Damper Basics Seminar [PDF]

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Damper Basics Damper Design, Testing and Tuning



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Presented to Formula SAE By Jim Kasprzak



May 15, 2010



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Damper Basics It is thought by many that dampers are a black art That there is some “magic” to developing and tuning dampers



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Damper Basics We are here to dispel those myths and give you tools to develop dampers However, there is art in damper tuning The art is optimizing the damper using engineering knowledge &the proper tools This document is property of Kaz Technologies. Not authorized for use by outside organizations



“Sometimes I think that I would have enjoyed



racing more in the days of the friction shock. Since you couldn’t do anything much to them or with them, I would have spent a lot less time being confused.” Carroll Smith Tune to Win, 1978 This document is property of Kaz Technologies. Not authorized for use by outside organizations



PLEASE ask questions at any time



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Course Outline      



Damper Basics Inside the Damper Damper Testing Damper Design Advanced Tools The Last Word



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KAZ Technologies  KAZ TECHNOLOGIES started in 1995  Staff of 5 Engineers



 Over 85 years of combined racing & automotive engineering experience



 Extensive vehicle suspension, ride and handling experience     



Damper design, development, testing and manufacturing All types of springs, stabilizer bars, oil seals, shock absorbers and struts Ride & handling on standard suspension and advanced technologies NVH, tire testing, vehicle stability systems, race chassis development 7-Post and 4-Post test development and testing



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Experience Racing experience includes: o Race driving o Race engineering o Chassis/Suspension development o Data acquisition and analysis o Suspension design, analysis & fabrication o Shock absorber development o 7-Post Testing



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KAZ TECHNOLOGIES  GM Racing    



Resident 7-post and shock technical specialists 7-post testing for GM Racing 7-Post & damper testing tools Race engineering



 Other



 Race engineering  Damper design & development  Damper sales & service



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Jim Kasprzak-Race Engineering  36 years racing experience  Developed 7-Post testing for GM  Expertise includes:     



Race Engineering 7-Post testing Suspension engineering Shock design, development & tuning Vehicle tuning



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Jim Kasprzak-Automotive  31 years automotive experience  Arvin Ride Control  Director, Original Equipment Engineering  Director, New Product Development



 Monroe Auto Equipment  Chief Engineer, Electronic Suspensions  Manager, Suspension System Programs



 Two shock design patents



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Course Outline      



Damper Basics Inside the Damper Damper Testing Damper Design Advanced Tools The Final Word



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Damper Basics    



A shock absorber is a damper! Functions of a damper Resonant frequencies How much damping?



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A Shock is a DAMPER! Dampens sprung and unsprung mass  Dissipates this energy into heat  Only produces force when in motion  Dampers 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) Spring



Damper



Unsprung Mass



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A Shock is a DAMPER! The damper controls the suspension  In broad terms:  Rebound controls sprung mass  Compression 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 Function  Controls vehicle at pitch, heave and roll resonant frequencies  Controls rate of weight transfer  Braking, corner entry, acceleration



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Functions of a Damper At best, dampers are “The frosting on the cake”  Dampens vibrations at resonant frequencies  Controls rate of weight transfer  Enhances vehicle performance



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Functions of a Damper In worst case, dampers “Hold the cake together!”  Compensates for structural deficiencies  Controls heave, pitch, roll imbalances  Used to compensate for deficiencies in design or other components  Compensates for lack of suspension travel



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Resonant Frequencies



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Resonant Frequencies A suspension is two spring/mass/damper systems in series



Sprung Mass (Chassis) Spring



Damper



 Body, chassis spring and damper  Suspension and tire



Unsprung Mass Suspension Tire Spring



Tire Damping



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Resonant Frequencies Sprung Mass



Unsprung Mass



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Typical Natural Frequencies Sprung Mass  FSAE  Passenger Car  NASCAR Cup Car  All 4 corners different!!  Indy Car



2.0 – 4 Hz 1 – 2 Hz 1.5 – 4 Hz 3 -5 Hz



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Typical Natural Frequencies Unsprung Mass    



FSAE Passenger Car NASCAR Cup Car Indy Car



22 - 26 Hz 10 - 12 Hz 15 - 17 Hz 23 - 27 Hz



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How Much Damping?



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How Much Damping? Resonance



Critically Damped



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Passenger Car



Non-Aero Racecars



Critical Damping



Aero Racecars Ride: 0.7-1.1 Roll: 6.0-9.0



Milliken



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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 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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Questions?



