Here's how it actually works... the shock is merely an actuator for the SUM...
Ever since I bought an R I've really wondered how 4C actually functions on a basic level, and since I go to school for engineering I've had the pleasure of taking courses on statics, dynamics, and vibrations (which my school is noted for if sound counts as a vibration)
The fundamental concept behind car suspension is the simple mass spring system, with a damper thrown in to attenuate the motion of the spring. Without a technology such as 4C most manufactures tune their dampers to be less than critically damped. Critical damping is the fastest way from a disturbance back to equilibrium, it is also characteristic of a "firm" suspension as all of the energy transmitted to the car must be attenuated in less than one cycle. Cruising around town you want the car to be underdamped so it soaks up bumps, on the race track you want it to be close to critically damped because that maximizes tire contact. How does an engineer reconcile these two things? Adjustable dampers.
Keeping the natural frequency of the car (ω=sqrt(k/m)) the same and changing the damping constant (c) (which is velocity dependent) of the car will change the damping ratio (zeta) ζ=c/(2*sqrt(km)). This is probably (at least that's what would make sense) what the buttons on the dash do. They change the base valve of c to something small for comfort and increase it for advanced to attain close to critical damping. Now that's not the whole story because the forcing frequency of the suspension is changing a lot. Car suspensions operate from around 1-100Hz (i.e. how many bumps there are), with varying amounts of force applied (i.e. how tall the bump is).
My assumption is that the accelerometer is there to tell the car the forcing frequency and force and allow it to correct back to its chosen ζ value by changing c (which it does with the solenoid in the shock). All of this is covered by a second order differential equation so I assume Volvo was lazy (like I am) and said: we know the car weighs 2000kg so we put [insert value here]N/m springs in the car. ω is a constant then. And with the level sensors in the car it can probably approximate loading the same way (I dunno if it does). 4C is known to use very soft springs and that's probably because the value of c is limited to some kinda small range and in order to change ζ a lot it needs to be able to change the ratio of c to ω. Also assuming the suspension operates above resonance (a decent assumption) the motion of the suspension is governed by damping, not the mass or spring.
Well I hope this helps anyone who wonders how 4C works. I'll probably add to it…
An interesting paper on the subject
http://www.nit.eu/czasopisma/JTIT/2012/1/83.pdf
http://forums.swedespeed.com/showthr...-understand-it
