Abstract:
A train analysis system for analyzing a wheel condition such as wheel bearing temperature includes circuitry for identifying the wheels of a railroad car, circuitry for averaging the condition of each wheel of a car, and circuitry for establishing a threshold level for said condition, dependent on said averaging. When a wheel cannot be identified, a threshold level is set which is below the maximum level for identified wheels.

Description:
BACKGROUND OF THE INVENTION 
     A. Field of Invention 
     This invention pertains to an apparatus for analyzing railroad car wheels to detect certain conditions which may result in a derailment, and more particularly to a system which performs the analysis after data has been collected from a moving car. 
     B. Description of the Prior Art 
     Derailments on railroads cause major problems because they may result in injuries, loss of life and they are also very expensive and cause extreme time delay. Since derailments are caused very often by either hot wheels or hot wheel bearings, extensive wheel monitoring systems have been installed for monitoring the wheel temperatures. These temperatures are then compared to certain threshold levels and if the temperature of a wheel (or bearing) exceeds a threshold, an abnormal condition is established. The level of the threshold is critical to the operation of the railroad. If this level is too high, an overheated wheel or bearing may not be detected until a derailment occurs. If the level is set too low, a false alarm may be generated. False alarms resulting in a stopped train are more tolerable then derailments because they normally do not result in loss of life or property, however they still cause delays, complications in train schedules and consequently are very expensive. 
     Some systems are known in which the temperature thresholds are not fixed but are adjusted dynamically between an absolute minimum and an absolute maximum level. For example the temperatures of all the wheels of a car, or train, could be averaged and then the threshold can be calculated using this average. However, this procedure requires the capability of identifying, differentiating and associating the wheels to a car. In the prior art systems, if a wheel is not identified as being associated with a particular car, then the absolute threshold level is used for the comparison. However, this solution is unsatisfactory because it may lead either to derailments due to missed hot bearings or false alarms and the absolute alarm thresholds cannot be modified to make effective use of alarm criteria based on car average temperatures. 
     OBJECTIVES AND SUMMARY OF THE INVENTION 
     In view of the above-disadvantages of the prior art, it is an objective of the present invention to provide a system which dynamically adjusts a temperature threshold, with means for handling unidentified wheels. 
     A further objective is to provide a method of handling unidentified wheels which is readily integrated into existing systems. 
     Other objectives and advantages of the invention shall become apparent from the following description. A train analysis system constructed in accordance with this invention includes a scanner for detecting a preselected condition of a wheel bearing and means of associating a group of wheels/axles to a particular car. If the wheel is not associated with a particular car (referred to as unidentified axles), the absolute and differential alarm thresholds can be reduced (by a user selection) below the maximum threshold for identified wheels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of a train analysis system constructed in accordance with the present invention; and 
     FIG. 2 shows a graph for the temperature threshold selection used by the system of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1 a train 10 is illustrated somewhat schematically as running on a rail 12 in the direction indicated by arrow A. The cars making up train 10 may have different lengths and different number of axles, with two wheels and wheel bearings on each axle (on opposite sides). Adjacent to rail 12 are two detectors: a wheel detector 14, and a scanner 16. Such detectors and scanners are well know to those skilled in the art and may, for example, be constructed as disclosed in U.S. Pat. Nos. 3,095,171; 3,408,493 or 3,545,005 . Scanner 16 monitors the temperature of the wheel bearings as the wheels run by, and provides a signal indicative of this bearing temperature to an a/d converter 16. A similar scanner (not shown) is disposed on the other side of the train to monitor the bearings of the left wheels. The output of this scanner is fed to another a/d converter 20. 
