Quote:
Originally Posted by mkoesel
Racer20, do you know details of how things have evolved and improved since the E9x M cars "EDC" (which I realize was not BMW's first active suspension offering, but it is the first one that many people here are likely to be familiar with) to today's Fxx generation "DDC". Also, how do today's M and non-M implementations differ? Are there distinguished hardware systems, or is it all in the software?
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Unfortunately I don't know the exact details of each BMW model. However, here are some things that could make the differences (Ignoring Magneride):
Hardware:
Triple tube dampers systems have a solenoid on the side that controls the damping pressure based on how much current is applied. The rebound to compression ratio (key to ride and handling performance) and min/max damping capability is determined by the passive valves in the damper, just like a normal shock.
Double solenoid triple tubes have TWO solenoids on the outside of the damper to allow separate tuning for rebound and compression. This allows faster response and more tunability.
Sachs newest system has the variable damping valve inside the shock absorber. I haven't seen one of these taken apart, but from what I understand they are very good. I would imaginee that the damping response time and hysteresis is better than an external solenoid system.
Software
One of the challenges that arises with these systems is making the car feel natural. You don't want to feel the damping changing as you're driving it, except for right when you change the modes. Tuning these systems involves a bunch of damping force maps and look up tables and "if X condition is detected, go to Y damping force table" type stuff, and getting all these different conditions and tables to blend well without jerking the car around is tough, and can be very time consuming.
Newer tuning and control software is "smarter" and some of them may have more accurate vehicle models embedded in them, and make it easier to blend these modes together with less manual tuning of complex damping force tables.
Vehicle
The more sensors you have, the more accurately the suspension ECU knows what's going on, and the better it can control the dampers. Ideally, you'd have lazer height sensors reading the ground, accelerometers on the sprung and unsprung mass at all 4 corners, a yaw sensor, and accurate GPS (In addition to steering/throttle/brake sensors) but all these sensors are expensive. So normally you get a couple accelerometers and maybe a yaw sensor. That means the system has to derive the rest of the information it needs mathematically, and the result is less accurate and increases response time.
The moral of the story is that these systems are very complex, and how it drives on one car has nothing to do with how it may drive on another. There is huge progress being made every year on this stuff, and there's really no question at this point that they ARE better than passive dampers in most respects.