Development and verification of a diagnostic cleat for detecting faults in military wheeled vehicles
Abstract
The U.S. military is pursuing technologies that enable Condition-Based Maintenance (CBM) of ground vehicles in an effort to ensure vehicle readiness and decrease maintenance costs. Current maintenance schedules for ground vehicles are primarily based on reliability predictions of a population of vehicles under anticipated operational loads. Therefore, vehicles are subjected to the possibility of unnecessary maintenance or the possibility of infield failure depending on how conservative the maintenance schedule exists. CBM aims to avoid unnecessary maintenance and operational failures by basing maintenance decisions on the current state (or health) of an individual vehicle. On-board instrumentation is usually used to enable CBM for vehicles. However, military vehicles, like the HMMWV, are usually not equipped with sensors nor the data acquisition systems that are required to acquire, process, and store data pertaining to the mechanical response of the wheels and suspension. The diagnostic cleat that was developed in this thesis sought to overcome the economic and technical barriers associated with equipping each and every ground vehicle to continuously monitor the condition of these vehicles. The instrumented diagnostic cleat is a completely off-board diagnostic system over which a vehicle traverses. The dynamic response of the vehicle is excited by an impulse delivered to the vehicle's tires while the vehicle traverses over the excitation portion of the diagnostic cleat system. In addition, the diagnostic cleat measures the response of the instrumented segment of the diagnostic cleat while the vehicle's tires are in contact with the instrumented segment using accelerometers mounted to the instrumented segment. The measured dynamic response is then compared to a reference (or healthy) response, and anomalies, which correspond to vehicle faults, are identified. The major advantages of the diagnostic cleat for enabling vehicle CBM are as follows: 1. The diagnostic cleat provides a consistent excitation to the vehicle, which limits the complexity of the algorithms required for diagnostics. 2. The diagnostic cleat is a global fault detection method and is not limited to specific vehicle faults or faults within a specific vehicle location. 3. One diagnostic cleat can be used to diagnose multiple vehicles, which reduces the cost of implementation. The capability of the diagnostic cleat to detect faults was demonstrated within this thesis research by simulating and then detecting tire and suspension faults within a HMMWV. The tire faults were simulated by decreasing the air pressure within the tires and suspension faults were simulated by disconnecting the damper. These faults were simulated in all four corners of the vehicle individually. The vehicle was then driven over the diagnostic cleat at 5 mph. The data indicated that the type of fault and location of the fault were identifiable with 90% confidence in 7 out of the 8 fault cases. Several sources of measurement error were also quantified such as vehicle speed. Variation in the diagnostic cleat response due to changes in vehicle speed was modeled in order to attempt to compensate for these changes in vehicle speed.
Degree
M.S.M.E.
Advisors
Adams, Purdue University.
Subject Area
Automotive engineering|Mechanical engineering|Military studies
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