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Damper Basics
Damper Design, Testing and Tuning
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By Jim Kasprzak
May 15, 2010
Presented to Formula SAE
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Damper Basics
It is thought by many that dampers are ablack art
That there is some magic to developingand tuning dampers
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Damper Basics
We are here to dispel those myths and giveyou tools to develop dampers
However, there is art in damper tuning
The art is optimizing the damper usingengineering knowledge &the proper tools
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Sometimes I think that I would have enjoyedracing more in the days of the friction shock.
Since you couldnt do anything much to them orwith them, I would have spent a lot less timebeing confused.
Carroll SmithTune to Win, 1978
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PLEASE ask questions
at any time
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Course Outline
Damper BasicsInside the DamperDamper TestingDamper Design
Advanced ToolsThe Last Word
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KAZ Technologies
KAZ TECHNOLOGIES started in 1995
Staff of 5 EngineersOver 85 years of combined racing & automotive engineering experience
Extensive vehicle suspension, ride and handling experienceDamper design, development, testing and manufacturing
All types of springs, stabilizer bars, oil seals, shock absorbers and strutsRide & handling on standard suspension and advanced technologies
NVH, tire testing, vehicle stability systems, race chassis development7-Post and 4-Post test development and testing
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ExperienceRacing experience includes:
o Race drivingo Race engineeringo Chassis/Suspension
developmento Data acquisition and
analysiso Suspension design,
analysis & fabricationo Shock absorber
developmento 7-Post Testing
http://www.indyracing.com/indycar/http://www.indyracing.com/indycar/http://www.indyracing.com/indycar/ -
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KAZ TECHNOLOGIES
GM RacingResident 7-post and shock technical specialists7-post testing for GM Racing
7-Post & damper testing toolsRace engineering
OtherRace engineeringDamper design & developmentDamper sales & service
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Jim Kasprzak-Race Engineering
36 years racing experienceDeveloped 7-Post testing for GM
Expertise includes:Race Engineering7-Post testingSuspension engineering
Shock design, development & tuningVehicle tuning
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Jim Kasprzak-Automotive
31 years automotive experience Arvin Ride Control
Director, Original Equipment EngineeringDirector, New Product Development
Monroe Auto EquipmentChief Engineer, Electronic Suspensions
Manager, Suspension System ProgramsTwo shock design patents
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Course Outline
Damper BasicsInside the DamperDamper TestingDamper Design
Advanced ToolsThe Final Word
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Damper Basics
A shock absorber is a damper!Functions of a damperResonant frequenciesHow much damping?
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A Shock is a DAMPER!
Dampens sprung and unsprung massDissipates this energy into heatOnly produces force when in motionDampers are VELOCITY sensitive device
Force produced is proportional to velocity
Damping is also a function of acceleration
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A Shock is a DAMPER!Sprung Mass
(Chassis)
Unsprung Mass
Spring Damper
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A Shock is a DAMPER!
The damper controls the suspensionIn broad terms:
Rebound controls sprung massCompression controls unsprung mass
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Functions of a Damper
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Functions of a Damper
How do we use dampers on vehicles?Primary Function
Dampen sprung & unsprung resonant frequencies
Secondary FunctionControls vehicle at pitch, heave and roll resonantfrequenciesControls rate of weight transfer
Braking, corner entry, acceleration
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Functions of a Damper
At best, dampers areThe frosting on the cake
Dampens vibrations at resonant frequenciesControls rate of weight transferEnhances vehicle performance
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Functions of a Damper
In worst case, dampersHold the cake together!
Compensates for structural deficienciesControls heave, pitch, roll imbalancesUsed to compensate for deficiencies in designor other componentsCompensates for lack of suspension travel
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Resonant Frequencies
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Resonant Frequencies
A suspension is twospring/mass/dampersystems in series
Body, chassis springand damperSuspension and tire
Sprung Mass(Chassis)
Unsprung MassSuspension
Spring
Tire Spring Tire Damping
Damper
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Resonant Frequencies
Sprung Mass
Unsprung Mass
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Typical Natural Frequencies
Sprung MassFSAE 2.0 4 Hz
Passenger Car 1 2 HzNASCAR Cup Car 1.5 4 Hz
All 4 corners different!!Indy Car 3 -5 Hz
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Typical Natural Frequencies
Unsprung MassFSAE 22 - 26 Hz
Passenger Car 10 - 12 HzNASCAR Cup Car 15 - 17 HzIndy Car 23 - 27 Hz
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How Much Damping?
