Shock Testing Maint Seminar 12-11-11
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Transcript of Shock Testing Maint Seminar 12-11-11
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Shock Testing & Maintenance
The Care & Feeding of Dampers
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5 things you MUST know
about YOUR shocks
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PleaseAsk questions
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First, some questions
for you
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Do you knowif your shocks
have the right travel?
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Did youdyno test your
shocks this year?
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Did you force match your shocks?
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Who checked the gas pressure in their shocks this
morning?
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Who checked the settings this morning to confirm they
were correct?
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What is the least maintained component in
an FSAE car?
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Besides the driver’s suit?
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Course Outline
Shock Travel Damper Testing Choosing the Correct Damping Keeping Them Working Right The Last Word
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Shock Travel
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Travel Considerations
Packaging Must fit on the car! No travel interference
Wheel travel requirements Motion ratio Wheel travel vs. shock travel
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Typical Packaging Smallest package for shock Least space Least weight
“Convenient” motion ratio Whatever fits
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Proper PackagingDesired motion ratio Higher shock to wheel travel ratios yield: Lower spring rates
Lower spring and shock friction Lower component loads
Higher shock velocities Packaging considerations
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Motion Ratio Comparison1:1 0.75:1 0.5:1
Wheel Travel 25 mm 25 mm 25 mmShock Travel 25 mm 18.8 mm 12.5 mm
Wheel Velocity 50 mm/sec 50 mm/sec 50 mm/secShock Velocity 50 mm/sec 37.5 mm/sec 25 mm/sec
Wheel Rate 25 N/mm 25 N/mm 25 N/mmSpring Rate 25 N/mm 44 N/mm 100N/mmSpring Preload 50 kg 67 kg 100 kg
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Shock Velocity Comparison
260
704
445360
840890
Bleed Disc Stack
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Shock Velocity Comparison
Bleed Disc Stack
260206155
324
550704
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Shock TravelMotion Ratio Considerations Maximize use of shock travel Anticipated wheel travel Anticipated shock velocities
Remember extreme events Curbs, pot holes
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Fit Check on Vehicle
Make sure shocks fit correctly! Correct travels Shock and spring
Jounce bumper engagement No binding or interferences
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Positioning Shock TravelMust properly position shock at ride height Typically mid stroke at ride height Determine shock travel on track Use data acquisition Check for bottoming/topping
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Damper Testing
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Dyno Graph Basics
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BDC TDCComp mid Reb mid
CompAccel
CompDecel
RebAccel
RebDecel
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Force – Displacement Graph
BDC TDC
Rotation
Compression mid-stroke
Rebound mid-stroke
Reb Decel
Comp Accel Comp Decel
Reb Accel
Compression Open Compression Closed
Rebound OpenRebound Closed
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Force – Absolute Velocity Plot
Quadrant 1
Quadrant 4
Quadrant 3
Quadrant 2
Comp Accel
Compression Open
Comp Decel
Compression Closed
Reb Accel
Rebound Closed
Rebound Open
Reb Decel
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Damper Dyno Curves
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Useful Dyno Plots Force – Velocity Force – Absolute Velocity Force – Displacement PVP or Peak Velocity Plot
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Force - Velocity
Rebound
Compression
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Force - Absolute Velocity
Compression
Rebound
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Force - Displacement
Compression
Rebound
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PVP – Peak Velocity Plot
Curve connectsIndividual points
17 Peak Velocities
Rebound
Compression
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PVP – Peak Velocity Plot
What is a PVP Plot? A collection of average forces at peak
velocities Each average force is plotted as a point A line is drawn through each point to generate the
curve Representation of “average” force at each velocity
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PVP – Peak Velocity Plot
Curve connectsIndividual points
17 Peak Velocities
Rebound
Compression
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Curve at a Single Velocity
Compression
Rebound
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Single Speed Plot
Typical Plot 1 or 2 inch fixed stroke 10 in/sec peak velocity Only one speed
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Single Speed Plot
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Single Speed Plot
Pluses Has become the default standard Because the standard, easy comparison
between teams Easy to compare your data to another team’s
Good overall view of damper forces
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Single Speed Plot
Minuses Only one speed Ignores acceleration affects
Shows poor representation of low speed controls Poor for comparison of damping performance
at low velocities
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Multiple Speed Plot
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Multiple Speed Plot
Pluses Able to see effects of acceleration Better analysis at each specific velocity Focus on velocity car is working Observe how valving is working at each specific
velocity
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Multiple Speed Plot
Minuses No standardized set of velocities Hard to compare results with other teams
Analysis is more difficult
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Dyno Curve Analysis
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Dyno Curve Analysis
Want smooth, uniform curve No lags No signs of cavitation No incongruities Minimal hysteresis
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Hydraulic Lag
HydraulicLag
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No Cavitation
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Minor Cavitation
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Slight Cavitation
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Cavitation
Loss of damping force from cavitation
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Massive Cavitation
Loss of damping force from cavitation
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Incongruity
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Hysteresis
Hysteresis
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Proper Curve
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Dyno Curve Analysis
Use opening side of curve This is the initial force seen by the vehicle
during any event Analyze entire cycle – NOT PVP Use Force/Velocity and Force/Displacement
Analyze multiple speeds
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Force – Absolute Velocity
Compression Open
Rebound Open
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Force – Displacement
Compression Open
Rebound Open
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Choosing the Correct Damping
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ButHow Much Damping?
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How Much Damping?
Under Damped Over Damped
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How Much Damping?
Damped
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How Much Damping?Effects of Different Damping
Courtesy of Kaz Technologies and GM Racing
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How much Damping?
Tire Force Variation Considerations Damping is only required at resonant
frequencies Primarily sprung & unsprung mass resonance Damping required to control resonance
Damping at other frequencies increases tire force variation
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How much Damping?
Courtesy of Kaz Technologies and GM Racing
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How much Damping?
So, how much damping?The correct amount To control resonances To control pitch and roll rates To control suspension travel Minimize tire force variation
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Keeping YOUR ShocksWorking Right
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Damper Care & Feeding
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Damper Care & Feeding
Main objective is repeatability and durability Dyno test shocks at least once a year Tune adjusters so forces match Check gas pressure before each test Look for oil leakage Check for rod and seal damage
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Same Adjustments – Not Force Matched
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Same Adjustments – Force Matched
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Oil on the Shock RodIf there is oil on the rod, is it leaking? Must have oil on rod to oil seal No oil, seal will quickly wear out
Will often see “halo” of oil on rod If you see a puddle, shock is leaking!
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Professional Damper Care
How race teams do it Dampers rebuilt and forces matched after
each race Dampers curved before race Gas pressure checked each day Damper settings checked with each setup and
set down
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The Last Word
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5 things you MUST know
about YOUR shocks
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5 Things You Must Know My shocks have the correct travel They fit correctly on the car The shocks are performing properly They have the correct damping My shocks are ready to race!
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Questions?
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Jim KasprzakKAZ TECHNOLOGIES
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Thanks!