Interesting Experience With Spheres, Over pressure spheres

[DerekW]

Hi George,

Not too sure about your idea of how the dampers work. Please forgive me if I'm teaching grandma to suck eggs, but they are fitted for one reason only and that is to damp down oscillations.

Without dampers any spring will oscillate at its natural frequency, with steadily reducing amplitude, for a dozen cycles or more. Obviously this would be dangerously uncomfortable and suspensions are therefore designed to damp out these oscillations as quickly as possible.

In the old days designers used friction dampers which, because they slowed down the springs' speed of response in both directions, resulted in harsh riding cars. Ideally for comfort the damper should not have any effect on spring compression, only on rebound. That way, the spring can react to a bump without any outside interference and the oscillations are damped out on the rebound stroke.

On our cars the small central hole is large enough to allow small quantities of fluid to pass through them with virtually no interference and this is enough to cope with small irregularities in the road surface. With the small suspension movement involved there's no tendency to oscillate. For larger suspension movements involving larger quantities of fluid movement, we need larger holes to minimise interference to flow. But these larger holes would upset the damping effect that we need on rebound. Hence the plate valve that opens against light spring pressure to allow minimum damping on compression and shuts on rebound forcing the returning fluid through the small central hole.

All that doesn't help in your case so it's only of academic interest.

Quote: "perhaps my front struts are leaking sooo much that, when the wheel hits a bump, some LHM also escapes through leaking back, instead of all being directed to the 3 spheres available to absorb the motion. Thus, perhaps, at those violent cases (sharper bumps/holes) the disks on the corner spheres don't quite have the chance to open up as designed to, and mostly the middle sphere is left to do the job -and it does it, but not well enough" If your legs were leaking that much, wouldn't the ride height be low after a bump?

Checking for internal leaks is easy enough, disconnect the return lines at the reservoir one at a time.

I don't think the strut top rubbers would have too much influence, they're fitted to allow the strut head to articulate during steering movements.

Perhaps it's not the hydraulics at fault, you seem to have covered all the bases. Might it be excessive stiffness in the mechanical side - wishbobe pivots, bottom balljoints and the antiroll bar bearings?

Derek

ps My car has 205/65/15 tyres

[jorgy9]

Thanks Derek for your comments. You make sense about the struts leaking also lowering the ride height. Good to know your 1999 car came with 205/65 too. I presume your XM rides impeccably then, and you don't feel the reactions mine presents. I'll check the returns first thing, and I keep the mechanical stiffness possibility in mind.

On the way the spheres work, I totally agree with your description, that's what I described too. As I and you said, smaller things are absorbed from the central orifice, without the plates opening up to allow LHM flow through the extra orifices. That central orifice is the one that determines degree of "wallowing" in a Citroen. Am I wrong?? Perhaps my writing is bad and difficult to understand, sorry.

Only one point: I'm not clear that the spheres have those extra valves for compression *only*. That's what I thought till recently -because I had read here- but I saw a couple of discussions and technical diagrams on other websites that suggested a sphere has in total eight (8) by-pass orifices, 4 of which open up (their plate, I mean) on compression, and 4 on rebound. I attach a schema pertaining to a DS sphere. The 2-way plate ("clapet") function is visible.

regards
George

[jorgy9]

...and another much more ...modern file, again in French. In thois case they were trying to remove hte valve from a sphere in order to use it as an accumulator sphere. Again, the 2-way plate-function is visible (and described), as well as the 8 in total peripheral orifices. In this case, as for any sphere, the plate visible on the sphere's exterior is the one that opens up on rebound.

regards
George

[jorgy9]

ps. the XM indeed does not oscillate almost at all -yet more than a conventional car- because the central orifices are so narrow, at 0.6mms. I've driven my XM with 1.1mms corner fronts and it was oscillating in a very pleasant manner, and with a lag also (bit after the irregularity was crossed), but was catastrophic in cornering. Imagine an XM with 1.65mms from a CX, like UFO did! Afair, my XM was still "crashy" on sharp bumps with those 1.1mm spheres, but was ironing any smaller irregularities.

G

[DerekW]

Sorry if I misunderstood your original description, George.

I haven't been able to open either of your files - the old problem of a Firefox browser I think. But having two sets of holes with two plate valves doesn't make sense to me, why not have just one set with no plate valves? Or just have a much bigger central hole? I believe the peripheral ring of holes are quite large, which I would expect if they are not to interfere with bump movement. Or if the requirement is for larger damper holes with different different sizes for bump and rebound, then have a larger central hole with a set of extra holes covered by a plate valve that opens only on bump? - and now we're back to where I thought we were!

