After Calculations-Vehicle Tuning Seminar May 2012

Copyright Kaz Technologies 2012

• Kaz Technologies was started in 1995 • We have a staff of 7 engineers – Over 91 years of combined racing and automotive engineering experience

• GM Racing – – – –

Resident 7-post and shock technical specialists 7-post testing for GM racing 7-post & damper testing tools Race Engineering

• What else do we do? – Race Engineering – Damper design and development – Damper sales and service


• Kaz Technologies was started in 1995 • We have a staff of 7 engineers – Over 91 years of combined racing and automotive engineering experience

• GM Racing – – – –

Resident 7-post and shock technical specialists 7-post testing for GM racing 7-post & damper testing tools Race Engineering

• What else do we do? – Race Engineering – Damper design and development – Damper sales and service


• Jim Kasprzak • • •

•

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 31 years automotive experience – Arvin Ride Control • Director, Director, Original Equipment Engineering • Director, New Product Development

–

Monroe Auto Equipment • Chief Engineer, Electronic Systems • Manager, Suspension System Programs Copyright Kaz Technologies 2012

• We asked YOU to send in your questions, and here they are! We’ll be covering: – Data Acquisition and Analysis – Shock Tuning on your car – Damping Calculations

• Please ASK QUESTIONS! We’re here to help and guide you through this process.

• When you see this

it means we’re answering one

of your questions! Copyright Kaz Technologies 2012


Vehicle Data

Motion Ratio

Wheel Rate Ride Rate

Natural Frequencies Sprung & Unsprung

Compression/Rebound Ratio

Compression Damping Low & High speed

Critical Damping Sprung & Unsprung

Knee Speed

Rebound Damping Low & High speed Copyright Kaz Technologies 2012

Damping Ratio

Desired Damping Ratio

• 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)



• The ratio 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)


Passenger Car

Non-Aero Racecars

Critical Damping

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

Milliken Copyright Kaz Technologies 2012

• 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.

• Choose Compression to Rebound Ratio Copyright Kaz Technologies 2012

High Speed Compression Low Speed Compression

Damping Rates N-s/mm

Low Speed Rebound

High Speed Rebound Copyright Kaz Technologies 2012

Control two different masses with one damper

•Sprung mass •Unsprung mass Damper

has many functions

•Control resonant frequencies •Control transient weight transfer rates


Compression

Low Speed Compression/Rebound Ratio

High Speed Compression/Rebound Ratio

Rebound


DP Car #1

DP Car #2


DP Car # 1

DP Car # 2


Typical Damping

Most sources I've read say that damping curves should be biased toward higher rebound damping and softer compression. Is there any truth behind this, and if so, why is this better than having symmetric damping curves or compressionbiased curves?

Compression

Rebound

Compression Biased

Compression

Rebound Copyright Kaz Technologies 2012

In your seminar on damping calculations last year there was no mention of anti roll bars. Other sources also neglect to mention them. Since ARB's can sometimes cause a significant increase in the wheel rate for single wheel bumps, shouldn't they be considered when specifying dampers for a racecar?


All my calculations were based on assumed weights. What do I do when I place a scale under each tire and get the true weight? Do I rework all my calculations?


K S = Spring Rate (N/m)

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/sec 2) Copyright Kaz Technologies 2012

KR= Ride Rate (N/m) KW= Wheel Rate (N/m) KT= Tire Spring Rate (N/m)


• Motion Ratio – The ratio of shock/spring travel to wheel travel



• Dyno test dampers • Damper adjustment range • Damper fit check • Setup sheet – Packer gap • Session sheet • Data analysis pages Copyright Kaz Technologies 2012

•Low Hysteresis •Smooth •No Incongruities •No Lag or Cavitation


Incongruities


Loss of damping force from cavitation and lag



S




Make sure shocks fit correctly! – Correct travels • Shock and spring

– Check jounce bumper engagement – No binding or interferences


Must properly position shock at ride height

• Typically mid stroke at ride height • Determine shock travel on track – Use data acquisition • Check for bottoming/topping

– Use travel indicator on shock rod


Event Information

Chassis Information

Packer Gap

Aero Information

Gearbox Information

Session Tabs Copyright Kaz Technologies 2012

Session Information

Tire Data

Tire Info

Driver Comments Changes Copyright Kaz Technologies 2012




Understeer Gradient = U/S Grad= (Steer -ATAN(WB/((Speed*1.467)^2/(Lat*32.167))))))/Lat U/S Grad = Understeer Gradient (Deg/G) Steer = Tire Steering Angle (deg) WB = Wheel Base (inches) Speed = Vehicle Speed (mph) Lat = Lateral Acceleration (G) Understeer = (Lat > 0.5)* U/S Grad Copyright Kaz Technologies 2012

Speed

Throttle Brake

Understeer

Lateral Accel erat io n




Do you have any tips for using data acquisition to evaluate damper performance (assuming we have the standard sensors like accelerometers and shock travel travel sensors). What should we be looking for in the data (i.e. targeting a specific damper velocity during cornering/braking, front and rear roll angles stay relatively close throughout corners etc) ?


Wheel Speed

Throttle Brake Pressure

Lateral Accel erat io n Understeer Gradient Steering Angle


Steering

Throttle

Damper Displacement

Damper Velocity


Packer Engagement

Rear Shock s

Steering

Throttle Brake

Understeer


Front Roll Gradient (1.34)

Rear Roll Gradient (1.4)


Damper Tuning on the Car

What vehicle dynamics test should I perform once the car is running?




 To

make car move at Sprung Mass Resonance

Observe visually Analyze

data

Fix

pitch, then heave May have to adjust spring rates


Steering

Throttle

Left Damper

Right Damper


Steering

Throttle

Left Damper

Right Damper


Illustration from Optimum G Spring and Dampers Tech Tip 1, Girafa Copyright Kaz Technologies 2012


 To

make wheels resonate or bounce

Observe visually Analyze

data

More AND

less compression More AND less rebound Copyright Kaz Technologies 2012

How do I verify my shocks are working as intended? Say I designed for 1 in bump/droop. How do I verify that's what I'm (not) getting?


Rear Shock s

Steering

Throttle Brake

Understeer Copyright Kaz Technologies 2012

Stable?

Yes, No

Neutral,

Understeer or Oversteer?

Neutral,

Understeer or Oversteer?


After Calculations-Vehicle Tuning Seminar May 2012

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