     The remaining portions of the system are best implemented by using a digital microprocessor. However, for the sake of clarity the system is described as having discrete components or circuits. Wheel detector 14 is used to generate a signal indicative of each wheel to a car identifier circuit 22. Circuit 22 determines the spacing between the wheels. The system is initially set up with information describing various cars by the spacing between the wheels. Circuit 22 uses this information and the spacing the wheels to identify each car of train 10 including the number of its axles, the type of bearings (i.e. plain or roller bearings) which is determined as the train passes the scanner 16 by the heat wave form and so on. The temperature of each wheel bearing, its axle number and the corresponding car information is all stored in a memory 26. Thus, memory 26 contains a whole temperature profile for the wheel bearings. 
     When all the cars of the train 10 have rolled past the detector 14 and scanner 16, the system proceeds to determine if any of its wheel bearings are hot as follows. It should be understood that the circuits shown in FIG. 1 may be implemented using a digital microprocessor, and they are shown as discrete circuits for the sake of clarity. First, an average temperature calculator circuit 28 recalls all the bearing temperatures from memory 26 and calculates separately the average temperatures on each rail of wheels bearing, regardless of bearing type. The two values are identified as: 
     R1TSA (Rail 1 Train Side Average) 
     R2TSA (Rail 2 Train Side Average) 
     During this calculation, if any of the bearing temperatures exceed a maximum alarm level (either absolute or differential (described below) they are excluded. 
     Circuit 28 also calculates the following two heat compensation factors, wherein the digits 1 and 2 indicate the rail numbers: 
     R1HCF=0.5(1+(R2TSA/R1TSA)) 
     R2HCF=0.5(1+(R1TSA/R2TSA)) 
     These compensation factors are fed to a temperature adjusting circuit 30 which also recalls each of the bearing temperatures from memory 26 and multiplies it with the appropriate compensating factors defined above; thereby normalizing the entire train. 
     Next, a threshold generator circuit 32 is used to generate a threshold level. For this purpose, circuit 32 obtains from memory 26 a list of all the wheels belonging to a particular car. Circuit 32 then get from circuit 30 the compensated bearing temperature for each wheel of that particular car, and generates therefrom average car bearing temperature (ACBT). In this scheme, if a particular compensated bearing temperature is below a minimum level, the compensated bearing temperature for that bearing may be assigned a minimum value. 
     After the average car bearing temperature has been calculated, circuit 32 calculate a threshold level for that car. More particularly, for low average car temperatures the threshold level is generated using the formula: 
     Threshold (car)=b*ACBT+abs.min. 
     where 0.5&lt;b&lt;5 and 
     abs. min. is an absolute minimum threshold level which is determined empirically and selected by a user. 
     As seen in FIG. 2, the threshold level increases linearly, as selected by the user, with ACBT until an absolute maximum (abs. max) threshold level is reached. Thereafter, the threshold level remains at abs. max. Again the value of abs. max. is determined empirically and selected by a user. 
     Finally, for each identified wheel, its compensated wheel bearing temperature is compared by comparator 34 to the threshold level generated by circuit 32. If this temperature is equal to or exceeds this threshold level, i.e. it falls into shaded area 36 in FIG. 2, then a hot bearing alarm signal 38 is generated by the system. 
     As described above, sometimes one or more wheels cannot be identified as belonging to a particular car. This may occur for example if the characteristics of a car are not in the car library of memory 24; if the wheel transducer generates a spurious pulse, or fails to generate a pulse because of noise; or if the train 10 is accelerating rapidly. When circuit 32 determines that a wheel is unidentified, it generates an unidentified threshold level by reducing the absolute maximum level by a preselected offset as shown in FIG. 2. This level is then used by comparator 34 as the reference value against the bearing temperature from circuit 30. 
     The values of b and the offset can be preset by the manufacturer of the system, or may be selectable by a customer, for example by using DIP switches 40. 
     The above description shows in detail a typical wheel bearing temperature monitoring system with means for handling unidentified wheels. Obviously, the same techniques may be adapted to systems using other types of monitoring systems. Moreover, modifications can be made to the invention without departing from its scope as defined in the appended claims.