Are there any forum members who have cut open a suspension sphere and can give us a definitive answer?

My car rides very well now, but I had my problems. The back end was behaving badly, giving an uncomfortable ride and rising and falling when stationary in traffic - and yes, that was a leaking rear cylinder; so perhaps you should check those return lines. Harshness at the front end - never bad, but just not up to the standard I expected - was cured by changing the hydractive sphere.

Derek

[jorgy9]

Hi Derek, I tried to download the files and they work OK for me. I could email them to you if u pm your email. In the pdf. u can clearly see the multitude of "plated" valves. The "Sphere diagram" though, you can find here:

http://www.citroencarclub.org.uk/ds/ at the "Sphere and Damper" paragraph. Note that the "Nota" says that number of orifices can differ for front and rear spheres, and in the same sphere (ie u could have 4 "plated" orifices for compression control and 2 for rebound).

Well, I understand that two sets of plates&orifices are needed, one for compression and one for rebound, for the exact reason you put forward as for rebound control: both these wheel movements need be controlled (=damped). The visible orifice serves only as a free passage for small irregularities. The other orifices open only for higher frequency motion of the wheel, i.e. more violent irregularities, and their threshold for opening obviously depends on the specs of the plates used. So a sphere alone is in reality automatically a sort of 2-level damper. Afaik, the "plated" orifices on the XM are all same size, for both compression and rebound. However I know that the C5 uses assymetrical orifices. The compression ones (diam.) are larger than the rebound. In the file I attach: the last column, "Diammetre du trou d'ammortiseur", first value refers to compression orifice, second to rebound. Note also the size of spheres of the C5: 385cc only!

I remember of your leaky rear cylinder. Mine leak too much also (the "internetic" jury has said), but not as much as the rear to go up-down continuously. My centre sphere is down at about 60 bars but I think that's still alright, isn't it?

Another thing I noticed: your 3lt 24v XMs (yours and Robert's) use a unique sphere spec for the front, that no other XM uses: it appears to be 40 bars, IFHS code XM40FC (Here: http://admin.triger.com.pl/SAS/img/CIT/34864/6199x.jpg)
Because of the low pressure, I bet the central orifice on these is larger than 0.6-0.7mms (the standard for other XMs). I.e. they allowed a softer damping but in the same time they needed to firm up the spring factor a bit, if not the car would bottom out easily. Albeit the very nice comfort you get, in combination with 65% profile tyres. Those are just hypotheses. I may contact IFHS and ask the detail of that sphere.

regards
George

[noz]

Hi George,

Here's your original sphere document translated into english. I haven't yet worked out why you would ever want to do this unless accumulator spheres (with the multilayer diaphragms) are in short supply but wheel spheres plentiful !?!. Otherwise just buy an accumulator sphere.

When you say 'rebound' do you mean when the wheel is on the way up into the wheel arch or on the way down out of the wheel arch. The greatest damping (ie the fewest number of open damper holes) is when the wheel is on the way out of the wheel arch. This is the same as a conventional shock absorber. It is easier to push the pushrod into the shock absorber than it is to pull it out.

cheers

noz

[jorgy9]

Thanks Noz,

this looks like a human translation -and a good one-, don't tell me web-machines have become that good!.

"Rebound" I mean when the wheel comes out of the arch. You are right about rebound damping being stronger, as the rule. Till recently though I thought that, in a sphere, only the visible central orifice was responsible for this, while evidence shows "rebound" damping also uses hidden orifices actioned by means of a disk-plate opening up, just like for compression damping.

BTW how's your XM's ride Noz? Anything ever reminded you my car's behavior? I guess your car also wears 205/65 ?

Do you think an XM's strut cylinder shaft could become slightly distorted if the car was used for many-many K's with flat spheres?

regards
George

[DerekW]

Hi George,

Whilst searching for info on diode wiring (I bought one of Roy's magic boxes but still don't have a clue where to connect it to!), I came across this posting that Noz sent to you about a year ago:

Quote " Hi George,

If I understand you correctly then the car was much better when you replaced the front spheres but degraded when the rears were replaced? I realise that descriptions of ride quality are all subjective but was the ride with the front-only change as good as you would have expected from a Citroen? If so then I suspect you have a problem with your electrovalves.

You need to understand how the mechanism in the neck of the sphere actually works. Although there is one hole in the middle which can be seen from the outside of the sphere this is only the outgoing orifice. ie when the fluid leaves the sphere it only comes out this hole. However, what you can't see is the spring washer inside which is covering the other 6 holes located radially around the centre one. The spring washer acts as a one-way valve. When the fluid is passing into the sphere it is passing through 7 orifices not just 1. This is consistent with the spring/damper arrangement on a 'normal' car. If you pull on a shock absorber it is much more difficult to move the shaft compared to pushing on it. This means that the 'resistance' is greater when running over a pothole compared with a hump.

