alan s wrote:In the hydractive system, there's a thing that works along the lines of a pendulum that triggers the suspension so that if it starts to dip on one side, this throws the pressure across to jck that side up, so I wondered if perhaps this was the cause.
Hmm,
Where do you get that idea from Alan ? There are no pendulum systems on Hydractive 2, and not even on the Activa. Might be time to read up on how Hydractive 2 works
(and I mean that in a friendly way, don't get the wrong idea...to be fair it is a fairly complex system, especially the Activa additions which are on top of Hydractive 2)
The Activa is the only model to "actively" counter body roll - Hydractive 2 simply switches to "hard mode" which has increased roll resistance, but it can't "undo" any roll which has already occured in a corner until the moment the switch occured, it can only limit further roll.
A lot of the reason why "sport mode" (selected by the console switch) reduces body roll more than "normal mode" is because it just switches to hard mode sooner, before the roll can occur, rather than part way through the rolling motion of the body...(and hence less total roll for a given corner)
The Activa measures body roll only at the front basically with a simple mechanical linkage that measures the differential position of the left and right end of the rollbar applied to what is basically a height corrector without a damper chamber - yep thats right, the active roll correction on an Activa is purely mechanical/hydraulic. (The computer only serves the same purpose as it does in Hydractive 2 - making decisions on whether hard or soft mode is appropriate)
Hydractive 2 doesn't even measure body roll at all, either electronically or mechanically - it measures road speed, steering wheel angle and velocity, front brake pressure, throttle pedal movement, and "body movement" by way of a single sensor clamped near the middle of the front rollbar - which only responds to up/down movements of the suspension. (Mainly to detect impending bottoming of the suspension, and stiffen it accordingly)
Also a little bit puzzled by Anders comment:
AndersDK wrote:
The hydractive valve unit contains those directional flow limiters to each wheel - to minimise roll. That way I suppose the 2 wheels on one axle is not directly connected like the old passive systems on BX, CX etc.
I'm not sure what he means by "directional flow limiters" - so I'll describe whats actually in the Hydractive block - basically there are two damper valves, one on each side where the large diameter pipes go in, which are identical in every way (except calibration) to the ones you'd find in a sphere. They are not directional, they have equal jounce/rebound calibration, eg 50/50.
Single wheel bumps only have to pass through one damper valve to reach the sphere in the middle so are lightly damped - but body roll means the oil has to travel through both damper valves in series to pass from one side to the other, so body roll movements are more heavily damped than bump absorbing movements. (which is good)
The above is soft mode, in hard mode a valve closes the 3 connections - the sphere becomes completely isolated but the left and right sides are also isolated from each other - no flow of oil can pass between left and right at all in this state, body roll can only occur due to oil passing in and out of the heavily damped strut spheres... hence very low body roll.
There is also a floating ball valve which bypasses the damper valves so that height correction can still work in the hard mode. (Without it the flow from height corrector to struts would be cut off completely in hard mode)
You really need to see a diagram to understand how it works but basically its designed to block crossflows of oil between left and right, but allow incoming and outgoing flows of oil to the height corrector to temporarily unblock it.
It's possible that if there was still some pressure left in the suspension at the time when the electrovalve shut off, that the ball valve would not allow both sides to drop to zero pressure, leaving a small amount of pressure in one side.
More than likely all that went wrong is that you didn't wait long enough from the time you lowered the height lever until you turned the engine off and opened the bleed screw. I wait a good 3-4 minutes of idling for this reason before opening the bleed screw and turning off the engine, if I'm going to be removing any spheres. (Yes, it really can take that long to guarentee its down to zero pressure, especially at the rear)
If you notice the same problem in future all you need to do is close the bleed screw and run the engine for 30 seconds or so, but leaving the height lever down - this will reactivate the electrovalves, allow the trapped pressure to escape, then you can turn the engine off and open the bleed screw again...
Another possible cause is that you have an unreliable/intermitant front electrovalve and that it is sometimes not in soft mode when it should be. (Which will definately cause trouble depressurizing)
If there is pressure in the middle sphere and the strut spheres are depressurized in hard mode there is still a small amount of leakage through the valve and it will gradually repressurize the outer spheres, or perhaps just one of them.
Regards,
Simon
needed new wipers etc etc. Quite why it happened with just the one (left front) I've never worked out though.
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