idle block  52  in  FIG. 2 .  
         [0042]     As can be appreciated, if a more sophisticated PSO transmitter is used that can convey more than 1 bit of information, for instance being able to dynamically switch between transmitting one or two code signatures, and if the PSO receiver can distinguish between these codes, then a single PSO transmitter could be used instead of a separate PSO transmitter for signal A  44  and a separate PSO transmitter for signal B  45 .  
         [0043]     The present invention also performs directional logic to prevent activation on the reverse move, such as a train moving from the crossing on the island  24  toward the remote controller  42 . In this situation, if controller  40  sees a low EZ level such as less than 10 (block  62  in  FIG. 2 ), then the island circuit is de-energized (block  64 ), and de-energization of PSO signal A is ignored (block  66 ), motion in an outward direction from the island  24  is determined (block  66 ). The outbound move logic will be set once the island energizes (block  68 ) and as long as outward motion is being sensed (block  70 ). As further shown in block  70 , an outbound motion cancellation timer is used to cancel the outbound motion logic in either of two conditions: 
        a) The train leaves the approach (EZ&gt;80 and no outbound motion is sensed), the cancellation timer is started with a time interval of about 5 to 10 seconds. After this time, if PSO signal A  44  is still down, the crossing controller  40  will activate.     b) A train stops on the outbound move, the outbound motion stops. A cancellation timer is started with a configurable time of up to 120 seconds, which is equivalent of the station stop time used in the enhanced detection. After this time, if PSO signal A is still de-energized, the crossing controller  40  will activate the warning devices  30 . If outbound motion restarts, the timer will be canceled. It should be noted that the outbound motion logic only overrides the PSO signal A circuit. If the stopped train were to reverse and approach the crossing while the outbound logic is set, the normal prediction process would occur and activate the warning devices  30  at the crossing  20 .        
 
         [0046]     The timers used above may not adequately cover all situations. For example, if a train transverses the crossing but stops on the receding circuit for a red signal just short of the insulated joints, then the train may stop for a long period waiting for a proceed signal. The outbound logic cancellation timer will have expired and the crossing would be activated. In order to prevent this situation, the present invention has provision for the controller  40  at the crossing to have a track occupied input that can be driven from the signaling systems track circuit information. Hence, the train can stay on the approach indefinitely and the crossing will not activate unless it reverses direction and approaches the crossing. For safety reasons, this input should be inverted. Thus, if the wayside system track circuit de-energizes, it energizes the track occupied input. While the track occupied input is energized, the crossing unit will not start the outbound motion cancellation timer. Therefore, under a failure condition of this input, the outbound motion cancellation timer is allowed to run.  
         [0047]     Typically, the crossing unit will be a bi-directional installation, and thus have no insulated joints  48 . Hence, the track circuit information is not usually available at this location. A third PSO  38  could be used to bring this information in, as shown in  FIG. 3 . If the track relay is down, PSO signal C  46  at the signal location will be up.  
         [0048]     Since PSO signal A  44  is used to establish direction, the application will work just as well if the remote controller  42  were a bi-directional controller  43  with no insulated joints as shown in  FIG. 4 .  
         [0049]     While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects.