Damper Basics

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

Damper Basics

Damper Design, Testing and Tuning


By Jim Kasprzak

May 15, 2010

Presented to Formula SAE

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

Damper Basics

It is thought by many that dampers are a black art

That there is some “magic” to developing

and tuning dampers


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


“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


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

http://www.indyracing.com/indycar/




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)

Unsprung Mass

Spring Damper


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



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



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



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 Body, chassis spring

and damper Suspension and tire

Sprung Mass (Chassis)

Unsprung Mass Suspension

Spring

Tire Spring Tire Damping

Damper


Resonant Frequencies

Sprung Mass Unsprung Mass


Typical Natural Frequencies

Sprung Mass FSAE 2.0 – 4 Hz Passenger Car 1 – 2 Hz NASCAR Cup Car 1.5 – 4 Hz

All 4 corners different!! Indy Car 3 -5 Hz


Typical Natural Frequencies

Unsprung Mass FSAE 22 - 26 Hz Passenger Car 10 - 12 Hz NASCAR Cup Car 15 - 17 Hz Indy Car 23 - 27 Hz


How Much Damping?


How Much Damping?

Resonance

Critically Damped


Milliken

Critical

Damping

Passenger

Car

Non-Aero

Racecars

Aero Racecars

Ride: 0.7-1.1

Roll: 6.0-9.0


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



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



Monotube Pressure in gas chamber must always

be greater than compression chamber



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



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

Base Valve Pressure

Compression Pressure

Rebound Pressure


Cavitation

Cavitation No Cavitation


Cavitation


Cavitation


Cavitation

Hydraulic

Lag


Cavitation

Red = 100 psi

Green = 75 psi


Cavitation

Cavitation is not always evident in Force/Velocity graph!

Red = 100 psi

Green = 75 psi


Hysteresis

Hysteresis is also caused by compression pressure imbalance

Hysteresis

Red = Baseline Green = Hysteresis


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

Rebound

Compression


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

Curve connects Individual points

17 Peak Velocities

Rebound

Compression


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



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



Adjusters


Adjusters

Various types of adjusters Rebound Compression Rebound & compression High speed compression & rebound Low speed compression & rebound

Must decide what is important !


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



Velocity for transients typically below 2 in/sec

Turn-in Braking Acceleration Aero control



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

Track Data

Low Freq Track Data

High Freq Track Data

Sine Sweep Based on Track Data Peak Velocity


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


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


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

Aero Information

Gearbox Information

Session Tabs

Packer Gap


Run Log

EXCEL File with Worksheets for: Race/Test Summary Worksheet for each session Data Analysis Summary Tire Summary Race Log


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

Opening Page: Event Summary


Session Information

Tire Info

Driver Comments

Tire Data

Changes


Tire Sheet


Race Information

Driver Comments

Tire Data

Lap Times & Leader Info




Event Information

Weekend Summary

Race Summary

Driver De-Briefs

Next Race

Session Lap Times


Track Data Files


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.



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!

mailto:[email protected]

http://www.facebook.com/Kaz.Technologies


Kaz Technologies

Jim Kasprzak

[email protected] 248-

855-3355

Tom Jaworski

[email protected]

734-536-3218

Jess Youngblood

[email protected]





Kaz Technologies

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

nologies




Thanks!

Documents

Damper Basics