Abstract:
A traction motor speed probe may include one or more accelerometers that report acceleration in three dimensions. The accelerometer signals may be compared to accelerometer signals associated with known conditions in either the motor or a machine on which the motor is operating, such as wheel lock-up, worn motor parts, or a flat spot on a wheel in a locomotive application. The accelerometer may also be useful in identifying when a zero reading from a speed sensor is because the motor speed probe is no longer firmly coupled to the motor or if motor or wheel are locked up.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a speed sensor for a motor and more particularly to a speed sensor with an integral accelerometer used for diagnostics of the motor and system in which the motor is installed. 
       BACKGROUND 
       [0002]    The accuracy of a speed sensor in a large motor, particularly a motor that is one of a set of motors used in a locomotive, is critical to the operation of the motor and in balancing the output between the motors in the set. The speed sensor may be used to identify operating conditions such as wheel slip but may also report important failure conditions such as wheel lock-up. Wheel lock-up is a dangerous condition that requires a train to be brought to a stop to allow a visual inspection protocol can be performed to test the wheel and axle, costing both time and money in delays and personnel costs. 
         [0003]    Failure of a speed sensor is generally interpreted as a wheel lock-up and requires the full locomotive visual inspection protocol to be performed to determine if the wheel is free or locked-up. A frequent cause of speed sensor failure is simply that the screws holding the motor speed probe with the sensor loosen or were never tightened properly so that the sensor moves out of position to make a reading. In a locomotive application, the probe/sensor is mounted on the motor behind one of the wheels making it difficult to access, especially outside a repair facility. 
         [0004]    U.S. patent publication 2013/0342362 (the &#39;362 publication) discloses are wireless unit for use in a rail car that includes, among other possibility sensors, an accelerometer. The wireless unit has a short range transmitter and a receiver. With one wireless unit on each car in a train, a daisy chain network connection can be created down a long train to a master site, e.g., on the locomotive, that communicates information from the wireless units and their associated sensors. The &#39;362 publication fails to disclose the use of an accelerometer mounted integral to a speed probe on a motor to diagnose a faulty probe mounting and other machine conditions. 
       SUMMARY OF THE DISCLOSURE 
       [0005]    In one aspect of the disclosure a motor speed probe for use in a locomotive includes a housing, a speed sensor disposed in the housing, and an accelerometer disposed in the housing. 
         [0006]    In another aspect of the disclosure, a system for diagnosing fault conditions in a locomotive having an electric motor includes a motor speed probe coupled to the motor. The motor speed probe may include a housing, a speed sensor and an accelerometer wherein both the speed sensor and the accelerometer are disposed in the housing. The system also includes a controller coupled to the motor speed probe, the controller including a processor and a memory having computer executable instructions. The computer executable instructions cause the processor to interpret the output of the speed sensor to determine a speed associated with the motor and to compare a signal output of the accelerometer with a stored signal to identify a fault condition in the locomotive. 
         [0007]    In yet another aspect of the disclosure, a method of identifying fault conditions in a motor includes coupling a motor speed probe to the motor, the motor speed probe including a housing containing i) a speed sensor configured to measure a speed of the motor, and ii) an accelerometer configured to measure acceleration in three-axes. The method also includes receiving at a controller a first signal from the speed sensor that is used to determine the speed of the motor, receiving at the controller a second signal from the accelerometer that is used to determine motion in three dimensions of the housing, and comparing the second signal to a database of pre-determined signals associated with one or more fault conditions. The method further includes providing an alert via the controller when the second signal matches one or more the pre-determined signals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a simplified block diagram of a locomotive; 
           [0009]      FIG. 2  is a side view of a motor speed probe; 
           [0010]      FIG. 3  is block diagram of a controller for use in the locomotive of  FIG. 1 ; 
           [0011]      FIGS. 4-7  are exemplary accelerometer output signals corresponding to different conditions; and 
           [0012]      FIG. 8  is a flowchart of a method of monitoring for locomotive conditions with an accelerometer in a speed sensor. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  is a simplified diagram of a machine  100 , such as a locomotive. The machine  100  may include one or more trucks  102 , sometimes called bogies, that include an axle  106  with two wheels  108 , a motor  110  and a motor speed probe  112 . There may be multiple trucks on a single machine. For example, some locomotives use 6 trucks. The motor  110  sometimes called a traction motor and may be a three phase alternating current motor, a switched reluctance motor, or other electric motor. 
         [0014]    Mechanical energy generated by an engine  114  may be converted to electrical energy at a generator  116 , with the electrical energy stored in an energy storage unit  118 , such as a battery or capacitor bank. A controller  120  may be used to supply electrical energy stored in the energy storage unit  118  to the motor  110  based on load, track grade, and control signals from an operator cab (not depicted). For example, the controller  120  may calculate torque requirements and convert that information into signals for applying current to different phases of the motor  110  based on a position of a rotor or armature of the motor  110 . 