With the above said it is completely inadvisable to 'drill' the orifices of spheres for the following reasons:
1. The ratio of spring to damper is what provides the resulting suspension function. The ratio between them is not intuitive and is linked by some complicated maths requiring the input of variables which are unknown to you. If you get the ratio wrong you could end up with instability just when you don't want it. Try explaining that to your insurance company.
2. You are only drilling the orifice you can see which is the one which controls fluid leaving the sphere. The one you want to affect is the fluid entering the sphere but you can't get access to those orifices.
3. When drilling the centre orifice you risk drilling right through the disc at the bottom of the internal diaphragm and leaking out 70Bar of nitrogen in your face.
4. For longevity the chances are the orifice material will be case hardened. Firstly it will then be difficult to drill and secondly you may leave unhardened material exposed at the orifice mouth which will wear quickly.
5. The swarf from any drilling exercise will end up in the sphere neck and in the hydraulic system.

I suggest some more investigation into whether the electrovalves are opening or not. The larger orifices in the spheres which you removed could have easily been masking an inoperative electrovalve(s). With the car on some ramps or axle stands crawl under the car so that your head is reasonably close to the electrovalve. Have someone open a door. Don't switch on the ignition, the noise of diesel solenoid valves or electric petrol pumps will mask the sound you are listening for. You should hear a very audible buzzing noise from the electrovalve. (You hava approximately 2 minutes to check this before the electrovalve shuts off again even with the door open. Close and re-open the door to re-energise.) The front one is very accessible. Try unplugging the electrical cable and then reconnecting it still with the door open. You should be able to tell if its functioning very easily. The rear electrovalve is not quite so accessible but the same check can be performed there too. Once your ears become attuned to the frequency and nature of the buzzing this test can be performed standing next to the car without the ramps etc.

The other possibility, even if the electrovalves are operating correctly, is that a faulty (intermittently) input sensor to the suspension ECU can cause the suspension to be switched to hard mode (electrovalves off) unnecessarily. The easy way to check tis is have your car plugged into a computer which will read the logs stored in there including faulty sensor operations. This is not as far fetched as it sounds. Using DJ's Elit machine we have diagnosed several faulty sensors (front roll bar position, steering wheel position, brake pedal switch). If you don't have access to a computer why not try your local Citroen agent. They have let me put the machine on the car before at no cost as long as there was no work to be done by them.

All is not lost but a little more investigation is required to get to the bottom of it.

Cheers

noz cool.gif"

So Noz agrees with me about the damper. I 'd be very interested in the 'photos, my email (usual explanation about the anti-spamming format) is: pe220tu at tiscali dot co dot uk.

Is your current problem the same one you were sufferibg from a year ago?

Derek

[jorgy9]

Hi Derek, hopefully you'll manage to plug Roy's box on your ecu, it's easy really once you get around to what those cables are.

Re. Noz's post, that's the only info I had on spheres and for a long time I though this was their design, but it proves they include plates+additional orifices for both ways of LHM flow, not just for compression only.

Since that post I've come a long way. Back then I was using some spheres with amazingly alrge (for the XM) centrla orifices of 1.1mms front and 0.9 rear, don't ask why, I was starting in hydraulics back then and that's what they sold me (buypartsby.co.uk, I ll never foget the rusty, regassed, wrong spec spheres they sold me online, without a mention they were not knew spheres). So car was very soft -still crashy when a single wheel met a sharp bump/hole-. Then I put new, correct spec XM spheres, from GSF (although I'm not 100% thsose are exaclty the right spec for my model but they are closer to what any XM needs). I changed the front ones only (all 3) and car was amazing. But when I also replaced the rear (all 3) it became not-so-soft. Then I adjusted the pressure regulator to 145-170 bars -I had found it to be too low at 137-157 bar). Then the car became amazing again, it was really ironing the road but in total control, without the instability of the 1.1mm-orifice spheres. I said "this is it, this is what they speak about". Then next day to compelte the operation I beld the brakes. Just after that, the car was again not-so-soft. I assumed I had created a leak somewhere -by leaving the car on highest for 2 hours, engine running- and the pressure was again not enough to keep the hydractive valves well-open. Since then I' m at that stage, having played alot with the pressure regulator pressures (upwards). My car exhibits strange symptoms. I.e. when I got the max pressure to 177 bars the suspension softened further (without being perfect), proving that it was a pressure-problem. then one day I loaded 100kg at the rear and drove for 10mins. Just after that the car was totally hard again, almost as if it had gone to hard mode. Now it is softer again, and this again happend from one day to another. How do you explain this? Thsoe days, the rear plays up, ie other days very soft, to harder. But it's not the electronics, I've checked them all, even driving with a voltmeter connected real time; both evalves, showded the voltage values and behavior described in literature.