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How Much Damping?
Resonance
Critically Damped
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Milliken
CriticalDamping
Passenger
Car
Non-AeroRacecars
Aero RacecarsRide: 0.7-1.1Roll: 6.0-9.0
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How Much Damping?
Critical Damping
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How Much Damping?
Critical Damping
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How Much Damping?
Proper Damping Ratio
0.2 -0.4 total system damping
Great for theoretical calculations, but not very practical!
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How Much Damping?Effects of Different Damping
Gillespie
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How much Damping?
Tire Force Variation ConsiderationsDamping is only required at resonantfrequencies
Primarily sprung & unsprung mass resonanceDamping required to control resonance
Damping at other frequencies increases tireforce 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 resonancesTo control pitch and roll ratesTo control suspension travelMinimize tire force variation
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Questions?
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Inside the Damper
Damping force calculationsGas pressureDamper valve operationCompression pressure balance
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Damping Force Calculations
Monotube
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Damping Force Calculations
Monotube with Basevalve
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Gas Pressure
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Gas Pressure
PurposePressurizes oil in damper
Reduces hysteresisCreates static rod forceProvides the pressure for gas spring
However, spring rate is low
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Gas Pressure Calculations
Gas Force
Ideal Gas Law
Gas Spring Rate
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Gas Pressure
In MonotubeBalances the pressure in
compression chamber (P 2)Prevents cavitation or lagHigh gas pressure typically required
Produces high friction and static rodforce
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Gas Pressure
In Monotube with BasevalveCompensates for minor fluid loss
Pressurizes oil in damperBalances pressure across base valve
P 4 vs. P 3
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Damper Valve Operation
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Rebound Flow
Low Speed ReboundControls 0 2 in/sec damping
In valvingBleed holesBy-pass jet
Leakage
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Rebound Low Speed
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Rebound Flow
Mid Speed ReboundControls 2-8 in/sec damping
In valvingDisc preloadDisc stack
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Rebound Mid Speed
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Rebound Flow
High Speed ReboundControls > 8 in/sec damping
In valvingPiston portsRestriction of disc stack travel
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Rebound High Speed
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Compression Flow
Low Speed CompressionControls 0 2 in/sec damping
In valvingBleed holesBy-pass jetLeakage
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Compression Low Speed
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Compression Flow
Mid Speed CompressionControls 2-8 in/sec damping
In valvingDisc preloadDisc stack
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Compression Mid Speed
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Compression Flow
High Speed CompressionControls > 8 in/sec damping
In valvingPiston portsRestriction of disc stack travel
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Compression High Speed
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Compression Pressure Balance
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Compression Pressure Balance
To maintain hydraulic integrity, you musthave a balance of pressure drops in
compressionIn Monotube between the piston and the gaspiston
In Monotube with base valve, between piston,base valve and gas pistion
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Compression Pressure Balance
MonotubePressure in gas chamber must always
be greater than compression chamber
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Compression Pressure Balance
Monotube with Base valvePressure drop across base valve must
always be greater than across piston
AndPressure in gas chamber must always begreater than below base valve
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Compression Pressure Balance
What results from pressure imbalance?
CavitationHydraulic lagHysteresis
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Cavitation
What is Cavitation?Negative pressure in rebound or compression
chamberCreates void in chamberResult is lag in force
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Cavitation
Base Valve Pressure
Compression Pressure
Rebound Pressure
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Cavitation
Cavitation No Cavitation
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Cavitation
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Cavitation
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Cavitation
HydraulicLag
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Cavitation
Red = 100 psi
Green = 75 psi
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Cavitation
Cavitation is notalways evident in
Force/Velocitygraph!Red = 100 psi
Green = 75 psi
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Hysteresis
Hysteresis is alsocaused by
compressionpressure imbalanceHysteresis
Red = BaselineGreen = Hysteresis
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Proper Pressure Balance
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Questions?
