If the wheel load is high, the damping coefficient may become too small. At low wheel load oscilations can become overdamping. I think playing with the load transfer on the axles, we also affect the damping coefficient.
When the value of anti roll bars increases, I think that damping can also change because stabilizers do not have dampers. That is, about it said Carroll Smith in the "Tune to win". To determine the type of damping we need to know the difference in b^2 - 4 * k*m. Where в is the stiffness of the shock absorbers,k-spring rate, m-mass. I do not know how this difference can change with the use of stabilizers. So we need to use another equation for springs with stabilizers.
Wheel rate is spring rate+damper rate+bushing rate(if applicable(ie poly/rubber bushes, but not spherical bushes))+heave and/or roll rate divided by the control arm motion ratio?
I recognise that the reference revealed by Rustem is an extract from course notes issued by one University, but for other people who might read this thread I should state that the contents represent one person's view (I guess). For example, from 5.1.1:
I don't think that "most buildings are mounted on top of special mounts".
The reference to Professor Smiths work suggests a lack of research, and the statement that "it is only a matter of time before it appears on vehicles available to the rest of us" is probably not true, mostly because of cost and reliability.
I recognise that the reference revealed by Rustem is an extract from course notes issued by one University, but for other people who might read this thread I should state that the contents represent one person's view (I guess). For example, from 5.1.1:
I began to doubt too.
Last edited by Rustem 1988 on 19 Feb 2018, 12:40, edited 1 time in total.
When the value of anti roll bars increases, I think that damping can also change because stabilizers do not have dampers.
Also, tires may have a damping rate less than springs with shock absorbers. The damping rate С should not be confused with damping ratio ζ (С/Сс). https://en.wikipedia.org/wiki/Damping_ratio
And yes, a typical 'rule of thumb' is to start of at 70% of critical wheel damping because it gives a good balance between response speed and overshoot.
Is it the reaction of a spring with a shock absorber to a step input force?
And yes, a typical 'rule of thumb' is to start of at 70% of critical wheel damping because it gives a good balance between response speed and overshoot.
Is it the reaction of a spring with a shock absorber to a step input force?
Yes but not just a step input. It's been shown to be a decent starting point for all vehicle loadcases. If you have no road input data it's all you can do. It's never going to be anything more than a sensible first iteration though.
When I look at primary ride I have found no meaningful way of designing the shocks without real road inputs.Once you have those, and good data to correlate to, then life suddenly gets more interesting. One of the guys built 3 levels of shocks for each end of the car, and then ran the full matrix, ie 9 setups, on measured roads. We got R^2 of up to 0.9 for some (bandwidth limited) sensors, between the models and the real results. We also got R^2 of ~0.3 for one particular sensor/road combination, investigating that was informative. For the model you need all 4 wheels, and you need to know the road profile (not just its spectrum). This is a very similar test to a 4 poster, yet driving a real 4 poster with real road profiles needs a lot of tweaking to get the same results (I don't get involved with 4 posters, we knew /some/ of the reasons why 30 years ago).
Mind you this approach only seems to work for some cars, so far I am achieving no useful results for primary ride on my current project.
When I look at primary ride I have found no meaningful way of designing the shocks without real road inputs.
What is "primary ride"?
Neglecting the influence of suspension isolators and power train mounts on road vehicles can lead to set-ups that are both uncomfortable and poorly controlled. Damper (and spring) set-ups can’t be neglected, but they are not necessarily "primary".
Perhaps that is the problem with your current project....
