"Passive" selective damping?

"Passive" selective damping?

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hedges88

Original Poster:

639 posts

144 months

Saturday 4th September 2021
quotequote all
I only found out today that my car (W169 A-Class) is fitted with something called selective damping. It's not anything that you can control in the car like a sport button or a comfort button but apparently it was fitted to help overcome the stability issues of the previous A-Class. How do these selective dampers work do they only firm up when they are under full load, ie cornering really hard or do they actually work all of the time to help improve the ride?

The only information I could find is that it doesn't seem to be electronic but that it has some sort of valve that controls the flow of oil in the shock absorber.

GreenV8S

30,150 posts

283 months

Saturday 4th September 2021
quotequote all
I have no idea what that car uses. I thought that electronically controlled damping was the most common method but a lower tech alternative uses a spool valve as an inertial control signal so that the dampers can stay hard for body control but go soft on a sidden wheel input.

hedges88

Original Poster:

639 posts

144 months

Saturday 4th September 2021
quotequote all
GreenV8S said:
I have no idea what that car uses. I thought that electronically controlled damping was the most common method but a lower tech alternative uses a spool valve as an inertial control signal so that the dampers can stay hard for body control but go soft on a sidden wheel input.
Ah okay it is not magnetic filings or anything and the only literature I could find referred to a valve that controlled the flow of oil from the shock absorber so that must be the lower tech alternative you have described. But it would seem that this inertial control signal would indeed be electronic so so it's in some ways an intelligent system if it responds to sudden changes of direction based on steering angle. I wonder if there's anything I might be able to do with them in XENTRY to change or alter their operation in any way. I have heard some owners say that correct tyre pressure is essential otherwise it throws them off and you get a bad ride.

hedges88

Original Poster:

639 posts

144 months

Sunday 5th September 2021
quotequote all
Finally found a proper diagram and cutaway of the system online, it's from 2004 so definitely referring to the W169. I translated the German text on the diagram

Damping with normal driving style Damping with dynamic driving style and in curves Bypass Bypass With small wheel movements, the oil flows out of the bypass chamber in a throttled manner. This reduces the overall attenuation. With large wheel movements, the piston closes the bypass chamber. This achieves the full damping effect. A smaller amount of oil flows through the working piston. As a result, a more comfortable damping effect is achieved. Shock absorbers of the new A-Class with selective damping system.