This invention relates to shaft cracking and incipient pinion slip, and more particularly, to monitoring shaft cracking and incipient pinion slip in an operating system such as a geared system of a locomotive.
In a geared system, the motion or torque from one shaft is transmitted to another shaft by means of direct contact between toothed wheels or gears. FIG. 1 illustrates one example of a geared system 10 for propelling a locomotive. Geared system 10 includes an electric motor 12 having a drive shaft 14 rotatably supported by bearings 16 which are attached to the locomotive, a rotor 11, a stator 19 with stator windings 21 and leads 23. Attached to one end of drive shaft 14 is a pinion 18. Typically, pinion 18 is fitted and shrunk onto a tapered end 15 of drive shaft 14. Pinion 18 engages a bull gear 20 which attaches to and drives a wheel shaft 22 rotatably supported by bearings 24. The ends of wheel shaft 22 are attached to respective wheels 26 of the locomotive.
Although electric motor 12 is resiliently supported to the locomotive, geared system 10 experiences large mechanical vibrations, e.g., shock loadings due to uneven portions of rails 30. Often, after some period of heavy usage, drive shaft 14 may crack due to fatigue. Similarly, pinion 18 may slip relative to drive shaft 14 without any advanced warning so that torque is no longer transmitted to wheels 26. Such failures can be catastrophic, and repairs such as removal of electric motor 12, refitting of pinion 18, or replacement of drive shaft 14, are expensive, labor intensive, and require that the locomotive be temporarily pulled from service.
Therefore, there is a need for an apparatus and method for low cost, on-line monitoring of an operating geared system in which the apparatus and method are capable of warning of shaft cracking or incipient pinion slip.
The above-mentioned need is met by the present invention which relates to diagnostic techniques for monitoring shaft cracking or incipient pinion slip in an operating system. In one aspect of the present invention, a method for monitoring shaft cracking or incipient pinion slip in an operating system includes the steps of determining a characteristic natural frequency of the operating system at a first time, determining the characteristic natural frequency at a second time, and comparing the characteristic natural frequency determined at the first time to the characteristic natural frequency determined at the second time to detect a shift in the characteristic natural frequency in response to at least one of shaft cracking and incipient pinion slip.
For monitoring shaft cracking, the characteristic natural frequency is a natural frequency of a shaft of the operating system. For monitoring pinion slip, the characteristic natural frequency is a natural frequency of an assembly including a pinion of the operating system or the characteristic natural frequencies of two coupled assemblies which includes the pinion.
The steps of determining the characteristic natural frequency may include measuring vibrations of the operating system, measuring current of a motor of the operating system, measuring torsional oscillations of the operating system, or measuring current and voltage of a motor of the operating system. Advantageously, the steps of determining the characteristic natural frequency may include the step of performing a fast Fourier transform analysis.
In another aspect of the present invention, an apparatus for monitoring shaft cracking or incipient pinion slip in an operating system, includes a controller adapted to determine a characteristic natural frequency of the operating system at a first time, determine the characteristic natural frequency at a second time, and compare the characteristic natural frequency determined at the first time to the characteristic natural frequency determined at the second time to detect a shift in the characteristic natural frequency in response to at least one of shaft cracking and incipient pinion slip.
In still another aspect of the present invention, an article of manufacture comprises at least one computer usable medium having computer readable program code means embodied therein for causing the monitoring of shaft cracking or incipient pinion slip in an operating system. The computer readable program code means in the article of manufacture comprises computer readable program code means for determining a characteristic natural frequency of the operating system at a first time, determining the characteristic natural frequency at a second time, and comparing the characteristic natural frequency determined at the first time to the characteristic natural frequency determined at the second time to detect a shift in the characteristic natural frequency in response to at least one of shaft cracking and incipient pinion slip.
In yet another aspect of the present invention, at least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine, performs a method for monitoring shaft cracking or incipient pinion slip in an operating system, as noted above.