Vehicle Shock Absorbers carl.howard @ adelaide.edu.au Carl Howard , - - PowerPoint PPT Presentation

Slide 1

Monitoring the Age of Vehicle Shock Absorbers

Carl Howard, Nataliia Sergiienko – The University of Adelaide Guy Gallasch - DST Group

Work Conducted for: DST Group, Land Vehicle Shock Absorber Health and Usage Monitoring to Support Emerging Army Logistics Concepts: Foundation Analytics.

Presented at: International Conference on Science and Innovation for Land Power 2018 (ICSILP 2018).

carl.howard @ adelaide.edu.au

Slide 2

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 3

Motivation

The Australian Army is interested in implementing Health and Usage Monitoring Systems (HUMS) to improve

• vehicle availability,
• fleet management,
• improve data integrity and
• reduce burden of manual data entry.

Slide 4

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 5

Typical Shock Absorber Construction

 Twin-tube (inner and outer) filled 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 through the valves and gets hot.  The main failures of a shock absorber are the rubber rod seal and piston seal.

Rod Seal Piston Seal

Slide 6

Shock absorber working principle

Slide 7

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

• f silent blocks.

 Inconsistency of properties or degradation of the shock absorber fluid.  Absence of gas in the shock absorber.

Slide 8

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 9

Failure Behaviour of Rubber

 Rubber materials could fail rapidly, or slowly  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.

Rapid failure

Linear scale

From: Shangguan et al. (2014)

Logarithmic scale

From: Zarrin et al. (2013)

Slide 10

Sensors for Monitoring Shock Absorbers

Sensor Evaluates Decision Algorithm Sampling Rate Pros Cons Pressure and acceleration Dynamic performance transmissibility Cumulative energy Falls outside normal bounds Reaches age limit High High Intermittent measurement required Pressure sensors must be robust Continuous measurement required Pressures Loss of gas pressure Detection of seal leakage Dynamic performance Infers damping force Falls outside normal bounds Falls outside normal bounds High High Intermittent measurement required Pressure sensors must be robust Temperatures Cumulative energy Thermal shock Reaches age limit Exceeds limit that causes crack formation Low Low Very low data rate, so easy to implement continuous storage Continuous measurement required, but very low data rate, so okay Accelerations Dynamic performance transmissibility Cumulative energy Falls outside normal bounds Reaches age limit High High Intermittent measurement required Continuous measurement required

Slide 11

Honeywell Patent

 Honeywell have patented a shock absorber concept with HUMS comprising an inbuilt temperature sensor.

Slide 12

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 13

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

 Hence, if we monitor the temperatures, one can calculate the energy (work done) that went into the shock absorber

Power (Force x Velocity) 𝑈𝑝𝑗𝑚 𝑈𝑑𝑧𝑚 𝑈𝑏𝑛𝑐𝑗𝑓𝑜𝑢 Heat Convective and radiant heat

Slide 14

Preliminary Results of Shock Absorber Model

𝑈

1

𝑈2 𝑈3

Slide 15

Estimation of the Cumulative Energy

Slide 16

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 17

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 18

Thanks Monitoring the Age of Vehicle Shock Absorbers

Carl Howard, Nataliia Sergiienko – The University of Adelaide Guy Gallasch - DST Group carl.howard @ adelaide.edu.au