After Calculations-Vehicle Tuning Seminar May 2012

7/28/2019 After Calculations-Vehicle Tuning Seminar May 2012

http://slidepdf.com/reader/full/after-calculations-vehicle-tuning-seminar-may-2012 1/77

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




• 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, Original Equipment Engineering

• Director, New Product Development

– Monroe Auto Equipment

• Chief Engineer, Electronic Systems

• Manager, Suspension System Programs




• 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!







Vehicle

Data

MotionRatio

Wheel RateRide Rate

Natural Frequencies

Sprung & Unsprung

Critical Damping

Sprung & Unsprung

Damping

Ratio

Desired

Damping Ratio

Knee

Speed

Compression/Rebound

Ratio

Compression Damping

Low & High speed

Rebound Damping

Low & High speedCopyright Kaz Technologies 2012



• 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)




Aero RacecarsRide: 0.7-1.1Roll: 6.0-9.0

Milliken

Non-Aero

Racecars

Passenger

Car

Critical

Damping




• 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




Damping Rates N-s/mm

High Speed

Compression

High Speed

Rebound

Low Speed

Compression

Low Speed

Rebound




Control two different masses with one damper•Sprung mass•Unsprung mass

Damper has many functions•Control resonant frequencies•Control transient weight transfer rates




Compression

Rebound

Low SpeedCompression/Rebound

Ratio

High SpeedCompression/Rebound

Ratio




DP Car #1 DP Car #2




DP Car # 1 DP Car # 2




Most sources I've

read say that

damping curves

should be biased

toward higher

rebound damping

and softer

compression. Is

there any truthbehind this, and if

so, why is this

better than having

symmetric damping

curves orcompression-

biased curves?

Typical Damping

Compression Biased

Compression

Compression

Rebound

Rebound




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 whenspecifying dampers for a racecar?




All my calculations were based on assumed

weights. What do I do when I place a scaleunder each tire and get the true weight?

Do I rework all my calculations?


( / )( / )



Unsprung Mass Natural Frequency

• The undamped resonant frequency of the unsprung mass

K S = Spring Rate (N/m) K S = Spring Rate (N/m)

KS = Spring Rate (N/m) KT =Tire Rate (N/m) WUS = Unsprung Weight (kg) g= Acceleration due to Gravity (m/sec2)




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




•Low Hysteresis•Smooth

•No Incongruities•No Lag orCavitation




Incongruities




Loss of dampingforce fromcavitation 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




EventInformation

Chassis Information

Gearbox Information

Aero Information

Session Tabs

Packer Gap




Session Information

Tire Data

Driver Comments

Changes

Tire Info













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




Speed

Throttle Brake

Understeer

Lateral

Accelerat ion










Do you have any tips for using data acquisition

to evaluate damper performance (assuming we

have the standard sensors like accelerometers

and shock travel sensors). What should we be

looking for in the data (i.e. targeting a specificdamper velocity during cornering/braking,

front and rear roll angles stay relatively close

throughout corners etc) ?




Wheel Speed

Throttle Brake

Pressure

Lateral

Accelerat ion

Understeer

Gradient

Steering Angle




Steering

Throttle

Damper Displacement

Damper

Velocity




Rear Shocks

Steering

Throttle Brake

Understeer

Packer Engagement




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 visuallyAnalyze data

Fix pitch, then heaveMay 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







To make wheels resonate or bounce

Observe visually

Analyze data

More AND less compressionMore AND less rebound




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 Shocks

Steering

Throttle Brake

Understeer






Stable? Yes, No

Neutral, Understeer or Oversteer?

Neutral, Understeer or Oversteer?




































Date post:	03-Apr-2018
Category:	Documents
Upload:	harikrishnan-rajendran
View:	217 times
Download:	0 times

After Calculations-Vehicle Tuning Seminar May 2012

Documents