Patent Application
20150134189
The present invention relates to systems and methods for estimating the remaining useful life of rotating machinery, and in particular drivetrains.
Drivetrains are used across a range of industries. For example, wind turbines include a drivetrain to transfer torque from a main rotor shaft to an electric generator, and gas turbines include a drivetrain to transfer torque from turbine blades to an electric generator. Also by example, wheeled and tracked vehicles include a drivetrain to transfer torque from a prime mover, such as an engine or a motor, to a drive axle. Drivetrains also include other rotating machinery having gears, bearings and/or shaft arrangements that transmit torque.
In these and other applications, drivetrains are typically designed to meet a design life that is suitable for the intended application. The design life normally assumes a range of expected torque loads. However, the expected torque loads almost always differ from the actual torque loads experienced under fielded operating conditions. As a result, drivetrains sometimes experience accelerated wear and deterioration to the point of failure long in advance of a scheduled inspection and/or drivetrain overhaul.
Though not widespread, some existing systems attempt to predict drivetrain failure based on averaged torque loads. However, averaged torque loads can mask significant fluctuations in torque that might accelerate the onset of fatigue failure. Consequently, existing systems can fall short of predicting drivetrain failure, ultimately leading to untimely service interruptions and costly emergency repairs.
Systems and methods for determining a remaining useful life are provided. The systems and methods determine a remaining useful life based on actual operating conditions, and in particular the torque loads at a location along a drivetrain as regularly sampled over a recurring measurement interval. By determining a remaining useful life based on actual operating conditions, and not predicted operating conditions, the systems and methods of the present invention can provide an increased measure of predictability in drivetrain systems.
In one embodiment, a system includes a torque transducer and a control module electrically coupled to the torque transducer. The torque transducer measures torque at a location along a drivetrain, and the control module converts the torque measurement into a duty cycle. The control module determines a useful life reduction based on the duty cycle and subtracts the useful life reduction from the then-existing remaining useful life to determine a new remaining useful life.
In another embodiment, a system and a method for estimating a remaining useful life includes determining each duty cycle based on drivetrain torque and one or more environmental variables. The duty cycle is determined based on the torque load, the number of revolutions at the torque load, and the operating time at the torque load. The environmental variables can include, for example, component temperatures, fluid pressures, fluid conditions, wind speeds, generator speeds, and system vibrations.
In another embodiment, a system and a method for estimating a remaining useful life includes measuring drivetrain torque and drivetrain speed. The method further includes determining a duty cycle for each torque measurement and speed measurement, and determining a remaining useful life based on drivetrain operation at each determined duty cycle. The method can include generating an alert if the remaining useful life is below a minimum value or approaches zero.
The systems and methods can continually update and share the remaining useful life with interested parties. In addition, the systems and methods can determine a remaining useful for multiple subcomponents of a single drivetrain, optionally using an original calculated design life as a baseline value. The systems and methods can be used in conjunction with essentially any drivetrain, including for example drivetrains associated with internal combustion engines, wind turbines, and gas turbines.
These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the accompanying drawings and appended claims.
The current embodiments include systems and methods for remaining useful life predictions in drivetrains. The current embodiments use torque measurements, speed measurements, and/or environmental variables to determine the remaining useful life based on actual drivetrain operating conditions. As used herein, drivetrains include essentially any system for transmitting torque loads, including systems having shafts, stators, rotors, gears, and/or bearings. Such drivetrains include rotary systems in wind turbines, gas turbines, wheeled vehicles and/or tracked vehicles, for example.
Referring now to
As also noted above, the system 10 of the present embodiment includes a rotational speed sensor 14. The rotational speed sensor 14 can include any sensor adapted to convert rotary speed of the drivetrain 100 into an electrical signal. For example, the speed sensor 14 can include a magneto-electric or an inducto-electric rotational speed sensor, while other speed sensors can be used in other embodiments as desired. The speed sensor 14 can optionally provide a 0 to 5 VDC signal that is proportional to the measured rotational speed of the drivetrain 100, and more particularly a gear, a shaft, a rotor, or other component of the drivetrain 100. The output of the speed sensor 100 is communicated to the control module 16 by direct or indirect electrical connections, as well as by wired or wireless electrical connection.
The control module 16 is adapted to process the output of the torque transducer 12 and the speed sensor 14. The control module 16 can include a processor, for example an application specific integrated circuit (ASIC) or a programmable logic controller (PLC), and a computer readable memory, for example a solid state memory. The processor is generally preprogrammed with a series of instructions that, when executed, cause the controller 16 to continually calculate a remaining useful life according to the method steps discussed below in connection with
As generally shown in
As more particularly shown in
More particularly, the method 20 generally includes measuring drivetrain torque and measuring drivetrain speed during operation the drivetrain 100 under fielded conditions at steps 32 and 34, respectively. In particular, a torque transducer converts drivetrain torque into a first electrical output at step 32, and a speed sensor converts drivetrain speed into a second electrical output at step 34. The control module 16 then stores the electrical output of each sensor to memory. The electrical outputs can be continuous or pulsed, for example, with the torque sensor output being indexed to coincide with the speed sensor output. For example, the electrical outputs can be entered in parallel into a single shift register in memory. In addition, the torque and speed measurements can relate to the same location along the drivetrain 100, including for example a shaft, a bearing assembly, a rotor assembly, or a gear assembly.
