There are various variations of similar themes:
The above bose system is "fully active" and "full bandwidth" (fast) in that each corners hydraulic ram (or other actuator) can both absorb or deliver energy (e.g. push a wheel down), in real time to react to bumps. They consume a lot of power. The ultimate realization of this would be like a big cat running across rough terrain. Each leg adjusts for the terrain at every touchdown of each foot. In contrast a damper just absorbs energy; Pushing a vehicle across rough terrain would be kinda like pushing it through treacle - the road undulations drive the dampers up and down which absorbs and wastes energy.
"Semi-active" systems can only absorb energy, such as dampers that change their damping curves in real-time. Various systems have various bandwidth (speed). Some are fast enough to react to the aftermath and oscillation after a bump, some can only change in half a second or so.
Here are some of the options
- active preload a la early 2000 Mercedes, and 1980s Williams F1 cars.
-- these change ride height to counteract body roll for corners or aero loads or changing passenger loads but aren't fast enough for reacting to bumps in real time. What this allows you to do is use soft springs so bump absorption is good. The coming Merc system will have a "look ahead" feature using video cameras to for example, raise the ride height and soften damping in anticipation of a speed bump, then stiffen the damping to damp oscillations afterwards.
- active swaybar preload, a la Porsche 991, 2006+ 750i, and 2008+ BMW sport suspension 5-series
-- these allow soft swaybars for good ride but wind-up (pre-load) for corners and work as part of the active stability control (My 750i is realllly good here, such as launching out of corners from a stop. It plants the rear tires, and general stability correction is very smooth)
- "automatic" adjustable dampers. Imagine Tein EDFC but which can decide on its own to stiffen up in < a second if it detects frisky driving or the push of a "sport" button. Early 2000 BMW "M sport" and other cars do this. Kinda lame if you ask me.
- MR dampers. These can change damping in 10s of milliseconds to improve ride and grip, so it will be well damped against body motions but soft to wheel motion from bumps. The damping forces can be changed over a wide continuous range. These are great.
- switching dampers. These are like a poor man's MR damper. But instead of a wide continuous range of damping curves available, it will switch between 2 or 3 presets. They are fast enough to kill oscillations after hitting bumps a certain way. Certain mid 2000 Jaguars had this for reacting to brake dive among other things. AFAIK
the F430 does too. The ride quality improvement is substantial (I've driven one in anger extensively)
see beginnings of my blog Jason's engineering and other musings: Bi-state or Tri-state semi-active vehicle damping
- Audi has proposed electromagnetic dampers. The dampers instead of being fluid filled, will be a linear motor which can absorb energy which will be recycled to the perhaps-hybrid powertrain. This will have similar advantages to MR shocks, but with faster control bandwidth and some energy regeneration. Shocks won't get hot! They can also probably push or pull a wheel up actively, but I doubt they'll have enough oomph to match the prototype Bose system. This system will probably provide better performance than MR dampers.