kaz tech damping calculation seminar
TRANSCRIPT
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Damping Calculations
The Proper Damping for my Vehicle
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By Jim Kasprzak
May 13, 2011
Presented to Formula SAE
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PLEASE ask questions
at any time
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Calculation RoadmapVehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculations
Data
Decisions
Results
Calculation Roadmap
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Data Calculation Roadmap
![Page 7: Kaz Tech Damping Calculation Seminar](https://reader034.vdocuments.net/reader034/viewer/2022050621/5438376bafaf9fb62e8b480b/html5/thumbnails/7.jpg)
This document is property of Kaz Technologies. Not authorized for use by outside organizations
Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculations
Calculation Roadmap
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This document is property of Kaz Technologies. Not authorized for use by outside organizations
Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Decisions
Calculation Roadmap
![Page 9: Kaz Tech Damping Calculation Seminar](https://reader034.vdocuments.net/reader034/viewer/2022050621/5438376bafaf9fb62e8b480b/html5/thumbnails/9.jpg)
This document is property of Kaz Technologies. Not authorized for use by outside organizations
Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Results
Calculation Roadmap
![Page 10: Kaz Tech Damping Calculation Seminar](https://reader034.vdocuments.net/reader034/viewer/2022050621/5438376bafaf9fb62e8b480b/html5/thumbnails/10.jpg)
This document is property of Kaz Technologies. Not authorized for use by outside organizations
Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculations
Data
Decisions
Results
Calculation Roadmap
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KAZ Technologies
KAZ TECHNOLOGIES started in 1995
Staff of 6 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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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
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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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“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 SmithTune to Win, 1978
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculations
Data
Decisions
Results
Calculation Roadmap
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Data Calculation Roadmap
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Vehicle Data
Total Vehicle weight % Front vehicle weight Front & rear unsprung weight Front & rear shock/wheel motion ratios Tire radial stiffness Front & rear spring rates
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Vehicle Data Definitions
Total Vehicle Weight Total vehicle weight ready to race with driver,
fluids and ½ tank of fuel
% Front Vehicle Weight Percentage of vehicle’s weight measured at the
front wheels
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Vehicle Data Definitions
Unsprung Weight The weight of those parts of the car which are
not carried by the suspension system, but are supported directly by the tire and wheel assembly and considered to move with it.
CarDictionary.com
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Vehicle Data Definitions
Motion Ratio The ratio of shock/spring travel to wheel travel
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Vehicle Data Definitions
Tire Radial Stiffness Vertical spring rate of the tire Obtained from tire test data Tire pressure dependant Data available as member of the FSAE Tire Test
Consortium
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Vehicle Data Definitions
Spring Rate The ratio of spring load to deflection
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Vehicle Data
Total Vehicle weight % Front vehicle weight Front & rear unsprung weight Front & rear shock/wheel motion ratios Tire radial stiffness Front & rear spring rates
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Spring Rates
SpringRate ?
Suspension Travel
Roll Rate(Handling)
Pitch(Braking)
Ride Frequency
Aero Load
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Vehicle Data Units
Total Vehicle weight (kilograms) % Front vehicle weight (percentage - %) Front & rear unsprung weight (kilograms) Front & rear shock/wheel motion ratios (unitless) Tire radial stiffness (Newton/millimeter) Front & rear spring rates (Newton/millimeter)
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculations
Calculation Roadmap
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Motion Ratio
The ratio of spring travel to wheel travel
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Wheel Rate = KW = KS * MR^2
KW = Wheel Rate (N/m)KS = Spring Rate (N/m)
MR = Motion Ratio (unitless)
The spring rate at the wheel
Wheel Rate
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Ride Rate
The effective stiffness of the suspension and tire springs in series
KR = Ride Rate (N/m)KW = Wheel Rate (N/m)
KT = Tire Spring Rate (N/m)
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Natural Frequency
The undamped resonant frequency of the system
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Natural Frequency
The undamped resonant frequency of the system
KS = Spring Rate (N/m)M = Mass (kg)
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Sprung Mass Natural Frequency
The undamped resonant frequency of the sprung mass
KR = Ride Rate (N/m)WS = Sprung Weight (kg)
g= Acceleration due to Gravity (m/sec2)
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Unsprung Mass Natural Frequency
The undamped resonant frequency of the unsprung mass
KS = Spring Rate (N/m)KT =Tire Rate (N/m)
WUS = Unsprung Weight (kg)g= Acceleration due to Gravity (m/sec2)
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Critical Damping
The level of damping that allows the mass to return to steady state most quickly with no overshoot is critical damping.
