|On the Road to Condition-Based
Maintenance for Army Vehicles
|by Mark S. Bounds, Mary Calomeris, Michael Pohland, and Marguerite Shepler
The Army Materiel Systems Analysis Activity is developing onboard systems for tactical wheeled vehicles that will allow maintainers and operators to base preventive maintenance actions on actual vehicle conditions.
Condition-based maintenance (CBM) is a strategy that bases the performance of maintenance on the actual condition of the system and not on fixed time intervals. This strategy is made possible by the application of usage characterization, diagnostic, and prognostic processes executed on a health and usage monitoring system (HUMS).
“Usage characterization” refers to the evaluation of the manner in which a system is being employed and indicates how and why things may be broken or in the process of breaking. Usage characteristics include hours run, miles driven, time at idle, fuel consumed, number of hard brakes and hard turns, vehicle speeds over specific terrains, and so forth. “Diagnostics” are based on the symptoms or indicators of problems and use methods to find what is broken or breaking in a system. “Prognostics” are based on a combination of indicators and physics of failure methods; they result in methods for predicting when components are going to break. [“Physics of failure” refers to the analysis of the physical processes that result in system failures. Such an analysis can be used to improve system reliability and maintainability.]
The Army Materiel Systems Analysis Activity (AMSAA) at Aberdeen Proving Ground, Maryland, in conforming to the common logistics operating environment (CLOE) concepts developed by the Logistics Innovation Agency, is focused on developing ways for vehicles to self-diagnose and self-report their conditions. Specifically, AMSAA is working on predictive maintenance algorithms using both the maintenance and operating histories of vehicles. The onboard system that AMSAA has designed in conjunction with the Aberdeen Test Center collects data from a vehicle’s onboard vehicle sensors, data bus, terrain sensors, and global positioning system (GPS) and analyzes the data to determine the vehicle’s condition.
AMSAA’s Strategy for CBM
CBM is being implemented in four phases. In phase 1, AMSAA identified appropriate hardware and software to be integrated into a HUMS that could be used for engineering development purposes—an engineering development HUMS (EDHUMS)—and completed initial testing and evaluation of these components in continental United States (CONUS) test and training environments. Phase 2 consisted of integrating these components into a robust, military-grade EDHUMS, designing a data analysis process, testing EDHUMS in the CONUS training environment, and beginning to field EDHUMS in operational units outside of CONUS, including the U.S. Central Command’s area of responsibility. AMSAA is currently developing a solution for the information management process.
Phase 3 (also underway) consists of identifying a small, inexpensive focused HUMS (FHUMS)—a HUMS with limited but very specific capabilities that can be deployed across larger fleets because of its lower cost and that can be programmed with algorithms developed on the EDHUMS. Phase 4 of AMSAA’s strategy includes integrating proven FHUMS hardware into platforms by the original equipment manufacturer at the time of manufacture or into other appropriate proven hardware.
AMSAA’s approach to implementing CBM also includes the use of two data “prongs,” which are diagnostics and prognostics and usage. AMSAA collects data from imbedded onboard sensors and added sensors, including the data bus, GPS, and terrain sensor. The data are fed into diagnostic and prognostic algorithms that then report impending failures and unsafe or damaging usage to the vehicle driver, maintainers, and commanders. The usage data are compiled and reported to fleet managers, engineers, and maintainers.
The final part of AMSAA’s strategy for CBM implementation is testing in “parallel environments.” Testing in both controlled and intheater environments allows for heavily-instrumented vehicles to be evaluated under many scenarios. Measurements can be made in a controlled and well-defined environment on known test courses. Such testing provides large data sets for developing damage models and prognostic algorithms. Although AMSAA is able to use a commercial off-the-shelf (COTS) system to collect data in the test environment, the system must be militarized for the intheater environment.
