Damper Basics Seminar

Damper Basics Damper Design, Testing and Tuning

This document is property of Kaz Technologies Not authorized for use by outside organizations

Presented to Formula SAE By Jim Kasprzak

May 15, 2010


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

This document is property of Kaz Technologies. Not authorized for use by outside organizations

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


Course Outline      

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


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


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


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


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


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


Course Outline      

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


Damper Basics    

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


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


A Shock is a DAMPER! Sprung Mass (Chassis) Spring

Damper

Unsprung Mass


A Shock is a DAMPER! The damper controls the suspension  In broad terms:  Rebound controls sprung mass  Compression controls unsprung mass


Functions of a Damper


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


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


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


Resonant Frequencies


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


Resonant Frequencies Sprung Mass

Unsprung Mass


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


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


How Much Damping?


How Much Damping? Resonance

Critically Damped


Passenger Car

Non-Aero Racecars

Critical Damping

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

Milliken


How Much Damping? Critical Damping


How Much Damping? Critical Damping


How Much Damping? Proper Damping Ratio  0.2 -0.4 total system damping Great for theoretical calculations, but not very practical!


How Much Damping? Effects of Different Damping

Gillespie


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


How much Damping?

Courtesy of Kaz Technologies and GM Racing


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


Questions?


Inside the Damper    

Damping force calculations Gas pressure Damper valve operation Compression pressure balance


Damping Force Calculations Monotube


Damping Force Calculations Monotube with Basevalve


Gas Pressure


Gas Pressure Purpose  Pressurizes oil in damper  Reduces hysteresis

 Creates static rod force  Provides the pressure for gas spring  However, spring rate is low


Gas Pressure Calculations Gas Force

Ideal Gas Law Gas Spring Rate


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


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


Damper Valve Operation


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


Rebound – Low Speed


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


Rebound – Mid Speed


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


Rebound – High Speed


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


Compression – Low Speed


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


Compression – Mid Speed


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


Compression – High Speed


Compression Pressure Balance


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


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


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


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


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


Cavitation Compression Pressure

Base Valve Pressure

Rebound Pressure


Cavitation Cavitation

No Cavitation


Cavitation


Cavitation


Cavitation

Hydraulic Lag


Cavitation Red = 100 psi Green = 75 psi


Cavitation

Green = 75 psi Red = 100 psi

Cavitation is not always evident in Force/Velocity graph!


Hysteresis Red = Baseline Green = Hysteresis

Hysteresis

Hysteresis is also caused by compression pressure imbalance


Proper Pressure Balance


Questions?


Damper Testing    

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


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

Or  Multiple speed  Peak force plot


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


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


Damper Dyno Curves


Roehrig Control Panel


Force - Velocity Compression

Rebound


Force - Absolute Velocity Compression

Rebound


Compression Open – Rebound Closed Compression

Rebound


Rebound Open – Compression Closed Compression

Rebound


Force - Displacement Compression

Rebound


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


PVP – Peak Velocity Plot 17 Peak Velocities

Compression

Curve connects Individual points Rebound


Complete Curve at Single Velocity Compression

Rebound


Single Speed Plot Typical Plot  1 or 2 inch fixed stroke  10 in/sec peak velocity  Only one speed


Single Speed Plot


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


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


Multiple Speed Plot


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


Multiple Speed Plot Minuses  No standardized set of velocities  Hard to compare results with other teams

 Analysis is more difficult


Dyno Curve Analysis


Dyno Curve Analysis Want smooth, uniform curve    

No lags No signs of cavitation No incongruities Minimal hysteresis


Hydraulic Lag

Hydraulic Lag


No Cavitation


Minor Cavitation


Slight Cavitation


Cavitation


Massive Cavitation


Incongruity


Hysteresis

Hysteresis


Proper Curve


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


Force – Absolute Velocity

Compression Open

Rebound Open


Force – Displacement

Compression Open

Rebound Open


Damper Test Methods


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


Questions?


Damper Design      

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


Damper Architecture      

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


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

Function Packaging Performance Price


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     


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

 Pressure balance between piston and gas force required


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


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


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


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


Adjusters


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


High Speed Compression Adjustment


Low Speed Compression Adjustment


Adjusters Single Adjusters  Typically rebound in rod  Typically compression in reservoir  Can adjust low speed, high speed or both


Damper Design Process


Damper Design Process Design Considerations      

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


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

Function Packaging Performance Price


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?


Packaging on Vehicle     

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


Dimensions      

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


Performance Characteristics    

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


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

Damper supplier recommendations Experience or records Calculations Simulation Guess


Tuning Process


Tuning Process     

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


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


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

 Jounce bumper engagement  No binding or interferences


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


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


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


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

Turn-in Braking Acceleration Aero control


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


Tuning Guides


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




Damper Care & Feeding


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


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


Questions?


Advance Tools  Damper testing  7-post testing


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


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


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


Multiple Input Test


Multiple Input Test Peak Velocity

Track Data

Low Freq Track Data

High Freq Track Data

Sine Sweep Based on Track Data


Kaz Tech Shock Testing Tools


Kaz Tech Shock Testing Tools  EMA Complex Drive File Generator  Graphical Plotting & Analysis Tool  Results Workbook  Analysis Metrics


7-Post Testing


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


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


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



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

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


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


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


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

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


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

  

  

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


Kaz Tech 7-Post Tools


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?


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


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!


Records     

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


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


Event Information

Chassis Information Packer Gap

Aero Information Gearbox Information Session Tabs


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

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


Opening Page: Event Summary

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


Session Information

Tire Data Tire Info

Driver Comments

Changes


Tire Sheet


Race Information

Lap Times & Leader Info

Driver Comments Tire Data




Event Information Weekend Summary Race Summary Driver De-Briefs

Next Race

Session Lap Times


Track Data Files


When Enough is Enough


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.


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


References


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


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


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


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


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


Kaz Technologies

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


Thanks!


Damper Basics Seminar

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