At step 36, the control module 16 determines the drivetrain duty cycle(s). The drivetrain duty cycle(s) can depend, entirely or in part, on the measured torque and speed values. In a first example, the drivetrain duty cycle(s) can depend on the torque value and/or speed value at each sample time t within the measurement interval T. For illustrative purposes, a first duty cycle might include any torque between 1.0 k-1.2 k newton-meters (N·m) at speeds between 2.0 k-2.5 k revolutions per minute (r/min), while a second duty cycle might include any torque between 1.2 k-1.4 k N·m at speeds between 2.0 k-2.5 k r/min. Further in this example, a measurement of 1.1 k N·m and 2.1 k r/min at time t1 would classify within the first duty cycle, while a measurement of 1.3 k N·m and 2.4 k r/min at time t2 would classify within the second duty cycle, wherein the measurement interval T includes sample times t1, t2 to tn. To adequately account for potential torque fluctuations—including bending and reversing bending—the time domain for each subinterval (Δt) is sufficiently small, being significantly less than the overall measurement interval T (Δt<<T). For example, the torque measurements can be sampled at least at 1 kHz, 100 kHz, or 1 MHz, while other sampling rates can be used in other embodiments as desired.
In a second example, the drivetrain duty cycle(s) can depend on the peak torque value and/or peak speed value within each subinterval of T, e.g., from time t0 to time t1, from time t1 to time t2, and from time t9 to t10. With the above parameters for duty cycles, a first duty cycle includes any peak torque between 1.0 k-1.2 k newton-meters (N·m) at speeds between 2.0 k-2.5 k r/min, while a second duty cycle includes any peak torque between 1.2 k-1.4 k N·m at speeds between 2.0 k-2.5 k r/min. Further in this example, measurements of 1.1 k N·m (peak torque) and 2.1 k r/min from time t0 to time t1 would classify within the first duty cycle, while measurements of 1.3 k N·m (peak torque) and 2.4 k r/min from time t1 to time t2 would classify within the second duty cycle.
At step 38, the control module determines a useful life reduction. The useful life reduction is based, entirely or in part, on the duty cycle(s) as determined by the control module 16 at step 36. The useful life reduction can be measured in units of time, optionally on the order of several minutes to several thousand hours. In one embodiment, the useful life reduction is calculated by multiplying the drivetrain running time at each duty cycle (e.g., tdc1, in units of time) by a life reduction factor for that duty cycle (e.g., fdc1, dimensionless) and summing each product over the measurement interval T:
Useful Life Reduction=tdc1·fdc1+tdc2·fdc2+ . . . tdcn·fdcn (1)
High duty cycles generally include a life reduction factor f that is greater than the life reduction factor f for low duty cycles. For example, operation of a drivetrain at a high duty cycle, i.e., near upper operating limits, generally includes a greater life reduction factor (e.g., f>>1) than operation of the drivetrain at a low duty cycle, i.e., near lower operating limits (e.g., f≈1). Further by example, operation of a drivetrain at its upper operating limits for 60% percent of the measurement interval T can result in a greater life reduction than operation of the drivetrain at its upper operating limits for 20% percent of the measurement interval T. The life reduction factors are generally stored to a look-up table in memory, but can be modified from time to time as desired. It should be noted that the above methodology is exemplary, and the useful life reduction may be determined according to other methodologies in other embodiments as desired.
A variety of environmental variables can be used to determine the useful life reduction as generally depicted at step 40. These variables can include component temperatures, fluid pressures, fluid conditions, wind speeds, generator speeds, and system vibrations. For example, operation of a drivetrain at a high duty cycle over low environmental temperatures can contribute to fatigue differently than operation the same drivetrain at the same duty cycle but at high environmental temperatures. Further by example, operation of a drivetrain at a high duty cycle in low mileage lubrication oils can contribute to fatigue differently than operation the same drivetrain at the same duty cycle but in high mileage lubrication oils. Accordingly, the control module 16 can process the useful life reduction to include these and other variables as desired.
At step 42, the control module determines a remaining useful life. The remaining useful life is generally determined by reducing the then-existing remaining useful life by the amount of the useful life reduction. The then-existing remaining useful life can be a value stored to computer readable memory. If the drivetrain has not yet been driven under a load, the then-existing remaining useful life is generally equal to the original calculated design life. If the drivetrain has been driven under a load, the then-existing remaining useful life is generally less than the original calculated design life, having been reduced by previous useful life reductions. In this regard, the present method 20 is recursive, applying the immediately prior output—a remaining useful life—as a starting point for the next iteration of method step 42.
As also depicted in
To reiterate, embodiments of the present invention provide a prognostic tool for determining a remaining useful life based on real time drivetrain measurements. The real time drivetrain measurements can include drivetrain torque, drivetrain speed, and one or more environmental conditions, including for example fluid condition, fluid flow, fluid pressure, bearing temperature, power production, wind speed, generator speed, and vibrations. The prognostic tool converts the measurements into a usable format to determine a continually updated remaining useful life. The remaining useful life is stored into memory for the drivetrain, or for subcomponent(s) of the drivetrain, and is shared with owners, operators, and/or drivetrain maintenance personnel. By determining a remaining useful life based on actual operating conditions, and not predicted operating conditions, the prognostic tool can provide an increased measure of reliability in drivetrain systems over existing methods of failure prediction.
The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to elements in the singular, for example, using the articles “a,” “an,” “the,” or “said,” is not to be construed as limiting the element to the singular.