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Inside the Damper    



Damping force calculations Gas pressure Damper valve operation Compression 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 Purpose  Pressurizes oil in damper  Reduces hysteresis



 Creates static rod force  Provides 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 Monotube  Balances the pressure in compression chamber (P2)  Prevents cavitation or lag  High gas pressure typically required  Produces high friction and static rod force



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Gas Pressure In Monotube with Basevalve  Compensates for minor fluid loss  Pressurizes oil in damper  Balances pressure across base valve  P4 vs. P3



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Damper Valve Operation



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Rebound Flow Low Speed Rebound  Controls 0 – 2 in/sec damping  In valving  Bleed holes  By-pass jet  Leakage



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Rebound – Low Speed



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Rebound Flow Mid Speed Rebound  Controls 2-8 in/sec damping  In valving  Disc preload  Disc stack



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Rebound – Mid Speed



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Rebound Flow High Speed Rebound  Controls > 8 in/sec damping  In valving  Piston ports  Restriction of disc stack travel



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Rebound – High Speed



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Compression Flow Low Speed Compression  Controls 0 – 2 in/sec damping  In valving  Bleed holes  By-pass jet  Leakage



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Compression – Low Speed



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Compression Flow Mid Speed Compression  Controls 2-8 in/sec damping  In valving  Disc preload  Disc stack



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Compression – Mid Speed



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Compression Flow High Speed Compression  Controls > 8 in/sec damping  In valving  Piston ports  Restriction 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 must have a balance of pressure drops in compression  In Monotube between the piston and the gas piston  In Monotube with base valve, between piston, base valve and gas pistion



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Compression Pressure Balance Monotube  Pressure in gas chamber must always be greater than compression chamber



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Compression Pressure Balance Monotube with Base valve  Pressure drop across base valve must always be greater than across piston And  Pressure in gas chamber must always be greater than below base valve



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Compression Pressure Balance What results from pressure imbalance?  Cavitation  Hydraulic lag  Hysteresis



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Cavitation What is Cavitation?  Negative pressure in rebound or compression chamber  Creates “void” in chamber  Result is “lag” in force



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Cavitation Compression Pressure



Base Valve 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



Hydraulic Lag



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Cavitation Red = 100 psi Green = 75 psi



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Cavitation



Green = 75 psi Red = 100 psi



Cavitation is not always evident in Force/Velocity graph!



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Hysteresis Red = Baseline Green = Hysteresis



Hysteresis



Hysteresis is also caused by compression pressure imbalance



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Proper Pressure Balance



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Questions?



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Damper Testing    



Traditional damper testing Traditional damper dyno curves Damper curve analysis Proper test methods



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Traditional Damper Testing Sine wave input  Fixed stroke  Single speed  Single speed plot



Or  Multiple speed  Peak force plot



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Traditional Damper Testing Mechanical Damper Tester  Fixed stroke  Mechanically adjustable



 Scotch yoke or crank design  Fixed speed for each test  Variable speed for multiple tests



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Traditional Damper Curves Standard Roehrig Curves      



Force – Velocity Force – Absolute Velocity Compression Open, Rebound Closed Rebound Open, Compression Closed Force – Displacement PVP – Peak Velocity Plot



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Damper Dyno Curves



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Roehrig Control Panel



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Force - Velocity Compression



Rebound



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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 the curve  Representation of peak force at each velocity



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PVP – Peak Velocity Plot 17 Peak Velocities



Compression



Curve connects Individual points Rebound



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Complete Curve at 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



Hydraulic Lag



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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 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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Damper Test Methods



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Proper Damper Test Methods      



Zero out damper weight Subtract gas force Test shock at operating temperature Test & analyze multiple speeds Analyze entire cycle, not PVP Use compression and rebound open



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Questions?



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Damper Design      



Damper architecture Adjusters Design process Tuning process Tuning guides Damper care & feeding



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Damper Architecture      



Twin tube Monotube Monotube with basevalve Twin tube with piggyback reservoir Monotube with remore reservoir Monotube with piggyback reservior



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Damper Architecture Choose the design that serves the application    



Function Packaging Performance Price



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Twin Tube Primarily used in OE applications Inexpensive Has to be mounted rod up Valving in piston and base valve Typically smaller piston OD than monotube  No separation between oil & gas  Pressure balance required     



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Monotube  Compression & rebound valving in piston  No base valve  Typically high gas pressure



 Pressure balance between piston and gas force required



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Monotube with Base Valve  Valving in piston and base valve  Can run low gas pressure  Pressure balance between piston and base valve required  Pressure balance between base valve and gas pressure required



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Monotube with Remote Reservoir  Valving in piston and base valve  Base valve typically in reservoir  Remote reservoir for packaging  Can cause hysteresis and lags



 Same pressure balance as monotube with base valve



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Monotube with Piggyback Reservoir    