Ccr = Critical Damping Coefficient (N-s/m)KS = System Spring Rate (N/m)
M = System Mass (kg)
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Critical Damping
Resonance
Critically Damped
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Sprung Mass Critical Damping
The critical damping coefficient for the sprung mass
Ccr(s) = Sprung mass critical damping coefficient (N-s/m)KR = Ride Rate (N/m)
WS = Sprung Weight (kg)g= Acceleration due to Gravity (m/sec2)
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Unsprung Mass Critical Damping
The critical damping coefficient for the unsprungmass
Ccr(us) = Unsprung mass critical damping coefficient (N-s/m)KS = Spring Rate (N/m)
KT =Tire Rate (N/m)WUS = Unsprung Weight (kg)
g= Acceleration due to Gravity (m/sec2)
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Damping Ratio
The relationship of the damping coefficient to the coefficient at critical damping. Think of it as a damping rate.
ξ = Damping Ratio (N-s/m)C = Damping coefficient (N-s/m)
Ccr = Critical damping coefficient (N-s/m)
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DampingRatio
Milliken
CriticalDamping
PassengerCar
Non-AeroRacecars
Aero RacecarsRide: 0.7-1.1Roll: 6.0-9.0
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Decisions!!
Calculation Roadmap
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculation Roadmap
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Desired Damping Ratio
Damping Ratio is based on YOUR decisions: Dynamic ride frequency Dynamic pitch frequency Dynamic roll rate Spring rates Sway bar rates Driver preferences
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Desired Damping Ratios
Choose Damping Ratios for: Low speed compression Low speed rebound High speed compression High speed rebound
Low speed is body control and transitions, high speed is control over bumps.
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Desired Damping Ratios
Low SpeedCompression
Low SpeedRebound
High SpeedCompression
High SpeedRebound
Damping Rates N-s/mm
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Desired Damping Ratios
Why four different damping ratios? Control two different masses with one damper Sprung mass Unsprung mass
Damper has many functions Control resonant frequencies Control transient weight transfer rate
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculation Roadmap
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Knee Speed
Knee speed is the velocity where the damping transitions from low speed to high speed, or from the low speed Damping Ratio to the high speed Damping Ratio.
Knee speed is the transition from body control to control over bumps. Usually chosen above velocity of sprung mass resonance.
May not be able to change due to valve design
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Knee Speed
Knee Speed 25 mm/sec
Compression Knee
ReboundKnee
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculation Roadmap
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Compression to Rebound Ratio
Compression to rebound ratio is the ratio of damping force at a specified velocity.
Typically specified at the Knee Speed and velocity of unspsrung mass resonance.
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Compression to Rebound Ratio
KneeComp/Reb
Ratio
Unsprung MassComp/Reb
Ratio
Compression
Rebound
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculations
Data
Decisions
Calculation Roadmap
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Results
Calculation Roadmap
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Calculations, Decisions, ResultsCalculations
Decisions
Results
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Damping Rate
The damping rate for a specific portion of the damping curve
DR = Damping Rate (N-s/m)Ccr = Critical damping coefficient (N-s/m)
ξ = Damping Ratio (N-s/m)
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Low Speed Comp Damping Rate
Calculate low speed compression damping rate using Sprung Mass Critical Damping and low speed Damping Ratio
DR(lsc) = Low speed comp Damping Rate (N-s/m)Ccr(s) = Sprung mass critical damping coefficient (N-s/m)
ξ(ls) = Low speed Damping Ratio (N-s/m)
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Low Speed Comp Damping Force
Calculate compression damping force at Knee Speed using low speed compression Damping Ratio and Knee Speed
CF(ls) = Low speed comp damping force (N)KS = Knee Speed (mm/sec)
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Calculation, Decision, ResultsCalculations
Decisions
Results
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High Speed Comp Damping Rate
Calculate high speed compression damping rate using Unsprung Mass Critical Damping and high speed Damping Ratio
DR(hsc) = High speed comp Damping Rate (N-s/m)Ccr(us) = Unsprung mass critical damping coefficient (N-s/m)
ξ(hs) = Low speed Damping Ratio (N-s/m)
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High Speed Comp Damping Force
Calculate high speed compression damping force using high speed compression Damping Ratio and high velocity speed
CF(hs) = High speed comp damping force (N)V(hs) = High speed velocity(mm/sec)
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Calculation, Decision, ResultsCalculations
Decisions
Results
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Low Speed Rebound Damping Rate
Calculate low speed rebound damping rate using low speed compression damping rate and low speed compression/rebound ratio
DR(lsr) = Low speed reb Damping Rate (N-s/m)DR(lsc) = Low speed comp Damping Rate (N-s/m)
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Low Speed Rebound Damping Force
