Quote:
Originally Posted by jm1234
I'd guess that the EDC in "normal" mode is a closed loop control system and thus the damping ratio is the controlling variable and not a constant. In comfort mode I would assume a slightly underdamped system and in race a critically damped system (or perhaps even slightly overdamped). In normal mode though it's a question of what is being controlled? Is it ride height at each wheel (to control compression/extension); is it roll/pitch frequency/rate; is it lateral/longitudinal acceleration; is it a combination; or something else entirely? Any portion of the control system based on ride height is going to be negatively impacted by changing the ride height. The control system will see a constant downward offset which could (just guessing here) result in a constantly overdamped system. Portions of the control system based on roll/pitch/acceleration should incorporate spring rates and by changing the spring rates you will impact the system response but how would be more difficult to predict.
I don't see how you can take a controlled system and swap parts to change the response values and not negatively impact the performance. It's comparable to open/restricting the intake and exhaust on the engine but not changing the computer and fuel maps. The car might "look" cooler with lowered springs but unless you change the dampers; control system; and/or keep the car in a static suspension setting (comfort or race) then I think you'll suffer a variably compromised ride with difficult to predict consequences. I'm not predicting dire things just crap suspension feel (too stiff, too soft, bouncing, bottoming out, excessive roll, etc...) some portion of the time while in "normal" mode.
Does anyone know the details of how BMW's adjustable dampers work? I'm still curious and some of you seem to have a lot of engineering knowledge about the car.
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"EDC-K is available for the first time in the E92 M3. EDC-K is an option and is based on the EDC-K in the E65.
Both dampers of one axis are always activated in parallel. The valve is installed internally in the damper in the damper oil system.
The driver can choose between three settings, the controlled programs "Comfort" and "Normal", or the uncontrolled fixed setting
"Sport". The program is selected using the EDC-K button on the center console or preset via the MDrive menu and activated using the M button on the steering wheel.
The input signals come from two vertical acceleration sensors in the front wheel arches and a third sensor in the rear right-hand wheel arch.
The steering column switch cluster sends the steering angle to the F-CAN. This is transmitted together with the wheel speeds from the DSC to the PT-CAN and evaluated in the EDC-K control unit.
The longitudinal, lateral and vertical accelerations calculated as a result are used as a basis for regulation. The EDC-K button signal enters the junction
box and is transmitted to the EDC-K on the PT-CAN." --
BMW Aftersales Training - Product Information
The only thing that is controlled is the shock damping, both compression and rebound. The following graph illustrates the damping force on the vertical axis "A" (compression below & rebound above) related to the damper piston speed on the horizontal axis "B". Controlling ride height would take some sort of air suspension or such. Also, the M3 does not have active anti-roll bars like the Range Rover and some other vehicles. Still, it is quite effective.