I'm convinced my problem is of hydraulic nature, all the events of last year show that it's either a case of lack of pressure (leak) or sticky hydractive valves or both. I have never heard anybody confirming sticky hydractive valves but then nobody would know, I think. In my case, it looks like there's either a leak that is playing up (ie degrading and again improving with time) or a seriously sticky valve that sticks and unsticks. Only thing I can say is it's not the electronics/electrics. Also, as my p.reg .clicks every 12 secs, it's obvious that my car leaks somewhere. Not catastrophically, but enough for the pressure not to keep the hydractive valve well open. However: in trying to bypass this last problem, I fitted a one-way-valve to a pipe feeding high pressure to the front evalve, and I supllied this directly from after the pressure regulator, with a T-union. So now my front evalve thepretically should not be affected by any pressure leak elsewhere in the system. It also got a new evalve, as old was found -visibly- leaky. Front is soft in general, but still 1/crashy, as described i nthis thread, and 2/it allows all smaller irregularities (eg tarmak repairs) pass to the car's body. That's why I think of sticky struts etc. (for the front).

Anyway, I'll check this leak now and take it from there and then we'll see what happens...I already have seen that one of my rear cylinders leaking too much -a drop every 5 secs- (from looking and asking all internet resources I know, it appears a Citroen cylinder must only "be wet" not "droping drops"). My car has a history that unfortunately can justify all the above extreme possibilities, it was used for 1 year/20k by a small company doing radiators/heating, God knows how much they've been loading it, AND, it was on flat spheres when I bought it = byebye O-rings etc....

regards
George

[robertmnorton]

Hi jorgy9,
Both my 2.1 autos run on the manual specified tyre size 205/65/15 V rated , both michelin.

[jorgy9]

Thank you for your input Robert.

I'm more and more tending to assume that Citroen has increased the tyre profile to 65% with the S2s in an attempt to improve ride in the respects of the details I find problematic on my car. Shame there are not many S1s left in the UK so we could have the owners' inputs on that. I think I'll try to contact IFHS and get the damper details for a few different spheres Cit used on each XM model across the years. This should give leads as to what they were trying to achieve.

Today on the motorway I deliberately drove over densely put cat's eyes, at my usual speed. It's absorbing them perfectly. It's some other frequency that causes vibrations (speaking of small-height irregularities).

regards
George

[DerekW]

Hi George,

Thanks for the pictures of the dampers. I was, as I'm sure you were, surprised to find the compression valves duplicated on the rebound side in the XM spheres. As they say, you learn something new every day.

The DS arrangement seems to conform to my previous ideas except that, instead of a central hole, you have that peripheral space under the shim to control rebound.

You seem to be homing in on the hydractive valve assemblies, I think you're going to finish up taking one off and stripping it to prove/disprove your theory of a sticking valve. Finding time to do it must be a problem for you but I have seen info on the valve, either here or on the French car forum.

Derek

[DrTim]

FWIW my new one is riding MUCH better with 3 new spheres on the back! When I've got a bit more cash it'll getnew LHM and maybe new fronts too.Still rolls a lot though.

[jorgy9]

Hi Derek,

are you going to be surprised if I said I've already tried to get hold of an "hydractive block" and try it on my car... It was citroenxm that kindly helpedith the part but, due to my dumbness, I got an Hydractive 1 block in the post -useless for my H2 car-. Since then I gave up...I maybe looking for another one soon, but it will have to be from a late model, as new as possible, not worthwhile getting one that will perhaps be as bad as mine. But first I have to tackle the leaks that make my p.reg. click every 12secs.

DrTim,

strange your XM rolls alot, they are not supposed to roll noticeably more than an average car -and in some occassions, you even feel they go "flat"-. There was a case when somebody's XM was rolling like a CX and he found out the antiroll-bar linkage was broken, but I guess in your case, with changing the spheres, they'd have noticed this? The other possibility is it's stuck in soft, but I don't know any way this can happen, unless someones' wired a constant current supply because he wanted the car always soft? Or perhaps it's fitted with wrong-spec spheres, like mine when I bought it? The front-corner orifices on an XM are 0.6 (or 0.7mm in the case of a 2lt, I think) so if you find anything larger it's out of Citroen spec. My fronts where 1.1mms and the car was like a CX (not that I've ever driven one, but if fitted the narratives I've read on them )

cheers
George