Download FSAE Damper Guide- Jim Kasprzak Kaz Tech Tip PDF

TitleFSAE Damper Guide- Jim Kasprzak Kaz Tech Tip
TagsSuspension (Vehicle) Resonance Tire Automobiles Applied And Interdisciplinary Physics
File Size3.1 MB
Total Pages25
Document Text Contents
Page 12

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Typical natural frequencies of sprung and unsprung mass are listed below:

Sprung Mass Natural Frequencies

 FSAE vehicle 2.5 – 3.5 Hz

 Passenger car 1 – 2 Hz

 NASCAR Cup car 1.5 – 4 Hz
o All 4 corners are different!

 Indy Car 5 – 7 Hz


Unsprung Mass Natural Frequencies

 FSAE vehicle 15 – 19 Hz

 Passenger car 10 – 12 Hz

 NASCAR Cup car 15 – 17 Hz

 Indy car 23 – 27 Hz

The undamped frequency at which the sprung mass will resonate or bounce is often called the ride frequency. This is
the same as the sprung natural frequency. Since the front and rear will resonate or bounce at different frequencies, we
typically reference a front and rear ride frequency. The reason the front and rear have different ride frequencies is to
reduce the pitch of the vehicle over bumps. The rear ride frequency istypically higher than the front, so that after
encountering a bump, the rear will “catch up” with the front, and the front and rear will move in phase. See the
illustration in Figure 14.


Different Front and Rear Ride Frequencies





Figure 14

Typically the ride frequencies for a FSAE vehicle are between 2.5 and 3.5 Hz, with the rear 0.2-0.4 Hz higher than the
front. What are the “right” ride frequencies? The ones that make YOUR car go the fastest! Don’t get hung up on ride
frequency numbers. They are for reference. Of course it is useful to calculate the front and rear ride frequency to
determine initial ride balance and starting spring rates. But ultimate spring rates and damping ratios that make the car
go fast are much more important than the theoretical numbers.

Damping Force Calculations
Most text books reference damping coefficients when discussing the amount of damping required for a vehicle. In the
real world, damper engineers talk in terms of damping force in compression and rebound at a damper velocity. You
need both. Once you derive your theoretical damping coefficients, you will need the actual damping force numbers to

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