Testing in an intheater environment is also beneficial. It provides immediate value by giving insights into real-world vehicle usage by Soldiers and the effect this usage can have on the prognostic algorithms that are being developed based on vehicle usage in a test environment. Installing HUMS in a theater provides a validation and verification process to determine if prognostic algorithms developed in a test environment are applicable to vehicles being used in current operations.
|The eDAQ-lite is a commercial off-the-shelf data acquisition system that can provide onboard self-diagnosis and self-reporting of a tactical wheeled vehicle’s health.
Vehicle Data Acquisition System
AMSAA engineers identified a rugged and modular COTS data acquisition system (eDAQ-lite) that has the functionality, flexibility, and ease of use needed to support the development of CBM and prognostic HUMS (PHUMS) algorithms and processes. (See photo above.) This system complies with the Army Integrated Logistics Architecture and with the CLOE strategy for onboard self-diagnosis and self-reporting of a vehicle system’s health. It is also 100-percent compatible with current AMSAA data analysis software (Glyphworks, Matlab, and MathCAD) and processes.
The COTS vehicle data acquisition system that will be used on tactical wheeled vehicles must—
- Be dust- and water-tight.
- Be small in overall size.
- Have robust, military-grade cable connections.
- Accept 12- and 24-volt power inputs.
- Provide a method for remotely switching the unit on and off.
- Be compatible with the vehicle bus, GPS, and displacement, strain, acceleration, and temperature gauges.
- Operate in maximum outside ambient temperature of 49 degrees Celsius (120 degrees Fahrenheit) with a solar radiation load up to 1,120 watts per square meter.
- Meet conducted emissions and susceptibility requirements of Military Standard 461, Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment.
- Survive the vibration levels typically experienced by various tactical wheeled vehicles.
The base of eDAQ-lite contains the computer processing unit, memory, serial communications port, power circuitry, and battery backup. The layers, which are interchangeable and removable, contain the circuitry
for handling analog and digital signals: the bridge layer for analog signals and the digital input/output for digital signals.
The eDAQ-lite design has some limitations. It was designed for industrial use, meaning use in an operating temperature of -10 to 65 degrees Celsius and with an operating voltage of 10 to 18 volts, and it has industrial-grade connectors. It has no additional electromagnetic interference (EMI) shielding and no tests for EMI, no internal relay for switching the unit on and off, and no internal motion sensors. Finally, the vehicle engine bus interface module is external to the unit.
Modifications and Additions to eDAQ-lite
Specific tasks in the POI call for specific pieces of equipment. In some cases,
different pieces of equipment have identical systems. For example, the engine,
transmission, and other systems of a heavy, expanded-mobility, tactical truck
(HEMMT) are basically the same whether it is a wrecker or fuel truck. However,
some similar items, such as M109A5 and M109A6 howitzers, have significant differences,
and sometimes new equipment is completely different from old equipment.
To ensure the survivability of eDAQ-lite in the field, enhance its functionality, and control EMI to and from communications gear, AMSAA made a few changes and additions. First, a military-grade superstructure was designed in Pro/Engineer (a three-dimensional computer package for modeling solids) to house the eDAQ-lite data acquisition system and other essential support equipment and cables.
Support equipment also was added, including EMI filters and fuses on the power lines; a direct current/direct current converter to enhance the operating voltage range from 10 to 18 volts to 9 to 36 volts and provide protection against under- and over-voltages; a solid-state relay to switch the eDAQ-lite on and off; a motion pack to provide three angular rates and acceleration information along three orthogonal [right-angled] directions; and a vehicle bus interface module to provide communication between the vehicle bus and the eDAQ-lite.
