Actual Ride frequency

[Mani_Namuduri]

Guys,
I had a doubt on how the concept of ride frequency works. Ride frequency should be the natural frequency at which my sprung mass vibrates in case of a purely undamped situation. in that case if we calculate the wheel center frequency shouldn't it be same as that of frequency of spring. I know the stiffness changes because of installation ratio provided by Rocker(or bell crank). In that case i guess frequency shouldn't depend on stiffness . Is this way of approach right? I have seen the other way round in many books.

[Claude Rouelle]

- You have another mass (non suspended) another spring (tire rate) to take into account. Also your damper: You damped frequency is different than the undamped one.
- You also could take the tire damping into account but this one is small (usually a small percentage of the critical damping)
- As you said other parameters like compliance are not taken into account and yet they could play an important role
- Try a simulation in the frequency domain and another one in the time domain (which allows you to have a non-linear and asymmetric damping)
- That is only in heave, in roll and pitch you will have to take into account your roll and pitch inertia.
- You effective frequency and amplitude will be depending on the input; can you simulate these inputs? In simplistic words these inputs are the ones "from the bottom" which is the the road profile and "the on from the top" which are the longitudinal, lateral and vertical forces (including aero) acting on the car suspended and non suspended masses.

And yet you will not take into account the damping hysteresis neither the damper frequency acceleration, temperature etc sensitivity.
Conclusions
1. Only believe what you measure (well as far as you trust your sensor and you understand how the hardware and software process the signal)
2. Calculate anyway: you will learn a lot.
3. There are too many parameters to be spot on; that is why you want to "work in delta" and make study of parameters sensitivity.


One more advice: If 2 result numbers are not the same...at least one of them is wrong. If the prediction from your simulation and the logged data are different, at least of them is wrong! Could be you model, could be your sensors calibration. Could be many things...

Mani_Namuduri... who are you?