         [0015]    A motor speed probe  112  provides an indication of wheel speed to the controller  120 . The motor speed probe  112  may also provide additional signals as described further below. The controller  120  may also provide a signal to an alert device  124  that provides an operator with an indication of a potential problem. The alert device  124  may have a light, an audible alarm or a combination of both. The controller  120  or the alert device  124  may also send a signal to a dispatcher or other maintenance facility. The alerts may include a notification of wheel lock-up. 
         [0016]      FIG. 2  is a side view of a motor speed probe  112 . The motor speed probe  112  may include a housing  140  that may have an integral bracket  142  so that mounting bolts  144  can be used to secure the motor speed probe  112  to a motor frame  146 . A speed wheel  148  may be attached to an armature shaft of the motor  110  so that one turn of the armature causes one rotation of the speed wheel  148 . The ratio of the speed wheel  148  rotation to the axle  106  rotation may be known for use in converting speed wheel speed to speed. Rotation of the axle  106  and therefore the speed wheel  148  cause the teeth  158  on the speed wheel  148  to alter an electric field around the speed sensors  160 , which in one embodiment are a Hall effect sensors. The altered field around the speed sensors  160  causes a pulse modulated signal to be developed which is carried via a wiring harness  170  with individual conductors  172  to the controller  120 . Dual Hall effect sensors may be used to provide a direction indication by a comparison of the phase of the respective output signals, as well as to provide redundancy in speed sensing. 
         [0017]    In addition to the speed sensors  160 , the motor speed probe  112  may include an accelerometer  162  that reports acceleration in three dimensions to the controller  120  as indicated by the A, B, and C directional arrows. A power conditioner  164  may supply power to the accelerometer  162  while a power conditioner  166  may supply power to the speed sensors  160 . Crosstalk noise between the accelerometer  162  and the speed sensors  160  may be minimized by using the separate power conditioners  164  and  166 . The signal conditioner  168  may be used to separately buffer, drive, and/or impedance match the outputs of the speed sensors  160  and the accelerometer  162  for transmission to the controller  120 . 
         [0018]    The electrical components of the motor speed probe  112 , that is the speed sensors  160 , the accelerometer  162 , the power conditioners  164 ,  166  and the signal conditioner  168  may be “potted” in the housing  140  using an epoxy resin or some other hardened compound to protect the wiring connections and components from damage caused by movement inside the housing  140  and from penetration by water, oil, or other contaminants. In addition, the electrical components themselves must be capable of surviving the high shock environment of a locomotive that uses steel wheels to ride on a steel track over joints, couplings, and switches. 
         [0019]      FIG. 3  is a block diagram of an exemplary controller  120  that may be used in the machine  100  of  FIG. 1 . The controller  120  may include a processor  200  and a memory  202  coupled by a data bus  204 . The controller  120  may also include inputs  206  that receive signals from a number of sources including, but not limited to, operator controls, the motor speed probe  112 , engine sensors, generator sensors, etc., used to implement a control strategy for operating the machine  100 . The controller  120  may also include a number of outputs  207  that may drive, among other things, the alert device  124 . 
         [0020]    A truck control  208  may include a bank of high power semiconductor devices that control delivery of power from the energy storage device  118  to the motor  110  for a particular truck  102  of the machine  100 . 
         [0021]    The memory  202  may be any of several physical memories, including without limitation combinations of volatile and non-volatile RAM, ROM, flash, PROM, EEPROM or other memory technologies and constructions. The memory  202  is a physical memory and does not include carrier wave or other propagated media transient memories. 
         [0022]    The memory  202  may include an operating system  216  and utilities  218  that are used to control, set up, and diagnose the overall operation of the controller  120 . A control strategy  220  may analyze values of inputs  206  to determine a current state of the machine  100  as well as a desired state of the machine  100  and make adjustments to the power delivered to the motor  110 , and in some cases, operation of the engine  114  and generator  116 , to achieve the desired state. 
         [0023]    The memory  202  may also include accelerometer routine  222  that analyzes the acceleration signals in three dimensions received from the accelerometer  162 . The accelerometer routine  222 , in an embodiment, may independently analyze a signal in each dimension to correlate patterns in the current signals to those stored in various accelerometer profiles  224 . The correlation between current and known signals may involve a complex convolution process to align and identify matches in the signals to those anticipated for certain conditions. 
         [0024]    Turning to  FIGS. 4-7  some exemplary accelerometer output signals corresponding to different conditions are illustrated. While the accelerometer  162  will experience routine acceleration in all directions, a filtering process may remove acceleration signal values associated with normal speed increases and decreases as well as single anomalies that may be associated with normal operation of the machine  100 , such as passing over a railway switch or crossing. The exemplary signals shown in  FIGS. 4-7  may be representative of acceleration in a single dimension, but may be a composite of signals for each of the three dimensions reported by the accelerometer  162 . Of interest are those signals in any direction that are known to be indicators of an undesirable condition.  FIG. 4  may illustrate a periodic pattern  250  in one dimension that may be associated with a worn motor bearing. For example, a cracked or flattened bearing may create a small acceleration or bump, each time the bearing rotates in its race. 