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Damper Testing
Traditional damper testingTraditional damper dyno curvesDamper curve analysisProper test methods
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Traditional Damper Testing
Sine wave inputFixed stroke
Single speedSingle speed plot
Or
Multiple speedPeak force plot
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Traditional Damper Testing
Mechanical Damper TesterFixed stroke
Mechanically adjustableScotch yoke or crank designFixed speed for each test
Variable speed for multiple tests
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Traditional Damper Curves
Standard Roehrig CurvesForce Velocity
Force Absolute VelocityCompression Open, Rebound ClosedRebound Open, Compression Closed
Force DisplacementPVP Peak Velocity Plot
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Damper Dyno Curves
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Roehrig Control Panel
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Force - Velocity
Rebound
Compression
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Force - Absolute Velocity
Compression
Rebound
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Compression Open Rebound Closed
Compression
Rebound
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Rebound Open Compression Closed
Compression
Rebound
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Force - Displacement
Compression
Rebound
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PVP Peak Velocity Plot
What is a PVP Plot? A collection of forces at peak velocities
Each force is plotted as a point A line is drawn through each point to generate thecurveRepresentation of peak force at each velocity
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PVP Peak Velocity Plot
Curve connectsIndividual points
17 Peak Velocities
Rebound
Compression
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Complete Curve at Single Velocity
Compression
Rebound
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Single Speed Plot
Typical Plot1 or 2 inch fixed stroke
10 in/sec peak velocityOnly one speed
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Single Speed Plot
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Single Speed Plot
PlusesHas become the default standard
Because the standard, easy comparisonbetween teams
Easy to compare your data to another teams
Good overall view of damper forces
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Single Speed Plot
MinusesOnly one speed
Ignores acceleration affectsShows poor representation of low speedcontrolsPoor for comparison of damping performanceat 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 velocityFocus on velocity car is workingObserve how valving is working at each specificvelocity
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Multiple Speed Plot
MinusesNo 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 curveNo lags
No signs of cavitationNo incongruitiesMinimal 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
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Massive 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 curveThis 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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Damper Test Methods
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Proper Damper Test Methods
Zero out damper weightSubtract gas force
Test shock at operating temperatureTest & analyze multiple speeds
Analyze entire cycle, not PVPUse compression and rebound open
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Questions?
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Damper Design
Damper architecture Adjusters
Design processTuning processTuning guidesDamper care & feeding
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Damper Architecture
Twin tubeMonotube
Monotube with basevalveTwin tube with piggyback reservoirMonotube with remore reservoirMonotube with piggyback reservior
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Damper Architecture
Choose the design that serves the applicationFunction
PackagingPerformancePrice
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Twin Tube
Primarily used in OE applicationsInexpensive
Has to be mounted rod upValving in piston and base valveTypically smaller piston OD thanmonotubeNo separation between oil & gasPressure balance required
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Monotube
Compression & rebound valvingin piston
No base valveTypically high gas pressure
Pressure balance between piston
and gas force required
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Monotube with Base Valve
Valving in piston and base valveCan run low gas pressure
Pressure balance between pistonand base valve requiredPressure balance between base
valve and gas pressure required
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Monotube with Remote Reservoir
Valving in piston and base valveBase valve typically in reservoir
Remote reservoir for packagingCan cause hysteresis and lags
Same pressure balance asmonotube with base valve
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Monotube with Piggyback Reservoir
Valving in piston and base valveBase valve typically in reservoir
Shorter length than monotubeSame pressure balance asmonotube with base valve
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Twin Tube with Piggyback Reservoir
Valving in piston and base valveBase valve typically in reservoir
Piston OD typically smaller thanmonotubeSame pressure balance as
monotube with base valve
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Adjusters
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Adjusters
Various types of adjustersRebound
CompressionRebound & compressionHigh speed compression & rebound
Low speed compression & reboundMust decide what is important !
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Adjusters
Multiple adjusters interactHigh speed and low speed adjusters interact
They are not totally independentThe setting of one adjuster will often determine theeffectiveness of the other adjuster
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High Speed Compression Adjustment
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Low Speed Compression Adjustment
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Adjusters
Single AdjustersTypically rebound in rod
Typically compression in reservoirCan adjust low speed, high speed or both
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Damper Design Process
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Damper Design Process
Design ConsiderationsDamper architecture
Damper featuresPackaging on vehicleDimensions
Performance characteristicsInitial damping characteristics
h
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Damper Architecture
Choose the architecture that serves theapplication
FunctionPackagingPerformancePrice
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Damper Features
Choose the features that serve your applicationPiston diameter
Number and type of adjustmentsPiston and valving designBase valve design
Jounce bumper?