Valving in piston and base valve Base valve typically in reservoir Shorter length than monotube Same pressure balance as monotube with base valve



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Twin Tube with Piggyback Reservoir  Valving in piston and base valve  Base valve typically in reservoir  Piston OD typically smaller than monotube  Same pressure balance as monotube with base valve



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Adjusters



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Adjusters Various types of adjusters     



Rebound Compression Rebound & compression High speed compression & rebound Low speed compression & rebound



Must decide what is important ! This document is property of Kaz Technologies. Not authorized for use by outside organizations



Adjusters Multiple adjusters interact  High speed and low speed adjusters interact  They are not totally independent  The setting of one adjuster will often determine the effectiveness 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 Adjusters  Typically rebound in rod  Typically compression in reservoir  Can adjust low speed, high speed or both



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Damper Design Process



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Damper Design Process Design Considerations      



Damper architecture Damper features Packaging on vehicle Dimensions Performance characteristics Initial damping characteristics



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Damper Architecture Choose the architecture that serves the application    



Function Packaging Performance Price



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Damper Features Choose the features that serve your application     



Piston diameter Number and type of adjustments Piston and valving design Base valve design Jounce bumper?



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Packaging on Vehicle     



Mountings Travel or stroke Is the damper a travel limiter? Coil-over spring travel on shock Jounce bumper travel



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Dimensions      



Compressed and extended length Stroke or travel Mounting dimensions External tube diameters Spring dimensions Jounce bumper dimensions



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Performance Characteristics    



Damping requirements Damping adjustment ranges Spring rates and travels Jounce bumper engagement point, rate and travel



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Initial Damping Characteristics How do you determine?     



Damper supplier recommendations Experience or records Calculations Simulation Guess



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Tuning Process



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Tuning Process     



Damping curves from dyno test Fit check on vehicle Basic vehicle testing Advanced tuning Tuning considerations



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Damper Curves from Dyno Need to know where you are starting!  Force/Absolute Velocity curves  Multiple velocities



 Curves for each shock  Tuned/adjusted to match



 Curves for range of adjustments



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Fit Check on Vehicle Make sure design is correct!  Correct travels  Shock and spring



 Jounce bumper engagement  No binding or interferences



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Base Vehicle Testing Basic motions and transistions  Basic ride motions  Low frequency input (Sprung resonance)  Bumps (Unsprung resonance)  Extreme travel events



 Transistions  Braking, turn-in, acceleration



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Advanced Tuning More than basic tuning  Track testing  Transition maneuvers  7-post testing



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Tuning Considerations  A damper is a VELOCITY sensitive device  Force is a function of velocity, not displacement



 Can be used as a dynamic spring  Generate force when in motion  Passive at steady state



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Tuning Considerations  Velocity for transients typically below 2 in/sec    



Turn-in Braking Acceleration Aero control



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Tuning Considerations  Velocities for bumps typically 2-10 in/sec  Velocities for extreme travel events above 10 in/sec



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Tuning Guides



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Tuning Guides  There are many ways to use dampers    



Dampen resonant frequencies Dynamic spring Hold down device Jack up device



 There are many correct answers



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Damper Care & Feeding



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Damper Care & Feeding Main objective is repeatability and durability     



Tune adjusters so forces match Check gas pressure often Dyno test at least once a year Look for oil leakage Check for rod and seal damage



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Professional Damper Care How race teams do it  Damper settings checked with each setup and set down  Gas pressure checked each day  Dampers curved before race  Dampers rebuilt and forces matched after each race



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Questions?



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Advance Tools  Damper testing  7-post testing



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Damper Testing Multi-Frequency Testing  Variable frequency and amplitude sine sweep  Actual vehicle data  Actual data  Low frequency (sprung resonance) data  High frequency (unsprung resonance) data



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Damper Testing Roehrig EMA Dyno  Electro-magnetic actuator  Triangle, sine, square and composite waves  Can play back shock displacement data from track data



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Damper Testing Multiple Input Test     



Traditional peak velocity sine wave Track data file Low frequency track data High frequency track data Sine sweep  Based on track data



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Multiple Input Test



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Multiple Input Test Peak Velocity



Track Data



Low Freq Track Data



High Freq Track Data



Sine Sweep Based on Track Data



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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



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What is 7-Post Testing?  Simulates track input in a lab test  Uses data from the race track to reproduce input to the car  Track input to the tires  Aero and banking loads to the body



 Sine sweep input for frequency testing



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What is a 7-post? The 7-post shaker is an engineering system



 Exerts forces on the vehicle  Records the forces that the vehicle puts back into the system  Records various system responses