         [0025]      FIG. 5  may illustrate a more random pattern  252  that may be indicative of the motor speed probe  112  having a loose mounting so that the motor speed probe  112  itself is shaking in one or more dimensions. When the motor speed probe  112  is not tightly coupled to the motor frame  146 , a gap between the speed wheel teeth  158  and the speed sensors  160  may become too large to get an effective speed reading. This may cause an inaccurate speed reading, or in the worst case, no reading at all which is interpreted as wheel lock-up.  FIG. 6  may illustrate a periodic pattern  254  associated with a flat spot on a wheel  108 . Identification of such a pattern  254  as a flat spot may be aided by its period being related to the current speed of the machine  100 . 
         [0026]      FIG. 7  may illustrate a pattern  256  showing a sudden change in acceleration followed by a random change in acceleration indicated by pattern  258 . The patterns  256  and  258  may be indicative of a wheel lock-up where the truck  102  decelerates as the wheel stops turning and then accelerates as the machine  100  overcomes the friction of the wheel  108  on the rail and drags the truck  102  unevenly. A combination of patterns  256  and  258  together with a low or zero speed signal from the speed sensors  160  may provide a cross-check that a wheel lock-up has occurred. 
       INDUSTRIAL APPLICABILITY 
       [0027]      FIG. 8  is a flow chart  260  of a method of monitoring for locomotive conditions using an accelerometer  162  in a motor speed probe  112 . At a block  262 , the motor speed probe  112  may be coupled to a motor housing  146 . The motor speed probe  112  may include a housing  140  containing i) one or more speed sensors  160 , in one embodiment in the form of a Hall effect sensor, configured to measure a speed of the axle  106  and wheels  108 , and ii) an accelerometer  162  configured to measure acceleration of the motor speed probe  112  in three axes. The speed sensors  160  may be any of a number of commercially available Hall effect sensor. The accelerometer  162  may be, for example, an ADXL377 accelerometer available from Analog Devices, Inc. The power conditioners  164  and  166  may be voltage regulators and may be provided to regulate power supplied to the accelerometer separate from any other power supplied to the motor speed probe. This helps avoid a condition where using a common voltage regulator could allow coupling of noise generated, for example, by the pulsed signals from the speed sensors  160 . Additionally, output signals from the speed sensors  160  and the accelerometer  162  may be buffered or impedance matched before providing the respective output signals to the controller  120 . 
         [0028]    At a block  264 , a first signal from one or both of the speed sensors  160  of the motor speed probe  112  may be received at a controller  120 . The first signal may be a pulse coded signal where the pulse frequency is directly proportional to the speed of the speed wheel  148  and thereby also the rotational speed of the wheel  108 . The first signal, that is, the speed signal may be used for any number of control and diagnostic functions including locomotive speed and power calculations, wheel slip estimation, engine  114  and generator  116  management, etc. 
         [0029]    At a block  266 , a second signal from accelerometer  162  of the motor speed probe  112  may also be received at the controller  120 . The second signal may be directly related to acceleration in three dimensions of the motor speed probe  112 . The second signal may be primarily used as a diagnostic indicator for the overall health of the truck  102 . As shown above in the exemplary waveforms of  FIGS. 4-7 , any number of characteristics related to normal operation, trouble indicators, and failures in truck-related systems may be cataloged and used for future reference for diagnostics. 
         [0030]    At a block  268 , the second signal may be processed and compared to a database of pre-determined signals associated with normal operation as well as one or more fault conditions in the truck  102 . These fault conditions may include, but are not limited to a faulty coupling of the motor speed probe  112  to the motor  110 , a worn bearing in the motor  110 ; damage to an axle  106  coupled to the motor  110 , a flat surface on a wheel  108  coupled to the motor  110 , or a loss of lubricating fluid in the motor  110 . 
         [0031]    At a block  270 , an alert device  124  may be activated via the controller  120  when the second signal matches one of more the pre-determined signals. The alert device  124  may include both visual and audible indicators to an operator of the locomotive as well as signal sent to remote locations both on and external to machine  100  and any train associated with the machine  100 . 
         [0032]    The ability to confirm wheel lock-up as well as the ability to diagnose other failures or potential failures through the use of an accelerometer  162  in the motor speed probe  112  provides a significant benefit to both locomotive manufacturers and railroad train operators. Railroad train operators benefit by reducing or eliminating unnecessary stoppages to identify false wheel lock-up conditions as well as receiving early warning on potentially harmful conditions such as flat wheels and motor bearing failures. Similarly locomotive manufacturers benefit by reduced warranty costs and increased customer satisfaction.