damper basics seminar

7/25/2019 Damper Basics Seminar

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

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

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



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



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/



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



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



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



Course Outline

Damper BasicsInside the DamperDamper TestingDamper Design

Advanced ToolsThe Final Word



Damper Basics

A shock absorber is a damper!Functions of a damperResonant frequenciesHow much damping?



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



A Shock is a DAMPER!Sprung Mass

(Chassis)

Unsprung Mass

Spring Damper



A Shock is a DAMPER!

The damper controls the suspensionIn broad terms:

Rebound controls sprung massCompression controls unsprung mass


18/199This document is property of Kaz Technologies Not authorized for use by outside organizations

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




At best, dampers areThe frosting on the cake

Dampens vibrations at resonant frequenciesControls rate of weight transferEnhances vehicle performance




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




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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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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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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MonotubePressure in gas chamber must always

be greater than compression chamber


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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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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


Shorter length than monotubeSame pressure balance asmonotube with base valve


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Twin Tube with Piggyback 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



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Velocity for transients typicallybelow 2 in/sec

Turn-inBraking

Acceleration

Aero control



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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



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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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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



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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 .



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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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[email protected]

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

Tom [email protected]

734-536-3218

Jess Youngblood [email protected]

Kaz Technologies
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