P k i V hi l
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Packaging on Vehicle
MountingsTravel or stroke
Is the damper a travel limiter?Coil-over spring travel on shockJounce bumper travel
Di i
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Dimensions
Compressed and extended lengthStroke or travel
Mounting dimensionsExternal tube diametersSpring dimensionsJounce bumper dimensions
P f Ch i i
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Performance Characteristics
Damping requirementsDamping adjustment ranges
Spring rates and travelsJounce bumper engagement point, rateand travel
I i i l D i Ch i i
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Initial Damping Characteristics
How do you determine?Damper supplier recommendations
Experience or recordsCalculationsSimulation
Guess
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Tuning Process
T i P
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Tuning Process
Damping curves from dyno testFit check on vehicle
Basic vehicle testing Advanced tuningTuning considerations
D C f D
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Damper Curves from Dyno
Need to know where you are starting!Force/Absolute Velocity curves
Multiple velocitiesCurves for each shock
Tuned/adjusted to match
Curves for range of adjustments
Fit Ch k V hi l
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Fit Check on Vehicle
Make sure design is correct!Correct travels
Shock and springJounce bumper engagementNo binding or interferences
B V hi l T ti g
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Base Vehicle Testing
Basic motions and transistionsBasic ride motions
Low frequency input (Sprung resonance)Bumps (Unsprung resonance)Extreme travel events
TransistionsBraking, turn-in, acceleration
Ad d T i g
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Advanced Tuning
More than basic tuningTrack testing
Transition maneuvers7-post testing
T ning Considerations
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Tuning Considerations
A damper is a VELOCITY sensitive deviceForce is a function of velocity, not
displacementCan be used as a dynamic spring
Generate force when in motion
Passive at steady state
Tuning Considerations
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Tuning Considerations
Velocity for transients typicallybelow 2 in/sec
Turn-inBraking
Acceleration
Aero control
Tuning Considerations
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Tuning Considerations
Velocities for bumps typically 2-10 in/sec
Velocities for extreme travel events above10 in/sec
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Tuning Guides
Tuning Guides
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Tuning Guides
There are many ways to use dampersDampen resonant frequencies
Dynamic springHold down deviceJack up device
There are many correct answers
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Damper Care & Feeding
Damper Care & Feeding
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Damper Care & Feeding
Main objective is repeatability and durabilityTune adjusters so forces match
Check gas pressure oftenDyno test at least once a yearLook for oil leakage
Check for rod and seal damage
Professional Damper Care
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Professional Damper Care
How race teams do itDamper settings checked with each setup andset downGas pressure checked each dayDampers curved before raceDampers rebuilt and forces matched aftereach race
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Questions?
Advance Tools
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Advance Tools
Damper testing
7-post testing
Damper Testing
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Damper Testing
Multi-Frequency TestingVariable frequency and amplitude sine sweep
Actual vehicle data Actual dataLow frequency (sprung resonance) dataHigh frequency (unsprung resonance) data
Damper Testing
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Damper Testing
Roehrig EMA DynoElectro-magnetic actuator
Triangle, sine, square andcomposite wavesCan play back shockdisplacement data from trackdata
Damper Testing
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Damper Testing
Multiple Input TestTraditional peak velocity sine wave
Track data fileLow frequency track dataHigh frequency track data
Sine sweepBased on track data
Multiple Input Test
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Multiple Input Test
Multiple Input Test
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Multiple Input Test
TrackData
LowFreqTrackData
HighFreqTrackData
Sine Sweep Based on Track DataPeakVelocity
Kaz Tech Shock Testing Tools
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Kaz Tech Shock Testing Tools
Kaz Tech Shock Testing Tools
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Kaz Tech Shock Testing Tools
EMA Complex Drive File Generator
Graphical Plotting & Analysis Tool
Results Workbook
Analysis Metrics
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7-Post Testing
What is 7-Post Testing?
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What is 7 Post Testing?
Simulates track input in a lab testUses data from the race track to
reproduce input to the carTrack input to the tires
Aero and banking loads to the body
Sine sweep input for frequency testing
What is a 7-post?
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What is a 7 post?
The 7-post shaker is an engineering systemExerts forces on the vehicleRecords the forces that the vehicle puts back into thesystemRecords various system responses
A 7-post consists of 7 hydraulic actuators
4 actuators with wheel pans input road3 actuators input aero loads
What is a 7-post?
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What is a 7 post?
