Monitoring the Age of Vehicle Shock Absorbers carl.howard @ adelaide.edu.au Carl Howard , Nataliia Sergiienko – The University of Adelaide Guy Gallasch - DST Group Presented at: International Conference on Science and Innovation for Land Power 2018 (ICSILP 2018). Work Conducted for: DST Group, Land Vehicle Shock Absorber Health and Usage Monitoring to Support Emerging Army Logistics Concepts: Foundation Analytics. Slide 1
Motivation Australian Army operates vehicles in very harsh conditions. Their vehicles are expected to survive. A catastrophic failure of vehicle suspension could lead to undesirable situations. Potentially avoidable by advanced warning and managed maintenance. Slide 2
Motivation The Australian Army is interested in implementing H ealth and U sage M onitoring S ystems (HUMS) to improve vehicle availability, fleet management, improve data integrity and reduce burden of manual data entry. Slide 3
Motivation Rheinmetall make vehicles for the Army: • Land 400 Boxer CRV program, • Land 121 Phase 3B, 5B Supashock make shock absorbers for Rheinmetall vehicles. Developing HUMS* for shock absorbers * HUMS = Health and Usage Monitoring Systems Slide 4
Typical Shock Absorber Construction Twin-tube (inner and outer) filled Rod Seal with oil and gas. Rubber seals at the top of the rod and in the piston (end of rod). Valves are in the piston and “foot valve” When the shock absorber is vibrated, it causes oil to pass Piston Seal through the valves and gets hot. The main failures of a shock absorber are the rubber rod seal and piston seal. Slide 5
Shock absorber working principle Slide 6
Other Failures The most common failure mechanisms of shock absorbers are [ATH&S Stellox] : Break of piston or rod seal in the shock-absorber. Internal damages of the shock absorber: destruction, failure or wear of the valve assembly or piston. Mechanical damage of the shock-absorber: crack, dent in a body, bent rod. Destruction of the shock absorber: breaking off the rod, disengaging the mounting lug, degradation or destruction of silent blocks. Inconsistency of properties or degradation of the shock absorber fluid. Absence of gas in the shock absorber. Slide 7
Methods of Monitoring for HUMS A HUMS could be implemented that: Monitors the “performance” of a vehicle’s suspension e.g. vibration isolation, damping ratio Requires sensors and data processing to determine whether system is operating “normally” (but a vehicle has a wide “normal” operating window) Monitors the “ use ” of a vehicle Require sensors to estimate how much energy (hence wear) has been imparted to the vehicle. (for a civilian road vehicle, we use an odometer, but this is not appropriate for an army off-road vehicle) No published data on run-to-failure of shock absorbers * HUMS = Health and Usage Monitoring Systems Slide 8
Failure Behaviour of Rubber Rubber materials could fail rapidly, or slowly From: Zarrin et al. (2013) From: Shangguan et al. (2014) Rapid failure Logarithmic scale Linear scale If a shock absorber fails Rapidly : a HUMS system monitoring performance won’t provide advanced notice -- Have to monitor the use / energy = wear. Slowly : a HUMS system monitoring performance might provide advanced warning. Slide 9
Sensors for Monitoring Shock Absorbers Sensor Evaluates Decision Sampling Pros Cons Algorithm Rate Pressure and Dynamic Falls outside High Intermittent Pressure sensors must be acceleration performance normal bounds measurement required robust transmissibility Reaches age limit High Cumulative Continuous measurement energy required Pressures Loss of gas Falls outside High Intermittent Pressure sensors must be pressure normal bounds measurement required robust Detection of seal leakage High Falls outside Dynamic normal bounds performance Infers damping force Temperatures Cumulative Reaches age limit Low Very low data rate, so Continuous measurement energy easy to implement required, but very low data Exceeds limit that Low continuous storage rate, so okay Thermal shock causes crack formation Accelerations Dynamic Falls outside High Intermittent performance normal bounds measurement required transmissibility Continuous measurement required Cumulative Reaches age limit High energy Slide 10
Honeywell Patent Honeywell have patented a shock absorber concept with HUMS comprising an inbuilt temperature sensor. Slide 11
Thermo-Mechanical Simulation of Shock Absorber Q: Is it possible to estimate the energy / work that goes into a shock absorber, just by monitoring temperatures? It appears that high temperatures and rapid temperature increases, lead to the degradation of rubber (seals) -> hence wear of shock absorber. Complicated thermo-mechanical models of shock absorbers exist. We devised a simplified model that can be used to predict the temperature of the oil and the metal body based on input forces and velocities of the piston. Motivation: validate that by monitoring temperatures, one can estimate the energy (= use / wear) that went into a shock absorber. Honeywell’s HUMS patent suggests that temperature can be used to monitor the age of a shock absorber. Slide 12
Proposed Model of Shock Absorber The thermo-mechanical model can be likened to an electric water kettle and calorimetry analysis: A heat source into a liquid (i.e. energy input) The liquid heats up the surrounding metal container Heat convects away from the outside of a cylinder Convective and radiant heat 𝑈 𝑑𝑧𝑚 Power 𝑈 𝑏𝑛𝑐𝑗𝑓𝑜𝑢 Heat 𝑈 𝑝𝑗𝑚 (Force x Velocity) Hence, if we monitor the temperatures, one can calculate the energy (work done) that went into the shock absorber Slide 13
Preliminary Results of Shock Absorber Model 𝑈 1 𝑈 2 𝑈 3 Slide 14
Estimation of the Cumulative Energy Slide 15
Conclusions Mathematical model suggests that temperatures can be used to monitor the age of a shock absorber. It is recommended that run-to-failure tests should be conducted on shock absorbers using three types of sensors installed: pressure, accelerations, temperature. The test results will enable identifying: whether the shock absorber has a rapid or gradual failure over time; the change in the dynamic performance over time; whether there has been a loss in gas pressure, which can be used to indicate a failure of a seal; whether a measure of cumulative energy (or damage) can be determined based on using temperature, accelerometer, or pressure data, which could be used to determine the “age” of the shock absorber. Slide 16
Conclusions The preferred pathway for the technology is to use temperature logging of the fluid, piston, and rod seals within the shock absorber, as this requires the lowest data rate, and hence least storage and processing requirements. Shock absorber test rig at Supashock Slide 17
Thanks Monitoring the Age of Vehicle Shock Absorbers carl.howard @ adelaide.edu.au Carl Howard , Nataliia Sergiienko – The University of Adelaide Guy Gallasch - DST Group Slide 18
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