Calculate low speed rebound damping force using low speed rebound Damping Ratio and low velocity speed
RF(ls) = Low speed rebound damping force (N)V(hs) = High speed velocity(mm/sec)
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Calculation, Decision, Results
Decisions
Results
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High Speed Rebound Damping Rate
Calculate high speed rebound damping rate using high speed compression damping rate and high speed compression/rebound ratio
RF(hs) = High speed rebound damping force (N)CF(hs) = High speed comp damping force (N)
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High Speed Reb Damping Force
Calculate high speed rebound damping force using high speed rebound Damping Ratio and high velocity speed
RF(hs) = High speed rebound damping force (N)V(hs) = High speed velocity(mm/sec)
![Page 69: Kaz Tech Damping Calculation Seminar](https://reader034.vdocuments.net/reader034/viewer/2022050621/5438376bafaf9fb62e8b480b/html5/thumbnails/69.jpg)
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Calculation, Decision, Results
Decisions
Results
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Decisions
Decisions
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Decision Example - Passenger Car
Compression
Rebound
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Decision Example Non-Aero Car Indy Car - Aero
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Decision Example Non-Aero Car Indy Car - Aero
CompressionCompression
ReboundRebound
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Decision Example – DP CarsDP Car #1 DP Car #2
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Decision Example – DP Cars DP Car #1 DP Car #2
CompressionCompression
Rebound Rebound
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Decision Example – FSAE CarsTypical FSAE Kaz Tech Approach
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Decision Example Typical FSAE Kaz Tech Approach
CompressionCompression
Rebound Rebound
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Vehicle Data
Wheel RateRide Rate
Natural FrequenciesSprung & Unsprung
Critical DampingSprung & Unsprung
Desired Damping Ratio
KneeSpeed
Compression/ReboundRatio
Compression DampingLow & High speed
Rebound DampingLow & High speed
Motion Ratio
Damping Ratio
Calculations
Data
Decisions
Results
Calculation Roadmap
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Decisions
Decisions
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Decisions
Damping RatiosKnee Speed
Comp/Reb Ratios
Spring Rates
Roll Rate
Transient Response
Ride Frequency
Aero Load
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Low & High Freq Damping Ratios
Why two Damping Ratios? Low Frequency
Ride motions Turn-in Brake dive Acceleration rise/squat
High Frequency Control over bumps Wheel hop
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Low Frequency Damping Ratio
Why high Low Frequency Damping Ratios? Compression
Load outside tire on turn-in (reduce turn-in understeer) Reduce rate of brake dive (even load distribution) Reduce squat on acceleration (reduce understeer)
Rebound Reduce roll Reduce rear lift in braking (even load distribution) Reduce front lift on acceleration (reduce understeer)
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High Frequency Damping Ratio
Why less High Frequency than Low Frequency Damping Ratio? High frequency primarily damping wheel Less weight to control, thus less damping required
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General Setup Examples
Soft spring Stiff sway bar High compression, low rebound damping ratiosOR Stiff springs Soft sway bar Low compression, high rebound damping ratios
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Decision Numbers
Decision Numbers are JUST numbers!!
Tire Force Variation
Bod
y C
ontro
l
2008DR
2009DR
2010DR
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Summary
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Summary
Many factors effect your damping decision Suspension design (Roll Center, Motion Ratio, etc.) Suspension variables (spring rates, bar rates,etc.) Tires Downforce Driver preference On and on…
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Summary
Damping is just one part of the SYSTEM Damping has to work in concert with the other
components They all have to work together You can achieve the objective in multiple ways
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The Last Word
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Damping calculations are a way to quantify normalized results
They are NOT the conclusion
They are the MEANS to the END!
The Last Word
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Like any other variable on the car, your damping decisions are JUST numbers! Choose these based on all the other factors in the car
There are MULTIPLE right solutions!
The Last Word
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Questions?
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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
BooksRace Car Vehicle Dynamics
William F. Milliken and Douglas L. Milliken
Fundamentals of Vehicle DynamicsThomas D. Gillespie
Shock Absorber HandbookJohn 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
Topics to Discuss?http://www.facebook.com/Kaz.Technologies
Start a discussion!
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Kaz TechnologiesJim Kasprzak
734-536-3218
Jess [email protected]
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Kaz Technologies
http://www.facebook.com/Kaz.Technologies
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Thanks!