Four wheel pan actuatorsInput simulated road displacement into the vehicleDisplacement driven
Same displacement throughout the testLoad and acceleration measured at the wheel pans or platensTypically driven up to 50 Hz
Three down force actuatorsLoad driven
Same load throughout the test (except when active aero is in use) Allows for vehicle displacement, acceleration, and velocities to
be a variableTypically driven up to 1 Hz
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7-Post Testing
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7 Post Testing
7-Post Drive InputsSine sweep
Track data based drive fileDiscreet eventLow frequency from track data
Why 7-Post Testing?
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Why 7 Post Testing?
Solution to limited track testsShock developmentSuspension set-ups
Measure response in the lab you cannotmeasure on the track
Tire grip Aero loading
Why 7-post Testing?
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W y post est g?
The 7-post will not give you the magic set ofshocks or setup! It will give you:
The knowledge of how each componentaffects the whole systemThe magnitude of each effect
An understanding on the cause and effect
The information to make educated decisionsat the racetrack
7-Post Testing is a Cycle
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g y
Track data gatheringDrive file developmentTest planningDrive file evaluationTest executionData analysis
Application at the racetrack
7-Post Testing Analysis
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g y
Required elements of analysisTire force variation (mechanical grip)
Body controlWheel control
Aerodynamic downforceDriver comfort
Kaz Tech 7-Post Testing
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g
GM Racing 7-Post Testing1977: First NASCAR 7-post testNumerous race winsDeveloped GM 7-Post Test Method
Test methods
Data analysis routinesData presentation
Results taken directly to racetrackContinuous test development
Data analysis & reportingTesting Methodology
On-going assessment of 7-Poststate-of-the-art
Kaz Tech 7-Post Tools
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Kaz Tech 7-Post Tools
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Data ProcessingResults WorkbookCustomized Team Results and Reports
Graphical Plotting & Analysis ToolTeam ConsoleDrive File Quality
7-Post PerformanceLoad Transformation
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Questions?
The Last Word
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Records
When enough is enough!
References
Records
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If you dont keep records, you start fromscratch every time you start the car!
You can only improve if you know where youare starting from!
Records
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Setup SheetsRun Log
Driver Evaluation SheetsRace/Test SummaryTrack Data Files
Setup Sheets
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p
Baseline or starting setupShop setup
Final setup at trackSet down setup at end of each sessionFinal set down set up at end of each test
Event Information
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Chassis Information
Aero Information
Gearbox Information
Session Tabs
Packer Gap
Run Log
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EXCEL File with Worksheets for:Race/Test Summary
Worksheet for each sessionData Analysis SummaryTire SummaryRace Log
Opening Page:
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Tabs for:-Summary-Data Analysis-Tire Sheet
-Session Sheets-Race Log
p g gEvent Summary
Session Information
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Tire Info
Driver Comments
Tire Data
Changes
Tire Sheet
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Race Information
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Race Information
Driver Comments
Tire Data
Lap Times&
Leader Info
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Event Information
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Weekend Summary
Race Summary
Driver De-Briefs
Next Race
Session Lap Times
Track Data Files
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When Enough is Enough
When Enough is Enough
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Patrick Head AT&T Williams F1 Director of Engineering
It is not the team that achieves the mosthorsepower or downforce that wins the race. Itis the team with the best compromise of all the
systems on that day that wins .
When Enough is Enough
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What does this mean?EVERYTHING is important!
No one system is more important that another
EVERYTING is a compromise!You dont have to have it all perfect to win
In fact, you wont get all of it right!
The best TOTAL package will win
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References
References
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Books by Carroll SmithTune to WinDrive to Win
Prepare to WinEngineer to WinNuts, Bolts, Fasteners and Plumbing HandbookEngineer In Your Pocket
References
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BooksRace Car Vehicle Dynamics
William F. Milliken and Douglas L. Milliken
Fundamentals of Vehicle DynamicsThomas D. Gillespie
Shock Absorber HandbookJohn C. Dixon
Kaz Technologies
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http://www.kaztechnologies.comInformation about Kaz Technologies
Product informationFSAE damper drawings, CAD and damping info Tech TipsSeminar downloads
e-Store for FSAE products
Kaz Technologies
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Topics to Discuss?http://www.facebook.com/Kaz.Technologies
Start a discussion!
Kaz Technologies
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Jim Kasprzak [email protected] 248-
855-3355
734-536-3218
Jess Youngblood [email protected]
Kaz Technologies
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Thanks!