MrFluffy
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| posted on 25/1/08 at 08:35 AM |
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Adapting citroen activa suspension spheres
Im still (quietly) plouging on with my middy project after all this time, although now I have a lotus esprit chassis to use as a jig and Im mostly
copying the geometry of that but with a spaceframe to improve the rigidity of the xform.
Ive been looking more at springs and suspension lately, and a rather off the wall idea has occurred to me, why not use the sphere based hydraulic
suspension from a citroen activa? Its credited as having almost no body roll (0.5degree), and can pull more g's on a skidpan than a honda nsx
and lots of other very well handling sports car, not bad for a production grocery getter fwd saloon. In fact the main failing of the activa was that
the people who traditionally bought citroens for their comfort hated it because it gave a stiff harsh well handing ride in place of the usual citroen
like mattress.
Ive been studying the layout, and it effectively uses two high rate (28mm) blade adjustable anti roll bars between the two sides one for the front
suspension and the second for the rear. A central "activa" sphere rotates the bar with body roll of more than 0.5 seconds duration (ie a
corner) to bring the blade round and stiffen up the suspension. If that doesnt take care of it, it can also supplement by allowing fluid into rams
mounted on the uprights themselves, I believe it can also do anti dive using these rams and offer some anti squat capability at the rear on hard
acceleration. Decisions on when to open the fluid valves for the anti roll bar and rams is taken by a central computer that takes its inputs from the
steering wheel angle, road speed and a couple of other sensors.
Body roll is taken care of by the usual cross linking of the spheres.
I'm looking at the activa because later models done away with the hydraulic control systems which make it still simple enough to be able to
adapt, and in fact the C3 and later have no active anti roll ability at all...
Plan is to buy a whole activa off ebay and remove the entire system then pass on the remains. I want to use the spheres but activate them via rocker
linkages, so I can still keep my double wishbone suspension. Spring rate is effectively set by system pressure and the blade in the anti roll bars so
should be adjustable.
Its as close as I am going to get for my build to active suspension...
Comments?
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TGR-ECOSSE
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| posted on 25/1/08 at 09:04 AM |
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Go for it. Its called a Citroen Xantia over here. You seem to have done your homework and if you think you can do it why not. Didn't Bentley use
the citroen suspension on some models?
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bonzoronnie
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 posted on 25/1/08 at 10:00 AM |
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Hydraulic suspension
I love the concept of Hydraulic suspension.
I have Driven two Citroens for the last 15 year's.
A BX from 1990 - 1998 & a Xantia until I changed to my current car a couple of years ago.
The hudraulic suspension on the BX was superb, Even better on the Xantia.
I am sure the system could be adapted to suit your needs.
It'll take a lot of research & hard work. I would give it a try.
Have you given any thought about the possible adjustments that may be needed to the spheres on the main uprighghts.
If memory serves me right. The suspension spheres are pre-loaded.
Front & rear spheres are not interchanable without factory adjustment.
My thinking is. Will the low weight of a kit car greatly affect the spheres performance.
Ronnie 
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paulf
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| posted on 25/1/08 at 10:25 AM |
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I once gave this some thought when i was starting building as i iwned a BX at the time.
The rear units looked easy to use as they were compact short struts, the fronts seemed to long to use as the were effectively Mcpherson struts.
If i remember correctly the suspension unit was just a cylinder, the sphere contained the valving that controlled the damping. The pressure in the
spheres can be adjusted and the sphere possibly dismantled and the valving adjusted as i think the valve is screwed in the base of it.
Paul
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UncleFista
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| posted on 25/1/08 at 11:19 AM |
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The car is called Xantia, the active suspension system is called Activa (it's the one with no body roll).
A couple of yeqars ago I saw a site where someone had installed the Citroen hydraulic suspension in a Land Rover, seemed to work well, he'd
fitted it for the adjustable ride height more than owt.
I can't remember the site, but if you have a search you might find it, there was loads of pics
Tony Bond / UncleFista
Love is like a snowmobile, speeding across the frozen tundra.
Which suddenly flips, pinning you underneath.
At night the ice-weasels come...
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Delinquent
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| posted on 26/1/08 at 12:05 PM |
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Glad to see I'm not the only nutter then 
This is exactly what I've been planning for my car, I've come up with a fairly complex adaptation which I'm still trying to
simplify, however till I get an activa to strip apart I'm not confident enough to be happy. Using the dims off my current Xantia (non activa)
I'm going to use the rear struts all round, and adjust the spring rate and damping by choice of spheres (They may all look the same, they
aren't) and also having the conversion done that allows you to adjust the gas pressure.
I've been told BX GT rear spheres are a good starting place as they have the smallest damping holes, so can be drilled out to relax the damping
- trial and error, admittedly, but they are cheap enough to be disposable nowadays.
The largest concerns for me are the computer assistance - the sensors and computer are set up based on the Xantia, don't see it being an option
to re-programme - and the additional rams that control roll / dive etc, which are not exactly small for packaging and cost £600 for replacements!
If all else fails I'll just go non-activa. The ARB can be uprated to remove a large proportion of the wallow that stand citroen suspension is
famed for.
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Doug68
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| posted on 26/1/08 at 01:15 PM |
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you guys might find this site interesting as a technology it works well enough to get
banned from the WRC
Doug. 1TG
Sports Car Builders WA
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MrFluffy
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| posted on 27/1/08 at 09:28 AM |
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Someone on ebay france lists the whole sphere pack of 8 spheres for 250e (about £160?) and Ive also seen mention of adjustable spheres, they run
35bar of pressure inside, but the person listing them offers a huge range so probably would be able to supply custom units if needed. You'd want
to change the spheres on a build anyway if nothing else. Theres plenty of secondhand rams to be had for a lot cheaper price.
What worries me about the computer system isnt the core program itself as much as what input it needs from external sensors. I want to run a corsa
steering column with the lotus rack, so would have to find a way to adapt the sensor from the donor to do this, but the activa was just old enough to
not have a canbus etc making things complex so I think its still *just* old enough tech to be able to slice out. But grey area is the speedo, does it
just sense the pulse readings from the gearbox sender (in which case I can fool it easily with a stimulator to give me some adjustment) or hooked into
the ecu proper...
Ive read somewhere that when a dealer is supplied a new suspension computer they have to program it initially to be either activa, xm or xantia and
once it is done it cannot be changed. Which suggests it has some sort of eprom in there, maybe it could be changed for a eeprom or something similar.
Id be interested in sawing one open for a look thats for sure...
If you take a look at this promo sheet for the prototype activa, this is what I am aiming for, lying the rocker activated spheres and struts down
horizontally as I have a very low front nose to fit it under. I could then change the leverage ratio on the rockers to alter spring rate.
I wont link the image direct in respect for the french activaclub's bandwidth, but that really is a top place for activa info :-
http://activaclubfrance.free.fr/Doc%20technique/Activa1988.jpg
Unc, I found the LR, if its the one with DS suspension rather than activa.
http://www.citroen-ds-id.com/ds/Landrover_with_Cit_Suspension.html
Research research...
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Delinquent
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| posted on 27/1/08 at 09:46 AM |
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I had originally planned to lay the struts down, but even using the shorter rear struts, I still couldn't get them both in there without
offsetting them (which I didn't really want to do)
I've ended up taking them horizontally, angled towards the corners of the screen.
Will be very interesting to see what you come up with - the control systems were definitely my greatest concern but a colleague shares your view that
it shouldn't be insurmountable. Electronics is definitely my largest weak spot so maybe I'll just let you go first 
Having seen the Kinetic site, I'll definitely be having a chat with them as well though!
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