Two thermal tests were performed to characterize the thermal behavior of the resulting Army eDAQ tactical wheeled vehicle system under desert operating conditions (as specified in Army Regulation 70–38, Research, Development, Test and Evaluation of Materiel for Extreme Climatic Conditions). The first test was a steady-state, natural convection test designed to determine the maximum operating temperature of the eDAQ system. The second test was a solar-loading test designed to validate the operation of the eDAQ system when exposed to high solar radiation in conjunction with high outside ambient temperatures. A conduction-based cooling scheme was selected for the interior components (including the eDAQ-lite) and a natural convection-based cooling scheme was selected for the exterior. Thermally conductive grease, room-temperature vulcanizing, and gaskets were used on all wall interfaces. The current design includes a protective cover plate.
AMSAA has successfully demonstrated the Army eDAQ tactical wheeled vehicle system’s hardware and software capabilities, data quality checks, and rudimentary usage characterization. Many vehicles have been fully instrumented, and data are being captured from over 80 analog channels, multiple SAE [Society of Automotive Engineers] J–1708 bus channels, and GPS sensors. These vehicles have run over all Aberdeen Proving Ground test courses multiple times, providing detailed data for developing prognostic algorithms. The Aberdeen Test Center and AMSAA also have measured and analyzed data from many wheeled vehicles of several different types in Iraq for over a year. This has provided a significant amount of usage data and operating parameters that will be extremely useful for optimizing testing. The data also are being aligned with maintenance records to identify specific prognostic algorithms.
Fielding of the EDHUMS has been underway since June 2006, starting with the instrumentation of eight tactical wheeled vehicles at the National Training Center at Fort Irwin, California, and followed by intheater installations. Five EDHUMS systems were installed in Kuwait and Iraq in December 2006 and five more in March 2007. Six vehicles were instrumented in Afghanistan in September 2007. In addition to these independent installations, AMSAA is actively participating in the tactical wheeled vehicle portion of the heavy brigade combat team condition-based reliability analysis demonstration that is currently taking place at Fort Knox, Kentucky. With system installations completed in May 2007, data are currently being collected, reduced, and analyzed for reporting to fleet managers, engineers, and maintainers. In all of the installations mentioned, usage characterization and initial versions of diagnostic and prognostic
algorithms are installed and, based on feedback from the field, are being refined.
Some of the analyses that AMSAA has been able to provide include time in gear, fuel consumption, Soldier thermal environment, time at speed, and some rudimentary terrain identification. AMSAA’s goal is to generate this information using onboard algorithms, which will help to reduce the quantity of data that would otherwise need to be collected, transferred, and processed off line. Information can be presented in many ways, including graphical displays or a two-page vehicle usage summary report.
AMSAA continues to meet with customers to further identify the type of information they need and how they would like it displayed. The data flow processes from acquisition to reporting are being refined, and AMSAA is phasing in usage, diagnostic, and prognostic algorithms for verification and validation as they are developed. AMSAA continues to work with Soldiers, private industry, and other Government organizations to develop a robust CBM process that will result in improved readiness and significant logistics cost savings to the Army. ALOG
Mark S. Bounds is a mechanical engineer on the Prognostics and Electronics Physics of Failure Team at the Army Materiel Systems Analysis Activity at Aberdeen Proving Ground, Maryland. He holds a B.S. degree in mechanical engineering from Temple University and is working on a master’s degree in systems architecture and engineering from the University of Southern California.
Mary Calomeris is a mechanical engineer with ManTech International Corporation, SRS Division, working under contract to the Army Materiel Systems Analysis Activity. She holds a B.S. degree in mechanical engineering from the University of Maryland, Baltimore County.
Michael Pohland is a mechanical engineer on the Prognostics and Electronics Physics of Failure Team at the Army Materiel Systems Analysis Activity. He holds a B.S. degree in mechanical engineering from the University of Maryland and an M.S. degree in mechanical engineering from Johns Hopkins University.
Marguerite Shepler is a mechanical engineer on the Prognostics and Electronics Physics of Failure Team at the Army Materiel Systems Analysis Activity. She holds a B.S. degree in mechanical engineering from Grove City College and is working on a master’s degree in operations research from the Florida Institute of Technology.