 A 7-post consists of 7 hydraulic actuators  4 actuators with wheel pans input road  3 actuators input aero loads



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What is a 7-post?  Four wheel pan actuators



 Input simulated road displacement into the vehicle  Displacement driven  Same displacement throughout the test



 Load and acceleration measured at the wheel pans or platens  Typically driven up to 50 Hz



 Three down force actuators  Load driven



 Same load throughout the test (except when active aero is in use)



 Allows for vehicle displacement, acceleration, and velocities to be a variable  Typically driven up to 1 Hz



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7-Post Testing 7-Post Drive Inputs    



Sine sweep Track data based drive file Discreet event Low frequency from track data



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Why 7-Post Testing?  Solution to limited track tests  Shock development  Suspension set-ups



 Measure response in the lab you cannot measure on the track  Tire grip  Aero loading



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Why 7-post Testing? The 7-post will not give you the magic set of shocks or setup! It will give you:  The knowledge of how each component affects the whole system  The magnitude of each effect  An understanding on the cause and effect  The information to make educated decisions at the racetrack This document is property of Kaz Technologies. Not authorized for use by outside organizations



7-Post Testing is a Cycle       



Track data gathering Drive file development Test planning Drive file evaluation Test execution Data analysis Application at the racetrack



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7-Post Testing Analysis Required elements of analysis     



Tire force variation (mechanical grip) Body control Wheel control Aerodynamic downforce Driver comfort



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Kaz Tech 7-Post Testing GM Racing 7-Post Testing



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1977: First NASCAR 7-post test Numerous race wins Developed GM 7-Post Test Method  Test methods  Data analysis routines  Data presentation Results taken directly to racetrack Continuous test development  Data analysis & reporting  Testing Methodology On-going assessment of 7-Post state-of-the-art



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Kaz Tech 7-Post Tools



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Kaz Tech 7-Post Tools        



Data Processing Results Workbook Customized Team Results and Reports Graphical Plotting & Analysis Tool Team Console Drive File Quality 7-Post Performance Load Transformation This document is property of Kaz Technologies. Not authorized for use by outside organizations



Questions?



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The Last Word  Records  When enough is enough!  References



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Records If you don’t keep records, you start from scratch every time you start the car! You can only improve if you know where you are starting from!



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Records     



Setup Sheets Run Log Driver Evaluation Sheets Race/Test Summary Track Data Files



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Setup Sheets  Baseline or starting setup  Shop setup  Final setup at track



 Set down setup at end of each session  Final set down set up at end of each test



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Event Information



Chassis Information Packer Gap



Aero Information Gearbox Information Session Tabs



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Run Log EXCEL File with Worksheets for:     



Race/Test Summary Worksheet for each session Data Analysis Summary Tire Summary Race Log



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Opening Page: Event Summary



Tabs for: -Summary -Data Analysis -Tire Sheet -Session Sheets -Race Log



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Session Information



Tire Data Tire Info



Driver Comments



Changes



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Tire Sheet



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Race Information



Lap Times & Leader Info



Driver Comments Tire Data



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Event Information Weekend Summary Race Summary Driver De-Briefs



Next Race



Session Lap Times



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Track Data Files



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When Enough is Enough



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When Enough is Enough Patrick Head AT&T Williams F1 Director of Engineering It is not the team that achieves the most horsepower or downforce that wins the race. It is the team with the best compromise of all the systems on that day that wins.



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When Enough is Enough What does this mean?  EVERYTHING is important!  No one system is more important that another



 EVERYTING is a compromise!  You don’t have to have it all perfect to win  In fact, you won’t get all of it right!



 The best TOTAL package will win



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References



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References Books by Carroll Smith      



Tune to Win Drive to Win Prepare to Win Engineer to Win Nuts, Bolts, Fasteners and Plumbing Handbook Engineer In Your Pocket



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References Books Race Car Vehicle Dynamics William F. Milliken and Douglas L. Milliken



Fundamentals of Vehicle Dynamics Thomas D. Gillespie



Shock Absorber Handbook John C. Dixon



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Kaz Technologies http://www.kaztechnologies.com  Information about Kaz Technologies



 Product information  FSAE damper drawings, CAD and damping info  Tech Tips  Seminar downloads



 e-Store for FSAE products



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Kaz Technologies Questions? [email protected] Topics to Discuss? http://www.facebook.com/Kaz.Technologies Start a discussion!



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Kaz Technologies Jim Kasprzak [email protected] 248855-3355 Tom Jaworski [email protected] 734-536-3218 Jess Youngblood [email protected]



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Kaz Technologies



http://www.facebook.com/Kaz.Tech nologies



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Thanks!



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